add bugsnag logrus hook

Signed-off-by: Matt Tescher <matthew.tescher@docker.com>

vendor/github.com/Shopify/logrus-bugsnag/bugsnag.go

@@ -0,0 +1,81 @@
+package logrus_bugsnag
+
+import (
+	"errors"
+
+	"github.com/sirupsen/logrus"
+	"github.com/bugsnag/bugsnag-go"
+	bugsnag_errors "github.com/bugsnag/bugsnag-go/errors"
+)
+
+type bugsnagHook struct{}
+
+// ErrBugsnagUnconfigured is returned if NewBugsnagHook is called before
+// bugsnag.Configure. Bugsnag must be configured before the hook.
+var ErrBugsnagUnconfigured = errors.New("bugsnag must be configured before installing this logrus hook")
+
+// ErrBugsnagSendFailed indicates that the hook failed to submit an error to
+// bugsnag. The error was successfully generated, but `bugsnag.Notify()`
+// failed.
+type ErrBugsnagSendFailed struct {
+	err error
+}
+
+func (e ErrBugsnagSendFailed) Error() string {
+	return "failed to send error to Bugsnag: " + e.err.Error()
+}
+
+// NewBugsnagHook initializes a logrus hook which sends exceptions to an
+// exception-tracking service compatible with the Bugsnag API. Before using
+// this hook, you must call bugsnag.Configure(). The returned object should be
+// registered with a log via `AddHook()`
+//
+// Entries that trigger an Error, Fatal or Panic should now include an "error"
+// field to send to Bugsnag.
+func NewBugsnagHook() (*bugsnagHook, error) {
+	if bugsnag.Config.APIKey == "" {
+		return nil, ErrBugsnagUnconfigured
+	}
+	return &bugsnagHook{}, nil
+}
+
+// skipStackFrames skips logrus stack frames before logging to Bugsnag.
+const skipStackFrames = 4
+
+// Fire forwards an error to Bugsnag. Given a logrus.Entry, it extracts the
+// "error" field (or the Message if the error isn't present) and sends it off.
+func (hook *bugsnagHook) Fire(entry *logrus.Entry) error {
+	var notifyErr error
+	err, ok := entry.Data["error"].(error)
+	if ok {
+		notifyErr = err
+	} else {
+		notifyErr = errors.New(entry.Message)
+	}
+
+	metadata := bugsnag.MetaData{}
+	metadata["metadata"] = make(map[string]interface{})
+	for key, val := range entry.Data {
+		if key != "error" {
+			metadata["metadata"][key] = val
+		}
+	}
+
+	errWithStack := bugsnag_errors.New(notifyErr, skipStackFrames)
+	bugsnagErr := bugsnag.Notify(errWithStack, metadata)
+	if bugsnagErr != nil {
+		return ErrBugsnagSendFailed{bugsnagErr}
+	}
+
+	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,
+	}
+}