Async WebAssembly compilation was implemented by adding two
bindings: `set_wasm_streaming_callback`, which registered a callback to
be called whenever a streaming wasm compilation was started, and
`wasm_streaming_feed`, which let the JS callback modify the state of the
v8 wasm compiler.
`set_wasm_streaming_callback` cannot currently be implemented as
anything other than a binding, but `wasm_streaming_feed` does not really
need to use anything specific to bindings, and could indeed be
implemented as one or more ops. This PR does that, resulting in a
simplification of the relevant code.
There are three operations on the state of the v8 wasm compiler that
`wasm_streaming_feed` allowed: feeding new bytes into the compiler,
letting it know that there are no more bytes coming from the network,
and aborting the compilation. This PR provides `op_wasm_streaming_feed`
to feed new bytes into the compiler, and `op_wasm_streaming_abort` to
abort the compilation. It doesn't provide an op to let v8 know that the
response is finished, but closing the resource with `Deno.core.close()`
will achieve that.
In the spec, a URL record has an associated "blob URL entry", which for
`blob:` URLs is populated during parsing to contain a reference to the
`Blob` object that backs that object URL. It is this blob URL entry that
the `fetch` API uses to resolve an object URL.
Therefore, since the `Request` constructor parses URL inputs, it will
have an associated blob URL entry which will be used when fetching, even
if the object URL has been revoked since the construction of the
`Request` object. (The `Request` constructor takes the URL as a string
and parses it, so the object URL must be live at the time it is called.)
This PR adds a new `blobFromObjectUrl` JS function (backed by a new
`op_blob_from_object_url` op) that, if the URL is a valid object URL,
returns a new `Blob` object whose parts are references to the same Rust
`BlobPart`s used by the original `Blob` object. It uses this function to
add a new `blobUrlEntry` field to inner requests, which will be `null`
or such a `Blob`, and then uses `Blob.prototype.stream()` as the
response's body. As a result of this, the `blob:` URL resolution from
`op_fetch` is now useless, and has been removed.
The streaming WASM support code inspects the Response object's
Content-Type header but if that was missing, it failed with a fairly
inscrutable "String.prototype.toLowerCase called on null or undefined"
exception. Now it raises a more legible "Invalid WebAssembly content
type" exception.
