Using the Fetch API simplifies and shortens the `downloadFile` function considerably, since among other things it handles redirects[1] by default.
Also, the regular expression in `downloadManifestFiles` can be replaced with a simple string function now.
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[1] Implementations of the Fetch API should already prevent e.g. redirect loops and limit the total number of redirects allowed.
This code already isn't used (or even bundled) in the Firefox PDF Viewer, and it also slightly reduces the number of import maps that need to be maintained.
Currently we have no less than three different, but very similar, factories for reading built-in CMap files, standard font files, and wasm files on the main-thread.[1]
These factories were added at different points in time, since I cannot imagine that we'd add essentially three copies of the same code otherwise.
Nowadays these factories are often not even used[2], since worker-thread fetching is used whenever possible to improve performance. In particular, they will *only* be used when either:
- The PDF.js library runs in Node.js environments.
- The user manually sets `useWorkerFetch = false` when calling `getDocument`.
- The user provides custom `CMapReaderFactory`, `StandardFontDataFactory`, and/or `WasmFactory` instances when calling `getDocument`.
By replacing these factories with *a single* new `BinaryDataFactory` factory/option the number of `getDocument` options are thus reduced, which cannot hurt.
This also reduces the total bundle-size of the Firefox PDF Viewer a little bit, and it slightly reduces the number of import maps that need to be maintained.
*Please note:* For users that provide custom `CMapReaderFactory`, `StandardFontDataFactory`, and `WasmFactory` instances when calling `getDocument` this will be a breaking change, however it's unlikely that (many) such users exist.
(The *internal* format data-format of `CMapReaderFactory` was changed in PR 18951, and there hasn't been a single question/complaint about it in well over a year.)
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[1] Any new functionality could easily lead to more such factories being added in the future, which wouldn't be great.
[2] Note that the Firefox PDF Viewer no longer use these factories, since it "forcibly" sets `useWorkerFetch = true` during building.
The `BaseCMapReaderFactory`, `BaseStandardFontDataFactory`, and `BaseWasmFactory` classes are all very similar, and the only difference is really in their respective `fetch` methods.
By have the worker-thread "compute" the complete `filename` it's possible to simplify the `BaseCMapReaderFactory.prototype.fetch` method, which will allow future improvements to all of these classes.
A couple of things to note:
- This code is unused, and it's not even bundled, in the Firefox PDF Viewer.
- In browsers it's unused by default, and worker-thread fetching will always be used when possible since that's more efficient.
*Please note:* For users that provide a custom `CMapReaderFactory` instance when calling `getDocument` this could be a breaking change, however it's unlikely that any such users exist.
(The *internal* format of this data was changed previously in PR 18951, and there hasn't been a single question/complaint about it in well over a year.)
Given that these classes are only used from the "FetchBinaryData" message handler, the `name`/`filename` parameters should never actually be missing and if they are that's a bug elsewhere in the code-base.
Furthermore a missing `name`/`filename` parameter would result in a "nonsense" URL and the actual data fetching would then fail instead, hence keeping this old validation code just doesn't seem necessary.
