Add deno.Buffer (#1121)

Do not confuse this with Node's Buffer. This is a direct port of Go's
bytes.Buffer - it allows buffering of Reader and Writer objects.

1 files changed, 230 insertions, 0 deletions

diff --git a/js/buffer.ts b/js/buffer.ts
new file mode 100644
index 000000000..ca92698d0
--- /dev/null
+++ b/js/buffer.ts
@@ -0,0 +1,230 @@
+// This code has been ported almost directly from Go's src/bytes/buffer.go
+// Copyright 2009 The Go Authors. All rights reserved. BSD license.
+// https://github.com/golang/go/blob/master/LICENSE
+
+//import * as io from "./io";
+import { Reader, Writer, ReadResult } from "./io";
+import { assert } from "./util";
+import { TextDecoder } from "./text_encoding";
+
+// MIN_READ is the minimum ArrayBuffer size passed to a read call by
+// buffer.ReadFrom. As long as the Buffer has at least MIN_READ bytes beyond
+// what is required to hold the contents of r, readFrom() will not grow the
+// underlying buffer.
+const MIN_READ = 512;
+const MAX_SIZE = 2 ** 32 - 2;
+
+// `off` is the offset into `dst` where it will at which to begin writing values
+// from `src`.
+// Returns the number of bytes copied.
+function copyBytes(dst: Uint8Array, src: Uint8Array, off = 0): number {
+  const r = dst.byteLength - off;
+  if (src.byteLength > r) {
+    src = src.subarray(0, r);
+  }
+  dst.set(src, off);
+  return src.byteLength;
+}
+
+/** A Buffer is a variable-sized buffer of bytes with read() and write()
+ * methods. Based on https://golang.org/pkg/bytes/#Buffer
+ */
+export class Buffer implements Reader, Writer {
+  private buf: Uint8Array; // contents are the bytes buf[off : len(buf)]
+  private off = 0; // read at buf[off], write at buf[buf.byteLength]
+
+  constructor(ab?: ArrayBuffer) {
+    if (ab == null) {
+      this.buf = new Uint8Array(0);
+    } else {
+      this.buf = new Uint8Array(ab);
+    }
+  }
+
+  /** bytes() 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()). 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(): Uint8Array {
+    return this.buf.subarray(this.off);
+  }
+
+  /** toString() returns the contents of the unread portion of the buffer
+   * as a string. Warning - if multibyte characters are present when data is
+   * flowing through the buffer, this method may result in incorrect strings
+   * due to a character being split.
+   */
+  toString(): string {
+    const decoder = new TextDecoder();
+    return decoder.decode(this.buf.subarray(this.off));
+  }
+
+  /** empty() returns whether the unread portion of the buffer is empty. */
+  empty() {
+    return this.buf.byteLength <= this.off;
+  }
+
+  /** length is a getter that returns the number of bytes of the unread
+   * portion of the buffer
+   */
+  get length() {
+    return this.buf.byteLength - this.off;
+  }
+
+  /** Returns the 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;
+  }
+
+  /** truncate() 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);
+  }
+
+  /** reset() resets the buffer to be empty, but it retains the underlying
+   * storage for use by future writes. reset() is the same as truncate(0)
+   */
+  reset(): void {
+    this._reslice(0);
+    this.off = 0;
+  }
+
+  /** _tryGrowByReslice() is a version of grow for the fast-case
+   * where the internal buffer only needs to be resliced. It returns the index
+   * where bytes should be written and whether it succeeded.
+   * It returns -1 if a reslice was not needed.
+   */
+  private _tryGrowByReslice(n: number): number {
+    const l = this.buf.byteLength;
+    if (n <= this.capacity - l) {
+      this._reslice(l + n);
+      return l;
+    }
+    return -1;
+  }
+
+  private _reslice(len: number): void {
+    assert(len <= this.buf.buffer.byteLength);
+    this.buf = new Uint8Array(this.buf.buffer, 0, len);
+  }
+
+  /** read() reads the next len(p) bytes from the buffer or until the buffer
+   * is drained. The return value n is the number of bytes read. If the
+   * buffer has no data to return, eof in the response will be true.
+   */
+  async read(p: ArrayBufferView): Promise<ReadResult> {
+    if (!(p instanceof Uint8Array)) {
+      throw Error("Only Uint8Array supported");
+    }
+    if (this.empty()) {
+      // Buffer is empty, reset to recover space.
+      this.reset();
+      if (p.byteLength === 0) {
+        // TODO This edge case should be tested by porting TestReadEmptyAtEOF
+        // from the Go tests.
+        return { nread: 0, eof: false };
+      }
+      return { nread: 0, eof: true };
+    }
+    const nread = copyBytes(p, this.buf.subarray(this.off));
+    this.off += nread;
+    return { nread, eof: false };
+  }
+
+  async write(p: ArrayBufferView): Promise<number> {
+    const m = this._grow(p.byteLength);
+    if (!(p instanceof Uint8Array)) {
+      throw Error("Only Uint8Array supported");
+    }
+    return copyBytes(this.buf, p, m);
+  }
+
+  /** _grow() grows the buffer to guarantee space for n more bytes.
+   * It returns the index where bytes should be written.
+   * If the buffer can't grow it will throw with ErrTooLarge.
+   */
+  private _grow(n: number): 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.
+      copyBytes(this.buf, this.buf.subarray(this.off));
+    } else if (c > MAX_SIZE - c - n) {
+      throw Error("ErrTooLarge"); // TODO DenoError(TooLarge)
+    } else {
+      // Not enough space anywhere, we need to allocate.
+      const buf = new Uint8Array(2 * c + n);
+      copyBytes(buf, this.buf.subarray(this.off));
+      this.buf = buf;
+    }
+    // Restore this.off and len(this.buf).
+    this.off = 0;
+    this._reslice(m + n);
+    return m;
+  }
+
+  /** grow() 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 panic. If
+   * the buffer can't grow it will throw ErrTooLarge.
+   * Based on https://golang.org/pkg/bytes/#Buffer.Grow
+   */
+  grow(n: number): void {
+    if (n < 0) {
+      throw Error("Buffer.grow: negative count");
+    }
+    const m = this._grow(n);
+    this._reslice(m);
+  }
+
+  /** readFrom() reads data from r until EOF and appends it to the buffer,
+   * growing the buffer as needed. It returns the number of bytes read. If the
+   * buffer becomes too large, readFrom will panic with ErrTooLarge.
+   * Based on https://golang.org/pkg/bytes/#Buffer.ReadFrom
+   */
+  async readFrom(r: Reader): Promise<number> {
+    let n = 0;
+    while (true) {
+      try {
+        const i = this._grow(MIN_READ);
+        this._reslice(i);
+        const fub = new Uint8Array(this.buf.buffer, i);
+        const { nread, eof } = await r.read(fub);
+        this._reslice(i + nread);
+        n += nread;
+        if (eof) {
+          return n;
+        }
+      } catch (e) {
+        return n;
+      }
+    }
+  }
+}