Add hook to send logs to custom writer #678

hooks/writer/README.md

@@ -0,0 +1,43 @@
+# Writer Hooks for Logrus
+
+Send logs of given levels to any object with `io.Writer` interface.
+
+## Usage
+
+If you want for example send high level logs to `Stderr` and
+logs of  normal execution to `Stdout`, you could do it like this:
+
+```go
+package main
+
+import (
+	"io/ioutil"
+	"os"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/sirupsen/logrus/hooks/writer"
+)
+
+func main() {
+	log.SetOutput(ioutil.Discard) // Send all logs to nowhere by default
+
+	log.AddHook(&writer.Hook{ // Send logs with level higher than warning to stderr
+		Writer: os.Stderr,
+		LogLevels: []log.Level{
+			log.PanicLevel,
+			log.FatalLevel,
+			log.ErrorLevel,
+			log.WarnLevel,
+		},
+	})
+	log.AddHook(&writer.Hook{ // Send info and debug logs to stdout
+		Writer: os.Stdout,
+		LogLevels: []log.Level{
+			log.InfoLevel,
+			log.DebugLevel,
+		},
+	})
+	log.Info("This will go to stdout")
+	log.Warn("This will go to stderr")
+}
+```

hooks/writer/writer.go

@@ -0,0 +1,29 @@
+package writer
+
+import (
+	"io"
+
+	log "github.com/sirupsen/logrus"
+)
+
+// Hook is a hook that writes logs of specified LogLevels to specified Writer
+type Hook struct {
+	Writer    io.Writer
+	LogLevels []log.Level
+}
+
+// Fire will be called when some logging function is called with current hook
+// It will format log entry to string and write it to appropriate writer
+func (hook *Hook) Fire(entry *log.Entry) error {
+	line, err := entry.String()
+	if err != nil {
+		return err
+	}
+	_, err = hook.Writer.Write([]byte(line))
+	return err
+}
+
+// Levels define on which log levels this hook would trigger
+func (hook *Hook) Levels() []log.Level {
+	return hook.LogLevels
+}

hooks/writer/writer_test.go

@@ -0,0 +1,37 @@
+package writer
+
+import (
+	"bytes"
+	"io/ioutil"
+	"testing"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDifferentLevelsGoToDifferentWriters(t *testing.T) {
+	var a, b bytes.Buffer
+
+	log.SetFormatter(&log.TextFormatter{
+		DisableTimestamp: true,
+	})
+	log.SetOutput(ioutil.Discard) // Send all logs to nowhere by default
+
+	log.AddHook(&Hook{
+		Writer: &a,
+		LogLevels: []log.Level{
+			log.WarnLevel,
+		},
+	})
+	log.AddHook(&Hook{ // Send info and debug logs to stdout
+		Writer: &b,
+		LogLevels: []log.Level{
+			log.InfoLevel,
+		},
+	})
+	log.Warn("send to a")
+	log.Info("send to b")
+
+	assert.Equal(t, a.String(), "level=warning msg=\"send to a\"\n")
+	assert.Equal(t, b.String(), "level=info msg=\"send to b\"\n")
+}