add a configurable logger

errors.go

@@ -13,6 +13,9 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"log"
+	"os"
+	"sync"
 )
 
 var (
@@ -24,8 +27,30 @@ var (
 	errPktSync     = errors.New("Commands out of sync. You can't run this command now")
 	errPktSyncMul  = errors.New("Commands out of sync. Did you run multiple statements at once?")
 	errPktTooLarge = errors.New("Packet for query is too large. You can change this value on the server by adjusting the 'max_allowed_packet' variable.")
+	errBusyBuffer  = errors.New("Busy buffer")
+	errNoLogger    = errors.New("logger is nil")
+
+	errLog     Logger = log.New(os.Stderr, "[MySQL] ", log.Ldate|log.Ltime|log.Lshortfile)
+	errLogLock        = &sync.Mutex{}
 )
 
+// Logger is used to log critical error messages.
+type Logger interface {
+	Print(v ...interface{})
+}
+
+// SetLogger is used to set the logger for critical errors.
+// The initial logger is stderr.
+func SetLogger(logger Logger) error {
+	if logger == nil {
+		return errNoLogger
+	}
+	errLogLock.Lock()
+	errLog = logger
+	errLogLock.Unlock()
+	return nil
+}
+
 // MySQLError is an error type which represents a single MySQL error
 type MySQLError struct {
 	Number  uint16

errors_test.go

@@ -0,0 +1,30 @@
+// Go MySQL Driver - A MySQL-Driver for Go's database/sql package
+//
+// Copyright 2013 The Go-MySQL-Driver Authors. All rights reserved.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package mysql
+
+import (
+	"bytes"
+	"log"
+	"testing"
+)
+
+func TestSetLogger(t *testing.T) {
+	previous := errLog
+	defer func() {
+		errLog = previous
+	}()
+	const expected = "prefix: test\n"
+	buffer := bytes.NewBuffer(make([]byte, 0, 64))
+	logger := log.New(buffer, "prefix: ", 0)
+	SetLogger(logger)
+	errLog.Print("test")
+	if actual := buffer.String(); actual != expected {
+		t.Errorf("expected %q, got %q", expected, actual)
+	}
+}

packets.go

@@ -228,7 +228,7 @@ func (mc *mysqlConn) writeAuthPacket(cipher []byte) error {
 	data := mc.buf.takeSmallBuffer(pktLen + 4)
 	if data == nil {
 		// can not take the buffer. Something must be wrong with the connection
-		errLog.Print("Busy buffer")
+		errLog.Print(errBusyBuffer.Error())
 		return driver.ErrBadConn
 	}
 
@@ -299,7 +299,7 @@ func (mc *mysqlConn) writeOldAuthPacket(cipher []byte) error {
 	data := mc.buf.takeSmallBuffer(pktLen + 4)
 	if data == nil {
 		// can not take the buffer. Something must be wrong with the connection
-		errLog.Print("Busy buffer")
+		errLog.Print(errBusyBuffer.Error())
 		return driver.ErrBadConn
 	}
 
@@ -320,7 +320,7 @@ func (mc *mysqlConn) writeCommandPacket(command byte) error {
 	data := mc.buf.takeSmallBuffer(4 + 1)
 	if data == nil {
 		// can not take the buffer. Something must be wrong with the connection
-		errLog.Print("Busy buffer")
+		errLog.Print(errBusyBuffer.Error())
 		return driver.ErrBadConn
 	}
 
@@ -339,7 +339,7 @@ func (mc *mysqlConn) writeCommandPacketStr(command byte, arg string) error {
 	data := mc.buf.takeBuffer(pktLen + 4)
 	if data == nil {
 		// can not take the buffer. Something must be wrong with the connection
-		errLog.Print("Busy buffer")
+		errLog.Print(errBusyBuffer.Error())
 		return driver.ErrBadConn
 	}
 
@@ -360,7 +360,7 @@ func (mc *mysqlConn) writeCommandPacketUint32(command byte, arg uint32) error {
 	data := mc.buf.takeSmallBuffer(4 + 1 + 4)
 	if data == nil {
 		// can not take the buffer. Something must be wrong with the connection
-		errLog.Print("Busy buffer")
+		errLog.Print(errBusyBuffer.Error())
 		return driver.ErrBadConn
 	}
 
@@ -751,7 +751,7 @@ func (stmt *mysqlStmt) writeExecutePacket(args []driver.Value) error {
 	}
 	if data == nil {
 		// can not take the buffer. Something must be wrong with the connection
-		errLog.Print("Busy buffer")
+		errLog.Print(errBusyBuffer.Error())
 		return driver.ErrBadConn
 	}
 

utils.go

@@ -16,23 +16,19 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"log"
 	"net/url"
-	"os"
 	"strings"
 	"time"
 )
 
 var (
-	errLog            *log.Logger            // Error Logger
 	tlsConfigRegister map[string]*tls.Config // Register for custom tls.Configs
 
 	errInvalidDSNUnescaped = errors.New("Invalid DSN: Did you forget to escape a param value?")
 	errInvalidDSNAddr      = errors.New("Invalid DSN: Network Address not terminated (missing closing brace)")
 )
 
 func init() {
-	errLog = log.New(os.Stderr, "[MySQL] ", log.Ldate|log.Ltime|log.Lshortfile)
 	tlsConfigRegister = make(map[string]*tls.Config)
 }
 
@@ -678,5 +674,5 @@ func appendLengthEncodedInteger(b []byte, n uint64) []byte {
 		return append(b, 0xfd, byte(n), byte(n>>8), byte(n>>16))
 	}
 	return append(b, 0xfe, byte(n), byte(n>>8), byte(n>>16), byte(n>>24),
-			byte(n>>32), byte(n>>40), byte(n>>48), byte(n>>56))
+		byte(n>>32), byte(n>>40), byte(n>>48), byte(n>>56))
 }