/* Include for communications with GNUstep Distributed Objects name server.
Copyright (C) 1996, 1997 Free Software Foundation, Inc.
Written by: Richard Frith-Macdonald <richard@brainstorm.co.uk>
Created: October 1996
This file is part of the GNUstep Base Library.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public
License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with this library; if not, write to the Free
Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02111 USA.
*/
/*
* About the GNU Distributed Objects name-server
*
* The name server is intended to work with both the UDP and the TCP
* protocols. It is intended that the TCP interface be used by
* GNUstep programs, while the UDP interface is intended primarily
* for communication between name servers on different machines.
*
* The communications protocol is identical for both TCP and UDP and
* consists of a simple request-response sequence.
*
* Each request is a single message consisting of -
* a single byte request type,
* a single byte giving name length,
* a single byte specifying the type of port being registered
* or looked up, or a nul byte for probe operations.
* a single nul byte.
* a four byte port number in network byte order must be
* present for register operations, otherwise this is zero.
* a service name of 0 to GDO_NAME_MAX_LEN bytes (or two IP
* addresses in network byte order and an optional list of
* additional addresseso for probe operations)
* 0 to GDO_NAME_MAX_LEN nul bytes padding the service name to its
* full size.
* a terminating nul byte.
* The total is always sent in a packet with everything after the
* service name (except the final byte) cleared to nul bytes.
*
* Each response consists of at least 4 bytes and depends on the
* corresponding request type and where it came from as follows -
*
* Request type Effect
*
* GDO_LOOKUP Looks up the server name and returns its port number.
* Response is the port number in network byte order,
* or zero if the named server was not registered.
*
* GDO_REGISTER Registers the given server name with a port number.
* This service is only available to processes on the
* same host as the name server.
* Response is the port number in network byte order,
* or zero if the named server was already registered.
*
* GDO_UNREG Un-register the server name and return old port number.
* If the server name is of length zero, and the port is
* non-zero then all names for the port are unregistered.
* This service is only available to a process on the
* same host as this name server.
* Response is the old port number in network byte order,
* or zero if the name could not be un-registered.
* If multiple names were unregistered the response is
* the port for those names.
*
* GDO_SERVERS Return a list of the known servers on the local net.
* Response is an unsigned long (in network byte order)
* saying how many servers the name server knows about,
* followed by a list of their IP addresses in network
* byte order.
* NB. This response may not be possible over UDP as the
* response length may exceed the maximum UDP packet size.
*
* GDO_NAMES Return a list of registered names known to the server.
* Response is an unsigned long (in network byte order)
* saying how many bytes of data are to follow,
* followed by a list of the names each preceded by the
* name length (a single byte) and port type (a byte).
* NB. This response may not be possible over UDP as the
* response length may exceed the maximum UDP packet size.
*
* The following are used for communications between name servers -
*
* GDO_PROBE Requests a response
* Passes two IP addresses in the name field - first the
* address of the sender, next that of the recipient.
* The packet may (optionally) include a variable number
* of addresses (as specified by the name length minus the
* size of the two addresses), each of which is an internet
* address on which the sender is also listening.
* For a request from a name server via UDP there is no
* response, but a GDO_REPLY request is sent.
* For a request from a non-name-server, or a TCP
* connect, the response is the port number of this
* server in network byte order.
*
* GDO_PREPLY Replies to a GDO_PROBE via UDP from a name server.
* The format of the message is as for GDO_PROBE.
* No response is sent.
*
*
* HOW IT WORKS AND WHY (implementation notes)
*
* 1. The fixed size of a request packet was chosen for maximum
* ease and speed of implementation of a non-blocking name server.
* The server knows how much it needs to read and can therefore
* usually do a read as a single operation since it doesn't have
* to read a little, figure out request length, allocate a buffer,
* and read the rest.
*
* The server name length (bytes) is specified - no assumptions
* should be made about whether the name contains nul characters
* or indeed about the name at all. This is future-proofing.
