Merge pull request #4545 from hairyhenderson/metrics-restrict-http-methods

metrics: Enforce smaller set of method labels

4 files changed, 74 insertions, 25 deletions

diff --git a/internal/metrics/metrics.go b/internal/metrics/metrics.go
new file mode 100644
index 0000000..7ae09b6
--- /dev/null
+++ b/internal/metrics/metrics.go
@@ -0,0 +1,39 @@
+package metrics
+
+import (
+	"net/http"
+	"strconv"
+)
+
+func SanitizeCode(s int) string {
+	switch s {
+	case 0, 200:
+		return "200"
+	default:
+		return strconv.Itoa(s)
+	}
+}
+
+// Only support the list of "regular" HTTP methods, see
+// https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods
+var methodMap = map[string]string{
+	"GET": http.MethodGet, "get": http.MethodGet,
+	"HEAD": http.MethodHead, "head": http.MethodHead,
+	"PUT": http.MethodPut, "put": http.MethodPut,
+	"POST": http.MethodPost, "post": http.MethodPost,
+	"DELETE": http.MethodDelete, "delete": http.MethodDelete,
+	"CONNECT": http.MethodConnect, "connect": http.MethodConnect,
+	"OPTIONS": http.MethodOptions, "options": http.MethodOptions,
+	"TRACE": http.MethodTrace, "trace": http.MethodTrace,
+	"PATCH": http.MethodPatch, "patch": http.MethodPatch,
+}
+
+// SanitizeMethod sanitizes the method for use as a metric label. This helps
+// prevent high cardinality on the method label. The name is always upper case.
+func SanitizeMethod(m string) string {
+	if m, ok := methodMap[m]; ok {
+		return m
+	}
+
+	return "OTHER"
+}
diff --git a/internal/metrics/metrics_test.go b/internal/metrics/metrics_test.go
new file mode 100644
index 0000000..c3f5965
--- /dev/null
+++ b/internal/metrics/metrics_test.go
@@ -0,0 +1,28 @@
+package metrics
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestSanitizeMethod(t *testing.T) {
+	tests := []struct {
+		method   string
+		expected string
+	}{
+		{method: "get", expected: "GET"},
+		{method: "POST", expected: "POST"},
+		{method: "OPTIONS", expected: "OPTIONS"},
+		{method: "connect", expected: "CONNECT"},
+		{method: "trace", expected: "TRACE"},
+		{method: "UNKNOWN", expected: "OTHER"},
+		{method: strings.Repeat("ohno", 9999), expected: "OTHER"},
+	}
+
+	for _, d := range tests {
+		actual := SanitizeMethod(d.method)
+		if actual != d.expected {
+			t.Errorf("Not same: expected %#v, but got %#v", d.expected, actual)
+		}
+	}
+}
diff --git a/metrics.go b/metrics.go
index ab9d797..325006f 100644
--- a/metrics.go
+++ b/metrics.go
@@ -2,9 +2,8 @@ package caddy
 
 import (
 	"net/http"
-	"strconv"
-	"strings"
 
+	"github.com/caddyserver/caddy/v2/internal/metrics"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/collectors"
 	"github.com/prometheus/client_golang/prometheus/promauto"
@@ -46,8 +45,8 @@ func instrumentHandlerCounter(counter *prometheus.CounterVec, next http.Handler)
 		d := newDelegator(w)
 		next.ServeHTTP(d, r)
 		counter.With(prometheus.Labels{
-			"code":   sanitizeCode(d.status),
-			"method": strings.ToUpper(r.Method),
+			"code":   metrics.SanitizeCode(d.status),
+			"method": metrics.SanitizeMethod(r.Method),
 		}).Inc()
 	})
 }
@@ -67,12 +66,3 @@ func (d *delegator) WriteHeader(code int) {
 	d.status = code
 	d.ResponseWriter.WriteHeader(code)
 }
-
-func sanitizeCode(s int) string {
-	switch s {
-	case 0, 200:
-		return "200"
-	default:
-		return strconv.Itoa(s)
-	}
-}
diff --git a/modules/caddyhttp/metrics.go b/modules/caddyhttp/metrics.go
index 3e5d639..458c22a 100644
--- a/modules/caddyhttp/metrics.go
+++ b/modules/caddyhttp/metrics.go
@@ -3,11 +3,10 @@ package caddyhttp
 import (
 	"context"
 	"net/http"
-	"strconv"
-	"strings"
 	"sync"
 	"time"
 
+	"github.com/caddyserver/caddy/v2/internal/metrics"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promauto"
 )
@@ -109,7 +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}
-	method := strings.ToUpper(r.Method)
+	method := metrics.SanitizeMethod(r.Method)
 	// the "code" value is set later, but initialized here to eliminate the possibility
 	// of a panic
 	statusLabels := prometheus.Labels{"server": server, "handler": h.handler, "method": method, "code": ""}
@@ -124,7 +123,7 @@ func (h *metricsInstrumentedHandler) ServeHTTP(w http.ResponseWriter, r *http.Re
 	// being called when the headers are written.
 	// Effectively the same behaviour as promhttp.InstrumentHandlerTimeToWriteHeader.
 	writeHeaderRecorder := ShouldBufferFunc(func(status int, header http.Header) bool {
-		statusLabels["code"] = sanitizeCode(status)
+		statusLabels["code"] = metrics.SanitizeCode(status)
 		ttfb := time.Since(start).Seconds()
 		httpMetrics.responseDuration.With(statusLabels).Observe(ttfb)
 		return false
@@ -143,7 +142,7 @@ func (h *metricsInstrumentedHandler) ServeHTTP(w http.ResponseWriter, r *http.Re
 	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())
+		statusLabels["code"] = metrics.SanitizeCode(wrec.Status())
 	}
 
 	httpMetrics.requestDuration.With(statusLabels).Observe(dur)
@@ -153,13 +152,6 @@ func (h *metricsInstrumentedHandler) ServeHTTP(w http.ResponseWriter, r *http.Re
 	return nil
 }
 
-func sanitizeCode(code int) string {
-	if code == 0 {
-		return "200"
-	}
-	return strconv.Itoa(code)
-}
-
 // taken from https://github.com/prometheus/client_golang/blob/6007b2b5cae01203111de55f753e76d8dac1f529/prometheus/promhttp/instrument_server.go#L298
 func computeApproximateRequestSize(r *http.Request) int {
 	s := 0