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XS_TCP(7)		     Crossroads	I/O Manual		     XS_TCP(7)

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:

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

       o   The primary IPv4 or IPv6 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 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:

       o   The DNS name	of the peer.

       o   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

Crossroads I/O 1.2.0		  02/28/2021			     XS_TCP(7)

NAME | SYNOPSIS | ADDRESSING | WIRE FORMAT | EXAMPLES | SEE ALSO | AUTHORS | NOTES

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