Declarative net request rule.json is not working - google-chrome-extension

Question

I'm trying to block a website with a chrome extension that uses the new declarative net request API for Manifest V3, but it isn't working. I have added the permission in the manifest and made sure to add the priority, id, action and conditions, but it still doesn't do anything at all. I am trying to modify the response headers. Here is the applicable part of my manifest.
Manifest.json
"background": {
"service_worker": "background.js"
},
"content_scripts": [
{
"matches": ["https://mail.google.com/*"],
"css": ["base.css"],
"js": [
"jquery-1.10.2.js",
"inboxsdk.js",
"loader.js"
]
},
{
"matches": [
"https://mail.google.com/*",
"https://localhost:1234/*",
"http://localhost:1234/*",
"http://localhost:5000/*"
],
"js": [
"version.js"
]
}
],
"host_permissions": [
"*://*.google.com/*",
"*://*.googleusercontent.com/*",
"https://localhost:1234/*",
"http://localhost:1234/*",
"http://localhost:5000/*"
],
"web_accessible_resources": [{
"resources": [
"icon128.png",
"logo-pink.svg",
"logo-white.png",
"logo.png"
],
"matches": [
"https://mail.google.com/*",
"https://localhost:1234/*",
"http://localhost:1234/*",
"http://localhost:5000/*"
]
}],
"declarative_net_request": {
"rule_resources": [{
"id": "ruleset_1",
"enabled": true,
"path": "rules.json"
}]
},
"permissions": [
"scripting",
"declarativeNetRequest",
"declarativeNetRequestWithHostAccess",
"declarativeNetRequestFeedback"
],
"manifest_version": 3
}
rules.json
[
{
"id": 1,
"priority": 1,
"action": {
"type": "modifyHeaders",
"responseHeaders": [
{
"header": "script-src",
"operation": "set",
"value": "script-src https://localhost:7000"
}
]
},
"condition": {
"regexFilter": "/content-security-policy/i",
"resourceTypes": [
"main_frame",
"sub_frame",
"script",
"object",
"xmlhttprequest",
"csp_report"
]
}
}
]
Is there any Idea how to test whether the headers are being modified or not

Answer 1

There are several problems.
regexFilter doesn't support JS RegExp literal syntax.
Solution: Remove / and the i flag.
regexFilter is for the URL of the request, not for a header name. Currently there's no way to match requests by checking a header.
Solution: Remove regexFilter or use a valid expression for the URL or use other types of conditions like urlFilter or requestDomains, see the documentation.
"header": "script-src" should be "header": "content-security-policy"
Example:
[{
"id": 1,
"action": {
"type": "modifyHeaders",
"responseHeaders": [{
"header": "content-security-policy",
"operation": "set",
"value": "script-src https://localhost:7000"
}]
},
"condition": {
"requestDomains": ["example.com"],
"resourceTypes": ["main_frame", "sub_frame"]
}
}]
P.S. To change script-src it's sufficient to process main_frame and sub_frame types.