Improve WebRTC candidates handling

internal/ngrok/ngrok.go

@@ -50,7 +50,7 @@ func Init() {
 
 				log.Info().Str("addr", address).Msg("[ngrok] add external candidate for WebRTC")
 
-				webrtc.AddCandidate(address, "tcp")
+				webrtc.AddCandidate("tcp", address)
 			}
 		}
 	})

internal/webrtc/README.md

@@ -1,13 +1,105 @@
+What you should to know about WebRTC:
+
+- It's almost always a **direct [peer-to-peer](https://en.wikipedia.org/wiki/Peer-to-peer) connection** from your browser to go2rtc app
+- When you use Home Assistant, Frigate, Nginx, Nabu Casa, Cloudflare and other software - they are only **involved in establishing** the connection, but they are **not involved in transferring** media data
+- WebRTC media cannot be transferred inside an HTTP connection
+- Usually, WebRTC uses random UDP ports on client and server side to establish a connection
+- Usually, WebRTC uses public [STUN](https://en.wikipedia.org/wiki/STUN) servers to establish a connection outside LAN, such servers are only needed to establish a connection and are not involved in data transfer
+- Usually, WebRTC will automatically discover all of your local addresses and all of your public addresses and try to establish a connection
+
+If an external connection via STUN is used:
+
+- Uses [UDP hole punching](https://en.wikipedia.org/wiki/UDP_hole_punching) technology to bypass NAT even if you not open your server to the World
+- For about 20% of users, the techology will not work because of the [Symmetric NAT](https://tomchen.github.io/symmetric-nat-test/)
+- UDP is not suitable for transmitting 2K and 4K high bitrate video over open networks because of the high loss rate
+
+## Default config
+
+```yaml
+webrtc:
+  listen: ":8555/tcp"
+  ice_servers:
+    - urls: [ "stun:stun.l.google.com:19302" ]
+```
+
 ## Config
 
-- supported TCP: fixed port (default), disabled 
-- supported UDP: random port (default), fixed port
+**Important!** This example is not for copypasting!
+
+```yaml
+webrtc:
+  # fix local TCP or UDP or both ports for WebRTC media
+  listen: ":8555/tcp"        # address of your local server
+
+  # add additional host candidates manually
+  # order is important, the first will have a higher priority
+  candidates:
+    - 216.58.210.174:8555    # if you have static public IP-address
+    - stun:8555              # if you have dynamic public IP-address
+    - home.duckdns.org:8555  # if you have domain
+
+  # add custom STUN and TURN servers
+  # use `ice_servers: []` for remove defaults and leave empty
+  ice_servers:
+    - urls: [ stun:stun1.l.google.com:19302 ]
+    - urls: [ turn:123.123.123.123:3478 ]
+      username: your_user
+      credential: your_pass
+
+  # optional filter list for auto discovery logic
+  # some settings only make sense if you don't specify a fixed UDP port  
+  filters:
+    # list of host candidates from auto discovery to be sent
+    # including candidates from the `listen` option
+    # use `candidates: []` to remove all auto discovery candidates
+    candidates: [ 192.168.1.123 ]
+
+    # list of network types to be used for connection
+    # including candidates from the `listen` option
+    networks: [ udp4, udp6, tcp4, tcp6 ]
+
+    # list of interfaces to be used for connection
+    # not related to the `listen` option
+    interfaces: [ eno1 ]
+
+    # list of host IP-addresses to be used for connection
+    # not related to the `listen` option
+    ips: [ 192.168.1.123 ]
+
+    # range for random UDP ports [min, max] to be used for connection
+    # not related to the `listen` option
+    udp_ports: [ 50000, 50100 ]
+```
+
+By default go2rtc uses **fixed TCP** port and multiple **random UDP** ports for each WebRTC connection - `listen: ":8555/tcp"`.
+
+You can set **fixed TCP** and **fixed UDP** port for all connections - `listen: ":8555"`. This may has lower performance, but it's your choice. 
+
+Don't know why, but you can disable TCP port and leave only random UDP ports - `listen: ""`.
+
+## Config filters
+
+Filters allow you to exclude unnecessary candidates. Extra candidates don't make your connection worse or better. But the wrong filter settings can break everything. Skip this setting if you don't understand it.
+
+For example, go2rtc is installed on the host system. And there are unnecessary interfaces. You can keep only the relevant via `interfaces` or `ips` options. You can also exclude IPv6 candidates if your server supports them but your home network does not.
+
+```yaml
+webrtc:
+  listen: ":8555/tcp"         # use fixed TCP port and random UDP ports
+  filters:
+    ips: [ 192.168.1.2 ]      # IP-address of your server
+    networks: [ udp4, tcp4 ]  # skip IPv6, if it's not supported for you
+```
+
+For example, go2rtc inside closed docker container (ex. [Frigate](https://frigate.video/)). You shouldn't filter docker interfaces, otherwise go2rtc will not be able to connect anywhere. But you can filter the docker candidates because no one can connect to them.
 
