Add simple daemon to take remote write and expose a scrape target

.gitignore

@@ -1,2 +1,3 @@
 cmd/promxy/promxy
+cmd/remote_write_exporter/remote_write_exporter
 build/*

cmd/remote_write_exporter/main.go

@@ -0,0 +1,139 @@
+// Copyright 2016 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 main
+
+import (
+	"bufio"
+	"io/ioutil"
+	"net/http"
+	"os"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/gogo/protobuf/proto"
+	"github.com/golang/snappy"
+	flags "github.com/jessevdk/go-flags"
+	"github.com/prometheus/common/model"
+	"github.com/sirupsen/logrus"
+
+	"github.com/prometheus/prometheus/prompb"
+)
+
+var opts struct {
+	BindAddr    string        `long:"bind-addr" description:"address to listen on" default:":8083"`
+	WritePath   string        `long:"write-path" description:"url path" default:"/receive"`
+	MetricsPath string        `long:"metrics-path" description:"url path" default:"/metrics"`
+	TTL         time.Duration `long:"metric-ttl" description:"how long until we TTL things out of the map" required:"true"`
+}
+
+func main() {
+	parser := flags.NewParser(&opts, flags.Default)
+	if _, err := parser.Parse(); err != nil {
+		// If the error was from the parser, then we can simply return
+		// as Parse() prints the error already
+		if _, ok := err.(*flags.Error); ok {
+			os.Exit(1)
+		}
+		logrus.Fatalf("Error parsing flags: %v", err)
+	}
+
+	l := sync.Mutex{}
+	m := make(map[string]*prompb.Sample)
+
+	// TODO: ttl things
+	go func() {
+		for {
+			time.Sleep(opts.TTL)
+			cutoff := int64(model.Now().Add(-opts.TTL))
+
+			l.Lock()
+			for k, v := range m {
+				if v.Timestamp < cutoff {
+					delete(m, k)
+				}
+			}
+			l.Unlock()
+		}
+	}()
+
+	http.HandleFunc(opts.WritePath, func(w http.ResponseWriter, r *http.Request) {
+		compressed, err := ioutil.ReadAll(r.Body)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+			return
+		}
+
+		reqBuf, err := snappy.Decode(nil, compressed)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+
+		var req prompb.WriteRequest
+		if err := proto.Unmarshal(reqBuf, &req); err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+
+		for _, ts := range req.Timeseries {
+			metric := make(model.Metric, len(ts.Labels))
+			for _, l := range ts.Labels {
+				metric[model.LabelName(l.Name)] = model.LabelValue(l.Value)
+			}
+
+			// pick which point
+			var sample *prompb.Sample
+			for _, s := range ts.Samples {
+				if sample == nil {
+					sample = s
+					continue
+				}
+				if s.Timestamp > sample.Timestamp {
+					sample = s
+				}
+			}
+
+			l.Lock()
+			m[metric.String()] = sample
+			l.Unlock()
+		}
+	})
+
+	http.HandleFunc(opts.MetricsPath, func(w http.ResponseWriter, r *http.Request) {
+		writer := bufio.NewWriter(w)
+		l.Lock()
+		for k, v := range m {
+			var sb strings.Builder
+
+			sb.WriteString(k)
+			sb.WriteRune(' ')
+
+			sb.WriteString(strconv.FormatFloat(float64(v.Value), 'f', -1, 64))
+
+			if v.Timestamp > 0 {
+				sb.WriteRune(' ')
+				sb.WriteString(strconv.FormatInt(v.Timestamp, 10))
+			}
+			sb.WriteByte('\n')
+
+			writer.WriteString(sb.String())
+		}
+		l.Unlock()
+		writer.Flush()
+	})
+
+	logrus.Fatal(http.ListenAndServe(opts.BindAddr, nil))
+}