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libssh2_session_callback_set(3)     libssh2    libssh2_session_callback_set(3)

NAME
       libssh2_session_callback_set - set a callback function

SYNOPSIS
       #include <libssh2.h>

       void *
       libssh2_session_callback_set(LIBSSH2_SESSION *session,
                                    int cbtype, void *callback);

DESCRIPTION
       Sets a custom callback handler for a previously initialized session
       object. Callbacks are triggered by the receipt of special packets at
       the Transport layer. To disable a callback, set it to NULL.

       session - Session instance as returned by libssh2_session_init_ex(3)

       cbtype - Callback type. One of the types listed in Callback Types.

       callback - Pointer to custom callback function. The prototype for this
       function must match the associated callback declaration macro.

CALLBACK TYPES
       LIBSSH2_CALLBACK_IGNORE
              Called when a SSH_MSG_IGNORE message is received

       LIBSSH2_CALLBACK_DEBUG
              Called when a SSH_MSG_DEBUG message is received

       LIBSSH2_CALLBACK_DISCONNECT
              Called when a SSH_MSG_DISCONNECT message is received

       LIBSSH2_CALLBACK_MACERROR
              Called when a mismatched MAC has been detected in the transport
              layer. If the function returns 0, the packet will be accepted
              nonetheless.

       LIBSSH2_CALLBACK_X11
              Called when an X11 connection has been accepted

       LIBSSH2_CALLBACK_SEND
              Called when libssh2 wants to send data on the connection.  Can
              be set to a custom function to handle I/O your own way.

              The prototype of the callback:

              ssize_t sendcb(libssh2_socket_t sockfd, const void *buffer,
                             size_t length, int flags, void **abstract);

              sockfd is the socket to write to, buffer points to the data to
              send, length is the size of the data, flags is the flags that
              would have been used to a send() call and abstract is a pointer
              to the abstract pointer set in the libssh2_session_init_ex(3)
              call.

              The callback returns the number of bytes sent, or -1 for error.
              The special return code -EAGAIN can be returned to signal that
              the send was aborted to prevent getting blocked and it needs to
              be called again.

       LIBSSH2_CALLBACK_RECV
              Called when libssh2 wants to read data from the connection. Can
              be set to a custom function to handle I/O your own way.

              The prototype of the callback:

              ssize_t recvcb(libssh2_socket_t sockfd, void *buffer,
                             size_t length, int flags, void **abstract);

              sockfd is the socket to read from, buffer where to store
              received data into, length is the size of the buffer, flags is
              the flags that would have been used to a recv() call and
              abstract is a pointer to the abstract pointer set in the
              libssh2_session_init_ex(3) call.

              The callback returns the number of bytes read, or -1 for error.
              The special return code -EAGAIN can be returned to signal that
              the read was aborted to prevent getting blocked and it needs to
              be called again.

       LIBSSH2_CALLBACK_AUTHAGENT
              Called during authentication process to allow the client to
              connect to the ssh-agent and perform any setup, such as
              configuring the agent or adding keys.

              The prototype of the callback:

              void authagent(LIBSSH2_SESSION* session, LIBSSH2_CHANNEL *channel,
                             void **abstract);

       LIBSSH2_CALLBACK_AUTHAGENT_IDENTITIES
              Not called by libssh2. The client is responsible for calling
              this method when a SSH2_AGENTC_REQUEST_IDENTITIES message has
              been received.

              The prototype of the callback:

              void identities(LIBSSH2_SESSION* session, void *buffer,
                              const char *agent_path,
                              void **abstract)

              buffer must be filled in by the callback. Different clients may
              implement this differently. For example, one client may pass in
              an unsigned char ** for this parameter, while another may pass
              in a pointer to a struct.

              Regardless of the type of buffer used, the client will need to
              send back a list of identities in the following format.

              uint32 buffer length uint32 number of entries entries

              Where each entry in the entries list is of the format:

              string data cstring comment

              agent_path The path to a running ssh-agent on the client
              machine, from which identities can be listed.

       LIBSSH2_CALLBACK_AUTHAGENT_SIGN
              Not called by libssh2. The client is responsible for calling
              this method when a SSH2_AGENTC_SIGN_REQUEST message has been
              received.

              The prototype of the callback:

              void sign(LIBSSH2_SESSION* session,
                        unsigned char *blob, unsigned int blen,
                        const unsigned char *data, unsigned int dlen,
                        unsigned char **sig, unsigned int *sig_len,
                        const char *agent_path,
                        void **abstract);

              When interfacing with an ssh-agent installed on the client
              system, this method can call libssh2_agent_sign(3) to perform
              signing.

RETURN VALUE
       Pointer to previous callback handler. Returns NULL if no prior callback
       handler was set or the callback type was unknown.

SEE ALSO
       libssh2_session_init_ex(3) libssh2_agent_sign(3)

libssh2 0.15                      1 Jun 2007   libssh2_session_callback_set(3)