Request cancellation mechanism similar to the browser's AbortController API.

This module provides a way to abort in-flight HTTP requests using an Agent-based controller. It's designed to work with the HTTP.fetch/2 function via the :signal option.

How It Works

1. Create an AbortController before making the request
2. Pass the controller to HTTP.fetch/2 via the :signal option
3. Call abort/1 on the controller to cancel the request
4. The awaiting Promise will receive an error result

Basic Usage

# Create a controller
controller = HTTP.AbortController.new()

# Start a long-running request with the controller
promise = HTTP.fetch("https://httpbin.org/delay/10",
  signal: controller,
  options: [timeout: 20_000]
)

# Abort the request (e.g., after 2 seconds)
:timer.sleep(2000)
HTTP.AbortController.abort(controller)

# The awaited promise will return an error
case HTTP.Promise.await(promise) do
  {:error, reason} ->
    IO.puts("Request was aborted: " <> inspect(reason))
  response ->
    IO.puts("Request completed before abort")
end

Advanced Usage

# Abort from another process
controller = HTTP.AbortController.new()

# Start request in background
Task.start(fn ->
  promise = HTTP.fetch("https://slow-api.example.com", signal: controller)
  result = HTTP.Promise.await(promise)
  IO.inspect(result)
end)

# Abort from main process after some condition
:timer.sleep(1000)
if some_condition?() do
  HTTP.AbortController.abort(controller)
end

Implementation Details

• Uses Elixir's Agent for state management
• Registers with a Registry for process tracking
• Calls :httpc.cancel_request/1 internally to abort the request
• Thread-safe and can be called from any process
• Idempotent - calling abort/1 multiple times is safe

State Management

The controller maintains the following state:

• request_id - PID of the active :httpc request (set automatically)
• signal_ref - Unique reference for registry lookup
• aborted - Boolean flag indicating abort status