SPREE(2) SPREE(2)
NAME
Spree - distributed interactive sessions.
SYNOPSIS
include "sys.m";
include "draw.m";
include "sets.m";
include "spree.m";
spree := load Spree Spree->PATH;
Range, Object, Clique, Member: import spree;
Set: import Sets;
Archive: import Archives;
Range: adt {
start: int;
end: int;
};
Object: adt {
transfer: fn(o: self ref Object,
r: Range, dst: ref Object, i: int);
setvisibility: fn(o: self ref Object,
visibility: Set);
setattrvisibility: fn(o: self ref Object,
name: string, visibility: Set);
setattr: fn(o: self ref Object,
name: string, val: string, vis: Set);
getattr: fn(o: self ref Object, name: string): string;
delete: fn(o: self ref Object);
deletechildren: fn(o: self ref Object, r: Range);
id: int;
parentid: int;
children: array of ref Object;
objtype: string;
visibility: Set;
# ...private data
};
Clique: adt {
new: fn(parent: self ref Clique, archive: ref Archive,
owner: string): (int, string, string);
newobject: fn(clique: self ref Clique, parent: ref Object,
visibility: int, objtype: string): ref Object;
action: fn(clique: self ref Clique, cmd: string,
objs: list of int, rest: string, whoto: int);
member: fn(clique: self ref Clique, id: int): ref Member;
start: fn(clique: self ref Clique);
breakmsg: fn(clique: self ref Clique, whoto: Sets->Set);
members: fn(clique: self ref Clique): list of ref Member;
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owner: fn(clique: self ref Clique): string;
hangup: fn(clique: self ref Clique);
notify: fn(clique: self ref Clique, cliqueid: int, msg: string);
objects: array of ref Object;
cliqueid: int;
# ...private data
};
Member: adt {
obj: fn(m: self ref Member, id: int): ref Object;
del: fn(m: self ref Member, suspend: int);
id: int;
name: string;
# ...private data
};
Engine: module {
init: fn(srvmod: Spree, clique: ref Clique, argv: list of string): string;
command: fn(member: ref Member, e: string): string;
join: fn(member: ref Member , e: string, suspended: int): string;
leave: fn(member: ref Member): int;
notify: fn(fromid: int, s: string);
readfile: fn(f: int, offset: big, count: int): array of byte;
};
Archives: module {
Archive: adt {
argv: list of string; # how to restart the session.
members: array of string; # members involved.
info: list of (string, string); # any other information.
objects: array of ref Object;
};
init: fn(mod: Spree);
write: fn(clique: ref Clique, info: list of (string, string), file: string, members: Set): string;
read: fn(file: string): (ref Archive, string);
readheader: fn(file: string): (ref Archive, string);
};
rand: fn(n: int): int;
DESCRIPTION
Spree provides a general server interface that allows sets
of distributed clients, cliques, to interact in a controlled
manner, with the interaction mediated by Limbo modules,
known as engines. Each engine decides on the rules of its
particular clique; the engine interface is described at the
end of this manual page, under ``Module Interface''.
This manual page describes the interface as presented to an
engine once it has been loaded by spree. A loaded instance
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of an engine is responsible for a particular clique, in
which one or more members participate. Messages sent by mem-
bers are interpreted by the engine, which responds by making
changes to the hierarchical object database held by the
clique. Behind the scenes spree distributes updates to this
database to members of the clique as appropriate (see
spree(4) for details).
Objects and visibility
Objects hold a clique's visible state. An object has a
unique integer id, which is an index into the array
clique.objects; it also holds a set of attribute-value
pairs, a type, and zero or more child objects. Together, all
the objects in the clique form a hierarchical tree, rooted
at the root object (id 0), which always exists. Each
attribute and each object also has an associated visibility
set, the set of member that sees updates to the attributes
or the children of the object. Each member has a unique id;
in a visibility set (see sets(2)), a member is ``visible''
if the set contains the member's id.
