1BIO_S_DATAGRAM(3ossl) OpenSSL BIO_S_DATAGRAM(3ossl)
2
6 BIO_s_datagram, BIO_new_dgram, BIO_ctrl_dgram_connect,
7 BIO_ctrl_set_connected, BIO_dgram_recv_timedout,
8 BIO_dgram_send_timedout, BIO_dgram_get_peer, BIO_dgram_set_peer,
9 BIO_dgram_get_mtu_overhead - Network BIO with datagram semantics
10
12 #include <openssl/bio.h>
13 BIO_METHOD *BIO_s_datagram(void);
15 BIO *BIO_new_dgram(int fd, int close_flag);
16 int BIO_ctrl_dgram_connect(BIO *bio, const BIO_ADDR *peer);
18 int BIO_ctrl_set_connected(BIO *bio, const BIO_ADDR *peer);
19 int BIO_dgram_recv_timedout(BIO *bio);
20 int BIO_dgram_send_timedout(BIO *bio);
21 int BIO_dgram_get_peer(BIO *bio, BIO_ADDR *peer);
22 int BIO_dgram_set_peer(BIO *bio, const BIO_ADDR *peer);
23 int BIO_dgram_get_mtu_overhead(BIO *bio);
24
26 BIO_s_datagram() is a BIO implementation designed for use with network
27 sockets which provide datagram semantics, such as UDP sockets. It is
28 suitable for use with DTLSv1.
29 Because BIO_s_datagram() has datagram semantics, a single BIO_write()
31 call sends a single datagram and a single BIO_read() call receives a
32 single datagram. If the size of the buffer passed to BIO_read() is
33 inadequate, the datagram is silently truncated.
34 When using BIO_s_datagram(), it is important to note that:
36 • This BIO can be used with either a connected or unconnected network
38 socket. A connected socket is a network socket which has had
39 BIO_connect(3) or a similar OS-specific function called on it. Such
40 a socket can only receive datagrams from the specified peer. Any
41 other socket is an unconnected socket and can receive datagrams
42 from any host.
43 • Despite their naming, neither BIO_ctrl_dgram_connect() nor
45 BIO_ctrl_set_connected() cause a socket to become connected. These
46 controls are provided to indicate to the BIO how the underlying
47 socket is configured and how it is to be used; see below.
48 • Use of BIO_s_datagram() with an unconnected network socket is
50 hazardous hecause any successful call to BIO_read() results in the
51 peer address used for any subsequent call to BIO_write() being set
52 to the source address of the datagram received by that call to
53 BIO_read(). Thus, unless the caller calls BIO_dgram_set_peer()
54 immediately prior to every call to BIO_write(), or never calls
55 BIO_read(), any host on the network may cause future datagrams
56 written to be redirected to that host. Therefore, it is recommended
57 that users use BIO_s_dgram() only with a connected socket. An
58 exception is where DTLSv1_listen(3) must be used; see
59 DTLSv1_listen(3) for further discussion.
60 Various controls are available for configuring the BIO_s_datagram()
62 using BIO_ctrl(3):
63 BIO_ctrl_dgram_connect (BIO_CTRL_DGRAM_CONNECT)
65 This is equivalent to calling BIO_dgram_set_peer(3).
66 Despite its name, this function does not cause the underlying
68 socket to become connected.
69 BIO_ctrl_set_connected (BIO_CTRL_SET_CONNECTED)
71 This informs the BIO_s_datagram() whether the underlying socket has
72 been connected, and therefore how the BIO_s_datagram() should
73 attempt to use the socket.
74 If the peer argument is non-NULL, BIO_s_datagram() assumes that the
76 underlying socket has been connected and will attempt to use the
77 socket using OS APIs which do not specify peer addresses (for
78 example, send(3) and recv(3) or similar). The peer argument should
79 specify the peer address to which the socket is connected.
80 If the peer argument is NULL, BIO_s_datagram() assumes that the
82 underlying socket is not connected and will attempt to use the
83 socket using an OS APIs which specify peer addresses (for example,
84 sendto(3) and recvfrom(3)).
85 BIO_dgram_get_peer (BIO_CTRL_DGRAM_GET_PEER)
87 This outputs a BIO_ADDR which specifies one of the following
88 values, whichever happened most recently:
89 • The peer address last passed to BIO_dgram_set_peer(),
91 BIO_ctrl_dgram_connect() or BIO_ctrl_set_connected().
92 • The peer address of the datagram last received by a call to
94 BIO_read().
95 BIO_dgram_set_peer (BIO_CTRL_DGRAM_SET_PEER)
97 Sets the peer address to be used for subsequent writes to this BIO.
98 Warning: When used with an unconnected network socket, the value
100 set may be modified by future calls to BIO_read(3), making use of
101 BIO_s_datagram() hazardous when used with unconnected network
102 sockets; see above.
