Added commit mode

The commit mode ensures pictures are not corrupted when Instaloader is
unexpectedly interrupted. In the case that the last picture is corrupted
because of an interruption, Instaloader will redownload the picture.
Since the metadata is the last object saved to disk, we can consider a
post as "committed" if its json metadata file exists and is not
malformed. Instaloader should download any posts which are not
committed. Downside is commit mode requires metadata to be saved.

docs/cli-options.rst

@@ -230,6 +230,12 @@ How to Download
    to ``3``. If a connection fails, it can be manually skipped by hitting
    :kbd:`Control-c`. Set this to ``0`` to retry infinitely.
 
+.. option:: --commit-mode
+
+   Tries to ensure downloaded images avoid corruption in case of unexpected
+   interruption. If the last picture is corrupted, Instaloader will fix the
+   picture the next time it is run.
+
 Miscellaneous Options
 ^^^^^^^^^^^^^^^^^^^^^
 

instaloader/__main__.py

@@ -320,6 +320,10 @@ def main():
                        help='Maximum number of connection attempts until a request is aborted. Defaults to 3. If a '
                             'connection fails, it can be manually skipped by hitting CTRL+C. Set this to 0 to retry '
                             'infinitely.')
+    g_how.add_argument('--commit-mode', action='store_true',
+                       help='Tries to ensure downloaded images avoid corruption in case of unexpected interruption. '
+                       'If the last picture is corrupted, Instaloader will fix the picture the next time it is run. '
+                       'Requires the JSON metadata to be saved .')
 
     g_misc = parser.add_argument_group('Miscellaneous Options')
     g_misc.add_argument('-q', '--quiet', action='store_true',
@@ -361,6 +365,9 @@ def main():
         download_posts = not (args.no_posts or args.stories_only or args.profile_pic_only)
         download_stories = args.stories or args.stories_only
 
+        if args.commit_mode and args.no_metadata_json:
+            raise SystemExit('--commit-mode requires JSON metadata to be saved.')
+
         loader = Instaloader(sleep=not args.no_sleep, quiet=args.quiet, user_agent=args.user_agent,
                              dirname_pattern=args.dirname_pattern, filename_pattern=args.filename_pattern,
                              download_pictures=not args.no_pictures,
@@ -371,7 +378,8 @@ def main():
                              post_metadata_txt_pattern=post_metadata_txt_pattern,
                              storyitem_metadata_txt_pattern=storyitem_metadata_txt_pattern,
                              graphql_rate_limit=args.graphql_rate_limit,
-                             max_connection_attempts=args.max_connection_attempts)
+                             max_connection_attempts=args.max_connection_attempts,
+                             commit_mode=args.commit_mode)
         _main(loader,
               args.profile,
               username=args.login.lower() if args.login is not None else None,

instaloader/instaloader.py

@@ -1,5 +1,6 @@
 import getpass
 import json
+import lzma
 import os
 import platform
 import re
@@ -15,7 +16,7 @@ from typing import Any, Callable, Iterator, List, Optional, Set, Union
 
 from .exceptions import *
 from .instaloadercontext import InstaloaderContext
-from .structures import Highlight, JsonExportable, Post, PostLocation, Profile, Story, StoryItem, save_structure_to_file
+from .structures import Highlight, JsonExportable, Post, PostLocation, Profile, Story, StoryItem, save_structure_to_file, load_structure_from_file
 
 
 def get_default_session_filename(username: str) -> str:
@@ -116,7 +117,8 @@ class Instaloader:
                  post_metadata_txt_pattern: str = None,
                  storyitem_metadata_txt_pattern: str = None,
                  graphql_rate_limit: Optional[int] = None,
-                 max_connection_attempts: int = 3):
+                 max_connection_attempts: int = 3,
+                 commit_mode: bool = False):
 
         self.context = InstaloaderContext(sleep, quiet, user_agent, graphql_rate_limit, max_connection_attempts)
 
@@ -134,6 +136,9 @@ class Instaloader:
             else post_metadata_txt_pattern
         self.storyitem_metadata_txt_pattern = '' if storyitem_metadata_txt_pattern is None \
             else storyitem_metadata_txt_pattern
+        self.commit_mode = commit_mode
+        if self.commit_mode and not self.save_metadata:
+            raise InvalidArgumentException("Commit mode requires JSON metadata to be saved.")
 
     @contextmanager
     def anonymous_copy(self):
@@ -173,9 +178,15 @@ class Instaloader:
         if filename_suffix is not None:
             filename += '_' + filename_suffix
         filename += '.' + file_extension
-        if os.path.isfile(filename):
-            self.context.log(filename + ' exists', end=' ', flush=True)
-            return False
+        # A post is considered "commited" if the json file exists and is not malformed.
+        if self.commit_mode:
+            if self._committed:
+                self.context.log(filename + ' exists', end=' ', flush=True)
+                return False
+        else:
+            if os.path.isfile(filename):
+                self.context.log(filename + ' exists', end=' ', flush=True)
+                return False
         self.context.get_and_write_raw(url, filename)
         os.utime(filename, (datetime.now().timestamp(), mtime.timestamp()))
         return True
@@ -359,6 +370,7 @@ class Instaloader:
 
         # Download the image(s) / video thumbnail and videos within sidecars if desired
         downloaded = True
+        self._committed = self.check_if_committed(filename)
         if self.download_pictures:
             if post.typename == 'GraphSidecar':
                 edge_number = 1
@@ -945,6 +957,21 @@ class Instaloader:
                 if fast_update and not downloaded:
                     break
 
+    def check_if_committed(self, filename: str) -> bool:
+        """Checks to see if the current post has been committed."""
+        # A post is considered committed if its json metadata file exists and is not malformed.
+        if os.path.isfile(filename + '.json.xz'):
+            filename += '.json.xz'
+        elif os.path.isfile(filename + '.json'):
+            filename += '.json'
+        else:
+            return False
+        try:
+            load_structure_from_file(self.context, filename)
+            return True
+        except (FileNotFoundError, lzma.LZMAError, json.decoder.JSONDecodeError):
+            return False
+
     def interactive_login(self, username: str) -> None:
         """Logs in and internally stores session, asking user for password interactively.