Use SET NAMES charset COLLATE collation. (#1437)

README.md

@@ -202,8 +202,7 @@ Default:        none
 
 Sets the charset used for client-server interaction (`"SET NAMES <value>"`). If multiple charsets are set (separated by a comma), the following charset is used if setting the charset failes. This enables for example support for `utf8mb4` ([introduced in MySQL 5.5.3](http://dev.mysql.com/doc/refman/5.5/en/charset-unicode-utf8mb4.html)) with fallback to `utf8` for older servers (`charset=utf8mb4,utf8`).
 
-Usage of the `charset` parameter is discouraged because it issues additional queries to the server.
-Unless you need the fallback behavior, please use `collation` instead.
+See also [Unicode Support](#unicode-support).
 
 ##### `checkConnLiveness`
 
@@ -232,6 +231,7 @@ The default collation (`utf8mb4_general_ci`) is supported from MySQL 5.5.  You s
 
 Collations for charset "ucs2", "utf16", "utf16le", and "utf32" can not be used ([ref](https://dev.mysql.com/doc/refman/5.7/en/charset-connection.html#charset-connection-impermissible-client-charset)).
 
+See also [Unicode Support](#unicode-support).
 
 ##### `clientFoundRows`
 
@@ -511,9 +511,11 @@ However, many want to scan MySQL `DATE` and `DATETIME` values into `time.Time` v
 ### Unicode support
 Since version 1.5 Go-MySQL-Driver automatically uses the collation ` utf8mb4_general_ci` by default.
 
-Other collations / charsets can be set using the [`collation`](#collation) DSN parameter.
+Other charsets / collations can be set using the [`charset`](#charset) or [`collation`](#collation) DSN parameter.
 
-Version 1.0 of the driver recommended adding `&charset=utf8` (alias for `SET NAMES utf8`) to the DSN to enable proper UTF-8 support. This is not necessary anymore. The [`collation`](#collation) parameter should be preferred to set another collation / charset than the default.
+- When only the `charset` is specified, the `SET NAMES <charset>` query is sent and the server's default collation is used.
+- When both the `charset` and `collation` are specified, the `SET NAMES <charset> COLLATE <collation>` query is sent.
+- When only the `collation` is specified, the collation is specified in the protocol handshake and the `SET NAMES` query is not sent. This can save one roundtrip, but note that the server may ignore the specified collation silently and use the server's default charset/collation instead.
 
 See http://dev.mysql.com/doc/refman/8.0/en/charset-unicode.html for more details on MySQL's Unicode support.
 

connection.go

@@ -49,14 +49,19 @@ type mysqlConn struct {
 // Handles parameters set in DSN after the connection is established
 func (mc *mysqlConn) handleParams() (err error) {
 	var cmdSet strings.Builder
+
 	for param, val := range mc.cfg.Params {
 		switch param {
 		// Charset: character_set_connection, character_set_client, character_set_results
 		case "charset":
 			charsets := strings.Split(val, ",")
-			for i := range charsets {
+			for _, cs := range charsets {
 				// ignore errors here - a charset may not exist
-				err = mc.exec("SET NAMES " + charsets[i])
+				if mc.cfg.Collation != "" {
+					err = mc.exec("SET NAMES " + cs + " COLLATE " + mc.cfg.Collation)
+				} else {
+					err = mc.exec("SET NAMES " + cs)
+				}
 				if err == nil {
 					break
 				}

dsn.go

@@ -70,7 +70,6 @@ type Config struct {
 // NewConfig creates a new Config and sets default values.
 func NewConfig() *Config {
 	return &Config{
-		Collation:            defaultCollation,
 		Loc:                  time.UTC,
 		MaxAllowedPacket:     defaultMaxAllowedPacket,
 		Logger:               defaultLogger,
@@ -100,7 +99,7 @@ func (cfg *Config) Clone() *Config {
 }
 
 func (cfg *Config) normalize() error {
-	if cfg.InterpolateParams && unsafeCollations[cfg.Collation] {
+	if cfg.InterpolateParams && cfg.Collation != "" && unsafeCollations[cfg.Collation] {
 		return errInvalidDSNUnsafeCollation
 	}
 
@@ -237,7 +236,7 @@ func (cfg *Config) FormatDSN() string {
 		writeDSNParam(&buf, &hasParam, "clientFoundRows", "true")
 	}
 
