Handle and log document-download-api request errors

Catches the requests exception for document-download-api calls, logs
a warning and returns a matching response code and message.

Connection errors to document download result in 503 response to the
user.

app/clients/document_download.py

@@ -2,6 +2,25 @@ import base64
 
 import requests
 
+from flask import current_app
+
+
+class DocumentDownloadError(Exception):
+    def __init__(self, message, status_code):
+        self.message = message
+        self.status_code = status_code
+
+    @classmethod
+    def from_exception(cls, e):
+        try:
+            message = e.response.json()['error']
+            status_code = e.response.status_code
+        except (TypeError, ValueError, AttributeError, KeyError):
+            message = 'connection error'
+            status_code = 503
+
+        return cls(message, status_code)
+
 
 class DocumentDownloadClient:
 
@@ -13,15 +32,24 @@ class DocumentDownloadClient:
         return "{}/services/{}/documents".format(self.api_host, service_id)
 
     def upload_document(self, service_id, file_contents):
-        response = requests.post(
-            self.get_upload_url(service_id),
-            headers={
-                'Authorization': "Bearer {}".format(self.auth_token),
-            },
-            files={
-                'document': base64.b64decode(file_contents)
-            }
-        )
-        response.raise_for_status()
+        try:
+            response = requests.post(
+                self.get_upload_url(service_id),
+                headers={
+                    'Authorization': "Bearer {}".format(self.auth_token),
+                },
+                files={
+                    'document': base64.b64decode(file_contents)
+                }
+            )
+
+            response.raise_for_status()
+        except requests.RequestException as e:
+            error = DocumentDownloadError.from_exception(e)
+            current_app.logger.warning(
+                'Document download request failed with error: {}'.format(error.message)
+            )
+
+            raise error
 
         return response.json()['document']['url']