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From "Duru Can Celasun (Jira)" <j...@apache.org>
Subject [jira] [Commented] (THRIFT-4985) Clean up logging in go library
Date Wed, 23 Oct 2019 20:34:00 GMT

    [ https://issues.apache.org/jira/browse/THRIFT-4985?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16958230#comment-16958230
] 

Duru Can Celasun commented on THRIFT-4985:
------------------------------------------

If that's the only line of log then yes, let's just remove it.

For principal 2, it doesn't cause any difficulty to callers since interfaces are implemented
implicitly. So keeping it unexported allows us to keep our public API small, which helps avoid
BC breaks in the future. A good example is the [causer interface|https://github.com/pkg/errors/blob/27936f6d90f9c8e1145f11ed52ffffbfdb9e0af7/errors.go#L270]
in the popular pkg/errors package.

> Clean up logging in go library
> ------------------------------
>
>                 Key: THRIFT-4985
>                 URL: https://issues.apache.org/jira/browse/THRIFT-4985
>             Project: Thrift
>          Issue Type: Improvement
>          Components: Go - Library
>            Reporter: Yuxuan Wang
>            Priority: Major
>
> As principals:
>  # As a library, the library itself shouldn't do any logging. It should always return
the error to the caller (library user), and let them to decide how to handle them (logging,
panic, etc.)
>  # In some cases it's not possible to return the error to the caller, so some logging
is necessary, but those should be kept minimal, and made more controllable to the caller.
> Looking at how we do logging in go library now:
>  # We have logging inside [TZlibTransport|https://github.com/apache/thrift/blob/6e4c581fddae9106c2c5a59c4d0bfbe6ad3e4560/lib/go/thrift/zlib_transport.go#L70],
which fits Principal 1 above and should be removed
>  # We have logging inside TSimpleServer, which fits Principal 2 above (those are in the
accept loop so there's no easy way to return the errors to the caller)
> For Principal 2, one of the problem is that we can't just force all the callers to use
the same logging library. There are a lot of logging libraries and it's not always possible
to convert them into each other. Some people might be using [go-kit logger|https://godoc.org/github.com/go-kit/kit/log]
because they want structured logging, or because they are already using go-kit for other things,
and some people might be using [zap|https://godoc.org/go.uber.org/zap] for its performance.
They are both incompatible to the stdlib log library.
> This, combined with the part that we should keep the logging minimal, is why I propose
a simple, common ground that's easy to wrap any logging library into:
> {code:go}
> type Logger func(msg string)
> {code}
> Whatever logging library the user is already using, it's easy to write a lambda to convert
that to this common ground, for example for the stdlib log library:
> {code:go}
> func StdLogger(logger *log.Logger) Logger {
>   return func(msg string) {
>     logger.Print(msg)
>   }
> }
> {code}
> You can even have one to be used in tests, because the purpose of logging is that it's
only used for situations that is bad, we can make it that whenever the logging is called we
should fail the test:
> {code:go}
> func TestLogger(tb testing.TB) Logger {
>   return func(msg string) {
>     tb.Errorf("logger called with msg: %q", msg)
>   }
> }
> {code}
> This way, the caller can make sure that the logging from inside the thrift library is
using the same logger as what they are already using, or they can suppress the logging entirely
if they choose to.



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