-| Config examples       | TCP   | UDP    |
-|-----------------------|-------|--------|
-| `listen: ":8555/tcp"` | fixed | random |
-| `listen: ":8555"`     | fixed | fixed  |
-| `listen: ""`          | no    | random |
+```yaml
+webrtc:
+  listen: ":8555"                   # use fixed TCP and UDP ports
+  candidates: [ 192.168.1.2:8555 ]  # add manual host candidate (use docker port forwarding)
+  filters:
+    candidates: []                  # skip all internal docker candidates
+```
 
 ## Userful links
 

internal/webrtc/candidates.go

@@ -2,57 +2,60 @@ package webrtc
 
 import (
 	"net"
+	"slices"
+	"strings"
 
 	"github.com/AlexxIT/go2rtc/internal/api/ws"
 	"github.com/AlexxIT/go2rtc/pkg/webrtc"
-	"github.com/pion/sdp/v3"
+	pion "github.com/pion/webrtc/v3"
 )
 
 type Address struct {
-	Host    string
-	Port    string
-	Network string
-	Offset  int
+	host     string
+	Port     string
+	Network  string
+	Priority uint32
 }
 
-func (a *Address) Marshal() string {
-	host := a.Host
-	if host == "stun" {
+func (a *Address) Host() string {
+	if a.host == "stun" {
 		ip, err := webrtc.GetCachedPublicIP()
 		if err != nil {
 			return ""
 		}
-		host = ip.String()
+		return ip.String()
 	}
+	return a.host
+}
 
-	switch a.Network {
-	case "udp":
-		return webrtc.CandidateManualHostUDP(host, a.Port, a.Offset)
-	case "tcp":
-		return webrtc.CandidateManualHostTCPPassive(host, a.Port, a.Offset)
+func (a *Address) Marshal() string {
+	if host := a.Host(); host != "" {
+		return webrtc.CandidateICE(a.Network, host, a.Port, a.Priority)
 	}
-
 	return ""
 }
 
 var addresses []*Address
+var filters webrtc.Filters
+
+func AddCandidate(network, address string) {
+	if network == "" {
+		AddCandidate("tcp", address)
+		AddCandidate("udp", address)
+		return
+	}
 
-func AddCandidate(address, network string) {
 	host, port, err := net.SplitHostPort(address)
 	if err != nil {
 		return
 	}
 
-	offset := -1 - len(addresses) // every next candidate will have a lower priority
+	// start from 1, so manual candidates will be lower than built-in
+	// and every next candidate will have a lower priority
+	candidateIndex := 1 + len(addresses)
 
-	switch network {
-	case "tcp", "udp":
-		addresses = append(addresses, &Address{host, port, network, offset})
-	default:
-		addresses = append(
-			addresses, &Address{host, port, "udp", offset}, &Address{host, port, "tcp", offset},
-		)
-	}
+	priority := webrtc.CandidateHostPriority(network, candidateIndex)
+	addresses = append(addresses, &Address{host, port, network, priority})
 }
 
 func GetCandidates() (candidates []string) {
@@ -64,6 +67,38 @@ func GetCandidates() (candidates []string) {
 	return
 }
 
+// FilterCandidate return true if candidate passed the check
+func FilterCandidate(candidate *pion.ICECandidate) bool {
+	if candidate == nil {
+		return false
+	}
+
+	// host candidate should be in the hosts list
+	if candidate.Typ == pion.ICECandidateTypeHost && filters.Candidates != nil {
+		if !slices.Contains(filters.Candidates, candidate.Address) {
+			return false
+		}
+	}
+
+	if filters.Networks != nil {
+		networkType := NetworkType(candidate.Protocol.String(), candidate.Address)
+		if !slices.Contains(filters.Networks, networkType) {
+			return false
+		}
+	}
+
+	return true
+}
+
+// NetworkType convert tcp/udp network to tcp4/tcp6/udp4/udp6
+func NetworkType(network, host string) string {
+	if strings.IndexByte(host, ':') >= 0 {
+		return network + "6"
+	} else {
+		return network + "4"
+	}
+}
+
 func asyncCandidates(tr *ws.Transport, cons *webrtc.Conn) {
 	tr.WithContext(func(ctx map[any]any) {
 		if candidates, ok := ctx["candidate"].([]string); ok {
@@ -86,30 +121,6 @@ func asyncCandidates(tr *ws.Transport, cons *webrtc.Conn) {
 	}
 }
 
