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1f2c92c7c8
Because many Reader/Writer implementations (e.g. bufio) assume their able to use subarray() with byte indexes and often ask for byte values, it makes sense to simply restrict all implementations to Uint8Array.
224 lines
7.3 KiB
TypeScript
224 lines
7.3 KiB
TypeScript
// This code has been ported almost directly from Go's src/bytes/buffer.go
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// Copyright 2009 The Go Authors. All rights reserved. BSD license.
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// https://github.com/golang/go/blob/master/LICENSE
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//import * as io from "./io";
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import { Reader, Writer, ReadResult } from "./io";
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import { assert } from "./util";
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import { TextDecoder } from "./text_encoding";
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// MIN_READ is the minimum ArrayBuffer size passed to a read call by
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// buffer.ReadFrom. As long as the Buffer has at least MIN_READ bytes beyond
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// what is required to hold the contents of r, readFrom() will not grow the
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// underlying buffer.
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const MIN_READ = 512;
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const MAX_SIZE = 2 ** 32 - 2;
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// `off` is the offset into `dst` where it will at which to begin writing values
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// from `src`.
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// Returns the number of bytes copied.
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function copyBytes(dst: Uint8Array, src: Uint8Array, off = 0): number {
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const r = dst.byteLength - off;
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if (src.byteLength > r) {
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src = src.subarray(0, r);
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}
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dst.set(src, off);
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return src.byteLength;
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}
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/** A Buffer is a variable-sized buffer of bytes with read() and write()
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* methods. Based on https://golang.org/pkg/bytes/#Buffer
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*/
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export class Buffer implements Reader, Writer {
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private buf: Uint8Array; // contents are the bytes buf[off : len(buf)]
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private off = 0; // read at buf[off], write at buf[buf.byteLength]
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constructor(ab?: ArrayBuffer) {
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if (ab == null) {
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this.buf = new Uint8Array(0);
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} else {
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this.buf = new Uint8Array(ab);
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}
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}
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/** bytes() returns a slice holding the unread portion of the buffer.
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* The slice is valid for use only until the next buffer modification (that
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* is, only until the next call to a method like read(), write(), reset(), or
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* truncate()). The slice aliases the buffer content at least until the next
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* buffer modification, so immediate changes to the slice will affect the
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* result of future reads.
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*/
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bytes(): Uint8Array {
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return this.buf.subarray(this.off);
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}
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/** toString() returns the contents of the unread portion of the buffer
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* as a string. Warning - if multibyte characters are present when data is
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* flowing through the buffer, this method may result in incorrect strings
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* due to a character being split.
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*/
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toString(): string {
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const decoder = new TextDecoder();
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return decoder.decode(this.buf.subarray(this.off));
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}
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/** empty() returns whether the unread portion of the buffer is empty. */
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empty() {
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return this.buf.byteLength <= this.off;
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}
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/** length is a getter that returns the number of bytes of the unread
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* portion of the buffer
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*/
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get length() {
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return this.buf.byteLength - this.off;
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}
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/** Returns the capacity of the buffer's underlying byte slice, that is,
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* the total space allocated for the buffer's data.
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*/
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get capacity(): number {
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return this.buf.buffer.byteLength;
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}
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/** truncate() discards all but the first n unread bytes from the buffer but
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* continues to use the same allocated storage. It throws if n is negative or
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* greater than the length of the buffer.
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*/
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truncate(n: number): void {
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if (n === 0) {
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this.reset();
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return;
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}
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if (n < 0 || n > this.length) {
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throw Error("bytes.Buffer: truncation out of range");
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}
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this._reslice(this.off + n);
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}
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/** reset() resets the buffer to be empty, but it retains the underlying
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* storage for use by future writes. reset() is the same as truncate(0)
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*/
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reset(): void {
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this._reslice(0);
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this.off = 0;
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}
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/** _tryGrowByReslice() is a version of grow for the fast-case
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* where the internal buffer only needs to be resliced. It returns the index
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* where bytes should be written and whether it succeeded.
