1 files changed, 122 insertions, 0 deletions
diff --git a/remote/domains/parent/IO.jsm b/remote/domains/parent/IO.jsm
new file mode 100644
index 0000000000..c6213cf862
--- /dev/null
+++ b/remote/domains/parent/IO.jsm
@@ -0,0 +1,122 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+var EXPORTED_SYMBOLS = ["IO", "streamRegistry"];
+
+const { XPCOMUtils } = ChromeUtils.import(
+  "resource://gre/modules/XPCOMUtils.jsm"
+);
+
+XPCOMUtils.defineLazyModuleGetters(this, {
+  OS: "resource://gre/modules/osfile.jsm",
+});
+
+const { Domain } = ChromeUtils.import(
+  "chrome://remote/content/domains/Domain.jsm"
+);
+const { StreamRegistry } = ChromeUtils.import(
+  "chrome://remote/content/StreamRegistry.jsm"
+);
+
+const DEFAULT_CHUNK_SIZE = 10 * 1024 * 1024;
+
+// Global singleton for managing open streams
+const streamRegistry = new StreamRegistry();
+
+class IO extends Domain {
+  // commands
+
+  /**
+   * Close the stream, discard any temporary backing storage.
+   *
+   * @param {Object} options
+   * @param {string} options.handle
+   *     Handle of the stream to close.
+   */
+  async close(options = {}) {
+    const { handle } = options;
+
+    if (typeof handle != "string") {
+      throw new TypeError(`handle: string value expected`);
+    }
+
+    await streamRegistry.remove(handle);
+  }
+
+  /**
+   * Read a chunk of the stream.
+   *
+   * @param {Object} options
+   * @param {string} options.handle
+   *     Handle of the stream to read.
+   * @param {number=} options.offset
+   *     Seek to the specified offset before reading. If not specificed,
+   *     proceed with offset following the last read.
+   *     Some types of streams may only support sequential reads.
+   * @param {number=} options.size
+   *     Maximum number of bytes to read (left upon the agent
+   *     discretion if not specified).
+   *
+   * @return {string, boolean, boolean}
+   *     Data that were read, including flags for base64-encoded, and end-of-file reached.
+   */
+  async read(options = {}) {
+    const { handle, offset, size } = options;
+
+    if (typeof handle != "string") {
+      throw new TypeError(`handle: string value expected`);
+    }
+
+    const stream = streamRegistry.get(handle);
+    const fileInfo = await stream.stat();
+
+    if (typeof offset != "undefined") {
+      if (typeof offset != "number") {
+        throw new TypeError(`offset: integer value expected`);
+      }
+
+      // To keep compatibility with Chrome clip invalid offsets
+      const seekTo = Math.max(0, Math.min(offset, fileInfo.size));
+      await stream.setPosition(seekTo, OS.File.POS_START);
+    }
+
+    const curPos = await stream.getPosition();
+    const remainingBytes = fileInfo.size - curPos;
+
+    let chunkSize;
+    if (typeof size != "undefined") {
+      if (typeof size != "number") {
+        throw new TypeError(`size: integer value expected`);
+      }
+
+      // Chromium currently crashes for negative sizes (https://bit.ly/2P6h0Fv),
+      // but might behave similar to the offset and clip invalid values
+      chunkSize = Math.max(0, Math.min(size, remainingBytes));
+    } else {
+      chunkSize = Math.min(DEFAULT_CHUNK_SIZE, remainingBytes);
+    }
+
+    const bytes = await stream.read(chunkSize);
+    // Each UCS2 character has an upper byte of 0 and a lower byte matching
+    // the binary data. Using a loop here prevents us from hitting the browser's
+    // internal `arguments.length` limit.
+    const ARGS_MAX = 262144;
+    const stringData = [];
+    for (let i = 0; i < bytes.length; i += ARGS_MAX) {
+      let argsChunk = Math.min(bytes.length, i + ARGS_MAX);
+      stringData.push(
+        String.fromCharCode.apply(null, bytes.slice(i, argsChunk))
+      );
+    }
+    const data = btoa(stringData.join(""));
+
+    return {
+      data,
+      base64Encoded: true,
+      eof: remainingBytes - bytes.length == 0,
+    };
+  }
+}