extmod/moduhashlib: allow multiple calls to digest() method #6850
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It was suggested in the past: #4488, but I guess we concluded not to do that |
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Closing for the same reason as #4488, see comment #4488 (comment) Also see #7316 which prevents calling |
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It's useful to be able to call
digest()multiple times on asha256object, and no way to code around the previous limitation of theuhashlibmodule which did not support that.Fix is to copy the context and do the finalize operation on the copy. Cost is minimal (stack depth, one copy), and IMO, required by the API imposed by PEP 452. As it was, the sha256() object was left in an invalid state after first digest call and subsequent calls were returning garbage.
In my opinion, the right API for embedded systems, is to keep this fully-featured object-oriented API for complex cases, but also provide a single-shot function that doesn't keep state, and simply returns the binary digest of its only argument. A simple functional API like that can also accommodate hardware acceleration, which would be very difficult with the OO API.