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sp-ipc-mapping-01.xml
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<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<rfc category="info" docName="sp-ipc-mapping-01">
<front>
<title abbrev="IPC mapping for SPs">
IPC Mapping for Scalability Protocols
</title>
<author fullname="Martin Sustrik" initials="M." role="editor"
surname="Sustrik">
<address>
<email>sustrik@250bpm.com</email>
</address>
</author>
<date month="November" year="2014" />
<area>Applications</area>
<workgroup>Internet Engineering Task Force</workgroup>
<keyword>IPC</keyword>
<keyword>UNIX</keyword>
<keyword>SP</keyword>
<abstract>
<t>This document defines the IPC mapping for scalability protocols.
It deals with how IPC (inter-process communication) should be
implemented on POSIX-compliant platforms.</t>
</abstract>
</front>
<middle>
<section title = "Underlying protocol">
<t>This mapping should be layered directly on the top of AF_UNIX
sockets of type SOCK_STREAM. On the platforms where AF_UNIX sockets
are not available IPC mapping may be done in a platform-specific way
and SHOULD be described in a separate RFC.</t>
<t>There's no fixed file to use for SP communication. Instead, filenames
are assigned to individual services by the user.</t>
</section>
<section title = "Connection initiation">
<t>Before binding the AF_UNIX socket the implementation SHOULD check
whether there's another process bound to the address. If not so
it SHOULD try to delete the associated file, if present. This measure
will prevent subsequent bind from failing if there's a leftover file
from the previous runs of the application.</t>
<t>The check can be performed in a platform-specific way, however,
a generic way to implement it is to try to connect to the address
and close the connection immediately if successful.</t>
<t>After establishing underlying AF_UNIX connection, both parties MUST
send the protocol header immediately. Both endpoints MUST then wait
for the protocol header from the peer before proceeding on.</t>
<t>The protocol header is 8 bytes long and looks like this:</t>
<figure>
<artwork>
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x00 | 0x53 | 0x50 | version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| type | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<t>First four bytes of the protocol header are used to make sure that
the peer's protocol is compatible with the protocol used by the local
endpoint.</t>
<t>First four bytes of the protocol header MUST be set to 0x00, 0x53, 0x50
and 0x00 respectively. If the protocol header received from the peer
differs, the TCP connection MUST be closed immediately.</t>
<t>The fact that the first byte of the protocol header is binary zero
eliminates any text-based protocols that were accidentally connected
to the endpoint. Subsequent two bytes make the check even more
rigorous. At the same time they can be used as a debugging hint to
indicate that the connection is supposed to use one of the scalability
protocols -- ASCII representation of these bytes is 'SP'. Finally,
the fourth byte rules out any incompatible versions of this
protocol.</t>
<t>Fifth and sixth bytes of the header form a 16-bit unsigned integer in
network byte order representing the type of SP endpoint on the layer
above. The value SHOULD NOT be interpreted by the mapping, rather
the interpretation should be delegated to the scalability protocol
above the mapping. For informational purposes, it should be noted that
the field encodes information such as SP protocol ID, protocol version
and the role of endpoint within the protocol. Individual values are
assigned by IANA.</t>
<t>Finally, the last two bytes of the protocol header are reserved for
future use and must be set to binary zeroes. If the protocol header
from the peer contains anything else than zeroes in this field, the
implementation MUST close the underlying TCP connection.</t>
</section>
<section title = "Message header">
<t>Once the protocol header is accepted, endpoint can send and receive
messages. Every message starts with a message header consisting of
of a single byte called 'message type'.</t>
<t>The only value of this field that is currently allowed is zero, which
means "in-band" message, i.e. message whose body is passed as a stream
of bytes via the AF_UNIX socket.</t>
<t>The intent of this field is to eventually allow out-of-band transfer
of the message bodies, e.g. via shared memory.</t>
<t>In-band message type MUST be implemented.</t>
</section>
<section title = "In-band messages">
<t>For in-band messages, message header is immediately followed by 64-bit
unsigned integer in network byte order representing the payload size,
in bytes. Thus, the message payload can be from 0 to 2^64-1 bytes long.
The payload of the specified size follows directly after the size
field:</t>
<figure>
<artwork>
+-----------+------------+-----------------+
| type (8b) | size (64b) | payload |
+-----------+------------+-----------------+
</artwork>
</figure>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This memo includes no request to IANA.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>The mapping isn't intended to provide any additional security in
addition to what AF_UNIX does.</t>
</section>
</middle>
</rfc>