From b9457a109268ef1c055f4aa5b4f92a42afc21c24 Mon Sep 17 00:00:00 2001
From: Cameron Sparr <cameronsparr@gmail.com>
Date: Tue, 21 Feb 2017 19:50:10 +0100
Subject: [PATCH] log error message when invalid regex is used

closes #2178
---
 CHANGELOG.md                               |  1 +
 plugins/inputs/logparser/grok/grok_test.go | 37 ++++++++++++++++++++++
 plugins/inputs/logparser/logparser.go      |  2 ++
 3 files changed, 40 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 509d6f2f1e7dc..2a43e844f993b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -65,6 +65,7 @@ be deprecated eventually.
 - [#2390](https://github.com/influxdata/telegraf/issues/2390): Empty tag value causes error on InfluxDB output.
 - [#2380](https://github.com/influxdata/telegraf/issues/2380): buffer_size field value is negative number from "internal" plugin.
 - [#2414](https://github.com/influxdata/telegraf/issues/2414): Missing error handling in the MySQL plugin leads to segmentation violation.
+- [#2178](https://github.com/influxdata/telegraf/issues/2178): logparser: regexp with lookahead.
 
 ## v1.2.1 [2017-02-01]
 
diff --git a/plugins/inputs/logparser/grok/grok_test.go b/plugins/inputs/logparser/grok/grok_test.go
index 1344896b84c40..4e0ead6e9a67d 100644
--- a/plugins/inputs/logparser/grok/grok_test.go
+++ b/plugins/inputs/logparser/grok/grok_test.go
@@ -57,6 +57,43 @@ func Benchmark_ParseLine_CustomPattern(b *testing.B) {
 	benchM = m
 }
 
+// Test a very simple parse pattern.
+func TestSimpleParse(t *testing.T) {
+	p := &Parser{
+		Patterns: []string{"%{TESTLOG}"},
+		CustomPatterns: `
+			TESTLOG %{NUMBER:num:int} %{WORD:client}
+		`,
+	}
+	assert.NoError(t, p.Compile())
+
+	m, err := p.ParseLine(`142 bot`)
+	assert.NoError(t, err)
+	require.NotNil(t, m)
+
+	assert.Equal(t,
+		map[string]interface{}{
+			"num":    int64(142),
+			"client": "bot",
+		},
+		m.Fields())
+}
+
+// Verify that patterns with a regex lookahead fail at compile time.
+func TestParsePatternsWithLookahead(t *testing.T) {
+	p := &Parser{
+		Patterns: []string{"%{MYLOG}"},
+		CustomPatterns: `
+			NOBOT ((?!bot|crawl).)*
+			MYLOG %{NUMBER:num:int} %{NOBOT:client}
+		`,
+	}
+	assert.NoError(t, p.Compile())
+
+	_, err := p.ParseLine(`1466004605359052000 bot`)
+	assert.Error(t, err)
+}
+
 func TestMeasurementName(t *testing.T) {
 	p := &Parser{
 		Measurement: "my_web_log",
diff --git a/plugins/inputs/logparser/logparser.go b/plugins/inputs/logparser/logparser.go
index 8ec32835829a1..a228322772c13 100644
--- a/plugins/inputs/logparser/logparser.go
+++ b/plugins/inputs/logparser/logparser.go
@@ -226,6 +226,8 @@ func (l *LogParserPlugin) parser() {
 				if m != nil {
 					l.acc.AddFields(m.Name(), m.Fields(), m.Tags(), m.Time())
 				}
+			} else {
+				log.Println("E! Error parsing log line: " + err.Error())
 			}
 		}
 	}