Use context.DeadlineExceeded error

Author: Evan Shaw

ctx_backport.go

@@ -59,3 +59,12 @@ var background = new(emptyCtx)
 func backgroundCtx() mysqlContext {
 	return background
 }
+
+var deadlineExceeded = deadlineExceededError{}
+
+// deadlineExceededError is copied from Go 1.7's context package.
+type deadlineExceededError struct{}
+
+func (deadlineExceededError) Error() string   { return "context deadline exceeded" }
+func (deadlineExceededError) Timeout() bool   { return true }
+func (deadlineExceededError) Temporary() bool { return true }

ctx_go18.go

@@ -25,3 +25,5 @@ type mysqlContext context.Context
 func backgroundCtx() mysqlContext {
 	return context.Background()
 }
+
+var deadlineExceeded = context.DeadlineExceeded

packets.go

@@ -84,12 +84,9 @@ func (mc *mysqlConn) readPacket() ([]byte, error) {
 
 // Write packet buffer 'data'
 func (mc *mysqlConn) writePacket(ctx mysqlContext, data []byte) error {
-	if ctx == nil {
-		panic("context cannot be nil")
-	}
 	ctxDeadline, isCtxDeadlineSet := ctx.Deadline()
 	if isCtxDeadlineSet && !ctxDeadline.After(time.Now()) {
-		return errors.New("timeout")
+		return deadlineExceeded
 	}
 
 	pktLen := len(data) - 4