http-grpc-filter

Overview

The API analyzes an HTTP user agent and decides to block or allow it. If the user agent header is from a Safari browser, it should return a decision to block the request. If it is from a Firefox browser, it should allow the request.

A gRPC client and server implements a single endpoint that receives the user agent string, analyzes it, and returns the result.

The terminal CLI uses the client to call the API.

Getting Started

Prerequisites

Install Protoc

The Protoc compiler is needed to generate the gRPC code.

If you are using MacOS, you can use Homebrew:

$ brew install protobuf

Verify Installation of Protoc

The protoc compiler should be included in your PATH. Verify by running the following command:

$ protoc --version
libprotoc 24.3 # this is an example version

Running

Open two terminals or tabs in a terminal.

Start the server in one terminal (or separate tab):

$ cargo run --bin echo-server

Start the client in another terminal (or separate tab):

The last part of the input string should be a HTTP User Agent. Mozilla has provided examples of user agent strings for different browsers.

$ cargo run --bin echo-client -- "Hello World\!"

Example 1: Firefox User Agent

Run client after starting the server:

$ cargo run --bin echo-client -- "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:101.0) Gecko/20100101 Firefox/101.0"

RESPONSE=EchoResponse { message: "Accepting the Request.", user_agent: "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:101.0) Gecko/20100101 Firefox/101.0" }"

Example 2: Safari User Agent

Run client after starting the server:

$ cargo run --bin echo-client -- "Mozilla/5.0 (iPhone; CPU iPhone OS 13_5_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.1.1 Mobile/15E148 Safari/604.1"

RESPONSE=EchoResponse { message: "Blocking the Request.", user_agent: "Mozilla/5.0 (iPhone; CPU iPhone OS 13_5_1 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/13.1.1 Mobile/15E148 Safari/604.1\n" }

Testing

$ cargo test

#################################### Sample output below ####################################
Finished test [unoptimized + debuginfo] target(s) in 0.04s
     Running unittests src/main.rs (target/debug/deps/echo_client-3d3566e115c08a41)

running 1 test
test tests::test_bad_client_connection ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

     Running unittests src/server.rs (target/debug/deps/echo_server-ffaaf4bd0ea8fe8a)

running 1 test
test tests::test_bad_address ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

Troubleshooting

• If you see a dquote> on the terminal when running the client, history expansion might be enabled in your terminal, so retry the input string and escape backspaces.
• Use CTRL+G to escape dquote>

Example

$ cargo run --bin echo-client --"Hello World!"

dquote>

Click CTRL+G then retype the following:

$ cargo run --bin echo-client --"Hello World\!"

Future Work

• See the issues for future feature and enchancement ideas.