Support Multiple Hosts in ConnConfig

Signed-off-by: Artemiy Ryabinkov <getlag@ya.ru>

conn.go

@@ -63,10 +63,29 @@ type DialFunc func(network, addr string) (net.Conn, error)
 
 // ConnConfig contains all the options used to establish a connection.
 type ConnConfig struct {
-	Host              string // host (e.g. localhost) or path to unix domain socket directory (e.g. /private/tmp)
+	// Name of host to connect to. (e.g. localhost)
-	Port              uint16 // default: 5432
+	// If a host name begins with a slash, it specifies Unix-domain communication
+	// rather than TCP/IP communication; the value is the name of the directory
+	// in which the socket file is stored. (e.g. /private/tmp)
+	// The default behavior when host is not specified, or is empty, is to connect to localhost.
+	//
+	// A comma-separated list of host names is also accepted,
+	// in which case each host name in the list is tried in order;
+	// an empty item in the list selects the default behavior as explained above.
+	// @see https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-MULTIPLE-HOSTS
+	Host string
+
+	// Port number to connect to at the server host,
+	// or socket file name extension for Unix-domain connections.
+	// An empty or zero value, specifies the default port number — 5432.
+	//
+	// If multiple hosts were given in the Host parameter, then
+	// this parameter may specify a single port number to be used for all hosts,
+	// or for those that haven't port explicitly defined.
+	Port     uint16
 	Database string
 	User     string // default: OS user name
+	// TODO: Allow password to be different for each host/port pair if a password file is used
 	Password          string
 	TLSConfig         *tls.Config // config for TLS connection -- nil disables TLS
 	UseFallbackTLS    bool        // Try FallbackTLSConfig if connecting with TLSConfig fails. Used for preferring TLS, but allowing unencrypted, or vice-versa
@@ -95,10 +114,34 @@ type ConnConfig struct {
 	//	"read-write", to disallow connections to read-only servers, hot standbys for example.
 	// @see https://www.postgresql.org/message-id/CAD__OuhqPRGpcsfwPHz_PDqAGkoqS1UvnUnOnAB-LBWBW=wu4A@mail.gmail.com
 	// @see https://paquier.xyz/postgresql-2/postgres-10-libpq-read-write/
+	//
+	// The query SHOW transaction_read_only will be sent upon any successful connection;
+	// if it returns on, the connection will be closed.
+	// If multiple hosts were specified in the connection string,
+	// any remaining servers will be tried just as if the connection attempt had failed.
+	// The default value of this parameter, any, regards all connections as acceptable.
 	TargetSessionAttrs string
 }
 
-func (cc *ConnConfig) networkAddress() net.Addr {
+// hostAddr represents network end point defined as hostname or IP + port.
+type hostAddr struct {
+	Host string
+	Port uint16
+}
+
+// Network returns the address's network name, "tcp".
+func (a *hostAddr) Network() string { return "tcp" }
+
+// String implements net.Addr String method.
+func (a *hostAddr) String() string {
+	if a == nil {
+		return "<nil>"
+	}
+
+	return net.JoinHostPort(a.Host, strconv.Itoa(int(a.Port)))
+}
+
+func (cc *ConnConfig) networkAddresses() ([]net.Addr, error) {
 	// See if host is a valid path, if yes connect with a unix socket
 	if _, err := os.Stat(cc.Host); err == nil {
 		// For backward compatibility accept socket file paths -- but directories are now preferred
@@ -109,13 +152,50 @@ func (cc *ConnConfig) networkAddress() net.Addr {
 			address = filepath.Join(address, ".s.PGSQL.") + strconv.FormatUint(uint64(cc.Port), 10)
 		}
 
-		return &net.UnixAddr{Name: address, Net: network}
+		addrs := []net.Addr{
+			&net.UnixAddr{Name: address, Net: network},
 		}
 
