uv_send_buffer_size does not allow you to set SO_SNDBUF to 0

[mikinho]

Using 0 to wrap getsockopt within uv__socket_sockopt prevents us from using uv_send_buffer_size to set SO_SNDBUF socket option to 0 (zero) which on Windows would allow the stack to send from your application buffer directly.

[mikinho]

Use case for setting SO_SNDBUF to zero: http://support.microsoft.com/kb/201213

Will be happy to submit a patch next week

[saghul]

Thanks for opening the issue here! What kind of fix do you have in mind?

[txdv]

Set the SO_SNDBUF socket option to 0 (zero) to allow the stack to send from your application buffer directly.

That is cool. Never knew that you could do something.

@mikinho Are you trying to use this particular feature or is it just a nice to have?

[mikinho]

I wanted to review the libuv guidelines on breaking backwards compatibility but my thought is to split uv__socket_sockopt into uv__socket_getsockopt / uv__socket_setsockopt and similarly uv_send_buffer_size into uv_send_buffer_get_size / uv_send_buffer_set_size and uv_recv_buffer_size into uv_recv_buffer_get_size / uv_recv_buffer_set_size.

uv_send_buffer_size could be left as is to maintain backwards compatibility.

I would also like to add a callback on uv_udp_s that is invoked after our socket is bound within uv__udp_bind. This would allow to set socket options before any datagrams are sent. Unless I'm missing something there is currently no way to set SNDBUF until after a send completes since no socket exists until then.

[mikinho]

@txdv I'm using it now within a project that I'm updating it use libuv. That lead me to find the welcome addition of uv_send_buffer_size and consequently the limitation of being able to set SO_SNDBUF to zero.

[txdv]

Well, the uv__socket_sockopt is internal, so yeah, we change that internally without modifying code. I did this way because I was unaware that 0 on windows would use the buffer directly from user space, which is an interesting feature.

We might change 'retrieve' value to -1, which would be the simplest hack. Unless you want to set your buffer to > 2gb. I guess going with the duality of socket_getsockopt, socket_setsockopt is the best way.

[saghul]

I wanted to review the libuv guidelines on breaking backwards compatibility but my thought is to split uv__socket_sockopt into uv__socket_getsockopt / uv__socket_setsockopt and similarly uv_send_buffer_size into uv_send_buffer_get_size / uv_send_buffer_set_size and uv_recv_buffer_size into uv_recv_buffer_get_size / uv_recv_buffer_set_size.

uv_send_buffer_size could be left as is to maintain backwards compatibility.

That would work for v1.x, since we can't break backwards compatibility. We can remove the deprecated functions in v2.x.

I would also like to add a callback on uv_udp_s that is invoked after our socket is bound within uv__udp_bind. This would allow to set socket options before any datagrams are sent. Unless I'm missing something there is currently no way to set SNDBUF until after a send completes since no socket exists until then.

Binding is synchronous, so there is no point in adding a callback there. If you want to set the buffer before sending any data just call uv_udp_bind, the socket will be created and you'll be able to set it.

[txdv]

We have a little corner case of uv_recv_bufer_set_size not really working with 0. I Don't think we need to wait for 2.0

[mikinho]

Binding is synchronous, so there is no point in adding a callback there. If you want to set the buffer before sending any data just call uv_udp_bind , the socket will be created and you'll be able to set it.

Thanks, its late and I didn't think to just call uv_udp_bind directly before sending. That works perfect.

[saghul]

We have a little corner case of uv_recv_bufer_set_size not really working with 0. I Don't think we need to wait for 2.0

It doesn't matter. We shouldn't limit the input, we just call the underlying setsockopt / getsockopt. I'm not a big fan of having 4 functions (well, 6 now) but it is what it is, and they are symmetrical, at least.

[saghul]

Thanks, its late and I didn't think to just call uv_udp_bind directly before sending. That works perfect.

No worries! Thanks for letting us know and volunteering to write the code!