Export appstream catalogue for preinstalled Flatpak apps

Although we have added the name and summary for each app to the JSON
manifest, there is no substitute for having all the data. XML compresses
very well!

It is better to capture this at build time rather than fetching it on
the fly later because apps can change or disappear, but we would like to
be able to describe exactly what is in any given image.

librsvg2-compose is required for apps which only ship an SVG file, because
appstream-compose really, really wants to export 64px and 128px bitmaps
for each app.

https://phabricator.endlessm.com/T35013

.editorconfig

@@ -14,6 +14,6 @@ indent_style = space
 indent_size = 2
 
 # Python
-[{*.py,eos-image-builder,run-build,helpers/{assemble-manifest,fetch-remote-collection-id,generate-ovf-files,kill-chroot-procs,kolibri-pick-content-from-channel,mutable-path,packages-manifest},hooks/{content/{50-flatpak,50-kolibri-content},image/{50-flatpak.chroot,52-ek-content-cache,62-kolibri-options,70-flatpak-manifest,70-ostree-manifest}}}]
+[{*.py,eos-image-builder,run-build,helpers/{assemble-manifest,fetch-remote-collection-id,generate-ovf-files,kill-chroot-procs,kolibri-pick-content-from-channel,mutable-path,packages-manifest},hooks/{content/{50-flatpak,50-kolibri-content},image/{50-flatpak.chroot,52-ek-content-cache,62-kolibri-options,70-flatpak-appstream-catalog,70-flatpak-manifest,70-ostree-manifest}}}]
 indent_size = 4
 max_line_length = 88

.flake8

@@ -17,6 +17,7 @@ filename =
     ./hooks/content/50-kolibri-content,
     ./hooks/image/50-flatpak.chroot,
     ./hooks/image/62-kolibri-options,
+    ./hooks/image/70-flatpak-appstream-catalog,
     ./hooks/image/70-flatpak-manifest,
     ./hooks/image/70-ostree-manifest,
     ./run-build

config/defaults.ini

@@ -65,6 +65,7 @@ base = bullseye
 
 # Packages to install in the buildroot
 packages_add =
+  appstream-util
   attr
   awscli
   ca-certificates
@@ -88,6 +89,7 @@ packages_add =
   json-glib-tools
   jq
   libfsapfs-utils
+  librsvg2-common
   mount
   openssh-client
   ostree
@@ -145,6 +147,7 @@ hooks_add =
   62-kolibri-automatic-provision
   62-kolibri-options
   63-icon-grid
+  70-flatpak-appstream-catalog
   70-flatpak-manifest
   70-ostree-manifest
   80-ldconfig-aux-cache.chroot

hooks/image/70-flatpak-appstream-catalog

@@ -0,0 +1,88 @@
+#!/usr/bin/env python3
+
+# Construct AppStream XML for preinstalled apps
+
+import glob
+import logging
+import os
+import subprocess
+
+logging.basicConfig(
+    level=logging.INFO,
+    format='+ %(asctime)s %(levelname)s %(name)s: %(message)s',
+    datefmt='%H:%M:%S'
+)
+logger = logging.getLogger(os.path.basename(__file__))
+
+
+def main():
+    root = os.path.join(os.environ['OSTREE_VAR'], 'lib/flatpak/exports')
+
+    # Find the metainfo files to include in the AppStream.
+    ids = []
+    for metainfo in glob.glob(os.path.join(root, 'share/metainfo/*.xml')):
+        # Everything here should end in .metainfo.xml or .appdata.xml, but
+        # let's be sure.
+        if not (metainfo.endswith('.metainfo.xml') or
+                metainfo.endswith('.appdata.xml')):
+            raise Exception(f'Unexpected metainfo file {metainfo}')
+
+        # It's kind of bad to reject these files here because they're obviously
+        # valid enough for Flathub to have published them. Reasons that appstream-util
+        # 0.7.18-1+deb11u1 considers appdata to be invalid include:
+        #
+        # - Using a <url type=''> attribute from a more recent version of the spec
+        #   (dozens of apps, including GIMP)
+        #
+        # - A <li> element contains a nested <em> element (Pods; OK this is not a
+        #   preinstalled app, but still)
+        #
+        # - <release> elements are not in order (FileRoller)
+        #
+        # None of these are reasons to exclude the app from the catalogue but there is
+        # no way to tell the tool to ignore them: if we pass these files to
+        # appstream-compose it will fail.
+        #
+        # TODO: Switch to appstreamcli validate-relax once we are on Bookworm and can
+        # use appstreamcli compose.
+        cmd = ('appstream-util', 'validate-relax', '--nonet', metainfo)
+        proc = subprocess.run(cmd)
+        if proc.returncode != 0:
+            logger.warning('Skipping %s considered invalid by appstream-util', metainfo)
+            continue
+
+        # Convert the filename to an "app-id" as expected by
+        # appstream-compose. This isn't necessarily the app ID but the stem
+        # of the metainfo XML file without .metainfo.xml or .appdata.xml.
+        # Most of the time these are the same.
+        metainfo_id = os.path.basename(metainfo)
+        if metainfo_id.endswith('.metainfo.xml'):
+            metainfo_id = metainfo_id.rpartition('.metainfo.xml')[0]
+        else:
+            metainfo_id = metainfo_id.rpartition('.appdata.xml')[0]
+        logger.info('Including metainfo ID %s', metainfo_id)
+        ids.append(metainfo_id)
+
+    # Exit if there aren't any desktop metainfo files.
+    if len(ids) == 0:
+        logger.info('No metainfo files')
+        return
+
+    # Compose the AppStream XML.
+    # TODO: Switch to appstreamcli compose once we are on Bookworm
+    cmd = [
+        'appstream-compose',
+        f'--origin={os.environ["EIB_OUTVERSION"]}',
+        f'--prefix={root}',
+        f'--output-dir={os.environ["EIB_OUTDIR"]}',
+        # We don't want to export the icons but we can't tell
+        # appstream-compose not to do so...
+        f'--icons-dir={os.environ["EIB_TMPDIR"]}/appstream-compose-icons',
+    ]
+    cmd += ids
+    logger.info('Composing AppStream XML: %s', ' '.join(cmd))
+    subprocess.run(cmd, check=True)
+
+
+if __name__ == '__main__':
+    main()