Feature: TCP Fast Open implementaion.

[cubicdaiya]

Introduced tcp-fastopen as the new directive. It takes 1 argument for the maximum queue length.
By default, the value of tcp-fastopen is zero (In this case, TCP Fast Open is disabled). Because TCP Fast Open is not always available.

Sample configuration

tcp-fastopen: 4096

[kazuho]

Thank you for the PR! Looks like a nice addition.

One little question: is there any reason not to have the feature turned on by default? If not, how about setting the default (in main) to 4,096 (instead of 0) if TCP_FASTOPEN is defined?

[cubicdaiya]

One little question: is there any reason not to have the feature turned on by default?

No. I think it is also turned on by default.

If not, how about setting the default (in main) to 4,096 (instead of 0) if TCP_FASTOPEN is defined?

👍

[cubicdaiya]

@kazuho Changed the default value and behavior. How about this?

[kazuho]

Thank you for the changes! Merged to master with safeguards for platforms other than Linux added.

[2vek]

I have a openvz virtual server, with very old kernel.

$ uname -r
2.6.32-042stab106.4

h2o refuses to start example config given in source code.

$  h2o -v
h2o version 1.3.0

$  h2o -c examples/h2o/h2o.conf 
failed to set TCP_FASTOPEN:Protocol not available
[examples/h2o/h2o.conf:3] failed to listen to port ANY:8080: Protocol not available

Most VPS providers don't update kernel often to boast their uptime.
Since, this is new kernel feature. I think h2o should just not use this feature if kernal don't support it, instead of refusing to start until tcp-fastopen: 0 added to config

[centminmod]

yeah OpenVZ VPS would have restrictions.. you can easily check if server environment is OpenVZ based by checking if this file exists /proc/user_beancounters and use that to determine if TCP Fast Open should be enabled or not

[kazuho]

@2vek Oh that's bad.

Until we fix the issue, I think setting tcp-fastopen: 0 in your configuration file would be a workaround. Woold you mind trying?

see also: https://h2o.examp1e.net/configure/base_directives.html#tcp-fastopen

[cubicdaiya]

Oh, sorry. The consideration seems to be not enough.

[kazuho]

@cubicdaiya It's not your fault. I suggested turning this knob on by default.

IMO it might be better to report an warning and continue (instead of reporting an error and exitting) when setting TCP_FASTOPEN fails.

[kazuho]

@2vek @centminmod I anticipate that the issue has been fixed with the merger of the pull-req above. Please open a new issue if you still have issues.

Thank you for your help.

[2vek]

👍 It is better now, just tested

$  ./h2o -v 
h2o version 1.3.1
$  ./h2o -c examples/h2o/h2o.conf 
[warning] failed to set TCP_FASTOPEN:Protocol not available
[warning] failed to set TCP_FASTOPEN:Protocol not available
[warning] failed to set TCP_FASTOPEN:Protocol not available
[warning] failed to set TCP_FASTOPEN:Protocol not available
[INFO] raised RLIMIT_NOFILE to 65536
h2o server (pid:30888) is ready to serve requests
fetch-ocsp-response (using OpenSSL 1.0.1k 8 Jan 2015)
fetch-ocsp-response (using OpenSSL 1.0.1k 8 Jan 2015)
fetch-ocsp-response (using OpenSSL 1.0.1k 8 Jan 2015)
fetch-ocsp-response (using OpenSSL 1.0.1k 8 Jan 2015)
failed to extract ocsp URI from examples/h2o/server.crt
[OCSP Stapling] disabled for certificate file:examples/h2o/server.crt
failed to extract ocsp URI from examples/h2o/alternate.crt
[OCSP Stapling] disabled for certificate file:examples/h2o/alternate.crt
failed to extract ocsp URI from examples/h2o/server.crt
[OCSP Stapling] disabled for certificate file:examples/h2o/server.crt
failed to extract ocsp URI from examples/h2o/alternate.crt
[OCSP Stapling] disabled for certificate file:examples/h2o/alternate.crt

Thanks.