add RejectReadOnly

Author: songgao

AUTHORS

@@ -59,4 +59,5 @@ Zhenye Xie <xiezhenye at gmail.com>
 
 Barracuda Networks, Inc.
 Google Inc.
+Keybase Inc.
 Stripe Inc.

dsn.go

@@ -54,6 +54,21 @@ type Config struct {
 	MultiStatements         bool // Allow multiple statements in one query
 	ParseTime               bool // Parse time values to time.Time
 	Strict                  bool // Return warnings as errors
+
+	// RejectreadOnly causes mysql driver to reject read-only connections. This
+	// is specifically for AWS Aurora: During a failover, there seems to be a
+	// race condition on Aurora, where we get connected to the [old master
+	// before failover], i.e. the [new read-only slave after failover].
+	//
+	// Note that this should be a fairly rare case, as automatic failover
+	// normally happens when master is down, and the race condition shouldn't
+	// happen unless it comes back up online as soon as the failover is kicked
+	// off. But it's pretty easy to reproduce using a manual failover. In case
+	// this happens, we should reconnect to the Aurora cluster by returning a
+	// driver.ErrBadConnection.
+	//
+	// tl;dr: Set this if you are using Aurora.
+	RejectReadOnly bool
 }
 
 // FormatDSN formats the given Config into a DSN string which can be passed to
@@ -195,6 +210,15 @@ func (cfg *Config) FormatDSN() string {
 		buf.WriteString(cfg.ReadTimeout.String())
 	}
 
+	if cfg.RejectReadOnly {
+		if hasParam {
+			buf.WriteString("&rejectReadOnly=true")
+		} else {
+			hasParam = true
+			buf.WriteString("?rejectReadOnly=true")
+		}
+	}
+
 	if cfg.Strict {
 		if hasParam {
 			buf.WriteString("&strict=true")
@@ -472,6 +496,14 @@ func parseDSNParams(cfg *Config, params string) (err error) {
 				return
 			}
 
+		// Reject read-only connections
+		case "rejectReadOnly":
+			var isBool bool
+			cfg.RejectReadOnly, isBool = readBool(value)
+			if !isBool {
+				return errors.New("invalid bool value: " + value)
+			}
+
 		// Strict mode
 		case "strict":
 			var isBool bool

packets.go

@@ -551,6 +551,11 @@ func (mc *mysqlConn) handleErrorPacket(data []byte) error {
 	// Error Number [16 bit uint]
 	errno := binary.LittleEndian.Uint16(data[1:3])
 
+	// 1792: ER_CANT_EXECUTE_IN_READ_ONLY_TRANSACTION
+	if errno == 1792 && mc.cfg.RejectReadOnly {
+		return driver.ErrBadConn
+	}
+
 	pos := 3
 
 	// SQL State [optional: # + 5bytes string]