1 files changed, 241 insertions, 0 deletions
diff --git a/runtime/js/13_buffer.js b/runtime/js/13_buffer.js
new file mode 100644
index 000000000..e06e2138b
--- /dev/null
+++ b/runtime/js/13_buffer.js
@@ -0,0 +1,241 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+
+// 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
+
+((window) => {
+  const { assert } = window.__bootstrap.util;
+
+  // 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 = 32 * 1024;
+  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(src, dst, off = 0) {
+    const r = dst.byteLength - off;
+    if (src.byteLength > r) {
+      src = src.subarray(0, r);
+    }
+    dst.set(src, off);
+    return src.byteLength;
+  }
+
+  class Buffer {
+    #buf = null; // contents are the bytes buf[off : len(buf)]
+    #off = 0; // read at buf[off], write at buf[buf.byteLength]
+
+    constructor(ab) {
+      if (ab == null) {
+        this.#buf = new Uint8Array(0);
+        return;
+      }
+
+      this.#buf = new Uint8Array(ab);
+    }
+
+    bytes(options = { copy: true }) {
+      if (options.copy === false) return this.#buf.subarray(this.#off);
+      return this.#buf.slice(this.#off);
+    }
+
+    empty() {
+      return this.#buf.byteLength <= this.#off;
+    }
+
+    get length() {
+      return this.#buf.byteLength - this.#off;
+    }
+
+    get capacity() {
+      return this.#buf.buffer.byteLength;
+    }
+
+    truncate(n) {
+      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) => {
+      const l = this.#buf.byteLength;
+      if (n <= this.capacity - l) {
+        this.#reslice(l + n);
+        return l;
+      }
+      return -1;
+    };
+
+    #reslice = (len) => {
+      assert(len <= this.#buf.buffer.byteLength);
+      this.#buf = new Uint8Array(this.#buf.buffer, 0, len);
+    };
+
+    readSync(p) {
+      if (this.empty()) {
+        // Buffer is empty, reset to recover space.
+        this.reset();
+        if (p.byteLength === 0) {
+          // this edge case is tested in 'bufferReadEmptyAtEOF' test
+          return 0;
+        }
+        return null;
+      }
+      const nread = copyBytes(this.#buf.subarray(this.#off), p);
+      this.#off += nread;
+      return nread;
+    }
+
+    read(p) {
+      const rr = this.readSync(p);
+      return Promise.resolve(rr);
+    }
+
+    writeSync(p) {
+      const m = this.#grow(p.byteLength);
+      return copyBytes(p, this.#buf, m);
+    }
+
+    write(p) {
+      const n = this.writeSync(p);
+      return Promise.resolve(n);
+    }
+
+    #grow = (n) => {
+      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.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));
+        copyBytes(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;
+    };
+
+    grow(n) {
+      if (n < 0) {
+        throw Error("Buffer.grow: negative count");
+      }
+      const m = this.#grow(n);
+      this.#reslice(m);
+    }
+
+    async readFrom(r) {
+      let n = 0;
+      const tmp = new Uint8Array(MIN_READ);
+      while (true) {
+        const shouldGrow = this.capacity - this.length < MIN_READ;
+        // read into tmp buffer if there's not enough room
+        // otherwise read directly into the internal buffer
+        const buf = shouldGrow
+          ? tmp
+          : new Uint8Array(this.#buf.buffer, this.length);
+
+        const nread = await r.read(buf);
+        if (nread === null) {
+          return n;
+        }
+
+        // write will grow if needed
+        if (shouldGrow) this.writeSync(buf.subarray(0, nread));
+        else this.#reslice(this.length + nread);
+
+        n += nread;
+      }
+    }
+
+    readFromSync(r) {
+      let n = 0;
+      const tmp = new Uint8Array(MIN_READ);
+      while (true) {
+        const shouldGrow = this.capacity - this.length < MIN_READ;
+        // read into tmp buffer if there's not enough room
+        // otherwise read directly into the internal buffer
+        const buf = shouldGrow
+          ? tmp
+          : new Uint8Array(this.#buf.buffer, this.length);
+
+        const nread = r.readSync(buf);
+        if (nread === null) {
+          return n;
+        }
+
+        // write will grow if needed
+        if (shouldGrow) this.writeSync(buf.subarray(0, nread));
+        else this.#reslice(this.length + nread);
+
+        n += nread;
+      }
+    }
+  }
+
+  async function readAll(r) {
+    const buf = new Buffer();
+    await buf.readFrom(r);
+    return buf.bytes();
+  }
+
+  function readAllSync(r) {
+    const buf = new Buffer();
+    buf.readFromSync(r);
+    return buf.bytes();
+  }
+
+  async function writeAll(w, arr) {
+    let nwritten = 0;
+    while (nwritten < arr.length) {
+      nwritten += await w.write(arr.subarray(nwritten));
+    }
+  }
+
+  function writeAllSync(w, arr) {
+    let nwritten = 0;
+    while (nwritten < arr.length) {
+      nwritten += w.writeSync(arr.subarray(nwritten));
+    }
+  }
+
+  window.__bootstrap.buffer = {
+    writeAll,
+    writeAllSync,
+    readAll,
+    readAllSync,
+    Buffer,
+  };
+})(this);