Prefix each output line with command in logs (#4)

app/service/log_prefixer.go

@@ -0,0 +1,71 @@
+package service
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+)
+
+const prefixCommandMaxlen = 16
+const prefixCutCommandSuffix = "..."
+
+// LogPrefixer implements `io.writer` interface and adds prefix to each output line.
+type LogPrefixer struct {
+	writer io.Writer
+	prefix []byte
+}
+
+// NewLogPrefixer initializes log prefixer.
+func NewLogPrefixer(writer io.Writer, command string) *LogPrefixer {
+	logPrefixer := &LogPrefixer{writer: writer}
+	logPrefixer.prefix = logPrefixer.prefixForCommand(command)
+	return logPrefixer
+}
+
+func (p *LogPrefixer) Write(data []byte) (int, error) {
+	reader := bufio.NewReader(bytes.NewReader(data))
+
+	var line []byte
+	var err error
+	var bytesWritten int = 0
+
+	for {
+		line, err = reader.ReadBytes('\n')
+
+		// There can be data to write in `line` even if `io.EOF` error is returned.
+		// Exit immediately only in case of unexpected error.
+		if err != nil && err != io.EOF {
+			return bytesWritten, err
+		}
+
+		if len(line) > 0 {
+			_, writeErr := p.writer.Write(p.prefix)
+			if writeErr != nil {
+				return bytesWritten, writeErr
+			}
+
+			n, writeErr := p.writer.Write(line)
+			bytesWritten += n
+			if writeErr != nil {
+				return bytesWritten, writeErr
+			}
+		}
+
+		if err == io.EOF {
+			break
+		}
+	}
+
+	return bytesWritten, nil
+}
+
+func (p *LogPrefixer) prefixForCommand(command string) []byte {
+	if len(command) > prefixCommandMaxlen {
+		command = command[:prefixCommandMaxlen]
+		command += prefixCutCommandSuffix
+	}
+
+	prefix := fmt.Sprintf("{%s} ", command)
+	return []byte(prefix)
+}

app/service/log_prefixer_test.go

@@ -0,0 +1,35 @@
+package service
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestLogPrefixer_Write(t *testing.T) {
+	out := bytes.NewBuffer(nil)
+	prefixer := NewLogPrefixer(out, "du /var/lib/monitoring")
+
+	n, err := prefixer.Write([]byte("first line of the output\n"))
+	require.NoError(t, err)
+	assert.Equal(t, 25, n)
+
+	n, err = prefixer.Write([]byte("second line of the output\n"))
+	require.NoError(t, err)
+	assert.Equal(t, 26, n)
+
+	expectedOutput :=
+		"{du /var/lib/moni...} first line of the output\n" +
+			"{du /var/lib/moni...} second line of the output\n"
+	assert.Equal(t, expectedOutput, out.String())
+}
+
+func TestLogPrefixer_prefixForCommand(t *testing.T) {
+	prefixer := &LogPrefixer{}
+
+	assert.Equal(t, []byte("{ls -la} "), prefixer.prefixForCommand("ls -la"))
+	assert.Equal(t, []byte("{cat /var/lib/pid} "), prefixer.prefixForCommand("cat /var/lib/pid"))
+	assert.Equal(t, []byte("{du /var/lib/moni...} "), prefixer.prefixForCommand("du /var/lib/monitoring"))
+}

app/service/service.go

@@ -150,7 +150,9 @@ func (s *Scheduler) executeCommand(command string, logWriter io.Writer) error {
 		cmd := exec.Command("sh", "-c", command) // nolint gosec
 		serr := NewErrorWriter(s.MaxLogLines)
 
-		logWithErr := io.MultiWriter(logWriter, serr)
+		prefixer := NewLogPrefixer(logWriter, command)
+
+		logWithErr := io.MultiWriter(prefixer, serr)
 		cmd.Stdout = logWithErr
 		cmd.Stderr = logWithErr
 		if e := cmd.Run(); e != nil {

app/service/service_test.go

@@ -76,7 +76,7 @@ func TestScheduler_DoIntegration(t *testing.T) {
 
 	svc.Do(ctx)
 	t.Log(out.String())
-	assert.Contains(t, out.String(), "123\n")
+	assert.Contains(t, out.String(), "{echo 123} 123\n")
 	notif.AssertExpectations(t)
 }
 
@@ -85,7 +85,7 @@ func TestScheduler_execute(t *testing.T) {
 	wr := bytes.NewBuffer(nil)
 	err := svc.executeCommand("echo 123", wr)
 	require.NoError(t, err)
-	assert.Equal(t, "123\n", wr.String())
+	assert.Equal(t, "{echo 123} 123\n", wr.String())
 }
 
 func TestScheduler_executeFailedNotFound(t *testing.T) {
@@ -118,7 +118,7 @@ func TestScheduler_jobFunc(t *testing.T) {
 	resmr.On("OnFinish", "resume.file").Return(nil).Once()
 
 	svc.jobFunc(crontab.JobSpec{Spec: "@startup", Command: "echo 123"}, scheduleMock).Run()
-	assert.Equal(t, "123\n", wr.String())
+	assert.Equal(t, "{echo 123} 123\n", wr.String())
 }
 
 func TestScheduler_jobFuncFailed(t *testing.T) {