351 lines
15 KiB
Plaintext
351 lines
15 KiB
Plaintext
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.\" ========================================================================
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.\"
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.IX Title "BIO_SENDMMSG 3ossl"
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.TH BIO_SENDMMSG 3ossl "2024-01-30" "3.2.1" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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BIO_sendmmsg, BIO_recvmmsg, BIO_dgram_set_local_addr_enable,
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BIO_dgram_get_local_addr_enable, BIO_dgram_get_local_addr_cap,
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BIO_err_is_non_fatal \- send and receive multiple datagrams in a single call
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/bio.h>
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\&
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\& typedef struct bio_msg_st {
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\& void *data;
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\& size_t data_len;
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\& BIO_ADDR *peer, *local;
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\& uint64_t flags;
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\& } BIO_MSG;
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\&
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\& int BIO_sendmmsg(BIO *b, BIO_MSG *msg,
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\& size_t stride, size_t num_msg, uint64_t flags,
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\& size_t *msgs_processed);
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\& int BIO_recvmmsg(BIO *b, BIO_MSG *msg,
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\& size_t stride, size_t num_msg, uint64_t flags,
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\& size_t *msgs_processed);
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\&
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\& int BIO_dgram_set_local_addr_enable(BIO *b, int enable);
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\& int BIO_dgram_get_local_addr_enable(BIO *b, int *enable);
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\& int BIO_dgram_get_local_addr_cap(BIO *b);
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\& int BIO_err_is_non_fatal(unsigned int errcode);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fIBIO_sendmmsg()\fR and \fIBIO_recvmmsg()\fR functions can be used to send and receive
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multiple messages in a single call to a \s-1BIO.\s0 They are analogous to \fIsendmmsg\fR\|(2)
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and \fIrecvmmsg\fR\|(2) on operating systems which provide those functions.
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.PP
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The \fB\s-1BIO_MSG\s0\fR structure provides a subset of the functionality of the \fBstruct
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msghdr\fR structure defined by \s-1POSIX.\s0 These functions accept an array of
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\&\fB\s-1BIO_MSG\s0\fR structures. On any particular invocation, these functions may process
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all of the passed structures, some of them, or none of them. This is indicated
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by the value stored in \fI*msgs_processed\fR, which expresses the number of
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messages processed.
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.PP
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The caller should set the \fIdata\fR member of a \fB\s-1BIO_MSG\s0\fR to a buffer containing
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the data to send, or to be filled with a received message. \fIdata_len\fR should be
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set to the size of the buffer in bytes. If the given \fB\s-1BIO_MSG\s0\fR is processed (in
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other words, if the integer returned by the function is greater than or equal to
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that \fB\s-1BIO_MSG\s0\fR's array index), \fIdata_len\fR will be modified to specify the
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actual amount of data sent or received.
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.PP
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The \fIflags\fR field of a \fB\s-1BIO_MSG\s0\fR provides input per-message flags to the
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invocation. If the invocation processes that \fB\s-1BIO_MSG\s0\fR, the \fIflags\fR field is
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written with output per-message flags, or zero if no such flags are applicable.
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.PP
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Currently, no input or output per-message flags are defined and this field
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should be set to zero before calling \fIBIO_sendmmsg()\fR or \fIBIO_recvmmsg()\fR.
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.PP
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The \fIflags\fR argument to \fIBIO_sendmmsg()\fR and \fIBIO_recvmmsg()\fR provides global
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flags which affect the entire invocation. No global flags are currently
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defined and this argument should be set to zero.
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.PP
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When these functions are used to send and receive datagrams, the \fIpeer\fR field
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of a \fB\s-1BIO_MSG\s0\fR allows the destination address of sent datagrams to be specified
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on a per-datagram basis, and the source address of received datagrams to be
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determined. The \fIpeer\fR field should be set to point to a \fB\s-1BIO_ADDR\s0\fR, which
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will be read by \fIBIO_sendmmsg()\fR and used as the destination address for sent
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datagrams, and written by \fIBIO_recvmmsg()\fR with the source address of received
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datagrams.
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.PP
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Similarly, the \fIlocal\fR field of a \fB\s-1BIO_MSG\s0\fR allows the source address of sent
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datagrams to be specified on a per-datagram basis, and the destination address
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of received datagrams to be determined. Unlike \fIpeer\fR, support for \fIlocal\fR
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must be explicitly enabled on a \fB\s-1BIO\s0\fR before it can be used; see
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\&\fIBIO_dgram_set_local_addr_enable()\fR. If \fIlocal\fR is non-NULL in a \fB\s-1BIO_MSG\s0\fR and
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support for \fIlocal\fR has not been enabled, processing of that \fB\s-1BIO_MSG\s0\fR fails.
