From 5997dc44d8ae6ec9b97db20e8610b2f48d352f79 Mon Sep 17 00:00:00 2001
From: stephen mcquay <stephen@mcquay.me>
Date: Fri, 26 Jan 2018 18:05:28 -0800
Subject: [PATCH] track http status codes in metrics

---
 cmd/hwtd/main.go   |  2 +-
 hooks.go           |  9 ++++++++-
 metrics/metrics.go |  4 ++++
 metrics/prom.go    | 11 +++++++++++
 4 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/cmd/hwtd/main.go b/cmd/hwtd/main.go
index 9b44a6d..e2775c2 100644
--- a/cmd/hwtd/main.go
+++ b/cmd/hwtd/main.go
@@ -23,7 +23,7 @@ func main() {
 	}
 
 	s := &hwt.Server{hn}
-	hs := hwt.NewMetricsHooks(metrics.HTTPLatency)
+	hs := hwt.NewMetricsHooks(metrics.HTTPLatency, metrics.HTTPCode)
 	th := pb.NewHelloWorldServer(s, hs)
 	sm := http.NewServeMux()
 	sm.HandleFunc("/", hwt.Auth(th.ServeHTTP))
diff --git a/hooks.go b/hooks.go
index 06ba8a0..af75cb9 100644
--- a/hooks.go
+++ b/hooks.go
@@ -10,8 +10,9 @@ import (
 var reqStartKey = new(int)
 
 type Timer func(path string, dur time.Duration)
+type Statuser func(path, status string)
 
-func NewMetricsHooks(timer Timer) *twirp.ServerHooks {
+func NewMetricsHooks(timer Timer, status Statuser) *twirp.ServerHooks {
 	hs := &twirp.ServerHooks{}
 
 	hs.RequestReceived = func(ctx context.Context) (context.Context, error) {
@@ -31,6 +32,12 @@ func NewMetricsHooks(timer Timer) *twirp.ServerHooks {
 		}
 		dur := time.Now().Sub(start)
 		timer(name, dur)
+
+		sc, ok := twirp.StatusCode(ctx)
+		if !ok {
+			panic("missing code")
+		}
+		status(name, sc)
 	}
 
 	return hs
diff --git a/metrics/metrics.go b/metrics/metrics.go
index 6dae5da..16e2c10 100644
--- a/metrics/metrics.go
+++ b/metrics/metrics.go
@@ -7,3 +7,7 @@ import (
 func HTTPLatency(path string, dur time.Duration) {
 	httpReqLat.WithLabelValues(path).Observe(float64(dur) / float64(time.Millisecond))
 }
+
+func HTTPCode(path string, status string) {
+	httpStatus.WithLabelValues(path, status).Inc()
+}
diff --git a/metrics/prom.go b/metrics/prom.go
index 3c4e2d2..984390e 100644
--- a/metrics/prom.go
+++ b/metrics/prom.go
@@ -21,11 +21,22 @@ var (
 		},
 		[]string{"path"},
 	)
+
+	httpStatus = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "hwt_http_requests_total",
+			Help: "How many HTTP requests processed, partitioned by status code and HTTP method.",
+		},
+		[]string{"path", "code"},
+	)
 )
 
 func RegisterPromMetrics() error {
 	if err := prometheus.Register(httpReqLat); err != nil {
 		return errors.Wrap(err, "registering http request latency")
 	}
+	if err := prometheus.Register(httpStatus); err != nil {
+		return errors.Wrap(err, "registering http request status")
+	}
 	return nil
 }