Log protocol errors

[hawkw]

Currently, there are many cases where h2 will fail a connection or
stream with a PROTOCOL_ERROR, without recording why the protocol error
occurred. Since protocol errors may result from a bug in h2 or from a
misbehaving peer, it is important to be able to debug the cause of
protocol errors.

This branch adds a log line to almost all cases where a protocol error
occurs. I've tried to make the new log lines consistent with the
existing logging, and in some cases, changed existing log lines to make
them internally consistant with other log lines in that module. I have
not tried to enforce a single style for log lines across all modules,
however, as the debug-level in some modules uses a different style than
the trace logging elsewhere. Presumably this is because it is expected
to be more user-facing.

Signed-off-by: Eliza Weisman eliza@buoyant.io

[olix0r]

why warn vs debug vs trace?

[hawkw]

@olix0r I used warn because I thought a situation likely resulting from a misbehaving client ought to result in a warning, but upon further consideration, those logs probably ought to be at the trace level, since almost all logging in h2 is at trace. I used debug in framed_read since that module was already logging protocol errors at the debug level.

[olix0r]

What do you think about making all of these logs at debug! so that we can more easily access them without getting the full firehose?

[seanmonstar]

Yea, I'd put logs about errors at debug level.

[hawkw]

Okay, will do! Should they also all be changed to use the format of the framed_read errors?

[hawkw]

I've updated this branch so that all protocol errors are logged at the debug level, and changed all the log lines to use a consistent formatting based on the protocol error log lines in framed_read, using a helper macro to reduce boilerplate.

[olix0r]

thanks!