parser: fix panic when label exceeds 16MB

Signed-off-by: Meher Assel <asselmeher@gmail.com>

model/labels/labels_stringlabels.go

@@ -16,6 +16,7 @@
 package labels
 
 import (
+	"errors"
 	"slices"
 	"strings"
 	"unsafe"
@@ -540,13 +541,16 @@ func marshalLabelToSizedBuffer(m *Label, data []byte) int {
 	return len(data) - i
 }
 
+// ErrLabelTooLong is returned when a label name or value exceeds the maximum allowed size.
+var ErrLabelTooLong = errors.New("string too long to encode as label")
+
 func sizeWhenEncoded(x uint64) (n int) {
 	if x < 255 {
 		return 1
 	} else if x <= 1<<24 {
 		return 4
 	}
-	panic("String too long to encode as label.")
+	panic(ErrLabelTooLong)
 }
 
 func encodeSize(data []byte, offset, v int) int {

promql/parser/parse.go

@@ -340,16 +340,23 @@ var errUnexpected = errors.New("unexpected error")
 // recover is the handler that turns panics into returns from the top level of Parse.
 func (*parser) recover(errp *error) {
 	e := recover()
-	switch _, ok := e.(runtime.Error); {
-	case ok:
+	if e == nil {
+		return
+	}
+
+	switch err := e.(type) {
+	case runtime.Error:
 		// Print the stack trace but do not inhibit the running application.
 		buf := make([]byte, 64<<10)
 		buf = buf[:runtime.Stack(buf, false)]
 
 		fmt.Fprintf(os.Stderr, "parser panic: %v\n%s", e, buf)
 		*errp = errUnexpected
-	case e != nil:
-		*errp = e.(error)
+	case error:
+		*errp = err
+	default:
+		// Handle non-error panic values (e.g., strings) gracefully.
+		*errp = fmt.Errorf("%v", e)
 	}
 }
 

promql/parser/parse_test.go

@@ -6004,6 +6004,28 @@ func TestRecoverParserError(t *testing.T) {
 	panic(e)
 }
 
+func TestRecoverParserString(t *testing.T) {
+	p := NewParser("foo bar")
+	var err error
+
+	defer func() {
+		require.Error(t, err)
+		require.EqualError(t, err, "some string panic")
+	}()
+	defer p.recover(&err)
+
+	panic("some string panic")
+}
+
+func TestParseLabelTooLong(t *testing.T) {
+	const maxLabelSize = 1 << 24
+	longValue := strings.Repeat("a", maxLabelSize+1)
+	input := `{job="` + longValue + `"}`
+
+	_, err := ParseMetric(input)
+	require.Error(t, err)
+}
+
 func TestExtractSelectors(t *testing.T) {
 	for _, tc := range [...]struct {
 		input    string