From 14e5817f0d3397eb8920c9193869f41fcc82e788 Mon Sep 17 00:00:00 2001
From: INADA Naoki <songofacandy@gmail.com>
Date: Fri, 28 Sep 2018 21:42:12 +0900
Subject: [PATCH 1/2] Add test for #858

---
 connection_test.go | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/connection_test.go b/connection_test.go
index dec376117..352c54ed7 100644
--- a/connection_test.go
+++ b/connection_test.go
@@ -9,6 +9,7 @@
 package mysql
 
 import (
+	"context"
 	"database/sql/driver"
 	"testing"
 )
@@ -79,3 +80,31 @@ func TestCheckNamedValue(t *testing.T) {
 		t.Fatalf("uint64 high-bit not converted, got %#v %T", value.Value, value.Value)
 	}
 }
+
+// TestCleanCancel tests passed context is cancelled at start.
+// No packet should be sent.  Connection should keep current status.
+func TestCleanCancel(t *testing.T) {
+	mc := &mysqlConn{
+		closech: make(chan struct{}),
+	}
+	mc.startWatcher()
+	defer mc.cleanup()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	for i := 0; i < 3; i++ { // Repeat same behavior
+		err := mc.Ping(ctx)
+		if err != context.Canceled {
+			t.Errorf("expected context.Canceled, got %#v", err)
+		}
+
+		if mc.closed.IsSet() {
+			t.Error("expected mc is not closed, closed actually")
+		}
+
+		if mc.watching {
+			t.Error("expected watching is false, but true")
+		}
+	}
+}

From ad1e76e701af38dcef45e5f99ef14f702ed5e73c Mon Sep 17 00:00:00 2001
From: INADA Naoki <songofacandy@gmail.com>
Date: Fri, 28 Sep 2018 22:01:51 +0900
Subject: [PATCH 2/2] Early return for context cancelled at start

Don't break the connection when cancelled context is passed.

Fix #858
---
 connection.go | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/connection.go b/connection.go
index 911be2060..f74235519 100644
--- a/connection.go
+++ b/connection.go
@@ -595,22 +595,21 @@ func (mc *mysqlConn) watchCancel(ctx context.Context) error {
 		mc.cleanup()
 		return nil
 	}
+	// When ctx is already cancelled, don't watch it.
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	// When ctx is not cancellable, don't watch it.
 	if ctx.Done() == nil {
 		return nil
 	}
-
-	mc.watching = true
-	select {
-	default:
-	case <-ctx.Done():
-		return ctx.Err()
-	}
+	// When watcher is not alive, can't watch it.
 	if mc.watcher == nil {
 		return nil
 	}
 
+	mc.watching = true
 	mc.watcher <- ctx
-
 	return nil
 }