# UPSCLI_CONNECT(3)

## 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)