allow setting the collation in auth handshake

client/auth.go

@@ -9,6 +9,7 @@ import (
 	. "github.com/go-mysql-org/go-mysql/mysql"
 	"github.com/go-mysql-org/go-mysql/packet"
 	"github.com/pingcap/errors"
+	"github.com/pingcap/tidb/pkg/parser/charset"
 )
 
 const defaultAuthPluginName = AUTH_NATIVE_PASSWORD
@@ -268,8 +269,25 @@ func (c *Conn) writeAuthHandshake() error {
 	data[11] = 0x00
 
 	// Charset [1 byte]
-	// use default collation id 33 here, is utf-8
-	data[12] = DEFAULT_COLLATION_ID
+	// use default collation id 33 here, is `utf8mb3_general_ci`
+	collationName := c.collation
+	if len(collationName) == 0 {
+		collationName = DEFAULT_COLLATION_NAME
+	}
+	collation, err := charset.GetCollationByName(collationName)
+	if err != nil {
+		return fmt.Errorf("invalid collation name %s", collationName)
+	}
+
+	// the MySQL protocol calls for the collation id to be sent as 1, where only the
+	// lower 8 bits are used in this field. But wireshark shows that the first byte of
+	// the 23 bytes of filler is used to send the right middle 8 bits of the collation id.
+	// see https://github.com/mysql/mysql-server/pull/541
+	data[12] = byte(collation.ID & 0xff)
+	// if the collation ID is <= 255 the middle 8 bits are 0s so this is the equivalent of
+	// padding the filler with a 0. If ID is > 255 then the first byte of filler will contain
+	// the right middle 8 bits of the collation ID.
+	data[13] = byte((collation.ID & 0xff00) >> 8)
 
 	// SSL Connection Request Packet
 	// http://dev.mysql.com/doc/internals/en/connection-phase-packets.html#packet-Protocol::SSLRequest
@@ -291,8 +309,12 @@ func (c *Conn) writeAuthHandshake() error {
 	}
 
 	// Filler [23 bytes] (all 0x00)
-	pos := 13
-	for ; pos < 13+23; pos++ {
+	// the filler starts at position 13, but the first byte of the filler
+	// has been set with the collation id earlier, so position 13 at this point
+	// will be either 0x00, or the right middle 8 bits of the collation id.
+	// Therefore, we start at position 14 and fill the remaining 22 bytes with 0x00.
+	pos := 14
+	for ; pos < 14+22; pos++ {
 		data[pos] = 0
 	}
 

client/auth_test.go

@@ -1,10 +1,14 @@
 package client
 
 import (
+	"net"
 	"testing"
 
-	"github.com/go-mysql-org/go-mysql/mysql"
+	"github.com/pingcap/tidb/pkg/parser/charset"
 	"github.com/stretchr/testify/require"
+
+	"github.com/go-mysql-org/go-mysql/mysql"
+	"github.com/go-mysql-org/go-mysql/packet"
 )
 
 func TestConnGenAttributes(t *testing.T) {
@@ -34,3 +38,75 @@ func TestConnGenAttributes(t *testing.T) {
 		require.Subset(t, data, fixt)
 	}
 }
+
+func TestConnCollation(t *testing.T) {
+	collations := []string{
+		"big5_chinese_ci",
+		"utf8_general_ci",
+		"utf8mb4_0900_ai_ci",
+		"utf8mb4_de_pb_0900_ai_ci",
+		"utf8mb4_ja_0900_as_cs",
+		"utf8mb4_0900_bin",
+		"utf8mb4_zh_pinyin_tidb_as_cs",
+	}
+
+	// test all supported collations by calling writeAuthHandshake() and reading the bytes
+	// sent to the server to ensure the collation id is set correctly
+	for _, c := range collations {
+		collation, err := charset.GetCollationByName(c)
+		require.NoError(t, err)
+		server := sendAuthResponse(t, collation.Name)
+		// read the all the bytes of the handshake response so that client goroutine can complete without blocking
+		// on the server read.
+		handShakeResponse := make([]byte, 128)
+		_, err = server.Read(handShakeResponse)
+		require.NoError(t, err)
+
+		// validate the collation id is set correctly
+		// if the collation ID is <= 255 the collation ID is stored in the 12th byte
+		if collation.ID <= 255 {
+			require.Equal(t, byte(collation.ID), handShakeResponse[12])
+			// the 13th byte should always be 0x00
+			require.Equal(t, byte(0x00), handShakeResponse[13])
+		} else {
+			// if the collation ID is > 255 the collation ID is stored in the 12th and 13th bytes
+			require.Equal(t, byte(collation.ID&0xff), handShakeResponse[12])
+			require.Equal(t, byte(collation.ID>>8), handShakeResponse[13])
+		}
+
+		// sanity check: validate the 22 bytes of filler with value 0x00 are set correctly
+		for i := 14; i < 14+22; i++ {
+			require.Equal(t, byte(0x00), handShakeResponse[i])
+		}
+
+		// and finally the username
+		username := string(handShakeResponse[36:40])
+		require.Equal(t, "test", username)
+
+		require.NoError(t, server.Close())
+	}
+}
+
+func sendAuthResponse(t *testing.T, collation string) net.Conn {
+	server, client := net.Pipe()
+	c := &Conn{
+		Conn: &packet.Conn{
+			Conn: client,
+		},
+		authPluginName: "mysql_native_password",
+		user:           "test",
+		db:             "test",
+		password:       "test",
+		proto:          "tcp",
+		collation:      collation,
+		salt:           ([]byte)("123456781234567812345678"),
+	}
+
+	go func() {
+		err := c.writeAuthHandshake()
+		require.NoError(t, err)
+		err = c.Close()
+		require.NoError(t, err)
+	}()
+	return server
+}