-	if col := cfg.Collation; col != defaultCollation && len(col) > 0 {
+	if col := cfg.Collation; col != "" {
 		writeDSNParam(&buf, &hasParam, "collation", col)
 	}
 

dsn_test.go

@@ -22,58 +22,58 @@ var testDSNs = []struct {
 	out *Config
 }{{
 	"username:password@protocol(address)/dbname?param=value",
-	&Config{User: "username", Passwd: "password", Net: "protocol", Addr: "address", DBName: "dbname", Params: map[string]string{"param": "value"}, Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
+	&Config{User: "username", Passwd: "password", Net: "protocol", Addr: "address", DBName: "dbname", Params: map[string]string{"param": "value"}, Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
 }, {
 	"username:password@protocol(address)/dbname?param=value&columnsWithAlias=true",
-	&Config{User: "username", Passwd: "password", Net: "protocol", Addr: "address", DBName: "dbname", Params: map[string]string{"param": "value"}, Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true, ColumnsWithAlias: true},
+	&Config{User: "username", Passwd: "password", Net: "protocol", Addr: "address", DBName: "dbname", Params: map[string]string{"param": "value"}, Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true, ColumnsWithAlias: true},
 }, {
 	"username:password@protocol(address)/dbname?param=value&columnsWithAlias=true&multiStatements=true",
-	&Config{User: "username", Passwd: "password", Net: "protocol", Addr: "address", DBName: "dbname", Params: map[string]string{"param": "value"}, Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true, ColumnsWithAlias: true, MultiStatements: true},
+	&Config{User: "username", Passwd: "password", Net: "protocol", Addr: "address", DBName: "dbname", Params: map[string]string{"param": "value"}, Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true, ColumnsWithAlias: true, MultiStatements: true},
 }, {
 	"user@unix(/path/to/socket)/dbname?charset=utf8",
-	&Config{User: "user", Net: "unix", Addr: "/path/to/socket", DBName: "dbname", Params: map[string]string{"charset": "utf8"}, Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
+	&Config{User: "user", Net: "unix", Addr: "/path/to/socket", DBName: "dbname", Params: map[string]string{"charset": "utf8"}, Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
 }, {
 	"user:password@tcp(localhost:5555)/dbname?charset=utf8&tls=true",
-	&Config{User: "user", Passwd: "password", Net: "tcp", Addr: "localhost:5555", DBName: "dbname", Params: map[string]string{"charset": "utf8"}, Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true, TLSConfig: "true"},
+	&Config{User: "user", Passwd: "password", Net: "tcp", Addr: "localhost:5555", DBName: "dbname", Params: map[string]string{"charset": "utf8"}, Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true, TLSConfig: "true"},
 }, {
 	"user:password@tcp(localhost:5555)/dbname?charset=utf8mb4,utf8&tls=skip-verify",
-	&Config{User: "user", Passwd: "password", Net: "tcp", Addr: "localhost:5555", DBName: "dbname", Params: map[string]string{"charset": "utf8mb4,utf8"}, Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true, TLSConfig: "skip-verify"},
+	&Config{User: "user", Passwd: "password", Net: "tcp", Addr: "localhost:5555", DBName: "dbname", Params: map[string]string{"charset": "utf8mb4,utf8"}, Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true, TLSConfig: "skip-verify"},
 }, {
 	"user:password@/dbname?loc=UTC&timeout=30s&readTimeout=1s&writeTimeout=1s&allowAllFiles=1&clientFoundRows=true&allowOldPasswords=TRUE&collation=utf8mb4_unicode_ci&maxAllowedPacket=16777216&tls=false&allowCleartextPasswords=true&parseTime=true&rejectReadOnly=true",
 	&Config{User: "user", Passwd: "password", Net: "tcp", Addr: "127.0.0.1:3306", DBName: "dbname", Collation: "utf8mb4_unicode_ci", Loc: time.UTC, TLSConfig: "false", AllowCleartextPasswords: true, AllowNativePasswords: true, Timeout: 30 * time.Second, ReadTimeout: time.Second, WriteTimeout: time.Second, Logger: defaultLogger, AllowAllFiles: true, AllowOldPasswords: true, CheckConnLiveness: true, ClientFoundRows: true, MaxAllowedPacket: 16777216, ParseTime: true, RejectReadOnly: true},
 }, {
 	"user:password@/dbname?allowNativePasswords=false&checkConnLiveness=false&maxAllowedPacket=0&allowFallbackToPlaintext=true",