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.PP
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\&\fIpeer\fR and \fIlocal\fR should be set to \s-1NULL\s0 if they are not required. Support for
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\&\fIlocal\fR may not be available on all platforms; on these platforms, these
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functions always fail if \fIlocal\fR is non-NULL.
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.PP
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If \fIlocal\fR is specified and local address support is enabled, but the operating
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system does not report a local address for a specific received message, the
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\&\fB\s-1BIO_ADDR\s0\fR it points to will be cleared (address family set to \f(CW\*(C`AF_UNSPEC\*(C'\fR).
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This is known to happen on Windows when a packet is received which was sent by
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the local system, regardless of whether the packet's destination address was the
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loopback address or the \s-1IP\s0 address of a local non-loopback interface. This is
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also known to happen on macOS in some circumstances, such as for packets sent
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before local address support was enabled for a receiving socket. These are
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OS-specific limitations. As such, users of this \s-1API\s0 using local address support
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should expect to sometimes receive a cleared local \fB\s-1BIO_ADDR\s0\fR instead of the
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correct value.
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.PP
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The \fIstride\fR argument must be set to \f(CW\*(C`sizeof(BIO_MSG)\*(C'\fR. This argument
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facilitates backwards compatibility if fields are added to \fB\s-1BIO_MSG\s0\fR. Callers
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must zero-initialize \fB\s-1BIO_MSG\s0\fR.
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.PP
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\&\fInum_msg\fR should be sent to the maximum number of messages to send or receive,
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which is also the length of the array pointed to by \fImsg\fR.
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.PP
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\&\fImsgs_processed\fR must be non-NULL and points to an integer written with the
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number of messages successfully processed; see the \s-1RETURN VALUES\s0 section for
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further discussion.
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.PP
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Unlike most \s-1BIO\s0 functions, these functions explicitly support multi-threaded
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use. Multiple concurrent writers and multiple concurrent readers of the same \s-1BIO\s0
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are permitted in any combination. As such, these functions do not clear, set, or
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otherwise modify \s-1BIO\s0 retry flags. The return value must be used to determine
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whether an operation should be retried; see below.
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.PP
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The support for concurrent use extends to \fIBIO_sendmmsg()\fR and \fIBIO_recvmmsg()\fR
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only, and no other function may be called on a given \s-1BIO\s0 while any call to
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\&\fIBIO_sendmmsg()\fR or \fIBIO_recvmmsg()\fR is in progress, or vice versa.
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.PP
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\&\fIBIO_dgram_set_local_addr_enable()\fR and \fIBIO_dgram_get_local_addr_enable()\fR control
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whether local address support is enabled. To enable local address support, call
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\&\fIBIO_dgram_set_local_addr_enable()\fR with an argument of 1. The call will fail if
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local address support is not available for the platform.
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\&\fIBIO_dgram_get_local_addr_enable()\fR retrieves the value set by
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\&\fIBIO_dgram_set_local_addr_enable()\fR.
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.PP
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\&\fIBIO_dgram_get_local_addr_cap()\fR determines if the \fB\s-1BIO\s0\fR is capable of supporting
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local addresses.
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.PP
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\&\fIBIO_err_is_non_fatal()\fR determines if a packed error code represents an error
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which is transient in nature.
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.SH "NOTES"
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.IX Header "NOTES"
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Some implementations of the \fIBIO_sendmmsg()\fR and \fIBIO_recvmmsg()\fR \s-1BIO\s0 methods might
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always process at most one message at a time, for example when OS-level
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functionality to transmit or receive multiple messages at a time is not
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available.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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On success, the functions \fIBIO_sendmmsg()\fR and \fIBIO_recvmmsg()\fR return 1 and write
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the number of messages successfully processed (which need not be nonzero) to
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\&\fImsgs_processed\fR. Where a positive value n is written to \fImsgs_processed\fR, all
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entries in the \fB\s-1BIO_MSG\s0\fR array from 0 through n\-1 inclusive have their
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\&\fIdata_len\fR and \fIflags\fR fields updated with the results of the operation on
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that message. If the call was to \fIBIO_recvmmsg()\fR and the \fIpeer\fR or \fIlocal\fR
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fields of that message are non-NULL, the \fB\s-1BIO_ADDR\s0\fR structures they point to
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are written with the relevant address.
