I keep reading about "well defined interfaces", as here, here or here, specially when talking about microservices.
What's an example of the opposite, an interface that is not well-defined?
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2Please make your question self contained (i.e. cite from the articles you have linked). – πάντα ῥεῖ Jun 21 '20 at 13:19
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1This is a good topic. But πάντα ῥεῖ is correct. We don't support link only questions. See also discuss this blog. – candied_orange Jun 21 '20 at 14:36
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3The links aren't necessary to understand the question. They are just in support of the claim. – Karl Bielefeldt Jun 21 '20 at 15:17
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"whatever the server actually does" – user253751 Jun 23 '20 at 16:15
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Any interface definition that isn't specific enough to determine whether a client or service implementation conforms to it is not well-defined. Some examples:
- unspecified character encoding (one side using utf-8 while the other uses iso8859-1)
- unspecified number representation (decimal point versus comma)
- implicit sequencing requirements (need to call
createFooListbefore you can calladdFoo) - incomplete specification of limits, constraints, semantic rules etc.
In general, if developers argue about the correct usage or implementation of an interface it's a good indicator that the interface is ill-defined (or that the developers didn't understand it, which also happens.)
Just being awkward or difficult to use doesn't make an interface ill-defined, though.
Hans-Martin Mosner
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... It makes ammending the interfaces definition to get it well-defined if even possible much more difficult though. And especially for the last part, +1 – Deduplicator Jun 21 '20 at 16:51