Clean up the torrent implementation

src/torrent.py

-import os
-import re
-import shutil
-import tempfile
-import datetime
-import zipfile
-
-from . import abstract, parser_factory
-
+from . import abstract
 
 
 class TorrentParser(abstract.AbstractParser):
     mimetypes = {'application/x-bittorrent', }
     whitelist = {b'announce', b'announce-list', b'info'}
 
-    def __init__(self, filename):
-        super().__init__(filename)
-        self.__decode_func = {
-                    ord('l'): self.__decode_list,
-                    ord('d'): self.__decode_dict,
-                    ord('i'): self.__decode_int
-            }
-        for i in range(0, 10):
-            self.__decode_func[ord(str(i))] = self.__decode_string
-
-        self.__encode_func = {
-                int: self.__encode_int,
-                bytes: self.__encode_string,
-                list: self.__encode_list,
-                dict: self.__encode_dict,
-        }
-
-
-    def get_meta(self):
+    def get_meta(self) -> dict:
         metadata = {}
         with open(self.filename, 'rb') as f:
-            d = self.__bdecode(f.read())
+            d = _BencodeHandler().bdecode(f.read())
+        if d is None:
+            return {'Unknown meta': 'Unable to parse torrent file "%s".' % self.filename}
         for k,v in d.items():
             if k not in self.whitelist:
                 metadata[k.decode('utf-8')] = v
         return metadata
 
 
-    def remove_all(self):
+    def remove_all(self) -> bool:
         cleaned = dict()
         with open(self.filename, 'rb') as f:
-            d = self.__bdecode(f.read())
+            d = _BencodeHandler().bdecode(f.read())
+        if d is None:
+            return False
         for k,v in d.items():
             if k in self.whitelist:
                 cleaned[k] = v
         with open(self.output_filename, 'wb') as f:
-            f.write(self.__bencode(cleaned))
+            f.write(_BencodeHandler().bencode(cleaned))
         return True
 
-    def __decode_int(self, s):
+
+class _BencodeHandler(object):
+    """
+    Since bencode isn't that hard to parse,
+    MAT2 comes with its own parser, based on the spec
+    https://wiki.theory.org/index.php/BitTorrentSpecification#Bencoding
+    """
+    def __init__(self):
+        self.__decode_func = {
+                    ord('d'): self.__decode_dict,
+                    ord('i'): self.__decode_int,
+                    ord('l'): self.__decode_list,
+            }
+        for i in range(0, 10):
+            self.__decode_func[ord(str(i))] = self.__decode_string
+
+        self.__encode_func = {
+                bytes: self.__encode_string,
+                dict: self.__encode_dict,
+                int: self.__encode_int,
+                list: self.__encode_list,
+        }
+
+    def __decode_int(self, s:str) -> (int, str):
         s = s[1:]
         next_idx = s.index(b'e')
         if s.startswith(b'-0'):
             raise ValueError  # negative zero doesn't exist
-        if s.startswith(b'0') and next_idx != 1:
+        elif s.startswith(b'0') and next_idx != 1:
             raise ValueError  # no leading zero except for zero itself
         return int(s[:next_idx]), s[next_idx+1:]
 
-    def __decode_string(self, s):
-        end = s.index(b':')
-        str_len = int(s[:end])
-        if s[0] == b'0' and end != 1:
+    def __decode_string(self, s:str) -> (str, str):
+        sep = s.index(b':')
+        str_len = int(s[:sep])
+        if str_len < 0:
             raise ValueError
-        s = s[1:]  # skip terminal `:`
-        return s[end:end+str_len], s[end+str_len:]
+        elif s[0] == b'0' and sep != 1:
+            raise ValueError
+        s = s[1:]
+        return s[sep:sep+str_len], s[sep+str_len:]
 
-    def __decode_list(self, s):
+    def __decode_list(self, s:str) -> (list, str):
         r = list()
         s = s[1:]  # skip leading `l`
         while s[0] != ord('e'):
@@ -77,47 +80,45 @@ class TorrentParser(abstract.AbstractParser):
             r.append(v)
         return r, s[1:]
 
-    def __decode_dict(self, s):
+    def __decode_dict(self, s:str) -> (dict, str):
         r = dict()
-        s = s[1:]
+        s = s[1:]  # skip leading `d`
         while s[0] != ord(b'e'):
             k, s = self.__decode_string(s)
             r[k], s = self.__decode_func[s[0]](s)
         return r, s[1:]
 
-    def __bdecode(self, s):
-        try:
-            r, l = self.__decode_func[s[0]](s)
-        except (IndexError, KeyError, ValueError) as e:
-            print("not a valid bencoded string: %s" % e)
-            return None
-        if l != b'':
-            print("invalid bencoded value (data after valid prefix)")
-            return None
-        return r
-
     @staticmethod
-    def __encode_int(x):
+    def __encode_int(x:str) -> bytes:
         return b'i' + bytes(str(x), 'utf-8') + b'e'
 
     @staticmethod
-    def __encode_string(x:str):
+    def __encode_string(x:str) -> bytes:
         return bytes((str(len(x))), 'utf-8') + b':' + x
 
-    def __encode_list(self, x):
+    def __encode_list(self, x:str) -> bytes:
         ret = b''
         for i in x:
             ret += self.__encode_func[type(i)](i)
         return b'l' + ret + b'e'
 
-    def __encode_dict(self, x):
+    def __encode_dict(self, x:str) -> bytes:
         ret = b''
         for k, v in sorted(x.items()):
             ret += self.__encode_func[type(k)](k)
             ret += self.__encode_func[type(v)](v)
         return b'd' + ret + b'e'
 
-    def __bencode(self, x):
-        return self.__encode_func[type(x)](x)
-
+    def bencode(self, s:str) -> bytes:
+        return self.__encode_func[type(s)](s)
 
+    def bdecode(self, s:str):
+        try:
+            r, l = self.__decode_func[s[0]](s)
+        except (IndexError, KeyError, ValueError) as e:
+            print("not a valid bencoded string: %s" % e)
+            return None
+        if l != b'':
+            print("invalid bencoded value (data after valid prefix)")
+            return None
+        return r