Add default connection attribute '_server_host' (#1506)

The `_server_host` connection attribute is supported in MariaDB (Connector/C)
https://mariadb.com/kb/en/mysql_optionsv/#connection-attribute-options

AUTHORS

@@ -50,6 +50,7 @@ INADA Naoki <songofacandy at gmail.com>
 Jacek Szwec <szwec.jacek at gmail.com>
 James Harr <james.harr at gmail.com>
 Janek Vedock <janekvedock at comcast.net>
+Jason Ng <oblitorum at gmail.com>
 Jean-Yves Pellé <jy at pelle.link>
 Jeff Hodges <jeff at somethingsimilar.com>
 Jeffrey Charles <jeffreycharles at gmail.com>
@@ -131,6 +132,7 @@ Multiplay Ltd.
 Percona LLC
 PingCAP Inc.
 Pivotal Inc.
+Shattered Silicon Ltd.
 Stripe Inc.
 Zendesk Inc.
 Dolthub Inc.

connector.go

@@ -11,7 +11,6 @@ package mysql
 import (
 	"context"
 	"database/sql/driver"
-	"fmt"
 	"net"
 	"os"
 	"strconv"
@@ -23,8 +22,8 @@ type connector struct {
 	encodedAttributes string  // Encoded connection attributes.
 }
 
-func encodeConnectionAttributes(textAttributes string) string {
-	connAttrsBuf := make([]byte, 0, 251)
+func encodeConnectionAttributes(cfg *Config) string {
+	connAttrsBuf := make([]byte, 0)
 
 	// default connection attributes
 	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrClientName)
@@ -35,9 +34,14 @@ func encodeConnectionAttributes(textAttributes string) string {
 	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrPlatformValue)
 	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrPid)
 	connAttrsBuf = appendLengthEncodedString(connAttrsBuf, strconv.Itoa(os.Getpid()))
+	serverHost, _, _ := net.SplitHostPort(cfg.Addr)
+	if serverHost != "" {
+		connAttrsBuf = appendLengthEncodedString(connAttrsBuf, connAttrServerHost)
+		connAttrsBuf = appendLengthEncodedString(connAttrsBuf, serverHost)
+	}
 
 	// user-defined connection attributes
-	for _, connAttr := range strings.Split(textAttributes, ",") {
+	for _, connAttr := range strings.Split(cfg.ConnectionAttributes, ",") {
 		k, v, found := strings.Cut(connAttr, ":")
 		if !found {
 			continue
@@ -49,15 +53,12 @@ func encodeConnectionAttributes(textAttributes string) string {
 	return string(connAttrsBuf)
 }
 
-func newConnector(cfg *Config) (*connector, error) {
-	encodedAttributes := encodeConnectionAttributes(cfg.ConnectionAttributes)
-	if len(encodedAttributes) > 250 {
-		return nil, fmt.Errorf("connection attributes are longer than 250 bytes: %dbytes (%q)", len(encodedAttributes), cfg.ConnectionAttributes)
-	}
+func newConnector(cfg *Config) *connector {
+	encodedAttributes := encodeConnectionAttributes(cfg)
 	return &connector{
 		cfg:               cfg,
 		encodedAttributes: encodedAttributes,
-	}, nil
+	}
 }
 
 // Connect implements driver.Connector interface.

connector_test.go

@@ -8,16 +8,13 @@ import (
 )
 
 func TestConnectorReturnsTimeout(t *testing.T) {
-	connector, err := newConnector(&Config{
+	connector := newConnector(&Config{
 		Net:     "tcp",
 		Addr:    "1.1.1.1:1234",
 		Timeout: 10 * time.Millisecond,
 	})
-	if err != nil {
-		t.Fatal(err)
-	}
 
-	_, err = connector.Connect(context.Background())
+	_, err := connector.Connect(context.Background())
 	if err == nil {
 		t.Fatal("error expected")
 	}

const.go

@@ -26,6 +26,7 @@ const (
 	connAttrPlatform        = "_platform"
 	connAttrPlatformValue   = runtime.GOARCH
 	connAttrPid             = "_pid"
+	connAttrServerHost      = "_server_host"
 )
 
 // MySQL constants documentation:

driver.go

@@ -83,10 +83,7 @@ func (d MySQLDriver) Open(dsn string) (driver.Conn, error) {
 	if err != nil {
 		return nil, err
 	}
-	c, err := newConnector(cfg)
-	if err != nil {
-		return nil, err
-	}
+	c := newConnector(cfg)
 	return c.Connect(context.Background())
 }
 
@@ -108,7 +105,7 @@ func NewConnector(cfg *Config) (driver.Connector, error) {
 	if err := cfg.normalize(); err != nil {
 		return nil, err
 	}
-	return newConnector(cfg)
+	return newConnector(cfg), nil
 }
 
 // OpenConnector implements driver.DriverContext.
@@ -117,5 +114,5 @@ func (d MySQLDriver) OpenConnector(dsn string) (driver.Connector, error) {
 	if err != nil {
 		return nil, err
 	}
-	return newConnector(cfg)
+	return newConnector(cfg), nil
 }

driver_test.go

@@ -24,6 +24,7 @@ import (
 	"os"
 	"reflect"
 	"runtime"
+	"strconv"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -3377,12 +3378,30 @@ func TestConnectionAttributes(t *testing.T) {
 		t.Skipf("MySQL server not running on %s", netAddr)
 	}
 
