1439165 - WebExtensions: browser.downloads.open - not open from content script

Status: RESOLVED DUPLICATE of bug 1398833

(WebExtensions :: General, defect)

Description

[Oleksandr]

User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:58.0) Gecko/20100101 Firefox/58.0
Build ID: 20180206200532

Steps to reproduce:

manifest.json
...
"content_scripts": [{
	"js": [ "test.js" ],
	"matches": [ "<all_urls>" ],
	"all_frames" : true
}],
...

test.js
------------
1.
ddata_box.addEventListener("click", function(event) {
	browser.downloads.open(event.target.id);
}, true);

--------
2.
ddata_box.addEventListener("click", function(event) {
	chrome.runtime.sendMessage({ 'action' : 'file_open', 'id' : event.target.id }, function(response) {});
}, true);

background.js
chrome.runtime.onMessage.addListener(function(request, sender, sendResponse) {
...
	chrome.downloads.open(request.id);
...
});



Actual results:

1. it's normal
TypeError: browser.downloads is undefined

2. GoogleChrome works correctly and file is opened, but Firefox WebExtensions gives this error:
Error: downloads.open may only be called from a user input handler


Expected results:

To use this function in your extension...
... you can only call this function from inside the handler for a user action, such as

* clicking the extension's browser action or page action
* selecting its context menu item
* activating a keyboard shortcut defined by the extension (note: this is not currently supported in Firefox)
* clicking a button in a page bundled with the extension.
https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/downloads/open

I'm porting my extension to WebExtensions: show downloads in statusbar
The feature of this extension is that it draws a statusbar with downloads at the bottom of each web page.

Tell me please - how to open a file by passing a message from content_script to background.js?

For the Google Chrome version there are no such restrictions for "downloads.open", but suddenly I ran into limitations in Firefox.

why did you add restrictions to "downloads.open" in WebExtensions? :(

Comment 2

[Levente Hunyadi]

Even while the issue is marked as "RESOLVED", it persists in Firefox 59.0.3 (64-bit). The root cause appears to be a loss of context information when a UI-triggered callback (such as "addEventListener") in a content script forwards to a background script via a "chrome.runtime.sendMessage" call, exactly as shown in the example highlighted in the bug report. The background script then sees the action as if it had not originated from a user action and throws the exception "Error: downloads.open may only be called from a user input handler". The current setup (as far as I can see) disallows "chrome.downloads.open" to be invoked in background script, which can only communicate with other scripts (e.g. content scripts) with the message passing infrastructure. Meanwhile, the same script runs without problems in Google Chrome, where the fact that the action had originally come from a user action is propagated via "chrome.runtime.sendMessage".