Security/Subresource Integrity

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Subresource Integrity is a mechanism by which user agents may verify that a fetched resource has been delivered without unexpected manipulation. It landed in Firefox 43.


The bulk of the code lives in these two classes:

which hook into:

Both of these hooks work in the same way:

  1. We start by creating an SRIMetadata object from the content of the integrity attribute as we process the element:
  2. We then wait until the file is downloaded and check that the hash of the contents matches the SRI hash:
  3. We return NS_ERROR_SRI_CORRUPT, which fails the load and triggers the error event on that element, if the hashes don't match.


The automated tests live in these two places:

To turn on debugging output, export the following environment variable: