dsn: percent-decode username and password

AUTHORS

@@ -156,5 +156,6 @@ PingCAP Inc.
 Pivotal Inc.
 Shattered Silicon Ltd.
 Stripe Inc.
+Team Humaki LLC
 ThousandEyes
 Zendesk Inc.

README.md

@@ -137,6 +137,8 @@ Alternatively, [Config.FormatDSN](https://godoc.org/github.com/go-sql-driver/mys
 #### Password
 Passwords can consist of any character. Escaping is **not** necessary.
 
+Usernames that contain `:` (the user/password separator) must percent-encode it as `%3A`, for example `user%3Aname:password@protocol(address)/dbname`. Prefer [NewConfig](https://pkg.go.dev/github.com/go-sql-driver/mysql#NewConfig) / [NewConnector](https://pkg.go.dev/github.com/go-sql-driver/mysql#NewConnector) when credentials can hold reserved DSN characters.
+
 #### Protocol
 See [net.Dial](https://golang.org/pkg/net/#Dial) for more information which networks are available.
 In general you should use a Unix domain socket if available and TCP otherwise for best performance.

dsn.go

@@ -294,10 +294,10 @@ func (cfg *Config) FormatDSN() string {
 
 	// [username[:password]@]
 	if len(cfg.User) > 0 {
-		buf.WriteString(cfg.User)
+		buf.WriteString(escapeUserinfo(cfg.User))
 		if len(cfg.Passwd) > 0 {
 			buf.WriteByte(':')
-			buf.WriteString(cfg.Passwd)
+			buf.WriteString(escapeUserinfo(cfg.Passwd))
 		}
 		buf.WriteByte('@')
 	}
@@ -483,11 +483,11 @@ func ParseDSN(dsn string) (cfg *Config, err error) {
 						// Find the first ':' in dsn[:j]
 						for k = 0; k < j; k++ { // We cannot use k = range j here, because we use dsn[:k] below
 							if dsn[k] == ':' {
-								cfg.Passwd = dsn[k+1 : j]
+								cfg.Passwd = unescapeUserinfo(dsn[k+1 : j])
 								break
 							}
 						}
-						cfg.User = dsn[:k]
+						cfg.User = unescapeUserinfo(dsn[:k])
 
 						break
 					}
@@ -541,6 +541,41 @@ func ParseDSN(dsn string) (cfg *Config, err error) {
 	return
 }
 
+// unescapeUserinfo percent-decodes a DSN username or password. Invalid
+// escapes are left as-is so a literal '%' in a credential still parses.
+func unescapeUserinfo(s string) string {
+	u, err := url.PathUnescape(s)
+	if err != nil {
+		return s
+	}
+	return u
+}
+
+// escapeUserinfo percent-encodes DSN delimiters so FormatDSN round-trips
+// credentials that contain ':', '@', or '/'.
+func escapeUserinfo(s string) string {
+	if !strings.ContainsAny(s, "%:@/") {
+		return s
+	}
+	var b strings.Builder
+	b.Grow(len(s) + 4)
+	for i := 0; i < len(s); i++ {
+		switch s[i] {
+		case '%':
+			b.WriteString("%25")
+		case ':':
+			b.WriteString("%3A")
+		case '@':
+			b.WriteString("%40")
+		case '/':
+			b.WriteString("%2F")
+		default:
+			b.WriteByte(s[i])
+		}
+	}
+	return b.String()
+}
+
 // parseDSNParams parses the DSN "query string"
 // Values must be url.QueryEscape'ed
 func parseDSNParams(cfg *Config, params string) (err error) {

dsn_test.go

@@ -53,6 +53,17 @@ var testDSNs = []struct {
 			cfg.paramOrder = []string{"param"}
 		}),
 	},
+	{
+		// percent-encoded ':' in the username (#1747)
+		in: "user%3Aname:p%40ss@protocol(address)/dbname",
+		out: newTestConfig(func(cfg *Config) {
+			cfg.User = "user:name"
+			cfg.Passwd = "p@ss"
+			cfg.Net = "protocol"
+			cfg.Addr = "address"
+			cfg.DBName = "dbname"
+		}),
+	},
 	{
 		in: "username:password@protocol(address)/dbname?param=value&columnsWithAlias=true",
 		out: newTestConfig(func(cfg *Config) {
@@ -310,6 +321,37 @@ func TestDSNReformat(t *testing.T) {
 	}
 }
 
+func TestParseDSNUsernameColon(t *testing.T) {
+	cfg, err := ParseDSN("user%3Aname:p%40ss@tcp(localhost:3306)/dbname")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if cfg.User != "user:name" {
+		t.Errorf("User = %q, want %q", cfg.User, "user:name")
+	}
+	if cfg.Passwd != "p@ss" {
+		t.Errorf("Passwd = %q, want %q", cfg.Passwd, "p@ss")
+	}
+
+	got := cfg.FormatDSN()
+	cfg2, err := ParseDSN(got)
+	if err != nil {
+		t.Fatalf("FormatDSN %q: %v", got, err)
+	}
+	if cfg2.User != cfg.User || cfg2.Passwd != cfg.Passwd {
+		t.Errorf("round-trip User/Passwd = %q/%q, want %q/%q", cfg2.User, cfg2.Passwd, cfg.User, cfg.Passwd)
+	}
+
+	// Unencoded colon in the username still splits as user:password (compat).
+	cfg3, err := ParseDSN("user:name@tcp(localhost:3306)/dbname")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if cfg3.User != "user" || cfg3.Passwd != "name" {
+		t.Errorf("compat User/Passwd = %q/%q, want user/name", cfg3.User, cfg3.Passwd)
+	}
+}
+
 func TestDSNServerPubKey(t *testing.T) {
 	baseDSN := "User:password@tcp(localhost:5555)/dbname?serverPubKey="