Pull request: 5044 Close upstreams

Merge in DNS/adguard-home from 5044-close-upstreams to master

Closes #5044.

Squashed commit of the following:

commit e121380ecb32bd2664d47f0968c68509156404c1
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Oct 19 15:54:17 2022 +0300

    all: upd proxy again

commit ce7fa539a7430a1a197fd45e7988697010c684db
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Oct 19 14:30:46 2022 +0300

    home: imp docs, names

commit 851c5b8128149941cc469e6192ec9b4b1f92b0b5
Merge: b9ee5d63 d2a09e49
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Oct 19 14:21:44 2022 +0300

    Merge branch 'master' into 5044-close-upstreams

commit b9ee5d6348e696ff0b44dabee601469c545c8bd9
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Oct 19 14:20:15 2022 +0300

    all: close upstreams more

commit eaca476319dc64e7986e26e67110005938cf1278
Merge: f924bc7a 8dba4ecd
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Oct 18 18:33:53 2022 +0300

    Merge branch 'master' into 5044-close-upstreams

commit f924bc7a836001f8bb7463de2b5ddaf1be1a53c1
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Oct 18 18:23:54 2022 +0300

    all: imp code, docs

commit 011fde16aa912fc78e3d6f60375cee73a0d88709
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Oct 18 17:26:40 2022 +0300

    all: upd dnsproxy

internal/home/clients.go

@@ -21,6 +21,8 @@ import (
 	"github.com/AdguardTeam/golibs/log"
 	"github.com/AdguardTeam/golibs/netutil"
 	"github.com/AdguardTeam/golibs/stringutil"
+	"golang.org/x/exp/maps"
+	"golang.org/x/exp/slices"
 )
 
 const clientsUpdatePeriod = 10 * time.Minute
@@ -50,6 +52,18 @@ type Client struct {
 	UseOwnBlockedServices bool
 }
 
+// closeUpstreams closes the client-specific upstream config of c if any.
+func (c *Client) closeUpstreams() (err error) {
+	if c.upstreamConfig != nil {
+		err = c.upstreamConfig.Close()
+		if err != nil {
+			return fmt.Errorf("closing upstreams of client %q: %w", c.Name, err)
+		}
+	}
+
+	return nil
+}
+
 type clientSource uint
 
 // Client sources.  The order determines the priority.
@@ -651,6 +665,10 @@ func (clients *clientsContainer) Del(name string) (ok bool) {
 		return false
 	}
 
+	if err := c.closeUpstreams(); err != nil {
+		log.Error("client container: removing client %s: %s", name, err)
+	}
+
 	// update Name index
 	delete(clients.list, name)
 
@@ -709,7 +727,7 @@ func (clients *clientsContainer) Update(name string, c *Client) (err error) {
 			}
 		}
 
-		// update ID index
+		//  Update ID index.
 		for _, id := range prev.IDs {
 			delete(clients.idIndex, id)
 		}
@@ -718,14 +736,17 @@ func (clients *clientsContainer) Update(name string, c *Client) (err error) {
 		}
 	}
 
-	// update Name index
+	// Update name index.
 	if prev.Name != c.Name {
 		delete(clients.list, prev.Name)
 		clients.list[c.Name] = prev
 	}
 
-	// update upstreams cache
-	c.upstreamConfig = nil
+	// Update upstreams cache.
+	err = c.closeUpstreams()
+	if err != nil {
+		return err
+	}
 
 	*prev = *c
 
@@ -910,3 +931,24 @@ func (clients *clientsContainer) updateFromDHCP(add bool) {
 
 	log.Debug("clients: added %d client aliases from dhcp", n)
 }
+
+// Close gracefully closes all the client-specific upstream configurations of
+// the persistent clients.
+func (clients *clientsContainer) Close() (err error) {
+	persistent := maps.Values(clients.list)
+	slices.SortFunc(persistent, func(a, b *Client) (less bool) { return a.Name < b.Name })
+
+	var errs []error
+
+	for _, cli := range persistent {
+		if err = cli.closeUpstreams(); err != nil {
+			errs = append(errs, err)
+		}
+	}
+
+	if len(errs) > 0 {
+		return errors.List("closing client specific upstreams", errs...)
+	}
+
+	return nil
+}