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How to Work With Groups

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Peer-to-peer Grouping is a technology that allows a developer to create a secure peer network quickly and effectively. The following list identifies the major considerations in creating a peer grouping application.

Obtaining a Peer Identity

Before creating or connecting to a group, a peer must obtain a peer identity, which is a name used to uniquely identify a peer to a group. To obtain an enumerated list of all peer identities defined on the peer, call PeerEnumIdentities, which returns a handle to the enumeration. To obtain the peer identities, call PeerGetNextItem with the enumeration handle and the number of members to retrieve. Continue calling PeerGetNextItem until the pCount parameter returns a value less than the number of peer identities requested.

If a peer identity for the peer does not exist, it can be created by calling PeerIdentityCreate. After creating a peer identity, the peer generates an identity XML blob that contains the public key assigned to it

The peer identity information is obtained by calling PeerIdentityGetXML. This peer identity information is used by the group creator or an administrator to issue the credentials needed to join the group, as an invitation XML blob.

For more information on peer identities, please refer to the Identity Manager API documentation

Starting Up the Peer Grouping Infrastructure

Before any function in the Peer Grouping API is called by an application, PeerGroupStartup must be called. This function initializes the Peer Grouping Infrastructure for the application and sets the supported version.

Obtaining a Group Handle

To connect to a group and begin participating, a handle to a peer group must be obtained. The following list identifies the three ways to connect to a peer group:

  • Creating a peer group by calling PeerGroupCreate, which initializes a new peer group and returns a valid handle with the peer as the owner and sole administrator.
  • Joining a peer group by calling PeerGroupJoin. To join a peer group, a peer must receive an invitation from a peer group administrator. To obtain an invitation, send the identity information XML blob to the administrator who creates an invitation and sends it to you by an external mechanism, such as email or FTP. The invitation and peer identity are passed to PeerGroupJoin, which returns a valid handle to the group.
  • Opening a peer group that a peer has joined previously by calling PeerGroupOpen. In this situation, obtaining an invitation is not necessary.

After you obtain a valid peer group handle from one of the above functions, you can connect to a peer group by calling PeerGroupConnect with the new handle.

Note

If the connection to a peer group fails, the PEER_GROUP_EVENT_CONNECTION_FAILED event occurs. The handler can attempt to reestablish the connection to the peer group.

 

Registering for Peer Grouping Events

Before a peer participates in a peer group, the peer must register for peer group events. To register for specific peer events, call PeerGroupRegisterEvent, and pass in one or more of the peer event types defined in PEER_GROUP_EVENT_TYPE. You must register for each peer event that applies to your application; for example, to receive data over a direct connection, register for the PEER_GROUP_EVENT_DIRECT_CONNECTION and PEER_GROUP_EVENT_INCOMING_DATA events. Each call takes an event handle and returns an HPEEREVENT handle for that peer event.

Event handlers can obtain the data associated with a peer event by passing the handle to registered peer events to PeerGroupGetEventData. This peer event data is returned as a PEER_GROUP_EVENT_DATA union. If the peer event queue is empty, this function returns PEER_S_NO_EVENT_DATA.

You can unregister for peer events by calling PeerGroupUnregisterEvent and providing the handle for the peer event you want to unregister. After the function is called, the peer events associated with the handle are no longer registered.

Creating Administrator and Member Roles

The peer who creates the peer group is known as the peer group creator, and has the administrator role by default. Only the peer group creator can set the group properties.

Peers invited to the peer group can be either an administrator or a member. If they are assigned an administrator role by the administrator issuing the invitation, they can invite new members to the peer group, and likewise assign the administrator role to other members.

The roles of peer group members are set in the invitations the administrator gives to a member. To add more administrators, set the value of the pRoles parameter of PeerGroupCreateInvitation to PEER_GROUP_ROLE_ADMIN when creating an invitation.

Members can participate in a peer group, but cannot invite and authorize new members, set group properties, or update or delete group records that they do not specifically create. To assign member status to a participating peer, set the value of the pRoles parameter of PeerGroupCreateInvitation to PEER_GROUP_ROLE_MEMBER when you create an invitation for that peer.

To change the role of a member, new credentials containing the new role must be issued to that member. To accomplish this, obtain the PEER_CREDENTIAL_INFO structure for this member from the PEER_MEMBER structure returned by PeerGroupEnumMembers. Change the pRoles field in PEER_CREDENTIAL_INFO to the new role, and pass the structure to PeerGroupIssueCredentials.

The new credentials will not go into effect for the peer until they connect to the peer group. If they are currently connected, they must close the group and reconnect to obtain the updated credentials.

Finding a Peer

To obtain an enumerated list of all peers participating in the peer group, call PeerGroupEnumMembers with the group handle, which returns a handle to the enumeration. To obtain the members, call PeerGetNextItem with the enum handle and the number of members to retrieve. Continue calling PeerGetNextItem until the pCount parameter returns a value less than the number of members requested. Note that the complete list of available members may not be returned.

Each member is represented as a PEER_MEMBER structure, which contains the identity of the peer, node IDs, and IP addresses for active peers.

When finished, close the enumeration and release the associated memory by calling PeerEndEnumeration.

Connecting Directly to a Peer

When a peer is connected to a peer group, direct one-to-one exchanges with other connected members are initiated by calling PeerGroupOpenDirectConnection and supplying the identity of the other peer. This call is asynchronous, and returns a 64-bit connection ID. If the call is successful, you receive the PEER_GROUP_EVENT_DIRECT_CONNECTION_EVENT peer event to indicate that the connection is successful. If the connection is successful, the connection ID is valid and can be used to send and receive data through the direct connection.

To be able to receive direct connections, the other peer must also have previously registered for the PEER_GROUP_EVENT_DIRECT_CONNECTION peer event.

To send data to a peer, call PeerGroupSendData with a valid connection ID. To receive data, the other peer must be registered for the PEER_GROUP_EVENT_INCOMING_DATA peer event. Likewise, if the sending peer wants to receive data in turn, it also must be registered for the PEER_GROUP_EVENT_INCOMING_DATA peer event.

To receive the total set of currently active direct connections with other peers in a group, call PeerGroupEnumConnections to open the enumeration and iterate through the list of connections by using PeerGetNextItem.

To close a direct connection, call PeerGroupCloseDirectConnection and pass in the connection ID.

Closing and Shutting Down a Peer Group

To close a connection to a peer group, call PeerGroupClose, which invalidates the group handle, but does not shut down the Peer Grouping Infrastructure. Peer-to-peer group data is deleted by calling PeerGroupDelete.

When the application is finished using the Peer Grouping Infrastructure, it must call PeerGroupShutdown.