Note that the visibility set of an object does not alter the
visibility of that object's attributes, but only that of its
children (and of their children: in general an object is
visible to a member if the intersection of all its ances-
tors' visibility sets contains that member).
Objects can be transferred inside the hierarchy from one
parent to another. If an object is moved to a parent whose
visibility conceals it from a member, then it will appear to
that member to have been deleted; if it is later made visi-
ble, then it will be recreated for that member. A clique
engine can almost always ignore this technicality, except
for one thing: the identifier used by a particular member to
identify an object is not necessarily the same as that used
by the clique engine. Thus when an engine receives an object
id in a member's message, it should convert it using the
member.obj() function.
Clique
The Clique type holds all the objects in a clique. It allows
the creation of new objects, and provides a way of communi-
cating with members directly. All data members of a Clique
should be treated as read-only.
clique.objects
This array holds the objects in the clique. An
object with identifier id is found at
clique.objects[id].
clique.new(archive,owner)
New creates a new clique. Archive is an archive
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of the game to be created; archive.argv should be
non-nil; its first element should name the engine
to be loaded (as a path relative to the engine
module directory, and without the .dis extension).
clique.newobject(parent, visibility, objtype)
Newobject creates a new object at the end of
parent's children; If parent is nil, the new
object is created under the root object. The new
object has visibility visibility, and type
objtype. An object's type cannot be changed once
it has been created.
clique.action(cmd, objs, rest, whoto)
Action sends a message to some members without
affecting the object hierarchy. It can be used to
send transient events that have no meaning when
stored statically (for example, network latency
probes). The message is sent to the set of mem-
bers given by whoto. Objs is assumed to be a list
of object ids, which are converted appropriately
for each member receiving the message; the final
message is a string built by concatenating cmd,
the list of object ids, and rest, separated by
spaces.
clique.breakmsg(whoto)
Messages are usually sent to clients in an unin-
terrupted stream (as documented in spree(4)), with
a single read returning a potentially large set of
messages. Breakmsg arranges that subsequent mes-
sages received by the members specified in whoto
will see not be merged with messages sent prior to
the call to breakmsg. This is used to enable a
new client module to be started without needing to
pass it data received in the previous read.
clique.member(id)
Member yields the member corresponding to identi-
fier id, or nil if there is none.
clique.membernamed(name)
Membernamed searches for a member of clique named
name and returns it if it finds it, otherwise nil.
clique.members()
Members returns a list of all the members of
clique, including those that have been suspended.
clique.owner()
Owner returns the name of the owner of the clique;
i.e. the user that created it.
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clique.hangup()
Hangup terminates a game and informs all the play-
ers of that fact.
clique.notify(cliqueid,msg)
Notify sends an informational message to another
clique. The clique so referenced must be either
the parent or a child of clique. The message is
not sent synchronously, and care should be taken
not to send messages that can cause an indefinite
recursion.
Member
The Member type represents a member of a clique.
member.id The member's identifier is an integer unique
across all current members of the clique, but ids
of members that have left the clique will be
reused. There may not be two members of the same
name in the same clique.
member.name
Name holds the authenticated name of the member.
This is necessarily unique over the members of a
clique.
member.obj(id)
Obj converts from a member's external object iden-
tifier to the clique's local Object that it repre-
sents. It returns nil if there is no such object.
member.del(suspend)
Del deletes member from the clique; no more
requests from member will be received by the
clique engine. If suspend is non-zero, if a mem-
ber of the same name joins again it will be allo-
cated the same object id, allowing a member to
leave and join again without losing state.
Object
The Object type is the basic unit of clique engine state.
