libdill: Structured Concurrency for C


mrecv, mrecvl - receive message from a socket


#include <libdill.h>

ssize_t mrecv(int s, void *buf, size_t len, int64_t deadline);

ssize_t mrecvl(int s, struct iolist *first, struct iolist *last, int64_t deadline);


Function mrecv() receives message from a socket. It is a blocking operation that unblocks only after entire message is received. There is no such thing as partial receive. Either entire message is received or no message at all.

buf points to the buffer len bytes long to write the received message to. If buf is NULL the message will be received but it will be dropped rather than returned to the user.

deadline is a point in time when the operation should time out. Use the now() function to get your current point in time. 0 means immediate timeout, i.e., perform the operation if possible or return without blocking if not. -1 means no deadline, i.e., the call will block forever if the operation cannot be performed.

Function mrecvl() accepts a linked list of buffers instead of a single buffer. first points to the first item in the list, last points to the last buffer in the list. Structure iolist has following members:

void *iol_base;          /* Pointer to the buffer. */
size_t iol_len;          /* Size of the buffer. */
struct iolist *iol_next; /* Next buffer. */
int iol_rsvd;            /* Reserved. Must be set to zero. */

mrecvl() returns EINVAL error in case the list is malformed:

The list can be temporarily modified while the function is in progress. However, once the function returns the list is guaranteed to be the same as before the call.

If both first and last arguments to mrecvl() are set to NULL the message is received and silently dropped. The function will still return the size of the message.


The function returns size of the message on success. On error, it returns -1 and sets errno to one of the values below.



char msg[100];
ssize_t msgsz = mrecv(s, msg, sizeof(msg), -1);