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29 lines
1.2 KiB
Markdown
29 lines
1.2 KiB
Markdown
# Writing middleware
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From the Caddy docs:
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> Oh yes, those pesky return values on ServeHTTP(). You read the documentation so you already know
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> what they mean. But what does that imply for the behavior of your middleware?
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>
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> Basically, return a status code only if you did NOT write to the response body. If you DO write to
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> the response body, return a status code of 0. Return an error value if your middleware encountered
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> an error that you want logged. It is common to return an error status and an error value together,
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> so that the error handler up the chain can write the correct error page.
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>
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> The returned status code is not logged directly; rather, it tells middleware higher up the chain
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> what status code to use if/when the response body is written. Again, return a 0 status if you've
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> already written a body!
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In the DNS status codes are called rcodes and it's slightly harder to return the correct
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answer in case of failure.
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So CoreDNS treats
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* SERVFAIL (dns.RcodeServerFailure)
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* REFUSED (dns.RecodeRefused)
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* FORMERR (dns.RcodeFormatError)
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* NOTIMP (dns.RcodeNotImplemented)
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as special and will then assume nothing has written to the client. In all other cases it is assume
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something has been written to the client.
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