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* It returns -1 if a reslice was not needed.
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*/
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private _tryGrowByReslice(n: number): number {
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const l = this.buf.byteLength;
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if (n <= this.capacity - l) {
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this._reslice(l + n);
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return l;
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}
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return -1;
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}
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private _reslice(len: number): void {
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assert(len <= this.buf.buffer.byteLength);
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this.buf = new Uint8Array(this.buf.buffer, 0, len);
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}
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/** read() reads the next len(p) bytes from the buffer or until the buffer
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* is drained. The return value n is the number of bytes read. If the
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* buffer has no data to return, eof in the response will be true.
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*/
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async read(p: Uint8Array): Promise<ReadResult> {
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if (this.empty()) {
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// Buffer is empty, reset to recover space.
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this.reset();
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if (p.byteLength === 0) {
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// TODO This edge case should be tested by porting TestReadEmptyAtEOF
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// from the Go tests.
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return { nread: 0, eof: false };
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}
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return { nread: 0, eof: true };
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}
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const nread = copyBytes(p, this.buf.subarray(this.off));
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this.off += nread;
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return { nread, eof: false };
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}
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async write(p: Uint8Array): Promise<number> {
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const m = this._grow(p.byteLength);
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return copyBytes(this.buf, p, m);
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}
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/** _grow() grows the buffer to guarantee space for n more bytes.
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* It returns the index where bytes should be written.
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* If the buffer can't grow it will throw with ErrTooLarge.
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*/
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private _grow(n: number): number {
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const m = this.length;
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// If buffer is empty, reset to recover space.
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if (m === 0 && this.off !== 0) {
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this.reset();
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}
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// Fast: Try to grow by means of a reslice.
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const i = this._tryGrowByReslice(n);
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if (i >= 0) {
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return i;
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}
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const c = this.capacity;
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if (n <= Math.floor(c / 2) - m) {
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// We can slide things down instead of allocating a new
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// ArrayBuffer. We only need m+n <= c to slide, but
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// we instead let capacity get twice as large so we
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// don't spend all our time copying.
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copyBytes(this.buf, this.buf.subarray(this.off));
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} else if (c > MAX_SIZE - c - n) {
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throw Error("ErrTooLarge"); // TODO DenoError(TooLarge)
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} else {
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// Not enough space anywhere, we need to allocate.
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const buf = new Uint8Array(2 * c + n);
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copyBytes(buf, this.buf.subarray(this.off));
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this.buf = buf;
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}
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// Restore this.off and len(this.buf).
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this.off = 0;
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this._reslice(m + n);
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return m;
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}
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/** grow() grows the buffer's capacity, if necessary, to guarantee space for
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* another n bytes. After grow(n), at least n bytes can be written to the
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* buffer without another allocation. If n is negative, grow() will panic. If
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* the buffer can't grow it will throw ErrTooLarge.
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* Based on https://golang.org/pkg/bytes/#Buffer.Grow
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*/
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grow(n: number): void {
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if (n < 0) {
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throw Error("Buffer.grow: negative count");
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}
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const m = this._grow(n);
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this._reslice(m);
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}
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/** readFrom() reads data from r until EOF and appends it to the buffer,
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* growing the buffer as needed. It returns the number of bytes read. If the
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* buffer becomes too large, readFrom will panic with ErrTooLarge.
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* Based on https://golang.org/pkg/bytes/#Buffer.ReadFrom
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*/
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async readFrom(r: Reader): Promise<number> {
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let n = 0;
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while (true) {
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try {
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const i = this._grow(MIN_READ);
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this._reslice(i);
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const fub = new Uint8Array(this.buf.buffer, i);
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const { nread, eof } = await r.read(fub);
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this._reslice(i + nread);
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n += nread;
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if (eof) {
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return n;
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}
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} catch (e) {
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return n;
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}
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}
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}
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}
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