*
* 2. Why UDP as well as TCP?
* The OpenStep specification says that a connection may be
* established to any host on the local network which supplys a
* named service if the host name is specified as '*'
*
* This means that the application must poll to see if it can
* find a server with the name it wants. The polling could take
* a huge amount of time!
*
* To make this all easier - the server is capable of supplying
* a list of those hosts on the local network which it knows to
* have (or have had) a name server running on them.
*
* The application then need only poll those name servers to find
* the service it wants.
*
* However - to give the application a list of hosts, the name
* server must have got the information from somewhere.
* To gather the information the server has to poll the machines
* on the net which would take ages using TCP since attempts to
* talk to machines which are down or do not exist will take a
* while to time out.
*
* To make things speedy, the server sends out GDO_PROBE requests
* on UDP to all the machines on the net when it starts up.
* Each machine which has a name server notes that the new name
* server has started up and sends back a GDOPREPLY packet so
* that the new name server will know about it.
*
* Things are never perfect though - if a name server dies, the
* other name servers won't know, and will continute to tell
* applications that it is there.
*
* 3. Port type codes - these are used to say what the port is for so
* that clients can look up only the names that are relevant to them.
* This is to permit the name server to be used for multiple
* communications protocols (at the moment, tcp or udp) and for
* different systems (distributed objects or others).
* This guarantees that if one app is using DO over UDP, its services
* will not be found by an app which is using DO over TCP.
*/
#define GDOMAP_PORT (538) /* The well-known port for name server. */
/*
* Request type codes
*/
#define GDO_REGISTER 'R'
#define GDO_LOOKUP 'L'
#define GDO_UNREG 'U'
#define GDO_SERVERS 'S'
#define GDO_PROBE 'P'
#define GDO_PREPLY 'p'
#define GDO_NAMES 'N'
/*
* Port type codes
*/
#define GDO_NET_MASK 0x70 /* Network protocol of port. */
#define GDO_NET_TCP 0x10
#define GDO_NET_UDP 0x10
#define GDO_SVC_MASK 0x0f /* High level protocol of port. */
#define GDO_SVC_GDO 0x01
#define GDO_SVC_FOREIGN 0x02
/* tcp/ip distributed object server. */
#define GDO_TCP_GDO (GDO_NET_TCP|GDO_SVC_GDO)
/* udp/ip distributed object server. */
#define GDO_UDP_GDO (GDO_NET_UDP|GDO_SVC_GDO)
/* tcp/ip simple socket connection. */
#define GDO_TCP_FOREIGN (GDO_NET_TCP|GDO_SVC_FOREIGN)
/* udp/ip simple socket connection. */
#define GDO_UDP_FOREIGN (GDO_NET_UDP|GDO_SVC_FOREIGN)
#define GDO_NAME_MAX_LEN 255 /* Max length registered name. */
/*
* Structure to hold a request.
*/
typedef struct {
unsigned char rtype; /* Type of request being made. */
unsigned char nsize; /* Length of the name to use. */
unsigned char ptype; /* Type of port registered. */
unsigned char dummy;
unsigned int port;
unsigned char name[GDO_NAME_MAX_LEN+1];
} gdo_req;
#define GDO_REQ_SIZE sizeof(gdo_req) /* Size of a request packet. */
/*
* If you have a fascist sysadmin who will not let you run gdomap
* as root and will not even let you modify /etc/services to point
* gdomap to another port, you can uncomment the next #define to
* run gdomap on port 6006 (or modify this to a port of your choice).
* Whatever port you choose, you should make sure that no other
* processes running on your network use that number!
*
* When you have done this you must recompile gdomap.c and
* NSPortNameServer.m and re-install the base library with
* the new NSPortNameServer.o
*
* NB. Doing this will render your system unable to communicate with
* other systems which have not performed the same remapping. You
* should not do it unless you have no choice.
*/
/* #define GDOMAP_PORT_OVERRIDE 6006 */
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