1SSL_CTX_SET_SPLIT_SEND_FRAGMENT(3) OpenSSL SSL_CTX_SET_SPLIT_SEND_FRAGMENT(3)
2
6 SSL_CTX_set_max_send_fragment, SSL_set_max_send_fragment,
7 SSL_CTX_set_split_send_fragment, SSL_set_split_send_fragment,
8 SSL_CTX_set_max_pipelines, SSL_set_max_pipelines,
9 SSL_CTX_set_default_read_buffer_len, SSL_set_default_read_buffer_len,
10 SSL_CTX_set_tlsext_max_fragment_length,
11 SSL_set_tlsext_max_fragment_length, SSL_SESSION_get_max_fragment_length
12 - Control fragment size settings and pipelining operations
13
15 #include <openssl/ssl.h>
16 long SSL_CTX_set_max_send_fragment(SSL_CTX *ctx, long);
18 long SSL_set_max_send_fragment(SSL *ssl, long m);
19 long SSL_CTX_set_max_pipelines(SSL_CTX *ctx, long m);
21 long SSL_set_max_pipelines(SSL_CTX *ssl, long m);
22 long SSL_CTX_set_split_send_fragment(SSL_CTX *ctx, long m);
24 long SSL_set_split_send_fragment(SSL *ssl, long m);
25 void SSL_CTX_set_default_read_buffer_len(SSL_CTX *ctx, size_t len);
27 void SSL_set_default_read_buffer_len(SSL *s, size_t len);
28 int SSL_CTX_set_tlsext_max_fragment_length(SSL_CTX *ctx, uint8_t mode);
30 int SSL_set_tlsext_max_fragment_length(SSL *ssl, uint8_t mode);
31 uint8_t SSL_SESSION_get_max_fragment_length(SSL_SESSION *session);
32
34 Some engines are able to process multiple simultaneous crypto
35 operations. This capability could be utilised to parallelise the
36 processing of a single connection. For example a single write can be
37 split into multiple records and each one encrypted independently and in
38 parallel. Note: this will only work in TLS1.1+. There is no support in
39 SSLv3, TLSv1.0 or DTLS (any version). This capability is known as
40 "pipelining" within OpenSSL.
41 In order to benefit from the pipelining capability. You need to have an
43 engine that provides ciphers that support this. The OpenSSL "dasync"
44 engine provides AES128-SHA based ciphers that have this capability.
45 However, these are for development and test purposes only.
46 SSL_CTX_set_max_send_fragment() and SSL_set_max_send_fragment() set the
48 max_send_fragment parameter for SSL_CTX and SSL objects respectively.
49 This value restricts the amount of plaintext bytes that will be sent in
50 any one SSL/TLS record. By default its value is
51 SSL3_RT_MAX_PLAIN_LENGTH (16384). These functions will only accept a
52 value in the range 512 - SSL3_RT_MAX_PLAIN_LENGTH.
53 SSL_CTX_set_max_pipelines() and SSL_set_max_pipelines() set the maximum
55 number of pipelines that will be used at any one time. This value
56 applies to both "read" pipelining and "write" pipelining. By default
57 only one pipeline will be used (i.e. normal non-parallel operation).
58 The number of pipelines set must be in the range 1 - SSL_MAX_PIPELINES
59 (32). Setting this to a value > 1 will also automatically turn on
60 "read_ahead" (see SSL_CTX_set_read_ahead(3)). This is explained further
61 below. OpenSSL will only every use more than one pipeline if a cipher
62 suite is negotiated that uses a pipeline capable cipher provided by an
63 engine.
64 Pipelining operates slightly differently for reading encrypted data
66 compared to writing encrypted data. SSL_CTX_set_split_send_fragment()
67 and SSL_set_split_send_fragment() define how data is split up into
68 pipelines when writing encrypted data. The number of pipelines used
69 will be determined by the amount of data provided to the SSL_write_ex()
70 or SSL_write() call divided by split_send_fragment.
71 For example if split_send_fragment is set to 2000 and max_pipelines is
73 4 then:
74 SSL_write/SSL_write_ex called with 0-2000 bytes == 1 pipeline used
76 SSL_write/SSL_write_ex called with 2001-4000 bytes == 2 pipelines used
78 SSL_write/SSL_write_ex called with 4001-6000 bytes == 3 pipelines used
80 SSL_write/SSL_write_ex called with 6001+ bytes == 4 pipelines used
82 split_send_fragment must always be less than or equal to
84 max_send_fragment. By default it is set to be equal to
85 max_send_fragment. This will mean that the same number of records will
86 always be created as would have been created in the non-parallel case,
87 although the data will be apportioned differently. In the parallel case
88 data will be spread equally between the pipelines.
