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Clean up shim initialization

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hensm
2019-06-19 01:39:19 +01:00
parent 290a1facdb
commit 0a9af09419
13 changed files with 66 additions and 88 deletions
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10
IMPLEMENTATION.md
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@@ -2,13 +2,13 @@
A bridge application instance (`statusBridge`) is created to keep track of receivers’ statuses. This is expected to exist throughout the lifetime of the extension and will automatically reconnect if unexpectedly disconnected.
The `shim/contentSetup.ts` content script is registered for all pages. It creates an empty `window.chrome` object in the page context since some sites may expect it to exist. It also intercepts any `src` attribute changes on `<script>` elements where the cast API may be loaded directly from a `chrome-extension://` URL, then sets them to the regular cast API script URL.
The `shim/content.ts` content script is registered for all pages. It creates an empty `window.chrome` object in the page context since some sites may expect it to exist. It also intercepts any `src` attribute changes on `<script>` elements where the cast API may be loaded directly from a `chrome-extension://` URL, then sets them to the regular cast API script URL.
## Shim Initialization
The background script registers a `webRequest.onBeforeRequest` listener that intercepts requests to Google’s Cast API library.
When a request is intercepted, the `shim/content.ts` script is executed in the content script context. This facilitates any message passing across content/page script isolation (the shim itself is executed in the page context, both for convenience — since it interacts substantially with page scripts — and security reasons).
When a request is intercepted, the `shim/contentBridge.ts` script is executed in the content script context. This facilitates any message passing across content/page script isolation (the shim itself is executed in the page context, both for convenience — since it interacts substantially with page scripts — and security reasons).
Messages passed to the shim are custom events of type `__castMessage`. Messages passed back from the shim are custom events of type `__castMessageResponse`. Event listening and creation is handled by the `shim/messageBridge.ts` module.
@@ -23,6 +23,12 @@ The cast API is now available to the web app.
The web app calls `chrome.cast.initialize` with an `ApiConfig` object containing the Chromecast receiver app ID to use. The shim sends a `main:/shimInitialized` message to the background script. The bridge sends `shim:/serviceUp` messages for any discovered devices with device info (address, port, label, etc…).
### Extension Sender Apps
The initialization for built-in sender apps (media/mirroring) works slightly differently. They run in the content script context and import the shim, rather than running in the page script context.
The exported shim comes from `shim/export.ts`. Instead of setting the `window.__onGCastApiAvailable` callback, the module provides an init function which returns a promise. The `shim/contentBridge.ts` script is executed from that module and the initialization process is identical until the `shim:/initialized` message is received, at which point the promise is resolved.
## User Interaction
A user will trigger casting through the web app interface and the app calls `chrome.cast.requestSession`. The shim sends a `main:/selectReceiverBegin` message to the background script to open the receiver selector.