server/posts: use SHA1 checksums

This changes the checksums to ones that are compatible with 1.x, which
relieves the migration script from recalculating the checksums for all
the posts.

server/szurubooru/func/posts.py

@@ -263,7 +263,7 @@ def update_post_content(post, content):
         raise InvalidPostContentError(
             'Unhandled file type: %r' % post.mime_type)
 
-    post.checksum = util.get_md5(content)
+    post.checksum = util.get_sha1(content)
     other_post = db.session \
         .query(db.Post) \
         .filter(db.Post.checksum == post.checksum) \

server/szurubooru/func/util.py

@@ -73,6 +73,14 @@ def get_md5(source):
     return md5.hexdigest()
 
 
+def get_sha1(source):
+    if not isinstance(source, bytes):
+        source = source.encode('utf-8')
+    sha1 = hashlib.sha1()
+    sha1.update(source)
+    return sha1.hexdigest()
+
+
 def flip(source):
     return {v: k for k, v in source.items()}
 

server/szurubooru/tests/func/test_posts.py

@@ -288,8 +288,8 @@ def test_update_post_content(
         expected_mime_type,
         expected_type,
         output_file_name):
-    with patch('szurubooru.func.util.get_md5'):
-        util.get_md5.return_value = 'crc'
+    with patch('szurubooru.func.util.get_sha1'):
+        util.get_sha1.return_value = 'crc'
         config_injector({
             'data_dir': str(tmpdir.mkdir('data')),
             'thumbnails': {