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.

js/buffer_test.ts

@@ -0,0 +1,185 @@
+// This code has been ported almost directly from Go's src/bytes/buffer_test.go
+// Copyright 2009 The Go Authors. All rights reserved. BSD license.
+// https://github.com/golang/go/blob/master/LICENSE
+import { test, assert, assertEqual } from "./test_util.ts";
+import { Buffer } from "deno";
+
+// N controls how many iterations of certain checks are performed.
+const N = 100;
+let testBytes: Uint8Array | null;
+let testString: string | null;
+
+function init() {
+  if (testBytes == null) {
+    testBytes = new Uint8Array(N);
+    for (let i = 0; i < N; i++) {
+      testBytes[i] = "a".charCodeAt(0) + (i % 26);
+    }
+    const decoder = new TextDecoder();
+    testString = decoder.decode(testBytes);
+  }
+}
+
+function check(buf: Buffer, s: string) {
+  const bytes = buf.bytes();
+  assertEqual(buf.length, bytes.byteLength);
+  const decoder = new TextDecoder();
+  const bytesStr = decoder.decode(bytes);
+  assertEqual(bytesStr, s);
+  assertEqual(buf.length, buf.toString().length);
+  assertEqual(buf.length, s.length);
+}
+
+// Fill buf through n writes of byte slice fub.
+// The initial contents of buf corresponds to the string s;
+// the result is the final contents of buf returned as a string.
+async function fillBytes(
+  buf: Buffer,
+  s: string,
+  n: number,
+  fub: Uint8Array
+): Promise<string> {
+  check(buf, s);
+  for (; n > 0; n--) {
+    let m = await buf.write(fub);
+    assertEqual(m, fub.byteLength);
+    const decoder = new TextDecoder();
+    s += decoder.decode(fub);
+    check(buf, s);
+  }
+  return s;
+}
+
+// Empty buf through repeated reads into fub.
+// The initial contents of buf corresponds to the string s.
+async function empty(buf: Buffer, s: string, fub: Uint8Array): Promise<void> {
+  check(buf, s);
+  while (true) {
+    const r = await buf.read(fub);
+    if (r.nread == 0) {
+      break;
+    }
+    s = s.slice(r.nread);
+    check(buf, s);
+  }
+  check(buf, "");
+}
+
+test(function bufferNewBuffer() {
+  init();
+  const buf = new Buffer(testBytes.buffer as ArrayBuffer);
+  check(buf, testString);
+});
+
+test(async function bufferBasicOperations() {
+  init();
+  let buf = new Buffer();
+  for (let i = 0; i < 5; i++) {
+    check(buf, "");
+
+    buf.reset();
+    check(buf, "");
+
+    buf.truncate(0);
+    check(buf, "");
+
+    let n = await buf.write(testBytes.subarray(0, 1));
+    assertEqual(n, 1);
+    check(buf, "a");
+
+    n = await buf.write(testBytes.subarray(1, 2));
+    assertEqual(n, 1);
+    check(buf, "ab");
+
+    n = await buf.write(testBytes.subarray(2, 26));
+    assertEqual(n, 24);
+    check(buf, testString.slice(0, 26));
+
+    buf.truncate(26);
+    check(buf, testString.slice(0, 26));
+
+    buf.truncate(20);
+    check(buf, testString.slice(0, 20));
+
+    await empty(buf, testString.slice(0, 20), new Uint8Array(5));
+    await empty(buf, "", new Uint8Array(100));
+
+    // TODO buf.writeByte()
+    // TODO buf.readByte()
+  }
+});
+
+test(async function bufferLargeByteWrites() {
+  init();
+  const buf = new Buffer();
+  const limit = 9;
+  for (let i = 3; i < limit; i += 3) {
+    const s = await fillBytes(buf, "", 5, testBytes);
+    await empty(buf, s, new Uint8Array(Math.floor(testString.length / i)));
+  }
+  check(buf, "");
+});
+
+test(async function bufferLargeByteReads() {
+  init();
+  const buf = new Buffer();
+  for (let i = 3; i < 30; i += 3) {
+    const n = Math.floor(testBytes.byteLength / i);
+    const s = await fillBytes(buf, "", 5, testBytes.subarray(0, n));
+    await empty(buf, s, new Uint8Array(testString.length));
+  }
+  check(buf, "");
+});
+
+test(function bufferCapWithPreallocatedSlice() {
+  const buf = new Buffer(new ArrayBuffer(10));
+  assertEqual(buf.capacity, 10);
+});
+
+test(async function bufferReadFrom() {
+  init();
+  const buf = new Buffer();
+  for (let i = 3; i < 30; i += 3) {
+    const s = await fillBytes(
+      buf,
+      "",
+      5,
+      testBytes.subarray(0, Math.floor(testBytes.byteLength / i))
+    );
+    const b = new Buffer();
+    await b.readFrom(buf);
+    const fub = new Uint8Array(testString.length);
+    await empty(b, s, fub);
+  }
+});
+
+function repeat(c: string, bytes: number): Uint8Array {
+  assertEqual(c.length, 1);
+  const ui8 = new Uint8Array(bytes);
+  ui8.fill(c.charCodeAt(0));
+  return ui8;
+}
+
+test(async function bufferTestGrow() {
+  const tmp = new Uint8Array(72);
+  for (let startLen of [0, 100, 1000, 10000, 100000]) {
+    const xBytes = repeat("x", startLen);
+    for (let growLen of [0, 100, 1000, 10000, 100000]) {
+      const buf = new Buffer(xBytes.buffer as ArrayBuffer);
+      // If we read, this affects buf.off, which is good to test.
+      const { nread, eof } = await buf.read(tmp);
+      buf.grow(growLen);
+      const yBytes = repeat("y", growLen);
+      await buf.write(yBytes);
+      // Check that buffer has correct data.
+      assertEqual(
+        buf.bytes().subarray(0, startLen - nread),
+        xBytes.subarray(nread)
+      );
+      assertEqual(
+        buf.bytes().subarray(startLen - nread, startLen - nread + growLen),
+        yBytes
+      );
+    }
+  }
+});