#include <nng/nng.h>
int nng_msg_append(nng_msg *msg, const void *val, size_t size);
int nng_msg_append_u16(nng_msg *msg, uint16_t val16);
int nng_msg_append_u32(nng_msg *msg, uint32_t val32);
int nng_msg_append_u64(nng_msg *msg, uint64_t val64);The nng_msg_append() family of functions appends data to
the end of the body of message msg, reallocating it if necessary.
The first function appends size bytes, copying them from val.
The remaining functions append the value specified (such as val32) in
network-byte order (big-endian).