Add receive_buffer_bytes config setting to optionally set socket receive buffer size in bytes

[IrlJidel]

Fixes #22

I used receive_buffer_bytes as config option name as kafka plugin uses that name as well.

Also an interesting thing I noticed during testing is that when run under jruby, it appears that the receive buffer is actually set to only half the configured value of net.core.rmem_default. Behavior is the same under OpenJDK and Oracle Java

:~$ sysctl net.core.rmem_default
net.core.rmem_default = 212992

:~$ rvm use jruby
Using jruby-9.0.5.0
:~$ ruby -ve  'require "socket"; @udp = UDPSocket.new(Socket::AF_INET); puts @udp.getsockopt(Socket::SOL_SOCKET, Socket::SO_RCVBUF).unpack("i")[0]'
jruby 9.0.5.0 (2.2.3) 2016-01-26 7bee00d OpenJDK 64-Bit Server VM 25.91-b14 on 1.8.0_91-8u91-b14-0ubuntu4~14.04-b14 +jit [linux-amd64]
106496

$ rvm use jruby-1.7
Using jruby-1.7.23
~$ ruby -ve  'require "socket"; @udp = UDPSocket.new(Socket::AF_INET); puts @udp.getsockopt(Socket::SOL_SOCKET, Socket::SO_RCVBUF).unpack("i")[0]'
jruby 1.7.23 (1.9.3p551) 2015-11-24 f496dd5 on OpenJDK 64-Bit Server VM 1.8.0_91-8u91-b14-0ubuntu4~14.04-b14 +jit [linux-amd64]
106496

~$ rvm use ruby
Using ruby-2.3.0
~$ ruby -ve  'require "socket"; @udp = UDPSocket.new(Socket::AF_INET); puts @udp.getsockopt(Socket::SOL_SOCKET, Socket::SO_RCVBUF).unpack("i")[0]'
ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-linux]
212992

:~$ rvm use ruby-1.9
Using ruby-1.9.3-p551
~$ ruby -ve  'require "socket"; @udp = UDPSocket.new(Socket::AF_INET); puts @udp.getsockopt(Socket::SOL_SOCKET, Socket::SO_RCVBUF).unpack("i")[0]'
ruby 1.9.3p551 (2014-11-13 revision 48407) [x86_64-linux]
212992

[jsvd]

@IrlJidel interesting, it seems like a misinterpretation of the documentation of the SO_RCVBUF:

              The kernel doubles this value (to allow space for bookkeeping
              overhead) when it is set using setsockopt(2), and this doubled
              value is returned by getsockopt(2).

[jsvd]

please use && instead of and

[jsvd]

very minor comment, will merge once addressed.

[IrlJidel]

@jsvd updated PR to address 'and' vs '&&' usage

[elasticsearch-bot]

João Duarte merged this into the following branches!

Branch	Commits
master	b3903b1, 23c7af6, c8e57c9