client - fix an initial handshake auth logic #2

Author: atercattus

client/auth.go

@@ -101,16 +101,18 @@ func (c *Conn) readInitialHandshake() error {
 if c.capability&CLIENT_SECURE_CONNECTION != 0 {
 // Rest of the plugin provided data (scramble)
 
+// https://dev.mysql.com/doc/dev/mysql-server/latest/page_protocol_connection_phase_packets_protocol_handshake_v10.html
 // $len=MAX(13, length of auth-plugin-data - 8)
+//
+// https://github.com/mysql/mysql-server/blob/1bfe02bdad6604d54913c62614bde57a055c8332/sql/auth/sql_authentication.cc#L1641-L1642
+// the first packet *must* have at least 20 bytes of a scramble.
+// if a plugin provided less, we pad it to 20 with zeros
 rest := int(authPluginDataLen) - 8
-if max := 13; rest < max {
+if max := 12 + 1; rest < max {
 rest = max
 }
-if data[pos+rest-1] != 0 {
-return errors.Errorf("expect 0x00 after scramble, got %q", rune(data[pos]))
-}
 
-authPluginDataPart2 := data[pos : pos+rest-1]
+authPluginDataPart2 := data[pos : pos+rest]
 pos += rest
 
 c.salt = append(c.salt, authPluginDataPart2...)