Initial commit

Note re ESLint setup: I used the TUI of `npm init @eslint/config@latest`
from https://eslint.org/docs/latest/use/getting-started, and that
generated the following warning, which I followed:

> Note that some plugins currently do not support ESLint v9 yet. You may
> need to use '--force' when installing, or add the following to your
> package.json: "overrides": { "eslint": "^9.7.0" }

.github/workflows/check.yml

@@ -0,0 +1,34 @@
+name: check
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      # Set up
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: "20" # Oldest LTS at time of writing
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.x"
+
+      - run: npm ci
+      - run: pip install mitmproxy websockets ruff mypy # TODO I’m not sure what is the right way of doing this; what's the package.json equivalent? Ditto for the installation instructions
+
+      # Run JS checks
+      - run: npm run format:check
+      - run: npm run lint:check
+      - run: npm run build
+
+      # Run Python checks
+      - run: ruff format --check
+      - run: ruff check
+      - run: mypy

.gitignore

@@ -0,0 +1,4 @@
+node_modules/
+/dist/
+__pycache__/
+.mypy_cache/

.prettierrc

@@ -0,0 +1 @@
+{}

CONTRIBUTING.md

@@ -0,0 +1,3 @@
+# Contributing
+
+Not much to say here, yet. There are no tests and the code is not particularly tidy; sorry.

COPYRIGHT

@@ -0,0 +1 @@
+Copyright 2024 Ably Real-time Ltd (ably.com)

LICENSE

@@ -0,0 +1,176 @@
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
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+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
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+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
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+      agreed to in writing, Licensor provides the Work (and each
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+   8. Limitation of Liability. In no event and under no legal theory,
+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
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+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS

MAINTAINERS.md

@@ -0,0 +1 @@
+This repository is owned by the Ably Ecosystems team.

README.md

@@ -0,0 +1,40 @@
+# Interception Proxy
+
+Web service to create proxies for intercepting and manipulating WebSocket traffic between an Ably client library and the Realtime service. Very much a prototype and a work in progress (see the abundant TODOs in the code). The motivation for this work is currently best described by [this internal RFC](https://ably.atlassian.net/wiki/x/IYDItQ).
+
+## Requirements
+
+- Node LTS — I tested on 20
+- Python 3.x — I tested on 3.12.4
+- mitmproxy ([PyPi](https://pypi.org/project/mitmproxy/)) — I tested on 10.3.1
+- websockets ([PyPi](https://pypi.org/project/websockets/)) — I tested on 12.0
+
+## Installation
+
+There are currently no NPM releases of this package, so you’ll need to install it directly from the Git repo:
+
+```bash
+npm install https://github.com/ably-labs/interception-proxy
+```
+
+## Commands
+
+### Setup
+
+- `npx --package interception-proxy generate-mitmproxy-certs`: Generates the mitmproxy TLS certificate, so that you can add it to the trust store used by the process under test.
+
+### Running locally
+
+- `npx interception-proxy`: Starts the interception proxy. Use this when running in a local development environment.
+
+### Running in CI
+
+- `npx --package interception-proxy start-service`: Starts the interception proxy as a background service. Useful for CI. The script uses `sudo` so it’s probably not something you want to use locally.
+
+## JSON-RPC API
+
+See [`docs/API.md`](docs/API.md).
+
+## Examples
+
+Currently the best example of how to use this server is https://github.com/ably/ably-js/pull/1816.

