NAME

       upscli_connect, upscli_tryconnect - Open a connection to a NUT upsd data server

SYNOPSIS

               #include <upsclient.h>

               /* Open a connection to a NUT upsd data server (blocking by default) */
               int upscli_connect(UPSCONN_t *ups, const char *host, uint16_t port, int flags);

               /* Open a connection to a NUT upsd data server with specified timeout */
               int upscli_tryconnect(UPSCONN_t *ups, const char *host, uint16_t port, int flags,
                       struct timeval * timeout);

DESCRIPTION

       The upscli_connect() function takes the pointer ups to a UPSCONN_t state structure and opens a TCP
       connection to the host on the given port.

       By default this makes a blocking connection attempt (until the system transport layer times out the
       underlying select(2) call). A program-wide default timeout for this method can be configured with the
       upscli_set_default_connect_timeout(3) or upscli_init_default_connect_timeout(3) methods. For operations
       with explicit operation-specific timeout please use the upscli_tryconnect() method instead.

           Note

           As part of general initialization, both the upscli_init(3) function or the first call to
           upscli_connect() function, can call the upscli_init_default_connect_timeout(3) method (if it was
           never used before): this allows unmodified (legacy) NUT clients to consistently benefit from presence
           of the NUT_DEFAULT_CONNECT_TIMEOUT environment variable for upscli_connect(3) attempts to be not
           blocking (as per default).

       flags may be either UPSCLI_CONN_TRYSSL to try a SSL connection, or UPSCLI_CONN_REQSSL to require a SSL
       connection.

       Introduced in version 2.7, an additional flag UPSCLI_CONN_CERTVERIF now exists to verify the signature
       offered during the SSL handshake. This flag should be used in conjunction with upscli_init(3) and/or
       upscli_add_host_cert(3) calls before connecting in order to define a CA certificate with which to verify.

       If SSL mode is required, this function will only return successfully if it is able to establish a SSL
       connection with the server. Possible reasons for failure include no SSL support on the server, and if
       upsclient itself hasn’t been compiled with SSL support.

       You must call upscli_disconnect(3) when finished with a connection, or your program will slowly leak
       memory and file descriptors.

RETURN VALUE

       The upscli_connect() function modifies the UPSCONN_t structure and returns 0 on success, or -1 if an
       error occurs.

SEE ALSO

       upscli_disconnect(3), upscli_fd(3), upscli_init(3), upscli_splitaddr(3), upscli_splitname(3),
       upscli_ssl(3), upscli_strerror(3), upscli_get_default_connect_timeout(3),
       upscli_set_default_connect_timeout(3), upscli_init_default_connect_timeout(3), upscli_upserror(3)

Network UPS Tools 2.8.3                            07/08/2025                                  UPSCLI_CONNECT(3)