-	return &net.TCPAddr{
+		return addrs, nil
-		Port: int(cc.Port),
-		IP:   net.ParseIP(cc.Host),
 	}
+
+	if cc.Host == "" {
+		addrs := []net.Addr{
+			&net.TCPAddr{Port: int(cc.Port)},
+		}
+
+		return addrs, nil
+	}
+
+	var addrs []net.Addr
+
+	hostports := strings.Split(cc.Host, ",")
+	for i, hostport := range hostports {
+		if hostport == "" {
+			return nil, fmt.Errorf("multi-host part %d is empty, at least host or port must be defined", i)
+		}
+
+		// It's not possible to use net.TCPAddr here, cuz host may be hostname.
+		addr := hostAddr{
+			Host: hostport,
+			Port: cc.Port,
+		}
+
+		pos := strings.IndexByte(hostport, ':')
+		if pos != -1 {
+			p, err := strconv.ParseUint(hostport[pos+1:], 10, 16)
+			if err != nil {
+				return nil, fmt.Errorf("multi-host part %d (%s) has invalid port format", i, hostport)
+			}
+
+			addr.Host = hostport[:pos]
+			addr.Port = uint16(p)
+		}
+
+		addrs = append(addrs, &addr)
+	}
+
+	return addrs, nil
 }
 
 // Conn is a PostgreSQL connection handle. It is not safe for concurrent usage.
@@ -156,6 +236,10 @@ type Conn struct {
 	ConnInfo *pgtype.ConnInfo
 
 	frontend *pgproto3.Frontend
+
+	// In case of Multiple Hosts we need to know what addr was used to connect.
+	// This address will be used to send a cancellation request.
+	addr net.Addr
 }
 
 // PreparedStatement is a description of a prepared statement
@@ -286,10 +370,10 @@ func connect(config ConnConfig, connInfo *pgtype.ConnInfo) (c *Conn, err error)
 		c.config.Dial = d.Dial
 	}
 
-	// TODO: Parse multi-hosts
+	addrs, err := c.config.networkAddresses()
-	hostAddr := c.config.networkAddress()
+	if err != nil {
-
+		return nil, err
-	addrs := []net.Addr{hostAddr}
+	}
 
 	var errs []error
 	for _, addr := range addrs {
@@ -323,12 +407,23 @@ func connect(config ConnConfig, connInfo *pgtype.ConnInfo) (c *Conn, err error)
 				})
 			}
 
+			// On any auth errors return immediately
+			if pgErr, ok := err.(PgError); ok {
+				switch pgErr.Code {
+				// @see: https://www.postgresql.org/docs/current/errcodes-appendix.html
+				case "28000", "28P01": // Invalid Authorization Specification
+					return nil, pgErr
+				}
+			}
+
 			errs = append(errs, err)
 			continue
 		}
 
-		err = c.writeable()
+		err = c.writable()
 		if err != nil {
+			c.die(err)
+
 			if c.shouldLog(LogLevelInfo) {
 				c.log(LogLevelInfo, "host is not writable", map[string]interface{}{
 					"err":     err,
@@ -341,6 +436,8 @@ func connect(config ConnConfig, connInfo *pgtype.ConnInfo) (c *Conn, err error)
 			continue
 		}
 
+		c.addr = addr
+
 		return c, nil
 	}
 
@@ -351,30 +448,34 @@ func connect(config ConnConfig, connInfo *pgtype.ConnInfo) (c *Conn, err error)
 
 	var errmsg string
 	for _, err := range errs {
-		errmsg += ";" + err.Error()
+		errmsg += "; " + err.Error()
 	}
 
 	return nil, errors.New(errmsg)
 }
 
-func (c *Conn) writeable() error {
+func (c *Conn) writable() error {
 	if c.config.TargetSessionAttrs == "" || c.config.TargetSessionAttrs == "any" {
 		return nil
 	}
 
 	var st string
 	err := c.QueryRowEx(context.Background(), "SHOW transaction_read_only", &QueryExOptions{SimpleProtocol: true}).
-		Scan(st)
+		Scan(&st)
 
 	if err != nil {
 		return errors.Wrap(err, "failed to fetch \"transaction_read_only\" state")
 	}
 
-	if st == "on" {
+	switch st {
+	case "on":
 		return errors.New("writable connection disabled by server")
+	case "off":
+		// If transaction_read_only = off, then connection is writable.
+		return nil
 	}
 
