Possible to check if msg.caller is a canister, as opposed to a user?

I’m currently writing a function that needs to treat canister- and user-principals differently. How might one check if msg.caller is a canister?

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Principal are generic identifiers for canisters, users and possibly other concepts in the future. As far as most uses of the system are concerned they are opaque binary blobs with a length between 0 and 29 bytes, and there is intentionally no mechanism to tell canister id and users ids apart.

This is from the Interface specification

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Ah missed this - thank you.

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i had the same problem and this solution also helped me

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