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135 lines
4.8 KiB
Plaintext
135 lines
4.8 KiB
Plaintext
= zmq_tcp(7)
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== NAME
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zmq_tcp - 0MQ unicast transport using TCP
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== SYNOPSIS
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TCP is an ubiquitous, reliable, unicast transport. When connecting distributed
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applications over a network with 0MQ, using the TCP transport will likely be
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your first choice.
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== ADDRESSING
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A 0MQ endpoint is a string consisting of a 'transport'`://` followed by an
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'address'. The 'transport' specifies the underlying protocol to use. The
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'address' specifies the transport-specific address to connect to.
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For the TCP transport, the transport is `tcp`, and the meaning of the
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'address' part is defined below.
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Assigning a local address to a socket
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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When assigning a local address to a socket using _zmq_bind()_ with the 'tcp'
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transport, the 'endpoint' shall be interpreted as an 'interface' followed by a
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colon and the TCP port number to use.
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An 'interface' may be specified by either of the following:
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* The wild-card `*`, meaning all available interfaces.
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* The primary IPv4 or IPv6 address assigned to the interface, in its numeric
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representation.
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* The non-portable interface name as defined by the operating system.
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The TCP port number may be specified by:
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* A numeric value, usually above 1024 on POSIX systems.
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* The wild-card `*`, meaning a system-assigned ephemeral port.
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When using ephemeral ports, the caller should retrieve the actual assigned
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port using the ZMQ_LAST_ENDPOINT socket option. See xref:zmq_getsockopt.adoc[zmq_getsockopt]
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for details.
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Unbinding wild-card address from a socket
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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When wild-card `*` 'endpoint' was used in _zmq_bind()_, the caller should use
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real 'endpoint' obtained from the ZMQ_LAST_ENDPOINT socket option to unbind
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this 'endpoint' from a socket using _zmq_unbind()_.
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Connecting a socket
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~~~~~~~~~~~~~~~~~~~
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When connecting a socket to a peer address using _zmq_connect()_ with the 'tcp'
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transport, the 'endpoint' shall be interpreted as a 'peer address' followed by
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a colon and the TCP port number to use.
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You can optionally specify a 'source_endpoint' which will be used as the source
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address for your connection; tcp://'source_endpoint';'endpoint', see the
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'interface' description above for details.
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A 'peer address' may be specified by either of the following:
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* The DNS name of the peer.
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* The IPv4 or IPv6 address of the peer, in its numeric representation.
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Note: A description of the ZeroMQ Message Transport Protocol (ZMTP) which is
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used by the TCP transport can be found at <http://rfc.zeromq.org/spec:23>
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== HWM
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For the TCP transport, the high water mark (HWM) mechanism works in conjunction
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with the TCP socket buffers handled at OS level.
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Depending on the OS and several other factors the size of such TCP buffers will
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be different. Moreover TCP buffers provided by the OS will accommodate a varying
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number of messages depending on the size of messages (unlike ZMQ HWM settings
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the TCP socket buffers are measured in bytes and not messages).
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This may result in apparently inexplicable behaviors: e.g., you may expect that
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setting ZMQ_SNDHWM to 100 on a socket using TCP transport will have the effect
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of blocking the transmission of the 101-th message if the receiver is slow.
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This is very unlikely when using TCP transport since OS TCP buffers will typically
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provide enough buffering to allow you sending much more than 100 messages.
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Of course if the receiver is slow, transmitting on a TCP ZMQ socket will eventually trigger
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the "mute state" of the socket; simply don't rely on the exact HWM value.
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Obviously the same considerations apply for the receive HWM (see ZMQ_RCVHWM).
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== EXAMPLES
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.Assigning a local address to a socket
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----
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// TCP port 5555 on all available interfaces
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rc = zmq_bind(socket, "tcp://*:5555");
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assert (rc == 0);
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// TCP port 5555 on the local loop-back interface on all platforms
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rc = zmq_bind(socket, "tcp://127.0.0.1:5555");
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assert (rc == 0);
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// TCP port 5555 on the first Ethernet network interface on Linux
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rc = zmq_bind(socket, "tcp://eth0:5555");
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assert (rc == 0);
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----
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.Connecting a socket
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----
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// Connecting using an IP address
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rc = zmq_connect(socket, "tcp://192.168.1.1:5555");
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assert (rc == 0);
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// Connecting using a DNS name
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rc = zmq_connect(socket, "tcp://server1:5555");
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assert (rc == 0);
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// Connecting using a DNS name and bind to eth1
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rc = zmq_connect(socket, "tcp://eth1:0;server1:5555");
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assert (rc == 0);
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// Connecting using a IP address and bind to an IP address
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rc = zmq_connect(socket, "tcp://192.168.1.17:5555;192.168.1.1:5555");
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assert (rc == 0);
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----
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== SEE ALSO
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* xref:zmq_bind.adoc[zmq_bind]
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* xref:zmq_connect.adoc[zmq_connect]
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* xref:zmq_pgm.adoc[zmq_pgm]
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* xref:zmq_ipc.adoc[zmq_ipc]
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* xref:zmq_inproc.adoc[zmq_inproc]
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* xref:zmq_vmci.adoc[zmq_vmci]
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* xref:zmq.adoc[zmq]
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== AUTHORS
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This page was written by the 0MQ community. To make a change please
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read the 0MQ Contribution Policy at <https://zeromq.org/how-to-contribute/>.
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