trace.go

/*
Copyright 2020 The Vitess Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package handlers

import (
	"net/http"

	"github.com/gorilla/mux"

	"vitess.io/vitess/go/trace"
)

// TraceHandler is a mux.MiddlewareFunc which creates a span with the route's
// name, as set by (mux.*Route).Name(), embeds it in the request context, and invokes
// the next middleware in the chain.
//
// It also annotates the span with the route_path_template, if it exists, and
// the route_uri. To add additional spans, extract the span in your
// VTAdminHTTPHandler like:
//
//		func Handler(ctx context.Context, r Request, api *API) *JSONResponse {
//			span, _ := trace.FromContext(ctx)
//			span.Annotate("foo", "bar")
//
//			return NewJSONResponse(api.Something(ctx))
//		}
//
// An unnamed route will get a span named "vtadmin:http:<unnamed route>".
func TraceHandler(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		route := mux.CurrentRoute(r)

		name := route.GetName()
		if name == "" {
			next.ServeHTTP(w, r)
			return
		}

		span, ctx := trace.NewSpan(r.Context(), "vtadmin:http:"+name)
		defer span.Finish()

		span.Annotate("route_uri", r.RequestURI)

		if tmpl, err := route.GetPathTemplate(); err != nil {
			span.Annotate("route_path_template", tmpl)
		}

		next.ServeHTTP(w, r.WithContext(ctx))
	})
}