NAME

       xs_tcp - Crossroads unicast transport using TCP

SYNOPSIS

       TCP is an ubiquitous, reliable, unicast transport. When connecting distributed
       applications over a network with Crossroads, using the TCP transport will likely be your
       first choice.

ADDRESSING

       A Crossroads address string consists of two parts as follows: transport://[source
       address;]endpoint. The transport part specifies the underlying transport protocol to use,
       and for the TCP transport shall be set to tcp. source address is optional. 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 xs_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:

       •   The wild-card *, meaning all available interfaces.

       •   The primary IPv4 or IPv6 address assigned to the interface, in its numeric
           representation.

       •   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 IP address may be used to specify an interface.

   Connecting a socket
       When connecting a socket to a peer address using xs_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:

       •   The DNS name of the peer.

       •   The IPv4 or IPv6 address of the peer, in it’s numeric representation.

WIRE FORMAT

       Crossroads 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 = xs_bind(socket, "tcp://*:5555");
           assert (rc != -1);
           /* TCP port 5555 on the local loop-back interface on all platforms */
           rc = xs_bind(socket, "tcp://127.0.0.1:5555");
           assert (rc != -1);
           /* TCP port 5555 on the first Ethernet network interface on Linux */
           rc = xs_bind(socket, "tcp://eth0:5555");
           assert (rc != -1);

       Connecting a socket.

           /* Connecting using an IP address */
           rc = xs_connect(socket, "tcp://192.168.1.1:5555");
           assert (rc != -1);
           /* Connecting using a DNS name */
           rc = xs_connect(socket, "tcp://server1:5555");
           assert (rc != -1);

SEE ALSO

       xs_bind(3) xs_connect(3) xs_pgm(7) xs_ipc(7) xs_inproc(7) xs(7)

AUTHORS

       The Crossroads documentation was written by Martin Sustrik <sustrik@250bpm.com[1]> and
       Martin Lucina <martin@lucina.net[2]>.

NOTES

        1. sustrik@250bpm.com
           mailto:sustrik@250bpm.com

        2. martin@lucina.net
           mailto:martin@lucina.net