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Summer of Code 2014: Implement XMLHttpRequest

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Josh Matthews edited this page Mar 7, 2014 · 7 revisions

Mentor: Josh Matthews (jdm in #servo on irc.mozilla.org, josh@joshmatthews.net)

Other knowledgeable people: Ms2ger, jgraham in #servo

Project breakdown

This project will focus on synchronous and asynchronous GET and POST requests. There are multiple parts:

  • create a Rust type that implements a very simplified version of the WebIDL interface supporting synchronous requests (the constructor, open, send, status, statusText, responseText)
  • implement a synchronous GET request using something like load_whole_resource in resource_task.rs. Create tests that demonstrate that it works.
  • create a simple test harness that runs a Python HTTP server to allow for automated testing.
  • implement asynchronous GET requests that integrate with the main event loop in script_task.rs (see ScriptMsg)
  • make the Rust XMLHttpRequest type implement the XMLHttpRequestEventTarget interface, focusing on simple events such as onerror and onload to start (see other EventTarget-derived examples such as Window and its associated load event). Dispatch these events based on events received in the ScriptTask event loop.
  • implement readyState and the onreadystatechange event.
  • implement a basic responseType that supports fetching either JSON or plain text
  • implement other APIs such as abort (and onabort), timeout (and ontimeout), setRequestHeader, getResponseHeader, and getAllResponseHeaders
  • assuming that https://github.com/chris-morgan/rust-http/pull/23 is complete, implement a very basic send that supports sending a string as the request content

Throughout this process, find good representative samples of real web sites that use XHR and figure out what is required to make them work correctly. In addition, strive to write tests for each new feature added to the Servo XHR implementation.

Spec: http://xhr.spec.whatwg.org/

Reference: https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest

Gecko's implementation: nsXMLHttpRequest.cpp and nsXMLHttpRequest.h

Suggestions for preparation

  • read DOM code (src/components/script/dom), and understand the relationship between WebIDL interfaces (src/components/script/dom/webidls) and their Rust implementations
  • read code that dispatches DOM events (search for the "load" event in script_task.rs)
  • understand how the ScriptTask event loop interacts with DOM code (see the timer API in window.rs, for example)
  • read code that interacts with the networking stack (see the HTML parser in hubbub_html_parser.rs, for example)
  • understand the rust-http API and how it relates to the needs of XMLHttpRequest
  • gain experience using Rust by solving an easy DOM issue. Please leave a comment saying that you're working on it.
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