From c66bfce8cfd71d0414264f7102ce60cb1bfa4c9b Mon Sep 17 00:00:00 2001
From: Brian Brazil <brian.brazil@robustperception.io>
Date: Fri, 23 Aug 2019 15:44:16 +0100
Subject: [PATCH] Don't panic on short input. (#5939)

Fixes #5935

Signed-off-by: Brian Brazil <brian.brazil@robustperception.io>
---
 pkg/textparse/openmetricsparse.go      | 5 ++++-
 pkg/textparse/openmetricsparse_test.go | 8 ++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/pkg/textparse/openmetricsparse.go b/pkg/textparse/openmetricsparse.go
index a1b0d6977..853076f1d 100644
--- a/pkg/textparse/openmetricsparse.go
+++ b/pkg/textparse/openmetricsparse.go
@@ -44,7 +44,10 @@ func (l *openMetricsLexer) buf() []byte {
 }
 
 func (l *openMetricsLexer) cur() byte {
-	return l.b[l.i]
+	if l.i < len(l.b) {
+		return l.b[l.i]
+	}
+	return byte(' ')
 }
 
 // next advances the openMetricsLexer to the next character.
diff --git a/pkg/textparse/openmetricsparse_test.go b/pkg/textparse/openmetricsparse_test.go
index 018b4be88..f8c792588 100644
--- a/pkg/textparse/openmetricsparse_test.go
+++ b/pkg/textparse/openmetricsparse_test.go
@@ -419,6 +419,14 @@ func TestOMNullByteHandling(t *testing.T) {
 			input: "a\x00{b=\"ddd\"} 1",
 			err:   "expected value after metric, got \"MNAME\"",
 		},
+		{
+			input: "#",
+			err:   "\"INVALID\" \" \" is not a valid start token",
+		},
+		{
+			input: "# H",
+			err:   "\"INVALID\" \" \" is not a valid start token",
+		},
 	}
 
 	for i, c := range cases {