1266654 - document.execCommand('copy') is unavailable for context menu command

Status: RESOLVED DUPLICATE of bug 1197451

(WebExtensions :: Untriaged, defect)

Description

[YUKI "Piro" Hiroshi]

Attachment: clipboard-command-from-context-menu.xpi

To implement a feature to copy generated text to the clipboard, document.execCommand('copy') in the background page is only one known method for WebExtensions-based addons.
(It is a known standard method for Chrome extensions:
http://stackoverflow.com/questions/27892282/copy-selected-text-via-a-context-menu-option-in-a-chrome-extension )
However, document.execCommand('copy') always fails if it is triggered from a context menu item added by the addon itself.

Steps to reproduce:

1) Define a function using "document.execCommand('copy')".
2) Define a context menu item using the function defined at 1).
3) Go to "about:debugging".
4) Click the "Load Temporary Add-on" button and load the addon.
5) Open the browser console by Ctrl-Shift-J.
6) Open the context menu on a webpage and choose the menu item defined at 2).

Actual result:
A warning "document.execCommand('cut'/'copy') was denied because it was not called from inside a short running user-generated event handler." appears in the browser console and nothing is copied to the clipboard.

Expected result:
Something is copied to the clipboard.


The attached addon is a minimum example. It includes only one background script:
---------------------------------------------------
function setClipBoard(aString) {
  var container = document.createElement('textarea');
  document.documentElement.appendChild(container);
  container.value = aString;
  container.select();
  document.execCommand('copy');
  container.parentNode.removeChild(container);
}

chrome.contextMenus.create({
  type     : 'normal',
  id       : 'context-copy-date',
  title    : 'Copy current date by addon',
  onclick  : function(aInfo, aTab) {
    setClipBoard(String(new Date()));
  }
});
---------------------------------------------------

The code adds a new context menu item "Copy current date by addon".
After installation, go to any webpage, open the context menu in the content area, and choose the added item. Then you'll see the "Actual result".

Comment 1

[YUKI "Piro" Hiroshi]

The message is from here:
http://mxr.mozilla.org/mozilla-central/source/dom/html/nsHTMLDocument.cpp#3244

---------------------------------------------------
3244   // special case for cut & copy
3245   // cut & copy are allowed in non editable documents
3246   if (isCutCopy) {
3247     if (!nsContentUtils::IsCutCopyAllowed()) {
3248       // We have rejected the event due to it not being performed in an
3249       // input-driven context therefore, we report the error to the console.
3250       nsContentUtils::ReportToConsole(nsIScriptError::warningFlag,
3251                                       NS_LITERAL_CSTRING("DOM"), this,
3252                                       nsContentUtils::eDOM_PROPERTIES,
3253                                       "ExecCommandCutCopyDeniedNotInputDriven");
3254       return false;
3255     }
---------------------------------------------------

"nsContentUtils::IsCutCopyAllowed()" seems to return "true" if the code is triggered from any user event or the script has the chrome privilege. I think the background script is also treated as a script with chrome privilege. I'm planning to implement a command to copy generated text with delay - because it requires inter-sandboxes communication to collect information from another content script. Even if context menu's "click" event is treated as an user event, the planned command will fail because deferred operations are processed after the "click" event finished.