Use default transport to close connections, set timeout at client

[trinchan]

Using current master under go version go1.3.1 linux/amd64, we found that many connections to sendgrid were being orphaned in a CLOSE_WAIT state, leading to file descriptors that are never released. We traced the issue to the use of a custom Transport to implement dial timeouts not setting deadlines on other TCP operations (read, write, etc). This PR uses the Client.Timeout field to let the stdlib handle the timing out of connections, while using the DefaultTransport so that other transport defaults are set.

The issue presents itself as thousands of CLOSE_WAIT connections to sendgrid when checking lsof -l

emails TCP ip-10-171-52-54.ec2.internal:39976->184.173.190.226-static.reverse.softlayer.com:https (CLOSE_WAIT)
emails TCP ip-10-171-52-54.ec2.internal:59229->184.173.190.227-static.reverse.softlayer.com:https (CLOSE_WAIT)
emails TCP ip-10-171-52-54.ec2.internal:39978->184.173.190.226-static.reverse.softlayer.com:https (CLOSE_WAIT)
emails TCP ip-10-171-52-54.ec2.internal:40039->184.173.190.226-static.reverse.softlayer.com:https (CLOSE_WAIT)
emails TCP ip-10-171-52-54.ec2.internal:59292->184.173.190.227-static.reverse.softlayer.com:https (CLOSE_WAIT)
emails TCP ip-10-171-52-54.ec2.internal:40041->184.173.190.226-static.reverse.softlayer.com:https (CLOSE_WAIT)
emails TCP ip-10-171-52-54.ec2.internal:59294->184.173.190.227-static.reverse.softlayer.com:https (CLOSE_WAIT)
emails TCP ip-10-171-52-54.ec2.internal:40043->184.173.190.226-static.reverse.softlayer.com:https (CLOSE_WAIT)

With this patch, the connections are properly closed after the request is finished and no such entries can be found.

The Client.Timeout field was added in Go 1.3, so I think the travis build will fail for Go 1.1. Please advise if a Go 1.1 solution is necessary as well.

[deckarep]

@eddiezane - this change looks solid. Let me know if you need me to help test it.

[eddiezane]

Thanks for contributing to SendGrid Open Source! We think it's awesome when community members contribute to our projects and want to celebrate that.

The following link will ask you to authenticate with Github (so we can verify your identity). You'll then be asked for your shipping address so that we can send you a thanks for contributing.

Click Here to Continue »

Once again, thank you!