-	return nil
+	return errors.New("unexpected \"transaction_read_only\" status")
 }
 
 func (c *Conn) connect(config ConnConfig, network, address string, tlsConfig *tls.Config) (err error) {
@@ -958,6 +1059,8 @@ func ParseDSN(s string) (ConnConfig, error) {
 // ParseConnectionString parses either a URI or a DSN connection string.
 // see ParseURI and ParseDSN for details.
 func ParseConnectionString(s string) (ConnConfig, error) {
+	// TODO: Multiple Hosts support
+	// @see: https://www.postgresql.org/docs/10/libpq-connect.html#LIBPQ-MULTIPLE-HOSTS
 	if u, err := url.Parse(s); err == nil && u.Scheme != "" {
 		return ParseURI(s)
 	}
@@ -981,6 +1084,8 @@ func ParseConnectionString(s string) (ConnConfig, error) {
 // PGSSLROOTCERT
 // PGAPPNAME
 // PGCONNECT_TIMEOUT
+// TODO: PGTARGETSESSIONATTRS support
+// @see: https://www.postgresql.org/docs/10/libpq-envars.html
 //
 // Important TLS Security Notes:
 // ParseEnvLibpq tries to match libpq behavior with regard to PGSSLMODE. This
@@ -1741,8 +1846,7 @@ func quoteIdentifier(s string) string {
 }
 
 func doCancel(c *Conn) error {
-	addr := c.config.networkAddress()
+	cancelConn, err := c.config.Dial(c.addr.Network(), c.addr.String())
-	cancelConn, err := c.config.Dial(addr.Network(), addr.String())
 	if err != nil {
 		return err
 	}

conn_config_test.go.example

@@ -7,6 +7,7 @@ import (
 	// "go/build"
 	// "io/ioutil"
 	// "path"
+	// "net"
 
 	"github.com/jackc/pgx"
 )
@@ -14,6 +15,7 @@ import (
 var defaultConnConfig *pgx.ConnConfig = &pgx.ConnConfig{Host: "127.0.0.1", User: "pgx_md5", Password: "secret", Database: "pgx_test"}
 
 // To skip tests for specific connection / authentication types set that connection param to nil
+var multihostConnConfig *pgx.ConnConfig = nil
 var tcpConnConfig *pgx.ConnConfig = nil
 var unixSocketConnConfig *pgx.ConnConfig = nil
 var md5ConnConfig *pgx.ConnConfig = nil
@@ -24,6 +26,7 @@ var customDialerConnConfig *pgx.ConnConfig = nil
 var replicationConnConfig *pgx.ConnConfig = nil
 var cratedbConnConfig *pgx.ConnConfig = nil
 
+// var multihostConnConfig *pgx.ConnConfig = &pgx.ConnConfig{Host: "2.2.2.2:1,127.0.0.1,4.2.4.2", User: "pgx_md5", Password: "secret", Database: "pgx_test", Dial: (&net.Dialer{KeepAlive: 5 * time.Minute, Timeout: 100 * time.Millisecond}).Dial}
 // var tcpConnConfig *pgx.ConnConfig = &pgx.ConnConfig{Host: "127.0.0.1", User: "pgx_md5", Password: "secret", Database: "pgx_test"}
 // var unixSocketConnConfig *pgx.ConnConfig = &pgx.ConnConfig{Host: "/private/tmp", User: "pgx_none", Database: "pgx_test"}
 // var md5ConnConfig *pgx.ConnConfig = &pgx.ConnConfig{Host: "127.0.0.1", User: "pgx_md5", Password: "secret", Database: "pgx_test"}

conn_config_test.go.travis

@@ -5,9 +5,11 @@ import (
   "github.com/jackc/pgx"
   "os"
   "strconv"
+  "net"
 )
 
 var defaultConnConfig = &pgx.ConnConfig{Host: "127.0.0.1", User: "pgx_md5", Password: "secret", Database: "pgx_test"}
+var multihostConnConfig *pgx.ConnConfig = &pgx.ConnConfig{Host: "2.2.2.2:1,127.0.0.1,4.2.4.2", User: "pgx_md5", Password: "secret", Database: "pgx_test", Dial: (&net.Dialer{KeepAlive: 5 * time.Minute, Timeout: 100 * time.Millisecond}).Dial}
 var tcpConnConfig = &pgx.ConnConfig{Host: "127.0.0.1", User: "pgx_md5", Password: "secret", Database: "pgx_test"}
 var unixSocketConnConfig = &pgx.ConnConfig{Host: "/var/run/postgresql", User: "postgres", Database: "pgx_test"}
 var md5ConnConfig = &pgx.ConnConfig{Host: "127.0.0.1", User: "pgx_md5", Password: "secret", Database: "pgx_test"}

