Add support for Unix sockets on Windows

Fixes #1199.

config.go

@@ -100,10 +100,29 @@ type FallbackConfig struct {
 	TLSConfig *tls.Config // nil disables TLS
 }
 
+// isAbsolutePath checks if the provided value is an absolute path either
+// beginning with a forward slash (as on Linux-based systems) or with a capital
+// letter A-Z followed by a colon and a backslash, e.g., "C:\", (as on Windows).
+func isAbsolutePath(path string) bool {
+	isWindowsPath := func(p string) bool {
+		if len(p) < 3 {
+			return false
+		}
+		drive := p[0]
+		colon := p[1]
+		backslash := p[2]
+		if drive >= 'A' && drive <= 'Z' && colon == ':' && backslash == '\\' {
+			return true
+		}
+		return false
+	}
+	return strings.HasPrefix(path, "/") || isWindowsPath(path)
+}
+
 // NetworkAddress converts a PostgreSQL host and port into network and address suitable for use with
 // net.Dial.
 func NetworkAddress(host string, port uint16) (network, address string) {
-	if strings.HasPrefix(host, "/") {
+	if isAbsolutePath(host) {
 		network = "unix"
 		address = filepath.Join(host, ".s.PGSQL.") + strconv.FormatInt(int64(port), 10)
 	} else {

config_test.go

@@ -231,6 +231,18 @@ func TestParseConfig(t *testing.T) {
 				RuntimeParams: map[string]string{},
 			},
 		},
+		{
+			name:       "database url unix domain socket host on windows",
+			connString: "postgres:///foo?host=C:\\tmp",
+			config: &pgconn.Config{
+				User:          osUserName,
+				Host:          "C:\\tmp",
+				Port:          5432,
+				Database:      "foo",
+				TLSConfig:     nil,
+				RuntimeParams: map[string]string{},
+			},
+		},
 		{
 			name:       "database url dbname",
 			connString: "postgres://localhost/?dbname=foo&sslmode=disable",
@@ -703,6 +715,55 @@ func TestConfigCopyCanBeUsedToConnect(t *testing.T) {
 	assert.NoError(t, err)
 }
 
+func TestNetworkAddress(t *testing.T) {
+	tests := []struct {
+		name    string
+		host    string
+		wantNet string
+	}{
+		{
+			name:    "Default Unix socket address",
+			host:    "/var/run/postgresql",
+			wantNet: "unix",
+		},
+		{
+			name:    "Windows Unix socket address (standard drive name)",
+			host:    "C:\\tmp",
+			wantNet: "unix",
+		},
+		{
+			name:    "Windows Unix socket address (first drive name)",
+			host:    "A:\\tmp",
+			wantNet: "unix",
+		},
+		{
+			name:    "Windows Unix socket address (last drive name)",
+			host:    "Z:\\tmp",
+			wantNet: "unix",
+		},
+		{
+			name:    "Assume TCP for unknown formats",
+			host:    "a/tmp",
+			wantNet: "tcp",
+		},
+		{
+			name:    "loopback interface",
+			host:    "localhost",
+			wantNet: "tcp",
+		},
+		{
+			name:    "IP address",
+			host:    "127.0.0.1",
+			wantNet: "tcp",
+		},
+	}
+	for i, tt := range tests {
+		gotNet, _ := pgconn.NetworkAddress(tt.host, 5432)
+
+		assert.Equalf(t, tt.wantNet, gotNet, "Test %d (%s)", i, tt.name)
+	}
+}
+
 func assertConfigsEqual(t *testing.T, expected, actual *pgconn.Config, testName string) {
 	if !assert.NotNil(t, expected) {
 		return

pgconn.go

@@ -187,7 +187,7 @@ func expandWithIPs(ctx context.Context, lookupFn LookupFunc, fallbacks []*Fallba
 
 	for _, fb := range fallbacks {
 		// skip resolve for unix sockets
-		if strings.HasPrefix(fb.Host, "/") {
+		if isAbsolutePath(fb.Host) {
 			configs = append(configs, &FallbackConfig{
 				Host:      fb.Host,
 				Port:      fb.Port,