Parser: Allow literal control chars in logfmt decoder (#3932)

* Allow literal control chars in decoder

* Ensure decoding control chars in logfmt works

pkg/logql/log/logfmt/jsonstring.go

@@ -36,7 +36,7 @@ func unquoteBytes(s []byte) (t []byte, ok bool) {
 	r := 0
 	for r < len(s) {
 		c := s[r]
-		if c == '\\' || c == '"' || c < ' ' {
+		if c == '\\' || c == '"' {
 			break
 		}
 		if c < utf8.RuneSelf {
@@ -118,8 +118,8 @@ func unquoteBytes(s []byte) (t []byte, ok bool) {
 				w += utf8.EncodeRune(b[w:], rr)
 			}
 
-		// Quote, control characters are invalid.
-		case c == '"', c < ' ':
+		// Unescaped quote is invalid.
+		case c == '"':
 			return
 
 		// ASCII

pkg/logql/log/parser_test.go

@@ -603,6 +603,50 @@ func Test_logfmtParser_Parse(t *testing.T) {
 				{Name: "foobar", Value: "foo bar"},
 			},
 		},
+		{
+			"escaped control chars in logfmt",
+			[]byte(`foobar="foo\nbar\tbaz"`),
+			labels.Labels{
+				{Name: "a", Value: "b"},
+			},
+			labels.Labels{
+				{Name: "a", Value: "b"},
+				{Name: "foobar", Value: "foo\nbar\tbaz"},
+			},
+		},
+		{
+			"literal control chars in logfmt",
+			[]byte("foobar=\"foo\nbar\tbaz\""),
+			labels.Labels{
+				{Name: "a", Value: "b"},
+			},
+			labels.Labels{
+				{Name: "a", Value: "b"},
+				{Name: "foobar", Value: "foo\nbar\tbaz"},
+			},
+		},
+		{
+			"escaped slash logfmt",
+			[]byte(`foobar="foo ba\\r baz"`),
+			labels.Labels{
+				{Name: "a", Value: "b"},
+			},
+			labels.Labels{
+				{Name: "a", Value: "b"},
+				{Name: "foobar", Value: `foo ba\r baz`},
+			},
+		},
+		{
+			"literal newline and escaped slash logfmt",
+			[]byte("foobar=\"foo bar\nb\\\\az\""),
+			labels.Labels{
+				{Name: "a", Value: "b"},
+			},
+			labels.Labels{
+				{Name: "a", Value: "b"},
+				{Name: "foobar", Value: "foo bar\nb\\az"},
+			},
+		},
 		{
 			"double property logfmt",
 			[]byte(`foobar="foo bar" latency=10ms`),