I prefer .iterator() for ReadableStream. The amount of data required to fill the 's queue. At least in tests we often check whether something's errored or closed by doing .getReader().closed.then(); we shouldn't break that, I think. I guess my implementation of return should be correct then, thanks! queue. Once the Closes the to which this controller is associated. Releases this reader's lock on the underlying . There's no reason for any consumer to forever hold a lock and not have any way of giving it back, even if the stream is definitely closed. I really look forward to this! Called by user-code to signal that an error has occurred while processing for await syntax. Creates a new ReadableStreamBYOBReader that is locked to the All queued writes will be The text was updated successfully, but these errors were encountered: https://jakearchibald.com/2017/async-iterators-and-generators/#making-streams-iterate - article on this, including basic implementation. to readableStreamBYOBRequest.view. The writableStream.locked property is false by default, and is switched to true while there is an active writer attached to this A TransformStream consists of a and a that Wrapping the async iterator with another async iterator and not forwarding the. If you iterator to the end, should we release the lock for you? The readableStream.locked property is false by default, and is is active. That seems like the most common scenario, and it doesn't make it impossible to get the multi consumer scenario to work. streams, and when using the ReadableStreamBYOBReader, Closes the WritableStream when no additional writes are expected. are connected such that the data written to the WritableStream is received, Pooled Buffer objects are created using Buffer.allocUnsafe(), Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1525852 The Here is the implementation that I currently use to convert a ReadableStream to an async iterator, and it works well enough for what I need from it. I.e., if you break out of a loop, should we assume you'll never want to continue looping from the current point and we should clean up for you? is used to gain access to the ArrayBuffer/TypedArray Creates a new WritableStreamDefaultWriter that is locked to the given ReadableStream's data will be forwarded. true. Every has a controller that is responsible for Chromium: https://bugs.chromium.org/p/chromium/issues/detail?id=929585 and has become the "standard" API for streaming data across many JavaScript https://jakearchibald.com/2017/async-iterators-and-generators/#making-streams-iterate, Add two demos using streams for PNG manipulation, add @@asyncIterator to ReadableStreamDefaultReader, Perf and binary-parse-stream/binary-parser, https://bugs.chromium.org/p/chromium/issues/detail?id=929585, https://bugzilla.mozilla.org/show_bug.cgi?id=1525852, https://bugs.webkit.org/show_bug.cgi?id=194379, getFilesFromPath works in Javascript but not in Typescript, Should the async iterator's return() (which is called, remember, when you break out of a for-await-of loop via return/break/throw) cancel the reader, or just release the lock? The must not be locked (that is, it must not have an existing // successfully without breaking or throwing. implementation for ReadableStreams that are not byte-oriented. method to acquire the async iterator and set the preventCancel option to NodeJS is looking into supporting async iterables as a way to stream data, and it would be great if fetch (or the readable stream part of fetch) supported the same interface. streams. callbacks. active reader). that represents the current read request. object that contains all of the data from all of Not auto-cancelling leads to simpler code when your input has a distinct header and body. Do not pass a pooled object instance in to this method. Appends a new chunk of data to the 's queue. These types of Buffers use a shared underlying Abruptly terminates the WritableStream. break invokes return(), which per the above design will cancel the stream. and provides methods for signaling that the data has Signals that a bytesWritten number of bytes have been written The WHATWG Streams Standard (or "web streams") defines an API for handling pipeline is configured, transform.readable is returned. This Appends a chunk of data to the readable side's queue. Use it as an async iterator that immediately ends. Returns the amount of data remaining to fill the 's I agree with auto-cancel as the default return() behavior. or Buffer.from(), or are often returned by various node:fs module switched to true while there is an active reader consuming the I don't think I favour auto-release. @devsnek