Storage: added function for setting content type, encoding, and attachmentness

These are used by Flamenco to store task logs as gzipped text files, but to
send them to the browser with such HTTP headers that the browser can gunzip
them and display directly (rather than having to download & gunzip yourself).

pillar/api/file_storage_backends/abstract.py

@@ -132,12 +132,19 @@ class Blob(metaclass=abc.ABCMeta):
                                   file_size=file_size)
 
     @abc.abstractmethod
-    def update_filename(self, filename: str):
+    def update_filename(self, filename: str, *, is_attachment=True):
         """Sets the filename which is used when downloading the file.
         
         Not all storage backends support this, and will use the on-disk filename instead.
         """
 
+    @abc.abstractmethod
+    def update_content_type(self, content_type: str, content_encoding: str = ''):
+        """Set the content type (and optionally content encoding).
+
+        Not all storage backends support this.
+        """
+
     @abc.abstractmethod
     def get_url(self, *, is_public: bool) -> str:
         """Returns the URL to access this blob.

pillar/api/file_storage_backends/gcs.py

@@ -174,7 +174,7 @@ class GoogleCloudStorageBlob(Blob):
         self.gblob.reload()
         self._size_in_bytes = self.gblob.size
 
-    def update_filename(self, filename: str):
+    def update_filename(self, filename: str, *, is_attachment=True):
         """Set the ContentDisposition metadata so that when a file is downloaded
         it has a human-readable name.
         """
@@ -182,7 +182,17 @@ class GoogleCloudStorageBlob(Blob):
         if '"' in filename:
             raise ValueError(f'Filename is not allowed to have double quote in it: {filename!r}')
 
-        self.gblob.content_disposition = f'attachment; filename="{filename}"'
+        if is_attachment:
+            self.gblob.content_disposition = f'attachment; filename="{filename}"'
+        else:
+            self.gblob.content_disposition = f'filename="{filename}"'
+        self.gblob.patch()
+
+    def update_content_type(self, content_type: str, content_encoding: str = ''):
+        """Set the content type (and optionally content encoding)."""
+
+        self.gblob.content_type = content_type
+        self.gblob.content_encoding = content_encoding
         self.gblob.patch()
 
     def get_url(self, *, is_public: bool) -> str:

pillar/api/file_storage_backends/local.py

@@ -113,10 +113,13 @@ class LocalBlob(Blob):
 
         self._size_in_bytes = file_size
 
-    def update_filename(self, filename: str):
+    def update_filename(self, filename: str, *, is_attachment=True):
         # TODO: implement this for local storage.
         self._log.info('update_filename(%r) not supported', filename)
 
+    def update_content_type(self, content_type: str, content_encoding: str = ''):
+        self._log.info('update_content_type(%r, %r) not supported', content_type, content_encoding)
+
     def make_public(self):
         # No-op on this storage backend.
         pass