gidm

Simple http proxy man-in-the-middle tool

Intro

gidm is a minimalist http proxy that can be used as "man-in-the-middle" tool capable of manipulating requests and responses.

Installation

Build from source

GO v1.15 or greater is required. Just clone this repo and build as usual:

go build

Or build & install:

go install

Download release binaries

You can also download Linux and MacOS pre-built binaries from releases section.

Docker Image

Docker image is also available from DockerHub. You will find some use cases in section Examples.

Usage

You can run the tool along with --help option to get a list of supported commands:

$ ./gidm --help
NAME:
   gidm - Simple midm tool

USAGE:
   gidm [global options] command [command options] [arguments...]

VERSION:
   v0.2.1

COMMANDS:
   help, h  Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --reqh value   inject request header
   --resh value   inject response header
   --reqb value   replace string in request body (/old/new/)
   --resb value   replace string in response body (/old/new/)
   -p value       listen to port (default: "8080")
   -u value       redirect to url (default: "http://localhost:9000")
   -i value       enable interactive mode (API server will listen on specified port)
   -d             enable debugging (default: false)
   --help, -h     show help (default: false)
   --version, -v  print version (default: false)

Examples

Inject Request Headers

Listen on port 8081 and forward to http://localhost:9000, show debug information and inject the following headers:

• x-custom-flag: true
• x-custom-id: 12345

gidm \
-p 8081 \
-u http://localhost:9000 \
-reqh "x-custom-flag: true" \
-reqh "x-custom-id: 12345" \
-d

POST something to localhost:8081:

curl -X POST \
http://localhost:8081/dummy \
-H "content-type: application/json" \
-d '{"name": "john doe"}'

You should get this output:

Listening on port: 8081
Redirecting to: http://localhost:9000

Request headers to be injected:
  x-custom-flag: true
  x-custom-id: 12345

2021/05/31 18:34:16 POST /dummy HTTP/1.1
Host: localhost:9000
Accept: */*
Content-Length: 20
Content-Type: application/json
User-Agent: curl/7.64.1
X-Custom-Flag: true
X-Custom-Id: 12345

{"name": "john doe"}

2021/05/31 18:34:16 HTTP/1.1 404 Not Found
Content-Length: 22
Content-Type: application/json
Date: Mon, 31 May 2021 21:34:16 GMT
Server: uvicorn

{"detail":"Not Found"}

Replace body strings

You can add string replacers for request and response body. For example, to replace every ok with BAD in your response body, you can use this command:

./gidm \
-p 8081 \
-u http://localhost:9000 \
-reqh "x-custom-flag: true" \
-reqh "x-custom-id: 12345" \
-resb "/ok/BAD/" \
-d

Run using Docker

Grab Docker image from DockerHub:

docker pull charlysan/gidm

Run and add the proper port-forwarding:

docker run \
-p 8081:8080 \
-p 9090:9090 \
charlysan/gidm \
-u https://api.chucknorris.io \
-resb "/Chuck Norris/John Doe/" \
-i 9090 \
-d

$ curl http://localhost:8081/jokes/random | json_pp
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   342  100   342    0     0    421      0 --:--:-- --:--:-- --:--:--   421
{
   "value" : "Most people have Microwave ovens. John Doe has a Megawave oven.",
   "url" : "https://api.chucknorris.io/jokes/t-ipnAxeTFCpF6cLvN9_-Q",
   "id" : "t-ipnAxeTFCpF6cLvN9_-Q",
   "created_at" : "2020-01-05 13:42:23.880601",
   "icon_url" : "https://assets.chucknorris.host/img/avatar/chuck-norris.png",
   "categories" : [],
   "updated_at" : "2020-01-05 13:42:23.880601"
}

Interactive Mode

Interactive Mode allows to modify the proxy behavior without restarting the app. Te proxy will listen on the port specified using -i <PORT> flag:

./gidm \
-p 8081 \
-u http://localhost:9000 \
-reqh "x-custom-flag: true" \
-reqh "x-custom-id: 12345" \
-resb "/ok/BAD/" \
-i 9090 \
-d

And it will expose the following endpoints:

PUT /requestHeaders
PUT /responseHeaders
PUT /requestBodyReplacers
PUT /responseBodyReplacers

So, supposing you want to change the response body string replacers you can hit the proxy with this payload:

curl -X PUT \
http://localhost:9090/responseBodyReplacers \
-d '{"ok": "WRONG!!"}'

And the proxy should show the following log:

Response Body string replacers updated
  ok -> WRONG!!