adding utilities for serving files

gracedb/core/http.py

+# Request/response utilities
+from django.http import HttpResponse
+
+from .vfile import VersionedFile
+
+import os
+
+
+def serve_file(file_path, ResponseClass=HttpResponse):
+    """
+    Take an absolute path to a file and construct a response.
+    Files are served by Apache through X-Sendfile.
+
+    If a certain response class is desired, it can be passed as an argument.
+    Typically will be django.http.HttpResponse or
+    rest_framework.response.Response.
+
+    This function does NOT check that the file exists and is readable,
+    or whether the user should be allowed to download the file.
+    """
+
+    # Try to guess file content type; if unknown, set as octet-stream
+    content_type, encoding = VersionedFile.guess_mimetype(file_path)
+    content_type = content_type or "application/octet-stream"
+
+    # Set up response object
+    response = ResponseClass()
+
+    # Configure response to have Apache serve the file with X-Sendfile
+    response['X-Sendfile'] = file_path
+
+    # For binary files, add the file as an attachment (direct download instead
+    # of opening in browser window)
+    if content_type == "application/octet-stream":
+        response['Content-Disposition'] = 'attachment; filename="{0}"'.format(
+            os.path.basename(file_path))
+
+    return response
+
+
+def check_and_serve_file(request, file_path, ResponseClass=HttpResponse):
+    """
+    Checks whether a file exists and is readable. If so, the file is served.
+    Does not check permissions - that should be done before this function
+    is called.
+
+    This function returns a response, so it should be called within a view,
+    not from within a view subfunction or method.
+    """
+
+    if not os.path.exists(file_path):
+        err_msg = "File {0} not found".format(os.path.basename(file_path))
+        # File not found - return 404 NOT FOUND response
+        response = ResponseClass(err_msg, status=404)
+    elif not os.access(file_path, os.R_OK):
+        err_msg = "File {0} is not readable".format(
+            os.path.basename(file_path))
+        # File not readable - return 500 SERVER ERROR response
+        response = ResponseClass(err_msg, status=500)
+    elif os.path.isfile(file_path):
+        response = serve_file(file_path, ResponseClass)
+
+    return response