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// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.import { assert } from "../_util/asserts.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 [Go Buffer](https://golang.org/pkg/bytes/#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,  });  get readable() {    return this.#readable;  }  #writable = new WritableStream<Uint8Array>({    write: (chunk) => {      const m = this.#grow(chunk.byteLength);      copy(chunk, this.#buf, m);    },  });  get writable() {    return this.#writable;  }
  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) {    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);  }
  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   * [Buffer.Grow](https://golang.org/pkg/bytes/#Buffer.Grow). */  grow(n: number) {    if (n < 0) {      throw Error("Buffer.grow: negative count");    }    const m = this.#grow(n);    this.#reslice(m);  }}