= nng_stream_listener_get(3str)
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//
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// Copyright 2019 Staysail Systems, Inc. <info@staysail.tech>
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// Copyright 2018 Capitar IT Group BV <info@capitar.com>
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// Copyright 2019 Devolutions <info@devolutions.net>
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//
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// This document is supplied under the terms of the MIT License, a
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// copy of which should be located in the distribution where this
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// file was obtained (LICENSE.txt). A copy of the license may also be
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// found online at https://opensource.org/licenses/MIT.
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//
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== NAME
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nng_stream_listener_get - get option from byte stream listener
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== SYNOPSIS
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[source, c]
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----
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#include <nng/nng.h>
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int nng_stream_listener_get(nng_stream_listener *l, const char *opt, void *val, size_t *sizep);
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int nng_stream_listener_get_bool(nng_stream_listener *l, const char *opt, bool *valp);
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int nng_stream_listener_get_int(nng_stream_listener *l, const char *opt, int *valp);
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int nng_stream_listener_get_ms(nng_stream_listener *l, const char *opt, nng_duration *valp);
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int nng_stream_listener_get_ptr(nng_stream_listener *l, const char *opt, void **valp);
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int nng_stream_listener_get_size(nng_stream_listener *l, const char *opt, size_t *valp);
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int nng_stream_listener_get_addr(nng_stream_listener *l, const char *opt, nng_sockaddr *valp);
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int nng_stream_listener_get_string(nng_stream_listener *l, const char *opt, char **valp);
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int nng_stream_listener_get_uint64(nng_stream_listener *l, const char *opt, uint64_t *valp);
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----
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== DESCRIPTION
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The `nng_stream_listener_get()` functions are used to retrieve option values
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for the
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xref:nng_stream_listener.5.adoc[byte stream listener] _l_.
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The actual options that may be retrieved in this way vary.
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A number of them are documented in
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xref:nng_options.5.adoc[nng_options(5)] and additional linked documents.
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=== Forms
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In all of these forms, the option _opt_ is retrieved from the connected
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byte stream listener _l_.
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The forms vary based on the type of the option they take.
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The details of the type, size, and semantics of the option will depend
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on the actual option, and will be documented with the option itself.
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`nng_stream_listener_get()`::
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This function is untyped and can be used to retrieve the value of any option.
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The caller must store a pointer to a buffer to receive the value in _val_,
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and the size of the buffer shall be stored at the location referenced by
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_sizep_.
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+
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When the function returns, the actual size of the data copied (or that
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would have been copied if sufficient space were present) is stored at
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the location referenced by _sizep_.
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If the caller's buffer is not large enough to hold the entire object,
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then the copy is truncated.
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Therefore the caller should check for truncation by verifying that the
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returned size in _sizep_ does not exceed the original buffer size.
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+
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It is acceptable to pass `NULL` for _val_ if the value in _sizep_ is zero.
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This can be used to determine the size of the buffer needed to receive
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the object.
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+
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TIP: It may be easier to use one of the typed forms of this function.
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`nng_stream_listener_get_bool()`::
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This function is for options which take a Boolean (`bool`).
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`nng_stream_listener_get_int()`::
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This function is for options which take an integer (`int`).
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`nng_stream_listener_get_ms()`::
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This function is used to retrieve time
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xref:nng_duration.5.adoc[durations]
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(such as timeouts), stored as a number of milliseconds.
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(The special value ((`NNG_DUR_INFINITE`)) means an infinite amount of time, and
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the special value ((`NNG_DUR_DEFAULT`)) means a context-specific default.)
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`nng_stream_listener_get_ptr()`::
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This function is used to retrieve a pointer to structured data.
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The data referenced is generally managed using other functions.
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Note that this form is somewhat special in that the object is generally
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not copied, but instead the *pointer* to the object is copied.
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+
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NOTE: Care must be taken to ensure that the application respects any
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considerations about the lifetime of the underyling object.
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See the documentation for the option for more specific guidance.
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`nng_stream_listener_get_size()`::
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This function is used to retrieve a size,
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typically for buffer sizes, message maximum sizes, and similar options.
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`nng_stream_listener_get_addr()`::
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This function is used to retrieve a
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xref:nng_sockaddr.5.adoc[socket address].
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`nng_stream_listener_get_string()`::
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This function is used to retrieve a `NULL`-terminated string.
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This string is created from the source using
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xref:nng_strdup.3.adoc[`nng_strdup()`]
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and consequently must be freed by the caller using
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xref:nng_strfree.3.adoc[`nng_strfree()`] when it is no longer needed.
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`nng_stream_listener_get_uint64()`::
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This function is used to retrieve a 64-bit unsigned value.
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This is typically used for identifiers, network
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numbers, and similar options.
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== RETURN VALUES
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These functions return 0 on success, and non-zero otherwise.
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== ERRORS
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[horizontal]
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`NNG_ECLOSED`:: The listener is closed.
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`NNG_EINVAL`:: There was insufficient space to receive the object.
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The amount of data actually needed is returned in _sizep_.
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`NNG_ENOTSUP`:: The option is not supported.
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`NNG_EWRITEONLY`:: The option may not read.
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== SEE ALSO
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[.text-left]
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xref:nng_strerror.3.adoc[nng_strerror(3)],
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xref:nng_stream_listener_set.3str.adoc[nng_stream_listener_set(3str)],
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xref:nng_options.5.adoc[nng_options(5)],
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xref:nng_stream_listener.5.adoc[nng_stream_listener(5)]
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