Check a sequential download against the complete length whenever one is known, and settle the unknown-total case on the 416. An empty body of unknown length, a 206 with no complete length, and a 206 starting past the resume offset all passed the size checks before and were renamed into place. Four restart paths spent no attempt, so a host that always answered the same way cycled forever.
One service needed session_id in its license call, which a near-duplicate of get_content_keys supplied behind a service-tag test. service_licence now passes each service only the arguments its own license function declares, so the duplicate and the branch are gone. The REST API license paths and the base PlayReady delegate get the same filtering, replacing their fixed argument set.
Two behaviour changes ride along: an empty license challenge now raises EmptyLicense for every service, not just the one, and a service that declares only challenge now receives a working call instead of a TypeError.
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