[feature] request blocking by http headers (#2409)

cmd/gotosocial/action/server/server.go

@@ -219,14 +219,19 @@ var Start action.GTSAction = func(ctx context.Context) error {
 	if err != nil {
 		return fmt.Errorf("error creating router: %s", err)
 	}
-	middlewares := []gin.HandlerFunc{
-		middleware.AddRequestID(config.GetRequestIDHeader()), // requestID middleware must run before tracing
-	}
 
+	// Start preparing middleware stack.
+	middlewares := make([]gin.HandlerFunc, 1)
+
+	// RequestID middleware must run before tracing!
+	middlewares[0] = middleware.AddRequestID(config.GetRequestIDHeader())
+
+	// Add tracing middleware if enabled.
 	if config.GetTracingEnabled() {
 		middlewares = append(middlewares, tracing.InstrumentGin())
 	}
 
+	// Add metrics middleware if enabled.
 	if config.GetMetricsEnabled() {
 		middlewares = append(middlewares, metrics.InstrumentGin())
 	}
@@ -235,6 +240,7 @@ var Start action.GTSAction = func(ctx context.Context) error {
 		// note: hooks adding ctx fields must be ABOVE
 		// the logger, otherwise won't be accessible.
 		middleware.Logger(config.GetLogClientIP()),
+		middleware.HeaderFilter(&state),
 		middleware.UserAgent(),
 		middleware.CORS(),
 		middleware.ExtraHeaders(),

docs/admin/request_filtering_modes.md

@@ -0,0 +1,33 @@
+# HTTP Request Header Filtering Modes
+
+GoToSocial currently offers 'block', 'allow' and disabled HTTP request header filtering modes, which can be set using the `advanced-header-filter-mode` setting in the config.yaml, or using the `GTS_ADVANCED_HEADER_FILTER_MODE` environment variable. These are described below.
+
+!!! warning
+    HTTP request header filtering is an advanced setting. If you are not well versed in the uses and intricacies of HTTP request headers, you may break federation or even access to your own instance by changing these.
+
+    HTTP request header filtering is also still considered "experimental". It should do what it says on the box, but it may cause bugs or edge cases to appear elsewhere, we're not sure yet!
+
+    Management via settings panel is TBA. Until then you will need to manage these directly via API endpoints.
+
+## Disabled header filtering mode (default)
+
+When `advanced-header-filter-mode` is set to `""`, i.e. an empty string, all request header filtering will be disabled.
+
+## Block filtering mode
+
+When `advanced-header-filter-mode` is set to `"block"`, your instance will accept HTTP requests as normal (pending API token checks, HTTP signature checks etc), with the exception of matching block header filters you have explicitly created via the settings panel.
+
+In block mode, an allow header filter can be used to override an existing block filter, providing an extra level of granularity.
+
+A request in block mode will be accepted if it is EXPLICITLY ALLOWED OR NOT EXPLICITLY BLOCKED.
+
+## Allow filtering mode
+
+When `advanced-header-filter-mode` is set to `"allow"`, your instance will only accept HTTP requests for which a matching allow header filter has been explicitly created via the settings panel. All other requests will be refused.
+
+In allow mode, a block header filter can be used to override an existing allow filter, providing an extra level of granularity.
+
+A request in allow mode will only be accepted if it is EXPLICITLY ALLOWED AND NOT EXPLICITLY BLOCKED.
+
+!!! danger
+    Allow filtering mode is an extremely restrictive mode that will almost certainly prevent many (legitimate) clients from being able to access your instance, including yourself. You should only enable this mode if you know exactly what you're trying to achieve.

docs/api/swagger.yaml

@@ -1193,6 +1193,20 @@ definitions:
         type: object
         x-go-name: Field
         x-go-package: github.com/superseriousbusiness/gotosocial/internal/api/model
+    headerFilterCreateRequest:
+        properties:
+            header:
+                description: The HTTP header to match against (e.g. User-Agent).
+                type: string
+                x-go-name: Header
+            regex:
+                description: The header value matching regular expression.
+                type: string
+                x-go-name: Regex
+        title: HeaderFilterRequest is the form submitted as a POST to create a new header filter entry (allow / block).
+        type: object
+        x-go-name: HeaderFilterRequest
+        x-go-package: github.com/superseriousbusiness/gotosocial/internal/api/model
     hostmeta:
         description: 'See: https://www.rfc-editor.org/rfc/rfc6415.html#section-3'
         properties:
@@ -2108,13 +2122,17 @@ definitions:
         x-go-package: github.com/superseriousbusiness/gotosocial/internal/api/model
     pollRequest:
         properties:
-            expires_in:
+            ExpiresIn:
                 description: |-
                     Duration the poll should be open, in seconds.
                     If provided, media_ids cannot be used, and poll[options] must be provided.
                 format: int64
                 type: integer
-                x-go-name: ExpiresIn
+            expires_in:
+                description: |-
+                    Duration the poll should be open, in seconds.
+                    If provided, media_ids cannot be used, and poll[options] must be provided.
+                x-go-name: ExpiresInI
             hide_totals:
                 description: Hide vote counts until the poll ends.
                 type: boolean
@@ -4563,6 +4581,232 @@ paths:
             summary: Send a generic test email to a specified email address.
             tags:
                 - admin
+    /api/v1/admin/header_allows:
+        get:
+            operationId: headerFilterAllowsGet
+            responses:
+                "200":
+                    description: All "allow" header filters currently in place.
+                    schema:
+                        items:
+                            $ref: '#/definitions/headerFilter'
+                        type: array
+                "400":
+                    description: bad request
+                "401":
+                    description: unauthorized
+                "403":
+                    description: forbidden
+                "404":
+                    description: not found
+                "500":
+                    description: internal server error
+            security:
+                - OAuth2 Bearer:
+                    - admin
+            summary: Get all "allow" header filters currently in place.
+            tags:
+                - admin
+        post:
+            consumes:
+                - application/json
+                - application/xml
+                - application/x-www-form-urlencoded
+            description: |-
+                The parameters can also be given in the body of the request, as JSON, if the content-type is set to 'application/json'.
+                The parameters can also be given in the body of the request, as XML, if the content-type is set to 'application/xml'.
+            operationId: headerFilterAllowCreate
+            produces:
+                - application/json
+            responses:
+                "200":
+                    description: The newly created "allow" header filter.
+                    schema:
+                        $ref: '#/definitions/headerFilter'
+                "400":
+                    description: bad request
+                "401":
+                    description: unauthorized
+                "403":
+                    description: forbidden
+                "500":
+                    description: internal server error
+            security:
+                - OAuth2 Bearer:
+                    - admin
+            summary: Create new "allow" HTTP request header filter.
+            tags:
+                - admin
+    /api/v1/admin/header_allows/{id}:
+        delete:
+            operationId: headerFilterAllowDelete
+            parameters:
+                - description: Target header filter ID.
+                  in: path
+                  name: id
+                  required: true
+                  type: string
+            responses:
+                "202":
+                    description: Accepted
+                "400":
+                    description: bad request
+                "401":
+                    description: unauthorized
+                "403":
+                    description: forbidden
+                "404":
+                    description: not found
+                "500":
+                    description: internal server error
+            security:
+                - OAuth2 Bearer:
+                    - admin
+            summary: Delete the "allow" header filter with the given ID.
+            tags:
+                - admin
+        get:
+            operationId: headerFilterAllowGet
+            parameters:
+                - description: Target header filter ID.
+                  in: path
+                  name: id
+                  required: true
+                  type: string
+            responses:
+                "200":
+                    description: The requested "allow" header filter.
+                    schema:
+                        $ref: '#/definitions/headerFilter'
+                "400":
+                    description: bad request
+                "401":
+                    description: unauthorized
+                "403":
+                    description: forbidden
+                "404":
+                    description: not found
+                "500":
+                    description: internal server error
+            security:
+                - OAuth2 Bearer:
+                    - admin
+            summary: Get "allow" header filter with the given ID.
+            tags:
+                - admin
+    /api/v1/admin/header_blocks:
+        get:
+            operationId: headerFilterBlocksGet
+            responses:
+                "200":
+                    description: All "block" header filters currently in place.
+                    schema:
+                        items:
+                            $ref: '#/definitions/headerFilter'
+                        type: array
+                "400":
+                    description: bad request
+                "401":
+                    description: unauthorized
+                "403":
+                    description: forbidden
+                "404":
+                    description: not found
+                "500":
+                    description: internal server error
+            security:
+                - OAuth2 Bearer:
+                    - admin
+            summary: Get all "allow" header filters currently in place.
+            tags:
+                - admin
+        post:
+            consumes:
+                - application/json
+                - application/xml
+                - application/x-www-form-urlencoded
+            description: |-
+                The parameters can also be given in the body of the request, as JSON, if the content-type is set to 'application/json'.
+                The parameters can also be given in the body of the request, as XML, if the content-type is set to 'application/xml'.
+            operationId: headerFilterBlockCreate
+            produces:
+                - application/json
+            responses:
+                "200":
+                    description: The newly created "block" header filter.
+                    schema:
+                        $ref: '#/definitions/headerFilter'
+                "400":
+                    description: bad request
+                "401":
+                    description: unauthorized
+                "403":
+                    description: forbidden
+                "500":
+                    description: internal server error
+            security:
+                - OAuth2 Bearer:
+                    - admin
+            summary: Create new "block" HTTP request header filter.
+            tags:
+                - admin
+    /api/v1/admin/header_blocks/{id}:
+        delete:
+            operationId: headerFilterBlockDelete
+            parameters:
+                - description: Target header filter ID.
+                  in: path
+                  name: id
+                  required: true
+                  type: string
+            responses:
+                "202":
+                    description: Accepted
+                "400":
+                    description: bad request
+                "401":
+                    description: unauthorized
+                "403":
+                    description: forbidden
+                "404":
+                    description: not found
+                "500":
+                    description: internal server error
+            security:
+                - OAuth2 Bearer:
+                    - admin
+            summary: Delete the "block" header filter with the given ID.
+            tags:
+                - admin
+        get:
+            operationId: headerFilterBlockGet
+            parameters:
+                - description: Target header filter ID.
+                  in: path
+                  name: id
+                  required: true
+                  type: string
+            responses:
+                "200":
+                    description: The requested "block" header filter.
+                    schema:
+                        $ref: '#/definitions/headerFilter'
+                "400":
+                    description: bad request
+                "401":
+                    description: unauthorized
+                "403":
+                    description: forbidden
+                "404":
+                    description: not found
+                "500":
+                    description: internal server error
+            security:
+                - OAuth2 Bearer:
+                    - admin
+            summary: Get "block" header filter with the given ID.
+            tags:
+                - admin
     /api/v1/admin/instance/rules:
         post:
             consumes:

example/config.yaml

@@ -361,6 +361,7 @@ instance-deliver-to-shared-inboxes: true
 # Default: false
 instance-inject-mastodon-version: false
 
