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= nng_pipe_getopt(3)
//
// Copyright 2018 Staysail Systems, Inc. <info@staysail.tech>
// Copyright 2018 Capitar IT Group BV <info@capitar.com>
//
// This document is supplied under the terms of the MIT License, a
// copy of which should be located in the distribution where this
// file was obtained (LICENSE.txt). A copy of the license may also be
// found online at https://opensource.org/licenses/MIT.
//
== NAME
nng_pipe_getopt - get pipe option
== SYNOPSIS
[source, c]
-----------
#include <nng/nng.h>
int nng_pipe_getopt(nng_pipe p, const char *opt, void *val, size_t *valszp);
int nng_pipe_getopt_int(nng_pipe p, const char *opt, int *ivalp);
int nng_pipe_getopt_ms(nng_pipe p, const char *opt, nng_duration *durp);
int nng_pipe_getopt_size(nng_pipe p, const char *opt, size_t *zp);
int nng_pipe_getopt_uint64(nng_pipe p, const char *opt, uint64_t *u64p);
-----------
== DESCRIPTION
The `nng_pipe_getopt()` functions are used to retrieve option values for
the pipe _p_. The actual options that may be retrieved in this way
vary, and are documented in the <<nng_getopt#,nng_getopt(3)>> manual.
Additionally some transport-specific options are documented with the
transports themselves, and some protocol-specific options are documented
with the protocol.
NOTE: All "options" on a pipe are read-only values, and intended to
facilitate understanding the identity of an associated peer; modification
of options must be done on the listener or dialer using either
<<nng_listener_setopt#,nng_listener_setopt(3)>> or
<<nng_dialer_getopt#,nng_dialer_getopt(3)>>
Any option that is set on an endpoint will be retrievable from pipes
created by that endpoint.
In all of these forms, the option _opt_ is retrieved from the pipe _p_.
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.
The first form of this function, `nng_pipe_getopt()`, can be used to
retrieve the value of any option. It is untyped. 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 _valszp_.
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 referened by _valszp_. If the caller's buffer is not large
enough to hold the entire object, then the copy is truncated. Therefore
the caller should validate that the returned size in _valszp_ does not
exceed the original buffer size to check for truncation.
It is acceptable to pass `NULL` for _val_ if the value in _valszp_ is zero.
This can be used to determine the size of the buffer needed to receive
the object.
Generally, it will be easier to use one of the typed forms instead. Note
however that no validation that the option is actually of the associated
type is performed, so the caller must take care to use the *correct* typed
form.
The second form, `nng_pipe_getopt_int()`,
is for options which take an integer (or boolean). The value will
be stored at _ivalp_. For booleans the value will be eiher 0 (false) or 1 (true).
The third form, `nng_pipe_getopt_ms()`, is used to retrieve time durations
(such as timeouts), stored in _durp_ as a number of milliseconds.
(The special value `NNG_DUR_INFINITE` means an infinite amount of time, and
the special value `NNG_DUR_DEFAULT` means a context-specific default.)
The fourth form, `nng_pipe_getopt_size()`, is used to retrieve a size
into the pointer _zp_, typically for buffer sizes, message maximum sizes, and
similar options.
The fifth form, `nng_pipe_getopt_uint64()`, is used to retrieve a
64-bit unsigned value into the value referenced by _u64p_.
This is typically used for options
related to identifiers, network numbers, and similar.
// XXX: nng_pipe_getopt_ptr is not support, and would carry some risks,
// as the pipe may not survive, and the endpoint options may not survive,
// leading to questions about pointer validity.
// The last form, `nng_pipe_getopt_ptr()`, is used to retrieve a
// pointer _ptr_ to structured data. The data referenced by _ptr_ 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.
== RETURN VALUES
This function returns 0 on success, and non-zero otherwise.
== ERRORS
`NNG_ECLOSED`:: Parameter _p_ does not refer to an open pipe.
`NNG_ENOTSUP`:: The option _opt_ is not supported.
`NNG_EWRITEONLY`:: The option _opt_ is write-only.
== SEE ALSO
<<nng_dialer_setopt#,nng_dialer_setopt(3)>>
<<nng_getopt#,nng_getopt(3)>>,
<<nng_listener_setopt#,nng_listener_setopt(3)>>
<<nng_msg_get_pipe#,nng_msg_get_pipe(3)>>
<<nng_strerror#,nng_strerror(3)>>,
<<nng#,nng(7)>>
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