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Update IMPLEMENTATION

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hensm
2020-02-27 17:31:54 +00:00
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IMPLEMENTATION.md
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# Extension Lifetime
A bridge application instance is created via the StatusManager (`background/StatusManager.ts`) to keep track of receivers’ statuses. The StatusManager emits events `serviceUp`, `serviceDown` and `statusUpdate` containing relevant data.
## StatusManager
This is expected to exist throughout the lifetime of the extension and will automatically reconnect with a 10-second interval if unexpectedly disconnected.
The StatusManager (`background/StatusManager.ts`) keeps a bridge instance active throughout the lifetime of the extension. It listens for `main:/serviceUp`, `main:/serviceDown` and `main:/receiverStatus` messages to keep track of and update a list of receiver devices that can be provided to other extension components. It also emits `serviceUp`, `serviceDown` and `statusUpdate` events containing relevant data.
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.
If the StatusManager unexpectedly loses its bridge connection, it will automatically reconnect with a 10-second interval.
## Shim Initialization
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.
The background script registers a `webRequest.onBeforeRequest` listener that intercepts requests to Google’s Cast API library.
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 to avoid page scripts calling into extension contexts).
@@ -23,7 +24,7 @@ The `shim:/initialized` message is sent to the shim and the `window.__onGCastApi
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…).
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 `main:/serviceUp` messages for any discovered devices with device info (address, port, label, etc…).
### ShimManager
@@ -99,7 +100,7 @@ Cast SDK API calls are translated into Chromecast protocol messages and sent via
`Session` and `Media` objects have a counterpart object within the bridge. Some messages are routed directly to these objects. For `Session`, these are in the format `bridge:/session/impl_<methodName>`.
# Message Table (OUTDATED)
# Message Table (VERY OUTDATED)
<!--<img src="diagram.png" width="866">-->