nixos/mattermost: correct file upload directory

Fix compatibility with previous versions by making sure all the uploads
and plugins end up in the correct directory. Add a test for the exact
path we care about to ensure that it doesn't work "on accident."

Discovered while updating instances to unstable.

nixos/modules/services/web-apps/mattermost.nix

···
   # The directory to store mutable data within dataDir.
   mutableDataDir = "${cfg.dataDir}/data";
 
-  # The plugin directory. Note that this is the *post-unpack* plugin directory,
-  # since Mattermost unpacks plugins to put them there. (Hence, mutable data.)
-  pluginDir = "${mutableDataDir}/plugins";
+  # The plugin directory. Note that this is the *pre-unpack* plugin directory,
+  # since Mattermost looks in mutableDataDir for a directory called "plugins".
+  # If Mattermost is installed with plugins defined in a Nix configuration, the plugins
+  # are symlinked here. Otherwise, this is a real directory and the tarballs are uploaded here.
+  pluginTarballDir = "${mutableDataDir}/plugins";
+
+  # We need a different unpack directory for Mattermost to sync things to at launch,
+  # since the above may be a symlink to the store.
+  pluginUnpackDir = "${mutableDataDir}/.plugins";
 
   # Mattermost uses this as a staging directory to unpack plugins, among possibly other things.
   # Ensure that it's inside mutableDataDir since it can get rather large.
···
           services.mattermost.environmentFile = "<your environment file>";
           services.mattermost.database.fromEnvironment = true;
         '' database;
-    FileSettings.Directory = cfg.dataDir;
-    PluginSettings.Directory = "${pluginDir}/server";
-    PluginSettings.ClientDirectory = "${pluginDir}/client";
+
+    # Note that the plugin tarball directory is not configurable, and is expected to be in FileSettings.Directory/plugins.
+    FileSettings.Directory = mutableDataDir;
+    PluginSettings.Directory = "${pluginUnpackDir}/server";
+    PluginSettings.ClientDirectory = "${pluginUnpackDir}/client";
+
     LogSettings = {
       FileLocation = cfg.logDir;
 
···
           "R- ${tempDir} - - - - -"
           "d= ${tempDir} 0750 ${cfg.user} ${cfg.group} - -"
 
-          # Ensure that pluginDir is a directory, as it could be a symlink on prior versions.
+          # Ensure that pluginUnpackDir is a directory.
           # Don't remove or clean it out since it should be persistent, as this is where plugins are unpacked.
-          "d= ${pluginDir} 0750 ${cfg.user} ${cfg.group} - -"
+          "d= ${pluginUnpackDir} 0750 ${cfg.user} ${cfg.group} - -"
 
           # Ensure that the plugin directories exist.
           "d= ${mattermostConf.PluginSettings.Directory} 0750 ${cfg.user} ${cfg.group} - -"
···
           if cfg.pluginsBundle == null then
             # Create the plugin tarball directory to allow plugin uploads.
             [
-              "d= ${cfg.dataDir}/plugins 0750 ${cfg.user} ${cfg.group} - -"
+              "d= ${pluginTarballDir} 0750 ${cfg.user} ${cfg.group} - -"
             ]
           else
             # Symlink the plugin tarball directory, removing anything existing, since it's managed by Nix.
-            [ "L+ ${cfg.dataDir}/plugins - - - - ${cfg.pluginsBundle}" ]
+            [ "L+ ${pluginTarballDir} - - - - ${cfg.pluginsBundle}" ]
         );
 
       systemd.services.mattermost = rec {
···
             # Logs too.
             oldLogs="$dataDir/logs"
             newLogs="$logDir"
-            if [ "$oldLogs" != "$newLogs" ] && [ -d "$oldLogs" ]; then
+            if [ "$oldLogs" != "$newLogs" ] && [ -d "$oldLogs" ] && [ ! -f "$newLogs/.initial-created" ]; then
               # Migrate the legacy log location to the new log location.
               # Allow this to fail if there aren't any logs to move.
               echo "Moving legacy logs at $oldLogs to $newLogs" >&2
               mkdir -p "$newLogs"
               mv "$oldLogs"/* "$newLogs" || true
+              touch "$newLogs/.initial-created"
             fi
           ''
           + optionalString (!cfg.mutableConfig) ''

nixos/tests/mattermost/default.nix

···
             if [ "$actualPostAttachmentHash" != "$postAttachmentHash" ]; then
               echo "Post attachment hash mismatched!" >&2
               exit 1
-            else
+            fi
+
+            # Make sure it's on the filesystem in the expected place
+            fsPath="$(find /var/lib/mattermost/data -name "$(basename -- "$postAttachment")" -print -quit)"
+            if [ -z "$fsPath" ] || [ ! -f "$fsPath" ]; then
+              echo "Attachment didn't exist on the filesystem!" >&2
+              exit 1
+            fi
+
+            # And that the hash matches.
+            actualFsAttachmentHash="$(sha256sum "$fsPath" | awk '{print $1}')"
+            if [ "$actualFsAttachmentHash" == "$postAttachmentHash" ]; then
               echo "Post attachment hash was OK!" >&2
               exit 0
+            else
+              echo "Attachment hash mismatched on disk!" >&2
+              exit 1
             fi
           else
             echo "Post didn't exist when it should have!" >&2
···
           # Switch to the newer config and make sure the plugins directory is replaced with a directory,
           # since it could have been a symlink on previous versions.
           mostlyMutable.systemctl("stop mattermost.service")
-          mostlyMutable.succeed(f"[ ! -L /var/lib/mattermost/data/plugins ] && rm -rf /var/lib/mattermost/data/plugins && ln -s {mostlyMutablePlugins} /var/lib/mattermost/data/plugins || true")
           mostlyMutable.succeed('[ -L /var/lib/mattermost/data/plugins ] && [ -d /var/lib/mattermost/data/plugins ]')
           switch_to_specialisation(mostlyMutable, mostlyMutableToplevel, "upgrade")
           wait_mattermost_up(mostlyMutable)
-          mostlyMutable.succeed('[ ! -L /var/lib/mattermost/data/plugins ] && [ -d /var/lib/mattermost/data/plugins ]')
 
           # HelpLink should be changed, still, and the post should still exist
           expect_config(mostlyMutable, esr, '.AboutLink == "https://nixos.org" and .HelpLink == "https://nixos.org/nixos/manual"')