fix: syslog and file backends always returned errors on write

backend.go

@@ -22,6 +22,8 @@ type Backend interface {
 // Backend to write in file-like objects
 //
 
+var _ Backend = &FileBackend{}
+
 // FileBackend is a backend that writes to a file.
 type FileBackend struct {
 	formatter Formatter
@@ -74,11 +76,15 @@ func NewIoBackend(buf io.Writer) *FileBackend {
 
 func (b FileBackend) Write(r *Record) error {
 	text := b.formatter(r)
-	_, err := io.WriteString(b.l, text)
 
+	_, err := io.WriteString(b.l, text)
+	if err != nil {
 		return fmt.Errorf("cannot write logs: %w", err)
 	}
 
+	return nil
+}
+
 // SetLevel changes the log level of the backend.
 func (b *FileBackend) SetLevel(l Level) {
 	b.level = l
@@ -130,6 +136,8 @@ func (b *FileBackend) Close() error {
 // Noop Backend
 //
 
+var _ Backend = &NoopBackend{}
+
 // NoopBackend does nothing and discards all log entries without writing them anywhere.
 type NoopBackend struct{}
 
@@ -144,7 +152,7 @@ func (*NoopBackend) Write(_ *Record) error {
 }
 
 // SetFormatter is a noop.
-func (*NoopBackend) SetFormatter(_ *Formatter) {}
+func (*NoopBackend) SetFormatter(_ Formatter) {}
 
 // SetLevel is a noop.
 func (*NoopBackend) SetLevel(_ Level) {}

backend_syslog_linux.go

@@ -16,6 +16,8 @@ var errUnknownFacility = errors.New("unknown facility")
 // Syslog Backend
 //
 
+var _ Backend = &SyslogBackend{}
+
 // SyslogBackend writes the logs to a syslog system.
 type SyslogBackend struct {
 	w         *syslog.Writer
@@ -70,9 +72,13 @@ func (sb *SyslogBackend) Write(r *Record) error {
 		err = sb.w.Emerg(text)
 	}
 
+	if err != nil {
 		return fmt.Errorf("cannot log to syslog: %w", err)
 	}
 
+	return nil
+}
+
 // SetFormatter defines the formatter for this backend.
 func (sb *SyslogBackend) SetFormatter(f Formatter) {
 	sb.formatter = f

backend_test.go

@@ -0,0 +1,48 @@
+package logging
+
+import (
+	"bytes"
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+type WriteErrorBuffer struct{}
+
+func (*WriteErrorBuffer) Write(_ []byte) (int, error) {
+	return 0, errors.New("cannot write")
+}
+
+func TestFileBackendWrite(t *testing.T) {
+	t.Parallel()
+
+	t.Run("It should write the logs to the buffer", func(t *testing.T) {
+		t.Parallel()
+
+		buf := new(bytes.Buffer)
+		b := NewIoBackend(buf)
+
+		err := b.Write(&Record{
+			Level:   Info,
+			Message: "my log line",
+		})
+
+		require.NoError(t, err)
+		require.Contains(t, buf.String(), "my log line")
+	})
+
+	t.Run("It should return an error if it cannot write the log", func(t *testing.T) {
+		t.Parallel()
+
+		buf := new(WriteErrorBuffer)
+		b := NewIoBackend(buf)
+
+		err := b.Write(&Record{
+			Level:   Info,
+			Message: "my log line",
+		})
+
+		require.Error(t, err)
+	})
+}

go.mod

@@ -1,3 +1,5 @@
 module code.bcarlin.xyz/go/logging
 
 go 1.13
+
+require github.com/stretchr/testify v1.7.1 // indirect

go.sum

@@ -0,0 +1,10 @@
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.7.1 h1:5TQK59W5E3v0r2duFAb7P95B6hEeOyEnHRa8MjYSMTY=
+github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=