+
 ###########################
 ##### ACCOUNTS CONFIG #####
 ###########################
@@ -1033,3 +1034,20 @@ advanced-sender-multiplier: 2
 # Example: ["s3.example.org", "some-bucket-name.s3.example.org"]
 # Default: []
 advanced-csp-extra-uris: []
+
+# String. HTTP request header filtering mode to use for this instance.
+#
+# "block" -- only requests that are explicitly blocked by header filters
+#            will be denied (unless they are also explicitly allowed).
+#
+# "allow" -- only requests that are explicitly allowed by header filters
+#            will be accepted (unless they are also explicitly blocked).
+#
+#   ""    -- request header filtering disabled.
+#
+# For more details on block and allow modes, check the documentation at:
+# https://docs.gotosocial.org/en/latest/admin/request_filtering_modes
+#
+# Options: ["block", "allow", ""]
+# Default: ""
+advanced-header-filter-mode: ""

internal/api/client/admin/admin.go

@@ -35,6 +35,10 @@ const (
 	DomainAllowsPath        = BasePath + "/domain_allows"
 	DomainAllowsPathWithID  = DomainAllowsPath + "/:" + IDKey
 	DomainKeysExpirePath    = BasePath + "/domain_keys_expire"
+	HeaderAllowsPath        = BasePath + "/header_allows"
+	HeaderAllowsPathWithID  = HeaderAllowsPath + "/:" + IDKey
+	HeaderBlocksPath        = BasePath + "/header_blocks"
+	HeaderBlocksPathWithID  = HeaderAllowsPath + "/:" + IDKey
 	AccountsPath            = BasePath + "/accounts"
 	AccountsPathWithID      = AccountsPath + "/:" + IDKey
 	AccountsActionPath      = AccountsPathWithID + "/action"
@@ -95,6 +99,16 @@ func (m *Module) Route(attachHandler func(method string, path string, f ...gin.H
 	attachHandler(http.MethodGet, DomainAllowsPathWithID, m.DomainAllowGETHandler)
 	attachHandler(http.MethodDelete, DomainAllowsPathWithID, m.DomainAllowDELETEHandler)
 
+	// header filtering administration routes
+	attachHandler(http.MethodGet, HeaderAllowsPathWithID, m.HeaderFilterAllowGET)
+	attachHandler(http.MethodGet, HeaderBlocksPathWithID, m.HeaderFilterBlockGET)
+	attachHandler(http.MethodGet, HeaderAllowsPath, m.HeaderFilterAllowsGET)
+	attachHandler(http.MethodGet, HeaderBlocksPath, m.HeaderFilterBlocksGET)
+	attachHandler(http.MethodPost, HeaderAllowsPath, m.HeaderFilterAllowPOST)
+	attachHandler(http.MethodPost, HeaderBlocksPath, m.HeaderFilterBlockPOST)
+	attachHandler(http.MethodDelete, HeaderAllowsPathWithID, m.HeaderFilterAllowDELETE)
+	attachHandler(http.MethodDelete, HeaderBlocksPathWithID, m.HeaderFilterBlockDELETE)
+
 	// domain maintenance stuff
 	attachHandler(http.MethodPost, DomainKeysExpirePath, m.DomainKeysExpirePOSTHandler)
 

internal/api/client/admin/headerfilter.go

@@ -0,0 +1,173 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package admin
+
+import (
+	"context"
+	"errors"
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
+	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/oauth"
+)
+
+// getHeaderFilter is a gin handler function that returns details of an HTTP header filter with provided ID, using given get function.
+func (m *Module) getHeaderFilter(c *gin.Context, get func(context.Context, string) (*apimodel.HeaderFilter, gtserror.WithCode)) {
+	authed, err := oauth.Authed(c, true, true, true, true)
+	if err != nil {
+		errWithCode := gtserror.NewErrorUnauthorized(err, err.Error())
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	if !*authed.User.Admin {
+		const text = "user not an admin"
+		errWithCode := gtserror.NewErrorForbidden(errors.New(text), text)
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	if _, err := apiutil.NegotiateAccept(c, apiutil.JSONAcceptHeaders...); err != nil {
+		errWithCode := gtserror.NewErrorNotAcceptable(err, err.Error())
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	filterID, errWithCode := apiutil.ParseID(c.Param("ID"))
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	filter, errWithCode := get(c.Request.Context(), filterID)
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	apiutil.JSON(c, http.StatusOK, filter)
+}
+
+// getHeaderFilters is a gin handler function that returns details of all HTTP header filters using given get function.
+func (m *Module) getHeaderFilters(c *gin.Context, get func(context.Context) ([]*apimodel.HeaderFilter, gtserror.WithCode)) {
+	authed, err := oauth.Authed(c, true, true, true, true)
+	if err != nil {
+		errWithCode := gtserror.NewErrorUnauthorized(err, err.Error())
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	if !*authed.User.Admin {
+		const text = "user not an admin"
+		errWithCode := gtserror.NewErrorForbidden(errors.New(text), text)
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	if _, err := apiutil.NegotiateAccept(c, apiutil.JSONAcceptHeaders...); err != nil {
+		errWithCode := gtserror.NewErrorNotAcceptable(err, err.Error())
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	filters, errWithCode := get(c.Request.Context())
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	apiutil.JSON(c, http.StatusOK, filters)
+}
+
+// createHeaderFilter is a gin handler function that creates a HTTP header filter entry using provided form data, passing to given create function.
+func (m *Module) createHeaderFilter(c *gin.Context, create func(context.Context, *gtsmodel.Account, *apimodel.HeaderFilterRequest) (*apimodel.HeaderFilter, gtserror.WithCode)) {
+	authed, err := oauth.Authed(c, true, true, true, true)
+	if err != nil {
+		errWithCode := gtserror.NewErrorUnauthorized(err, err.Error())
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	if !*authed.User.Admin {
+		const text = "user not an admin"
+		errWithCode := gtserror.NewErrorForbidden(errors.New(text), text)
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	if _, err := apiutil.NegotiateAccept(c, apiutil.JSONAcceptHeaders...); err != nil {
+		errWithCode := gtserror.NewErrorNotAcceptable(err, err.Error())
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	var form apimodel.HeaderFilterRequest
+
+	if err := c.ShouldBind(&form); err != nil {
+		errWithCode := gtserror.NewErrorBadRequest(err, err.Error())
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	filter, errWithCode := create(
+		c.Request.Context(),
+		authed.Account,
+		&form,
+	)
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	apiutil.JSON(c, http.StatusOK, filter)
+}
+
+// deleteHeaderFilter is a gin handler function that deletes an HTTP header filter with provided ID, using given delete function.
+func (m *Module) deleteHeaderFilter(c *gin.Context, delete func(context.Context, string) gtserror.WithCode) {
+	authed, err := oauth.Authed(c, true, true, true, true)
+	if err != nil {
+		errWithCode := gtserror.NewErrorUnauthorized(err, err.Error())
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	if !*authed.User.Admin {
+		const text = "user not an admin"
+		errWithCode := gtserror.NewErrorForbidden(errors.New(text), text)
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	filterID, errWithCode := apiutil.ParseID(c.Param("ID"))
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	errWithCode = delete(c.Request.Context(), filterID)
+	if errWithCode != nil {
+		apiutil.ErrorHandler(c, errWithCode, m.processor.InstanceGetV1)
+		return
+	}
+
+	c.Status(http.StatusAccepted)
+}

internal/api/client/admin/headerfilter_create.go

@@ -0,0 +1,102 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package admin
+
+import (
+	"github.com/gin-gonic/gin"
+)
+
+// HeaderFilterAllowPOST swagger:operation POST /api/v1/admin/header_allows headerFilterAllowCreate
+//
+// Create new "allow" HTTP request header filter.
+//
+// The parameters can also be given in the body of the request, as JSON, if the content-type is set to 'application/json'.
+// The parameters can also be given in the body of the request, as XML, if the content-type is set to 'application/xml'.
+//
+//	---
+//	tags:
+//	- admin
+//
+//	consumes:
+//	- application/json
+//	- application/xml
+//	- application/x-www-form-urlencoded
+//
+//	produces:
+//	- application/json
+//
+//	security:
+//	- OAuth2 Bearer:
+//		- admin
+//
+//	responses:
+//		'200':
+//			description: The newly created "allow" header filter.
+//			schema:
+//				"$ref": "#/definitions/headerFilter"
+//		'400':
+//			description: bad request
+//		'401':
+//			description: unauthorized
+//		'403':
+//			description: forbidden
+//		'500':
+//			description: internal server error
+func (m *Module) HeaderFilterAllowPOST(c *gin.Context) {
+	m.createHeaderFilter(c, m.processor.Admin().CreateAllowHeaderFilter)
+}
+
+// HeaderFilterBlockPOST swagger:operation POST /api/v1/admin/header_blocks headerFilterBlockCreate
+//
+// Create new "block" HTTP request header filter.
+//
+// The parameters can also be given in the body of the request, as JSON, if the content-type is set to 'application/json'.
+// The parameters can also be given in the body of the request, as XML, if the content-type is set to 'application/xml'.
+//
+//	---
+//	tags:
+//	- admin
+//
+//	consumes:
+//	- application/json
+//	- application/xml
+//	- application/x-www-form-urlencoded
+//
+//	produces:
+//	- application/json
+//
+//	security:
+//	- OAuth2 Bearer:
+//		- admin
+//
+//	responses:
+//		'200':
+//			description: The newly created "block" header filter.
+//			schema:
+//				"$ref": "#/definitions/headerFilter"
+//		'400':
+//			description: bad request
+//		'401':
+//			description: unauthorized
+//		'403':
+//			description: forbidden
+//		'500':
+//			description: internal server error
+func (m *Module) HeaderFilterBlockPOST(c *gin.Context) {
+	m.createHeaderFilter(c, m.processor.Admin().CreateBlockHeaderFilter)
+}

internal/api/client/admin/headerfilter_delete.go

@@ -0,0 +1,96 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package admin
+
+import (
+	"github.com/gin-gonic/gin"
+)
+
+// HeaderFilterAllowDELETE swagger:operation DELETE /api/v1/admin/header_allows/{id} headerFilterAllowDelete
+//
+// Delete the "allow" header filter with the given ID.
+//
+//	---
+//	tags:
+//	- admin
+//
+//	parameters:
+//	-
+//		name: id
+//		type: string
+//		description: Target header filter ID.
+//		in: path
+//		required: true
+//
+//	security:
+//	- OAuth2 Bearer:
+//		- admin
+//
+//	responses:
+//		'202':
+//			description: Accepted
+//		'400':
+//			description: bad request
+//		'401':
+//			description: unauthorized
+//		'403':
+//			description: forbidden
+//		'404':
+//			description: not found
+//		'500':
+//			description: internal server error
+func (m *Module) HeaderFilterAllowDELETE(c *gin.Context) {
+	m.deleteHeaderFilter(c, m.processor.Admin().DeleteAllowHeaderFilter)
+}
+
+// HeaderFilterBlockDELETE swagger:operation DELETE /api/v1/admin/header_blocks/{id} headerFilterBlockDelete
+//
+// Delete the "block" header filter with the given ID.
+//
+//	---
+//	tags:
+//	- admin
+//
+//	parameters:
+//	-
+//		name: id
+//		type: string
+//		description: Target header filter ID.
+//		in: path
+//		required: true
+//
+//	security:
+//	- OAuth2 Bearer:
+//		- admin
+//
+//	responses:
+//		'202':
+//			description: Accepted
+//		'400':
+//			description: bad request
+//		'401':
+//			description: unauthorized
+//		'403':
+//			description: forbidden
+//		'404':
+//			description: not found
+//		'500':
+//			description: internal server error
+func (m *Module) HeaderFilterBlockDELETE(c *gin.Context) {
+	m.deleteHeaderFilter(c, m.processor.Admin().DeleteAllowHeaderFilter)
+}

