net/http: only decrement connection count if we removed a connection

The connection count must only be decremented if the persistent
connection was also removed.

Fixes #34941

Change-Id: I5070717d5d9effec78016005fa4910593500c8cf
Reviewed-on: https://go-review.googlesource.com/c/go/+/202087
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 56 insertions, 0 deletions

diff --git a/src/net/http/transport_test.go b/src/net/http/transport_test.go
index 3673ed29f0..0d63e46d4f 100644
--- a/src/net/http/transport_test.go
+++ b/src/net/http/transport_test.go
@@ -5893,3 +5893,59 @@ func TestDontCacheBrokenHTTP2Conn(t *testing.T) {
 		t.Errorf("GotConn calls = %v; want %v", got, want)
 	}
 }
+
+// Issue 34941
+// When the client has too many concurrent requests on a single connection,
+// http.http2noCachedConnError is reported on multiple requests. There should
+// only be one decrement regardless of the number of failures.
+func TestTransportDecrementConnWhenIdleConnRemoved(t *testing.T) {
+	defer afterTest(t)
+
+	h := HandlerFunc(func(w ResponseWriter, r *Request) {
+		_, err := w.Write([]byte("foo"))
+		if err != nil {
+			t.Fatalf("Write: %v", err)
+		}
+	})
+
+	ts := httptest.NewUnstartedServer(h)
+	ts.EnableHTTP2 = true
+	ts.StartTLS()
+	defer ts.Close()
+
+	c := ts.Client()
+	tr := c.Transport.(*Transport)
+	tr.MaxConnsPerHost = 1
+	if err := ExportHttp2ConfigureTransport(tr); err != nil {
+		t.Fatalf("ExportHttp2ConfigureTransport: %v", err)
+	}
+
+	errCh := make(chan error, 300)
+	doReq := func() {
+		resp, err := c.Get(ts.URL)
+		if err != nil {
+			errCh <- fmt.Errorf("request failed: %v", err)
+			return
+		}
+		defer resp.Body.Close()
+		_, err = ioutil.ReadAll(resp.Body)
+		if err != nil {
+			errCh <- fmt.Errorf("read body failed: %v", err)
+		}
+	}
+
+	var wg sync.WaitGroup
+	for i := 0; i < 300; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			doReq()
+		}()
+	}
+	wg.Wait()
+	close(errCh)
+
+	for err := range errCh {
+		t.Errorf("error occurred: %v", err)
+	}
+}