metrics/RequestMeter: add label for X-From-Cache (sourcegraph#55774)

internal/metrics/metrics.go

@@ -35,10 +35,11 @@ type RequestMeter struct {
 }
 
 const (
- labelCategory = "category"
- labelCode = "code"
- labelHost = "host"
- labelTask = "task"
+ labelCategory = "category"
+ labelCode = "code"
+ labelHost = "host"
+ labelTask = "task"
+ labelFromCache = "from_cache"
 )
 
 var taskKey struct{}
@@ -64,7 +65,7 @@ func NewRequestMeter(subsystem, help string) *RequestMeter {
  Subsystem: subsystem,
  Name: "requests_total",
  Help: help,
- }, []string{labelCategory, labelCode, labelHost, labelTask})
+ }, []string{labelCategory, labelCode, labelHost, labelTask, labelFromCache})
  registerer.MustRegister(requestCounter)
 
  // TODO(uwedeportivo):
@@ -136,12 +137,20 @@ func (t *requestCounterMiddleware) RoundTrip(r *http.Request) (resp *http.Respon
  code = strconv.Itoa(resp.StatusCode)
  }
 
+ // X-From-Cache=1 if the returned response is from the cache created by
+ // httpcli.NewCachedTransportOpt
+ var fromCache = "false"
+ if resp != nil && resp.Header.Get("X-From-Cache") != "" {
+ fromCache = "true"
+ }
+
  d := time.Since(start)
  t.meter.counter.With(map[string]string{
- labelCategory: category,
- labelCode: code,
- labelHost: r.URL.Host,
- labelTask: TaskFromContext(r.Context()),
+ labelCategory: category,
+ labelCode: code,
+ labelHost: r.URL.Host,
+ labelTask: TaskFromContext(r.Context()),
+ labelFromCache: fromCache,
  }).Inc()
 
  t.meter.duration.WithLabelValues(category, code, r.URL.Host).Observe(d.Seconds())

internal/metrics/metrics_test.go

@@ -68,7 +68,13 @@ func TestRequestMeterTransport(t *testing.T) {
  t.Error(err)
  }
 
- c, err := rm.counter.GetMetricWith(map[string]string{labelCategory: "/apiCallA", labelCode: "200", labelHost: "foosystem.com", labelTask: "unknown"})
+ c, err := rm.counter.GetMetricWith(map[string]string{
+ labelCategory: "/apiCallA",
+ labelCode: "200",
+ labelHost: "foosystem.com",
+ labelTask: "unknown",
+ labelFromCache: "false",
+ })
  if err != nil {
  t.Error(err)
  }