feat(std/io): add fromStreamReader, fromStreamWriter (#5789)

2 files changed, 168 insertions, 0 deletions

diff --git a/std/io/streams.ts b/std/io/streams.ts
new file mode 100644
index 000000000..3969746ef
--- /dev/null
+++ b/std/io/streams.ts
@@ -0,0 +1,34 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+
+export function fromStreamWriter(
+  streamWriter: WritableStreamDefaultWriter<Uint8Array>
+): Deno.Writer {
+  return {
+    async write(p: Uint8Array): Promise<number> {
+      await streamWriter.ready;
+      await streamWriter.write(p);
+      return p.length;
+    },
+  };
+}
+
+export function fromStreamReader(
+  streamReader: ReadableStreamDefaultReader<Uint8Array>
+): Deno.Reader {
+  const buffer = new Deno.Buffer();
+
+  return {
+    async read(p: Uint8Array): Promise<number | null> {
+      if (buffer.empty()) {
+        const res = await streamReader.read();
+        if (res.done) {
+          return null; // EOF
+        }
+
+        await Deno.writeAll(buffer, res.value);
+      }
+
+      return buffer.read(p);
+    },
+  };
+}
diff --git a/std/io/streams_test.ts b/std/io/streams_test.ts
new file mode 100644
index 000000000..00d056e2f
--- /dev/null
+++ b/std/io/streams_test.ts
@@ -0,0 +1,134 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+
+import { assertEquals, assert } from "../testing/asserts.ts";
+import { fromStreamWriter, fromStreamReader } from "./streams.ts";
+
+function repeat(c: string, bytes: number): Uint8Array {
+  assertEquals(c.length, 1);
+  const ui8 = new Uint8Array(bytes);
+  ui8.fill(c.charCodeAt(0));
+  return ui8;
+}
+
+Deno.test("toWriterCheck", async function (): Promise<void> {
+  const written: string[] = [];
+  const chunks: string[] = ["hello", "deno", "land"];
+  const writableStream = new WritableStream({
+    write(chunk): void {
+      const decoder = new TextDecoder();
+      written.push(decoder.decode(chunk));
+    },
+  });
+
+  const encoder = new TextEncoder();
+  const writer = fromStreamWriter(writableStream.getWriter());
+
+  for (const chunk of chunks) {
+    const n = await writer.write(encoder.encode(chunk));
+    // stream writers always write all the bytes
+    assertEquals(n, chunk.length);
+  }
+
+  assertEquals(written, chunks);
+});
+
+Deno.test("toReaderCheck", async function (): Promise<void> {
+  const chunks: string[] = ["hello", "deno", "land"];
+  const expected = chunks.slice();
+  const readChunks: Uint8Array[] = [];
+  const readableStream = new ReadableStream({
+    pull(controller): void {
+      const encoder = new TextEncoder();
+      const chunk = chunks.shift();
+      if (!chunk) return controller.close();
+      controller.enqueue(encoder.encode(chunk));
+    },
+  });
+
+  const decoder = new TextDecoder();
+  const reader = fromStreamReader(readableStream.getReader());
+
+  let i = 0;
+
+  while (true) {
+    const b = new Uint8Array(1024);
+    const n = await reader.read(b);
+
+    if (n === null) break;
+
+    readChunks.push(b.subarray(0, n));
+    assert(i < expected.length);
+
+    i++;
+  }
+
+  assertEquals(
+    expected,
+    readChunks.map((chunk) => decoder.decode(chunk))
+  );
+});
+
+Deno.test("toReaderBigChunksCheck", async function (): Promise<void> {
+  const bufSize = 1024;
+  const chunkSize = 3 * bufSize;
+  const writer = new Deno.Buffer();
+
+  // A readable stream can enqueue chunks bigger than Copy bufSize
+  // Reader returned by toReader should enqueue exceeding bytes
+  const chunks: string[] = [
+    "a".repeat(chunkSize),
+    "b".repeat(chunkSize),
+    "c".repeat(chunkSize),
+  ];
+  const expected = chunks.slice();
+  const readableStream = new ReadableStream({
+    pull(controller): void {
+      const encoder = new TextEncoder();
+      const chunk = chunks.shift();
+      if (!chunk) return controller.close();
+
+      controller.enqueue(encoder.encode(chunk));
+    },
+  });
+
+  const reader = fromStreamReader(readableStream.getReader());
+  const n = await Deno.copy(reader, writer, { bufSize });
+
+  const expectedWritten = chunkSize * expected.length;
+  assertEquals(n, chunkSize * expected.length);
+  assertEquals(writer.length, expectedWritten);
+});
+
+Deno.test("toReaderBigIrregularChunksCheck", async function (): Promise<void> {
+  const bufSize = 1024;
+  const chunkSize = 3 * bufSize;
+  const writer = new Deno.Buffer();
+
+  // A readable stream can enqueue chunks bigger than Copy bufSize
+  // Reader returned by toReader should enqueue exceeding bytes
+  const chunks: Uint8Array[] = [
+    repeat("a", chunkSize),
+    repeat("b", chunkSize + 253),
+    repeat("c", chunkSize + 8),
+  ];
+  const expected = new Uint8Array(
+    chunks
+      .slice()
+      .map((chunk) => [...chunk])
+      .flat()
+  );
+  const readableStream = new ReadableStream({
+    pull(controller): void {
+      const chunk = chunks.shift();
+      if (!chunk) return controller.close();
+
+      controller.enqueue(chunk);
+    },
+  });
+
+  const reader = fromStreamReader(readableStream.getReader());
+
+  const n = await Deno.copy(reader, writer, { bufSize });
+  assertEquals(n, expected.length);
+  assertEquals(expected, writer.bytes());
+});