File type detection now looks inside the file to determine the type, in addition to using the file extension

lbry/schema/mime_types.py

@@ -1,4 +1,6 @@
 import os
+import filetype
+import logging
 
 types_map = {
     # http://www.iana.org/assignments/media-types
@@ -166,10 +168,38 @@
     '.wmv': ('video/x-ms-wmv', 'video')
 }
 
+# maps detected extensions to the possible analogs
+# i.e. .cbz file is actually a .zip
+synonyms_map = {
+    '.zip': ['.cbz'],
+    '.rar': ['.cbr'],
+    '.ar': ['.a']
+}
+
+log = logging.getLogger(__name__)
+
 
 def guess_media_type(path):
     _, ext = os.path.splitext(path)
     extension = ext.strip().lower()
+
+    try:
+        kind = filetype.guess(path)
+        if kind:
+            real_extension = f".{kind.extension}"
+
+            if extension != real_extension:
+                if extension:
+                    log.warning(f"file extension does not match it's contents: {path}, identified as {real_extension}")
+                else:
+                    log.debug(f"file {path} does not have extension, identified by it's contents as {real_extension}")
+
+                if extension not in synonyms_map.get(real_extension, []):
+                    extension = real_extension
+
+    except OSError as error:
+        pass
+
     if extension[1:]:
         if extension in types_map:
             return types_map[extension]

setup.py

@@ -56,7 +56,8 @@
         'attrs==18.2.0',
         'pylru==1.1.0',
         'elasticsearch==7.10.1',
-        'grpcio==1.38.0'
+        'grpcio==1.38.0',
+        'filetype==1.0.9'
     ] + PLYVEL,
     extras_require={
         'torrent': ['lbry-libtorrent'],

tests/unit/schema/test_mime_types.py

@@ -0,0 +1,51 @@
+import unittest
+import tempfile
+import os
+
+from lbry.schema.mime_types import guess_media_type
+
+class MediaTypeTests(unittest.TestCase):
+    def test_guess_media_type_from_path_only(self):
+        kind = guess_media_type('/tmp/test.mkv')
+        self.assertEqual(kind, ('video/x-matroska', 'video'))
+
+    def test_defaults_for_no_extension(self):
+        kind = guess_media_type('/tmp/test')
+        self.assertEqual(kind, ('application/octet-stream', 'binary'))
+
+    def test_defaults_for_unknown_extension(self):
+        kind = guess_media_type('/tmp/test.unk')
+        self.assertEqual(kind, ('application/x-ext-unk', 'binary'))
+
+    def test_spoofed_unknown(self):
+        with tempfile.TemporaryDirectory() as temp_dir:
+            file = os.path.join(temp_dir, 'spoofed_unknown.txt')
+            with open(file, 'wb') as fd:
+                bytes_lz4 = bytearray([0x04,0x22,0x4d,0x18])
+                fd.write(bytes_lz4)
+                fd.close()
+
+            kind = guess_media_type(file)
+            self.assertEqual(kind, ('application/x-ext-lz4', 'binary'))
+
+    def test_spoofed_known(self):
+        with tempfile.TemporaryDirectory() as temp_dir:
+            file = os.path.join(temp_dir, 'spoofed_known.avi')
+            with open(file, 'wb') as fd:
+                bytes_zip = bytearray([0x50,0x4b,0x03,0x06])
+                fd.write(bytes_zip)
+                fd.close()
+
+            kind = guess_media_type(file)
+            self.assertEqual(kind, ('application/zip', 'binary'))
+
+    def test_spoofed_synonym(self):
+        with tempfile.TemporaryDirectory() as temp_dir:
+            file = os.path.join(temp_dir, 'spoofed_known.cbz')
+            with open(file, 'wb') as fd:
+                bytes_zip = bytearray([0x50,0x4b,0x03,0x06])
+                fd.write(bytes_zip)
+                fd.close()
+
+            kind = guess_media_type(file)
+            self.assertEqual(kind, ('application/vnd.comicbook+zip', 'document'))