bin/generate-mitmproxy-certs

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+set -e
+
+if [[ -z $BASH_SOURCE ]]
+then
+  echo "This script must be run from a file."
+  exit 1
+fi
+
+# https://mywiki.wooledge.org/BashFAQ/028 for BASH_SOURCE
+#
+# When invoked via NPM, this script is invoked as a symlink in node_modules/.bin, so we use readlink to dereference the symlink (see https://stackoverflow.com/questions/421772/how-can-a-bash-script-know-the-directory-it-is-installed-in-when-it-is-sourced-w)
+mitmdump -s $(dirname $(readlink -f "${BASH_SOURCE}"))/../dist/python/mitmproxy_addon_generate_certs_and_exit.py

bin/interception-proxy

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+#!/usr/bin/env node
+// This is the script which will be run when you run this package via `npx`.
+require("../dist/js/server.js");

bin/start-service

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+#!/usr/bin/env bash
+
+# Runs the server as a background service, exiting once the server is ready to receive requests.
+#
+# Intended for use in SDKs’ CI jobs. Must be run from the root of this repository.
+#
+# Adapted from https://github.com/ably/sdk-test-proxy/blob/82e93a746c0cfaa3f75324e62d57921d14d8591a/start-service.
+
+set -e
+
+# We run as the current user so that we can access the generated server certificate (in ~/.mitmproxy) without having to worry about permissions. TODO consider instead generating our own cert and telling mitmproxy to use it, then we also won’t have to have that step where we run mitmproxy once (via npx interception-proxy generate-mitmproxy-certs) just to generate the certs
+start_systemd_service () {
+  systemd_service=$(cat <<SYSTEMD_SERVICE
+[Unit]
+Description=Ably SDK Test Proxy
+
+[Service]
+WorkingDirectory=$(pwd)
+ExecStart=npx interception-proxy
+User=$USER
+
+[Install]
+WantedBy=multi-user.target
+SYSTEMD_SERVICE
+)
+
+  # https://stackoverflow.com/questions/84882/sudo-echo-something-etc-privilegedfile-doesnt-work
+  echo "${systemd_service}" | sudo tee /etc/systemd/system/ably-sdk-test-proxy.service 1>/dev/null
+
+  echo "Starting ably-sdk-test-proxy systemd service..." 1>&2
+  sudo systemctl start ably-sdk-test-proxy.service
+  echo "Started ably-sdk-test-proxy systemd service." 1>&2
+}
+
+start_launchd_daemon () {
+  launchd_daemon=$(cat <<LAUNCHD_DAEMON
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+    <key>Label</key>
+    <string>com.ably.test.proxy</string>
+    <key>WorkingDirectory</key>
+    <string>$(pwd)</string>
+    <key>ProgramArguments</key>
+    <array>
+        <string>npx</string>
+        <string>interception-proxy</string>
+    </array>
+    <key>RunAtLoad</key>
+    <true/>
+</dict>
+</plist>
+LAUNCHD_DAEMON
+)
+
+  # https://stackoverflow.com/questions/84882/sudo-echo-something-etc-privilegedfile-doesnt-work
+  echo "${launchd_daemon}" | sudo tee /Library/LaunchDaemons/com.ably.test.proxy.plist
+
+  echo "Loading ably-sdk-test-proxy launchd daemon..." 1>&2
+  sudo launchctl load /Library/LaunchDaemons/com.ably.test.proxy.plist
+  echo "Loaded ably-sdk-test-proxy launchd daemon." 1>&2
+}
+
+check_daemon_still_running () {
+  if uname | grep Linux 1>/dev/null
+  then
+    systemctl is-active --quiet ably-sdk-test-proxy.service
+  elif uname | grep Darwin 1>/dev/null
+  then
+    launchctl print system/com.ably.test.proxy 1>/dev/null
+  fi
+}
+
+if uname | grep Linux 1>/dev/null
+then
+  start_systemd_service
+elif uname | grep Darwin 1>/dev/null
+then
+  start_launchd_daemon
+else
+  echo "Unsupported system $(uname); exiting" 1>&2
+  exit 1
+fi
+
+echo "Waiting for sdk-test-proxy server to start on port 8001..." 1>&2
+
+# https://stackoverflow.com/questions/27599839/how-to-wait-for-an-open-port-with-netcat
+while ! nc -z localhost 8001; do
+  # Check that the service hasn’t failed (else we’ll be waiting forever)
+  check_daemon_still_running
+  sleep 0.5
+done
+
+echo "sdk-test-proxy server is now listening on port 8001." 1>&2