libdill: Structured Concurrency for C


prefix_attach_mem - creates PREFIX protocol on top of underlying socket


#include <libdill.h>

int prefix_attach_mem(
    int s,
    size_t hdrlen,
    int flags,
    struct prefix_storage* mem);


PREFIX is a message-based protocol to send binary messages prefixed by size. The protocol has no initial handshake. Terminal handshake is accomplished by each peer sending size field filled by 0xff bytes.

This function instantiates PREFIX protocol on top of the underlying protocol.

This function allows to avoid one dynamic memory allocation by storing the object in user-supplied memory. Unless you are hyper-optimizing use prefix_attach instead.

s: Handle of the underlying socket. It must be a bytestream protocol.

hdrlen: Size of the length field, in bytes.

flags: If set to PREFIX_BIG_ENDIAN (also known as network byte order, the default option) the most significant byte of the size will be sent first on the wire. If set to PREFIX_LITTLE_ENDIAN the least signiticant byte will come first.

mem: The structure to store the newly created object in. It must not be deallocated before the object is closed.

The socket can be cleanly shut down using prefix_detach function.

This function is not available if libdill is compiled with --disable-sockets option.


In case of success the function returns newly created socket handle. In case of error it returns -1 and sets errno to one of the values below.



int s = tcp_connect(&addr, -1);
s = prefix_attach(s, 2, 0);
msend(s, "ABC", 3, -1);
char buf[256];
ssize_t sz = mrecv(s, buf, sizeof(buf), -1);
s = prefix_detach(s, -1);


hclose(3) mrecv(3) mrecvl(3) msend(3) msendl(3) prefix_attach(3) prefix_detach(3)