internal/api/client/admin/headerfilter_get.go

@@ -0,0 +1,164 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package admin
+
+import "github.com/gin-gonic/gin"
+
+// HeaderFilterAllowGET swagger:operation GET /api/v1/admin/header_allows/{id} headerFilterAllowGet
+//
+// Get "allow" header filter with the given ID.
+//
+//	---
+//	tags:
+//	- admin
+//
+//	parameters:
+//	-
+//		name: id
+//		type: string
+//		description: Target header filter ID.
+//		in: path
+//		required: true
+//
+//	security:
+//	- OAuth2 Bearer:
+//		- admin
+//
+//	responses:
+//		'200':
+//			description: The requested "allow" header filter.
+//			schema:
+//				"$ref": "#/definitions/headerFilter"
+//		'400':
+//			description: bad request
+//		'401':
+//			description: unauthorized
+//		'403':
+//			description: forbidden
+//		'404':
+//			description: not found
+//		'500':
+//			description: internal server error
+func (m *Module) HeaderFilterAllowGET(c *gin.Context) {
+	m.getHeaderFilter(c, m.processor.Admin().GetAllowHeaderFilter)
+}
+
+// HeaderFilterBlockGET swagger:operation GET /api/v1/admin/header_blocks/{id} headerFilterBlockGet
+//
+// Get "block" header filter with the given ID.
+//
+//	---
+//	tags:
+//	- admin
+//
+//	parameters:
+//	-
+//		name: id
+//		type: string
+//		description: Target header filter ID.
+//		in: path
+//		required: true
+//
+//	security:
+//	- OAuth2 Bearer:
+//		- admin
+//
+//	responses:
+//		'200':
+//			description: The requested "block" header filter.
+//			schema:
+//				"$ref": "#/definitions/headerFilter"
+//		'400':
+//			description: bad request
+//		'401':
+//			description: unauthorized
+//		'403':
+//			description: forbidden
+//		'404':
+//			description: not found
+//		'500':
+//			description: internal server error
+func (m *Module) HeaderFilterBlockGET(c *gin.Context) {
+	m.getHeaderFilter(c, m.processor.Admin().GetBlockHeaderFilter)
+}
+
+// HeaderFilterAllowsGET swagger:operation GET /api/v1/admin/header_allows headerFilterAllowsGet
+//
+// Get all "allow" header filters currently in place.
+//
+//	---
+//	tags:
+//	- admin
+//
+//	security:
+//	- OAuth2 Bearer:
+//		- admin
+//
+//	responses:
+//		'200':
+//			description: All "allow" header filters currently in place.
+//			schema:
+//				type: array
+//				items:
+//					"$ref": "#/definitions/headerFilter"
+//		'400':
+//			description: bad request
+//		'401':
+//			description: unauthorized
+//		'403':
+//			description: forbidden
+//		'404':
+//			description: not found
+//		'500':
+//			description: internal server error
+func (m *Module) HeaderFilterAllowsGET(c *gin.Context) {
+	m.getHeaderFilters(c, m.processor.Admin().GetAllowHeaderFilters)
+}
+
+// HeaderFilterBlocksGET swagger:operation GET /api/v1/admin/header_blocks headerFilterBlocksGet
+//
+// Get all "allow" header filters currently in place.
+//
+//	---
+//	tags:
+//	- admin
+//
+//	security:
+//	- OAuth2 Bearer:
+//		- admin
+//
+//	responses:
+//		'200':
+//			description: All "block" header filters currently in place.
+//			schema:
+//				type: array
+//				items:
+//					"$ref": "#/definitions/headerFilter"
+//		'400':
+//			description: bad request
+//		'401':
+//			description: unauthorized
+//		'403':
+//			description: forbidden
+//		'404':
+//			description: not found
+//		'500':
+//			description: internal server error
+func (m *Module) HeaderFilterBlocksGET(c *gin.Context) {
+	m.getHeaderFilters(c, m.processor.Admin().GetBlockHeaderFilters)
+}

internal/api/model/headerfilter.go

@@ -0,0 +1,55 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package model
+
+// HeaderFilter represents a regex value filter applied to one particular HTTP header (allow / block).
+type HeaderFilter struct {
+	// The ID of the header filter.
+	// example: 01FBW21XJA09XYX51KV5JVBW0F
+	// readonly: true
+	ID string `json:"id"`
+
+	// The HTTP header to match against.
+	// example: User-Agent
+	Header string `json:"header"`
+
+	// The header value matching regular expression.
+	// example: .*Firefox.*
+	Regex string `json:"regex"`
+
+	// The ID of the admin account that created this header filter.
+	// example: 01FBW2758ZB6PBR200YPDDJK4C
+	// readonly: true
+	CreatedBy string `json:"created_by"`
+
+	// Time at which the header filter was created (ISO 8601 Datetime).
+	// example: 2021-07-30T09:20:25+00:00
+	// readonly: true
+	CreatedAt string `json:"created_at"`
+}
+
+// HeaderFilterRequest is the form submitted as a POST to create a new header filter entry (allow / block).
+//
+// swagger:model headerFilterCreateRequest
+type HeaderFilterRequest struct {
+	// The HTTP header to match against (e.g. User-Agent).
+	Header string `form:"header" json:"header" xml:"header"`
+
+	// The header value matching regular expression.
+	Regex string `form:"regex" json:"regex" xml:"regex"`
+}

internal/api/util/response.go

@@ -39,14 +39,17 @@ var (
 	StatusAcceptedJSON = mustJSON(map[string]string{
 		"status": http.StatusText(http.StatusAccepted),
 	})
+	StatusForbiddenJSON = mustJSON(map[string]string{
+		"status": http.StatusText(http.StatusForbidden),
+	})
 	StatusInternalServerErrorJSON = mustJSON(map[string]string{
 		"status": http.StatusText(http.StatusInternalServerError),
 	})
 	ErrorCapacityExceeded = mustJSON(map[string]string{
-		"error": "server capacity exceeded!",
+		"error": "server capacity exceeded",
 	})
-	ErrorRateLimitReached = mustJSON(map[string]string{
-		"error": "rate limit reached!",
+	ErrorRateLimited = mustJSON(map[string]string{
+		"error": "rate limit reached",
 	})
 	EmptyJSONObject = mustJSON("{}")
 	EmptyJSONArray  = mustJSON("[]")

internal/cache/cache.go

@@ -18,21 +18,26 @@
 package cache
 
 import (
+	"github.com/superseriousbusiness/gotosocial/internal/cache/headerfilter"
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
 	"github.com/superseriousbusiness/gotosocial/internal/log"
 )
 
 type Caches struct {
-	// GTS provides access to the collection of gtsmodel object caches.
-	// (used by the database).
+	// GTS provides access to the collection of
+	// gtsmodel object caches. (used by the database).
 	GTS GTSCaches
 
-	// AP provides access to the collection of ActivityPub object caches.
-	// (planned to be used by the typeconverter).
-	AP APCaches
+	// AllowHeaderFilters provides access to
+	// the allow []headerfilter.Filter cache.
+	AllowHeaderFilters headerfilter.Cache
 
-	// Visibility provides access to the item visibility cache.
-	// (used by the visibility filter).
+	// BlockHeaderFilters provides access to
+	// the block []headerfilter.Filter cache.
+	BlockHeaderFilters headerfilter.Cache
+
+	// Visibility provides access to the item visibility
+	// cache. (used by the visibility filter).
 	Visibility VisibilityCache
 
 	// prevent pass-by-value.
@@ -45,7 +50,6 @@ func (c *Caches) Init() {
 	log.Infof(nil, "init: %p", c)
 
 	c.GTS.Init()
-	c.AP.Init()
 	c.Visibility.Init()
 
 	// Setup cache invalidate hooks.
@@ -58,7 +62,6 @@ func (c *Caches) Start() {
 	log.Infof(nil, "start: %p", c)
 
 	c.GTS.Start()
-	c.AP.Start()
 	c.Visibility.Start()
 }
 
@@ -67,7 +70,6 @@ func (c *Caches) Stop() {
 	log.Infof(nil, "stop: %p", c)
 
 	c.GTS.Stop()
-	c.AP.Stop()
 	c.Visibility.Stop()
 }
 

internal/cache/domain/domain.go

@@ -21,7 +21,6 @@ import (
 	"fmt"
 	"strings"
 	"sync/atomic"
-	"unsafe"
 
 	"golang.org/x/exp/slices"
 )
@@ -37,17 +36,17 @@ import (
 // The .Clear() function can be used to invalidate the cache,
 // e.g. when an entry is added / deleted from the database.
 type Cache struct {
-	// atomically updated ptr value to the
 	// current domain cache radix trie.
-	rootptr unsafe.Pointer
+	rootptr atomic.Pointer[root]
 }
 
 // Matches checks whether domain matches an entry in the cache.
 // If the cache is not currently loaded, then the provided load
 // function is used to hydrate it.
 func (c *Cache) Matches(domain string, load func() ([]string, error)) (bool, error) {
-	// Load the current root pointer value.
-	ptr := atomic.LoadPointer(&c.rootptr)
+	// Load the current
+	// root pointer value.
+	ptr := c.rootptr.Load()
 
 	if ptr == nil {
 		// Cache is not hydrated.
@@ -60,35 +59,32 @@ func (c *Cache) Matches(domain string, load func() ([]string, error)) (bool, err
 
 		// Allocate new radix trie
 		// node to store matches.
-		root := new(root)
+		ptr = new(root)
 
 		// Add each domain to the trie.
 		for _, domain := range domains {
-			root.Add(domain)
+			ptr.Add(domain)
 		}
 
 		// Sort the trie.
-		root.Sort()
+		ptr.Sort()
 
-		// Store the new node ptr.
-		ptr = unsafe.Pointer(root)
-		atomic.StorePointer(&c.rootptr, ptr)
+		// Store new node ptr.
+		c.rootptr.Store(ptr)
 	}
 
-	// Look for a match in the trie node.
-	return (*root)(ptr).Match(domain), nil
+	// Look for match in trie node.
+	return ptr.Match(domain), nil
 }
 
 // Clear will drop the currently loaded domain list,
 // triggering a reload on next call to .Matches().
-func (c *Cache) Clear() {
-	atomic.StorePointer(&c.rootptr, nil)
-}
+func (c *Cache) Clear() { c.rootptr.Store(nil) }
 
