Document and add support to input plugins for logging alias (#6357)

plugins/inputs/tail/tail.go

@@ -3,8 +3,6 @@
 package tail
 
 import (
-	"fmt"
-	"log"
 	"strings"
 	"sync"
 
@@ -31,6 +29,8 @@ type Tail struct {
 	Pipe          bool
 	WatchMethod   string
 
+	Log telegraf.Logger
+
 	tailers    map[string]*tail.Tail
 	offsets    map[string]int64
 	parserFunc parsers.ParserFunc
@@ -124,7 +124,7 @@ func (t *Tail) tailNewFiles(fromBeginning bool) error {
 	for _, filepath := range t.Files {
 		g, err := globpath.Compile(filepath)
 		if err != nil {
-			t.acc.AddError(fmt.Errorf("glob %s failed to compile, %s", filepath, err))
+			t.Log.Errorf("Glob %q failed to compile: %s", filepath, err.Error())
 		}
 		for _, file := range g.Match() {
 			if _, ok := t.tailers[file]; ok {
@@ -135,7 +135,7 @@ func (t *Tail) tailNewFiles(fromBeginning bool) error {
 			var seek *tail.SeekInfo
 			if !t.Pipe && !fromBeginning {
 				if offset, ok := t.offsets[file]; ok {
-					log.Printf("D! [inputs.tail] using offset %d for file: %v", offset, file)
+					t.Log.Debugf("Using offset %d for %q", offset, file)
 					seek = &tail.SeekInfo{
 						Whence: 0,
 						Offset: offset,
@@ -163,11 +163,11 @@ func (t *Tail) tailNewFiles(fromBeginning bool) error {
 				continue
 			}
 
-			log.Printf("D! [inputs.tail] tail added for file: %v", file)
+			t.Log.Debugf("Tail added for %q", file)
 
 			parser, err := t.parserFunc()
 			if err != nil {
-				t.acc.AddError(fmt.Errorf("error creating parser: %v", err))
+				t.Log.Errorf("Creating parser: %s", err.Error())
 			}
 
 			// create a goroutine for each "tailer"
@@ -213,7 +213,7 @@ func (t *Tail) receiver(parser parsers.Parser, tailer *tail.Tail) {
 	var firstLine = true
 	for line := range tailer.Lines {
 		if line.Err != nil {
-			t.acc.AddError(fmt.Errorf("error tailing file %s, Error: %s", tailer.Filename, line.Err))
+			t.Log.Errorf("Tailing %q: %s", tailer.Filename, line.Err.Error())
 			continue
 		}
 		// Fix up files with Windows line endings.
@@ -221,8 +221,8 @@ func (t *Tail) receiver(parser parsers.Parser, tailer *tail.Tail) {
 
 		metrics, err := parseLine(parser, text, firstLine)
 		if err != nil {
-			t.acc.AddError(fmt.Errorf("malformed log line in %s: [%s], Error: %s",
-				tailer.Filename, line.Text, err))
+			t.Log.Errorf("Malformed log line in %q: [%q]: %s",
+				tailer.Filename, line.Text, err.Error())
 			continue
 		}
 		firstLine = false
@@ -233,10 +233,10 @@ func (t *Tail) receiver(parser parsers.Parser, tailer *tail.Tail) {
 		}
 	}
 
-	log.Printf("D! [inputs.tail] tail removed for file: %v", tailer.Filename)
+	t.Log.Debugf("Tail removed for %q", tailer.Filename)
 
 	if err := tailer.Err(); err != nil {
-		t.acc.AddError(fmt.Errorf("error tailing file %s, Error: %s", tailer.Filename, err))
+		t.Log.Errorf("Tailing %q: %s", tailer.Filename, err.Error())
 	}
 }
 
