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registries - access services registry


include "registries.m";
registries := load Registries Registries->PATH;

init: fn();

Attributes: adt {
   attrs: list of (string, string);

   get:   fn(a: self ref Attributes, attr: string): string;
   set:   fn(a: self ref Attributes, attr, val: string);
   new:   fn(attrs: list of (string, string)): ref Attributes;

Attached: adt {
   fd:           ref Sys->FD;  # connection to the service
   signerpkhash: string;     # hash of signer's key
   localuser:    string;     # user name here
   remoteuser:   string;     # user name there

Service: adt {
   addr:    string;          # dial this to connect to the service
   attrs:   ref Attributes;  # service description

   attach:  fn(s: self ref Service, user: string,
               keydir: string): ref Attached;

Registered: adt {
   addr:    string;          # address where registered
   reg:     ref Registry;    # registry where registered
   fd:      ref Sys->FD;     # file representing registration entry

Registry: adt {
   dir:     string;

   new:        fn(dir: string): ref Registry;
   connect:    fn(svc: ref Service, user: string, keydir: string):
                  ref Registry;
   services:   fn(r: self ref Registry):
                  (list of ref Service, string);
   find:       fn(r: self ref Registry, a: list of (string, string)):
                  (list of ref Service, string);
   register:   fn(r: self ref Registry, addr: string,
                  attrs: ref Attributes, persist: int):
                  (ref Registered, string);
   unregister: fn(r: self ref Registry, addr: string): string;


Registries helps access and update the contents of one or more registry (4) servers. Each registry lists services, each described by a set of attribute/value pairs. The attributes need not identify the service uniquely.

Init must be called before any other function in the module.

Attributes represents a set of attribute/value pairs; a given attribute name cannot appear more than once. It provides the following members and operations:

The current value of the set, as a list of (attr,value) tuples.
Return a new Attributes value given attrs, a list of (attr,value) tuples.
Return the value of attr in attribute set a.
a.set(attr, value)
Set the value of attr in attribute set a.

A Service value represents a service registered in some registry. It has the following members and operations:

A string that represents where the service can be reached: it is often a dial(2) address string, but might be a name in the name space; the interpretation is internal to Registries.
The service's attributes (complete service description).
Attempts to attach to the service svc, and if successful returns an Attached value to represent the connection; otherwise returns nil and sets the system error string. User is the local name of the user making the connection; if nil, the contents of /dev/user are used by default. Keydir is the name of a directory containing the user's certified keys for authentication; if nil, the default is /usr/user/keyring. If an error occurs, the return value is nil and the system error string contains a diagnostic. Not all services demand authentication, and either or both values can be nil to select suitable defaults. If authentication is done, the certified data determines the remote identity, not user, which is used only to help find a suitable set of keys and has no effect on security.

Attached holds data about an active connection to a particular service. (There can be several distinct connections to the same Service.) It provides the following members:

A file descriptor that can be read and written to exchange data with the service. The meaning of the data depends on the service (eg, it might be a 9P connection or a SOAP implementation). Typically an attribute of the service description hints at the protocol.
A hexadecimal string giving the SHA-1 hash of the key of the signer used for mutual authentication (ie, its thumbprint); if no authentication was needed or did not use public key methods, it is nil.
If authentication was required, the name used as the local name for authentication; otherwise nil.
If authentication was required, the remote identity for this connection; otherwise nil.

A service provider registers using one of the Registry functions listed below. An active registration is represented by a value of type Registered:

Location of service, as registered.
The registry that registered the service.
File descriptor open for on the service file in registry(4) that holds the service description. Unless the service has a non-zero persist attribute, the service registration will be removed when this file is closed (eg, when this Registration value is freed by the garbage collector if there is no other copy of fd). The file can be written as described in registry(4) to change the some or all of current set of attributes and/or values in the service description.

A Registry represents a connection to a single registry(4) instance. It provides the following members and operations:

Location of the registry in the name space.
Return a new Registry value for the registry located at dir in the name space; if dir is nil, the default is /mnt/registry.
Registry.connect(svc, user, keydir)
Connect to the registry at the location determined by the service description svc; if svc is nil, the default is to try dial(2) to net!$registry!registry, the symbolic name of the default registry for the current host. (The registry might or might not be local.) Attributes of svc determine the method used to connect to the registry and whether authentication is required. User and keydir provide user name and certificate directory (see getauthinfo(8)) if authentication is required; either or both can be nil to select the defaults for the given authentication method. On successful connection, connect returns a Registry value that can subsequently be used to access that registry and its services. It returns nil on an error and sets the system error string.
Returns a tuple (svcs,err) where svcs is a list of Service values, one for each service registered by reg at time of asking. If no services are registered, both values are nil. If an error occurred, svcs is nil but err is a diagnostic string.
Return a tuple (svcs,err) where svcs is a list of Service values, one for each service registered by reg that (at time of asking) matched all of the attribute/value pairs in attrs. A value of * matches any value. If no services matched, both values are nil. If an error occurred, svcs is nil but err is a diagnostic string.
reg.register(addr, attrs, persist)
Attempts to register with reg a service named addr and the given attributes attrs, and returns a tuple (r,err) where r is a non-nil Registration value for the entry if successful, and err is a diagnostic otherwise. Persist is non-zero if the service registration should survive the Registration value (connection); normally it is zero and the registry entry vanishes when the service frees the Registration value.
Attempt to remove the registration entry at reg for the service named addr. Only the service owner can do so. Returns nil on success and a diagnostic otherwise.


attrdb(2), registry(4), svc(8)

REGISTRIES(2 ) Rev:  Tue Mar 31 02:42:39 GMT 2015