The Network UPS Tools (NUT) upsclient library provides a number of useful functions for programs to use when communicating with upsd(8). Many of the low-level socket and protocol details are handled automatically when using this interface.
State is maintained across calls in an opaque structure called UPSCONN_t. Callers are expected to create one per connection. These will be provided to most of the upsclient functions. The format of this structure is subject to change, and client programs must not reference elements within it directly.
To create a new connection, use upscli_connect(3). This will also initialize the UPSCONN_t structure. To verify that a connection has been established later, upscli_fd(3) can be used to return the file descriptor. Clients wishing to check for the presence and operation of SSL on a connection may call upscli_ssl(3).
The majority of clients will use upscli_get(3) to retrieve single items from the server. To retrieve a list, use upscli_list_start(3) to get it started, then call upscli_list_next(3) for each element.
Raw lines of text may be sent to upsd(8) with upscli_sendline(3). Reading raw lines is possible with upscli_readline(3). Client programs are expected to format these lines according to the protocol, as no checking will be performed before transmission.
At the end of a connection, you must call upsclient_disconnect(3) to disconnect from upsd and release any dynamic memory associated with the UPSCONN_t structure. Failure to call this function will result in memory and file descriptor leaks in your program.
In the event of an error, upscli_strerror(3) will provide human-readable details on what happened. upscli_upserror(3) may also be used to retrieve the error number. These numbers are defined in upsclient.h as UPSCLI_ERR_*.
libupsclient-config(1), upscli_connect(3), upscli_disconnect(3), upscli_fd(3), upscli_getvar(3), upscli_list_next(3), upscli_list_start(3), upscli_readline(3), upscli_sendline(3), upscli_splitaddr(3), upscli_splitname(3), upscli_ssl(3), upscli_strerror(3), upscli_upserror(3)