Refactor and implement download code natively

- Use modified port of Django 2.2 FileResponse.
- Remove Django DownloadView library.

Signed-off-by: Roberto Rosario <roberto.rosario@mayan-edms.com>

mayan/apps/common/compat.py

@@ -1,8 +1,14 @@
 from __future__ import unicode_literals
 
+import os
 import types
 
+from django.conf import settings
+from django.http.response import StreamingHttpResponse
 from django.utils import six
+from django.utils.six.moves.urllib.parse import quote
+
+from mayan.apps.mimetype.api import get_mimetype
 
 if six.PY3:
     dict_type = dict
@@ -22,3 +28,75 @@ except NameError:
     FileNotFoundErrorException = IOError
 else:
     FileNotFoundErrorException = FileNotFoundError  # NOQA
+
+
+class FileResponse(StreamingHttpResponse):
+    """
+    Port of Django's 2.2 FileResponse
+    Modified to allows downloading non file like content as attachment
+    A streaming HTTP response class optimized for files.
+    TODO: To be remove when the code moves to Django 2.2
+    """
+    block_size = 4096
+
+    def __init__(self, as_attachment=False, filename='', *args, **kwargs):
+        self.as_attachment = as_attachment
+        self.filename = filename
+        super(FileResponse, self).__init__(*args, **kwargs)
+
+    def _set_as_attachment(self, filename):
+        if self.as_attachment:
+            filename = self.filename or os.path.basename(filename)
+            if filename:
+                try:
+                    filename.encode('ascii')
+                    file_expr = 'filename="{}"'.format(filename)
+                except UnicodeEncodeError:
+                    file_expr = "filename*=utf-8''{}".format(quote(filename))
+                self['Content-Disposition'] = 'attachment; {}'.format(file_expr)
+
+    def _set_streaming_content(self, value):
+        if not hasattr(value, 'read'):
+            self.file_to_stream = None
+            result = super(FileResponse, self)._set_streaming_content(value)
+            self._set_as_attachment(filename=self.filename)
+
+            return result
+
+        self.file_to_stream = filelike = value
+        if hasattr(filelike, 'close'):
+            self._closable_objects.append(filelike)
+        value = iter(lambda: filelike.read(self.block_size), b'')
+        self.set_headers(filelike)
+        super(FileResponse, self)._set_streaming_content(value)
+
+    def set_headers(self, filelike):
+        """
+        Set some common response headers (Content-Length, Content-Type, and
+        Content-Disposition) based on the `filelike` response content.
+        """
+        encoding_map = {
+            'bzip2': 'application/x-bzip',
+            'gzip': 'application/gzip',
+            'xz': 'application/x-xz',
+        }
+        filename = getattr(filelike, 'name', None)
+        filename = filename if (isinstance(filename, str) and filename) else self.filename
+        if os.path.isabs(filename):
+            self['Content-Length'] = os.path.getsize(filelike.name)
+        elif hasattr(filelike, 'getbuffer'):
+            self['Content-Length'] = filelike.getbuffer().nbytes
+
+        if self.get('Content-Type', '').startswith(settings.DEFAULT_CONTENT_TYPE):
+            if self.file_to_stream:
+                content_type, encoding = get_mimetype(
+                    file_object=self.file_to_stream, mimetype_only=True
+                )
+                # Encoding isn't set to prevent browsers from automatically
+                # uncompressing files.
+                content_type = encoding_map.get(encoding, content_type)
+                self['Content-Type'] = content_type or 'application/octet-stream'
+            else:
+                self['Content-Type'] = 'application/octet-stream'
+
+        self._set_as_attachment(filename=filename)