typedef struct { ... } SilcClientOperations;

    SILC Client Operations. These must be implemented by the application.
    The Client library may call any of these routines at any time.  The
    routines are used to deliver certain information to the application
    or from the application to the client library.

    typedef struct {
      /* Message sent to the application by library. `conn' associates the
         message to a specific connection.  `conn', however, may be NULL.
         The `type' indicates the type of the message sent by the library.
         The application can for example filter the message according the
         type.  The variable argument list is arguments to the formatted
         message that `msg' may be. */
      void (*say)(SilcClient client, SilcClientConnection conn,
                  SilcClientMessageType type, char *msg, ...);
    
      /* Message for a channel. The `sender' is the sender of the message
         The `channel' is the channel. The `message' is the message.  Note
         that `message' maybe NULL.  The `flags' indicates message flags
         and it is used to determine how the message can be interpreted
         (like it may tell the message is multimedia message). */
      void (*channel_message)(SilcClient client, SilcClientConnection conn,
                              SilcClientEntry sender, SilcChannelEntry channel,
                              SilcMessagePayload payload,
                              SilcChannelPrivateKey key, SilcMessageFlags flags,
                              const unsigned char *message,
                              SilcUInt32 message_len);
    
      /* Private message to the client. The `sender' is the sender of the
         message. The message is `message'and maybe NULL.  The `flags'
         indicates message flags  and it is used to determine how the message
         can be interpreted (like it may tell the message is multimedia
         message). */
      void (*private_message)(SilcClient client, SilcClientConnection conn,
                              SilcClientEntry sender, SilcMessagePayload payload,
                              SilcMessageFlags flags,
                              const unsigned char *message,
                              SilcUInt32 message_len);
    
      /* Notify message to the client. The notify arguments are sent in the
         same order as servers sends them. The arguments are same as received
         from the server except for ID's.  If ID is received application receives
         the corresponding entry to the ID. For example, if Client ID is received
         application receives SilcClientEntry.  Also, if the notify type is
         for channel the channel entry is sent to application (even if server
         does not send it because client library gets the channel entry from
         the Channel ID in the packet's header). */
      void (*notify)(SilcClient client, SilcClientConnection conn,
                     SilcNotifyType type, ...);
    
      /* Command handler. This function is called always in the command function.
         If error occurs it will be called as well. `conn' is the associated
         client connection. `cmd_context' is the command context that was
         originally sent to the command. `success' is FALSE if error occurred
         during command. `command' is the command being processed. It must be
         noted that this is not reply from server. This is merely called just
         after application has called the command. Just to tell application
         that the command really was processed. */
      void (*command)(SilcClient client, SilcClientConnection conn,
                      SilcClientCommandContext cmd_context, bool success,
                      SilcCommand command, SilcStatus status);
    
      /* Command reply handler. This function is called always in the command reply
         function. If error occurs it will be called as well. Normal scenario
         is that it will be called after the received command data has been parsed
         and processed. The function is used to pass the received command data to
         the application.
    
         `conn' is the associated client connection. `cmd_payload' is the command
         payload data received from server and it can be ignored. It is provided
         if the application would like to re-parse the received command data,
         however, it must be noted that the data is parsed already by the library
         thus the payload can be ignored. `success' is FALSE if error occurred.
         In this case arguments are not sent to the application. The `status' is
         the command reply status server returned. The `command' is the command
         reply being processed. The function has variable argument list and each
         command defines the number and type of arguments it passes to the
         application (on error they are not sent).
    
         The arguments are sent in the same order as servers sends them.  The
         arguments are same as received from the server except for ID's.  If
         ID is received application receives the corresponding entry to the
         ID. For example, if Client ID is receives application receives
         SilcClientEntry. */
      void (*command_reply)(SilcClient client, SilcClientConnection conn,
                            SilcCommandPayload cmd_payload, bool success,
                            SilcCommand command, SilcStatus status, ...);
    
      /* Called to indicate that connection was either successfully established
         or connecting failed.  This is also the first time application receives
         the SilcClientConnection object which it should save somewhere.
         The `status' indicated whether the connection were successful.  If it
         is error value the application must always call the function
         silc_client_close_connection. */
      void (*connected)(SilcClient client, SilcClientConnection conn,
                        SilcClientConnectionStatus status);
    