client/client_test.go

@@ -31,7 +31,11 @@ func TestClientSuite(t *testing.T) {
 func (s *clientTestSuite) SetupSuite() {
 	var err error
 	addr := fmt.Sprintf("%s:%s", *test_util.MysqlHost, s.port)
-	s.c, err = Connect(addr, *testUser, *testPassword, "")
+	s.c, err = Connect(addr, *testUser, *testPassword, "", func(conn *Conn) {
+		// test the collation logic, but this is essentially a no-op since
+		// the collation set is the default value
+		_ = conn.SetCollation(mysql.DEFAULT_COLLATION_NAME)
+	})
 	require.NoError(s.T(), err)
 
 	var result *mysql.Result
@@ -228,6 +232,22 @@ func (s *clientTestSuite) TestConn_SetCharset() {
 	require.NoError(s.T(), err)
 }
 
+func (s *clientTestSuite) TestConn_SetCollationAfterConnect() {
+	err := s.c.SetCollation("latin1_swedish_ci")
+	require.Error(s.T(), err)
+	require.ErrorContains(s.T(), err, "cannot set collation after connection is established")
+}
+
+func (s *clientTestSuite) TestConn_SetCollation() {
+	addr := fmt.Sprintf("%s:%s", *test_util.MysqlHost, s.port)
+	_, err := Connect(addr, *testUser, *testPassword, "", func(conn *Conn) {
+		// test the collation logic
+		_ = conn.SetCollation("invalid_collation")
+	})
+
+	require.Error(s.T(), err)
+}
+
 func (s *clientTestSuite) testStmt_DropTable() {
 	str := `drop table if exists mixer_test_stmt`
 

client/conn.go

@@ -37,6 +37,8 @@ type Conn struct {
 	status uint16
 
 	charset string
+	// sets the collation to be set on the auth handshake, this does not issue a 'set names' command
+	collation string
 
 	salt           []byte
 	authPluginName string
@@ -67,15 +69,19 @@ func Connect(addr string, user string, password string, dbName string, options .
 	ctx, cancel := context.WithTimeout(context.Background(), time.Second*10)
 	defer cancel()
 
-	dialer := &net.Dialer{}
+	return ConnectWithContext(ctx, addr, user, password, dbName, options...)
+}
 
+// ConnectWithContext to a MySQL addr using the provided context.
+func ConnectWithContext(ctx context.Context, addr string, user string, password string, dbName string, options ...func(*Conn)) (*Conn, error) {
+	dialer := &net.Dialer{}
 	return ConnectWithDialer(ctx, "", addr, user, password, dbName, dialer.DialContext, options...)
 }
 
 // Dialer connects to the address on the named network using the provided context.
 type Dialer func(ctx context.Context, network, address string) (net.Conn, error)
 
-// Connect to a MySQL server using the given Dialer.
+// ConnectWithDialer to a MySQL server using the given Dialer.
 func ConnectWithDialer(ctx context.Context, network string, addr string, user string, password string, dbName string, dialer Dialer, options ...func(*Conn)) (*Conn, error) {
 	c := new(Conn)
 
@@ -357,6 +363,19 @@ func (c *Conn) SetCharset(charset string) error {
 	}
 }
 
+func (c *Conn) SetCollation(collation string) error {
+	if len(c.serverVersion) != 0 {
+		return errors.Trace(errors.Errorf("cannot set collation after connection is established"))
+	}
+
+	c.collation = collation
+	return nil
+}
+
+func (c *Conn) GetCollation() string {
+	return c.collation
+}
+
 func (c *Conn) FieldList(table string, wildcard string) ([]*Field, error) {
 	if err := c.writeCommandStrStr(COM_FIELD_LIST, table, wildcard); err != nil {
 		return nil, errors.Trace(err)