-	&Config{User: "user", Passwd: "password", Net: "tcp", Addr: "127.0.0.1:3306", DBName: "dbname", Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: 0, Logger: defaultLogger, AllowFallbackToPlaintext: true, AllowNativePasswords: false, CheckConnLiveness: false},
+	&Config{User: "user", Passwd: "password", Net: "tcp", Addr: "127.0.0.1:3306", DBName: "dbname", Loc: time.UTC, MaxAllowedPacket: 0, Logger: defaultLogger, AllowFallbackToPlaintext: true, AllowNativePasswords: false, CheckConnLiveness: false},
 }, {
 	"user:p@ss(word)@tcp([de:ad:be:ef::ca:fe]:80)/dbname?loc=Local",
-	&Config{User: "user", Passwd: "p@ss(word)", Net: "tcp", Addr: "[de:ad:be:ef::ca:fe]:80", DBName: "dbname", Collation: "utf8mb4_general_ci", Loc: time.Local, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
+	&Config{User: "user", Passwd: "p@ss(word)", Net: "tcp", Addr: "[de:ad:be:ef::ca:fe]:80", DBName: "dbname", Loc: time.Local, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
 }, {
 	"/dbname",
-	&Config{Net: "tcp", Addr: "127.0.0.1:3306", DBName: "dbname", Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
+	&Config{Net: "tcp", Addr: "127.0.0.1:3306", DBName: "dbname", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
 }, {
 	"/dbname%2Fwithslash",
-	&Config{Net: "tcp", Addr: "127.0.0.1:3306", DBName: "dbname/withslash", Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
+	&Config{Net: "tcp", Addr: "127.0.0.1:3306", DBName: "dbname/withslash", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
 }, {
 	"@/",
-	&Config{Net: "tcp", Addr: "127.0.0.1:3306", Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
+	&Config{Net: "tcp", Addr: "127.0.0.1:3306", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
 }, {
 	"/",
-	&Config{Net: "tcp", Addr: "127.0.0.1:3306", Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
+	&Config{Net: "tcp", Addr: "127.0.0.1:3306", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
 }, {
 	"",
-	&Config{Net: "tcp", Addr: "127.0.0.1:3306", Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
+	&Config{Net: "tcp", Addr: "127.0.0.1:3306", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
 }, {
 	"user:p@/ssword@/",
-	&Config{User: "user", Passwd: "p@/ssword", Net: "tcp", Addr: "127.0.0.1:3306", Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
+	&Config{User: "user", Passwd: "p@/ssword", Net: "tcp", Addr: "127.0.0.1:3306", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
 }, {
 	"unix/?arg=%2Fsome%2Fpath.ext",
-	&Config{Net: "unix", Addr: "/tmp/mysql.sock", Params: map[string]string{"arg": "/some/path.ext"}, Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
+	&Config{Net: "unix", Addr: "/tmp/mysql.sock", Params: map[string]string{"arg": "/some/path.ext"}, Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
 }, {
 	"tcp(127.0.0.1)/dbname",
-	&Config{Net: "tcp", Addr: "127.0.0.1:3306", DBName: "dbname", Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
+	&Config{Net: "tcp", Addr: "127.0.0.1:3306", DBName: "dbname", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
 }, {
 	"tcp(de:ad:be:ef::ca:fe)/dbname",
-	&Config{Net: "tcp", Addr: "[de:ad:be:ef::ca:fe]:3306", DBName: "dbname", Collation: "utf8mb4_general_ci", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
+	&Config{Net: "tcp", Addr: "[de:ad:be:ef::ca:fe]:3306", DBName: "dbname", Loc: time.UTC, MaxAllowedPacket: defaultMaxAllowedPacket, Logger: defaultLogger, AllowNativePasswords: true, CheckConnLiveness: true},
 },
 }
 

packets.go

@@ -14,7 +14,6 @@ import (
 	"database/sql/driver"
 	"encoding/binary"
 	"encoding/json"
-	"errors"
 	"fmt"
 	"io"
 	"math"
@@ -346,14 +345,18 @@ func (mc *mysqlConn) writeHandshakeResponsePacket(authResp []byte, plugin string
 	data[10] = 0x00
 	data[11] = 0x00
 
-	// Charset [1 byte]
+	// Collation ID [1 byte]
+	cname := mc.cfg.Collation
+	if cname == "" {
+		cname = defaultCollation
+	}
 	var found bool
-	data[12], found = collations[mc.cfg.Collation]
+	data[12], found = collations[cname]
 	if !found {
 		// Note possibility for false negatives:
 		// could be triggered  although the collation is valid if the
 		// collations map does not contain entries the server supports.
-		return errors.New("unknown collation")
+		return fmt.Errorf("unknown collation: %q", cname)
 	}
 
 	// Filler [23 bytes] (all 0x00)