      /* Called to indicate that connection was disconnected to the server.
         The `status' may tell the reason of the disconnection, and if the
         `message' is non-NULL it may include the disconnection message
         received from server. Application must not call the
         silc_client_close_connection in this callback.  The 'conn' is also
         invalid after this function returns back to library. */
      void (*disconnected)(SilcClient client, SilcClientConnection conn,
                           SilcStatus status, const char *message);
    
      /* Find authentication method and authentication data by hostname and
         port. The hostname may be IP address as well. When the authentication
         method has been resolved the `completion' callback with the found
         authentication method and authentication data is called. The `conn'
         may be NULL. */
      void (*get_auth_method)(SilcClient client, SilcClientConnection conn,
                              char *hostname, SilcUInt16 port,
                              SilcGetAuthMeth completion, void *context);
    
      /* Verifies received public key. The `conn_type' indicates which entity
         (server, client etc.) has sent the public key. If user decides to trust
         the application may save the key as trusted public key for later
         use. The `completion' must be called after the public key has been
         verified. */
      void (*verify_public_key)(SilcClient client, SilcClientConnection conn,
                                SilcSocketType conn_type, unsigned char *pk,
                                SilcUInt32 pk_len, SilcSKEPKType pk_type,
                                SilcVerifyPublicKey completion, void *context);
    
      /* Ask (interact, that is) a passphrase from user. The passphrase is
         returned to the library by calling the `completion' callback with
         the `context'. The returned passphrase SHOULD be in UTF-8 encoded,
         if not then the library will attempt to encode. */
      void (*ask_passphrase)(SilcClient client, SilcClientConnection conn,
                             SilcAskPassphrase completion, void *context);
    
      /* Notifies application that failure packet was received.  This is called
         if there is some protocol active in the client.  The `protocol' is the
         protocol context.  The `failure' is opaque pointer to the failure
         indication.  Note, that the `failure' is protocol dependant and
         application must explicitly cast it to correct type.  Usually `failure'
         is 32 bit failure type (see protocol specs for all protocol failure
         types). */
      void (*failure)(SilcClient client, SilcClientConnection conn,
                      SilcProtocol protocol, void *failure);
    
      /* Asks whether the user would like to perform the key agreement protocol.
         This is called after we have received an key agreement packet or an
         reply to our key agreement packet. This returns TRUE if the user wants
         the library to perform the key agreement protocol and FALSE if it is not
         desired (application may start it later by calling the function
         silc_client_perform_key_agreement). If TRUE is returned also the
         `completion' and `context' arguments must be set by the application. */
      bool (*key_agreement)(SilcClient client, SilcClientConnection conn,
                            SilcClientEntry client_entry, const char *hostname,
                            SilcUInt16 port, SilcKeyAgreementCallback *completion,
                            void **context);
    
      /* Notifies application that file transfer protocol session is being
         requested by the remote client indicated by the `client_entry' from
         the `hostname' and `port'. The `session_id' is the file transfer
         session and it can be used to either accept or reject the file
         transfer request, by calling the silc_client_file_receive or
         silc_client_file_close, respectively. */
      void (*ftp)(SilcClient client, SilcClientConnection conn,
                  SilcClientEntry client_entry, SilcUInt32 session_id,
                  const char *hostname, SilcUInt16 port);
    
      /* Delivers SILC session detachment data indicated by `detach_data' to the
         application.  If application has issued SILC_COMMAND_DETACH command
         the client session in the SILC network is not quit.  The client remains
         in the network but is detached.  The detachment data may be used later
         to resume the session in the SILC Network.  The appliation is
         responsible of saving the `detach_data', to for example in a file.
    
         The detachment data can be given as argument to the functions
         silc_client_connect_to_server, or silc_client_add_connection when
         creating connection to remote server, inside SilcClientConnectionParams
         structure.  If it is provided the client library will attempt to resume
         the session in the network.  After the connection is created
         successfully, the application is responsible of setting the user
         interface for user into the same state it was before detaching (showing
         same channels, channel modes, etc).  It can do this by fetching the
         information (like joined channels) from the client library. */
      void (*detach)(SilcClient client, SilcClientConnection conn,
                     const unsigned char *detach_data,
                     SilcUInt32 detach_data_len);
    } SilcClientOperations;