Provided by: libssl-doc_3.4.1-1ubuntu3_all 
NAME
BIO_sendmmsg, BIO_recvmmsg, BIO_dgram_set_local_addr_enable, BIO_dgram_get_local_addr_enable,
BIO_dgram_get_local_addr_cap, BIO_err_is_non_fatal - send and receive multiple datagrams in a single call
SYNOPSIS
#include <openssl/bio.h>
typedef struct bio_msg_st {
void *data;
size_t data_len;
BIO_ADDR *peer, *local;
uint64_t flags;
} BIO_MSG;
int BIO_sendmmsg(BIO *b, BIO_MSG *msg,
size_t stride, size_t num_msg, uint64_t flags,
size_t *msgs_processed);
int BIO_recvmmsg(BIO *b, BIO_MSG *msg,
size_t stride, size_t num_msg, uint64_t flags,
size_t *msgs_processed);
int BIO_dgram_set_local_addr_enable(BIO *b, int enable);
int BIO_dgram_get_local_addr_enable(BIO *b, int *enable);
int BIO_dgram_get_local_addr_cap(BIO *b);
int BIO_err_is_non_fatal(unsigned int errcode);
DESCRIPTION
BIO_sendmmsg() and BIO_recvmmsg() functions can be used to send and receive multiple messages in a single
call to a BIO. They are analogous to sendmmsg(2) and recvmmsg(2) on operating systems which provide those
functions.
The BIO_MSG structure provides a subset of the functionality of the struct msghdr structure defined by
POSIX. These functions accept an array of BIO_MSG structures. On any particular invocation, these
functions may process all of the passed structures, some of them, or none of them. This is indicated by
the value stored in *msgs_processed, which expresses the number of messages processed.
The caller should set the data member of a BIO_MSG to a buffer containing the data to send, or to be
filled with a received message. data_len should be set to the size of the buffer in bytes. If the given
BIO_MSG is processed (in other words, if the integer returned by the function is greater than or equal to
that BIO_MSG's array index), data_len will be modified to specify the actual amount of data sent or
received.
The flags field of a BIO_MSG provides input per-message flags to the invocation. If the invocation
processes that BIO_MSG, the flags field is written with output per-message flags, or zero if no such
flags are applicable.
Currently, no input or output per-message flags are defined and this field should be set to zero before
calling BIO_sendmmsg() or BIO_recvmmsg().
The flags argument to BIO_sendmmsg() and BIO_recvmmsg() provides global flags which affect the entire
invocation. No global flags are currently defined and this argument should be set to zero.
When these functions are used to send and receive datagrams, the peer field of a BIO_MSG allows the
destination address of sent datagrams to be specified on a per-datagram basis, and the source address of
received datagrams to be determined. The peer field should be set to point to a BIO_ADDR, which will be
read by BIO_sendmmsg() and used as the destination address for sent datagrams, and written by
BIO_recvmmsg() with the source address of received datagrams.
Similarly, the local field of a BIO_MSG allows the source address of sent datagrams to be specified on a
per-datagram basis, and the destination address of received datagrams to be determined. Unlike peer,
support for local must be explicitly enabled on a BIO before it can be used; see
BIO_dgram_set_local_addr_enable(). If local is non-NULL in a BIO_MSG and support for local has not been
enabled, processing of that BIO_MSG fails.
peer and local should be set to NULL if they are not required. Support for local may not be available on
all platforms; on these platforms, these functions always fail if local is non-NULL.
If local is specified and local address support is enabled, but the operating system does not report a
local address for a specific received message, the BIO_ADDR it points to will be cleared (address family
set to "AF_UNSPEC"). This is known to happen on Windows when a packet is received which was sent by the
local system, regardless of whether the packet's destination address was the loopback address or the IP
address of a local non-loopback interface. This is also known to happen on macOS in some circumstances,
such as for packets sent before local address support was enabled for a receiving socket. These are OS-
specific limitations. As such, users of this API using local address support should expect to sometimes
receive a cleared local BIO_ADDR instead of the correct value.
The stride argument must be set to sizeof(BIO_MSG). This argument facilitates backwards compatibility if
fields are added to BIO_MSG. Callers must zero-initialize BIO_MSG.
num_msg should be sent to the maximum number of messages to send or receive, which is also the length of
the array pointed to by msg.
msgs_processed must be non-NULL and points to an integer written with the number of messages successfully
processed; see the RETURN VALUES section for further discussion.