 // String returns a string representation of stored domains in cache.
 func (c *Cache) String() string {
-	if ptr := atomic.LoadPointer(&c.rootptr); ptr != nil {
-		return (*root)(ptr).String()
+	if ptr := c.rootptr.Load(); ptr != nil {
+		return ptr.String()
 	}
 	return "<empty>"
 }

internal/cache/headerfilter/filter.go

@@ -0,0 +1,105 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package headerfilter
+
+import (
+	"fmt"
+	"net/http"
+	"sync/atomic"
+
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/headerfilter"
+)
+
+// Cache provides a means of caching headerfilter.Filters in
+// memory to reduce load on an underlying storage mechanism.
+type Cache struct {
+	// current cached header filters slice.
+	ptr atomic.Pointer[headerfilter.Filters]
+}
+
+// RegularMatch performs .RegularMatch() on cached headerfilter.Filters, loading using callback if necessary.
+func (c *Cache) RegularMatch(h http.Header, load func() ([]*gtsmodel.HeaderFilter, error)) (string, string, error) {
+	// Load ptr value.
+	ptr := c.ptr.Load()
+
+	if ptr == nil {
+		// Cache is not hydrated.
+		// Load filters from callback.
+		filters, err := loadFilters(load)
+		if err != nil {
+			return "", "", err
+		}
+
+		// Store the new
+		// header filters.
+		ptr = &filters
+		c.ptr.Store(ptr)
+	}
+
+	// Deref and perform match.
+	return ptr.RegularMatch(h)
+}
+
+// InverseMatch performs .InverseMatch() on cached headerfilter.Filters, loading using callback if necessary.
+func (c *Cache) InverseMatch(h http.Header, load func() ([]*gtsmodel.HeaderFilter, error)) (string, string, error) {
+	// Load ptr value.
+	ptr := c.ptr.Load()
+
+	if ptr == nil {
+		// Cache is not hydrated.
+		// Load filters from callback.
+		filters, err := loadFilters(load)
+		if err != nil {
+			return "", "", err
+		}
+
+		// Store the new
+		// header filters.
+		ptr = &filters
+		c.ptr.Store(ptr)
+	}
+
+	// Deref and perform match.
+	return ptr.InverseMatch(h)
+}
+
+// Clear will drop the currently loaded filters,
+// triggering a reload on next call to ._Match().
+func (c *Cache) Clear() { c.ptr.Store(nil) }
+
+// loadFilters will load filters from given load callback, creating and parsing raw filters.
+func loadFilters(load func() ([]*gtsmodel.HeaderFilter, error)) (headerfilter.Filters, error) {
+	// Load filters from callback.
+	hdrFilters, err := load()
+	if err != nil {
+		return nil, fmt.Errorf("error reloading cache: %w", err)
+	}
+
+	// Allocate new header filter slice to store expressions.
+	filters := make(headerfilter.Filters, 0, len(hdrFilters))
+
+	// Add all raw expression to filter slice.
+	for _, filter := range hdrFilters {
+		if err := filters.Append(filter.Header, filter.Regex); err != nil {
+			return nil, fmt.Errorf("error appending exprs: %w", err)
+		}
+	}
+
+	return filters, nil
+}

internal/config/config.go

@@ -163,6 +163,7 @@ type Configuration struct {
 	AdvancedThrottlingRetryAfter time.Duration `name:"advanced-throttling-retry-after" usage:"Retry-After duration response to send for throttled requests."`
 	AdvancedSenderMultiplier     int           `name:"advanced-sender-multiplier" usage:"Multiplier to use per cpu for batching outgoing fedi messages. 0 or less turns batching off (not recommended)."`
 	AdvancedCSPExtraURIs         []string      `name:"advanced-csp-extra-uris" usage:"Additional URIs to allow when building content-security-policy for media + images."`
+	AdvancedHeaderFilterMode     string        `name:"advanced-header-filter-mode" usage:"Set incoming request header filtering mode."`
 
 	// HTTPClient configuration vars.
 	HTTPClient HTTPClientConfiguration `name:"http-client"`

internal/config/const.go

@@ -17,10 +17,16 @@
 
 package config
 
-// Instance federation mode determines how this
-// instance federates with others (if at all).
 const (
+	// Instance federation mode determines how this
+	// instance federates with others (if at all).
 	InstanceFederationModeBlocklist = "blocklist"
 	InstanceFederationModeAllowlist = "allowlist"
 	InstanceFederationModeDefault   = InstanceFederationModeBlocklist
+
+	// Request header filter mode determines how
+	// this instance will perform request filtering.
+	RequestHeaderFilterModeAllow    = "allow"
+	RequestHeaderFilterModeBlock    = "block"
+	RequestHeaderFilterModeDisabled = ""
 )

internal/config/defaults.go

@@ -135,6 +135,7 @@ var Defaults = Configuration{
 	AdvancedThrottlingRetryAfter: time.Second * 30,
 	AdvancedSenderMultiplier:     2, // 2 senders per CPU
 	AdvancedCSPExtraURIs:         []string{},
+	AdvancedHeaderFilterMode:     RequestHeaderFilterModeDisabled,
 
 	Cache: CacheConfiguration{
 		// Rough memory target that the total

internal/config/flags.go

@@ -158,6 +158,7 @@ func (s *ConfigState) AddServerFlags(cmd *cobra.Command) {
 		cmd.Flags().Duration(AdvancedThrottlingRetryAfterFlag(), cfg.AdvancedThrottlingRetryAfter, fieldtag("AdvancedThrottlingRetryAfter", "usage"))
 		cmd.Flags().Int(AdvancedSenderMultiplierFlag(), cfg.AdvancedSenderMultiplier, fieldtag("AdvancedSenderMultiplier", "usage"))
 		cmd.Flags().StringSlice(AdvancedCSPExtraURIsFlag(), cfg.AdvancedCSPExtraURIs, fieldtag("AdvancedCSPExtraURIs", "usage"))
+		cmd.Flags().String(AdvancedHeaderFilterModeFlag(), cfg.AdvancedHeaderFilterMode, fieldtag("AdvancedHeaderFilterMode", "usage"))
 
 		cmd.Flags().String(RequestIDHeaderFlag(), cfg.RequestIDHeader, fieldtag("RequestIDHeader", "usage"))
 	})

internal/config/helpers.gen.go

@@ -2600,6 +2600,31 @@ func GetAdvancedCSPExtraURIs() []string { return global.GetAdvancedCSPExtraURIs(
 // SetAdvancedCSPExtraURIs safely sets the value for global configuration 'AdvancedCSPExtraURIs' field
 func SetAdvancedCSPExtraURIs(v []string) { global.SetAdvancedCSPExtraURIs(v) }
 
+// GetAdvancedHeaderFilterMode safely fetches the Configuration value for state's 'AdvancedHeaderFilterMode' field
+func (st *ConfigState) GetAdvancedHeaderFilterMode() (v string) {
+	st.mutex.RLock()
+	v = st.config.AdvancedHeaderFilterMode
+	st.mutex.RUnlock()
+	return
+}
+
+// SetAdvancedHeaderFilterMode safely sets the Configuration value for state's 'AdvancedHeaderFilterMode' field
+func (st *ConfigState) SetAdvancedHeaderFilterMode(v string) {
+	st.mutex.Lock()
+	defer st.mutex.Unlock()
+	st.config.AdvancedHeaderFilterMode = v
+	st.reloadToViper()
+}
+
+// AdvancedHeaderFilterModeFlag returns the flag name for the 'AdvancedHeaderFilterMode' field
+func AdvancedHeaderFilterModeFlag() string { return "advanced-header-filter-mode" }
+
+// GetAdvancedHeaderFilterMode safely fetches the value for global configuration 'AdvancedHeaderFilterMode' field
+func GetAdvancedHeaderFilterMode() string { return global.GetAdvancedHeaderFilterMode() }
+
+// SetAdvancedHeaderFilterMode safely sets the value for global configuration 'AdvancedHeaderFilterMode' field
+func SetAdvancedHeaderFilterMode(v string) { global.SetAdvancedHeaderFilterMode(v) }
+
 // GetHTTPClientAllowIPs safely fetches the Configuration value for state's 'HTTPClient.AllowIPs' field
 func (st *ConfigState) GetHTTPClientAllowIPs() (v []string) {
 	st.mutex.RLock()

internal/db/basic.go

@@ -25,10 +25,6 @@ type Basic interface {
 	// For implementations that don't use tables, this can just return nil.
 	CreateTable(ctx context.Context, i interface{}) error
 
-	// CreateAllTables creates *all* tables necessary for the running of GoToSocial.
-	// Because it uses the 'if not exists' parameter it is safe to run against a GtS that's already been initialized.
-	CreateAllTables(ctx context.Context) error
-
 	// DropTable drops the table for the given interface.
 	// For implementations that don't use tables, this can just return nil.
 	DropTable(ctx context.Context, i interface{}) error

internal/db/bundb/basic.go

@@ -22,7 +22,6 @@ import (
 	"errors"
 
 	"github.com/superseriousbusiness/gotosocial/internal/db"
-	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
 	"github.com/superseriousbusiness/gotosocial/internal/log"
 	"github.com/uptrace/bun"
 )
@@ -120,39 +119,6 @@ func (b *basicDB) CreateTable(ctx context.Context, i interface{}) error {
 	return err
 }
 
-func (b *basicDB) CreateAllTables(ctx context.Context) error {
-	models := []interface{}{
-		&gtsmodel.Account{},
-		&gtsmodel.Application{},
-		&gtsmodel.Block{},
-		&gtsmodel.DomainBlock{},
-		&gtsmodel.EmailDomainBlock{},
-		&gtsmodel.Follow{},
-		&gtsmodel.FollowRequest{},
-		&gtsmodel.MediaAttachment{},
-		&gtsmodel.Mention{},
-		&gtsmodel.Status{},
-		&gtsmodel.StatusToEmoji{},
-		&gtsmodel.StatusFave{},
-		&gtsmodel.StatusBookmark{},
-		&gtsmodel.ThreadMute{},
-		&gtsmodel.Tag{},
-		&gtsmodel.User{},
-		&gtsmodel.Emoji{},
-		&gtsmodel.Instance{},
-		&gtsmodel.Notification{},
-		&gtsmodel.RouterSession{},
-		&gtsmodel.Token{},
-		&gtsmodel.Client{},
-	}
-	for _, i := range models {
-		if err := b.CreateTable(ctx, i); err != nil {
-			return err
-		}
-	}
-	return nil
-}
-
 func (b *basicDB) DropTable(ctx context.Context, i interface{}) error {
 	_, err := b.db.NewDropTable().Model(i).IfExists().Exec(ctx)
 	return err

internal/db/bundb/bundb.go

@@ -67,6 +67,7 @@ type DBService struct {
 	db.Basic
 	db.Domain
 	db.Emoji
+	db.HeaderFilter
 	db.Instance
 	db.List
 	db.Marker
@@ -193,6 +194,10 @@ func NewBunDBService(ctx context.Context, state *state.State) (db.DB, error) {
 			db:    db,
 			state: state,
 		},
+		HeaderFilter: &headerFilterDB{
+			db:    db,
+			state: state,
+		},
 		Instance: &instanceDB{
 			db:    db,
 			state: state,

