This project demonstrates how do you wire in a proxy server (in our case it's Browser Mob Proxy) so that it sits between two servers and is capable of doing things that a browser mob proxy server does (altering requests, dropping headers etc.,)

The following components are involved in this exercise.

We have a simple dockerised version of BrowserMobProxy published into Github Container Registry.

The source code of the dockerised BMP is available here

When this container comes up, it basically opens up and is listening on 2 ports.

• 8080 - This is the HTTP Port on which the BMP server listens to and will respond back to the REST calls.
• 8081 - This is the port of the proxy server that gets created and is now readily available for usage.

This dockerised springboot app listens on port 10020 port and has a single HTTP GET api that looks like below

GET http://localhost:10020/worker/greet HTTP/1.1

This returns a json that would look like

{
    "message": "Greetings from worker e62c2a66-36c7-4726-a552-baeb83980bef"
}

and also a custom header X-Worker-Id:"88c4aff8-1964-46b7-b6f4-61a8262bdaf9" apart from copying all the headers that were sent as part of the request.

The source code of the dockerised MasterApp is available here

This dockerised springboot app listens on port 10010 port and also has a single HTTP GET api that looks like below

GET http://localhost:10010/master/greet HTTP/1.1

along with a mandatory header named "dragon-warrior": "kungfu-panda"

This returns a json that would look like

{
    "message": "Hello Greetings from worker e62c2a66-36c7-4726-a552-baeb83980bef",
    "dragonWarrior": "[Vary:\"Origin\", \"Access-Control-Request-Method\", \"Access-Control-Request-Headers\", X-Worker-Id:\"88c4aff8-1964-46b7-b6f4-61a8262bdaf9\", user-agent:\"Java/17.0.10\", host:\"worker:10020\", accept:\"text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2\", dragon-warrior:\"My-Custom-User-Agent-String 1.0\", Content-Type:\"application/json\", Transfer-Encoding:\"chunked\", Date:\"Fri, 19 Apr 2024 09:43:46 GMT\", Via:\"1.1 browsermobproxy\", \"1.1 browsermobproxy\"]"
}

Run the commands from the directory which contains the docker-compose.yml file available in this repository.

• docker-compose up

Now run the below command to enable API call interception as explained here

curl -i -X POST -H 'Content-Type: text/plain' -d "request.headers().remove('dragon-warrior'); request.headers().add('dragon-warrior', 'My-Custom-User-Agent-String 1.0');" http://localhost:8080/proxy/8081/filter/request

So here we are instructing browser mob proxy via its http port 8080 that the proxy that runs on the port 8081 should start filtering requests using the Javascript snippet shared above. The javascript is basically altering the value of the header dragon-warrior and setting it to My-Custom-User-Agent-String 1.0

Now when you invoke the below HTTP Call against our MasterApp using

curl --location 'http://localhost:10010/master/greet' \
--header 'krishnan: mahadevan' \
--header 'rest-client: true'

you should see a response like below (The complete logs from Postman)

GET http://localhost:10010/master/greet: {
  "Network": {
    "addresses": {
      "local": {
        "address": "::1",
        "family": "IPv6",
        "port": 55897
      },
      "remote": {
        "address": "::1",
        "family": "IPv6",
        "port": 10010
      }
    }
  },
  "Request Headers": {
    "krishnan": "mahadevan",
    "rest-client": "true",
    "user-agent": "PostmanRuntime/7.37.3",
    "accept": "*/*",
    "postman-token": "73df4a0d-8436-4155-84d6-91d88415b7bb",
    "host": "localhost:10010",
    "accept-encoding": "gzip, deflate, br",
    "connection": "keep-alive"
  },
  "Response Headers": {
    "vary": [
      "Origin",
      "Access-Control-Request-Method",
      "Access-Control-Request-Headers"
    ],
    "x-worker-id": "6d07a07c-5915-4fdd-b759-8381fa00b5b4",
    "user-agent": "Java/17.0.10",
    "host": "worker:10020",
    "accept": "text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2",
    "dragon-warrior": "My-Custom-User-Agent-String 1.0",
    "transfer-encoding": [
      "chunked",
      "chunked"
    ],
    "date": "Fri, 19 Apr 2024 10:33:35 GMT",
    "via": [
      "1.1 browsermobproxy",
      "1.1 browsermobproxy"
    ],
    "content-type": "application/json",
    "keep-alive": "timeout=60",
    "connection": "keep-alive"
  },
  "Response Body": "{\"message\":\"Hello Greetings from worker bf889c6d-35e2-4a0e-b4d9-869e13842248\",\"dragonWarrior\":\"[Vary:\\\"Origin\\\", \\\"Access-Control-Request-Method\\\", \\\"Access-Control-Request-Headers\\\", X-Worker-Id:\\\"6d07a07c-5915-4fdd-b759-8381fa00b5b4\\\", user-agent:\\\"Java/17.0.10\\\", host:\\\"worker:10020\\\", accept:\\\"text/html, image/gif, image/jpeg, *; q=.2, */*; q=.2\\\", dragon-warrior:\\\"My-Custom-User-Agent-String 1.0\\\", Content-Type:\\\"application/json\\\", Transfer-Encoding:\\\"chunked\\\", Date:\\\"Fri, 19 Apr 2024 10:33:35 GMT\\\", Via:\\\"1.1 browsermobproxy\\\", \\\"1.1 browsermobproxy\\\"]\"}"
}

Notice how the proxy server changed the value of the header dragon-warrior from kungfu-panda to My-Custom-User-Agent-String 1.0

Well, that's it. This entire exercise was to show how to plugin a proxy server into a containerised environment and get it to work.

• docker-compose stop - Stops all the services that are listed in the docker-compose.yml file.
• docker-compose rm - Removes all the services that are listed in the docker-compose.yml file.
• docker-compose pull - Fetches the latest images for the services that are listed in the docker-compose.yml file.