Adding better support for elements offsets

.gitignore

@@ -8,3 +8,5 @@
 vendor/github.com/buger/goterm/
 prof.cpu
 prof.mem
+
+.idea

errors.go

@@ -0,0 +1,75 @@
+package jsonparser
+
+// Errors
+var (
+	keyPathNotFoundError       = 1
+	unknownValueTypeError      = 2
+	malformedJsonError         = 3
+	malformedStringError       = 4
+	malformedArrayError        = 5
+	malformedObjectError       = 6
+	malformedValueError        = 7
+	malformedStringEscapeError = 8
+)
+
+type ParserError struct {
+	offset int
+	s string
+	errorType int
+}
+
+func (err *ParserError) Error() string {
+	return err.s
+}
+
+func (err *ParserError) Offset() int {
+	return err.offset
+}
+
+func MalformedObjectError(offset int) error {
+	return &ParserError{s: "Value looks like object, but can't find closing '}' symbol", offset: offset, errorType: malformedObjectError}
+}
+
+func UnknownValueTypeError(offset int) error {
+	return &ParserError{s:"Unknown value type", offset: offset, errorType: unknownValueTypeError}
+}
+
+func KeyPathNotFoundError(offset int) error {
+	return &ParserError{s: "Key path not found", offset: offset, errorType: keyPathNotFoundError}
+}
+
+func MalformedJsonError(offset int) error {
+	return &ParserError{s: "Malformed JSON error", offset: offset, errorType: malformedJsonError}
+}
+
+func MalformedStringError(offset int) error {
+	return &ParserError{s: "Value is string, but can't find closing '\"' symbol", offset: offset, errorType: malformedStringError}
+}
+
+func MalformedArrayError(offset int) error {
+	return &ParserError{s: "Value is array, but can't find closing ']' symbol", offset: offset, errorType: malformedArrayError}
+}
+
+func MalformedValueError(offset int) error {
+	return &ParserError{s: "Value looks like Number/Boolean/None, but can't find its end: ',' or '}' symbol", offset: offset, errorType: malformedValueError}
+}
+
+func MalformedStringEscapeError(offset int) error {
+	return &ParserError{s: "Encountered an invalid escape sequence in a string", offset: offset, errorType: malformedStringEscapeError}
+}
+
+func addToErrorOffset(err error, offset int) error {
+	if parserError, ok := err.(*ParserError); ok {
+		parserError.offset = parserError.offset + offset
+	}
+	return err
+}
+
+func isKeyPathNotFoundError(err error) bool {
+	return isParserErrorOfType(err, keyPathNotFoundError)
+}
+
+func isParserErrorOfType(err error, errorType int) bool {
+	parserError, ok := err.(*ParserError)
+	return ok && parserError.errorType == errorType
+}

escape.go

@@ -149,7 +149,7 @@ func Unescape(in, out []byte) ([]byte, error) {
 		// Unescape the next escaped character
 		inLen, bufLen := unescapeToUTF8(in, buf)
 		if inLen == -1 {
-			return nil, MalformedStringEscapeError
+			return nil, MalformedStringEscapeError(firstBackslash)
 		}
 
 		in = in[inLen:]