live: add cache contents to the /refresh payload

Add the list of images in the client's cache partition in the
payload sent to the server.
The information sent is a list of {image_name, img_size, checksum}
elements where img_size is the size of the respective image in bytes.

Resquest response structure:
{
    ...
    'cache': [
        {'name': 'windows.img', 'size': 2432370213, checksum: '5d4dcc677bc19f40a647d0002f4ade90'},
        {'name': 'linux.img', 'size': 243234534213, checksum: '3eb22f888f88a55ad954f55644e1192e'}
    ]
    ...
}

src/live/ogOperations.py

@@ -29,7 +29,7 @@ from src.utils.menu import generate_menu
 from src.utils.fs import *
 from src.utils.probe import os_probe, get_cache_dev_path
 from src.utils.disk import *
-from src.utils.cache import generate_cache_txt, umount_cache, init_cache
+from src.utils.cache import *
 from src.utils.tiptorrent import *
 from src.utils.uefi import *
 from src.utils.boot import *
@@ -111,6 +111,44 @@ class OgLiveOperations:
             part_setup['filesystem'] = 'CACHE'
             part_setup['code'] = 'ca'
 
+    def _get_cache_contents(self):
+        cache_contents = []
+
+        if not mount_cache():
+            return cache_contents
+
+        img_dir = OG_CACHE_IMAGE_PATH
+
+        if not os.path.isdir(img_dir):
+            return cache_contents
+
+        for file_name in os.listdir(img_dir):
+            file_path = os.path.join(img_dir, file_name)
+
+            if not os.path.isfile(file_path):
+                continue
+            if not file_name.endswith('.img'):
+                continue
+
+            checksum_file_path = file_path + '.full.sum'
+            image_checksum = ''
+
+            try:
+                with open(checksum_file_path, 'r') as f:
+                    image_checksum = f.read()
+            except (FileNotFoundError, PermissionError, OSError) as e:
+                logging.info(f'Error reading file at {checksum_file_path}: {e}')
+
+            if not image_checksum:
+                logging.info(f'Warning: empty checksum for image {file_name}')
+
+            image_size = os.stat(file_path).st_size
+            cache_contents.append({
+                'name': file_name,
+                'size': image_size,
+                'checksum': image_checksum})
+        return cache_contents
+
     def _compute_md5(self, path, bs=2**20):
         m = hashlib.md5()
         with open(path, 'rb') as f:
@@ -568,6 +606,8 @@ class OgLiveOperations:
                 self._refresh_part_setup_cache(cxt, pa, part_setup, cache)
                 json_body['partition_setup'].append(part_setup)
 
+        json_body['cache'] = self._get_cache_contents()
+
         generate_menu(json_body['partition_setup'])
         generate_cache_txt()
         self._restartBrowser(self._url)