internal/db/bundb/headerfilter.go

@@ -0,0 +1,207 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package bundb
+
+import (
+	"context"
+	"net/http"
+	"time"
+	"unsafe"
+
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/state"
+	"github.com/uptrace/bun"
+)
+
+type headerFilterDB struct {
+	db    *DB
+	state *state.State
+}
+
+func (h *headerFilterDB) AllowHeaderRegularMatch(ctx context.Context, hdr http.Header) (string, string, error) {
+	return h.state.Caches.AllowHeaderFilters.RegularMatch(hdr, func() ([]*gtsmodel.HeaderFilter, error) {
+		return h.GetAllowHeaderFilters(ctx)
+	})
+}
+
+func (h *headerFilterDB) AllowHeaderInverseMatch(ctx context.Context, hdr http.Header) (string, string, error) {
+	return h.state.Caches.AllowHeaderFilters.InverseMatch(hdr, func() ([]*gtsmodel.HeaderFilter, error) {
+		return h.GetAllowHeaderFilters(ctx)
+	})
+}
+
+func (h *headerFilterDB) BlockHeaderRegularMatch(ctx context.Context, hdr http.Header) (string, string, error) {
+	return h.state.Caches.BlockHeaderFilters.RegularMatch(hdr, func() ([]*gtsmodel.HeaderFilter, error) {
+		return h.GetBlockHeaderFilters(ctx)
+	})
+}
+
+func (h *headerFilterDB) BlockHeaderInverseMatch(ctx context.Context, hdr http.Header) (string, string, error) {
+	return h.state.Caches.BlockHeaderFilters.InverseMatch(hdr, func() ([]*gtsmodel.HeaderFilter, error) {
+		return h.GetBlockHeaderFilters(ctx)
+	})
+}
+
+func (h *headerFilterDB) GetAllowHeaderFilter(ctx context.Context, id string) (*gtsmodel.HeaderFilter, error) {
+	filter := new(gtsmodel.HeaderFilterAllow)
+	if err := h.db.NewSelect().
+		Model(filter).
+		Where("? = ?", bun.Ident("id"), id).
+		Scan(ctx); err != nil {
+		return nil, err
+	}
+	return fromAllowFilter(filter), nil
+}
+
+func (h *headerFilterDB) GetBlockHeaderFilter(ctx context.Context, id string) (*gtsmodel.HeaderFilter, error) {
+	filter := new(gtsmodel.HeaderFilterBlock)
+	if err := h.db.NewSelect().
+		Model(filter).
+		Where("? = ?", bun.Ident("id"), id).
+		Scan(ctx); err != nil {
+		return nil, err
+	}
+	return fromBlockFilter(filter), nil
+}
+
+func (h *headerFilterDB) GetAllowHeaderFilters(ctx context.Context) ([]*gtsmodel.HeaderFilter, error) {
+	var filters []*gtsmodel.HeaderFilterAllow
+	err := h.db.NewSelect().
+		Model(&filters).
+		Scan(ctx, &filters)
+	return fromAllowFilters(filters), err
+}
+
+func (h *headerFilterDB) GetBlockHeaderFilters(ctx context.Context) ([]*gtsmodel.HeaderFilter, error) {
+	var filters []*gtsmodel.HeaderFilterBlock
+	err := h.db.NewSelect().
+		Model(&filters).
+		Scan(ctx, &filters)
+	return fromBlockFilters(filters), err
+}
+
+func (h *headerFilterDB) PutAllowHeaderFilter(ctx context.Context, filter *gtsmodel.HeaderFilter) error {
+	if _, err := h.db.NewInsert().
+		Model(toAllowFilter(filter)).
+		Exec(ctx); err != nil {
+		return err
+	}
+	h.state.Caches.AllowHeaderFilters.Clear()
+	return nil
+}
+
+func (h *headerFilterDB) PutBlockHeaderFilter(ctx context.Context, filter *gtsmodel.HeaderFilter) error {
+	if _, err := h.db.NewInsert().
+		Model(toBlockFilter(filter)).
+		Exec(ctx); err != nil {
+		return err
+	}
+	h.state.Caches.BlockHeaderFilters.Clear()
+	return nil
+}
+
+func (h *headerFilterDB) UpdateAllowHeaderFilter(ctx context.Context, filter *gtsmodel.HeaderFilter, cols ...string) error {
+	filter.UpdatedAt = time.Now()
+	if len(cols) > 0 {
+		// If we're updating by column,
+		// ensure "updated_at" is included.
+		cols = append(cols, "updated_at")
+	}
+	if _, err := h.db.NewUpdate().
+		Model(toAllowFilter(filter)).
+		Column(cols...).
+		Where("? = ?", bun.Ident("id"), filter.ID).
+		Exec(ctx); err != nil {
+		return err
+	}
+	h.state.Caches.AllowHeaderFilters.Clear()
+	return nil
+}
+
+func (h *headerFilterDB) UpdateBlockHeaderFilter(ctx context.Context, filter *gtsmodel.HeaderFilter, cols ...string) error {
+	filter.UpdatedAt = time.Now()
+	if len(cols) > 0 {
+		// If we're updating by column,
+		// ensure "updated_at" is included.
+		cols = append(cols, "updated_at")
+	}
+	if _, err := h.db.NewUpdate().
+		Model(toBlockFilter(filter)).
+		Column(cols...).
+		Where("? = ?", bun.Ident("id"), filter.ID).
+		Exec(ctx); err != nil {
+		return err
+	}
+	h.state.Caches.BlockHeaderFilters.Clear()
+	return nil
+}
+
+func (h *headerFilterDB) DeleteAllowHeaderFilter(ctx context.Context, id string) error {
+	if _, err := h.db.NewDelete().
+		Table("header_filter_allows").
+		Where("? = ?", bun.Ident("id"), id).
+		Exec(ctx); err != nil {
+		return err
+	}
+	h.state.Caches.AllowHeaderFilters.Clear()
+	return nil
+}
+
+func (h *headerFilterDB) DeleteBlockHeaderFilter(ctx context.Context, id string) error {
+	if _, err := h.db.NewDelete().
+		Table("header_filter_blocks").
+		Where("? = ?", bun.Ident("id"), id).
+		Exec(ctx); err != nil {
+		return err
+	}
+	h.state.Caches.BlockHeaderFilters.Clear()
+	return nil
+}
+
+// NOTE:
+// all of the below unsafe cast functions
+// are only possible because HeaderFilterAllow{},
+// HeaderFilterBlock{}, HeaderFilter{} while
+// different types in source, have exactly the
+// same size and layout in memory. the unsafe
+// cast simply changes the type associated with
+// that block of memory.
+
+func toAllowFilter(filter *gtsmodel.HeaderFilter) *gtsmodel.HeaderFilterAllow {
+	return (*gtsmodel.HeaderFilterAllow)(unsafe.Pointer(filter))
+}
+
+func toBlockFilter(filter *gtsmodel.HeaderFilter) *gtsmodel.HeaderFilterBlock {
+	return (*gtsmodel.HeaderFilterBlock)(unsafe.Pointer(filter))
+}
+
+func fromAllowFilter(filter *gtsmodel.HeaderFilterAllow) *gtsmodel.HeaderFilter {
+	return (*gtsmodel.HeaderFilter)(unsafe.Pointer(filter))
+}
+
+func fromBlockFilter(filter *gtsmodel.HeaderFilterBlock) *gtsmodel.HeaderFilter {
+	return (*gtsmodel.HeaderFilter)(unsafe.Pointer(filter))
+}
+
+func fromAllowFilters(filters []*gtsmodel.HeaderFilterAllow) []*gtsmodel.HeaderFilter {
+	return *(*[]*gtsmodel.HeaderFilter)(unsafe.Pointer(&filters))
+}
+
+func fromBlockFilters(filters []*gtsmodel.HeaderFilterBlock) []*gtsmodel.HeaderFilter {
+	return *(*[]*gtsmodel.HeaderFilter)(unsafe.Pointer(&filters))
+}

internal/db/bundb/headerfilter_test.go

@@ -0,0 +1,125 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package bundb_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/suite"
+	"github.com/superseriousbusiness/gotosocial/internal/db"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+)
+
+type HeaderFilterTestSuite struct {
+	BunDBStandardTestSuite
+}
+
+func (suite *HeaderFilterTestSuite) TestAllowHeaderFilterGetPutUpdateDelete() {
+	suite.testHeaderFilterGetPutUpdateDelete(
+		suite.db.GetAllowHeaderFilter,
+		suite.db.GetAllowHeaderFilters,
+		suite.db.PutAllowHeaderFilter,
+		suite.db.UpdateAllowHeaderFilter,
+		suite.db.DeleteAllowHeaderFilter,
+	)
+}
+
+func (suite *HeaderFilterTestSuite) TestBlockHeaderFilterGetPutUpdateDelete() {
+	suite.testHeaderFilterGetPutUpdateDelete(
+		suite.db.GetBlockHeaderFilter,
+		suite.db.GetBlockHeaderFilters,
+		suite.db.PutBlockHeaderFilter,
+		suite.db.UpdateBlockHeaderFilter,
+		suite.db.DeleteBlockHeaderFilter,
+	)
+}
+
+func (suite *HeaderFilterTestSuite) testHeaderFilterGetPutUpdateDelete(
+	get func(context.Context, string) (*gtsmodel.HeaderFilter, error),
+	getAll func(context.Context) ([]*gtsmodel.HeaderFilter, error),
+	put func(context.Context, *gtsmodel.HeaderFilter) error,
+	update func(context.Context, *gtsmodel.HeaderFilter, ...string) error,
+	delete func(context.Context, string) error,
+) {
+	t := suite.T()
+
+	// Create new example header filter.
+	filter := gtsmodel.HeaderFilter{
+		ID:       "some unique id",
+		Header:   "Http-Header-Key",
+		Regex:    ".*",
+		AuthorID: "some unique author id",
+	}
+
+	// Create new cancellable test context.
+	ctx := context.Background()
+	ctx, cncl := context.WithCancel(ctx)
+	defer cncl()
+
+	// Insert the example header filter into db.
+	if err := put(ctx, &filter); err != nil {
+		t.Fatalf("error inserting header filter: %v", err)
+	}
+
+	// Now fetch newly created filter.
+	check, err := get(ctx, filter.ID)
+	if err != nil {
+		t.Fatalf("error fetching header filter: %v", err)
+	}
+
+	// Check all expected fields match.
+	suite.Equal(filter.ID, check.ID)
+	suite.Equal(filter.Header, check.Header)
+	suite.Equal(filter.Regex, check.Regex)
+	suite.Equal(filter.AuthorID, check.AuthorID)
+
+	// Fetch all header filters.
+	all, err := getAll(ctx)
+	if err != nil {
+		t.Fatalf("error fetching header filters: %v", err)
+	}
+
+	// Ensure contains example.
+	suite.Equal(len(all), 1)
+	suite.Equal(all[0].ID, filter.ID)
+
+	// Update the header filter regex value.
+	check.Regex = "new regex value"
+	if err := update(ctx, check); err != nil {
+		t.Fatalf("error updating header filter: %v", err)
+	}
+
+	// Ensure 'updated_at' was updated on check model.
+	suite.True(check.UpdatedAt.After(filter.UpdatedAt))
+
+	// Now delete the header filter from db.
+	if err := delete(ctx, filter.ID); err != nil {
+		t.Fatalf("error deleting header filter: %v", err)
+	}
+
+	// Ensure we can't refetch it.
+	_, err = get(ctx, filter.ID)
+	if err != db.ErrNoEntries {
+		t.Fatalf("deleted header filter returned unexpected error: %v", err)
+	}
+}
+
+func TestHeaderFilterTestSuite(t *testing.T) {
+	suite.Run(t, new(HeaderFilterTestSuite))
+}

internal/db/bundb/migrations/20231212144715_add_header_filters.go

@@ -0,0 +1,54 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package migrations
+
+import (
+	"context"
+
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/uptrace/bun"
+)
+
+func init() {
+	up := func(ctx context.Context, db *bun.DB) error {
+		for _, model := range []any{
+			&gtsmodel.HeaderFilterAllow{},
+			&gtsmodel.HeaderFilterBlock{},
+		} {
+			_, err := db.NewCreateTable().
+				IfNotExists().
+				Model(model).
+				Exec(ctx)
+			if err != nil {
+				return err
+			}
+		}
+
+		return nil
+	}
+
+	down := func(ctx context.Context, db *bun.DB) error {
+		return db.RunInTx(ctx, nil, func(ctx context.Context, tx bun.Tx) error {
+			return nil
+		})
+	}
+
+	if err := Migrations.Register(up, down); err != nil {
+		panic(err)
+	}
+}

