Add simpler reading methods to Blob interface. #117

mkruisselbrink · 2019-03-07T00:49:11Z

This fixes #40

For now this just more or less copies the hand-wavy text of "perform a read operation". We'll need to better specify what actually reading from a blob does. Separately in a follow-up I would also like to rephrase the existing FileReader/FileReaderSync spec text in terms of readable stream operations, being much more precise when and how state is updated and events are queued.

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mkruisselbrink · 2019-03-07T00:49:30Z

@annevk would you mind taking a look at this?

annevk

Thanks for working on this!

index.bs

annevk · 2019-03-07T09:08:34Z

index.bs

+    1. [=ReadableStream/Enqueue=] |bytes| into |stream|.
+
+    Issue: We need to specify more concretely what reading from a Blob actually does, and what
+    possible errors can happen.


Yeah, and how large is a chunk? Is there some POSIX operation we can hint at?

Not sure if size of chunks is ever going to really matter, as that shouldn't really be observable anyway... These new methods only return the whole stream in one go anyway, and while the existing FileReader methods do give you progress events those are more time-limited (with the same ~50ms as used by XHR) rather than directly tied to chunks that are pushed in the stream. And I expect this always to be somewhat hand-wavy, but at least I hope to have one place that describes how to get a ReadableStream out of a blob, and then the rest of the spec can just use that stream and not have any hand-waving or ambiguities... This "algorithm" at least doesn't seem worse than the current defintion of read operations.

Well, the stream() method gives you incremental access, right? I was interested in that.

Good point, yeah. Not sure what we can helpfully say about chunk sizes though... What does fetch do for example? Especially when a response is read from the http cache it seems like that is sort of a similar situation as this one? Does it specify anything about how the body is streamed?

It uses https://fetch.spec.whatwg.org/#concept-read-chunk-from-readablestream. As I mentioned in the other issue though there are some problems with how the construct works.

No, that is for reading chunks from the stream. The bit I can't find is how it is specified what chunks you're going to get out of a stream. I.e. if you call (await fetch('....')).body, and read from that. I don't think it is specified what those chunks are either? I can imagine if the fetch hit the network it would depend on what the server returns, but if it is loaded from the cache it is less clear. Fetch just seems to link to https://tools.ietf.org/html/rfc7234#section-4 for how the Response (and its body) are created when loaded from the cache, but also doesn't mention anything about chunk size etc.

Ah sorry, see step 13 of https://fetch.spec.whatwg.org/#http-network-fetch. It basically waits for a number of bytes to arrive and then enqueues a Uint8Array. That's probably what you want to mimic to some extent, until there's better infra.

index.bs

mkruisselbrink · 2019-03-12T22:43:48Z

(of course this will need tests before landing as well)

This fixes #40

mkruisselbrink · 2019-03-15T21:47:53Z

Okay, rebased this on top of the FileReader changes.

annevk

Looks good to me % nits. With tests and implementation bugs this'll be a great addition to the platform. Hopefully everyone picks it up quickly.

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Jamesernator · 2019-03-22T06:07:14Z

Any possibility of including .dataURL() as well?

annevk · 2019-03-22T08:46:22Z

@Jamesernator let's track that separately.

mkruisselbrink · 2019-03-26T16:53:29Z

Tests are in progress in https://chromium-review.googlesource.com/c/chromium/src/+/1526796.

Implementation bugs: Chromium, WebKit, FireFox

jarryd999 · 2019-04-04T23:13:38Z

Hey @annevk, do you think Mozilla will implement this soon? I'm filing the Intent to Implement/Ship for blink and I'd like to accurately represent Mozilla's stance.

annevk · 2019-04-05T08:17:25Z

I can't really comment on a timeline, but we're supportive of these methods being added to the web platform.

jimmywarting · 2019-04-06T00:40:09Z

Any possibility of including .dataURL() as well?

I would suggest using URL.createObjectURL(blob) instead of using a base64 string
if you want to upload/save a file you should send it as a binary

base64 is ~3x larger

Broken by w3c#117

Broken by #117

jimmywarting · 2019-04-16T11:45:53Z

Should the FileReader change how it gets the stream?

- Should Let stream be the result of calling get stream on blob .
+ Should Let stream be the result of calling blob.stream()

That would make fileReader a self contained module and it dosen't have to have any internal access to blobs private methods

annevk · 2019-04-16T11:54:19Z

@jimmywarting please file a new issue if you feel strongly, but generally we don't use that pattern to describe platform objects. If someone were to modify Blob.prototype.stream it shouldn't affect FileReader. It would actually add quite some complexity as we'd have to handle all the exceptional cases that might arise from such a setup.

jimmywarting · 2019-04-16T13:33:11Z

hmm okey, will stay on the fence. will trust that you know what is best

annevk · 2019-04-16T13:54:41Z

@jimmywarting happy to discuss this further somewhere somehow. It kinda falls out of IDL and how browsers implement platform objects. https://annevankesteren.nl/2015/01/javascript-web-platform explains some of this, but doesn't really go into why we try to avoid invoking JavaScript once we cross the IDL boundary.

annevk reviewed Mar 7, 2019

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mkruisselbrink force-pushed the blob-to-stream branch from bd36b34 to e5aea2f Compare March 8, 2019 22:58

mkruisselbrink added 4 commits March 15, 2019 14:14

Add simpler reading methods to Blob interface.

26bf46a

This fixes #40

fix typo

b997a56

Address some comments.

d0b650a

Rebase to match FileReader changes.

1b65277

mkruisselbrink force-pushed the blob-to-stream branch from e5aea2f to 1b65277 Compare March 15, 2019 21:14

annevk approved these changes Mar 16, 2019

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Address last few comments

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mkruisselbrink mentioned this pull request Mar 26, 2019

Additional reading methods on Blob and File w3ctag/design-reviews#359

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5 tasks

jarryd999 mentioned this pull request Apr 6, 2019

Add simpler reading methods to Blob interface. w3ctag/design-reviews#363

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5 tasks

annevk mentioned this pull request Apr 8, 2019

Add method to read file into user given Uint8Array #83

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mkruisselbrink merged commit b0fa7ef into master Apr 12, 2019

annevk deleted the blob-to-stream branch April 13, 2019 07:39

foolip added a commit to foolip/FileAPI that referenced this pull request Apr 13, 2019

Fix escaping that doesn't work in <xmp>

1e7c394

Broken by w3c#117

foolip mentioned this pull request Apr 13, 2019

Fix escaping that doesn't work in <xmp> #127

Merged

mkruisselbrink pushed a commit that referenced this pull request Apr 13, 2019

Fix escaping that doesn't work in <xmp> (#127)

427cdb2

Broken by #117

jimmywarting mentioned this pull request Apr 15, 2019

Implement Blob.stream, Blob.text and Blob.arrayBuffer jsdom/jsdom#2555

Open

jimmywarting mentioned this pull request Aug 8, 2019

added new blob reading methods mdn/browser-compat-data#4581

Merged

saschanaz mentioned this pull request Sep 27, 2019

General type updates microsoft/TypeScript-DOM-lib-generator#762

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fisker mentioned this pull request May 13, 2021

Rule proposal: prefer-blob-reading-methods sindresorhus/eslint-plugin-unicorn#1269

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yvele mentioned this pull request Jul 25, 2023

Is Blob arrayBuffer() method being polyfilled? zloirock/core-js#1273

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Add simpler reading methods to Blob interface. #117

Add simpler reading methods to Blob interface. #117

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Add simpler reading methods to Blob interface. #117

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