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readable_stream_from_reader.ts
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readable_stream_from_reader.ts
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// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
import { DEFAULT_CHUNK_SIZE } from "./_common.ts";
import type { Closer, Reader } from "../types.d.ts";
function isCloser(value: unknown): value is Closer {
return typeof value === "object" && value != null && "close" in value &&
// deno-lint-ignore no-explicit-any
typeof (value as Record<string, any>)["close"] === "function";
}
export interface ReadableStreamFromReaderOptions {
/** If the `reader` is also a `Closer`, automatically close the `reader`
* when `EOF` is encountered, or a read error occurs.
*
* @default {true}
*/
autoClose?: boolean;
/** The size of chunks to allocate to read, the default is ~16KiB, which is
* the maximum size that Deno operations can currently support. */
chunkSize?: number;
/** The queuing strategy to create the `ReadableStream` with. */
strategy?: { highWaterMark?: number | undefined; size?: undefined };
}
/**
* Create a `ReadableStream<Uint8Array>` from a `Reader`.
*
* When the pull algorithm is called on the stream, a chunk from the reader
* will be read. When `null` is returned from the reader, the stream will be
* closed along with the reader (if it is also a `Closer`).
*
* An example converting a `Deno.FsFile` into a readable stream:
*
* ```ts
* import { readableStreamFromReader } from "https://deno.land/std@$STD_VERSION/streams/readable_stream_from_reader.ts";
*
* const file = await Deno.open("./file.txt", { read: true });
* const fileStream = readableStreamFromReader(file);
* ```
*/
export function readableStreamFromReader(
reader: Reader | (Reader & Closer),
options: ReadableStreamFromReaderOptions = {},
): ReadableStream<Uint8Array> {
const {
autoClose = true,
chunkSize = DEFAULT_CHUNK_SIZE,
strategy,
} = options;
return new ReadableStream({
async pull(controller) {
const chunk = new Uint8Array(chunkSize);
try {
const read = await reader.read(chunk);
if (read === null) {
if (isCloser(reader) && autoClose) {
reader.close();
}
controller.close();
return;
}
controller.enqueue(chunk.subarray(0, read));
} catch (e) {
controller.error(e);
if (isCloser(reader)) {
reader.close();
}
}
},
cancel() {
if (isCloser(reader) && autoClose) {
reader.close();
}
},
}, strategy);
}