recv, recvfrom, recvmsg - receive a message from a socket
cc [ flag... ] file... -lsocket -lnsl [ library... ] #include <sys/types.h> #include <sys/socket.h> #include <sys/uio.h> ssize_t recv(int s, void *buf, size_t len, int flags);
ssize_t recvfrom(int s, void *buf, size_t len, int flags, struct sockaddr *from, socklen_t *fromlen);
ssize_t recvmsg(int s, struct msghdr *msg, int flags);
The recv(), recvfrom(), and recvmsg() functions are used to receive messages from another socket. The s socket is created with socket(3SOCKET).
If from is a non-NULL pointer, the source address of the message is filled in. The value-result parameter fromlen is initialized to the size of the buffer associated with from and modified on return to indicate the actual size of the address stored in the buffer. The length of the message is returned. If a message is too long to fit in the supplied buffer, excess bytes may be discarded depending on the type of socket from which the message is received. See socket(3SOCKET).
If no messages are available at the socket, the receive call waits for a message to arrive. If the socket is non-blocking, -1 is returned with the external variable errno set to EWOULDBLOCK. See fcntl(2).
For processes on the same host, recvmsg() can be used to receive a file descriptor from another process, but it cannot receive ancillary data. See libxnet(3LIB).
If a zero-length buffer is specified for a message, an EOF condition results that is indistinguishable from the successful transfer of a file descriptor. For that reason, one or more bytes of data should be provided when recvmsg() passes a file descriptor.
The select(3C) call can be used to determine when more data arrives.
The flags parameter is formed by an OR operation on one or more of the following:
The recvmsg() function call uses a msghdr structure defined in <sys/socket.h> to minimize the number of directly supplied parameters.
Upon successful completion, these functions return the number of bytes received. Otherwise, they return -1 and set errno to indicate the error.
The recv(), recvfrom(), and recvmsg() functions return errors under the following conditions:
The recv() and recvfrom() functions fail under the following conditions:
The recvmsg() function returns errors under the following conditions:
See attributes(5) for descriptions of the following attributes:
fcntl(2), ioctl(2), read(2), connect(3SOCKET), getsockopt(3SOCKET), libxnet(3LIB), select(3C), send(3SOCKET), socket(3SOCKET), socket.h(3HEAD), attributes(5)
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Created 1996-2023 by Maxim Chirkov
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