Can I allow the extension user to choose matching domains? - google-chrome-extension

Question

Can I allow the domain matching for my extension to be user configurable?
I'd like to let my users choose when the extension runs.

Answer 1

To implement customizable "match patterns" for content scripts, the Content script need to be executed in by the background page using the chrome.tabs.executeScript method (after detecting a page load using the chrome.tabs.onUpdated event listener).
Because the match pattern check is not exposed in any API, you have to create the method yourself. It is implemented in url_pattern.cc, and the specification is available at match patterns.
Here's an example of a parser:
/**
* #param String input A match pattern
* #returns null if input is invalid
* #returns String to be passed to the RegExp constructor */
function parse_match_pattern(input) {
if (typeof input !== 'string') return null;
var match_pattern = '(?:^'
, regEscape = function(s) {return s.replace(/[[^$.|?*+(){}\\]/g, '\\$&');}
, result = /^(\*|https?|file|ftp|chrome-extension):\/\//.exec(input);
// Parse scheme
if (!result) return null;
input = input.substr(result[0].length);
match_pattern += result[1] === '*' ? 'https?://' : result[1] + '://';
// Parse host if scheme is not `file`
if (result[1] !== 'file') {
if (!(result = /^(?:\*|(\*\.)?([^\/*]+))(?=\/)/.exec(input))) return null;
input = input.substr(result[0].length);
if (result[0] === '*') { // host is '*'
match_pattern += '[^/]+';
} else {
if (result[1]) { // Subdomain wildcard exists
match_pattern += '(?:[^/]+\\.)?';
}
// Append host (escape special regex characters)
match_pattern += regEscape(result[2]);
}
}
// Add remainder (path)
match_pattern += input.split('*').map(regEscape).join('.*');
match_pattern += '$)';
return match_pattern;
}
Example: Run content script on pages which match the pattern
In the example below, the array is hard-coded. In practice, you would store the match patterns in an array using localStorage or chrome.storage.
// Example: Parse a list of match patterns:
var patterns = ['*://*/*', '*exampleofinvalid*', 'file://*'];
// Parse list and filter(exclude) invalid match patterns
var parsed = patterns.map(parse_match_pattern)
.filter(function(pattern){return pattern !== null});
// Create pattern for validation:
var pattern = new RegExp(parsed.join('|'));
// Example of filtering:
chrome.tabs.onUpdated.addListener(function(tabId, changeInfo, tab) {
if (changeInfo.status === 'complete') {
var url = tab.url.split('#')[0]; // Exclude URL fragments
if (pattern.test(url)) {
chrome.tabs.executeScript(tabId, {
file: 'contentscript.js'
// or: code: '<JavaScript code here>'
// Other valid options: allFrames, runAt
});
}
}
});
To get this to work, you need to request the following permissions in the manifest file:
"tabs" - To enable the necessary tabs API.
"<all_urls>" - To be able to use chrome.tabs.executeScript to execute a content script in a specific page.
A fixed list of permissions
If the set of match patterns is fixed (ie. the user cannot define new ones, only toggle patterns), "<all_urls>" can be replaced with this set of permissions. You may even use optional permissions to reduce the initial number of requested permissions (clearly explained in the documentation of chrome.permissions).