internal/db/db.go

@@ -30,6 +30,7 @@ type DB interface {
 	Basic
 	Domain
 	Emoji
+	HeaderFilter
 	Instance
 	List
 	Marker

internal/db/headerfilter.go

@@ -0,0 +1,73 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package db
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+)
+
+type HeaderFilter interface {
+	// AllowHeaderRegularMatch performs an headerfilter.Filter.RegularMatch() on cached allow header filters.
+	// (Note: the actual matching code can be found under ./internal/headerfilter/ ).
+	AllowHeaderRegularMatch(ctx context.Context, hdr http.Header) (string, string, error)
+
+	// AllowHeaderInverseMatch performs an headerfilter.Filter.InverseMatch() on cached allow header filters.
+	// (Note: the actual matching code can be found under ./internal/headerfilter/ ).
+	AllowHeaderInverseMatch(ctx context.Context, hdr http.Header) (string, string, error)
+
+	// BlockHeaderRegularMatch performs an headerfilter.Filter.RegularMatch() on cached block header filters.
+	// (Note: the actual matching code can be found under ./internal/headerfilter/ ).
+	BlockHeaderRegularMatch(ctx context.Context, hdr http.Header) (string, string, error)
+
+	// BlockHeaderInverseMatch performs an headerfilter.Filter.InverseMatch() on cached block header filters.
+	// (Note: the actual matching code can be found under ./internal/headerfilter/ ).
+	BlockHeaderInverseMatch(ctx context.Context, hdr http.Header) (string, string, error)
+
+	// GetAllowHeaderFilter fetches the allow header filter with ID from the database.
+	GetAllowHeaderFilter(ctx context.Context, id string) (*gtsmodel.HeaderFilter, error)
+
+	// GetBlockHeaderFilter fetches the block header filter with ID from the database.
+	GetBlockHeaderFilter(ctx context.Context, id string) (*gtsmodel.HeaderFilter, error)
+
+	// GetAllowHeaderFilters fetches all allow header filters from the database.
+	GetAllowHeaderFilters(ctx context.Context) ([]*gtsmodel.HeaderFilter, error)
+
+	// GetBlockHeaderFilters fetches all block header filters from the database.
+	GetBlockHeaderFilters(ctx context.Context) ([]*gtsmodel.HeaderFilter, error)
+
+	// PutAllowHeaderFilter inserts the given allow header filter into the database.
+	PutAllowHeaderFilter(ctx context.Context, filter *gtsmodel.HeaderFilter) error
+
+	// PutBlockHeaderFilter inserts the given block header filter into the database.
+	PutBlockHeaderFilter(ctx context.Context, filter *gtsmodel.HeaderFilter) error
+
+	// UpdateAllowHeaderFilter updates the given allow header filter in the database, only updating given columns if provided.
+	UpdateAllowHeaderFilter(ctx context.Context, filter *gtsmodel.HeaderFilter, cols ...string) error
+
+	// UpdateBlockHeaderFilter updates the given block header filter in the database, only updating given columns if provided.
+	UpdateBlockHeaderFilter(ctx context.Context, filter *gtsmodel.HeaderFilter, cols ...string) error
+
+	// DeleteAllowHeaderFilter deletes the allow header filter with ID from the database.
+	DeleteAllowHeaderFilter(ctx context.Context, id string) error
+
+	// DeleteBlockHeaderFilter deletes the block header filter with ID from the database.
+	DeleteBlockHeaderFilter(ctx context.Context, id string) error
+}

internal/gtsmodel/headerfilter.go

@@ -0,0 +1,54 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package gtsmodel
+
+import (
+	"time"
+	"unsafe"
+)
+
+func init() {
+	// Note that since all of the below calculations are
+	// constant, these should be optimized out of builds.
+	const filterSz = unsafe.Sizeof(HeaderFilter{})
+	if unsafe.Sizeof(HeaderFilterAllow{}) != filterSz {
+		panic("HeaderFilterAllow{} needs to have the same in-memory size / layout as HeaderFilter{}")
+	}
+	if unsafe.Sizeof(HeaderFilterBlock{}) != filterSz {
+		panic("HeaderFilterBlock{} needs to have the same in-memory size / layout as HeaderFilter{}")
+	}
+}
+
+// HeaderFilterAllow represents an allow HTTP header filter in the database.
+type HeaderFilterAllow struct{ HeaderFilter }
+
+// HeaderFilterBlock represents a block HTTP header filter in the database.
+type HeaderFilterBlock struct{ HeaderFilter }
+
+// HeaderFilter represents an HTTP request filter in
+// the database, with a header to match against, value
+// matching regex, and details about its creation.
+type HeaderFilter struct {
+	ID        string    `bun:"type:CHAR(26),pk,nullzero,notnull,unique"`                    // ID of this item in the database
+	Header    string    `bun:",nullzero,notnull,unique:header_regex"`                       // Request header this filter pertains to
+	Regex     string    `bun:",nullzero,notnull,unique:header_regex"`                       // Request header value matching regular expression
+	AuthorID  string    `bun:"type:CHAR(26),nullzero,notnull"`                              // Account ID of the creator of this filter
+	Author    *Account  `bun:"-"`                                                           // Account corresponding to AuthorID
+	CreatedAt time.Time `bun:"type:timestamptz,nullzero,notnull,default:current_timestamp"` // when was item created
+	UpdatedAt time.Time `bun:"type:timestamptz,nullzero,notnull,default:current_timestamp"` // when was item last updated
+}

internal/headerfilter/filter.go

@@ -0,0 +1,136 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package headerfilter
+
+import (
+	"errors"
+	"fmt"
+	"net/http"
+	"net/textproto"
+	"regexp"
+)
+
+// Maximum header value size before we return
+// an instant negative match. They shouldn't
+// go beyond this size in most cases anywho.
+const MaxHeaderValue = 1024
+
+// ErrLargeHeaderValue is returned on attempting to match on a value > MaxHeaderValue.
+var ErrLargeHeaderValue = errors.New("header value too large")
+
+// Filters represents a set of http.Header regular
+// expression filters built-in statistic tracking.
+type Filters []headerfilter
+
+type headerfilter struct {
+	// key is the header key to match against
+	// in canonical textproto mime header format.
+	key string
+
+	// exprs contains regular expressions to
+	// match values against for this header key.
+	exprs []*regexp.Regexp
+}
+
+// Append will add new header filter expression under given header key.
+func (fs *Filters) Append(key string, expr string) error {
+	var filter *headerfilter
+
+	// Ensure in canonical mime header format.
+	key = textproto.CanonicalMIMEHeaderKey(key)
+
+	// Look for existing filter
+	// with key in filter slice.
+	for i := range *fs {
+		if (*fs)[i].key == key {
+			filter = &((*fs)[i])
+			break
+		}
+	}
+
+	if filter == nil {
+		// No existing filter found, create new.
+
+		// Append new header filter to slice.
+		(*fs) = append((*fs), headerfilter{})
+
+		// Then take ptr to this new filter
+		// at the last index in the slice.
+		filter = &((*fs)[len((*fs))-1])
+
+		// Setup new key.
+		filter.key = key
+	}
+
+	// Compile regular expression.
+	reg, err := regexp.Compile(expr)
+	if err != nil {
+		return fmt.Errorf("error compiling regexp %q: %w", expr, err)
+	}
+
+	// Append regular expression to filter.
+	filter.exprs = append(filter.exprs, reg)
+
+	return nil
+}
+
+// RegularMatch returns whether any values in http header
+// matches any of the receiving filter regular expressions.
+// This returns the matched header key, and matching regexp.
+func (fs Filters) RegularMatch(h http.Header) (string, string, error) {
+	for _, filter := range fs {
+		for _, value := range h[filter.key] {
+			// Don't perform match on large values
+			// to mitigate denial of service attacks.
+			if len(value) > MaxHeaderValue {
+				return "", "", ErrLargeHeaderValue
+			}
+
+			// Compare against regular exprs.
+			for _, expr := range filter.exprs {
+				if expr.MatchString(value) {
+					return filter.key, expr.String(), nil
+				}
+			}
+		}
+	}
+	return "", "", nil
+}
+
+// InverseMatch returns whether any values in http header do
+// NOT match any of the receiving filter regular expressions.
+// This returns the matched header key, and matching regexp.
+func (fs Filters) InverseMatch(h http.Header) (string, string, error) {
+	for _, filter := range fs {
+		for _, value := range h[filter.key] {
+			// Don't perform match on large values
+			// to mitigate denial of service attacks.
+			if len(value) > MaxHeaderValue {
+				return "", "", ErrLargeHeaderValue
+			}
+
+			// Compare against regular exprs.
+			for _, expr := range filter.exprs {
+				if !expr.MatchString(value) {
+					return filter.key, expr.String(), nil
+				}
+			}
+		}
+	}
+	return "", "", nil
+}

