VEDUHSF Fixes -Research & remediate MimeType validation failure

[freeheeling]

Review and identify cause of Sidekiq job exhaustions related to EVSS_15005 - MimeType validation failures. Can any validation improvements be made to prevent or limit the occurrence of document uploads failing downstream acceptance, given the following details from earlier research?

EVSS validation check for doc upload:

• EVSS_15005: uploaded files's actual MimeType does not equal the implied File name based on the extension of the file

from https://dsva.slack.com/archives/C1VBAHWQL/p1537980384000100:

On uploads of attachments to wss-document-services, one of the validations the service performs is to sanity check the given file extension (e.g., “.pdf”) to the “detected” mime type of the file itself. If there’s a mismatch, the service will return the EVSS_15005. So chances are the service was not able to recognize the upload as a valid pdf file.
It seems that when document-services analyzes the actual content of a problematic attachment, it’s determining the attachment to be a “plain/text” file. and with the file extension being a .pdf is why document-services is returning the 15005

Primary path validations

• EVSSClaimDocumentUploaderBase, LighthouseDocumentUploaderBase (currently only called from ClaimsAndAppeals and BenefitsDocuments controllers
  • each ensures file extension matches mime type, and attempt to fix the file extension (however, it does not appear an error is returned if conversion is unsuccessful or if the new fixed extension is a disallowed type)

FE UI validations

• file extension matches file type
  • Updates in PR #19509 check an uploaded file's extension against the file (mime) type and then searches the file content for a matching format signature. An error is returned if there is a mismatch.
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