Add support for connection attributes.

This sets attribute _client_name with the value "Go MySQL Driver"
Also sets _os, _platform, _pid and program_name by default.

Author: dveeden

AUTHORS

@@ -15,6 +15,7 @@ Aaron Hopkins <go-sql-driver at die.net>
 Arne Hormann <arnehormann at gmail.com>
 Carlos Nieto <jose.carlos at menteslibres.net>
 Chris Moos <chris at tech9computers.com>
+Daniël van Eeden <daniel.van.eeden at myname.nl>
 DisposaBoy <disposaboy at dby.me>
 Frederick Mayle <frederickmayle at gmail.com>
 Gustavo Kristic <gkristic at gmail.com>

packets.go

@@ -16,6 +16,10 @@ import (
 	"fmt"
 	"io"
 	"math"
+	"os"
+	"path"
+	"runtime"
+	"strconv"
 	"time"
 )
 
@@ -219,6 +223,7 @@ func (mc *mysqlConn) writeAuthPacket(cipher []byte) error {
 		clientTransactions |
 		clientLocalFiles |
 		clientPluginAuth |
+		clientConnectAttrs |
 		mc.flags&clientLongFlag
 
 	if mc.cfg.clientFoundRows {
@@ -233,7 +238,22 @@ func (mc *mysqlConn) writeAuthPacket(cipher []byte) error {
 	// User Password
 	scrambleBuff := scramblePassword(cipher, []byte(mc.cfg.passwd))
 
+	attrs := make(map[string]string)
+	attrs["_os"] = runtime.GOOS
+	attrs["_client_name"] = "Go MySQL Driver"
+	attrs["_pid"] = strconv.Itoa(os.Getpid())
+	attrs["_platform"] = runtime.GOARCH
+	attrs["program_name"] = path.Base(os.Args[0])
+
+	attrlen := 0
+	for attrname, attrvalue := range attrs {
+		attrlen += len(attrname) + len(attrvalue)
+		// one byte to store attrname length and one byte to store attrvalue length
+		attrlen += 2
+	}
+
 	pktLen := 4 + 4 + 1 + 23 + len(mc.cfg.user) + 1 + 1 + len(scrambleBuff) + 21 + 1
+	pktLen += attrlen + 1 // one byte to store the total length of attrs
 
 	// To specify a db name
 	if n := len(mc.cfg.dbname); n > 0 {
@@ -301,6 +321,19 @@ func (mc *mysqlConn) writeAuthPacket(cipher []byte) error {
 		data[pos] = 0x00
 		pos++
 	}
+	pos++
+
+	// Connection attributes
+	data[pos] = byte(attrlen)
+	pos++
+
+	for attrname, attrvalue := range attrs {
+		data[pos] = byte(len(attrname))
+		pos += 1 + copy(data[pos+1:], attrname)
+
+		data[pos] = byte(len(attrvalue))
+		pos += 1 + copy(data[pos+1:], attrvalue)
+	}
 
 	// Assume native client during response
 	pos += copy(data[pos:], "mysql_native_password")