Make a chrome extension download all PDFs with `declarativeNetRequest` - google-chrome-extension

Question

I have to migrate a chrome extension from MV2 to MV3, and that means replacing usages of the blocking chrome.webRequest API with declarativeNetRequest. One usage is this:
function enableDownloadPDFListener() {
chrome.webRequest.onHeadersReceived.addListener(downloadPDFListener);
}
function downloadPDFListener(details) {
const header = details.responseHeaders.find(e => e.name.toLowerCase() === 'content-type');
if (header.value && header.value === 'application/pdf') {
const headerDisposition = details.responseHeaders.find(
e => e.name.toLowerCase() === 'content-disposition'
);
if (headerDisposition) {
headerDisposition.value = headerDisposition.value.replace('inline', 'attachment');
} else {
details.responseHeaders.push({ name: 'Content-Disposition', value: 'attachment' });
}
}
return { responseHeaders: details.responseHeaders };
}
Explanation: This function intercepts requests, checks if their Content-Type header is application/pdf, and if that's the case, sets Content-Disposition: attachment to force downloading the file. We have this functionality to save our employees time when downloading lots of PDF files from various websites.
The problem I'm facing is that this API is deprecated and can't be used in Manifest V3, and I wasn't able to migrate it to the declarativeNetRequest API. I tried the following:
[
{
"id": 1,
"priority": 1,
"action": {
"type": "modifyHeaders",
"responseHeaders": [
{
"header": "content-disposition",
"operation": "set",
"value": "attachment"
}
]
},
"condition": {
// what should I put here?
}
}
]
But I don't know how to filter files with a certain Content-Type header. From what I understand, this is currently not possible. Is there any other way to get this functionality in Chrome's MV3?
I tried { "urlFilter": "*.pdf" } as a condition, which isn't correct, but might be good enough. However, although the badge indicates that the rule was executed, the Content-Disposition header isn't set in the network tab, and the file isn't downloaded. What went wrong here?

Answer 1

At a glance, I don't think there's a condition that would work here. It seems like a reasonable use case and something that may make a good issue at https://bugs.chromium.org/p/chromium though.
In the meantime - could you have an extension which injects a content script that listens to the click event on links? Or alternatively you could perhaps wait for the PDF to open and then close the tab and perform a download.