added logging to HTTP errors w/ url, status and response content

[andymccurdy]

This change adds a "slumber" logger and uses it to emit ERROR level messages w/ the URL, HTTP Status and response content in the event of an HTTP error. This should make it easier to debug server errors on the client side.

[andymccurdy]

I believe this will also satisfy #68 and #17.

[merwok]

Thanks for this! I’m not sure if error is the right level though; for production servers that could be too much logging. What about debug? /cc @hadrien @pior

[merwok]

A library should not configure logging handlers. I would revert this.

[dstufft]

This is a common trick because the logging library is stupid and shoves messages to stderr if there are no handlers present.

[dstufft]

iow if you don't do this trick, then end users are forced to configure logging if they don't want spurious output.

[andymccurdy]

If zero handlers are present, Python will yell every time the log line is hit with "No handlers could be found for logger "slumber"".

I've seen the NullHandler pattern in quite a few libs. In fact, I borrowed the above code directly out of requests.

[andymccurdy]

I'm fine using whatever log level you deem appropriate. Obviously an easy change. :)

[pior]

@merwok I agree with the error level. There is a "slumber" logger, so it's configurable.

[merwok]

OK for the null handler.

@pior: are you saying you agree with the proposed error level?