Add HTTPClient and STUNServers to unbounded options

Allow callers to inject an http.Client and a static list of STUN
servers into UnboundedOutboundOptions. When HTTPClient is set, it is
used directly instead of building one from the sing-box dialer. When
STUNServers is set (and STUNBatch is not), a batch function is
created that returns from the provided list.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: myleshorton

option/unbounded.go

@@ -1,6 +1,8 @@
 package option
 
 import (
+	"net/http"
+
 	"github.com/sagernet/sing-box/option"
 )
 
@@ -20,12 +22,14 @@ type UnboundedOutboundOptions struct {
 	BusBufferSz int    `json:"bus_buffer_sz,omitempty"`
 	Netstated   string `json:"netstated,omitempty"`
 	// WebRTCOptions
-	DiscoverySrv      string `json:"discovery_srv,omitempty"`
-	DiscoveryEndpoint string `json:"discovery_endpoint,omitempty"`
-	GenesisAddr       string `json:"genesis_addr,omitempty"`
-	NATFailTimeout    int    `json:"nat_fail_timeout,omitempty"`
-	STUNBatchSize     int    `json:"stun_batch_size,omitempty"`
+	DiscoverySrv      string   `json:"discovery_srv,omitempty"`
+	DiscoveryEndpoint string   `json:"discovery_endpoint,omitempty"`
+	GenesisAddr       string   `json:"genesis_addr,omitempty"`
+	NATFailTimeout    int      `json:"nat_fail_timeout,omitempty"`
+	STUNBatchSize     int      `json:"stun_batch_size,omitempty"`
+	STUNServers       []string `json:"stun_servers,omitempty"`
 	STUNBatch         func(size uint32) (batch []string, err error)
+	HTTPClient        *http.Client
 	Tag               string `json:"tag,omitempty"`
 	Patience          int    `json:"patience,omitempty"`
 	ErrorBackoff      int    `json:"error_backoff,omitempty"`

protocol/unbounded/outbound.go

@@ -102,6 +102,15 @@ func NewOutbound(
 
 	if options.STUNBatch != nil {
 		rtcOpt.STUNBatch = options.STUNBatch
+	} else if len(options.STUNServers) > 0 {
+		servers := make([]string, len(options.STUNServers))
+		copy(servers, options.STUNServers)
+		rtcOpt.STUNBatch = func(size uint32) ([]string, error) {
+			if int(size) >= len(servers) {
+				return servers, nil
+			}
+			return servers[:size], nil
+		}
 	}
 
 	if options.Tag != "" {
@@ -156,16 +165,20 @@ func NewOutbound(
 		return nil, err
 	}
 	rtcOpt.Net = rtcNet
-	dialContext := func(ctx context.Context, network, addr string) (net.Conn, error) {
-		return outboundDialer.DialContext(ctx, network, M.ParseSocksaddr(addr))
-	}
-	rtcOpt.HTTPClient = &http.Client{
-		Transport: &http.Transport{
-			Dial: func(network, addr string) (net.Conn, error) {
-				return dialContext(ctx, network, addr)
+	if options.HTTPClient != nil {
+		rtcOpt.HTTPClient = options.HTTPClient
+	} else {
+		dialContext := func(ctx context.Context, network, addr string) (net.Conn, error) {
+			return outboundDialer.DialContext(ctx, network, M.ParseSocksaddr(addr))
+		}
+		rtcOpt.HTTPClient = &http.Client{
+			Transport: &http.Transport{
+				Dial: func(network, addr string) (net.Conn, error) {
+					return dialContext(ctx, network, addr)
+				},
+				DialContext: dialContext,
 			},
-			DialContext: dialContext,
-		},
+		}
 	}
 
 	o := &Outbound{