docs: Add tutorial for packaging 3rd party software as ExApp (#265)

Signed-off-by: provokateurin <[email protected]>
Co-authored-by: Alexander Piskun <[email protected]>

docs/NextcloudApp3rdParty.rst

@@ -0,0 +1,82 @@
+Packaging 3rd party software as a Nextcloud Application
+=======================================================
+
+This chapter explains how you can package any 3rd party software to be compatible with Nextcloud.
+You should already be familiar with :doc:`NextcloudApp` before reading this part.
+
+You should also have a bit of knowledge about classic PHP Nextcloud apps and `how to develop them <https://docs.nextcloud.com/server/stable/developer_manual/app_development/index.html>`_.
+
+Architecture
+------------
+
+The packaged ExApp will contain two pieces of software:
+
+#. The ExApp itself which is talking to Nextcloud directly and responsible for the whole lifecycle.
+#. The 3rd party software you want to package.
+#. Frontend code which will be loaded by Nextcloud to display your iframe.
+
+Due to current restrictions of ExApps they can only utilize a single port, which means all requests for the 3rd part software have to be proxied through the ExApp.
+This will be improved in future released, by allowing multiple ports, so that no proxying is necessary anymore.
+
+Everything will be packaged into a single Docker image which will be used for deployments.
+Therefore it is an advantage if the 3rd party software is already able to run inside a Docker container and has a public Docker image available.
+
+Steps
+------------------
+
+Creating the ExApp
+^^^^^^^^^^^^^^^^^^
+
+Please follow the instructions in :doc:`NextcloudApp` and then return here.
+
+Adding the frontend
+^^^^^^^^^^^^^^^^^^^
+
+To be able to access the 3rd party software via the browser it is necessary to embed an iframe into Nextcloud.
+The frontend has to be added in the same way how you add it in a classic PHP app.
+The iframe ``src`` needs to point to ``/apps/app_api/proxy/APP_ID``, but it is necessary to use the ``generateUrl`` method to ensure the path will also work with Nextcloud instances hosted at a sub-path.
+If you require some features like clipboard read/write you need to allow them for the iframe using the ``allow`` attribute.
+
+To now show the frontend inside Nextcloud add the following to your enabled handler:
+
+.. code-block:: python
+
+    def enabled_handler(enabled: bool, nc: NextcloudApp) -> str:
+        if enabled:
+            nc.ui.resources.set_script("top_menu", "APP_ID", "js/APP_ID-main")
+            nc.ui.top_menu.register("APP_ID", "App Name", "img/app.svg")
+        else:
+            nc.ui.resources.delete_script("top_menu", "APP_ID", "js/APP_ID-main")
+            nc.ui.top_menu.unregister("APP_ID")
+        return ""
+
+Proxying the requests
+^^^^^^^^^^^^^^^^^^^^^
+
+For proxying the requests to the 3rd party software you need to register a new route:
+
+.. code-block:: python
+
+    @APP.api_route("/{path:path}", methods=["GET", "POST", "PUT", "DELETE", "OPTIONS", "HEAD", "PATCH", "TRACE"])
+    async def proxy_requests(request: Request, path: str):
+        pass
+
+This route should have the lowest priority of all your routes, as it catches all requests that didn't match any previous route.
+
+In this request handler you need to send a new HTTP request to the 3rd party software and copy all incoming parameters like sub-path, query parameters, body and headers.
+When returning the response including body, headers and status code, make sure to add or override the CSP and CORS headers if necessary.
+
+Adjusting the Dockerfile
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+The Dockerfile should be based on the 3rd party software you want to package.
+In case a Docker image is already available you should use that, otherwise you need to first create your own Docker image (it doesn't have to be a separate image, it can just be a stage in the Dockerfile for your ExApp).
+
+The 3rd party software needs to be adapted to be able to handle the proxied requests and generated correct URLs in the frontend.
+Depending on how the software works this might only be a config option you need to set or you need to modify the source code within the Docker image (and potentially rebuild the software afterwards).
+The root path of the software will be hosted at ``/index.php/apps/app_api/proxy/APP_ID`` which is the same location that was configured in the iframe ``src``.
+
+After these steps you can just continue with the normal ExApp Dockerfile steps of installing the dependencies and copying the source code.
+Be aware that you will need to install Python manually in your image in case the Docker image you used so far doesn't include it.
+
+At the end you will have to add a custom entrypoint script that runs the ExApp and the 3rd party software side-by-side to allow them to live in the same container.

docs/index.rst

@@ -31,6 +31,7 @@ Have a great time with Python and Nextcloud!
     FirstSteps
     MoreAPIs
     NextcloudApp
+    NextcloudApp3rdParty
     NextcloudTalkBot
     NextcloudTalkBotTransformers
     NextcloudUiApp