NN_SEND(3)

📦
version 1.2.2 · 5 versions
, in fedora 44

💌 NN_SEND(3) — the nanomsg page, bestie edition

okay so real quick: this is nn_send(3) from nanomsg 1.2.2, and it's literally the "yeet a message into the void (but like, a targeted void)" function. pull up a chair, we're doing this together 🫶

✨ NAME ✨

nn_send — send a message 💅

🌸 SYNOPSIS 🌸

#include <nanomsg/nn.h>

int nn_send (int s, const void *buf, size_t len, int flags);

🦋 DESCRIPTION 🦋

so the vibe is: this function sends a message made of the data sitting in the buffer that buf points at, out through the socket s. that message is gonna be exactly len bytes long. periodt.

✨ plot twist option ✨ — if you'd rather send a buffer that was allocated by nn_allocmsg(3), you do it differently: point buf at the pointer to the buffer, and set len to the NN_MSG constant. in that case, a successful nn_send call deallocates the buffer for you. and bestie, listen to me: if you try to deallocate it yourself afterwards, that's undefined behaviour. not cute. do not.

which of the peers actually receives your message? that's not up to this function — it's determined by the particular socket type. iykyk 💫

the flags argument is a combination of the flags listed below:

  • NN_DONTWAIT — says "do this in non-blocking mode, pls". if the message can't be sent straight away, the function will fail with errno set to EAGAIN. no waiting, no patience, we move 💨

💖 RETURN VALUE 💖

if it works? you get back the number of bytes in the message. slay.

if it doesn't? you get -1, and errno is set to one of the values down below. 😭

🔥 ERRORS 🔥

  • EFAULT — buf is NULL, or len is NN_MSG and the message pointer (the one buf points to) is NULL.
  • EBADF — the socket you handed over is invalid. not a real socket, bestie.
  • ENOTSUP — this socket type just doesn't support this operation. it's not you, it's the socket.
  • EFSM — the operation can't happen right now because the socket isn't in the right state. this one shows up with socket types that switch between several states — main character energy, honestly.
  • EAGAIN — non-blocking mode was requested and the message can't be sent at the moment.
  • EINTR — a signal showed up mid-operation and interrupted it before the message was sent. rude.
  • ETIMEDOUT — individual socket types may define their own specific timeouts. if such a timeout gets hit, you get this error.
  • ETERM — the library is terminating. it's over, we're done here 💀

🌈 EXAMPLE 🌈

using data directly:

nbytes = nn_send (s, "ABC", 3, 0);
assert (nbytes == 3);

using a pre-allocated message buffer:

void *msg = nn_allocmsg(3, 0);
strncpy(msg, "ABC", 3);
nbytes = nn_send (s, &msg, NN_MSG, 0);
assert (nbytes == 3);

notice how the second one passes &msg and NN_MSG? yeah. that's the whole bit. 🎀

👑 SEE ALSO 👑

🧚 AUTHORS 🧚

Martin Sustrik <sustrik@250bpm.com>

⭐ and that's the whole page, no cap. go forth and send responsibly, my love 🫶

this has been NN_SEND(3) from nanomsg 1.2.2, dated 2026-01-16. mwah. 💜

📦 where this page comes from