Support DSN without 'user:password@' (go-mysql-org#888)

* correctly parseDSN when username is not present

* one more test caset

* fixing golangci-lint errors

* added collation to README.md

* fixing incorrect comment

Author: dvilaverde

README.md

@@ -368,6 +368,14 @@ Configuration options can be provided by the standard DSN (Data Source Name).
 [user[:password]@]addr[/db[?param=X]]
 ```
 
+#### `collation`
+
+Set a collation during the Auth handshake.
+
+| Type      | Default         | Example                                               |
+| --------- | --------------- | ----------------------------------------------------- |
+| string    | utf8_general_ci | user:pass@localhost/mydb?collation=latin1_general_ci  |
+
 #### `compress`
 
 Enable compression between the client and the server. Valid values are 'zstd','zlib','uncompressed'.

client/auth.go

@@ -285,10 +285,8 @@ func (c *Conn) writeAuthHandshake() error {
 		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
+	// the MySQL protocol calls for the collation id to be sent as 1 byte, where only the
+	// lower 8 bits are used in this field.
 	data[12] = byte(collation.ID & 0xff)
 
 	// SSL Connection Request Packet

driver/driver.go

@@ -11,6 +11,7 @@ import (
 	"io"
 	"net/url"
 	"regexp"
+	"strings"
 	"sync"
 	"time"
 
@@ -24,6 +25,7 @@ var customTLSMutex sync.Mutex
 
 // Map of dsn address (makes more sense than full dsn?) to tls Config
 var (
+	dsnRegex           = regexp.MustCompile("@[^@]+/[^@/]+")
 	customTLSConfigMap = make(map[string]*tls.Config)
 	options            = make(map[string]DriverOption)
 
@@ -55,13 +57,16 @@ type connInfo struct {
 //
 // Optional parameters are supported in the standard DSN form
 func parseDSN(dsn string) (connInfo, error) {
-	var matchErr error
 	ci := connInfo{}
 
 	// If a "/" occurs after "@" and then no more "@" or "/" occur after that
-	ci.standardDSN, matchErr = regexp.MatchString("@[^@]+/[^@/]+", dsn)
-	if matchErr != nil {
-		return ci, errors.Errorf("invalid dsn, must be user:password@addr[/db[?param=X]]")
+	if strings.Contains(dsn, "@") {
+		ci.standardDSN = dsnRegex.MatchString(dsn)
+	} else {
+		// when the `@` char is not present in the dsn, then look for `/` as the db separator
+		// to indicate a standard DSN. The legacy form uses the `?` char as the db separator.
+		// If neither `/` or `?` are in the dsn, simply treat the dsn as the legacy form.
+		ci.standardDSN = strings.Contains(dsn, "/")
 	}
 
 	// Add a prefix so we can parse with url.Parse

driver/driver_test.go

@@ -92,6 +92,12 @@ func TestParseDSN(t *testing.T) {
 		"user:password@5.domain.com/db?readTimeout=1m":  {standardDSN: true, addr: "5.domain.com", user: "user", password: "password", db: "db", params: url.Values{"readTimeout": []string{"1m"}}},
 		"user:password@5.domain.com/db?writeTimeout=1m": {standardDSN: true, addr: "5.domain.com", user: "user", password: "password", db: "db", params: url.Values{"writeTimeout": []string{"1m"}}},
 		"user:password@5.domain.com/db?compress=zlib":   {standardDSN: true, addr: "5.domain.com", user: "user", password: "password", db: "db", params: url.Values{"compress": []string{"zlib"}}},
+
+		// per the documentation in the README, the 'user:password@' is optional as are the '/db?param=X' portions of the DSN
+		"6.domain.com":                  {standardDSN: false, addr: "6.domain.com", user: "", password: "", db: "", params: url.Values{}},
+		"7.domain.com?db":               {standardDSN: false, addr: "7.domain.com", user: "", password: "", db: "db", params: url.Values{}},
+		"8.domain.com/db":               {standardDSN: true, addr: "8.domain.com", user: "", password: "", db: "db", params: url.Values{}},
+		"9.domain.com/db?compress=zlib": {standardDSN: true, addr: "9.domain.com", user: "", password: "", db: "db", params: url.Values{"compress": []string{"zlib"}}},
 	}
 
 	for supplied, expected := range testDSNs {