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.PP
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On failure, the functions \fIBIO_sendmmsg()\fR and \fIBIO_recvmmsg()\fR return 0 and write
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zero to \fImsgs_processed\fR. Thus \fImsgs_processed\fR is always written regardless
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of the outcome of the function call.
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.PP
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If \fIBIO_sendmmsg()\fR and \fIBIO_recvmmsg()\fR fail, they always raise an \fB\s-1ERR_LIB_BIO\s0\fR
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error using \fIERR_raise\fR\|(3). Any error may be raised, but the following in
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particular may be noted:
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.IP "\fB\s-1BIO_R_LOCAL_ADDR_NOT_AVAILABLE\s0\fR" 2
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.IX Item "BIO_R_LOCAL_ADDR_NOT_AVAILABLE"
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The \fIlocal\fR field was set to a non-NULL value, but local address support is not
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available or not enabled on the \s-1BIO.\s0
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.IP "\fB\s-1BIO_R_PEER_ADDR_NOT_AVAILABLE\s0\fR" 2
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.IX Item "BIO_R_PEER_ADDR_NOT_AVAILABLE"
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The \fIpeer\fR field was set to a non-NULL value, but peer address support is not
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available on the \s-1BIO.\s0
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.IP "\fB\s-1BIO_R_UNSUPPORTED_METHOD\s0\fR" 2
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.IX Item "BIO_R_UNSUPPORTED_METHOD"
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The \fIBIO_sendmmsg()\fR or \fIBIO_recvmmsg()\fR method is not supported on the \s-1BIO.\s0
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.IP "\fB\s-1BIO_R_NON_FATAL\s0\fR" 2
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.IX Item "BIO_R_NON_FATAL"
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The call failed due to a transient, non-fatal error (for example, because the
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\&\s-1BIO\s0 is in nonblocking mode and the call would otherwise have blocked).
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.Sp
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Implementations of this interface which do not make system calls and thereby
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pass through system error codes using \fB\s-1ERR_LIB_SYS\s0\fR (for example, memory-based
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implementations) should issue this reason code to indicate a transient failure.
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However, users of this interface should not test for this reason code directly,
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as there are multiple possible packed error codes representing a transient
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failure; use \fIBIO_err_is_non_fatal()\fR instead (discussed below).
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.IP "Socket errors" 2
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.IX Item "Socket errors"
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OS-level socket errors are reported using an error with library code
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\&\fB\s-1ERR_LIB_SYS\s0\fR; for a packed error code \fBerrcode\fR where
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\&\f(CW\*(C`ERR_SYSTEM_ERROR(errcode) == 1\*(C'\fR, the OS-level socket error code can be
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retrieved using \f(CW\*(C`ERR_GET_REASON(errcode)\*(C'\fR. The packed error code can be
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retrieved by calling \fIERR_peek_last_error\fR\|(3) after the call to \fIBIO_sendmmsg()\fR
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or \fIBIO_recvmmsg()\fR returns 0.
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.IP "Non-fatal errors" 2
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.IX Item "Non-fatal errors"
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Whether an error is transient can be determined by passing the packed error code
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to \fIBIO_err_is_non_fatal()\fR. Callers should do this instead of testing the reason
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code directly, as there are many possible error codes which can indicate a
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transient error, many of which are system specific.
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.PP
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Third parties implementing custom BIOs supporting the \fIBIO_sendmmsg()\fR or
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\&\fIBIO_recvmmsg()\fR methods should note that it is a required part of the \s-1API\s0
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contract that an error is always raised when either of these functions return 0.
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.PP
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\&\fIBIO_dgram_set_local_addr_enable()\fR returns 1 if local address support was
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successfully enabled or disabled and 0 otherwise.
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.PP
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\&\fIBIO_dgram_get_local_addr_enable()\fR returns 1 if the local address support enable
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flag was successfully retrieved.
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.PP
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\&\fIBIO_dgram_get_local_addr_cap()\fR returns 1 if the \fB\s-1BIO\s0\fR can support local
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addresses.
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.PP
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\&\fIBIO_err_is_non_fatal()\fR returns 1 if the passed packed error code represents an
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error which is transient in nature.
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.SH "HISTORY"
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.IX Header "HISTORY"
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These functions were added in OpenSSL 3.2.
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2000\-2023 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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