SDK GetTDFType should validate the TDF

[jrschumacher]

The sdk.GetTDFType() should validate the TDF rather than just checking the nanotdf magic number and ZTDF if its a valid zip format.

The issue with IsValidTDF() is that it checks for strict manifest compliance which is not required to decrypt the data, we only need partial compliance.

[jrschumacher]

@strantalis @biscoe916 mind taking a look at this. Feedback from internal PEP development.

[biscoe916]

Definitely agree that GetTDFType needs to do more than just check whether or not it's a ZIP. We had spoken in the past about adding a strict flag to IsValidTDF in order to allow for a lighter weight check that doesn't require strict JSON Schema validation.

Something like this:

func IsValidTdf(reader io.ReadSeeker, strict bool) (bool, error) {
	// create tdf reader
	tdfReader, err := archive.NewTDFReader(reader)
	if err != nil {
		return false, fmt.Errorf("archive.NewTDFReader failed: %w", err)
	}
	manifest, err := tdfReader.Manifest()
	if err != nil {
		return false, fmt.Errorf("tdfReader.Manifest failed: %w", err)
	}

	if strict {
		return isValidManifest(manifest, Strict)
	}

	// if not strict, assume valid
	return true, nil
}

For reference, the current IsValidTdf function:

func IsValidTdf(reader io.ReadSeeker) (bool, error) {
	// create tdf reader
	tdfReader, err := archive.NewTDFReader(reader)
	if err != nil {
		return false, fmt.Errorf("archive.NewTDFReader failed: %w", err)
	}

	manifest, err := tdfReader.Manifest()
	if err != nil {
		return false, fmt.Errorf("tdfReader.Manifest failed: %w", err)
	}

	return isValidManifest(manifest, Lax)
}

Then, in GetTDFType, instead of checking whether or not it is a zip, we should just run IsValidTdf(reader, false), to determine if it's a ZTDF type.