@@ -249,14 +249,14 @@ func (t *Tail) Stop() {
 			// store offset for resume
 			offset, err := tailer.Tell()
 			if err == nil {
-				log.Printf("D! [inputs.tail] recording offset %d for file: %v", offset, tailer.Filename)
+				t.Log.Debugf("Recording offset %d for %q", offset, tailer.Filename)
 			} else {
-				t.acc.AddError(fmt.Errorf("error recording offset for file %s", tailer.Filename))
+				t.Log.Errorf("Recording offset for %q: %s", tailer.Filename, err.Error())
 			}
 		}
 		err := tailer.Stop()
 		if err != nil {
-			t.acc.AddError(fmt.Errorf("error stopping tail on file %s", tailer.Filename))
+			t.Log.Errorf("Stopping tail on %q: %s", tailer.Filename, err.Error())
 		}
 	}
 

plugins/inputs/tail/tail_test.go

@@ -1,7 +1,9 @@
 package tail
 
 import (
+	"bytes"
 	"io/ioutil"
+	"log"
 	"os"
 	"runtime"
 	"testing"
@@ -28,6 +30,7 @@ func TestTailFromBeginning(t *testing.T) {
 	require.NoError(t, err)
 
 	tt := NewTail()
+	tt.Log = testutil.Logger{}
 	tt.FromBeginning = true
 	tt.Files = []string{tmpfile.Name()}
 	tt.SetParserFunc(parsers.NewInfluxParser)
@@ -61,6 +64,7 @@ func TestTailFromEnd(t *testing.T) {
 	require.NoError(t, err)
 
 	tt := NewTail()
+	tt.Log = testutil.Logger{}
 	tt.Files = []string{tmpfile.Name()}
 	tt.SetParserFunc(parsers.NewInfluxParser)
 	defer tt.Stop()
@@ -97,6 +101,7 @@ func TestTailBadLine(t *testing.T) {
 	defer os.Remove(tmpfile.Name())
 
 	tt := NewTail()
+	tt.Log = testutil.Logger{}
 	tt.FromBeginning = true
 	tt.Files = []string{tmpfile.Name()}
 	tt.SetParserFunc(parsers.NewInfluxParser)
@@ -105,13 +110,17 @@ func TestTailBadLine(t *testing.T) {
 
 	acc := testutil.Accumulator{}
 	require.NoError(t, tt.Start(&acc))
+
+	buf := &bytes.Buffer{}
+	log.SetOutput(buf)
+
 	require.NoError(t, acc.GatherError(tt.Gather))
 
 	_, err = tmpfile.WriteString("cpu mytag= foo usage_idle= 100\n")
 	require.NoError(t, err)
 
-	acc.WaitError(1)
-	assert.Contains(t, acc.Errors[0].Error(), "malformed log line")
+	time.Sleep(500 * time.Millisecond)
+	assert.Contains(t, buf.String(), "Malformed log line")
 }
 
 func TestTailDosLineendings(t *testing.T) {
@@ -122,6 +131,7 @@ func TestTailDosLineendings(t *testing.T) {
 	require.NoError(t, err)
 
 	tt := NewTail()
+	tt.Log = testutil.Logger{}
 	tt.FromBeginning = true
 	tt.Files = []string{tmpfile.Name()}
 	tt.SetParserFunc(parsers.NewInfluxParser)
@@ -160,6 +170,7 @@ cpu,42
 	require.NoError(t, err)
 
 	plugin := NewTail()
+	plugin.Log = testutil.Logger{}
 	plugin.FromBeginning = true
 	plugin.Files = []string{tmpfile.Name()}
 	plugin.SetParserFunc(func() (parsers.Parser, error) {
@@ -217,6 +228,7 @@ func TestMultipleMetricsOnFirstLine(t *testing.T) {
 	require.NoError(t, err)
 
 	plugin := NewTail()
+	plugin.Log = testutil.Logger{}
 	plugin.FromBeginning = true
 	plugin.Files = []string{tmpfile.Name()}
 	plugin.SetParserFunc(func() (parsers.Parser, error) {