Do not set TCP_USER_TIMEOUT on Unix sockets

The option only exists for TCP, so every connection over a socket (host=/var/run/postgresql) failed with "operation not supported".

Claude-Session: https://claude.ai/code/session_01DeXuhSjq5Gta5qPJgSceFe

db/pg/dialer_linux.go

@@ -2,6 +2,7 @@ package pg
 
 import (
 	"net"
+	"strings"
 	"syscall"
 
 	"golang.org/x/sys/unix"
@@ -14,6 +15,9 @@ import (
 func newDialer() *net.Dialer {
 	return &net.Dialer{
 		Control: func(network, address string, c syscall.RawConn) error {
+			if !strings.HasPrefix(network, "tcp") {
+				return nil // Unix sockets (host=/var/run/postgresql) have no TCP_USER_TIMEOUT
+			}
 			var sockErr error
 			err := c.Control(func(fd uintptr) {
 				sockErr = unix.SetsockoptInt(int(fd), syscall.IPPROTO_TCP, unix.TCP_USER_TIMEOUT, int(tcpUserTimeout.Milliseconds()))

db/pg/dialer_linux_test.go

@@ -3,6 +3,7 @@ package pg
 import (
 	"context"
 	"net"
+	"path/filepath"
 	"syscall"
 	"testing"
 
@@ -53,3 +54,17 @@ func TestParseConnConfig_DialsWithTCPUserTimeout(t *testing.T) {
 	require.Nil(t, sockErr)
 	require.Equal(t, int(tcpUserTimeout.Milliseconds()), timeout)
 }
+
+func TestParseConnConfig_DialsUnixSocket(t *testing.T) {
+	// TCP_USER_TIMEOUT does not exist for Unix sockets (host=/var/run/postgresql), so the dialer
+	// must not set it there, or every connection fails with "operation not supported"
+	path := filepath.Join(t.TempDir(), ".s.PGSQL.5432")
+	listener, err := net.Listen("unix", path)
+	require.Nil(t, err)
+	defer listener.Close()
+	config, err := parseConnConfig("postgres://user:pass@/db?host=" + filepath.Dir(path))
+	require.Nil(t, err)
+	conn, err := config.DialFunc(context.Background(), "unix", path)
+	require.Nil(t, err)
+	require.Nil(t, conn.Close())
+}