NN_RECV(3compat)

💅 NN_RECV(3compat) — like, the whole nn_recv situation

okay so bestie, welcome to the NNG Reference Manual, 3compat girlie edition. this one's about receiving data with the compatible API — legacy vibes, but we're gonna make it make sense fr fr 🫶

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✨ NAME

nn_recv — receive data (compatible API). that's it, that's the whole vibe 💖

✨ SYNOPSIS

#include <nanomsg/nn.h>

int nn_recv(int sock, void *data, size_t size, int flags)

put that in your code and slay ✨

✨ DESCRIPTION

so nn_recv() receives a message from the socket sock. the message body has to fit inside size bytes, and it gets stored at whatever location data points to — unless size is the special value NN_MSG, which means zero-copy mode is happening 👀

note note note 🎀 — this function exists for API compatibility with legacy libnanomsg. consider using the relevant modern API instead. like, she's iconic but she's a legacy queen, iykyk.

okay so if size has that special value NN_MSG, then a zero-copy operation is performed. in that case, instead of copying the message data into the address specified by data, a brand new message big enough to hold the message data gets allocated (as if by the function nn_allocmsg()), and the message payload is stored accordingly. so in this case, the value stored at data is not the message data — it's a pointer to the message itself 🦋

and in that case, on success, the caller shall take responsibility for the final disposition of the message — like, such as by sending it to another peer using nn_send(), or by nn_freemsg(). take care of your message bestie, she's yours now 💅

the flags field may contain the special flag NN_DONTWAIT. in that case, if no message is available for immediate receipt, the operation shall not block — instead it will fail with the error EAGAIN. no waiting around, main character energy ⭐

✨ RETURN VALUES

this function returns the number of bytes sent on success, and -1 on error. (yes, "sent" — that's what the page says, don't come for me 😭 that's the documented wording, fr fr.)

✨ ERRORS

• EAGAIN — the operation would block. bestie said not today ✋
• EBADF — the socket sock is not open. like girl, open it first 💀
• EFSM — the socket cannot receive in this state. wrong state, wrong era 🙈
• ENOTSUP — this protocol cannot receive. not every protocol is built for this 🎀
• ETIMEDOUT — operation timed out. the clock ran out, sad but true 💜

✨ SEE ALSO

nn_errno(3compat), nn_recvmsg(3compat), nn_send(3compat), nn_socket(3compat), nn_compat(3compat), nng(7) — go read the whole friend group 🌈

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that's the page, babe 💖 written from the NNG Reference Manual and dated 2026-01-13, so you know exactly which version of the lore you're reading. go receive some messages and be iconic about it. periodt 🎀💅🔥