103 BIO_dgram_recv_timeout (BIO_CTRL_DGRAM_GET_RECV_TIMER_EXP)
105 Returns 1 if the last I/O operation performed on the BIO (for
106 example, via a call to BIO_read(3)) may have been caused by a
107 receive timeout.
108 BIO_dgram_send_timedout (BIO_CTRL_DGRAM_GET_SEND_TIMER_EXP)
110 Returns 1 if the last I/O operation performed on the BIO (for
111 example, via a call to BIO_write(3)) may have been caused by a send
112 timeout.
113 BIO_dgram_get_mtu_overhead (BIO_CTRL_DGRAM_GET_MTU_OVERHEAD)
115 Returns a quantity in bytes which is a rough estimate of the number
116 of bytes of overhead which should typically be added to a datagram
117 payload size in order to estimate the final size of the Layer 3
118 (e.g. IP) packet which will contain the datagram. In most cases,
119 the maximum datagram payload size which can be transmitted can be
120 determined by determining the link MTU in bytes and subtracting the
121 value returned by this call.
122 The value returned by this call depends on the network layer
124 protocol being used.
125 The value returned is not fully reliable because datagram overheads
127 can be higher in atypical network configurations, for example where
128 IPv6 extension headers or IPv4 options are used.
129 BIO_CTRL_DGRAM_SET_DONT_FRAG
131 If num is nonzero, configures the underlying network socket to
132 enable Don't Fragment mode, in which datagrams will be set with the
133 IP Don't Fragment (DF) bit set. If num is zero, Don't Fragment mode
134 is disabled.
135 BIO_CTRL_DGRAM_QUERY_MTU
137 Queries the OS for its assessment of the Path MTU for the
138 destination to which the underlying network socket, and returns
139 that Path MTU in bytes. This control can only be used with a
140 connected socket.
141 This is not supported on all platforms and depends on OS support
143 being available. Returns 0 on failure.
144 BIO_CTRL_DGRAM_MTU_DISCOVER
146 This control requests that Path MTU discovery be enabled on the
147 underlying network socket.
148 BIO_CTRL_DGRAM_GET_FALLBACK_MTU
150 Returns the estimated minimum size of datagram payload which should
151 always be supported on the BIO. This size is determined by the
152 minimum MTU required to be supported by the applicable underlying
153 network layer. Use of datagrams of this size may lead to suboptimal
154 performance, but should be routable in all circumstances. The value
155 returned is the datagram payload size in bytes and does not include
156 the size of layer 3 or layer 4 protocol headers.
157 BIO_CTRL_DGRAM_MTU_EXCEEDED
159 Returns 1 if the last attempted write to the BIO failed due to the
160 size of the attempted write exceeding the applicable MTU.
161 BIO_CTRL_DGRAM_SET_NEXT_TIMEOUT
163 Accepts a pointer to a struct timeval. If the time specified is
164 zero, disables receive timeouts. Otherwise, configures the
165 specified time interval as the receive timeout for the socket for
166 the purposes of future BIO_read(3) calls.
167 BIO_CTRL_DGRAM_SET_PEEK_MODE
169 If num is nonzero, enables peek mode; otherwise, disables peek
170 mode. Where peek mode is enabled, calls to BIO_read(3) read
171 datagrams from the underlying network socket in peek mode, meaning
172 that a future call to BIO_read(3) will yield the same datagram
173 until peek mode is disabled.
174 BIO_new_dgram() is a helper function which instantiates a
176 BIO_s_datagram() and sets the BIO to use the socket given in fd by
177 calling BIO_set_fd().
178
180 BIO_s_datagram() returns a BIO method.
181 BIO_new_dgram() returns a BIO on success and NULL on failure.
183 BIO_ctrl_dgram_connect(), BIO_ctrl_set_connected(),
185 BIO_dgram_get_peer(), BIO_dgram_set_peer() return 1 on success and 0 on
186 failure.
187 BIO_dgram_recv_timedout() and BIO_dgram_send_timedout() return 0 or 1
189 depending on the circumstance; see discussion above.
190 BIO_dgram_get_mtu_overhead() returns a value in bytes.
192
194 DTLSv1_listen(3), bio(7)
195
197 Copyright 2022-2023 The OpenSSL Project Authors. All Rights Reserved.
198 Licensed under the Apache License 2.0 (the "License"). You may not use
200 this file except in compliance with the License. You can obtain a copy
201 in the file LICENSE in the source distribution or at
202 <https://www.openssl.org/source/license.html>.
2033.0.9 2023-07-27 BIO_S_DATAGRAM(3ossl)