Add support for authenticated media

CHANGELOG.md

@@ -1,6 +1,14 @@
 # v0.7.0 (unreleased)
 
 * Bumped minimum Go version to 1.21.
+* Added support for Matrix v1.11 authenticated media.
+  * This also changes how avatars are sent to Discord when using relay webhooks.
+    To keep avatars working, you must configure `public_address` in the *bridge*
+    section of the config and proxy `/mautrix-discord/avatar/*` from that
+    address to the bridge.
+* Added `create-portal` command to create individual portals bypassing the
+  bridging mode. When used in combination with the `if-portal-exists` bridging
+  mode, this can be used to bridge individual channels from a guild.
 * Changed how direct media access works to make it compatible with Discord's
   signed URL requirement. The new system must be enabled manually, see
   [docs](https://docs.mau.fi/bridges/go/discord/direct-media.html) for info.

config/bridge.go

@@ -37,6 +37,9 @@ type BridgeConfig struct {
 
 	PortalMessageBuffer int `yaml:"portal_message_buffer"`
 
+	PublicAddress  string `yaml:"public_address"`
+	AvatarProxyKey string `yaml:"avatar_proxy_key"`
+
 	DeliveryReceipts            bool `yaml:"delivery_receipts"`
 	MessageStatusEvents         bool `yaml:"message_status_events"`
 	MessageErrorNotices         bool `yaml:"message_error_notices"`

config/upgrade.go

@@ -26,8 +26,6 @@ import (
 func DoUpgrade(helper *up.Helper) {
 	bridgeconfig.Upgrader.DoUpgrade(helper)
 
-	helper.Copy(up.Str|up.Null, "homeserver", "public_address")
-
 	helper.Copy(up.Str, "bridge", "username_template")
 	helper.Copy(up.Str, "bridge", "displayname_template")
 	helper.Copy(up.Str, "bridge", "channel_name_template")
@@ -42,6 +40,12 @@ func DoUpgrade(helper *up.Helper) {
 		helper.Copy(up.Str, "bridge", "private_chat_portal_meta")
 	}
 	helper.Copy(up.Int, "bridge", "startup_private_channel_create_limit")
+	helper.Copy(up.Str|up.Null, "bridge", "public_address")
+	if apkey, ok := helper.Get(up.Str, "bridge", "avatar_proxy_key"); !ok || apkey == "generate" {
+		helper.Set(up.Str, random.String(32), "bridge", "avatar_proxy_key")
+	} else {
+		helper.Copy(up.Str, "bridge", "avatar_proxy_key")
+	}
 	helper.Copy(up.Int, "bridge", "portal_message_buffer")
 	helper.Copy(up.Bool, "bridge", "delivery_receipts")
 	helper.Copy(up.Bool, "bridge", "message_status_events")

example-config.yaml

@@ -2,9 +2,6 @@
 homeserver:
     # The address that this appservice can use to connect to the homeserver.
     address: https://matrix.example.com
-    # Publicly accessible base URL for media, used for avatars in relay mode.
-    # If not set, the connection address above will be used.
-    public_address: null
     # The domain of the homeserver (also known as server_name, used for MXIDs, etc).
     domain: example.com
 
@@ -113,6 +110,13 @@ bridge:
     # If set to `never`, DM rooms will never have names and avatars set.
     private_chat_portal_meta: default
 
+    # Publicly accessible base URL that Discord can use to reach the bridge, used for avatars in relay mode.
+    # If not set, avatars will not be bridged. Only the /mautrix-discord/avatar/{server}/{id}/{hash} endpoint is used on this address.
+    # This should not have a trailing slash, the endpoint above will be appended to the provided address.
+    public_address: null
+    # A random key used to sign the avatar URLs. The bridge will only accept requests with a valid signature.
+    avatar_proxy_key: generate
+
     portal_message_buffer: 128
 
