# UPSCLIENT(3)

## NAME

upsclient - Network UPS Tools client access library

## DESCRIPTION

The Network UPS Tools (NUT) upsclient library provides a number of useful functions for client programs to use when communicating with upsd(8). Many of the low-level socket and protocol details are handled automatically when using this interface, also known as "upscli" API.

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.

## INITIALIZATION AND CLEANUP

Before creating any connection, and in general using any upscli function, you must call upscli_init(3) with proper parameters to initialize upscli module.

To register a specific host security policy, you must call upscli_add_host_cert(3) before initializing a connection to it.

In the same way, just before exiting, and after all upscli usage, you must call upscli_cleanup(3) to flush cache files and perform other cleanup.

## NETWORK FUNCTIONS

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.

## STRING FUNCTIONS

To parse the `ups.status` values (check whether a particular token is present) you are encouraged to use the upscli_str_contains_token(3) method.

To collect unique tokens into a string in the same manner a NUT driver does, the upscli_str_add_unique_token(3) can be helpful.

You are welcome to consult the NUT source code base for use of equivalent methods to implement such features as `status_init()`, `status_get()`, `status_set()` and `status_commit()` methods in its data-processing loops.

## ERROR HANDLING

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_*.

## SEE ALSO

nutclient(3), libupsclient-config(1), upscli_init(3), upscli_cleanup(3), upscli_add_host_cert(3), 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), upscli_str_add_unique_token(3), upscli_str_contains_token(3)