Improve mime_type guessing by using Python's imghdr.what to detect image types

.gitignore

@@ -39,3 +39,4 @@ nosetests.xml
 
 venv/
 .env
+/tmp-emails/

AUTHORS.rst

@@ -10,6 +10,7 @@ With inputs and contributions from (in chronological order):
 - `@smihai <https://github.com/smihai>`_
 - `@Daviey <https://github.com/Daviey>`_
 - `@positiveviking <https://github.com/positiveviking>`_
+- `@MrTango <https://github.com/MrTango>`_
 
 See `all Github contributors <https://github.com/lavr/python-emails/graphs/contributors>`_
 

emails/store/file.py

@@ -1,6 +1,7 @@
 # encoding: utf-8
 from __future__ import unicode_literals
 
+import imghdr
 import uuid
 from mimetypes import guess_type
 from email.mime.base import MIMEBase
@@ -99,6 +100,10 @@ def get_mime_type(self):
             filename = self.filename
             if filename:
                 r = self._mime_type = guess_type(filename)[0]
+                if not r:
+                    img_mime_type = imghdr.what(filename, h=self.data)
+                    if img_mime_type:
+                        r = "image/{0}".format(img_mime_type)
         if not r:
             r = MIMETYPE_UNKNOWN
         self._mime_type = r

emails/testsuite/store/test_store.py

@@ -25,6 +25,35 @@ def test_attachment_headers():
     assert 'X-Header: X' in part
 
 
+def test_get_mime_type_by_extension():
+    f = emails.store.BaseFile(data='x', filename='logo.jpg')
+    assert f.mime_type == 'image/jpeg'
+
+
+def test_get_mime_type_from_data_jpeg():
+    f = emails.store.BaseFile(
+        data=b'\xff\xd8\xff\xe0\x00\x10JFIF\x00\x01\x01\x01',
+        filename='thumb',
+    )
+    assert f.mime_type == 'image/jpeg'
+
+
+def test_get_mime_type_from_data_png():
+    f = emails.store.BaseFile(
+        data=b'\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR\x00\x00\x00d',
+        filename='thumb',
+    )
+    assert f.mime_type == 'image/png'
+
+
+def test_get_mime_type_from_data_gif():
+    f = emails.store.BaseFile(
+        data=b'GIF89a\xd3\x00G\x00\xf7\x00\x00\xff\xff',
+        filename='thumb',
+    )
+    assert f.mime_type == 'image/gif'
+
+
 def test_store_commons():
     FILES = [{'data': 'aaa', 'filename': 'aaa.txt'}, {'data': 'bbb', 'filename': 'bbb.txt'}, ]
     store = emails.store.MemoryFileStore()