     # Number of private channel portals to create on bridge startup.

go.mod

@@ -14,11 +14,11 @@ require (
 	github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e
 	github.com/stretchr/testify v1.8.4
 	github.com/yuin/goldmark v1.6.0
-	go.mau.fi/util v0.2.1
+	go.mau.fi/util v0.2.2-0.20231228160422-22fdd4bbddeb
 	golang.org/x/exp v0.0.0-20231219180239-dc181d75b848
 	golang.org/x/sync v0.5.0
 	maunium.net/go/maulogger/v2 v2.4.1
-	maunium.net/go/mautrix v0.16.3-0.20240218195727-4ceb1123b660
+	maunium.net/go/mautrix v0.16.3-0.20240712164054-e6046fbf432c
 )
 
 require (

go.sum

@@ -45,8 +45,8 @@ github.com/tidwall/sjson v1.2.5 h1:kLy8mja+1c9jlljvWTlSazM7cKDRfJuR/bOJhcY5NcY=
 github.com/tidwall/sjson v1.2.5/go.mod h1:Fvgq9kS/6ociJEDnK0Fk1cpYF4FIW6ZF7LAe+6jwd28=
 github.com/yuin/goldmark v1.6.0 h1:boZcn2GTjpsynOsC0iJHnBWa4Bi0qzfJjthwauItG68=
 github.com/yuin/goldmark v1.6.0/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
-go.mau.fi/util v0.2.1 h1:eazulhFE/UmjOFtPrGg6zkF5YfAyiDzQb8ihLMbsPWw=
+go.mau.fi/util v0.2.2-0.20231228160422-22fdd4bbddeb h1:Is+6vDKgINRy9KHodvi7NElxoDaWA8sc2S3cF3+QWjs=
-go.mau.fi/util v0.2.1/go.mod h1:MjlzCQEMzJ+G8RsPawHzpLB8rwTo3aPIjG5FzBvQT/c=
+go.mau.fi/util v0.2.2-0.20231228160422-22fdd4bbddeb/go.mod h1:tiBX6nxVSOjU89jVQ7wBh3P8KjM26Lv1k7/I5QdSvBw=
 go.mau.fi/zeroconfig v0.1.2 h1:DKOydWnhPMn65GbXZOafgkPm11BvFashZWLct0dGFto=
 go.mau.fi/zeroconfig v0.1.2/go.mod h1:NcSJkf180JT+1IId76PcMuLTNa1CzsFFZ0nBygIQM70=
 golang.org/x/crypto v0.15.0 h1:frVn1TEaCEaZcn3Tmd7Y2b5KKPaZ+I32Q2OA3kYp5TA=
@@ -72,5 +72,5 @@ maunium.net/go/mauflag v1.0.0 h1:YiaRc0tEI3toYtJMRIfjP+jklH45uDHtT80nUamyD4M=
 maunium.net/go/mauflag v1.0.0/go.mod h1:nLivPOpTpHnpzEh8jEdSL9UqO9+/KBJFmNRlwKfkPeA=
 maunium.net/go/maulogger/v2 v2.4.1 h1:N7zSdd0mZkB2m2JtFUsiGTQQAdP0YeFWT7YMc80yAL8=
 maunium.net/go/maulogger/v2 v2.4.1/go.mod h1:omPuYwYBILeVQobz8uO3XC8DIRuEb5rXYlQSuqrbCho=
-maunium.net/go/mautrix v0.16.3-0.20240218195727-4ceb1123b660 h1:ZPg1i0wsyEs5ee7z6Gn4mSRsq9BtDV//rfYTGs82l8c=
+maunium.net/go/mautrix v0.16.3-0.20240712164054-e6046fbf432c h1:LHjqti3fFzrC8LXkkxxKYlLbuI/CJcwa2JN4Ppg2GK0=
-maunium.net/go/mautrix v0.16.3-0.20240218195727-4ceb1123b660/go.mod h1:YL4l4rZB46/vj/ifRMEjcibbvHjgxHftOF1SgmruLu4=
+maunium.net/go/mautrix v0.16.3-0.20240712164054-e6046fbf432c/go.mod h1:gCgLw/4c1a8QsiOWTdUdXlt5cYdE0rJ9wLeZQKPD58Q=

main.go

@@ -18,6 +18,7 @@ package main
 
 import (
 	_ "embed"
+	"net/http"
 	"sync"
 
 	"go.mau.fi/util/configupgrade"
@@ -105,6 +106,9 @@ func (br *DiscordBridge) Start() {
 	if br.Config.Bridge.Provisioning.SharedSecret != "disable" {
 		br.provisioning = newProvisioningAPI(br)
 	}
+	if br.Config.Bridge.PublicAddress != "" {
+		br.AS.Router.HandleFunc("/mautrix-discord/avatar/{server}/{mediaID}/{checksum}", br.serveMediaProxy).Methods(http.MethodGet)
+	}
 	br.DMA = newDirectMediaAPI(br)
 	br.WaitWebsocketConnected()
 	go br.startUsers()

portal.go

@@ -3,9 +3,13 @@ package main
 import (
 	"bytes"
 	"context"
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/base64"
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"net/http"
 	"reflect"
 	"regexp"
@@ -17,6 +21,7 @@ import (
 
