NAME

       ares_set_socket_functions - Set socket io callbacks

SYNOPSIS

       #include <ares.h>

       struct ares_socket_functions {
           ares_socket_t (*asocket)(int, int, int, void *);
           int (*aclose)(ares_socket_t, void *);
           int (*aconnect)(ares_socket_t, const struct sockaddr *, ares_socklen_t, void *);
           ares_ssize_t (*arecvfrom)(ares_socket_t, void *, size_t, int,
                                     struct sockaddr *, ares_socklen_t *, void *);
           ares_ssize_t (*asendv)(ares_socket_t, const struct iovec *, int, void *);
       };

       void ares_set_socket_functions(ares_channel_t *channel,
                                      const struct ares_socket_functions * functions,
                                      void *user_data);

DESCRIPTION

       This  function  sets  a  set of callback functions in the given ares channel handle.  Cannot be used when
       ARES_OPT_EVENT_THREAD is passed to ares_init_options(3).

       These callback functions will be invoked to create/destroy socket objects and perform io, instead of  the
       normal  system  calls.  A  client  application  can  override normal network operation fully through this
       functionality, and provide its own transport layer. You can choose to only implement some of  the  socket
       functions, and provide NULL to any others and c-ares will use its built-in system functions in that case.

       All  callback  functions are expected to operate like their system equivalents, and to set errno(3) to an
       appropriate error code on failure. C-ares also expects all io functions to behave asynchronously, i.e. as
       if  the  socket object has been set to non-blocking mode. Thus read/write calls (for TCP connections) are
       expected to often generate EAGAIN or EWOULDBLOCK.

       The user_data value is provided to each callback function invocation to serve as context.

       The ares_socket_functions must provide the following callbacks:

       asocket           ares_socket_t(*)(int domain, int type, int protocol, void * user_data)
                         Creates an endpoint for communication and  returns  a  descriptor.  domain,  type,  and
                         protocol  each correspond to the parameters of socket(2).  Returns ahandle to the newly
                         created socket, or -1 on error.

       aclose            int(*)(ares_socket_t fd, void * user_data)
                         Closes the socket endpoint indicated by fd. See close(2)

       aconnect          int(*)(ares_socket_t fd, const struct sockaddr * addr, ares_socklen_t addr_len, void  *
                         user_data)
                         Initiate a connection to the address indicated by addr on a socket. See connect(2)

       arecvfrom         ares_ssize_t(*)(ares_socket_t  fd,  void  *  buffer, size_t buf_size, int flags, struct
                         sockaddr * addr, ares_socklen_t * addr_len, void * user_data)
                         Receives data from remote socket endpoint, if available. If the addr parameter  is  not
                         NULL  and the connection protocol provides the source address, the callback should fill
                         this in. See recvfrom(2)

       asendv            ares_ssize_t(*)(ares_socket_t fd, const struct iovec * data, int len, void * user_data)
                         Send data, as provided by the iovec array data, to the socket endpoint. See writev(2),

       The ares_socket_functions struct provided is not copied but directly referenced,  and  must  thus  remain
       valid through out the channels and any created socket's lifetime.

AVAILABILITY

       Added in c-ares 1.13.0

SEE ALSO

       ares_init_options(3), socket(2), close(2), connect(2), recv(2), recvfrom(2), send(2), writev(2)

AUTHOR

       Carl Wilund

                                                   13 Dec 2016                      ARES_SET_SOCKET_FUNCTIONS(3)