updated implementation of rules

internal/route/rules/parser.go

@@ -0,0 +1,78 @@
+package rules
+
+import (
+	"strings"
+
+	E "github.com/yusing/go-proxy/internal/error"
+)
+
+var escapedChars = map[rune]rune{
+	'n':  '\n',
+	't':  '\t',
+	'r':  '\r',
+	'\'': '\'',
+	'"':  '"',
+	' ':  ' ',
+}
+
+// parse expression to subject and args
+// with support for quotes and escaped chars, e.g.
+//
+//	error 403 "Forbidden 'foo' 'bar'"
+//	error 403 Forbidden\ \"foo\"\ \"bar\".
+func parse(v string) (subject string, args []string, err E.Error) {
+	v = strings.TrimSpace(v)
+	var buf strings.Builder
+	escaped := false
+	quotes := make([]rune, 0, 4)
+	flush := func() {
+		if subject == "" {
+			subject = buf.String()
+		} else {
+			args = append(args, buf.String())
+		}
+		buf.Reset()
+	}
+	for _, r := range v {
+		if escaped {
+			if ch, ok := escapedChars[r]; ok {
+				buf.WriteRune(ch)
+			} else {
+				err = ErrUnsupportedEscapeChar.Subjectf("\\%c", r)
+				return
+			}
+			escaped = false
+			continue
+		}
+		switch r {
+		case '\\':
+			escaped = true
+			continue
+		case '"', '\'':
+			switch {
+			case len(quotes) > 0 && quotes[len(quotes)-1] == r:
+				quotes = quotes[:len(quotes)-1]
+				if len(quotes) == 0 {
+					flush()
+				} else {
+					buf.WriteRune(r)
+				}
+			case len(quotes) == 0:
+				quotes = append(quotes, r)
+			default:
+				buf.WriteRune(r)
+			}
+		case ' ':
+			flush()
+		default:
+			buf.WriteRune(r)
+		}
+	}
+
+	if len(quotes) > 0 {
+		err = ErrUnterminatedQuotes
+	} else {
+		flush()
+	}
+	return
+}