hooks: Add BugSnag hook

hooks/bugsnag/bugsnag.go

diff --git a/hooks/bugsnag/bugsnag.go b/hooks/bugsnag/bugsnag.go
new file mode 100644
index 0000000..a0cfe84
--- /dev/null
+++ b/hooks/bugsnag/bugsnag.go
@@ -0,0 +1,53 @@
+package logrus_bugsnag
+
+import (
+	"github.com/Sirupsen/logrus"
+	"github.com/bugsnag/bugsnag-go"
+)
+
+// BugsnagHook sends exceptions to an exception-tracking service compatible
+// with the Bugsnag API. Before using this hook, you must call
+// bugsnag.Configure().
+//
+// Entries that trigger an Error, Fatal or Panic should now include an "error"
+// field to send to Bugsnag
+type BugsnagHook struct{}
+
+// Fire forwards an error to Bugsnag. Given a logrus.Entry, it extracts the
+// implicitly-required "error" field and sends it off.
+func (hook *BugsnagHook) Fire(entry *logrus.Entry) error {
+	if entry.Data["error"] == nil {
+		entry.Logger.WithFields(logrus.Fields{
+			"source": "bugsnag",
+		}).Warn("Exceptions sent to Bugsnag must have an 'error' key with the error")
+		return nil
+	}
+
+	err, ok := entry.Data["error"].(error)
+	if !ok {
+		entry.Logger.WithFields(logrus.Fields{
+			"source": "bugsnag",
+		}).Warn("Exceptions sent to Bugsnag must have an `error` key of type `error`")
+		return nil
+	}
+
+	bugsnagErr := bugsnag.Notify(err)
+	if bugsnagErr != nil {
+		entry.Logger.WithFields(logrus.Fields{
+			"source": "bugsnag",
+			"error":  bugsnagErr,
+		}).Warn("Failed to send error to Bugsnag")
+	}
+
+	return nil
+}
+
+// Levels enumerates the log levels on which the error should be forwarded to
+// bugsnag: everything at or above the "Error" level.
+func (hook *BugsnagHook) Levels() []logrus.Level {
+	return []logrus.Level{
+		logrus.ErrorLevel,
+		logrus.FatalLevel,
+		logrus.PanicLevel,
+	}
+}

hooks/bugsnag/bugsnag_test.go

diff --git a/hooks/bugsnag/bugsnag_test.go b/hooks/bugsnag/bugsnag_test.go
new file mode 100644
index 0000000..7db5136
--- /dev/null
+++ b/hooks/bugsnag/bugsnag_test.go
@@ -0,0 +1,64 @@
+package logrus_bugsnag
+
+import (
+	"encoding/json"
+	"errors"
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/Sirupsen/logrus"
+	"github.com/bugsnag/bugsnag-go"
+)
+
+type notice struct {
+	Events []struct {
+		Exceptions []struct {
+			Message string `json:"message"`
+		} `json:"exceptions"`
+	} `json:"events"`
+}
+
+func TestNoticeReceived(t *testing.T) {
+	msg := make(chan string, 1)
+	expectedMsg := "foo"
+
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var notice notice
+		data, _ := ioutil.ReadAll(r.Body)
+		if err := json.Unmarshal(data, &notice); err != nil {
+			t.Error(err)
+		}
+		_ = r.Body.Close()
+
+		msg <- notice.Events[0].Exceptions[0].Message
+	}))
+	defer ts.Close()
+
+	hook := &BugsnagHook{}
+
+	bugsnag.Configure(bugsnag.Configuration{
+		Endpoint:     ts.URL,
+		ReleaseStage: "production",
+		APIKey:       "12345678901234567890123456789012",
+		Synchronous:  true,
+	})
+
+	log := logrus.New()
+	log.Hooks.Add(hook)
+
+	log.WithFields(logrus.Fields{
+		"error": errors.New(expectedMsg),
+	}).Error("Bugsnag will not see this string")
+
+	select {
+	case received := <-msg:
+		if received != expectedMsg {
+			t.Errorf("Unexpected message received: %s", received)
+		}
+	case <-time.After(time.Second):
+		t.Error("Timed out; no notice received by Bugsnag API")
+	}
+}