Merge master into breakout_swarm

Signed-off-by: Alex Ellis <alexellis2@gmail.com>

gateway/vendor/github.com/prometheus/common/promlog/log.go

@@ -0,0 +1,63 @@
+// Copyright 2017 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package promlog defines standardised ways to initialize Go kit loggers
+// across Prometheus components.
+// It should typically only ever be imported by main packages.
+package promlog
+
+import (
+	"os"
+
+	"github.com/go-kit/kit/log"
+	"github.com/go-kit/kit/log/level"
+	"github.com/pkg/errors"
+)
+
+// AllowedLevel is a settable identifier for the minimum level a log entry
+// must be have.
+type AllowedLevel struct {
+	s string
+	o level.Option
+}
+
+func (l *AllowedLevel) String() string {
+	return l.s
+}
+
+// Set updates the value of the allowed level.
+func (l *AllowedLevel) Set(s string) error {
+	switch s {
+	case "debug":
+		l.o = level.AllowDebug()
+	case "info":
+		l.o = level.AllowInfo()
+	case "warn":
+		l.o = level.AllowWarn()
+	case "error":
+		l.o = level.AllowError()
+	default:
+		return errors.Errorf("unrecognized log level %q", s)
+	}
+	l.s = s
+	return nil
+}
+
+// New returns a new leveled oklog logger in the logfmt format. Each logged line will be annotated
+// with a timestamp. The output always goes to stderr.
+func New(al AllowedLevel) log.Logger {
+	l := log.NewLogfmtLogger(log.NewSyncWriter(os.Stderr))
+	l = level.NewFilter(l, al.o)
+	l = log.With(l, "ts", log.DefaultTimestampUTC, "caller", log.DefaultCaller)
+	return l
+}