net/http: do not cancel request context on response body read

When sending a Request with a non-context deadline, we create a
context with a timeout. This context is canceled when closing the
response body, and also if a read from the response body returns
an error (including io.EOF).

Cancelling the context in Response.Body.Read interferes with the
HTTP/2 client cleaning up after a request is completed, and is
unnecessary: The user should always close the body, the impact
from not canceling the context is minor (the context timer leaks
until it fires).

Fixes #49366.

Change-Id: Ieaed866116916261d9079f71d8fea7a7b303b8fb
Reviewed-on: https://go-review.googlesource.com/c/go/+/361919
Trust: Damien Neil <dneil@google.com>
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/client.go

@@ -965,7 +965,6 @@ func (b *cancelTimerBody) Read(p []byte) (n int, err error) {
 	if err == nil {
 		return n, nil
 	}
-	b.stop()
 	if err == io.EOF {
 		return n, err
 	}

src/net/http/client_test.go

@@ -1368,6 +1368,33 @@ func TestClientTimeoutCancel(t *testing.T) {
 	}
 }
 
+func TestClientTimeoutDoesNotExpire_h1(t *testing.T) { testClientTimeoutDoesNotExpire(t, h1Mode) }
+func TestClientTimeoutDoesNotExpire_h2(t *testing.T) { testClientTimeoutDoesNotExpire(t, h2Mode) }
+
+// Issue 49366: if Client.Timeout is set but not hit, no error should be returned.
+func testClientTimeoutDoesNotExpire(t *testing.T, h2 bool) {
+	setParallel(t)
+	defer afterTest(t)
+
+	cst := newClientServerTest(t, h2, HandlerFunc(func(w ResponseWriter, r *Request) {
+		w.Write([]byte("body"))
+	}))
+	defer cst.close()
+
+	cst.c.Timeout = 1 * time.Hour
+	req, _ := NewRequest("GET", cst.ts.URL, nil)
+	res, err := cst.c.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err = io.Copy(io.Discard, res.Body); err != nil {
+		t.Fatalf("io.Copy(io.Discard, res.Body) = %v, want nil", err)
+	}
+	if err = res.Body.Close(); err != nil {
+		t.Fatalf("res.Body.Close() = %v, want nil", err)
+	}
+}
+
 func TestClientRedirectEatsBody_h1(t *testing.T) { testClientRedirectEatsBody(t, h1Mode) }
 func TestClientRedirectEatsBody_h2(t *testing.T) { testClientRedirectEatsBody(t, h2Mode) }
 func testClientRedirectEatsBody(t *testing.T, h2 bool) {