Enable Debug Dynamically in Production

In the production environment, we may often have HTTP calls between services. When the API is abnormal, it is often difficult to reproduce in the test environment. We often hope to debug directly in the production environment. This article will give an example of using req to dynamically enable Debug in a production environment to help us troubleshoot problems.

Enable Debug via API Call

The server provides the /debug API endpoint. When the /debug?enable=true API is called, Debug will be dynamically enabled. When the /debug?enable=false API is called, the Debug will be dynamically disabled:

package main

import (
	"fmt"
	"github.com/gin-gonic/gin"
	"github.com/imroc/req/v3"
	"time"
)

var globalClient = req.C()

func main() {
	go func() {
    gin.SetMode(gin.ReleaseMode)
		r := gin.New()
		r.GET("/debug", func(c *gin.Context) {
			query := c.Query("enable")
			switch query {
			case "true": // Turn on dump with `curl 127.0.0.1:80/dump?enable=true`
				globalClient.EnableDumpAll()
				globalClient.EnableDebugLog()
				fmt.Println("Debug is enabled")
			case "false": // Turn off dump with `curl 127.0.0.1:80/dump?enable=false`
				globalClient.DisableDumpAll()
				globalClient.DisableDebugLog()
				fmt.Println("Debug is disabled")
			}
		})
		r.Run("0.0.0.0:80")
	}()

	for {
		time.Sleep(5 * time.Second)

		var result struct {
			Uuid string `json:"uuid"`
		}

		resp, err := globalClient.R().
			SetResult(&result). // Read uuid response into struct.
			Get("https://httpbin.org/uuid")

		if err != nil {
			fmt.Println("ERROR:", err.Error())
			continue
		}

		if resp.IsSuccess() { // Print uuid returned by the API.
			fmt.Println(result.Uuid)
		} else {
			fmt.Println("bad status", resp.Status)
		}
	}
}

Build and run:

$ go build -o test
$ ./test
6478d352-88c6-48f3-a481-4c355107fb03
2323dbab-342e-4dfa-8a93-f22e1a7037e8
3dc8f364-ed26-4e7b-887e-c808fc534df1

Enable debug by curl 'http://127.0.0.1:80/debug?enable=true', and then look at the changes in the output:

Debug is enabled
2022/05/25 19:51:13.740297 DEBUG [req] HTTP/2 GET https://httpbin.org/uuid
:authority: httpbin.org
:method: GET
:path: /uuid
:scheme: https
accept-encoding: gzip
user-agent: req/v3 (https://github.com/imroc/req)

:status: 200
date: Wed, 25 May 2022 11:51:13 GMT
content-type: application/json
content-length: 53
server: gunicorn/19.9.0
access-control-allow-origin: *
access-control-allow-credentials: true

{
  "uuid": "66c361ab-dadb-4377-97f0-6aff0bbae49e"
}

66c361ab-dadb-4377-97f0-6aff0bbae49e

Disable debug by curl 'http://127.0.0.1:80/debug?enable=false', and then look at the changes in the output again:

Debug is disabled
5d88b365-b137-463a-ba42-cf1c59b15d24
af96df78-bf6f-4c6c-b98d-427abc13ae03

Enable Debug via Signal

package main

import (
	"fmt"
	"github.com/imroc/req/v3"
	"os"
	"os/signal"
	"syscall"
	"time"
)

var globalClient = req.C()

func main() {
	sigs := make(chan os.Signal, 1)
	signal.Notify(sigs, syscall.SIGUSR1, syscall.SIGUSR2)

	go func() {
		for sig := range sigs {
			switch sig {
			case syscall.SIGUSR1: // Enable debug by `kill -SIGUSR1 PID`
				globalClient.EnableDumpAll()
				globalClient.EnableDebugLog()
				fmt.Println("Debug is enabled")
			case syscall.SIGUSR2: // Disable debug by `kill -SIGUSR2 PID`
				globalClient.DisableDumpAll()
				globalClient.DisableDebugLog()
				fmt.Println("Debug is disabled")
			}
		}
	}()

	for {
		time.Sleep(5 * time.Second)

		var result struct {
			Uuid string `json:"uuid"`
		}

		resp, err := globalClient.R().
			SetResult(&result). // Read uuid response into struct.
			Get("https://httpbin.org/uuid")

		if err != nil {
			fmt.Println("ERROR:", err.Error())
			continue
		}

		if resp.IsSuccess() { // Print uuid returned by the API.
			fmt.Println(result.Uuid)
		} else {
			fmt.Println("bad status", resp.Status)
		}
	}
}

