1376060 - webRequest.onHeadersReceived modified content type ignored on 304 Not Modified

Status: RESOLVED DUPLICATE of bug 1376932

(WebExtensions :: Request Handling, defect, P3)

Description

[Will Elwood (:Will)]

User Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:54.0) Gecko/20100101 Firefox/54.0
Build ID: 20170608105825

Steps to reproduce:

1) Extract attached minimal testing webext.
2) > web-ext run --browser-console --start-url https://ftp.mozilla.org/favicon.ico --firefox nightly
3) Ctrl-Shift-E
4) F5
5) Navigate to https://ftp.mozilla.org/pub/data/PerformanceAndFootprints.html
6) F5


Actual results:

2) Binary data appears as plain text when the browser opens.
4) The tab's network monitor confirms the 304 Not Modified response code.
4) The image appears.
5) HTML document appears as plain text.
6) The tab's network monitor confirms the 304 Not Modified response code.
6) HTML document loads as webpage.

Encountered in release channel 54.0 (64-bit) and confirmed in nightly 56.0a1 (2017-06-22) (64-bit), both on Windows 8.1 x64.


Expected results:

2) Binary data appears as plain text when the browser opens.
4) The tab's network monitor confirms the 304 Not Modified response code.
4) Binary data continues to appear as plain text.
5) HTML document appears as plain text.
6) The tab's network monitor confirms the 304 Not Modified response code.
6) HTML document continues to appear as plain text.

The same/equivalent steps run in Chrome 59 result in the image consistently appearing (as if the webext is never able to override the content type). For HTML pages, Chrome consistently displays them as plain text (as if the webext is always able to override the content type).

It's not clear how Chrome should be behaving, but at least in the case of Firefox MDN says "Modification of the 'Content-Type' header is supported from version 51".

Potentially related to bug 1376045 since F5 refresh and 304 Not Modified responses are involved in both cases.

Comment 1

[Will Elwood (:Will)]

Attachment: bug_304_not_modified_-_change_content_type_in_webrequest.onheadersreceived-1.0.0.zip