Add ability to set DialContext/ListenPacket for tracker announcements (#760)

This is useful if you want to use a custom dialer to proxy requests via
an external server since the HTTPProxy can only be used with tcp
trackers and not udp.

config.go

@@ -1,6 +1,7 @@
 package torrent
 
 import (
+	"context"
 	"net"
 	"net/http"
 	"net/url"
@@ -90,6 +91,10 @@ type ClientConfig struct {
 	// Defines proxy for HTTP requests, such as for trackers. It's commonly set from the result of
 	// "net/http".ProxyURL(HTTPProxy).
 	HTTPProxy func(*http.Request) (*url.URL, error)
+	// Defines DialContext func to use for HTTP tracker announcements
+	TrackerDialContext func(ctx context.Context, network, addr string) (net.Conn, error)
+	// Defines ListenPacket func to use for UDP tracker announcements
+	TrackerListenPacket func(network, addr string) (net.PacketConn, error)
 	// Takes a tracker's hostname and requests DNS A and AAAA records.
 	// Used in case DNS lookups require a special setup (i.e., dns-over-https)
 	LookupTrackerIp func(*url.URL) ([]net.IP, error)

tracker/client.go

@@ -2,6 +2,7 @@ package tracker
 
 import (
 	"context"
+	"net"
 	"net/url"
 
 	"github.com/anacrolix/log"
@@ -21,6 +22,7 @@ type NewClientOpts struct {
 	// Overrides the network in the scheme. Probably a legacy thing.
 	UdpNetwork   string
 	Logger       log.Logger
+	ListenPacket func(network, addr string) (net.PacketConn, error)
 }
 
 func NewClient(urlStr string, opts NewClientOpts) (Client, error) {
@@ -40,6 +42,7 @@ func NewClient(urlStr string, opts NewClientOpts) (Client, error) {
 			Network:      network,
 			Host:         _url.Host,
 			Logger:       opts.Logger,
+			ListenPacket: opts.ListenPacket,
 		})
 		if err != nil {
 			return nil, err

tracker/http/client.go

@@ -1,7 +1,9 @@
 package http
 
 import (
+	"context"
 	"crypto/tls"
+	"net"
 	"net/http"
 	"net/url"
 )
@@ -12,9 +14,11 @@ type Client struct {
 }
 
 type ProxyFunc func(*http.Request) (*url.URL, error)
+type DialContextFunc func(ctx context.Context, network, addr string) (net.Conn, error)
 
 type NewClientOpts struct {
 	Proxy          ProxyFunc
+	DialContext    DialContextFunc
 	ServerName     string
 	AllowKeepAlive bool
 }
@@ -24,6 +28,7 @@ func NewClient(url_ *url.URL, opts NewClientOpts) Client {
 		url_: url_,
 		hc: &http.Client{
 			Transport: &http.Transport{
+				DialContext: opts.DialContext,
 				Proxy: opts.Proxy,
 				TLSClientConfig: &tls.Config{
 					InsecureSkipVerify: true,

tracker/tracker.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"net"
 	"net/http"
 	"net/url"
 	"time"
@@ -37,6 +38,8 @@ type Announce struct {
 	Request      AnnounceRequest
 	HostHeader   string
 	HTTPProxy    func(*http.Request) (*url.URL, error)
+	DialContext  func(ctx context.Context, network, addr string) (net.Conn, error)
+	ListenPacket func(network, addr string) (net.PacketConn, error)
 	ServerName   string
 	UserAgent    string
 	UdpNetwork   string
@@ -55,10 +58,12 @@ func (me Announce) Do() (res AnnounceResponse, err error) {
 	cl, err := NewClient(me.TrackerUrl, NewClientOpts{
 		Http: trHttp.NewClientOpts{
 			Proxy:       me.HTTPProxy,
+			DialContext: me.DialContext,
 			ServerName:  me.ServerName,
 		},
 		UdpNetwork:   me.UdpNetwork,
 		Logger:       me.Logger.WithContextValue(fmt.Sprintf("tracker client for %q", me.TrackerUrl)),
+		ListenPacket: me.ListenPacket,
 	})
 	if err != nil {
 		return

tracker/udp/conn-client.go

@@ -9,6 +9,8 @@ import (
 	"github.com/anacrolix/missinggo/v2"
 )
 
+type listenPacketFunc func(network, addr string) (net.PacketConn, error)
+
 type NewConnClientOpts struct {
 	// The network to operate to use, such as "udp4", "udp", "udp6".
 	Network string
@@ -18,6 +20,8 @@ type NewConnClientOpts struct {
 	Ipv6 *bool
 	// Logger to use for internal errors.
 	Logger log.Logger
+	// Custom function to use as a substitute for net.ListenPacket
+	ListenPacket listenPacketFunc
 }
 
 // Manages a Client with a specific connection.
@@ -80,7 +84,13 @@ func (me clientWriter) Write(p []byte) (n int, err error) {
 }
 
 func NewConnClient(opts NewConnClientOpts) (cc *ConnClient, err error) {
-	conn, err := net.ListenPacket(opts.Network, ":0")
+	var conn net.PacketConn
+	if opts.ListenPacket != nil {
+		conn, err = opts.ListenPacket(opts.Network, ":0")
+	} else {
+		conn, err = net.ListenPacket(opts.Network, ":0")
+	}
+
 	if err != nil {
 		return
 	}

tracker_scraper.go

@@ -158,6 +158,8 @@ func (me *trackerScraper) announce(ctx context.Context, event tracker.AnnounceEv
 	res, err := tracker.Announce{
 		Context:      ctx,
 		HTTPProxy:    me.t.cl.config.HTTPProxy,
+		DialContext:  me.t.cl.config.TrackerDialContext,
+		ListenPacket: me.t.cl.config.TrackerListenPacket,
 		UserAgent:    me.t.cl.config.HTTPUserAgent,
 		TrackerUrl:   me.trackerUrl(ip),
 		Request:      req,