support client connection attributes on the client side

Author: skoef

client/auth.go

@@ -139,6 +139,20 @@ func (c *Conn) genAuthResponse(authData []byte) ([]byte, bool, error) {
 	}
 }
 
+// generate connection attributes data
+func (c *Conn) genAttributes() []byte {
+	if len(c.attributes) == 0 {
+		return nil
+	}
+
+	attrData := make([]byte, 0)
+	for k, v := range c.attributes {
+		attrData = append(attrData, PutLengthEncodedString([]byte(k))...)
+		attrData = append(attrData, PutLengthEncodedString([]byte(v))...)
+	}
+	return append(PutLengthEncodedInt(uint64(len(attrData))), attrData...)
+}
+
 // See: http://dev.mysql.com/doc/internals/en/connection-phase-packets.html#packet-Protocol::HandshakeResponse
 func (c *Conn) writeAuthHandshake() error {
 	if !authPluginAllowed(c.authPluginName) {
@@ -195,6 +209,12 @@ func (c *Conn) writeAuthHandshake() error {
 		capability |= CLIENT_CONNECT_WITH_DB
 		length += len(c.db) + 1
 	}
+	// connection attributes
+	attrData := c.genAttributes()
+	if len(attrData) > 0 {
+		capability |= CLIENT_CONNECT_ATTRS
+		length += len(attrData)
+	}
 
 	data := make([]byte, length+4)
 
@@ -264,6 +284,12 @@ func (c *Conn) writeAuthHandshake() error {
 	// Assume native client during response
 	pos += copy(data[pos:], c.authPluginName)
 	data[pos] = 0x00
+	pos++
+
+	// connection attributes
+	if len(attrData) > 0 {
+		copy(data[pos:], attrData)
+	}
 
 	return c.WritePacket(data)
 }

client/auth_test.go

@@ -0,0 +1,42 @@
+package client
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/go-mysql-org/go-mysql/mysql"
+)
+
+func TestConnGenAttributes(t *testing.T) {
+	c := &Conn{
+		// example data from
+		// https://dev.mysql.com/doc/internals/en/connection-phase-packets.html#packet-Protocol::HandshakeResponse41
+		attributes: map[string]string{
+			"_os":             "debian6.0",
+			"_client_name":    "libmysql",
+			"_pid":            "22344",
+			"_client_version": "5.6.6-m9",
+			"_platform":       "x86_64",
+			"foo":             "bar",
+		},
+	}
+
+	data := c.genAttributes()
+
+	// the order of the attributes map cannot be guaranteed so to test the content
+	// of the attribute data we need to check its partial contents
+
+	if len(data) != 98 {
+		t.Fatalf("unexpected data length, got %d", len(data))
+	}
+	if data[0] != 0x61 {
+		t.Fatalf("unexpected length-encoded int, got %#x", data[0])
+	}
+
+	for k, v := range c.attributes {
+		fixt := append(mysql.PutLengthEncodedString([]byte(k)), mysql.PutLengthEncodedString([]byte(v))...)
+		if !bytes.Contains(data, fixt) {
+			t.Fatalf("%s attribute not found", k)
+		}
+	}
+}

client/conn.go

@@ -28,6 +28,8 @@ type Conn struct {
 	// client-set capabilities only
 	ccaps uint32
 
+	attributes map[string]string
+
 	status uint16
 
 	charset string
@@ -302,6 +304,10 @@ func (c *Conn) Rollback() error {
 	return errors.Trace(err)
 }
 
+func (c *Conn) SetAttributes(attributes map[string]string) {
+	c.attributes = attributes
+}
+
 func (c *Conn) SetCharset(charset string) error {
 	if c.charset == charset {
 		return nil