has generously volunteered to help with the spec and tests here, and I'm very excited. When called, the will be aborted, I didn't like the sound of auto-cancel, but given @domenic's code example it sounds like the better thing to do. @mcollina see the above comments for API discussion so far. mark. Closes the readable side of the transport and causes the writable side Use a reader to observe that the stream is closed, which it always will be. Releases this writer's lock on the underlying . Returns a pair of new instances to which this I think we should have auto-release. Here they are: You signed in with another tab or window. privacy statement. been provided. Already on GitHub? Summing up some IRC discussion: In a large code base using our own stream->to->async iterator transition we did this and are pretty happy with that as a default. the internal state and management of the stream's queue. closed. The value will be true if the decoding result will include the byte order A instance can be transferred using a . ReadableStream was created). You can break out of the first loop when you get to the end of the header, and then have a second loop which processes the body. to your account, (I'm adding this mostly as a tracking bug after I asked about it in the wrong place). of the TransformStream. ReadableStreamDefaultController is the default controller This is a niche use case, and there's other ways of doing it. pattern that allows for more efficient reading of byte-oriented

@jakearchibald @domenic I would like Node.js Readable to be as close as possible to whatwg Readable when used with for await, i.e. At least in tests we often check whether something's errored or closed by doing, I agree with auto-cancel as the default return() behavior. Uhm, at the moment it's called .getIterator() instead of .iterator(). Then stream[Symbol.asyncIterator] could alias stream.iterator. Is there somewhere we can read up on the justifications and tradeoffs for the pattern node is shipping? I forgot to file implementer bugs yesterday. thrown. the pooled Buffer instances. Unwise. underlyingSource.type set equal to 'bytes' when the By default, calling readableStream.getReader() with no arguments It's an experimental feature that is shipping for the first time in 2 weeks (it will print a warning and notify the users). If you want to rename it, let me know in #980. This would make easier to move code between nodejs and the browser. and returns a promise that is fulfilled with the data once it is The object The TransformStreamDefaultController manages the internal state Pointless. We hope to solicit feedback through a Node.js foundation survey which we hope to send in about a month. reader treats the chunks of data passed through the stream as opaque ReadableStream should be an async iterable, // Might throw if the reader is still locked because we finished. An implementation of the WHATWG Streams Standard. We also do this and find it quite useful. The async iterator will consume the until it terminates. Basically a really obfuscated way of closing a WritableStream. available. Appends a new chunk of data to the 's queue. Creates and returns an async iterator usable for consuming this I think the api should be optimized for single consumer and require a small wrapper for cases where it should not automatically close. Creates and creates a new writer instance that can be used to write The default Signals that the request has been fulfilled with bytes written Creates a new TextEncoderStream instance. values, which allows the to work with generally any A instance can be transferred using a . data into the WritableStream. The utility consumer functions provide common options for consuming the internal state and management of the stream's queue. This is somewhat of an edge case, and just governs what happens if someone tries to acquire a new iterator or lock after iterating to the end. will return an instance of ReadableStreamDefaultReader. Each will receive the But, does anyone think the former would be better? Sign in is used to read the data from the stream. ReadableByteStreamController is for byte-oriented ReadableStreams. Signals to both the readable and writable side that an error has occurred I am wondering whether we should rename .iterator() to .values(), hmm.

One thing that is not obvious, is if we should close the stream when there is a break. byte-oriented s (those that are created with I don't think I ever cancel iterating the stream though, maybe only when throwing an exception in a loop. return, or a throw), the will be closed. Successfully merging a pull request may close this issue.

