Added understanding of error messages from server

conn.go

@@ -132,6 +132,8 @@ func (c *conn) processContextFreeMsg(t byte, r *messageReader) (err error) {
 	case 'S':
 		c.rxParameterStatus(r)
 		return nil
+	case errorResponse:
+		return c.rxErrorResponse(r)
 	default:
 		return fmt.Errorf("Received unknown message type: %c", t)
 	}
@@ -190,6 +192,25 @@ func (c *conn) rxParameterStatus(r *messageReader) {
 	c.runtimeParams[key] = value
 }
 
+func (c *conn) rxErrorResponse(r *messageReader) (err PgError) {
+	for {
+		switch r.readByte() {
+		case 'S':
+			err.Severity = r.readString()
+		case 'C':
+			err.Code = r.readString()
+		case 'M':
+			err.Message = r.readString()
+		case 0: // End of error message
+			return
+		default: // Ignore other error fields
+			r.readString();
+		}
+	}
+
+	panic("Unreachable")
+}
+
 func (c *conn) rxBackendKeyData(r *messageReader) {
 	c.pid = r.readInt32()
 	c.secretKey = r.readInt32()

conn_test.go

@@ -34,6 +34,13 @@ func TestConnect(t *testing.T) {
 	}
 }
 
+func TestConnectWithInvalidUser(t *testing.T) {
+	_, err := Connect(map[string]string{"socket": "/private/tmp/.s.PGSQL.5432", "user": "invalid_user", "database": "pgx_test"})
+	pgErr := err.(PgError)
+	if pgErr.Code != "28000" {
+		t.Fatal("Did not receive expected error when connecting with invalid user")
+	}
+}
 func TestQuery(t *testing.T) {
 	conn, err := Connect(map[string]string{"socket": "/private/tmp/.s.PGSQL.5432", "user": "pgx", "database": "pgx_test"})
 	if err != nil {

messages.go

@@ -15,6 +15,7 @@ const (
 	rowDescription  = 'T'
 	dataRow         = 'D'
 	commandComplete = 'C'
+	errorResponse = 'E'
 )
 
 type startupMessage struct {
@@ -50,3 +51,13 @@ type fieldDescription struct {
 	modifier        int32
 	formatCode      int16
 }
+
+type PgError struct {
+	Severity string
+	Code string
+	Message string
+}
+
+func (self PgError) Error() string {
+	return self.Severity + ": " + self.Message + " (SQLSTATE " + self.Code + ")"
+}