What is the second paramenter of TCPSocket.send in Ruby?

Question

I am using this line to send a message via a Ruby (1.8.7) socket:

@@socket.send login_message, 0

(This works fine)

What is the second parameter for? I can't find the send method in the Ruby API docs...

I first thought that it was some C style length of the message. This is why I used login_message.length as second parameter. That worked but I encountered a strange behavior:

Everything works fine when the second parameter is a odd number. If it's an even number the last character gets lost at receiving on the other side (The other side is a C++ program with a C socket). I inspected the network traffic with Wireshark and noticed that the packets look good. All the data is complete. Why is the last character lost when I receive it?

Thank you Lennart

Answer 1

This is the flags parameter, the same as the last parameter to the send() system call. Normally it should be 0, but may be something like Socket::MSG_OOB (to send out-of-band data). For Ruby 1.9 this is documented under BasicSocket.