[webchannel] Add JavaScript client implementation

webchannel/README.md

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+# WebChannel
+
+WebChannel is a bidirectional communication protocol designed to provide reliable, full-duplex communication channels over HTTP.
+
+This directory is the multi-language home for WebChannel client implementations.
+
+## Directory Structure
+
+- [js/](js/) - JavaScript client implementation (based on Closure Library).
+  - [imported_src/](js/imported_src/) - Imported source files from Closure Library.
+- [objc/](objc/) - (Planned) Objective-C client implementation.
+
+## JavaScript Client (`webchannel/js`)
+
+The JavaScript implementation of the WebChannel client is based on the Google Closure Library.
+
+The raw imported source files are located in `js/imported_src/`.

webchannel/js/imported_src/channel.js

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+/**
+ * @license
+ * Copyright The Closure Library Authors.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @fileoverview A core interface for WebChannelBase.
+ *
+ */
+goog.module('goog.labs.net.webChannel.Channel');
+goog.module.declareLegacyNamespace();
+
+const ChannelRequest = goog.requireType('goog.labs.net.webChannel.ChannelRequest');
+const ConnectionState = goog.requireType('goog.labs.net.webChannel.ConnectionState');
+const Uri = goog.requireType('goog.Uri');
+const XhrIo = goog.requireType('goog.net.XhrIo');
+
+/**
+ * Core interface for WebChannelBase.
+ *
+ * @interface
+ */
+function Channel() {}
+
+/**
+ * Determines whether to use a secondary domain when the server gives us
+ * a host prefix. This allows us to work around browser per-domain
+ * connection limits.
+ *
+ * If you need to use secondary domains on different browsers and IE10,
+ * you have two choices:
+ *     1) If you only care about browsers that support CORS
+ *        (https://developer.mozilla.org/en-US/docs/HTTP_access_control), you
+ *        can use {@link #setSupportsCrossDomainXhrs} and set the appropriate
+ *        CORS response headers on the server.
+ *     2) Or, override this method in a subclass, and make sure that those
+ *        browsers use some messaging mechanism that works cross-domain (e.g
+ *        iframes and window.postMessage).
+ *
+ * @return {boolean} Whether to use secondary domains.
+ * @see http://code.google.com/p/closure-library/issues/detail?id=339
+ */
+Channel.prototype.shouldUseSecondaryDomains = goog.abstractMethod;
+
+/**
+ * Called when creating an XhrIo object.  Override in a subclass if
+ * you need to customize the behavior, for example to enable the creation of
+ * XHR's capable of calling a secondary domain. Will also allow calling
+ * a secondary domain if withCredentials (CORS) is enabled.
+ * @param {?string} hostPrefix The host prefix, if we need an XhrIo object
+ *     capable of calling a secondary domain.
+ * @param {boolean=} isStreaming Whether or not fetch/streams are enabled for
+ *     the underlying HTTP request.
+ * @return {!XhrIo} A new XhrIo object.
+ */
+Channel.prototype.createXhrIo = goog.abstractMethod;
+
+/**
+ * Callback from ChannelRequest that indicates a request has completed.
+ * @param {!ChannelRequest} request
+ *     The request object.
+ */
+Channel.prototype.onRequestComplete = goog.abstractMethod;
+
+/**
+ * Returns whether the channel is closed
+ * @return {boolean} true if the channel is closed.
+ */
+Channel.prototype.isClosed = goog.abstractMethod;
+
+/**
+ * Callback from ChannelRequest for when new data is received
+ * @param {ChannelRequest} request
+ *     The request object.
+ * @param {string} responseText The text of the response.
+ */
+Channel.prototype.onRequestData = goog.abstractMethod;
+
+/**
+ * Callback from ChannelRequest for when the first byte of response body has
+ * been received. This is needed for detecting buffering proxies.
+ * @param {!ChannelRequest} request
+ *     The request object.
+ * @param {string} responseText The text of the response.
+ */
+Channel.prototype.onFirstByteReceived = goog.abstractMethod;
+
+/**
+ * Gets whether this channel is currently active. This is used to determine the
+ * length of time to wait before retrying. This call delegates to the handler.
+ * @return {boolean} Whether the channel is currently active.
+ */
+Channel.prototype.isActive = goog.abstractMethod;
+
+/**
+ * Not needed for testchannel.
+ *
+ * Gets the Uri used for the connection that sends data to the server.
+ * @param {string} path The path on the host.
+ * @return {Uri} The forward channel URI.
+ */
+Channel.prototype.getForwardChannelUri = goog.abstractMethod;
+
+/**
+ * Not needed for testchannel.
+ *
+ * Gets the Uri used for the connection that receives data from the server.
+ * @param {?string} hostPrefix The host prefix.
+ * @param {string} path The path on the host.
+ * @return {Uri} The back channel URI.
+ */
+Channel.prototype.getBackChannelUri = goog.abstractMethod;
+
+/**
+ * Not needed for testchannel.
+ *
+ * Allows the handler to override a host prefix provided by the server.  Will
+ * be called whenever the channel has received such a prefix and is considering
+ * its use.
+ * @param {?string} serverHostPrefix The host prefix provided by the server.
+ * @return {?string} The host prefix the client should use.
+ */
+Channel.prototype.correctHostPrefix = goog.abstractMethod;
+
+/**
+ * Not needed for testchannel.
+ *
+ * Creates a data Uri applying logic for secondary hostprefix, port
+ * overrides, and versioning.
+ * @param {?string} hostPrefix The host prefix.
+ * @param {string} path The path on the host (may be absolute or relative).
+ * @param {number=} opt_overridePort Optional override port.
+ * @return {Uri} The data URI.
+ */
+Channel.prototype.createDataUri = goog.abstractMethod;
+
+/**
+ * Not needed for testchannel.
+ * Gets the result of previous connectivity tests.
+ *
+ * @return {!ConnectionState} The connectivity state.
+ */
+Channel.prototype.getConnectionState = goog.abstractMethod;
+
+/**
+ * Sets the parameter name for the http session id.
+ *
+ * @param {?string} httpSessionIdParam The parameter name for http session id
+ */
+Channel.prototype.setHttpSessionIdParam = goog.abstractMethod;
+
+/**
+ * Gets the parameter name for the http session id.
+ *
+ * @return {?string} The parameter name for the http session id.
+ */
+Channel.prototype.getHttpSessionIdParam = goog.abstractMethod;
+
+/**
+ * Sets the http session id.
+ *
+ * @param {string} httpSessionId The http session id
+ */
+Channel.prototype.setHttpSessionId = goog.abstractMethod;
+
+/**
+ * Gets the http session id.
+ *
+ * @return {?string} The http session id if there is one in effect.
+ */
+Channel.prototype.getHttpSessionId = goog.abstractMethod;
+
+/**
+ * Whether or not this channel uses WHATWG Fetch/streams.
+ *
+ * @return {boolean} true if use Fetch streams.
+ */
+Channel.prototype.usesFetchStreams = goog.abstractMethod;
+
+// MOE:begin_strip
+// Ensure ES2021 inputs. go/transpile-js
+null?.(6_6);
+// MOE:end_strip
+
+exports = Channel;