internal/middleware/headerfilter.go

@@ -0,0 +1,251 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package middleware
+
+import (
+	"sync"
+
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/headerfilter"
+	"github.com/superseriousbusiness/gotosocial/internal/log"
+	"github.com/superseriousbusiness/gotosocial/internal/state"
+)
+
+var (
+	allowMatches = matchstats{m: make(map[string]uint64)}
+	blockMatches = matchstats{m: make(map[string]uint64)}
+)
+
+// matchstats is a simple statistics
+// counter for header filter matches.
+// TODO: replace with otel.
+type matchstats struct {
+	m map[string]uint64
+	l sync.Mutex
+}
+
+func (m *matchstats) Add(hdr, regex string) {
+	m.l.Lock()
+	key := hdr + ":" + regex
+	m.m[key]++
+	m.l.Unlock()
+}
+
+// HeaderFilter returns a gin middleware handler that provides HTTP
+// request blocking (filtering) based on database allow / block filters.
+func HeaderFilter(state *state.State) gin.HandlerFunc {
+	switch mode := config.GetAdvancedHeaderFilterMode(); mode {
+	case config.RequestHeaderFilterModeDisabled:
+		return func(ctx *gin.Context) {}
+
+	case config.RequestHeaderFilterModeAllow:
+		return headerFilterAllowMode(state)
+
+	case config.RequestHeaderFilterModeBlock:
+		return headerFilterBlockMode(state)
+
+	default:
+		panic("unrecognized filter mode: " + mode)
+	}
+}
+
+func headerFilterAllowMode(state *state.State) func(c *gin.Context) {
+	_ = *state //nolint
+	// Allowlist mode: explicit block takes
+	// precedence over explicit allow.
+	//
+	// Headers that have neither block
+	// or allow entries are blocked.
+	return func(c *gin.Context) {
+
+		// Check if header is explicitly blocked.
+		block, err := isHeaderBlocked(state, c)
+		if err != nil {
+			respondInternalServerError(c, err)
+			return
+		}
+
+		if block {
+			respondBlocked(c)
+			return
+		}
+
+		// Check if header is missing explicit allow.
+		notAllow, err := isHeaderNotAllowed(state, c)
+		if err != nil {
+			respondInternalServerError(c, err)
+			return
+		}
+
+		if notAllow {
+			respondBlocked(c)
+			return
+		}
+
+		// Allowed!
+		c.Next()
+	}
+}
+
+func headerFilterBlockMode(state *state.State) func(c *gin.Context) {
+	_ = *state //nolint
+	// Blocklist/default mode: explicit allow
+	// takes precedence over explicit block.
+	//
+	// Headers that have neither block
+	// or allow entries are allowed.
+	return func(c *gin.Context) {
+
+		// Check if header is explicitly allowed.
+		allow, err := isHeaderAllowed(state, c)
+		if err != nil {
+			respondInternalServerError(c, err)
+			return
+		}
+
+		if !allow {
+			// Check if header is explicitly blocked.
+			block, err := isHeaderBlocked(state, c)
+			if err != nil {
+				respondInternalServerError(c, err)
+				return
+			}
+
+			if block {
+				respondBlocked(c)
+				return
+			}
+		}
+
+		// Allowed!
+		c.Next()
+	}
+}
+
+func isHeaderBlocked(state *state.State, c *gin.Context) (bool, error) {
+	var (
+		ctx = c.Request.Context()
+		hdr = c.Request.Header
+	)
+
+	// Perform an explicit is-blocked check on request header.
+	key, expr, err := state.DB.BlockHeaderRegularMatch(ctx, hdr)
+	switch err {
+	case nil:
+		break
+
+	case headerfilter.ErrLargeHeaderValue:
+		log.Warn(ctx, "large header value")
+		key = "*" // block large headers
+
+	default:
+		err := gtserror.Newf("error checking header: %w", err)
+		return false, err
+	}
+
+	if key != "" {
+		if expr != "" {
+			// Increment block matches stat.
+			// TODO: replace expvar with build
+			// taggable metrics types in State{}.
+			blockMatches.Add(key, expr)
+		}
+
+		// A header was matched against!
+		// i.e. this request is blocked.
+		return true, nil
+	}
+
+	return false, nil
+}
+
+func isHeaderAllowed(state *state.State, c *gin.Context) (bool, error) {
+	var (
+		ctx = c.Request.Context()
+		hdr = c.Request.Header
+	)
+
+	// Perform an explicit is-allowed check on request header.
+	key, expr, err := state.DB.AllowHeaderRegularMatch(ctx, hdr)
+	switch err {
+	case nil:
+		break
+
+	case headerfilter.ErrLargeHeaderValue:
+		log.Warn(ctx, "large header value")
+		key = "" // block large headers
+
+	default:
+		err := gtserror.Newf("error checking header: %w", err)
+		return false, err
+	}
+
+	if key != "" {
+		if expr != "" {
+			// Increment allow matches stat.
+			// TODO: replace expvar with build
+			// taggable metrics types in State{}.
+			allowMatches.Add(key, expr)
+		}
+
+		// A header was matched against!
+		// i.e. this request is allowed.
+		return true, nil
+	}
+
+	return false, nil
+}
+
+func isHeaderNotAllowed(state *state.State, c *gin.Context) (bool, error) {
+	var (
+		ctx = c.Request.Context()
+		hdr = c.Request.Header
+	)
+
+	// Perform an explicit is-NOT-allowed check on request header.
+	key, expr, err := state.DB.AllowHeaderInverseMatch(ctx, hdr)
+	switch err {
+	case nil:
+		break
+
+	case headerfilter.ErrLargeHeaderValue:
+		log.Warn(ctx, "large header value")
+		key = "*" // block large headers
+
+	default:
+		err := gtserror.Newf("error checking header: %w", err)
+		return false, err
+	}
+
+	if key != "" {
+		if expr != "" {
+			// Increment allow matches stat.
+			// TODO: replace expvar with build
+			// taggable metrics types in State{}.
+			allowMatches.Add(key, expr)
+		}
+
+		// A header was matched against!
+		// i.e. request is NOT allowed.
+		return true, nil
+	}
+
+	return false, nil
+}

internal/middleware/headerfilter_test.go

@@ -0,0 +1,299 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package middleware_test
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/config"
+	"github.com/superseriousbusiness/gotosocial/internal/db/bundb"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/headerfilter"
+	"github.com/superseriousbusiness/gotosocial/internal/id"
+	"github.com/superseriousbusiness/gotosocial/internal/middleware"
+	"github.com/superseriousbusiness/gotosocial/internal/state"
+	"github.com/superseriousbusiness/gotosocial/testrig"
+)
+
+func TestHeaderFilter(t *testing.T) {
+	testrig.InitTestLog()
+	testrig.InitTestConfig()
+
+	for _, test := range []struct {
+		mode   string
+		allow  []filter
+		block  []filter
+		input  http.Header
+		expect bool
+	}{
+		{
+			// Allow mode with expected 200 OK.
+			mode: config.RequestHeaderFilterModeAllow,
+			allow: []filter{
+				{"User-Agent", ".*Firefox.*"},
+			},
+			block: []filter{},
+			input: http.Header{
+				"User-Agent": []string{"Firefox v169.42; Extra Tracking Info"},
+			},
+			expect: true,
+		},
+		{
+			// Allow mode with expected 403 Forbidden.
+			mode: config.RequestHeaderFilterModeAllow,
+			allow: []filter{
+				{"User-Agent", ".*Firefox.*"},
+			},
+			block: []filter{},
+			input: http.Header{
+				"User-Agent": []string{"Chromium v169.42; Extra Tracking Info"},
+			},
+			expect: false,
+		},
+		{
+			// Allow mode with too long header value expecting 403 Forbidden.
+			mode: config.RequestHeaderFilterModeAllow,
+			allow: []filter{
+				{"User-Agent", ".*"},
+			},
+			block: []filter{},
+			input: http.Header{
+				"User-Agent": []string{func() string {
+					var buf strings.Builder
+					for i := 0; i < headerfilter.MaxHeaderValue+1; i++ {
+						buf.WriteByte(' ')
+					}
+					return buf.String()
+				}()},
+			},
+			expect: false,
+		},
+		{
+			// Allow mode with explicit block expecting 403 Forbidden.
+			mode: config.RequestHeaderFilterModeAllow,
+			allow: []filter{
+				{"User-Agent", ".*Firefox.*"},
+			},
+			block: []filter{
+				{"User-Agent", ".*Firefox v169\\.42.*"},
+			},
+			input: http.Header{
+				"User-Agent": []string{"Firefox v169.42; Extra Tracking Info"},
+			},
+			expect: false,
+		},
+		{
+			// Block mode with an expected 403 Forbidden.
+			mode:  config.RequestHeaderFilterModeBlock,
+			allow: []filter{},
+			block: []filter{
+				{"User-Agent", ".*Firefox.*"},
+			},
+			input: http.Header{
+				"User-Agent": []string{"Firefox v169.42; Extra Tracking Info"},
+			},
+			expect: false,
+		},
+		{
+			// Block mode with an expected 200 OK.
+			mode:  config.RequestHeaderFilterModeBlock,
+			allow: []filter{},
+			block: []filter{
+				{"User-Agent", ".*Firefox.*"},
+			},
+			input: http.Header{
+				"User-Agent": []string{"Chromium v169.42; Extra Tracking Info"},
+			},
+			expect: true,
+		},
+		{
+			// Block mode with too long header value expecting 403 Forbidden.
+			mode:  config.RequestHeaderFilterModeBlock,
+			allow: []filter{},
+			block: []filter{
+				{"User-Agent", "none"},
+			},
+			input: http.Header{
+				"User-Agent": []string{func() string {
+					var buf strings.Builder
+					for i := 0; i < headerfilter.MaxHeaderValue+1; i++ {
+						buf.WriteByte(' ')
+					}
+					return buf.String()
+				}()},
+			},
+			expect: false,
+		},
+		{
+			// Block mode with explicit allow expecting 200 OK.
+			mode: config.RequestHeaderFilterModeBlock,
+			allow: []filter{
+				{"User-Agent", ".*Firefox.*"},
+			},
+			block: []filter{
+				{"User-Agent", ".*Firefox v169\\.42.*"},
+			},
+			input: http.Header{
+				"User-Agent": []string{"Firefox v169.42; Extra Tracking Info"},
+			},
+			expect: true,
+		},
+		{
+			// Disabled mode with an expected 200 OK.
+			mode: config.RequestHeaderFilterModeDisabled,
+			allow: []filter{
+				{"Key1", "only-this"},
+				{"Key2", "only-this"},
+				{"Key3", "only-this"},
+			},
+			block: []filter{
+				{"Key1", "Value"},
+				{"Key2", "Value"},
+				{"Key3", "Value"},
+			},
+			input: http.Header{
+				"Key1": []string{"Value"},
+				"Key2": []string{"Value"},
+				"Key3": []string{"Value"},
+			},
+			expect: true,
+		},
+	} {
+		// Generate a unique name for this test case.
+		name := fmt.Sprintf("%s allow=%v block=%v => expect=%v",
+			test.mode,
+			test.allow,
+			test.block,
+			test.expect,
+		)
+
+		// Update header filter mode to test case.
+		config.SetAdvancedHeaderFilterMode(test.mode)
+
+		// Run this particular test case.
+		ok := t.Run(name, func(t *testing.T) {
+			testHeaderFilter(t,
+				test.allow,
+				test.block,
+				test.input,
+				test.expect,
+			)
+		})
+
+		if !ok {
+			return
+		}
+	}
+}
+
+func testHeaderFilter(t *testing.T, allow, block []filter, input http.Header, expect bool) {
+	var err error
+
+	// Create test context with cancel.
+	ctx := context.Background()
+	ctx, cncl := context.WithCancel(ctx)
+	defer cncl()
+
+	// Initialize caches.
+	var state state.State
+	state.Caches.Init()
+
+	// Create new database instance with test config.
+	state.DB, err = bundb.NewBunDBService(ctx, &state)
+	if err != nil {
+		t.Fatalf("error opening database: %v", err)
+	}
+
+	// Insert all allow filters into DB.
+	for _, filter := range allow {
+		filter := &gtsmodel.HeaderFilter{
+			ID:       id.NewULID(),
+			Header:   filter.header,
+			Regex:    filter.regex,
+			AuthorID: "admin-id",
+			Author:   nil,
+		}
+
+		if err := state.DB.PutAllowHeaderFilter(ctx, filter); err != nil {
+			t.Fatalf("error inserting allow filter into database: %v", err)
+		}
+	}
+
+	// Insert all block filters into DB.
+	for _, filter := range block {
+		filter := &gtsmodel.HeaderFilter{
+			ID:       id.NewULID(),
+			Header:   filter.header,
+			Regex:    filter.regex,
+			AuthorID: "admin-id",
+			Author:   nil,
+		}
+
+		if err := state.DB.PutBlockHeaderFilter(ctx, filter); err != nil {
+			t.Fatalf("error inserting block filter into database: %v", err)
+		}
+	}
+
+	// Gin test http engine
+	// (used for ctx init).
+	e := gin.New()
+
+	// Create new filter middleware to test against.
+	middleware := middleware.HeaderFilter(&state)
+	e.Use(middleware)
+
+	// Set the empty gin handler (always returns okay).
+	e.Handle("GET", "/", func(ctx *gin.Context) { ctx.Status(200) })
+
+	// Prepare a gin test context.
+	r := httptest.NewRequest("GET", "/", nil)
+	rw := httptest.NewRecorder()
+
+	// Set input headers.
+	r.Header = input
+
+	// Pass req through
+	// engine handler.
+	e.ServeHTTP(rw, r)
+
+	// Get http result.
+	res := rw.Result()
+
+	switch {
+	case expect && res.StatusCode != http.StatusOK:
+		t.Errorf("unexpected response (should allow): %s", res.Status)
+
+	case !expect && res.StatusCode != http.StatusForbidden:
+		t.Errorf("unexpected response (should block): %s", res.Status)
+	}
+}
+
+type filter struct {
+	header string
+	regex  string
+}
+
+func (hf *filter) String() string {
+	return fmt.Sprintf("%s=%q", hf.header, hf.regex)
+}

internal/middleware/ratelimit.go

@@ -146,7 +146,7 @@ func RateLimit(limit int, exceptions []string) gin.HandlerFunc {
 			apiutil.Data(c,
 				http.StatusTooManyRequests,
 				apiutil.AppJSON,
-				apiutil.ErrorRateLimitReached,
+				apiutil.ErrorRateLimited,
 			)
 			c.Abort()
 			return

internal/middleware/useragent.go

@@ -18,21 +18,22 @@
 package middleware
 
 import (
-	"errors"
 	"net/http"
 
