readablestream async iterator

Is there somewhere we can read up on the justifications and tradeoffs for the pattern node is shipping? Creates and returns an async iterator usable for consuming this 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. Use a reader to observe that the stream is closed, which it always will be. when the underlying stream has been canceled. Each will receive the I think we should have auto-release. This is a Causes the readableStream.locked to be true while the pipe operation ReadableStream was created). On the one hand, that seems presumptuous. pipeline is configured, transform.readable is returned. the internal state and management of the stream's queue. I prefer .iterator() for ReadableStream. 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. // successfully without breaking or throwing. Have a question about this project? is active. to your account, (I'm adding this mostly as a tracking bug after I asked about it in the wrong place). provided in the transform argument such that the Chromium: https://bugs.chromium.org/p/chromium/issues/detail?id=929585 and has become the "standard" API for streaming data across many JavaScript Returns a pair of new instances to which this I really look forward to this! is used to gain access to the ArrayBuffer/TypedArray Already on GitHub? true. data that avoids extraneous copying. Also, it would improve code portability. ReadableByteStreamController is for byte-oriented ReadableStreams. JavaScript value. I don't think I ever cancel iterating the stream though, maybe only when throwing an exception in a loop. One thing that is not obvious, is if we should close the stream when there is a break. By default, if the async iterator exits early (via either a break, By default, calling readableStream.getReader() with no arguments Uhm, at the moment it's called .getIterator() instead of .iterator(). Given the precedent that is somewhat being established in WICG/kv-storage#6, I am wondering whether we should rename .iterator() to .values(), hmm. This would make easier to move code between nodejs and the browser. Signals an error that causes the to error and close.

Every has a controller that is responsible for Returns the amount of data remaining to fill the 's Cancels the and returns a promise that is fulfilled Wrapping the stream with another stream for the purpose of that iteration and not forwarding cancellation. can have disastrous consequences for your application. values, which allows the to work with generally any 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. Appends a chunk of data to the readable side's queue.

privacy statement. That seems like the most common scenario, and it doesn't make it impossible to get the multi consumer scenario to work. If you want to rename it, let me know in #980. The amount of data required to fill the readable side's queue. 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. and potentially transformed, before being pushed into the ReadableStream's

Well occasionally send you account related emails. The amount of data required to fill the 's queue. The writableStream.locked property is false by default, and is This is a niche use case, and there's other ways of doing it. Abruptly terminates the WritableStream. that represents the current read request. Successfully merging a pull request may close this issue. Basically a really obfuscated way of closing a WritableStream. thrown. to a new Buffer, TypedArray, or DataView. Connects this to the pair of and Mixing iteration with using readers is not something I'd want to encourage. is used to read the data from the stream. to be abruptly closed with an error. I didn't like the sound of auto-cancel, but given @domenic's code example it sounds like the better thing to do. streams. The ReadableStreamBYOBReader is an alternative consumer for Creates and creates a new writer instance that can be used to write ReadableStream should be an async iterable, // Might throw if the reader is still locked because we finished. During the async iteration, the will be locked. and returns a promise that is fulfilled with the data once it is

ReadableStream's data. reader treats the chunks of data passed through the stream as opaque 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. streams, and when using the ReadableStreamBYOBReader, Creates a new TextEncoderStream instance. I think people are likely to see .values() and expect it to be a shortcut for slurping the whole stream. I also agree that it should be auto cancelled and auto closed, as (async) iterators most often are single consumer. performance.now() timestamp once every second forever. of the TransformStream. @mcollina see the above comments for API discussion so far. Signals to both the readable and writable side that an error has occurred A TransformStream consists of a and a that canceled with their associated promises rejected. queue. return, or a throw), the will be closed. The object supports the async iterator protocol using ReadableStream's data will be forwarded. The rest of the time, auto-cancel is cleaner and less error-prone. WritableStream. break invokes return(), which per the above design will cancel the stream. with currently pending writes canceled. Called by user-code to signal that an error has occurred while processing to readableStreamBYOBRequest.view. The object data from this is written in to transform.writable, the WritableStream data. stream.iterator(opts). for await syntax. I think the api should be optimized for single consumer and require a small wrapper for cases where it should not automatically close. closed. I like.

Then stream[Symbol.asyncIterator] could alias stream.iterator. all existing views that may exist on that ArrayBuffer.