Unlike most BIO functions, these functions explicitly support multi-threaded use. Multiple concurrent
writers and multiple concurrent readers of the same BIO are permitted in any combination. As such, these
functions do not clear, set, or otherwise modify BIO retry flags. The return value must be used to
determine whether an operation should be retried; see below.
The support for concurrent use extends to BIO_sendmmsg() and BIO_recvmmsg() only, and no other function
may be called on a given BIO while any call to BIO_sendmmsg() or BIO_recvmmsg() is in progress, or vice
versa.
BIO_dgram_set_local_addr_enable() and BIO_dgram_get_local_addr_enable() control whether local address
support is enabled. To enable local address support, call BIO_dgram_set_local_addr_enable() with an
argument of 1. The call will fail if local address support is not available for the platform.
BIO_dgram_get_local_addr_enable() retrieves the value set by BIO_dgram_set_local_addr_enable().
BIO_dgram_get_local_addr_cap() determines if the BIO is capable of supporting local addresses.
BIO_err_is_non_fatal() determines if a packed error code represents an error which is transient in
nature.
NOTES
Some implementations of the BIO_sendmmsg() and BIO_recvmmsg() BIO methods might always process at most
one message at a time, for example when OS-level functionality to transmit or receive multiple messages
at a time is not available.
RETURN VALUES
On success, the functions BIO_sendmmsg() and BIO_recvmmsg() return 1 and write the number of messages
successfully processed (which need not be nonzero) to msgs_processed. Where a positive value n is written
to msgs_processed, all entries in the BIO_MSG array from 0 through n-1 inclusive have their data_len and
flags fields updated with the results of the operation on that message. If the call was to BIO_recvmmsg()
and the peer or local fields of that message are non-NULL, the BIO_ADDR structures they point to are
written with the relevant address.
On failure, the functions BIO_sendmmsg() and BIO_recvmmsg() return 0 and write zero to msgs_processed.
Thus msgs_processed is always written regardless of the outcome of the function call.
If BIO_sendmmsg() and BIO_recvmmsg() fail, they always raise an ERR_LIB_BIO error using ERR_raise(3). Any
error may be raised, but the following in particular may be noted:
BIO_R_LOCAL_ADDR_NOT_AVAILABLE
The local field was set to a non-NULL value, but local address support is not available or not enabled
on the BIO.
BIO_R_PEER_ADDR_NOT_AVAILABLE
The peer field was set to a non-NULL value, but peer address support is not available on the BIO.
BIO_R_UNSUPPORTED_METHOD
The BIO_sendmmsg() or BIO_recvmmsg() method is not supported on the BIO.
BIO_R_NON_FATAL
The call failed due to a transient, non-fatal error (for example, because the BIO is in nonblocking
mode and the call would otherwise have blocked).
Implementations of this interface which do not make system calls and thereby pass through system error
codes using ERR_LIB_SYS (for example, memory-based implementations) should issue this reason code to
indicate a transient failure. However, users of this interface should not test for this reason code
directly, as there are multiple possible packed error codes representing a transient failure; use
BIO_err_is_non_fatal() instead (discussed below).
Socket errors
OS-level socket errors are reported using an error with library code ERR_LIB_SYS; for a packed error
code errcode where "ERR_SYSTEM_ERROR(errcode) == 1", the OS-level socket error code can be retrieved
using ERR_GET_REASON(errcode). The packed error code can be retrieved by calling ERR_peek_last_error(3)
after the call to BIO_sendmmsg() or BIO_recvmmsg() returns 0.
Non-fatal errors
Whether an error is transient can be determined by passing the packed error code to
BIO_err_is_non_fatal(). Callers should do this instead of testing the reason code directly, as there
are many possible error codes which can indicate a transient error, many of which are system specific.
Third parties implementing custom BIOs supporting the BIO_sendmmsg() or BIO_recvmmsg() methods should
note that it is a required part of the API contract that an error is always raised when either of these
functions return 0.
BIO_dgram_set_local_addr_enable() returns 1 if local address support was successfully enabled or disabled
and 0 otherwise.
BIO_dgram_get_local_addr_enable() returns 1 if the local address support enable flag was successfully
retrieved.
BIO_dgram_get_local_addr_cap() returns 1 if the BIO can support local addresses.
BIO_err_is_non_fatal() returns 1 if the passed packed error code represents an error which is transient
in nature.
HISTORY
These functions were added in OpenSSL 3.2.
COPYRIGHT
Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance
with the License. You can obtain a copy in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.4.1 2025-04-03 BIO_SENDMMSG(3SSL)