Connects this to the pair of and The value will be true if decoding errors result in a TypeError being when the underlying stream has been canceled. to be abruptly closed with an error. By default, if the async iterator exits early (via either a break, The Creates a new TextDecoderStream instance. I think it would help defining a best practice on how iterators should be used. same data. stream's data. It is similar to the Node.js Streams API but emerged later Causes the readableStream.locked to be true while the async iterator On the one hand, that seems presumptuous. Mixing iteration with using readers is not something I'd want to encourage. given . JavaScript value. I like. with currently pending writes canceled. I've also been using async iterators with Node streams which have been working well - though I admit a lot less than I'd like to - I have been trying to (as in emailing relevant parties) solicit feedback but haven't been able to get it. After realizing we'd have to make releaseLock() return an empty object, I'm leaning toward the latter. the WritableStream data. During the async iteration, the will be locked. The rest of the time, auto-cancel is cleaner and less error-prone. data from this is written in to transform.writable, The WritableStreamDefaultController manage's the 's This class is now exposed on the global object. Have a question about this project? . Wrapper object seems like a clear winner. canceled with their associated promises rejected. ReadableStream's data. queue. I also agree that it should be auto cancelled and auto closed, as (async) iterators most often are single consumer. stream.iterator(opts). WritableStream. the readableByteStreamController.byobRequest property Wrapping the stream with another stream for the purpose of that iteration and not forwarding cancellation. To prevent This is a @jakearchibald I added AsyncIterators based on what I thought it might make sense for Node.js Streams, we also did a couple of implementations and this turned out to be more performant*. Well occasionally send you account related emails. The WritableStream is a destination to which stream data is sent. A instance can be transferred using a . Get a reader. data that avoids extraneous copying. The ReadableStreamBYOBReader is an alternative consumer for pipeTo or pipeThrough. The amount of data required to fill the readable side's queue. WebKit: https://bugs.webkit.org/show_bug.cgi?id=194379. can have disastrous consequences for your application. Creates a new that is locked to the We can definitely change any part of what I did in implementation before it gets out of experimental (ideally before Node 10 goes LTS in October, but even later if things are in flux). Signals an error that causes the to error and close. streaming data. The encoding supported by the TextDecoderStream instance. Cancels the and returns a promise that is fulfilled Requests the next chunk of data from the underlying WritableStream. Every has a controller that is responsible for Also, it would improve code portability. By clicking Sign up for GitHub, you agree to our terms of service and and potentially transformed, before being pushed into the ReadableStream's Is this API spec'd yet? automatic closing of the , use the readableStream.values() Given the precedent that is somewhat being established in WICG/kv-storage#6, I am wondering whether we should rename .iterator() to .values(), hmm. I think people are likely to see .values() and expect it to be a shortcut for slurping the whole stream. given . Sign up for a free GitHub account to open an issue and contact its maintainers and the community. I'm not sure it's "obvious" that it should cancel the stream, but it's probably better for the common case, and @jakearchibald had a good idea for how we could allow an escape hatch for the uncommon case. Causes the readableStream.locked to be true. the view's underlying ArrayBuffer is detached, invalidating Causes the readableStream.locked to be true while the pipe operation or is passed in to readableStreamBYOBReader.read(), possibly transformed, then pushed to transform.readable. When using ReadableByteStreamController in byte-oriented

Use of this API no longer emit a runtime warning. provides access to a ReadableStreamBYOBRequest instance When a Buffer, , all existing views that may exist on that ArrayBuffer. break invokes return(), which per the above design will cancel the stream. The encoding supported by the TextEncoderStream instance. to a new Buffer, TypedArray, or DataView. that has been provided for the read request to fill, The object supports the async iterator protocol using Could I be involved in the process? It will need to be benchmarked again in the future, V8 is shipping a lot of optimizations for promises, generators and AsyncIterators. There are three primary types of objects: This example creates a simple ReadableStream that pushes the current performance.now() timestamp once every second forever. is active. Assuming we have auto-cancel and auto-close, then there are extremely limited extra capabilities you'd gain from auto-release: Maybe auto-release has some aesthetic benefits I haven't considered. Excellent! Pointless. It is also easy to opt out of even without providing .iterator({ preventCancel: true }) by either: That said, I am not objecting to a .iterator({ preventCancel: true }) just saying that we haven't had to use it in our own code. An async iterable .iterator() is more specific about the functionality it provides. provided in the transform argument such that the internal state. environments. On the other hand, it's kind of annoying to make people manually acquire a new reader and call. while processing the transform data, causing both sides to be abruptly The BYOB is short for "bring your own buffer".
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