Build and run:

$ go build -o test
$ ./test
3559ef3f-4a9e-4d08-969e-c92f5f8cd284
733d03b8-d680-4d65-aefc-27fb30e591c9
40af3a84-867e-4d2d-9cdb-aa1a16a52471

Enable debug by kill -SIGUSR1 PID, and then look at the changes in the output:

Debug is enabled
2022/05/25 11:36:50.801032 DEBUG [req] HTTP/2 GET https://httpbin.org/uuid
:authority: httpbin.org
:method: GET
:path: /uuid
:scheme: https
accept-encoding: gzip
user-agent: req/v3 (https://github.com/imroc/req)

:status: 200
date: Wed, 25 May 2022 03:36:51 GMT
content-type: application/json
content-length: 53
server: gunicorn/19.9.0
access-control-allow-origin: *
access-control-allow-credentials: true

{
  "uuid": "733d03b8-d680-4d65-aefc-27fb30e591c9"
}

733d03b8-d680-4d65-aefc-27fb30e591c9

Disable debug by kill -SIGUSR2 PID, and then look at the changes in the output again:

Debug is disabled
90b7648f-b195-44d4-80e4-7ab84a0b06b8
dd193d44-f0e6-40c4-b804-a36b5890a048
df0d8c10-1615-4b5f-b444-1453a7b0128b

Enable Debug only for Matched Requests

package main

import (
	"fmt"
	"github.com/gin-gonic/gin"
	"github.com/imroc/req/v3"
	"strings"
	"time"
)

var debugKeyword string

var globalClient = req.OnBeforeRequest(func(c *req.Client, r *req.Request) error {
	r.EnableDump() // Enable dump at the request level for all requests.
	return nil
}).OnAfterResponse(func(c *req.Client, resp *req.Response) error {
	if !resp.IsSuccess() { // Dump and record unexpected response as error.
		return fmt.Errorf("bad response from %s %s, dump content:\n%s", resp.Request.Method, resp.Request.RawURL, resp.Dump())
	}

	// Conditional Debugging: Only display the dump content whose URL contains the specified keyword.
	if debugKeyword != "" && strings.Contains(resp.Request.RawURL, debugKeyword) {
		fmt.Println(resp.Request.Method, resp.Request.RawURL)
		fmt.Println(resp.Dump())
	}
	return nil
})

func main() {
	go func() {
		gin.SetMode(gin.ReleaseMode)
		r := gin.New()
		r.GET("/debug", func(c *gin.Context) {
			debugKeyword = c.Query("keyword") // Enable conditional debug via API: /debug?url=keyword
			if debugKeyword == "off" {
				debugKeyword = ""
				fmt.Println("Debug is disabled")
			} else if debugKeyword != "" {
				fmt.Println("Start to debug", debugKeyword)
			}
		})
		r.Run("0.0.0.0:80")
	}()

	urls := []string{
		"https://httpbin.org/get",
		"https://httpbin.org/uuid",
		"https://httpbin.org/json",
		"https://httpbin.org/html",
		"https://httpbin.org/robots.txt",
		"https://httpbin.org/xml",
		"https://httpbin.org/headers",
		"https://httpbin.org/ip",
		"https://httpbin.org/user-agent",
		"https://api.github.com/users/imroc",
	}
	for {
		time.Sleep(5 * time.Second)
		for _, url := range urls {
			_, err := globalClient.R().
				Get(url)
			if err != nil {
				fmt.Println("ERROR:", err.Error())
				continue
			}
		}
		fmt.Println("all requests completed")
	}
}

