Today we had a monthly meeting with everyone, and it was gooood . Special thanks to Scott for the pep talk! Also, we picked and ate figs from the fig tree by Jeena’s home as a break .
Promise in Fetch
Today was indeed a different day! I started working on implementing the FetchResponseListener. FetchResponseListener is invoked when (I think) the network level fetch gets some data back. For example, a method in FetchResponseListener is process_response, which will update the response object with the data it got back from fetching.
Josh suggested not worrying about the FetchContext, which will be the struct to hold promise and response together, until later. Creating the FetchContext will require a lot of wrappings.
The fetch listener (FetchContext) has to be Arc<Mutex<T>>. Inside FetchContext, there will be response_object with type Response and promise with type Rc<Promise>. Both response_object and promise will need to be wrapped with Trusted to be shared across threads safely. Trusted is a “safe wrapper around a raw pointer to a DOM object”, so response_object and promise can be Trusted<Response> and Trusted<Promise>.
I think response_object should be wrapped wtih DOMRefCell to allow inner mutability, but we shall see. If this is true, response_object will be DOMRefCell<Trusted<Response>>..? Josh said that since FetchResponseListener will be implemented on FetchContext, calling self.response_object.root() will obtain a Root<Response> value in the callbacks that can be manipulated like usual.
promise is Rc<T> so we will need a method that will pull out Rc<T> from Trusted<T>, like self.response_object.root() would.
Body
Wrote step 34 of Request constructor to extract Body contents. The extract body method still doesn’t use ReadableStream so I’m not sure if it will need to be rewritten.
Step 7.3 of Response
Things we learned:
The difference between Mutex types and regular-ol’-mutable-rust-variables. Both only allow mutation of their data one thing at a time, through either & mut or for mutex lock() and unlock(). What makes Mutex special? It is specifically designed for sharing across threads (often used in conjunction with Arc), whereas regular mutable borrow is not. So, only one thread can safely access the same data at one time. On the other hand, regular-ol’-& mut will not be allowed by the borrow checker if you try to use it across threads.
A whole lot about network-level fetch! Network level fetch is the communication with the core resource thread that invokes fetch algorithms, as described in the spec. There are a couple Servo parts that already use the network-level fetch: XMLHttpRequest and script.
Rc<T> is not thread-safe, but Trusted<T> is, like in Trusted<XMLHttpRequest>.
TODO:
Promise in Fetch
make FetchContext struct (on hold)
Impl FetchResponseListener for FetchContext (may require helper functions)
resolve/reject promise in fetch (figure out how to use maybe_reject_error, etc.)
Body
implement the rest of the body interface for dom::Response
. Special thanks to Scott for the pep talk! Also, we picked and ate figs from the fig tree by Jeena’s home as a break 
.