 	"github.com/bwmarrin/discordgo"
 	"github.com/gabriel-vasile/mimetype"
+	"github.com/gorilla/mux"
 	"github.com/rs/zerolog"
 	"go.mau.fi/util/exsync"
 	"go.mau.fi/util/variationselector"
@@ -1370,6 +1375,64 @@ func (portal *Portal) sendMessageMetrics(evt *event.Event, err error, part strin
 	}
 }
 
+func (br *DiscordBridge) serveMediaProxy(w http.ResponseWriter, r *http.Request) {
+	vars := mux.Vars(r)
+	mxc := id.ContentURI{
+		Homeserver: vars["server"],
+		FileID:     vars["mediaID"],
+	}
+	checksum, err := base64.RawURLEncoding.DecodeString(vars["checksum"])
+	if err != nil || len(checksum) != 32 {
+		w.WriteHeader(http.StatusNotFound)
+		return
+	}
+	_, expectedChecksum := br.hashMediaProxyURL(mxc)
+	if !hmac.Equal(checksum, expectedChecksum) {
+		w.WriteHeader(http.StatusNotFound)
+		return
+	}
+	reader, err := br.Bot.Download(mxc)
+	if err != nil {
+		br.ZLog.Warn().Err(err).Msg("Failed to download media to proxy")
+		w.WriteHeader(http.StatusInternalServerError)
+		return
+	}
+	buf := make([]byte, 32*1024)
+	n, err := io.ReadFull(reader, buf)
+	if err != nil && (!errors.Is(err, io.EOF) && !errors.Is(err, io.ErrUnexpectedEOF)) {
+		br.ZLog.Warn().Err(err).Msg("Failed to read first part of media to proxy")
+		w.WriteHeader(http.StatusBadGateway)
+		return
+	}
+	w.Header().Add("Content-Type", http.DetectContentType(buf[:n]))
+	if n < len(buf) {
+		w.Header().Add("Content-Length", strconv.Itoa(n))
+	}
+	w.WriteHeader(http.StatusOK)
+	_, err = w.Write(buf[:n])
+	if err != nil {
+		return
+	}
+	if n >= len(buf) {
+		_, _ = io.CopyBuffer(w, reader, buf)
+	}
+}
+
+func (br *DiscordBridge) hashMediaProxyURL(mxc id.ContentURI) (string, []byte) {
+	path := fmt.Sprintf("/mautrix-discord/avatar/%s/%s/", mxc.Homeserver, mxc.FileID)
+	checksum := hmac.New(sha256.New, []byte(br.Config.Bridge.AvatarProxyKey))
+	checksum.Write([]byte(path))
+	return path, checksum.Sum(nil)
+}
+
+func (br *DiscordBridge) makeMediaProxyURL(mxc id.ContentURI) string {
+	if br.Config.Bridge.PublicAddress == "" {
+		return ""
+	}
+	path, checksum := br.hashMediaProxyURL(mxc)
+	return br.Config.Bridge.PublicAddress + path + base64.RawURLEncoding.EncodeToString(checksum)
+}
+
 func (portal *Portal) getRelayUserMeta(sender *User) (name, avatarURL string) {
 	member := portal.bridge.StateStore.GetMember(portal.MXID, sender.MXID)
 	name = member.Displayname
@@ -1377,11 +1440,8 @@ func (portal *Portal) getRelayUserMeta(sender *User) (name, avatarURL string) {
 		name = sender.MXID.String()
 	}
 	mxc := member.AvatarURL.ParseOrIgnore()
-	if !mxc.IsEmpty() {
+	if !mxc.IsEmpty() && portal.bridge.Config.Bridge.PublicAddress != "" {
-		avatarURL = mautrix.BuildURL(
+		avatarURL = portal.bridge.makeMediaProxyURL(mxc)
-			portal.bridge.PublicHSAddress,
-			"_matrix", "media", "v3", "download", mxc.Homeserver, mxc.FileID,
-		).String()
 	}
 	return
 }