Add RegisterConnConfig to stdlib

This restored functionality lost in the v3 to v4 transition when
RegisterDriverConfig was removed.

fixes #617

stdlib/sql.go

@@ -14,27 +14,14 @@
 //		return err
 //	}
 //
-// A DriverConfig can be used to further configure the connection process. This
-// allows configuring TLS configuration, setting a custom dialer, logging, and
-// setting an AfterConnect hook.
+// Or a pgx.ConnConfig can be used to set configuration not accessible via connection string. In this case the
+// pgx.ConnConfig must first be registered with the driver. This registration returns a connection string which is used
+// with sql.Open.
 //
-//	driverConfig := stdlib.DriverConfig{
-// 		ConnConfig: pgx.ConnConfig{
-//			Logger:   logger,
-//		},
-//		AfterConnect: func(c *pgx.Conn) error {
-//			// Ensure all connections have this temp table available
-//			_, err := c.Exec("create temporary table foo(...)")
-//			return err
-//		},
-//	}
-//
-//	stdlib.RegisterDriverConfig(&driverConfig)
-//
-//	db, err := sql.Open("pgx", driverConfig.ConnectionString("postgres://pgx_md5:secret@127.0.0.1:5432/pgx_test"))
-//	if err != nil {
-//		return err
-//	}
+//	connConfig, _ := pgx.ParseConfig(os.Getenv("DATABASE_URL"))
+//	connConfig.Logger = myLogger
+//	connStr := stdlib.RegisterConnConfig(connConfig)
+//	db, _ := sql.Open("pgx", connStr)
 //
 // pgx uses standard PostgreSQL positional parameters in queries. e.g. $1, $2.
 // It does not support named parameters.
@@ -99,7 +86,9 @@ var ctxKeyFakeTx ctxKey = 0
 var ErrNotPgx = errors.New("not pgx *sql.DB")
 
 func init() {
-	pgxDriver = &Driver{}
+	pgxDriver = &Driver{
+		configs: make(map[string]*pgx.ConnConfig),
+	}
 	fakeTxConns = make(map[*pgx.Conn]*sql.Tx)
 	sql.Register("pgx", pgxDriver)
 
@@ -125,12 +114,24 @@ var (
 	fakeTxConns map[*pgx.Conn]*sql.Tx
 )
 
-type Driver struct{}
+type Driver struct {
+	configMutex sync.Mutex
+	configs     map[string]*pgx.ConnConfig
+}
 
 func (d *Driver) Open(name string) (driver.Conn, error) {
-	connConfig, err := pgx.ParseConfig(name)
-	if err != nil {
-		return nil, err
+	var connConfig *pgx.ConnConfig
+
+	d.configMutex.Lock()
+	connConfig = d.configs[name]
+	d.configMutex.Unlock()
+
+	if connConfig == nil {
+		var err error
+		connConfig, err = pgx.ParseConfig(name)
+		if err != nil {
+			return nil, err
+		}
 	}
 
 	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second) // Ensure eventual timeout
@@ -144,6 +145,30 @@ func (d *Driver) Open(name string) (driver.Conn, error) {
 	return c, nil
 }
 
+func (d *Driver) registerConnConfig(c *pgx.ConnConfig) string {
+	d.configMutex.Lock()
+	connStr := fmt.Sprintf("registeredConnConfig%d", len(d.configs))
+	d.configs[connStr] = c
+	d.configMutex.Unlock()
+	return connStr
+}
+
+func (d *Driver) unregisterConnConfig(connStr string) {
+	d.configMutex.Lock()
+	delete(d.configs, connStr)
+	d.configMutex.Unlock()
+}
+
+// RegisterConnConfig registers a ConnConfig and returns the connection string to use with Open.
+func RegisterConnConfig(c *pgx.ConnConfig) string {
+	return pgxDriver.registerConnConfig(c)
+}
+
+// UnregisterConnConfig removes the ConnConfig registration for connStr.
+func UnregisterConnConfig(connStr string) {
+	pgxDriver.unregisterConnConfig(connStr)
+}
+
 type Conn struct {
 	conn       *pgx.Conn
 	psCount    int64 // Counter used for creating unique prepared statement names