conn_test.go

@@ -84,6 +84,107 @@ func TestConnect(t *testing.T) {
 	}
 }
 
+
+func TestConnectWithMultiHost(t *testing.T) {
+	t.Parallel()
+
+	if multihostConnConfig == nil {
+		t.Skip("Skipping due to undefined multihostConnConfig")
+	}
+
+	conn, err := pgx.Connect(*multihostConnConfig)
+	if err != nil {
+		t.Fatalf("Unable to establish connection: %v", err)
+	}
+
+	if _, present := conn.RuntimeParams["server_version"]; !present {
+		t.Error("Runtime parameters not stored")
+	}
+
+	if conn.PID() == 0 {
+		t.Error("Backend PID not stored")
+	}
+
+	var currentDB string
+	err = conn.QueryRow("select current_database()").Scan(&currentDB)
+	if err != nil {
+		t.Fatalf("QueryRow Scan unexpectedly failed: %v", err)
+	}
+	if currentDB != defaultConnConfig.Database {
+		t.Errorf("Did not connect to specified database (%v)", defaultConnConfig.Database)
+	}
+
+	var user string
+	err = conn.QueryRow("select current_user").Scan(&user)
+	if err != nil {
+		t.Fatalf("QueryRow Scan unexpectedly failed: %v", err)
+	}
+	if user != defaultConnConfig.User {
+		t.Errorf("Did not connect as specified user (%v)", defaultConnConfig.User)
+	}
+
+	err = conn.Close()
+	if err != nil {
+		t.Fatal("Unable to close connection")
+	}
+}
+
+
+func TestConnectWithMultiHostWritable(t *testing.T) {
+	t.Parallel()
+
+	if multihostConnConfig == nil {
+		t.Skip("Skipping due to undefined multihostConnConfig")
+	}
+
+	connConfig := *multihostConnConfig
+	connConfig.TargetSessionAttrs = "read-write"
+
+	conn := mustConnect(t, connConfig)
+	defer closeConn(t, conn)
+
+	if _, present := conn.RuntimeParams["server_version"]; !present {
+		t.Error("Runtime parameters not stored")
+	}
+
+	if conn.PID() == 0 {
+		t.Error("Backend PID not stored")
+	}
+
+	var currentDB string
+	err := conn.QueryRow("select current_database()").Scan(&currentDB)
+	if err != nil {
+		t.Fatalf("QueryRow Scan unexpectedly failed: %v", err)
+	}
+	if currentDB != defaultConnConfig.Database {
+		t.Errorf("Did not connect to specified database (%v)", defaultConnConfig.Database)
+	}
+
+	var user string
+	err = conn.QueryRow("select current_user").Scan(&user)
+	if err != nil {
+		t.Fatalf("QueryRow Scan unexpectedly failed: %v", err)
+	}
+	if user != defaultConnConfig.User {
+		t.Errorf("Did not connect as specified user (%v)", defaultConnConfig.User)
+	}
+
+	var st string
+	err = conn.QueryRow("SHOW transaction_read_only").Scan(&st)
+	if err != nil {
+		t.Fatalf("QueryRow Scan unexpectedly failed: %v", err)
+	}
+
+	if st == "on" {
+		t.Error("Connection is not writable")
+	}
+
+	err = conn.Close()
+	if err != nil {
+		t.Fatal("Unable to close connection")
+	}
+}
+
 func TestConnectWithUnixSocketDirectory(t *testing.T) {
 	t.Parallel()
 

pgpass.go

@@ -57,6 +57,7 @@ func parsepgpass(line, cfgHost, cfgPort, cfgDatabase, cfgUsername string) *strin
 	return &parts[4]
 }
 
+// TODO: Multi-host support
 func pgpass(cfg *ConnConfig) (found bool) {
 	passfile := os.Getenv("PGPASSFILE")
 	if passfile == "" {