httpstat

httpstat is a net/http handler for Go, which reports various metrics about a given http server. It natively supports exporting stats to expvar (this is actually how it tracks all of it's stats). httpstat also has support for taking historical snapshots of the data. An example usecase and feature of this is the statgraph subpackage, as documented here.

An example usecase (also see _examples/) is shown below:

package main

import (
	_ "expvar"
	"fmt"
	"net/http"

	"github.com/lrstanley/httpstat"
)

func main() {
	stats := httpstat.New("", nil)
	defer stats.Close()

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        fmt.Fprintln(w, "Hello Gopher")
    })

	http.ListenAndServe(":8080", stats.Record(http.DefaultServeMux))
}

Example output, using the expvar's default endpoint, /debug/vars:

{
    "cmdline": [
        "/tmp/go-build807700005/command-line-arguments/_obj/exe/main"
    ],
    "httpstat_invoked": "2018-01-11T07:58:40-05:00",
    "httpstat_invoked_seconds": 1170,
    "httpstat_invoked_unix": 1515675520,
    "httpstat_pid": 17135,
    "httpstat_request_bytes_total": 8894,
    "httpstat_request_errors_total": 0,
    "httpstat_request_total": 23,
    "httpstat_request_total_seconds": 0.004517135,
    "httpstat_response_bytes_total": 50748,
    "httpstat_status_total": {
        "200": 22,
        "404": 1
    },
    "memstats": "..."
    }
}

You can also mount the ServeHTTP endpoint (here) to a custom location, which will only return the expvar variables that were created by this application.

Statgraph

There is an optional subpackage you can use, which will allow you to mount a net/http handler, which can return svg/png rendered graphs of the historical snapshots. Below is an example of going to the mounted http handlers /:

Notes

• Make sure you register the handler/middleware as far up the stack that you want to track metrics on. Also make sure that your handlers do not return early, and continue writing to the ResponseWriter after they have returned, as httpstat cannot monitor those writes.
• Using this library will introduce a ~550ns overhead to the total request processing time, however it shouldn't introduce any measurable delay during the server->client response times, since tracking measurement compilation occurs after the child middleware/handler has finished being invoked.
• Using History will add a minor amount of additional overhead during snapshot pauses. This may be reduced in future iterations.
• Each invocation of a new HTTPStats struct must be under it's own namespace, as expvar only allows variables with a given name to be registered once. See httpstat.New for details.
• The request size ("bytes in") can only be roughly calculated, as net/http strips some of the data of the request as it is being processed.

Why?

There are a few packages similar to this one (thoas/stats and felixge/httpsnoop to name a few), however I wanted one with builtin support for historical snapshots, as well as one which was built with expvar in mind. With support for expvar, this can allow other packages to introspect the data that this package exports, in a standardized way. Not all of these packages support concurrent writes to the ResponseWriter, which httpstat does.

License

LICENSE: The MIT License (MIT)
Copyright (c) 2017 Liam Stanley <me@liamstanley.io>

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.