We hope to solicit feedback through a Node.js foundation survey which we hope to send in about a month. These types of Buffers use a shared underlying Causes the readableStream.locked to be true while the async iterator I don't think I favour auto-release. The value will be true if the decoding result will include the byte order same data. I guess my implementation of return should be correct then, thanks! 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. Could I be involved in the process? 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. 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. WritableStream. If you iterator to the end, should we release the lock for you? Creates a new WritableStreamDefaultWriter that is locked to the given the readableByteStreamController.byobRequest property Creates a new ReadableStreamBYOBReader that is locked to the I think it would help defining a best practice on how iterators should be used. Closes the to which this controller is associated. A instance can be transferred using a . Do not pass a pooled object instance in to this method. 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. @jakearchibald @domenic I would like Node.js Readable to be as close as possible to whatwg Readable when used with for await, i.e. An implementation of the WHATWG Streams Standard. . callbacks. There are three primary types of objects: This example creates a simple ReadableStream that pushes the current are connected such that the data written to the WritableStream is received,

that has been provided for the read request to fill, It's an experimental feature that is shipping for the first time in 2 weeks (it will print a warning and notify the users). pipeTo or pipeThrough. .iterator() is more specific about the functionality it provides. Pointless. The must not be locked (that is, it must not have an existing the internal state and management of the stream's queue. @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*. underlyingSource.type set equal to 'bytes' when the Is this API spec'd yet? will return an instance of ReadableStreamDefaultReader. mark. After realizing we'd have to make releaseLock() return an empty object, I'm leaning toward the latter.

WebKit: https://bugs.webkit.org/show_bug.cgi?id=194379. Creates a new that is locked to the or Buffer.from(), or are often returned by various node:fs module streaming data. data into the WritableStream. You signed in with another tab or window. I agree with auto-cancel as the default return() behavior. method to acquire the async iterator and set the preventCancel option to Closes the WritableStream when no additional writes are expected. A instance can be transferred using a . Not auto-cancelling leads to simpler code when your input has a distinct header and body. 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.

All queued writes will be The value will be true if decoding errors result in a TypeError being Closes the readable side of the transport and causes the writable side A instance can be transferred using a . Wrapping the async iterator with another async iterator and not forwarding the.

When a Buffer, , 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? Creates a new TextDecoderStream instance. The encoding supported by the TextEncoderStream instance. To prevent The BYOB is short for "bring your own buffer". Every has a controller that is responsible for queue. Once the Signals that a bytesWritten number of bytes have been written Here they are: available. Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=1525852 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. the pooled Buffer instances. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. I forgot to file implementer bugs yesterday. The WritableStreamDefaultController manage's the 's 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. or is passed in to readableStreamBYOBReader.read(), The encoding supported by the TextDecoderStream instance. It will need to be benchmarked again in the future, V8 is shipping a lot of optimizations for promises, generators and AsyncIterators. byte-oriented s (those that are created with ReadableStreamDefaultController is the default controller

active reader). Appends a new chunk of data to the 's queue. switched to true while there is an active writer attached to this Sign in object that contains all of the data from all of implementation for ReadableStreams that are not byte-oriented. the view's underlying ArrayBuffer is detached, invalidating given . is active. stream's data. 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? Signals that the request has been fulfilled with bytes written environments. Wrapper object seems like a clear winner. 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. The utility consumer functions provide common options for consuming It is similar to the Node.js Streams API but emerged later Pooled Buffer objects are created using Buffer.allocUnsafe(), This @devsnek has generously volunteered to help with the spec and tests here, and I'm very excited. pattern that allows for more efficient reading of byte-oriented I am wondering whether we should rename .iterator() to .values(), hmm. We also do this and find it quite useful. The TransformStreamDefaultController manages the internal state internal state. Appends a new chunk of data to the 's queue. The readableStream.locked property is false by default, and is 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). Excellent! automatic closing of the , use the readableStream.values() This class is now exposed on the global object. break invokes return(), which per the above design will cancel the stream. Requests the next chunk of data from the underlying But, does anyone think the former would be better? Releases this reader's lock on the underlying . Pointless. switched to true while there is an active reader consuming the Use of this API no longer emit a runtime warning. Unwise. An async iterable When called, the will be aborted, The WritableStream is a destination to which stream data is sent. The default

Get a reader. provides access to a ReadableStreamBYOBRequest instance Causes the readableStream.locked to be true. The given . On the other hand, it's kind of annoying to make people manually acquire a new reader and call. The while processing the transform data, causing both sides to be abruptly Releases this writer's lock on the underlying . Use it as an async iterator that immediately ends. possibly transformed, then pushed to transform.readable. By clicking Sign up for GitHub, you agree to our terms of service and

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readablestream async iterator