An object's children can be selectively concealed from mem-
bers; it holds a set of (attribute, value) pairs, each of
which can be concealed likewise. Where an argument r, of
Range type is used, it refers to a range of an object's
children starting at index r.start, and finishing at
r.end-1. All the data members of an Object should be
treated as read-only.
obj.setattr(name, val, vis)
Setattr sets attribute name in obj to val. If the
attribute is being created for the first time,
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then it will be given visibility vis. Name should
be non-empty, and should not contain any space
characters. Note that it is not possible for an
attribute to refer directly to an object by its
identifier; if this facility is needed, another
identifying scheme should be used. This also
applies to member identifiers, which will change
if the clique is saved and loaded again.
obj.getattr(name)
Getattr yields the current value of the attribute
name in obj. If an attribute is not set, it yields
nil.
obj.delete()
Delete removes obj from the object hierarchy.
obj.deletechildren(r)
Deletechildren deletes children in range r from
obj.
obj.transfer(r, dst, i)
Transfer transfers the children in range r from
obj to just before the object at index i in dst.
It is permissible for obj and dst to be the same
object.
obj.setvisibility(visibility)
Setvisibility allows the set of members given in
visibility to see the children of obj, and denies
access to all others. Members are notified of the
change.
obj.setattrvisibility(name, visibility)
Setattrvisibility allows the set of members given
in visibility to see the value of obj's attribute
name, and denies access to all others. Members
are not notified of the change; if there is a need
to communicate the fact of an attribute becoming
invisible to members, it should be done by using
another (visible) attribute to communicate the
change.
Archives
The Archives module provides a means of committing a clique
to permanent storage and retrieving it later. It should
first be initialised by calling init, passing the Spree mod-
ule in mod. Write writes clique to the file file. Info gives
a set of attributes and values associated with the clique;
members gives the set of clique members for which visibility
information will be archived; visibility information for
other members is forgotten.
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Read opens file and returns it as an Archive adt, say a.
A.argv holds the command line arguments to the clique module
(including the name of the module, its first element);
a.members gives the names of all archived members - the id
of an archived member is given by its index in the array;
a.info gives the list of attributes an values as stored by
write; a.objects holds the clique objects. Readheader is
just like read except that it parses the header only, so
will return an Archive adt such that a.objects is nil.
Module Interface
An engine module, mod, must implement the following func-
tions. Where a function returns a string, it is interpreted
as an error response to the member responsible for the
request; an empty string signifies no error.
mod->init(srvmod,clique,argv)
Init initialises the clique engine. Clique is the
clique that the engine is controlling, and srvmod is
the Spree module holding its associated data. An error
response from this function causes the clique to be
aborted. Argv gives a list of arguments to the engine,
starting with its module name.
mod->join(member,e,suspended)
Member has made a request to join the clique; an error
response causes the request to be refused, otherwise
the member joins the clique. E is a message from the
client about how it would like to join the clique (e.g.
join, watch, etc). Suspended is non-zero if the member
was previously suspended from the clique.
mod->leave(member)
Member has left the clique. If leave returns zero, the
member will not be deleted from the clique, but merely
suspended until they should join again.
mod->command(member, e)
Member has sent the command e. The command usually fol-
lows the simple message conventions used in spree(4),
i.e. simple space-separated tokens.
mod->notify(cliqueid,s)
A notification, s, has been posted to the current
clique by the clique identified by cliqueid. The post-
ing clique is either a parent or a child of the current
clique.
mod.
EXAMPLE
The following is a small, but working example of a clique
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engine that acts as a chat server (parsing error checking
omitted, and white-space compressed to save paper):
implement Cliquemodule;
include "sys.m";
sys: Sys;
include "draw.m";
include "../spree.m";
spree: Spree;
Clique, Member: import spree;
clique: ref Clique;
clienttype(): string
{
return "chat";
}
init(g: ref Clique, srvmod: Spree): string
{
(sys, clique, spree) = (load Sys Sys->PATH, g, srvmod);
return nil;
}
join(nil: ref Member): string
{
return nil;
}
leave(nil: ref Member)
{
}
command(member: ref Member, cmd: string): string
{
clique.action("say " + string member.id + " " + cmd, nil, nil, ~0);
return nil;
}
SOURCE
/appl/cmd/cliques/spree.b
SEE ALSO
spree(4), spree-objstore(2), spree-cardlib(2), spree-
allow(2),
BUGS
The reuse of object ids can lead to problems when objects
are deleted and recreated on the server before clients
become aware of the changes.
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