Deno Native Messaging Host - fetch duplex

See Fetch body streams are not full duplex #1254.

Installation and usage on Chrome and Chromium

1. Navigate to chrome://extensions.
2. Toggle Developer mode.
3. Click Load unpacked.
4. Select native-messaging-deno folder.
5. Note the generated extension ID.
6. Open nm_deno.json in a text editor, set "path" to absolute path of nm_deno.js and chrome-extension://<ID>/ using ID from 5 in "allowed_origins" array.
7. Copy the file to Chrome or Chromium configuration folder, e.g., Chromium on *nix ~/.config/chromium/NativeMessagingHosts; Chrome dev channel on *nix ~/.config/google-chrome-unstable/NativeMessagingHosts.
8. Make sure deno executable and nm_deno.js are executable. To download deno executable into the cloned GitHub directory that is used as the local unpacked extension directory (and optionally strip symbolic information from the deno executable to reduce size) you can run

    wget --show-progress \
    --progress=bar \
    --output-document deno.zip \
    https://github.com/denoland/deno/releases/latest/download/deno-x86_64-unknown-linux-gnu.zip \
    && unzip deno.zip \
    && rm deno.zip \
    && strip deno 

9. This uses Deno's fetch() for full duplex streaming (writing to the uploaded ReadableStream and reading from the ReadableStream from the Response body using a single request). Each native message passed to the host from the Web page is written to the writable side of a TransformStream() where the readable side is set as value of body in second parameter passed to Request() passed to fetch(). To test navigate to an origin listed in "matches" array in "externally_connectable" in manifest.json, in source code, Sources => Snippets, or in console run something like

if (port) {
  port = null;
};
// Where <ID> is the generated unpacked extension ID
var port = chrome.runtime.connect('<ID>'); 
port.onMessage.addListener((message) => {
  console.log(message);
});
port.onDisconnect.addListener((message) => {
  console.log(message);
});
// Set in Request() passed to fetch() with readable side of TransformStream set as body
port.postMessage({url:'https://comfortable-deer-52.deno.dev', method:'post'});
await new Promise((resolve) => setTimeout(resolve, 200));
port.postMessage({a:'b',c:'d'}); // Transformed to uppercase {A: 'B', C: 'D'}
// Close WritableStreamDefaultWriter from writable side of TransformStream
port.postMessage(`CLOSE_STREAM`);
// Abort the request, reload the extension.
// port.postMessage(`ABORT_STREAM`);

Note: Deno Deploy times out the server (the same server code used for local development commented in nm_deno.js) in ~5 1/2 minutes.

It looks like Deno Deploy behaves similar to Chromium/Chrome MV3 extension ServiceWorker where without a persistent Native Messaging connection or other means, e.g., https://github.com/guest271314/persistent-serviceworker the ServiceWorker becomes inactive in ~5 minutes.

So we have to write to the writable side of TransformStream to keep the readable side that is uploaded via POST active in the server.

Something like

var bool = 1;
async function keepalive() {
  while (bool) {
    port.postMessage(null);
    await new Promise((resolve) => setTimeout(resolve, 1000 * 15));
  }
  return 'Done streaming';
};
await new Promise((resolve) => setTimeout(resolve, 200));
keepalive().then(console.log).catch(console.warn);

For differences between OS and browser implementations see Chrome incompatibilities.

License

Do What the Fuck You Want to Public License WTFPLv2