net/http: fix Server.ConnContext modifying context for all new connections

Fixes #35750

Change-Id: I65d38cfc5ddd66131777e104c269cc3559b2471d
GitHub-Last-Rev: 953fdfd49b2be665be43f8148d2a6180dae3b91c
GitHub-Pull-Request: golang/go#35751
Reviewed-on: https://go-review.googlesource.com/c/go/+/208318
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/http/serve_test.go

@@ -6126,6 +6126,39 @@ func TestServerContextsHTTP2(t *testing.T) {
 	}
 }
 
+// Issue 35750: check ConnContext not modifying context for other connections
+func TestConnContextNotModifyingAllContexts(t *testing.T) {
+	setParallel(t)
+	defer afterTest(t)
+	type connKey struct{}
+	ts := httptest.NewUnstartedServer(HandlerFunc(func(rw ResponseWriter, r *Request) {
+		rw.Header().Set("Connection", "close")
+	}))
+	ts.Config.ConnContext = func(ctx context.Context, c net.Conn) context.Context {
+		if got := ctx.Value(connKey{}); got != nil {
+			t.Errorf("in ConnContext, unexpected context key = %#v", got)
+		}
+		return context.WithValue(ctx, connKey{}, "conn")
+	}
+	ts.Start()
+	defer ts.Close()
+
+	var res *Response
+	var err error
+
+	res, err = ts.Client().Get(ts.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	res.Body.Close()
+
+	res, err = ts.Client().Get(ts.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	res.Body.Close()
+}
+
 // Issue 30710: ensure that as per the spec, a server responds
 // with 501 Not Implemented for unsupported transfer-encodings.
 func TestUnsupportedTransferEncodingsReturn501(t *testing.T) {

src/net/http/server.go

@@ -2920,16 +2920,17 @@ func (srv *Server) Serve(l net.Listener) error {
 			}
 			return err
 		}
+		connCtx := ctx
 		if cc := srv.ConnContext; cc != nil {
-			ctx = cc(ctx, rw)
+			connCtx = cc(connCtx, rw)
-			if ctx == nil {
+			if connCtx == nil {
 				panic("ConnContext returned nil")
 			}
 		}
 		tempDelay = 0
 		c := srv.newConn(rw)
 		c.setState(c.rwc, StateNew) // before Serve can return
-		go c.serve(ctx)
+		go c.serve(connCtx)
 	}
 }