-func syncCanditates(answer string) (string, error) {
-	if len(addresses) == 0 {
-		return answer, nil
-	}
-
-	sd := &sdp.SessionDescription{}
-	if err := sd.Unmarshal([]byte(answer)); err != nil {
-		return "", err
-	}
-
-	md := sd.MediaDescriptions[0]
-
-	for _, candidate := range GetCandidates() {
-		md.WithPropertyAttribute(candidate)
-	}
-
-	data, err := sd.Marshal()
-	if err != nil {
-		return "", err
-	}
-
-	return string(data), nil
-}
-
 func candidateHandler(tr *ws.Transport, msg *ws.Message) error {
 	// process incoming candidate in sync function
 	tr.WithContext(func(ctx map[any]any) {

internal/webrtc/server.go

@@ -178,10 +178,7 @@ func inputWebRTC(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	answer, err := prod.GetCompleteAnswer()
-	if err == nil {
-		answer, err = syncCanditates(answer)
-	}
+	answer, err := prod.GetCompleteAnswer(GetCandidates(), FilterCandidate)
 	if err != nil {
 		log.Warn().Err(err).Caller().Send()
 		http.Error(w, err.Error(), http.StatusInternalServerError)

internal/webrtc/webrtc.go

@@ -20,6 +20,7 @@ func Init() {
 			Listen     string           `yaml:"listen"`
 			Candidates []string         `yaml:"candidates"`
 			IceServers []pion.ICEServer `yaml:"ice_servers"`
+			Filters    webrtc.Filters   `yaml:"filters"`
 		} `yaml:"webrtc"`
 	}
 
@@ -32,20 +33,15 @@ func Init() {
 
 	log = app.GetLogger("webrtc")
 
-	address, network, _ := strings.Cut(cfg.Mod.Listen, "/")
+	filters = cfg.Mod.Filters
 
-	var candidateHost []string
+	address, network, _ := strings.Cut(cfg.Mod.Listen, "/")
 	for _, candidate := range cfg.Mod.Candidates {
-		if strings.HasPrefix(candidate, "host:") {
-			candidateHost = append(candidateHost, candidate[5:])
-			continue
-		}
-
-		AddCandidate(candidate, network)
+		AddCandidate(network, candidate)
 	}
 
 	// create pionAPI with custom codecs list and custom network settings
-	serverAPI, err := webrtc.NewServerAPI(address, network, candidateHost)
+	serverAPI, err := webrtc.NewServerAPI(network, address, &filters)
 	if err != nil {
 		log.Error().Err(err).Caller().Send()
 		return
@@ -55,8 +51,7 @@ func Init() {
 	clientAPI := serverAPI
 
 	if address != "" {
-		log.Info().Str("addr", address).Msg("[webrtc] listen")
-
+		log.Info().Str("addr", cfg.Mod.Listen).Msg("[webrtc] listen")
 		clientAPI, _ = webrtc.NewAPI()
 	}
 
@@ -139,6 +134,9 @@ func asyncHandler(tr *ws.Transport, msg *ws.Message) error {
 			}
 
 		case *pion.ICECandidate:
+			if !FilterCandidate(msg) {
+				return
+			}
 			_ = sendAnswer.Wait()
 
 			s := msg.ToJSON().Candidate
@@ -248,10 +246,7 @@ func ExchangeSDP(stream *streams.Stream, offer, desc, userAgent string) (answer
 		stream.AddProducer(conn)
 	}
 
-	answer, err = conn.GetCompleteAnswer()
-	if err == nil {
-		answer, err = syncCanditates(answer)
-	}
+	answer, err = conn.GetCompleteAnswer(GetCandidates(), FilterCandidate)
 	log.Trace().Msgf("[webrtc] answer\n%s", answer)
 
 	if err != nil {