storage: make GET /storage return the last successful probe when requ…

…ested

In the following patch:

  4c59e1e never return a PROBING response from guided_POST

we fixed a UI crash occurring when a storage probing operation was
ongoing while the user would enter the partitioning screen with "Use
an entire disk".

To address the issue, we made POST /storage/guided return the last
(cached) successful probe result rather than returning a potential
PROBING status result.

That being said, when "Custom Storage Layout" is selected, we are using
a different HTTP call: GET /storage which can also return a PROBING
status result. So our fix was only partial.

This patch adds a "use_cached_result" parameter (which defaults to
false) to GET /storage. This makes the call return the last successful
probe result.

When the client selects "Custom Storage Layout" we now explicitly
request a cached result so that we don't have to deal with a potential
PROBING status response.

Ideally, we should either:

 * make the client aware that a PROBING status can be returned and act
   accordingly.
 * pass the wait=true argument to GET /storage or POST /storage/guided

But doing so has other implications and the kinetic release is imminent.

Signed-off-by: Olivier Gayot <[email protected]>

subiquity/client/controllers/filesystem.py

@@ -236,10 +236,17 @@ async def _answers_action(self, action):
             raise Exception("could not process action {}".format(action))
 
     async def _guided_choice(self, choice):
+        # FIXME It would seem natural here to pass the wait=true flag to the
+        # below HTTP calls, especially because we wrap the coroutine in
+        # wait_with_progress.
+        # Having said that, making the server return a cached result seems like
+        # the least risky option to address https://launchpad.net/bugs/1993257
+        # before the kinetic release. This is also similar to what we did for
+        # https://launchpad.net/bugs/1962205
         if choice is not None:
             coro = self.endpoint.guided.POST(choice)
         else:
-            coro = self.endpoint.GET()
+            coro = self.endpoint.GET(use_cached_result=True)
         status = await self.app.wait_with_progress(coro)
         self.model = FilesystemModel(status.bootloader)
         self.model.load_server_data(status)

subiquity/common/apidef.py

@@ -250,7 +250,9 @@ def POST(data: Payload[GuidedChoice]) \
                     -> StorageResponse:
                 pass
 
-        def GET(wait: bool = False) -> StorageResponse: ...
+        def GET(wait: bool = False, use_cached_result: bool = False) \
+            -> StorageResponse: ...
+
         def POST(config: Payload[list]): ...
 
         class reset:

subiquity/server/controllers/filesystem.py

@@ -293,10 +293,12 @@ def _done_response(self):
             dasd=self.model._probe_data.get('dasd', {}),
             storage_version=self.model.storage_version)
 
-    async def GET(self, wait: bool = False) -> StorageResponse:
-        probe_resp = await self._probe_response(wait, StorageResponse)
-        if probe_resp is not None:
-            return probe_resp
+    async def GET(self, wait: bool = False, use_cached_result: bool = False) \
+            -> StorageResponse:
+        if not use_cached_result:
+            probe_resp = await self._probe_response(wait, StorageResponse)
+            if probe_resp is not None:
+                return probe_resp
         return self._done_response()
 
     async def POST(self, config: list):