report SQLState in MySQLError

to allow library users to distinguish user-defined from client / server errors

errors.go

@@ -56,11 +56,16 @@ func SetLogger(logger Logger) error {
 
 // MySQLError is an error type which represents a single MySQL error
 type MySQLError struct {
-	Number  uint16
-	Message string
+	Number   uint16
+	SQLState [5]byte
+	Message  string
 }
 
 func (me *MySQLError) Error() string {
+	if me.SQLState != [5]byte{} {
+		return fmt.Sprintf("Error %d (%s): %s", me.Number, string(me.SQLState[:]), me.Message)
+	}
+
 	return fmt.Sprintf("Error %d: %s", me.Number, me.Message)
 }
 
@@ -70,3 +75,10 @@ func (me *MySQLError) Is(err error) bool {
 	}
 	return false
 }
+
+func (me *MySQLError) IsWithSQLState(err error) bool {
+	if merr, ok := err.(*MySQLError); ok {
+		return merr.Number == me.Number && merr.SQLState == me.SQLState
+	}
+	return false
+}

errors_test.go

@@ -43,13 +43,13 @@ func TestErrorsStrictIgnoreNotes(t *testing.T) {
 }
 
 func TestMySQLErrIs(t *testing.T) {
-	infraErr := &MySQLError{1234, "the server is on fire"}
-	otherInfraErr := &MySQLError{1234, "the datacenter is flooded"}
+	infraErr := &MySQLError{Number: 1234, Message: "the server is on fire"}
+	otherInfraErr := &MySQLError{Number: 1234, Message: "the datacenter is flooded"}
 	if !errors.Is(infraErr, otherInfraErr) {
 		t.Errorf("expected errors to be the same: %+v %+v", infraErr, otherInfraErr)
 	}
 
-	differentCodeErr := &MySQLError{5678, "the server is on fire"}
+	differentCodeErr := &MySQLError{Number: 5678, Message: "the server is on fire"}
 	if errors.Is(infraErr, differentCodeErr) {
 		t.Fatalf("expected errors to be different: %+v %+v", infraErr, differentCodeErr)
 	}
@@ -59,3 +59,22 @@ func TestMySQLErrIs(t *testing.T) {
 		t.Fatalf("expected errors to be different: %+v %+v", infraErr, nonMysqlErr)
 	}
 }
+
+func TestMySQLErrIsWithSQLState(t *testing.T) {
+	toState := func(s string) [5]byte {
+		var b [5]byte
+		copy(b[:], s)
+		return b
+	}
+
+	infraErr := &MySQLError{Number: 1234, SQLState: toState("HY000"), Message: "the server is on fire"}
+	otherInfraErr := &MySQLError{Number: 1234, SQLState: toState("HY000"), Message: "the datacenter is flooded"}
+	if !infraErr.IsWithSQLState(otherInfraErr) {
+		t.Errorf("expected errors to be the same: %+v %+v", infraErr, otherInfraErr)
+	}
+
+	differentStateErr := &MySQLError{Number: 1234, SQLState: toState("45000"), Message: "the server is on fire"}
+	if infraErr.IsWithSQLState(differentStateErr) {
+		t.Fatalf("expected errors to be different: %+v %+v", infraErr, differentStateErr)
+	}
+}

packets.go

@@ -587,19 +587,20 @@ func (mc *mysqlConn) handleErrorPacket(data []byte) error {
 		return driver.ErrBadConn
 	}
 
+	me := &MySQLError{Number: errno}
+
 	pos := 3
 
 	// SQL State [optional: # + 5bytes string]
 	if data[3] == 0x23 {
-		//sqlstate := string(data[4 : 4+5])
+		copy(me.SQLState[:], data[4:4+5])
 		pos = 9
 	}
 
 	// Error Message [string]
-	return &MySQLError{
-		Number:  errno,
-		Message: string(data[pos:]),
-	}
+	me.Message = string(data[pos:])
+
+	return me
 }
 
 func readStatus(b []byte) statusFlag {