 	"github.com/gin-gonic/gin"
+	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
 )
 
 // UserAgent returns a gin middleware which aborts requests with
 // empty user agent strings, returning code 418 - I'm a teapot.
 func UserAgent() gin.HandlerFunc {
 	// todo: make this configurable
+	var rsp = []byte(`{"error": "I'm a teapot: no user-agent sent with request"}`)
 	return func(c *gin.Context) {
 		if ua := c.Request.UserAgent(); ua == "" {
-			code := http.StatusTeapot
-			err := errors.New(http.StatusText(code) + ": no user-agent sent with request")
-			c.AbortWithStatusJSON(code, gin.H{"error": err.Error()})
+			apiutil.Data(c,
+				http.StatusTeapot, apiutil.AppJSON, rsp)
+			c.Abort()
 		}
 	}
 }

internal/middleware/util.go

@@ -0,0 +1,51 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package middleware
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+	apiutil "github.com/superseriousbusiness/gotosocial/internal/api/util"
+)
+
+// respondBlocked responds to the given gin context with
+// status forbidden, and a generic forbidden JSON response,
+// finally aborting the gin handler chain.
+func respondBlocked(c *gin.Context) {
+	apiutil.Data(c,
+		http.StatusForbidden,
+		apiutil.AppJSON,
+		apiutil.StatusForbiddenJSON,
+	)
+	c.Abort()
+}
+
+// respondInternalServerError responds to the given gin context
+// with status internal server error, a generic internal server
+// error JSON response, sets the given error on the gin context
+// for later logging, finally aborting the gin handler chain.
+func respondInternalServerError(c *gin.Context, err error) {
+	apiutil.Data(c,
+		http.StatusInternalServerError,
+		apiutil.AppJSON,
+		apiutil.StatusInternalServerErrorJSON,
+	)
+	_ = c.Error(err)
+	c.Abort()
+}

internal/processing/admin/headerfilter.go

@@ -0,0 +1,215 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package admin
+
+import (
+	"context"
+	"errors"
+	"net/textproto"
+	"regexp"
+
+	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
+	"github.com/superseriousbusiness/gotosocial/internal/db"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
+	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
+	"github.com/superseriousbusiness/gotosocial/internal/headerfilter"
+	"github.com/superseriousbusiness/gotosocial/internal/id"
+	"github.com/superseriousbusiness/gotosocial/internal/util"
+)
+
+// GetAllowHeaderFilter fetches allow HTTP header filter with provided ID from the database.
+func (p *Processor) GetAllowHeaderFilter(ctx context.Context, id string) (*apimodel.HeaderFilter, gtserror.WithCode) {
+	return p.getHeaderFilter(ctx, id, p.state.DB.GetAllowHeaderFilter)
+}
+
+// GetBlockHeaderFilter fetches block HTTP header filter with provided ID from the database.
+func (p *Processor) GetBlockHeaderFilter(ctx context.Context, id string) (*apimodel.HeaderFilter, gtserror.WithCode) {
+	return p.getHeaderFilter(ctx, id, p.state.DB.GetBlockHeaderFilter)
+}
+
+// GetAllowHeaderFilters fetches all allow HTTP header filters stored in the database.
+func (p *Processor) GetAllowHeaderFilters(ctx context.Context) ([]*apimodel.HeaderFilter, gtserror.WithCode) {
+	return p.getHeaderFilters(ctx, p.state.DB.GetAllowHeaderFilters)
+}
+
+// GetBlockHeaderFilters fetches all block HTTP header filters stored in the database.
+func (p *Processor) GetBlockHeaderFilters(ctx context.Context) ([]*apimodel.HeaderFilter, gtserror.WithCode) {
+	return p.getHeaderFilters(ctx, p.state.DB.GetBlockHeaderFilters)
+}
+
+// CreateAllowHeaderFilter inserts the incoming allow HTTP header filter into the database, marking as authored by provided admin account.
+func (p *Processor) CreateAllowHeaderFilter(ctx context.Context, admin *gtsmodel.Account, request *apimodel.HeaderFilterRequest) (*apimodel.HeaderFilter, gtserror.WithCode) {
+	return p.createHeaderFilter(ctx, admin, request, p.state.DB.PutAllowHeaderFilter)
+}
+
+// CreateBlockHeaderFilter inserts the incoming block HTTP header filter into the database, marking as authored by provided admin account.
+func (p *Processor) CreateBlockHeaderFilter(ctx context.Context, admin *gtsmodel.Account, request *apimodel.HeaderFilterRequest) (*apimodel.HeaderFilter, gtserror.WithCode) {
+	return p.createHeaderFilter(ctx, admin, request, p.state.DB.PutBlockHeaderFilter)
+}
+
+// DeleteAllowHeaderFilter deletes the allowing HTTP header filter with provided ID from the database.
+func (p *Processor) DeleteAllowHeaderFilter(ctx context.Context, id string) gtserror.WithCode {
+	return p.deleteHeaderFilter(ctx, id, p.state.DB.DeleteAllowHeaderFilter)
+}
+
+// DeleteBlockHeaderFilter deletes the blocking HTTP header filter with provided ID from the database.
+func (p *Processor) DeleteBlockHeaderFilter(ctx context.Context, id string) gtserror.WithCode {
+	return p.deleteHeaderFilter(ctx, id, p.state.DB.DeleteBlockHeaderFilter)
+}
+
+// getHeaderFilter fetches an HTTP header filter with
+// provided ID, using given get function, converting the
+// resulting filter to returnable frontend API model.
+func (p *Processor) getHeaderFilter(
+	ctx context.Context,
+	id string,
+	get func(context.Context, string) (*gtsmodel.HeaderFilter, error),
+) (
+	*apimodel.HeaderFilter,
+	gtserror.WithCode,
+) {
+	// Select filter by ID from db.
+	filter, err := get(ctx, id)
+
+	switch {
+	// Successfully found.
+	case err == nil:
+		return toAPIHeaderFilter(filter), nil
+
+	// Filter does not exist with ID.
+	case errors.Is(err, db.ErrNoEntries):
+		const text = "filter not found"
+		return nil, gtserror.NewErrorNotFound(errors.New(text), text)
+
+	// Any other error type.
+	default:
+		err := gtserror.Newf("error selecting from database: %w", err)
+		return nil, gtserror.NewErrorInternalError(err)
+	}
+}
+
+// getHeaderFilters fetches all HTTP header filters
+// using given get function, converting the resulting
+// filters to returnable frontend API models.
+func (p *Processor) getHeaderFilters(
+	ctx context.Context,
+	get func(context.Context) ([]*gtsmodel.HeaderFilter, error),
+) (
+	[]*apimodel.HeaderFilter,
+	gtserror.WithCode,
+) {
+	// Select all filters from DB.
+	filters, err := get(ctx)
+
+	if err != nil && !errors.Is(err, db.ErrNoEntries) {
+		// Only handle errors other than not-found types.
+		err := gtserror.Newf("error selecting from database: %w", err)
+		return nil, gtserror.NewErrorInternalError(err)
+	}
+
+	// Convert passed header filters to apimodel filters.
+	apiFilters := make([]*apimodel.HeaderFilter, len(filters))
+	for i := range filters {
+		apiFilters[i] = toAPIHeaderFilter(filters[i])
+	}
+
+	return apiFilters, nil
+}
+
+// createHeaderFilter inserts the given HTTP header
+// filter into database, marking as authored by the
+// provided admin, using the given insert function.
+func (p *Processor) createHeaderFilter(
+	ctx context.Context,
+	admin *gtsmodel.Account,
+	request *apimodel.HeaderFilterRequest,
+	insert func(context.Context, *gtsmodel.HeaderFilter) error,
+) (
+	*apimodel.HeaderFilter,
+	gtserror.WithCode,
+) {
+	// Convert header key to canonical mime header format.
+	request.Header = textproto.CanonicalMIMEHeaderKey(request.Header)
+
+	// Validate incoming header filter.
+	if errWithCode := validateHeaderFilter(
+		request.Header,
+		request.Regex,
+	); errWithCode != nil {
+		return nil, errWithCode
+	}
+
+	// Create new database model with ID.
+	var filter gtsmodel.HeaderFilter
+	filter.ID = id.NewULID()
+	filter.Header = request.Header
+	filter.Regex = request.Regex
+	filter.AuthorID = admin.ID
+	filter.Author = admin
+
+	// Insert new header filter into the database.
+	if err := insert(ctx, &filter); err != nil {
+		err := gtserror.Newf("error inserting into database: %w", err)
+		return nil, gtserror.NewErrorInternalError(err)
+	}
+
+	// Finally return API model response.
+	return toAPIHeaderFilter(&filter), nil
+}
+
+// deleteHeaderFilter deletes the HTTP header filter
+// with provided ID, using the given delete function.
+func (p *Processor) deleteHeaderFilter(
+	ctx context.Context,
+	id string,
+	delete func(context.Context, string) error,
+) gtserror.WithCode {
+	if err := delete(ctx, id); err != nil && !errors.Is(err, db.ErrNoEntries) {
+		err := gtserror.Newf("error deleting from database: %w", err)
+		return gtserror.NewErrorInternalError(err)
+	}
+	return nil
+}
+
+// toAPIFilter performs a simple conversion of database model HeaderFilter to API model.
+func toAPIHeaderFilter(filter *gtsmodel.HeaderFilter) *apimodel.HeaderFilter {
+	return &apimodel.HeaderFilter{
+		ID:        filter.ID,
+		Header:    filter.Header,
+		Regex:     filter.Regex,
+		CreatedBy: filter.AuthorID,
+		CreatedAt: util.FormatISO8601(filter.CreatedAt),
+	}
+}
+
+// validateHeaderFilter validates incoming filter's header key, and regular expression.
+func validateHeaderFilter(header, regex string) gtserror.WithCode {
+	// Check header validity (within our own bound checks).
+	if header == "" || len(header) > headerfilter.MaxHeaderValue {
+		const text = "invalid request header key (empty or too long)"
+		return gtserror.NewErrorBadRequest(errors.New(text), text)
+	}
+
+	// Ensure this is compilable regex.
+	_, err := regexp.Compile(regex)
+	if err != nil {
+		return gtserror.NewErrorBadRequest(err, err.Error())
+	}
+
+	return nil
+}

test/envparsing.sh

@@ -12,6 +12,7 @@ EXPECT=$(cat << "EOF"
     "accounts-registration-open": true,
     "advanced-cookies-samesite": "strict",
     "advanced-csp-extra-uris": [],
+    "advanced-header-filter-mode": "",
     "advanced-rate-limit-exceptions": [
         "192.0.2.0/24",
         "127.0.0.1/32"