// Copyright 2020 Marc-Antoine Ruel. All rights reserved.

// Use of this source code is governed under the Apache License, Version 2.0

// that can be found in the LICENSE file.

package webstack_test

import (

"log"

"net"

"net/http"

"strings"

"sync"

"time"

"github.com/maruel/panicparse/v2/stack/webstack"

)

func ExampleSnapshotHandler() {

http.HandleFunc("/debug/panicparse", webstack.SnapshotHandler)

// Access as http://localhost:6060/debug/panicparse

log.Println(http.ListenAndServe("localhost:6060", nil))

}

func ExampleSnapshotHandler_complex() {

// This example does a few things:

// - Diables "augment" by default, can be enabled manually with "?augment=1".

// - Forces the "maxmem" value to reduce memory pressure in worst case.

// - Serializes handler to one at a time.

// - Throttles requests to once per second.

// - Limit request source IP to localhost and 100.64.x.x/10. (e.g.

// Tailscale).

const delay = time.Second

mu := sync.Mutex{}

var last time.Time

http.HandleFunc("/debug/panicparse", func(w http.ResponseWriter, req *http.Request) {

// Only allow requests from localhost or in the 100.64.x.x/10 IPv4 range.

ok := false

if i := strings.LastIndexByte(req.RemoteAddr, ':'); i != -1 {

switch ip := req.RemoteAddr[:i]; ip {

case "localhost", "127.0.0.1", "[::1]", "::1":

ok = true

default:

p := net.ParseIP(ip).To4()

ok = p != nil && p[0] == 100 && p[1] >= 64 && p[1] < 128

}

}

if !ok {

http.Error(w, "forbidden", http.StatusForbidden)

return

}

// Serialize the handler.

mu.Lock()

defer mu.Unlock()

// Throttle requests.

if time.Since(last) < delay {

http.Error(w, "retry later", http.StatusTooManyRequests)

return

}

// Must be called before touching req.Form.

req.ParseForm()

// Disables source scanning by default since it's heavy.

if req.FormValue("augment") == "" {

req.Form.Set("augment", "0")

}

// Reduces maximum memory usage to 32MiB (from 64MiB) for the goroutines

// snapshot.

req.Form.Set("maxmem", "33554432")

webstack.SnapshotHandler(w, req)

last = time.Now()

})

// Access as http://localhost:6060/debug/panicparse

log.Println(http.ListenAndServe("localhost:6060", nil))

}