zmq_recv(3) [debian man page]
ZMQ_RECV(3) 0MQ Manual ZMQ_RECV(3) NAME
zmq_recv - receive a message from a socket SYNOPSIS
int zmq_recv (void *socket, zmq_msg_t *msg, int flags); DESCRIPTION
The zmq_recv() function shall receive a message from the socket referenced by the socket argument and store it in the message referenced by the msg argument. Any content previously stored in msg shall be properly deallocated. If there are no messages available on the specified socket the zmq_recv() function shall block until the request can be satisfied. The flags argument is a combination of the flags defined below: ZMQ_NOBLOCK Specifies that the operation should be performed in non-blocking mode. If there are no messages available on the specified socket, the zmq_recv() function shall fail with errno set to EAGAIN. Multi-part messages A 0MQ message is composed of 1 or more message parts; each message part is an independent zmq_msg_t in its own right. 0MQ ensures atomic delivery of messages; peers shall receive either all message parts of a message or none at all. The total number of message parts is unlimited. An application wishing to determine if a message is composed of multiple parts does so by retrieving the value of the ZMQ_RCVMORE socket option on the socket it is receiving the message from. If there are no message parts to follow, or if the message is not composed of multiple parts, ZMQ_RCVMORE shall report a value of zero. Otherwise, ZMQ_RCVMORE shall report a value of 1, indicating that more message parts are to follow. RETURN VALUE
The zmq_recv() function shall return zero if successful. Otherwise it shall return -1 and set errno to one of the values defined below. ERRORS
EAGAIN Non-blocking mode was requested and no messages are available at the moment. ENOTSUP The zmq_recv() operation is not supported by this socket type. EFSM The zmq_recv() operation cannot be performed on this socket at the moment due to the socket not being in the appropriate state. This error may occur with socket types that switch between several states, such as ZMQ_REP. See the messaging patterns section of zmq_socket(3) for more information. ETERM The 0MQ context associated with the specified socket was terminated. ENOTSOCK The provided socket was invalid. EINTR The operation was interrupted by delivery of a signal before a message was available. EFAULT The message passed to the function was invalid. EXAMPLE
Receiving a message from a socket. /* Create an empty 0MQ message */ zmq_msg_t msg; int rc = zmq_msg_init (&msg); assert (rc == 0); /* Block until a message is available to be received from socket */ rc = zmq_recv (socket, &msg, 0); assert (rc == 0); /* Release message */ zmq_msg_close (&msg); Receiving a multi-part message. int64_t more; size_t more_size = sizeof more; do { /* Create an empty 0MQ message to hold the message part */ zmq_msg_t part; int rc = zmq_msg_init (&part); assert (rc == 0); /* Block until a message is available to be received from socket */ rc = zmq_recv (socket, &part, 0); assert (rc == 0); /* Determine if more message parts are to follow */ rc = zmq_getsockopt (socket, ZMQ_RCVMORE, &more, &more_size); assert (rc == 0); zmq_msg_close (&part); } while (more); SEE ALSO
zmq_send(3) zmq_getsockopt(3) zmq_socket(7) zmq(7) AUTHORS
This manual page was written by the 0MQ community. 0MQ 2.2.0 04/04/2012 ZMQ_RECV(3)
Check Out this Related Man Page
ZMQ_TCP(7) 0MQ Manual ZMQ_TCP(7) NAME
zmq_tcp - 0MQ unicast transport using TCP SYNOPSIS
TCP is an ubiquitous, reliable, unicast transport. When connecting distributed applications over a network with 0MQ, using the TCP transport will likely be your first choice. ADDRESSING
A 0MQ address string consists of two parts as follows: transport://endpoint. The transport part specifies the underlying transport protocol to use, and for the TCP transport shall be set to tcp. The meaning of the endpoint part for the TCP transport is defined below. Assigning a local address to a socket When assigning a local address to a socket using zmq_bind() with the tcp transport, the endpoint shall be interpreted as an interface followed by a colon and the TCP port number to use. An interface may be specified by either of the following: o The wild-card *, meaning all available interfaces. o The primary IPv4 address assigned to the interface, in its numeric representation. o The interface name as defined by the operating system. Note Interface names are not standardised in any way and should be assumed to be arbitrary and platform dependent. On Win32 platforms no short interface names exist, thus only the primary IPv4 address may be used to specify an interface. Connecting a socket When connecting a socket to a peer address using zmq_connect() with the tcp transport, the endpoint shall be interpreted as a peer address followed by a colon and the TCP port number to use. A peer address may be specified by either of the following: o The DNS name of the peer. o The IPv4 address of the peer, in its numeric representation. WIRE FORMAT
0MQ messages are transmitted over TCP in frames consisting of an encoded payload length, followed by a flags field and the message body. The payload length is defined as the combined length in octets of the message body and the flags field. For frames with a payload length not exceeding 254 octets, the payload length shall be encoded as a single octet. The minimum valid payload length of a frame is 1 octet, thus a payload length of 0 octets is invalid and such frames SHOULD be ignored. For frames with a payload length exceeding 254 octets, the payload length shall be encoded as a single octet with the value 255 followed by the payload length represented as a 64-bit unsigned integer in network byte order. The flags field consists of a single octet containing various control flags: Bit 0 (MORE): More message parts to follow. A value of 0 indicates that there are no more message parts to follow; or that the message being sent is not a multi-part message. A value of 1 indicates that the message being sent is a multi-part message and more message parts are to follow. Bits 1-7: Reserved. Bits 1-7 are reserved for future expansion and MUST be set to zero. The following ABNF grammar represents a single frame: frame = (length flags data) length = OCTET / (escape 8OCTET) flags = OCTET escape = %xFF data = *OCTET The following diagram illustrates the layout of a frame with a payload length not exceeding 254 octets: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Payload length| Flags | Message body ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message body ... +-+-+-+-+-+-+- ... The following diagram illustrates the layout of a frame with a payload length exceeding 254 octets: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0xff | Payload length ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Payload length ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Payload length| Flags | Message body ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message body ... +-+-+-+-+-+-+-+ ... EXAMPLES
Assigning a local address to a socket. /* TCP port 5555 on all available interfaces */ rc = zmq_bind(socket, "tcp://*:5555"); assert (rc == 0); /* TCP port 5555 on the local loop-back interface on all platforms */ rc = zmq_bind(socket, "tcp://127.0.0.1:5555"); assert (rc == 0); /* TCP port 5555 on the first Ethernet network interface on Linux */ rc = zmq_bind(socket, "tcp://eth0:5555"); assert (rc == 0); Connecting a socket. /* Connecting using an IP address */ rc = zmq_connect(socket, "tcp://192.168.1.1:5555"); assert (rc == 0); /* Connecting using a DNS name */ rc = zmq_connect(socket, "tcp://server1:5555"); assert (rc == 0); SEE ALSO
zmq_bind(3) zmq_connect(3) zmq_pgm(7) zmq_ipc(7) zmq_inproc(7) zmq(7) AUTHORS
This manual page was written by the 0MQ community. 0MQ 2.2.0 04/04/2012 ZMQ_TCP(7)