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metrics: Fix panic when headers aren't written (#3737)
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Signed-off-by: Dave Henderson <[email protected]>
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hairyhenderson authored Sep 21, 2020
1 parent d16ede3 commit b1d456d
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Showing 2 changed files with 27 additions and 1 deletion.
10 changes: 9 additions & 1 deletion modules/caddyhttp/metrics.go
Original file line number Diff line number Diff line change
Expand Up @@ -108,7 +108,7 @@ func newMetricsInstrumentedHandler(handler string, mh MiddlewareHandler) *metric
func (h *metricsInstrumentedHandler) ServeHTTP(w http.ResponseWriter, r *http.Request, next Handler) error {
server := serverNameFromContext(r.Context())
labels := prometheus.Labels{"server": server, "handler": h.handler}
statusLabels := prometheus.Labels{"server": server, "handler": h.handler, "method": r.Method}
statusLabels := prometheus.Labels{"server": server, "handler": h.handler, "method": r.Method, "code": ""}

inFlight := httpMetrics.requestInFlight.With(labels)
inFlight.Inc()
Expand All @@ -134,6 +134,14 @@ func (h *metricsInstrumentedHandler) ServeHTTP(w http.ResponseWriter, r *http.Re
return err
}

// If the code hasn't been set yet, and we didn't encounter an error, we're
// probably falling through with an empty handler.
if statusLabels["code"] == "" {
// we still sanitize it, even though it's likely to be 0. A 200 is
// returned on fallthrough so we want to reflect that.
statusLabels["code"] = sanitizeCode(wrec.Status())
}

httpMetrics.requestDuration.With(statusLabels).Observe(dur)
httpMetrics.requestSize.With(statusLabels).Observe(float64(computeApproximateRequestSize(r)))
httpMetrics.responseSize.With(statusLabels).Observe(float64(wrec.Size()))
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18 changes: 18 additions & 0 deletions modules/caddyhttp/metrics_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -57,6 +57,24 @@ func TestMetricsInstrumentedHandler(t *testing.T) {
if err := ih.ServeHTTP(w, r, h); err != nil {
t.Errorf("Received unexpected error: %w", err)
}

// an empty handler - no errors, no header written
mh = middlewareHandlerFunc(func(w http.ResponseWriter, r *http.Request, h Handler) error {
return nil
})
ih = newMetricsInstrumentedHandler("empty", mh)
r = httptest.NewRequest("GET", "/", nil)
w = httptest.NewRecorder()

if err := ih.ServeHTTP(w, r, h); err != nil {
t.Errorf("Received unexpected error: %w", err)
}
if actual := w.Result().StatusCode; actual != 200 {
t.Errorf("Not same: expected status code %#v, but got %#v", 200, actual)
}
if actual := w.Result().Header; len(actual) != 0 {
t.Errorf("Not empty: expected headers to be empty, but got %#v", actual)
}
}

type middlewareHandlerFunc func(http.ResponseWriter, *http.Request, Handler) error
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