From 5279d50d92c7259b1a20e6978f871827bbdfcbe1 Mon Sep 17 00:00:00 2001
From: Fabian Reinartz <fab.reinartz@gmail.com>
Date: Sun, 2 Aug 2015 13:37:42 +0200
Subject: [PATCH] Handle parser runtime panics gracefully

---
 promql/parse.go      | 13 +++++++++++--
 promql/parse_test.go | 27 +++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/promql/parse.go b/promql/parse.go
index 237670323..a51e0c550 100644
--- a/promql/parse.go
+++ b/promql/parse.go
@@ -20,7 +20,10 @@ import (
 	"strings"
 	"time"
 
+	"github.com/prometheus/log"
+
 	clientmodel "github.com/prometheus/client_golang/model"
+
 	"github.com/prometheus/prometheus/storage/metric"
 	"github.com/prometheus/prometheus/util/strutil"
 )
@@ -323,9 +326,15 @@ func (p *parser) recover(errp *error) {
 	e := recover()
 	if e != nil {
 		if _, ok := e.(runtime.Error); ok {
-			panic(e)
+			// Print the stack trace but do not inhibit the running application.
+			buf := make([]byte, 64<<10)
+			buf = buf[:runtime.Stack(buf, false)]
+
+			log.Errorf("parser panic: %v\n%s", e, buf)
+			*errp = fmt.Errorf("unexpected error")
+		} else {
+			*errp = e.(error)
 		}
-		*errp = e.(error)
 	}
 	return
 }
diff --git a/promql/parse_test.go b/promql/parse_test.go
index b46dc4a1c..341fe8e99 100644
--- a/promql/parse_test.go
+++ b/promql/parse_test.go
@@ -1354,3 +1354,30 @@ func TestParseSeries(t *testing.T) {
 		}
 	}
 }
+
+func TestRecoverRuntime(t *testing.T) {
+	var p *parser
+	var err error
+	defer p.recover(&err)
+
+	// Cause a runtime panic.
+	var a []int
+	a[123] = 1
+
+	if err.Error() != "unexpected error" {
+		t.Fatalf("wrong error message: %q, expected %q", err, "unexpected error")
+	}
+}
+
+func TestRecoverError(t *testing.T) {
+	var p *parser
+	var err error
+	defer p.recover(&err)
+
+	e := fmt.Errorf("custom error")
+	panic(e)
+
+	if err.Error() != e.Error() {
+		t.Fatalf("wrong error message: %q, expected %q", err, e)
+	}
+}