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std/streams/buffer.ts

Deno standard library
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// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.// This module is browser compatible.
import { assert } from "../assert/assert.ts";import { copy } from "../bytes/copy.ts";
const MAX_SIZE = 2 ** 32 - 2;const DEFAULT_CHUNK_SIZE = 16_640;
/** A variable-sized buffer of bytes with `read()` and `write()` methods. * * Buffer is almost always used with some I/O like files and sockets. It allows * one to buffer up a download from a socket. Buffer grows and shrinks as * necessary. * * Buffer is NOT the same thing as Node's Buffer. Node's Buffer was created in * 2009 before JavaScript had the concept of ArrayBuffers. It's simply a * non-standard ArrayBuffer. * * ArrayBuffer is a fixed memory allocation. Buffer is implemented on top of * ArrayBuffer. * * Based on {@link https://golang.org/pkg/bytes/#Buffer | Go Buffer}. */export class Buffer { #buf: Uint8Array; // contents are the bytes buf[off : len(buf)] #off = 0; // read at buf[off], write at buf[buf.byteLength] #readable: ReadableStream<Uint8Array> = new ReadableStream({ type: "bytes", pull: (controller) => { const view = new Uint8Array(controller.byobRequest!.view!.buffer); if (this.empty()) { // Buffer is empty, reset to recover space. this.reset(); controller.close(); controller.byobRequest!.respond(0); return; } const nread = copy(this.#buf.subarray(this.#off), view); this.#off += nread; controller.byobRequest!.respond(nread); }, autoAllocateChunkSize: DEFAULT_CHUNK_SIZE, });
/** Getter returning the instance's {@linkcode ReadableStream}. */ get readable(): ReadableStream<Uint8Array> { return this.#readable; }
#writable = new WritableStream<Uint8Array>({ write: (chunk) => { const m = this.#grow(chunk.byteLength); copy(chunk, this.#buf, m); }, });
/** Getter returning the instance's {@linkcode WritableStream}. */ get writable(): WritableStream<Uint8Array> { return this.#writable; }
/** Constructs a new instance. */ constructor(ab?: ArrayBufferLike | ArrayLike<number>) { this.#buf = ab === undefined ? new Uint8Array(0) : new Uint8Array(ab); }
/** Returns a slice holding the unread portion of the buffer. * * The slice is valid for use only until the next buffer modification (that * is, only until the next call to a method like `read()`, `write()`, * `reset()`, or `truncate()`). If `options.copy` is false the slice aliases * the buffer content at least until the next buffer modification, so * immediate changes to the slice will affect the result of future reads. */ bytes(options = { copy: true }): Uint8Array { if (options.copy === false) return this.#buf.subarray(this.#off); return this.#buf.slice(this.#off); }
/** Returns whether the unread portion of the buffer is empty. */ empty(): boolean { return this.#buf.byteLength <= this.#off; }
/** A read only number of bytes of the unread portion of the buffer. */ get length(): number { return this.#buf.byteLength - this.#off; }
/** The read only capacity of the buffer's underlying byte slice, that is, * the total space allocated for the buffer's data. */ get capacity(): number { return this.#buf.buffer.byteLength; }
/** * Discards all but the first `n` unread bytes from the buffer but * continues to use the same allocated storage. It throws if `n` is * negative or greater than the length of the buffer. */ truncate(n: number): void { if (n === 0) { this.reset(); return; } if (n < 0 || n > this.length) { throw Error("bytes.Buffer: truncation out of range"); } this.#reslice(this.#off + n); }
/** Resets to an empty buffer. */ reset() { this.#reslice(0); this.#off = 0; }
#tryGrowByReslice(n: number) { const l = this.#buf.byteLength; if (n <= this.capacity - l) { this.#reslice(l + n); return l; } return -1; }
#reslice(len: number) { assert(len <= this.#buf.buffer.byteLength); this.#buf = new Uint8Array(this.#buf.buffer, 0, len); }
#grow(n: number) { const m = this.length; // If buffer is empty, reset to recover space. if (m === 0 && this.#off !== 0) { this.reset(); } // Fast: Try to grow by means of a reslice. const i = this.#tryGrowByReslice(n); if (i >= 0) { return i; } const c = this.capacity; if (n <= Math.floor(c / 2) - m) { // We can slide things down instead of allocating a new // ArrayBuffer. We only need m+n <= c to slide, but // we instead let capacity get twice as large so we // don't spend all our time copying. copy(this.#buf.subarray(this.#off), this.#buf); } else if (c + n > MAX_SIZE) { throw new Error("The buffer cannot be grown beyond the maximum size."); } else { // Not enough space anywhere, we need to allocate. const buf = new Uint8Array(Math.min(2 * c + n, MAX_SIZE)); copy(this.#buf.subarray(this.#off), buf); this.#buf = buf; } // Restore this.#off and len(this.#buf). this.#off = 0; this.#reslice(Math.min(m + n, MAX_SIZE)); return m; }
/** Grows the buffer's capacity, if necessary, to guarantee space for * another `n` bytes. After `.grow(n)`, at least `n` bytes can be written to * the buffer without another allocation. If `n` is negative, `.grow()` will * throw. If the buffer can't grow it will throw an error. * * Based on Go Lang's * {@link https://golang.org/pkg/bytes/#Buffer.Grow | Buffer.Grow}. */ grow(n: number) { if (n < 0) { throw Error("Buffer.grow: negative count"); } const m = this.#grow(n); this.#reslice(m); }}