CCNET HACKING

CCNET

---

Terminology

• Peer
• Ccnet daemon
• Client
• Service daemon: for example seafile daemon.

Peer Transfer Layer

Communication between peer is packet oriented.

The packet structure is defined in lib/packet.h as

struct ccnet_header {
    uint8_t  version;
    uint8_t  type;
    uint16_t length;            /* length of payload */
    uint32_t id;                /* for identify a service session id */
};

struct ccnet_packet {
    struct ccnet_header header;
    char data[0];
};

So the max length of payload is 65535.

Service Invocation

Ccnet provide a service invocation layer upon transfer layer.

Local Service Invoking

A local service is provided either by ccnet daemon or a service
daemon. To invoke a local service, client first sends a REQUEST
packet containing the service name and arguments to ccnet
daemon. Ccnet daemon will find the daemon who provide the service and
start the service. This starts a service session. A service session
is identified by a unique id. Later communication for this session
using REQUEST and UPDATE packets. These packets constains the unique
id in their header for the partners to identify the session.

        <service-name>               <service-name>
 Client --------------> Ccnet Daemon --------------> Service Daemon

            UPDATE                      UPDATE
 Client --------------> Ccnet Daemon ------------> Service Daemon
        <-------------              <------------
           RESPONSE                    RESPONSE

Remote Service Invoking

      remote <peer-id> <service-name>          <service-name>
 Client -----------------------> Ccnet Daemon --------------> Remote Ccnet

              UPDATE                               UPDATE
 Client -----------------------> Ccnet Daemon --------------> Remote Ccnet
        <-----------------------              <--------------
              RESPONSE                            RESPONSE

Note: if is self, remote service invoking will be
automatically turned to local service invoking.

Service Registration

The daemons implements a service by a subclass of CcnetProcessor and
registers it to ccnet daemon by calling ccnet_register_service():

CcnetClient *client;
ccnet_register_service (client, "seafile-rpcserver",
                        CCNET_TYPE_RPCSERVER_PROC);

This is used by the seafile daemon to register service
"seafile-rpcserver" to ccnet daemon.

Inside the ccnet daemon, a service is registered simply by calling

void
ccnet_proc_factory_register_processor (CcnetProcFactory *factory,
                                       const char *proc_name,
                                       GType type);

Processor Management

Local Service Invoking

To support local service invoking, a service proxy processor and a
service stub processor will be started when necessary. The runtime
configuration is as following:

Local Client               Ccnet Daemon                      Service Daemon
                     ----------------------------------
Client Processor ---> | Service Proxy --> Service Stub | --> Daemon Processor
                     ----------------------------------

Remote Service Invoking

The runtime configuration is as following:

Local Client               Ccnet Daemon                    Remote Ccnet Daemon
                     ----------------------------------    
Client Processor ---> | Service Proxy --> Service Stub | -->  Daemon Processor
                     ----------------------------------

Notes when using processor

• A class of processor may provide different services, we use 'processor->name'
  to remember which service an instance of a processor class provided.