# nng_stream_listener_get(3str) Manual Page

## NAME

nng_stream_listener_get - get option from byte stream listener

## SYNOPSIS

    #include <nng/nng.h>

    int nng_stream_listener_get(nng_stream_listener *l, const char *opt, void *val, size_t *sizep);

    int nng_stream_listener_get_bool(nng_stream_listener *l, const char *opt, bool *valp);

    int nng_stream_listener_get_int(nng_stream_listener *l, const char *opt, int *valp);

    int nng_stream_listener_get_ms(nng_stream_listener *l, const char *opt, nng_duration *valp);

    int nng_stream_listener_get_ptr(nng_stream_listener *l, const char *opt, void **valp);

    int nng_stream_listener_get_size(nng_stream_listener *l, const char *opt, size_t *valp);

    int nng_stream_listener_get_addr(nng_stream_listener *l, const char *opt, nng_sockaddr *valp);

    int nng_stream_listener_get_string(nng_stream_listener *l, const char *opt, char **valp);

    int nng_stream_listener_get_uint64(nng_stream_listener *l, const char *opt, uint64_t *valp);

## DESCRIPTION

The `nng_stream_listener_get()` functions are used to retrieve option values for the byte stream listener l.

The actual options that may be retrieved in this way vary. A number of them are documented in nng_options(5) and additional linked documents.

### Forms

In all of these forms, the option opt is retrieved from the connected byte stream listener l. The forms vary based on the type of the option they take.

The details of the type, size, and semantics of the option will depend on the actual option, and will be documented with the option itself.

`nng_stream_listener_get()`

  This function is untyped and can be used to retrieve the value of any option. The caller must store a pointer to a buffer to receive the value in val, and the size of the buffer shall be stored at the location referenced by sizep.

  When the function returns, the actual size of the data copied (or that would have been copied if sufficient space were present) is stored at the location referenced by sizep. If the caller’s buffer is not large enough to hold the entire object, then the copy is truncated. Therefore the caller should check for truncation by verifying that the returned size in sizep does not exceed the original buffer size.

  It is acceptable to pass `NULL` for val if the value in sizep is zero. This can be used to determine the size of the buffer needed to receive the object.

  | This function is deprecated. Use one of the typed functions below instead.

`nng_stream_listener_get_bool()`

  This function is for options which take a Boolean (`bool`).

`nng_stream_listener_get_int()`

  This function is for options which take an integer (`int`).

`nng_stream_listener_get_ms()`

  This function is used to retrieve time durations (such as timeouts), stored as a number of milliseconds. (The special value `NNG_DURATION_INFINITE` means an infinite amount of time, and the special value `NNG_DURATION_DEFAULT` means a context-specific default.)

`nng_stream_listener_get_ptr()`

  This function is used to retrieve a pointer to structured data. The data referenced is generally managed using other functions. Note that this form is somewhat special in that the object is generally not copied, but instead the pointer to the object is copied.

  | Care must be taken to ensure that the application respects any considerations about the lifetime of the underyling object. See the documentation for the option for more specific guidance.

`nng_stream_listener_get_size()`

  This function is used to retrieve a size, typically for buffer sizes, message maximum sizes, and similar options.

`nng_stream_listener_get_addr()`

  This function is used to retrieve a socket address.

`nng_stream_listener_get_string()`

  This function is used to retrieve a `NULL`-terminated string. This string is created from the source using `nng_strdup()` and consequently must be freed by the caller using `nng_strfree()` when it is no longer needed.

`nng_stream_listener_get_uint64()`

  This function is used to retrieve a 64-bit unsigned value. This is typically used for identifiers, network numbers, and similar options.

## RETURN VALUES

These functions return 0 on success, and non-zero otherwise.

## ERRORS

`NNG_ECLOSED` | The listener is closed.
`NNG_EINVAL` | There was insufficient space to receive the object. The amount of data actually needed is returned in sizep.
`NNG_ENOTSUP` | The option is not supported.
`NNG_EWRITEONLY` | The option may not read.

## SEE ALSO

nng_strerror(3), nng_stream_listener_set(3str), nng_options(5), nng_stream_listener(5)