Fix parsing multiple metrics on the first line of tailed file (#6289)

plugins/inputs/tail/tail.go

@@ -9,11 +9,11 @@ import (
 	"sync"
 
 	"github.com/influxdata/tail"
-
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/internal/globpath"
 	"github.com/influxdata/telegraf/plugins/inputs"
 	"github.com/influxdata/telegraf/plugins/parsers"
+	"github.com/influxdata/telegraf/plugins/parsers/csv"
 )
 
 const (
@@ -172,55 +172,64 @@ func (t *Tail) tailNewFiles(fromBeginning bool) error {
 
 			// create a goroutine for each "tailer"
 			t.wg.Add(1)
-			go t.receiver(parser, tailer)
+			go func() {
+				defer t.wg.Done()
+				t.receiver(parser, tailer)
+			}()
 			t.tailers[tailer.Filename] = tailer
 		}
 	}
 	return nil
 }
 
-// this is launched as a goroutine to continuously watch a tailed logfile
+// ParseLine parses a line of text.
+func parseLine(parser parsers.Parser, line string, firstLine bool) ([]telegraf.Metric, error) {
+	switch parser.(type) {
+	case *csv.Parser:
+		// The csv parser parses headers in Parse and skips them in ParseLine.
+		// As a temporary solution call Parse only when getting the first
+		// line from the file.
+		if firstLine {
+			return parser.Parse([]byte(line))
+		} else {
+			m, err := parser.ParseLine(line)
+			if err != nil {
+				return nil, err
+			}
+
+			if m != nil {
+				return []telegraf.Metric{m}, nil
+			}
+			return []telegraf.Metric{}, nil
+		}
+	default:
+		return parser.Parse([]byte(line))
+	}
+}
+
+// Receiver is launched as a goroutine to continuously watch a tailed logfile
 // for changes, parse any incoming msgs, and add to the accumulator.
 func (t *Tail) receiver(parser parsers.Parser, tailer *tail.Tail) {
-	defer t.wg.Done()
-
 	var firstLine = true
-	var metrics []telegraf.Metric
-	var m telegraf.Metric
-	var err error
-	var line *tail.Line
-	for line = range tailer.Lines {
+	for line := range tailer.Lines {
 		if line.Err != nil {
-			t.acc.AddError(fmt.Errorf("error tailing file %s, Error: %s", tailer.Filename, err))
+			t.acc.AddError(fmt.Errorf("error tailing file %s, Error: %s", tailer.Filename, line.Err))
 			continue
 		}
 		// Fix up files with Windows line endings.
 		text := strings.TrimRight(line.Text, "\r")
 
-		if firstLine {
-			metrics, err = parser.Parse([]byte(text))
-			if err == nil {
-				if len(metrics) == 0 {
-					firstLine = false
-					continue
-				} else {
-					m = metrics[0]
-				}
-			}
-			firstLine = false
-		} else {
-			m, err = parser.ParseLine(text)
-		}
-
-		if err == nil {
-			if m != nil {
-				tags := m.Tags()
-				tags["path"] = tailer.Filename
-				t.acc.AddFields(m.Name(), m.Fields(), tags, m.Time())
-			}
-		} else {
+		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))
+			continue
+		}
+		firstLine = false
+
+		for _, metric := range metrics {
+			metric.AddTag("path", tailer.Filename)
+			t.acc.AddMetric(metric)
 		}
 	}