[bugfix] fix media limit reader check (#3363)

* return nicer errors for frontend when media / emoji upload limit reached

* fix reader limit check

* add code comment

internal/gtserror/error.go

@@ -40,8 +40,22 @@ const (
 	notRelevantKey
 	spamKey
 	notPermittedKey
+	limitReachedKey
 )
 
+// LimitReached indicates that this error was caused by
+// some kind of limit being reached, e.g. media upload limit.
+func LimitReached(err error) bool {
+	_, ok := errors.Value(err, limitReachedKey).(struct{})
+	return ok
+}
+
+// SetLimitReached will wrap the given error to store a "limit reached"
+// flag, returning wrapped error. See LimitReached() for example use-cases.
+func SetLimitReached(err error) error {
+	return errors.WithValue(err, limitReachedKey, struct{}{})
+}
+
 // IsUnretrievable indicates that a call to retrieve a resource
 // (account, status, attachment, etc) could not be fulfilled, either
 // because it was not found locally, or because some prerequisite

internal/media/util.go

@@ -29,6 +29,7 @@ import (
 	"codeberg.org/gruf/go-bytesize"
 	"codeberg.org/gruf/go-iotools"
 	"codeberg.org/gruf/go-mimetypes"
+	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 )
 
 // file represents one file
@@ -143,8 +144,9 @@ func drainToTmp(rc io.ReadCloser) (string, error) {
 
 	// Check to see if limit was reached,
 	// (produces more useful error messages).
-	if lr != nil && !iotools.AtEOF(lr.R) {
+	if lr != nil && lr.N <= 0 {
-		return path, fmt.Errorf("reached read limit %s", bytesize.Size(limit))
+		err := fmt.Errorf("reached read limit %s", bytesize.Size(limit))
+		return path, gtserror.SetLimitReached(err)
 	}
 
 	return path, nil

internal/processing/common/media.go

@@ -22,6 +22,7 @@ import (
 	"errors"
 	"fmt"
 
+	"github.com/superseriousbusiness/gotosocial/internal/config"
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
 	"github.com/superseriousbusiness/gotosocial/internal/media"
@@ -51,11 +52,18 @@ func (p *Processor) StoreLocalMedia(
 
 	// Immediately trigger write to storage.
 	attachment, err := processing.Load(ctx)
-	if err != nil {
+	switch {
-		const text = "error processing emoji"
+	case gtserror.LimitReached(err):
+		limit := config.GetMediaLocalMaxSize()
+		text := fmt.Sprintf("local media size limit reached: %s", limit)
+		return nil, gtserror.NewErrorUnprocessableEntity(err, text)
+
+	case err != nil:
+		const text = "error processing media"
 		err := gtserror.Newf("error processing media: %w", err)
 		return nil, gtserror.NewErrorUnprocessableEntity(err, text)
-	} else if attachment.Type == gtsmodel.FileTypeUnknown {
+
+	case attachment.Type == gtsmodel.FileTypeUnknown:
 		text := fmt.Sprintf("could not process %s type media", attachment.File.ContentType)
 		return nil, gtserror.NewErrorUnprocessableEntity(errors.New(text), text)
 	}
@@ -86,9 +94,15 @@ func (p *Processor) StoreLocalEmoji(
 		return nil, gtserror.NewErrorInternalError(err)
 	}
 
-	// Immediately write to storage.
+	// Immediately trigger write to storage.
 	emoji, err := processing.Load(ctx)
-	if err != nil {
+	switch {
+	case gtserror.LimitReached(err):
+		limit := config.GetMediaEmojiLocalMaxSize()
+		text := fmt.Sprintf("local emoji size limit reached: %s", limit)
+		return nil, gtserror.NewErrorUnprocessableEntity(err, text)
+
+	case err != nil:
 		const text = "error processing emoji"
 		err := gtserror.Newf("error processing emoji %s: %w", shortcode, err)
 		return nil, gtserror.NewErrorUnprocessableEntity(err, text)