Architecture

Fetch exposes several layers for different use cases:

1. Global functions in Fetch\Support\helpers.php provide fetch(), fetch_client(), verb helpers, and streaming helpers.
2. Fetch\Http\Client implements PSR-18 and delegates to a ClientHandler.
3. Fetch\Http\ClientHandler owns Fetch-specific configuration and orchestrates request execution.
4. Request, Response, and StreamedResponse provide PSR-7-compatible message objects and convenience methods.
5. Concerns, cache, middleware, events, retry, testing, and pool classes provide supporting features.

RequestCoordinator owns the buffered lifecycle. RequestBuilder constructs the middleware request; optional validation checks the transformed request before mock, cache, or transport selection. Responses are validated before returning or caching them. RequestExecutor handles synchronous transport; AsyncRequestExecutor uses an injected AsyncTransport. Both use the same RetryStrategy, with Matrix timers providing asynchronous retry delays.

The default GuzzleAsyncTransport pumps cURL multi and Guzzle's promise queue from ReactPHP. PromiseManager composes Matrix operations, while ConnectionPoolManager holds handler configuration for shared pool services. The separate Fetch pool and DNS cache are not wired into transport selection. Guzzle manages connections in the active transport.

StreamingRequestExecutor uses Guzzle's incremental stream handler. Streaming is synchronous and bypasses middleware, validation, mocks, retries, and caching; a configured validation policy raises an explicit configuration exception.

For the source-level map, see CODE_MAP.md. Verify behavior against source and tests when working on implementation details.