Fix metrics with high cardininality in otelhttp (open-telemetry#3765)

instrumentation/net/http/otelhttp/handler.go

@@ -219,7 +219,7 @@ func (h *middleware) serveHTTP(w http.ResponseWriter, r *http.Request, next http
 	setAfterServeAttributes(span, bw.read, rww.written, rww.statusCode, bw.err, rww.err)
 
 	// Add metrics
-	attributes := append(labeler.Get(), semconvutil.HTTPServerRequest(h.server, r)...)
+	attributes := append(labeler.Get(), semconvutil.HTTPServerRequestMetric(h.server, r)...)
 	if rww.statusCode > 0 {
 		attributes = append(attributes, semconv.HTTPStatusCode(rww.statusCode))
 	}

instrumentation/net/http/otelhttp/internal/semconvutil/httpconv.go

@@ -80,7 +80,20 @@ func HTTPClientStatus(code int) (codes.Code, string) {
 // "net.sock.peer.addr", "net.sock.peer.port", "http.user_agent", "enduser.id",
 // "http.client_ip".
 func HTTPServerRequest(server string, req *http.Request) []attribute.KeyValue {
-	return hc.ServerRequest(server, req)
+	attrs, _ := hc.ServerRequest(server, req)
+	return attrs
+}
+
+// HTTPServerRequestMetric returns metric attributes for an HTTP request received by a
+// server.
+//
+// See HTTPServerRequest for requirements.
+//
+// The following attributes are always returned: "http.method", "http.scheme",
+// "http.flavor", "net.host.name".
+func HTTPServerRequestMetric(server string, req *http.Request) []attribute.KeyValue {
+	_, attrs := hc.ServerRequest(server, req)
+	return attrs
 }
 
 // HTTPServerStatus returns a span status code and message for an HTTP status code
@@ -187,13 +200,16 @@ func (c *httpConv) ClientResponse(resp *http.Response) []attribute.KeyValue {
 	return attrs
 }
 
-// ClientRequest returns attributes for an HTTP request made by a client. The
-// following attributes are always returned: "http.url", "http.flavor",
+// ClientRequest returns attributes for an HTTP request made by a client. The first
+// slice of attributes contains full information, while the second one only preserve
+// those won't causing high cardinality.
+//
+// The following attributes are always returned: "http.url", "http.flavor",
 // "http.method", "net.peer.name". The following attributes are returned if the
 // related values are defined in req: "net.peer.port", "http.user_agent",
 // "http.request_content_length", "enduser.id".
 func (c *httpConv) ClientRequest(req *http.Request) []attribute.KeyValue {
-	n := 3 // URL, peer name, proto, and method.
+	n := 4 // URL, peer name, proto, and method.
 	var h string
 	if req.URL != nil {
 		h = req.URL.Host
@@ -215,7 +231,6 @@ func (c *httpConv) ClientRequest(req *http.Request) []attribute.KeyValue {
 		n++
 	}
 	attrs := make([]attribute.KeyValue, 0, n)
-
 	attrs = append(attrs, c.method(req.Method))
 	attrs = append(attrs, c.proto(req.Proto))
 
@@ -251,6 +266,8 @@ func (c *httpConv) ClientRequest(req *http.Request) []attribute.KeyValue {
 }
 
 // ServerRequest returns attributes for an HTTP request received by a server.
+// The first slice of attributes contains full information, while the second
+// one only preserve those won't causing high cardinality.
 //
 // The server must be the primary server name if it is known. For example this
 // would be the ServerName directive
@@ -271,7 +288,9 @@ func (c *httpConv) ClientRequest(req *http.Request) []attribute.KeyValue {
 // returned if they related values are defined in req: "net.host.port",
 // "net.sock.peer.addr", "net.sock.peer.port", "http.user_agent", "enduser.id",
 // "http.client_ip".
-func (c *httpConv) ServerRequest(server string, req *http.Request) []attribute.KeyValue {
+func (c *httpConv) ServerRequest(server string, req *http.Request) (
+	[]attribute.KeyValue, []attribute.KeyValue,
+) {
 	// TODO: This currently does not add the specification required
 	// `http.target` attribute. It has too high of a cardinality to safely be
 	// added. An alternate should be added, or this comment removed, when it is
@@ -280,6 +299,7 @@ func (c *httpConv) ServerRequest(server string, req *http.Request) []attribute.K
 	// should be removed as well.
 
 	n := 4 // Method, scheme, proto, and host name.
+	attrsLowCardinality := make([]attribute.KeyValue, 0, n)
 	var host string
 	var p int
 	if server == "" {
@@ -316,10 +336,11 @@ func (c *httpConv) ServerRequest(server string, req *http.Request) []attribute.K
 	}
 	attrs := make([]attribute.KeyValue, 0, n)
 
-	attrs = append(attrs, c.method(req.Method))
-	attrs = append(attrs, c.scheme(req.TLS != nil))
-	attrs = append(attrs, c.proto(req.Proto))
-	attrs = append(attrs, c.NetConv.HostName(host))
+	attrsLowCardinality = append(attrsLowCardinality, c.method(req.Method))
+	attrsLowCardinality = append(attrsLowCardinality, c.scheme(req.TLS != nil))
+	attrsLowCardinality = append(attrsLowCardinality, c.proto(req.Proto))
+	attrsLowCardinality = append(attrsLowCardinality, c.NetConv.HostName(host))
+	attrs = append(attrs, attrsLowCardinality...)
 
 	if hostPort > 0 {
 		attrs = append(attrs, c.NetConv.HostPort(hostPort))
@@ -346,7 +367,7 @@ func (c *httpConv) ServerRequest(server string, req *http.Request) []attribute.K
 		attrs = append(attrs, c.HTTPClientIPKey.String(clientIP))
 	}
 
-	return attrs
+	return attrs, attrsLowCardinality
 }
 
 func (c *httpConv) method(method string) attribute.KeyValue {

instrumentation/net/http/otelhttp/internal/semconvutil/httpconv_test.go

@@ -165,6 +165,41 @@ func TestHTTPServerRequest(t *testing.T) {
 		HTTPServerRequest("", req))
 }
 
+func TestHTTPServerRequestMetric(t *testing.T) {
+	got := make(chan *http.Request, 1)
+	handler := func(w http.ResponseWriter, r *http.Request) {
+		got <- r
+		w.WriteHeader(http.StatusOK)
+	}
+
+	srv := httptest.NewServer(http.HandlerFunc(handler))
+	defer srv.Close()
+
+	srvURL, err := url.Parse(srv.URL)
+	require.NoError(t, err)
+
+	resp, err := srv.Client().Get(srv.URL)
+	require.NoError(t, err)
+	require.NoError(t, resp.Body.Close())
+
+	req := <-got
+
+	const user = "alice"
+	req.SetBasicAuth(user, "pswrd")
+
+	const clientIP = "127.0.0.5"
+	req.Header.Add("X-Forwarded-For", clientIP)
+
+	assert.ElementsMatch(t,
+		[]attribute.KeyValue{
+			attribute.String("http.method", "GET"),
+			attribute.String("http.scheme", "http"),
+			attribute.String("http.flavor", "1.1"),
+			attribute.String("net.host.name", srvURL.Hostname()),
+		},
+		HTTPServerRequestMetric("", req))
+}
+
 func TestHTTPServerName(t *testing.T) {
 	req := new(http.Request)
 	var got []attribute.KeyValue