-	attr1 := "attr1"
-	value1 := "value1"
-	attr2 := "fo/o"
-	value2 := "bo/o"
-	dsn += "&connectionAttributes=" + url.QueryEscape(fmt.Sprintf("%s:%s,%s:%s", attr1, value1, attr2, value2))
+	defaultAttrs := []string{
+		connAttrClientName,
+		connAttrOS,
+		connAttrPlatform,
+		connAttrPid,
+		connAttrServerHost,
+	}
+	host, _, _ := net.SplitHostPort(addr)
+	defaultAttrValues := []string{
+		connAttrClientNameValue,
+		connAttrOSValue,
+		connAttrPlatformValue,
+		strconv.Itoa(os.Getpid()),
+		host,
+	}
+
+	customAttrs := []string{"attr1", "fo/o"}
+	customAttrValues := []string{"value1", "bo/o"}
 
+	customAttrStrs := make([]string, len(customAttrs))
+	for i := range customAttrs {
+		customAttrStrs[i] = fmt.Sprintf("%s:%s", customAttrs[i], customAttrValues[i])
+	}
+	dsn += "&connectionAttributes=" + url.QueryEscape(strings.Join(customAttrStrs, ","))
 
 	var db *sql.DB
 	if _, err := ParseDSN(dsn); err != errInvalidDSNUnsafeCollation {
@@ -3395,40 +3414,24 @@ func TestConnectionAttributes(t *testing.T) {
 
 	dbt := &DBTest{t, db}
 
-	var attrValue string
-	queryString := "SELECT ATTR_VALUE FROM performance_schema.session_account_connect_attrs WHERE PROCESSLIST_ID = CONNECTION_ID() and ATTR_NAME = ?"
-	rows := dbt.mustQuery(queryString, connAttrClientName)
-	if rows.Next() {
-		rows.Scan(&attrValue)
-		if attrValue != connAttrClientNameValue {
-			dbt.Errorf("expected %q, got %q", connAttrClientNameValue, attrValue)
-		}
-	} else {
-		dbt.Errorf("no data")
-	}
-	rows.Close()
+	queryString := "SELECT ATTR_NAME, ATTR_VALUE FROM performance_schema.session_account_connect_attrs WHERE PROCESSLIST_ID = CONNECTION_ID()"
+	rows := dbt.mustQuery(queryString)
+	defer rows.Close()
 
-	rows = dbt.mustQuery(queryString, attr1)
-	if rows.Next() {
-		rows.Scan(&attrValue)
-		if attrValue != value1 {
-			dbt.Errorf("expected %q, got %q", value1, attrValue)
-		}
-	} else {
-		dbt.Errorf("no data")
+	rowsMap := make(map[string]string)
+	for rows.Next() {
+		var attrName, attrValue string
+		rows.Scan(&attrName, &attrValue)
+		rowsMap[attrName] = attrValue
 	}
-	rows.Close()
 
-	rows = dbt.mustQuery(queryString, attr2)
-	if rows.Next() {
-		rows.Scan(&attrValue)
-		if attrValue != value2 {
-			dbt.Errorf("expected %q, got %q", value2, attrValue)
+	connAttrs := append(append([]string{}, defaultAttrs...), customAttrs...)
+	expectedAttrValues := append(append([]string{}, defaultAttrValues...), customAttrValues...)
+	for i := range connAttrs {
+		if gotValue := rowsMap[connAttrs[i]]; gotValue != expectedAttrValues[i] {
+			dbt.Errorf("expected %q, got %q", expectedAttrValues[i], gotValue)
 		}
-	} else {
-		dbt.Errorf("no data")
 	}
-	rows.Close()
 }
 
 func TestErrorInMultiResult(t *testing.T) {

packets.go

@@ -292,15 +292,14 @@ func (mc *mysqlConn) writeHandshakeResponsePacket(authResp []byte, plugin string
 		pktLen += n + 1
 	}
 
-	// 1 byte to store length of all key-values
-	// NOTE: Actually, this is length encoded integer.
-	// But we support only len(connAttrBuf) < 251 for now because takeSmallBuffer
-	// doesn't support buffer size more than 4096 bytes.
-	// TODO(methane): Rewrite buffer management.
-	pktLen += 1 + len(mc.connector.encodedAttributes)
+	// encode length of the connection attributes
+	var connAttrsLEIBuf [9]byte
+	connAttrsLen := len(mc.connector.encodedAttributes)
+	connAttrsLEI := appendLengthEncodedInteger(connAttrsLEIBuf[:0], uint64(connAttrsLen))
+	pktLen += len(connAttrsLEI) + len(mc.connector.encodedAttributes)
 
 	// Calculate packet length and get buffer with that size
-	data, err := mc.buf.takeSmallBuffer(pktLen + 4)
+	data, err := mc.buf.takeBuffer(pktLen + 4)
 	if err != nil {
 		// cannot take the buffer. Something must be wrong with the connection
 		mc.cfg.Logger.Print(err)
@@ -380,8 +379,7 @@ func (mc *mysqlConn) writeHandshakeResponsePacket(authResp []byte, plugin string
 	pos++
 
 	// Connection Attributes
-	data[pos] = byte(len(mc.connector.encodedAttributes))
-	pos++
+	pos += copy(data[pos:], connAttrsLEI)
 	pos += copy(data[pos:], []byte(mc.connector.encodedAttributes))
 
 	// Send Auth packet

packets_test.go

@@ -96,10 +96,7 @@ var _ net.Conn = new(mockConn)
 
 func newRWMockConn(sequence uint8) (*mockConn, *mysqlConn) {
 	conn := new(mockConn)
-	connector, err := newConnector(NewConfig())
-	if err != nil {
-		panic(err)
-	}
+	connector := newConnector(NewConfig())
 	mc := &mysqlConn{
 		buf:              newBuffer(conn),
 		cfg:              connector.cfg,