#6276 Improve message parsing for signed message

[martgil]

This PR improve message parsing for signed message and prevents recursive parsing.

close #6276

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Tests (delete all except exactly one):

• Tests added or updated

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To be filled by reviewers

I have reviewed that this PR... (tick whichever items you personally focused on during this review):

• addresses the issue it closes (if any)
• code is readable and understandable
• is accompanied with tests, or tests are not needed
• is free of vulnerabilities
• is documented clearly and usefully, or doesn't need documentation

[martgil]

Hi @sosnovsky - This one is ready for a review. Thanks!

[sosnovsky]

works well, just a couple minor improvements 👍

[sosnovsky]

there is similar recursive call in

flowcrypt-browser/extension/js/common/message-renderer.ts

Line 618 in 78f34e3

if (!sigResult?.match && signedContentInDecryptedData) {

which can cause extension lag for nested signed content. we'll need to implement similar fix there, but let's leave it for separate PR

[martgil]

Got it - Will remember this one and fix it on separate PR after this one.

[sosnovsky]

it's possible for multipart/mixed content to include both signed and unsigned parts. current code stops when it encounters a non-signed node, so it can miss a nested signed node. let’s perform search for another signed node in this case:

const currentSubject = current.headers.subject?.[0]?.value;
fallbackSubject = currentSubject || fallbackSubject;
if (!Mime.isSignedContentNode(current)) {
    const nestedSignedContentNode = Mime.retrieveSignedContentNode([current]);
    if (!nestedSignedContentNode) {
          return fallbackSubject;
    }
    current = nestedSignedContentNode;
    continue;
}

[martgil]

I apologize, I missed that part. I have rechecked it again and fix the said behavior.

[martgil]

Hi @sosnovsky - This one is ready for a review. Thanks!

[sosnovsky]

all good now, thanks!