Build and run:

$ go build -o test
$ ./test
./test
all requests completed
all requests completed
all requests completed
all requests completed

Then enable debug dynamically, and only debug /robots.txt API:

curl 'http://127.0.0.1:80/debug?keyword=/robots.txt'

Take a look at the output changes of our program:

Start to debug /robots.txt
GET https://httpbin.org/robots.txt
:authority: httpbin.org
:method: GET
:path: /robots.txt
:scheme: https
accept-encoding: gzip
user-agent: req/v3 (https://github.com/imroc/req)

:status: 200
date: Fri, 27 May 2022 13:25:18 GMT
content-type: text/plain
content-length: 30
server: gunicorn/19.9.0
access-control-allow-origin: *
access-control-allow-credentials: true

User-agent: *
Disallow: /deny


all requests completed

Try only debug GitHub’s /users API:

curl 'http://127.0.0.1:80/debug?keyword=https://api.github.com/users'

Take a look at the output changes of our program again:

Start to debug https://api.github.com/users
GET https://api.github.com/users/imroc
:authority: api.github.com
:method: GET
:path: /users/imroc
:scheme: https
accept-encoding: gzip
user-agent: req/v3 (https://github.com/imroc/req)

:status: 200
server: GitHub.com
date: Fri, 27 May 2022 13:32:58 GMT
content-type: application/json; charset=utf-8
cache-control: public, max-age=60, s-maxage=60
vary: Accept, Accept-Encoding, Accept, X-Requested-With
etag: W/"27cfedd070da5ec89d2bcf17b2cb05ac7d8a2dba510f9f8be1578ed6f845a468"
last-modified: Tue, 03 May 2022 12:12:52 GMT
x-github-media-type: github.v3; format=json
access-control-expose-headers: ETag, Link, Location, Retry-After, X-GitHub-OTP, X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Used, X-RateLimit-Resource, X-RateLimit-Reset, X-OAuth-Scopes, X-Accepted-OAuth-Scopes, X-Poll-Interval, X-GitHub-Media-Type, X-GitHub-SSO, X-GitHub-Request-Id, Deprecation, Sunset
access-control-allow-origin: *
strict-transportWrapper-security: max-age=31536000; includeSubdomains; preload
x-frame-options: deny
x-content-type-options: nosniff
x-xss-protection: 0
referrer-policy: origin-when-cross-origin, strict-origin-when-cross-origin
content-security-policy: default-src 'none'
content-encoding: gzip
x-ratelimit-limit: 60
x-ratelimit-remaining: 25
x-ratelimit-reset: 1653660880
x-ratelimit-resource: core
x-ratelimit-used: 35
accept-ranges: bytes
content-length: 486
x-github-request-id: DA88:054C:446B5:51534:6290D30A

{"login":"imroc","id":7448852,"node_id":"MDQ6VXNlcjc0NDg4NTI=","avatar_url":"https://avatars.githubusercontent.com/u/7448852?v=4","gravatar_id":"","url":"https://api.github.com/users/imroc","html_url":"https://github.com/imroc","followers_url":"https://api.github.com/users/imroc/followers","following_url":"https://api.github.com/users/imroc/following{/other_user}","gists_url":"https://api.github.com/users/imroc/gists{/gist_id}","starred_url":"https://api.github.com/users/imroc/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/imroc/subscriptions","organizations_url":"https://api.github.com/users/imroc/orgs","repos_url":"https://api.github.com/users/imroc/repos","events_url":"https://api.github.com/users/imroc/events{/privacy}","received_events_url":"https://api.github.com/users/imroc/received_events","type":"User","site_admin":false,"name":"roc","company":"Tencent","blog":"https://imroc.cc","location":"China","email":null,"hireable":true,"bio":"I'm roc","twitter_username":"imrocchan","public_repos":136,"public_gists":0,"followers":406,"following":155,"created_at":"2014-04-30T10:50:46Z","updated_at":"2022-05-03T12:12:52Z"}

all requests completed