From 425a91c9219638a12c9e9fa583638a562ab14828 Mon Sep 17 00:00:00 2001
From: Matt Joiner <anacrolix@gmail.com>
Date: Tue, 6 Dec 2022 15:59:06 +1100
Subject: [PATCH] Support alternate remote host resolution

---
 tracker/http/server/server.go | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/tracker/http/server/server.go b/tracker/http/server/server.go
index 88457826..0840fe96 100644
--- a/tracker/http/server/server.go
+++ b/tracker/http/server/server.go
@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"net/netip"
 	"net/url"
+	"strconv"
 
 	"github.com/anacrolix/dht/v2/krpc"
 	"github.com/anacrolix/log"
@@ -18,6 +19,9 @@ import (
 
 type Handler struct {
 	AnnounceTracker udpTrackerServer.AnnounceTracker
+	// Called to derive an announcer's IP if non-nil. If not specified, the Request.RemoteAddr is
+	// used. Necessary for instances running behind reverse proxies for example.
+	RequestHost func(r *http.Request) (netip.Addr, error)
 }
 
 func unmarshalQueryKeyToArray(w http.ResponseWriter, key string, query url.Values) (ret [20]byte, ok bool) {
@@ -31,6 +35,20 @@ func unmarshalQueryKeyToArray(w http.ResponseWriter, key string, query url.Value
 	return
 }
 
+var Logger = log.NewLogger("anacrolix", "torrent", "tracker", "http", "server")
+
+// Returns false if there was an error and it was served.
+func (me Handler) requestHostAddr(r *http.Request) (_ netip.Addr, err error) {
+	if me.RequestHost != nil {
+		return me.RequestHost(r)
+	}
+	host, _, err := net.SplitHostPort(r.RemoteAddr)
+	if err != nil {
+		return
+	}
+	return netip.ParseAddr(host)
+}
+
 func (me Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	vs := r.URL.Query()
 	var event tracker.AnnounceEvent
@@ -47,13 +65,15 @@ func (me Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	if !ok {
 		return
 	}
-	host, _, err := net.SplitHostPort(r.RemoteAddr)
+	Logger.WithNames("request").Levelf(log.Debug, "request RemoteAddr=%q, header=%q", r.RemoteAddr, r.Header)
+	addr, err := me.requestHostAddr(r)
 	if err != nil {
-		log.Printf("error splitting remote port: %v", err)
-		http.Error(w, "error determining your IP", http.StatusInternalServerError)
+		log.Printf("error getting requester IP: %v", err)
+		http.Error(w, "error determining your IP", http.StatusBadGateway)
 		return
 	}
-	addrPort, err := netip.ParseAddrPort(net.JoinHostPort(host, vs.Get("port")))
+	portU64, err := strconv.ParseUint(vs.Get("port"), 0, 16)
+	addrPort := netip.AddrPortFrom(addr, uint16(portU64))
 	err = me.AnnounceTracker.TrackAnnounce(r.Context(), tracker.AnnounceRequest{
 		InfoHash: infoHash,
 		PeerId:   peerId,
-- 
2.44.0