Use pattern to determine endpoint metrics. (#2689)

This ensures we don't create infinite metrics based on users hitting
non-existent endpoints.

cmd/ocsp-responder/main.go

@@ -235,14 +235,16 @@ as generated by Boulder's single-ocsp command.
 }
 
 func mux(scope metrics.Scope, responderPath string, source cfocsp.Source) http.Handler {
-	m := http.StripPrefix(responderPath, cfocsp.NewResponder(source))
+	stripPrefix := http.StripPrefix(responderPath, cfocsp.NewResponder(source))
 	h := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if r.Method == "GET" && r.URL.Path == "/" {
 			w.Header().Set("Cache-Control", "max-age=43200") // Cache for 12 hours
 			w.WriteHeader(200)
 			return
 		}
-		m.ServeHTTP(w, r)
+		stripPrefix.ServeHTTP(w, r)
 	})
-	return measured_http.New(h, clock.Default())
+	m := http.NewServeMux()
+	m.Handle("/", h)
+	return measured_http.New(m, clock.Default())
 }

metrics/measured_http/http.go

@@ -3,8 +3,6 @@ package measured_http
 import (
 	"fmt"
 	"net/http"
-	"regexp"
-	"strings"
 
 	"github.com/jmhodges/clock"
 	"github.com/prometheus/client_golang/prometheus"
@@ -38,56 +36,32 @@ func (r *responseWriterWithStatus) WriteHeader(code int) {
 
 // MeasuredHandler wraps an http.Handler and records prometheus stats
 type MeasuredHandler struct {
-	http.Handler
+	*http.ServeMux
 	clk clock.Clock
 	// Normally this is always responseTime, but we override it for testing.
 	stat *prometheus.HistogramVec
 }
 
-func New(h http.Handler, clk clock.Clock) *MeasuredHandler {
+func New(m *http.ServeMux, clk clock.Clock) *MeasuredHandler {
 	return &MeasuredHandler{
-		Handler: h,
-		clk:     clk,
-		stat:    responseTime,
+		ServeMux: m,
+		clk:      clk,
+		stat:     responseTime,
 	}
 }
 
-var endpointShortNameRegexp = regexp.MustCompile("^[a-z-]*$")
-
-// endpointFromPath turns a request path into a value suitable for a Prometheus
-// label value, by eliminating path components that vary widely (like user ids
-// and authorization ids). It uses a simple heuristic: Remove everything after
-// the first path component that doesn't match lowercase a-z, plus hyphen. This
-// happens to work very well with Boulder's WFE.
-func endpointFromPath(path string) string {
-	// Remove any query
-	path = strings.Split(path, "?")[0]
-	components := strings.Split(path, "/")
-	var i int
-	var v string
-	for i, v = range components {
-		matched := endpointShortNameRegexp.MatchString(v)
-		if !matched {
-			return strings.Join(components[:i], "/")
-		}
-	}
-	return path
-}
-
 func (h *MeasuredHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	begin := h.clk.Now()
 	rwws := &responseWriterWithStatus{w, 0}
-	// Copy in case handlers down the chain use StripPrefix, which modifies
-	// URL path.
-	endpoint := endpointFromPath(r.URL.Path)
 
+	subHandler, pattern := h.Handler(r)
 	defer func() {
 		h.stat.With(prometheus.Labels{
-			"endpoint": endpoint,
+			"endpoint": pattern,
 			"method":   r.Method,
 			"code":     fmt.Sprintf("%d", rwws.code),
 		}).Observe(h.clk.Since(begin).Seconds())
 	}()
 
-	h.Handler.ServeHTTP(rwws, r)
+	subHandler.ServeHTTP(rwws, r)
 }

metrics/measured_http/http_test.go

@@ -12,27 +12,6 @@ import (
 	io_prometheus_client "github.com/prometheus/client_model/go"
 )
 
-func TestEndpointFromPath(t *testing.T) {
-	tc := []struct {
-		input, expected string
-	}{
-		{"/", "/"},
-		{"/acme", "/acme"},
-		{"/acme/new-authz", "/acme/new-authz"},
-		{"/acme/new-authz/", "/acme/new-authz/"},
-		{"/acme/authz/1234", "/acme/authz"},
-		{"/acme/authz/aGVsbG8K/1234", "/acme/authz"},
-		{"/directory?foo=bar", "/directory"},
-	}
-	for _, c := range tc {
-		output := endpointFromPath(c.input)
-		if output != c.expected {
-			t.Errorf("endpointFromPath(%q) = %q (expected %q)",
-				c.input, output, c.expected)
-		}
-	}
-}
-
 type sleepyHandler struct {
 	clk clock.FakeClock
 }
@@ -54,10 +33,12 @@ func TestMeasuring(t *testing.T) {
 		},
 		[]string{"endpoint", "method", "code"})
 
+	mux := http.NewServeMux()
+	mux.Handle("/foo", sleepyHandler{clk})
 	mh := MeasuredHandler{
-		Handler: sleepyHandler{clk},
-		clk:     clk,
-		stat:    stat,
+		ServeMux: mux,
+		clk:      clk,
+		stat:     stat,
 	}
 	mh.ServeHTTP(httptest.NewRecorder(), &http.Request{
 		URL:    &url.URL{Path: "/foo"},