net/http: provide access to the listener address an HTTP request arrived on

This adds a context key named LocalAddrContextKey (for now, see #15229) to
let users access the net.Addr of the net.Listener that accepted the connection
that sent an HTTP request. This is similar to ServerContextKey which provides
access to the *Server. (A Server may have multiple Listeners)

Fixes #6732

Change-Id: I74296307b68aaaab8df7ad4a143e11b5227b5e62
Reviewed-on: https://go-review.googlesource.com/22672
Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 7 insertions, 0 deletions

diff --git a/src/net/http/server.go b/src/net/http/server.go
index c36f5a06ba..23fb84fcda 100644
--- a/src/net/http/server.go
+++ b/src/net/http/server.go
@@ -176,6 +176,12 @@ var (
 	// started the handler. The associated value will be of
 	// type *Server.
 	ServerContextKey = &contextKey{"http-server"}
+
+	// LocalAddrContextKey is a context key. It can be used in
+	// HTTP handlers with context.WithValue to access the address
+	// the local address the connection arrived on.
+	// The associated value will be of type net.Addr.
+	LocalAddrContextKey = &contextKey{"local-addr"}
 )
 
 // A conn represents the server side of an HTTP connection.
@@ -2189,6 +2195,7 @@ func (srv *Server) Serve(l net.Listener) error {
 	// use cases yet.
 	baseCtx := context.Background()
 	ctx := context.WithValue(baseCtx, ServerContextKey, srv)
+	ctx = context.WithValue(ctx, LocalAddrContextKey, l.Addr())
 	for {
 		rw, e := l.Accept()
 		if e != nil {