89 Read pipelining is controlled in a slightly different way than with
91 write pipelining. While reading we are constrained by the number of
92 records that the peer (and the network) can provide to us in one go.
93 The more records we can get in one go the more opportunity we have to
94 parallelise the processing. As noted above when setting max_pipelines
95 to a value greater than one, read_ahead is automatically set. The
96 read_ahead parameter causes OpenSSL to attempt to read as much data
97 into the read buffer as the network can provide and will fit into the
98 buffer. Without this set data is read into the read buffer one record
99 at a time. The more data that can be read, the more opportunity there
100 is for parallelising the processing at the cost of increased memory
101 overhead per connection. Setting read_ahead can impact the behaviour of
102 the SSL_pending() function (see SSL_pending(3)).
103 The SSL_CTX_set_default_read_buffer_len() and
105 SSL_set_default_read_buffer_len() functions control the size of the
106 read buffer that will be used. The len parameter sets the size of the
107 buffer. The value will only be used if it is greater than the default
108 that would have been used anyway. The normal default value depends on a
109 number of factors but it will be at least SSL3_RT_MAX_PLAIN_LENGTH +
110 SSL3_RT_MAX_ENCRYPTED_OVERHEAD (16704) bytes.
111 SSL_CTX_set_tlsext_max_fragment_length() sets the default maximum
113 fragment length negotiation mode via value mode to ctx. This setting
114 affects only SSL instances created after this function is called. It
115 affects the client-side as only its side may initiate this extension
116 use.
117 SSL_set_tlsext_max_fragment_length() sets the maximum fragment length
119 negotiation mode via value mode to ssl. This setting will be used
120 during a handshake when extensions are exchanged between client and
121 server. So it only affects SSL sessions created after this function is
122 called. It affects the client-side as only its side may initiate this
123 extension use.
124 SSL_SESSION_get_max_fragment_length() gets the maximum fragment length
126 negotiated in session.
127
129 All non-void functions return 1 on success and 0 on failure.
130
132 The Maximum Fragment Length extension support is optional on the server
133 side. If the server does not support this extension then
134 SSL_SESSION_get_max_fragment_length() will return:
135 TLSEXT_max_fragment_length_DISABLED.
136 The following modes are available:
138 TLSEXT_max_fragment_length_DISABLED
140 Disables Maximum Fragment Length Negotiation (default).
141 TLSEXT_max_fragment_length_512
143 Sets Maximum Fragment Length to 512 bytes.
144 TLSEXT_max_fragment_length_1024
146 Sets Maximum Fragment Length to 1024.
147 TLSEXT_max_fragment_length_2048
149 Sets Maximum Fragment Length to 2048.
150 TLSEXT_max_fragment_length_4096
152 Sets Maximum Fragment Length to 4096.
153 With the exception of SSL_CTX_set_default_read_buffer_len()
155 SSL_set_default_read_buffer_len(),
156 SSL_CTX_set_tlsext_max_fragment_length(),
157 SSL_set_tlsext_max_fragment_length() and
158 SSL_SESSION_get_max_fragment_length() all these functions are
159 implemented using macros.
160
162 SSL_CTX_set_read_ahead(3), SSL_pending(3)
163
165 The SSL_CTX_set_max_pipelines(), SSL_set_max_pipelines(),
166 SSL_CTX_set_split_send_fragment(), SSL_set_split_send_fragment(),
167 SSL_CTX_set_default_read_buffer_len() and
168 SSL_set_default_read_buffer_len() functions were added in OpenSSL
169 1.1.0.
170 The SSL_CTX_set_tlsext_max_fragment_length(),
172 SSL_set_tlsext_max_fragment_length() and
173 SSL_SESSION_get_max_fragment_length() functions were added in OpenSSL
174 1.1.1.
175
177 Copyright 2016-2020 The OpenSSL Project Authors. All Rights Reserved.
178 Licensed under the OpenSSL license (the "License"). You may not use
180 this file except in compliance with the License. You can obtain a copy
181 in the file LICENSE in the source distribution or at
182 <https://www.openssl.org/source/license.html>.
1831.1.1q 2022-07-21SSL_CTX_SET_SPLIT_SEND_FRAGMENT(3)