1=pod 2 3=head1 NAME 4 5SSL_CTX_set_max_send_fragment, SSL_set_max_send_fragment, 6SSL_CTX_set_split_send_fragment, SSL_set_split_send_fragment, 7SSL_CTX_set_max_pipelines, SSL_set_max_pipelines, 8SSL_CTX_set_default_read_buffer_len, SSL_set_default_read_buffer_len, 9SSL_CTX_set_tlsext_max_fragment_length, 10SSL_set_tlsext_max_fragment_length, 11SSL_SESSION_get_max_fragment_length - Control fragment size settings and pipelining operations 12 13=head1 SYNOPSIS 14 15 #include <openssl/ssl.h> 16 17 long SSL_CTX_set_max_send_fragment(SSL_CTX *ctx, long); 18 long SSL_set_max_send_fragment(SSL *ssl, long m); 19 20 long SSL_CTX_set_max_pipelines(SSL_CTX *ctx, long m); 21 long SSL_set_max_pipelines(SSL_CTX *ssl, long m); 22 23 long SSL_CTX_set_split_send_fragment(SSL_CTX *ctx, long m); 24 long SSL_set_split_send_fragment(SSL *ssl, long m); 25 26 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 29 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(const SSL_SESSION *session); 32 33=head1 DESCRIPTION 34 35Some engines are able to process multiple simultaneous crypto operations. This 36capability could be utilised to parallelise the processing of a single 37connection. For example a single write can be split into multiple records and 38each one encrypted independently and in parallel. Note: this will only work in 39TLS1.1+. There is no support in SSLv3, TLSv1.0 or DTLS (any version). This 40capability is known as "pipelining" within OpenSSL. 41 42In order to benefit from the pipelining capability. You need to have an engine 43that provides ciphers that support this. The OpenSSL "dasync" engine provides 44AES128-SHA based ciphers that have this capability. However, these are for 45development and test purposes only. 46 47SSL_CTX_set_max_send_fragment() and SSL_set_max_send_fragment() set the 48B<max_send_fragment> parameter for SSL_CTX and SSL objects respectively. This 49value restricts the amount of plaintext bytes that will be sent in any one 50SSL/TLS record. By default its value is SSL3_RT_MAX_PLAIN_LENGTH (16384). These 51functions will only accept a value in the range 512 - SSL3_RT_MAX_PLAIN_LENGTH. 52 53SSL_CTX_set_max_pipelines() and SSL_set_max_pipelines() set the maximum number 54of pipelines that will be used at any one time. This value applies to both 55"read" pipelining and "write" pipelining. By default only one pipeline will be 56used (i.e. normal non-parallel operation). The number of pipelines set must be 57in the range 1 - SSL_MAX_PIPELINES (32). Setting this to a value > 1 will also 58automatically turn on "read_ahead" (see L<SSL_CTX_set_read_ahead(3)>). This is 59explained further below. OpenSSL will only ever use more than one pipeline if 60a cipher suite is negotiated that uses a pipeline capable cipher provided by an 61engine. 62 63Pipelining operates slightly differently for reading encrypted data compared to 64writing encrypted data. SSL_CTX_set_split_send_fragment() and 65SSL_set_split_send_fragment() define how data is split up into pipelines when 66writing encrypted data. The number of pipelines used will be determined by the 67amount of data provided to the SSL_write_ex() or SSL_write() call divided by 68B<split_send_fragment>. 69 70For example if B<split_send_fragment> is set to 2000 and B<max_pipelines> is 4 71then: 72 73SSL_write/SSL_write_ex called with 0-2000 bytes == 1 pipeline used 74 75SSL_write/SSL_write_ex called with 2001-4000 bytes == 2 pipelines used 76 77SSL_write/SSL_write_ex called with 4001-6000 bytes == 3 pipelines used 78 79SSL_write/SSL_write_ex called with 6001+ bytes == 4 pipelines used 80 81B<split_send_fragment> must always be less than or equal to 82B<max_send_fragment>. By default it is set to be equal to B<max_send_fragment>. 83This will mean that the same number of records will always be created as would 84have been created in the non-parallel case, although the data will be 85apportioned differently. In the parallel case data will be spread equally 86between the pipelines. 87 88Read pipelining is controlled in a slightly different way than with write 89pipelining. While reading we are constrained by the number of records that the 90peer (and the network) can provide to us in one go. The more records we can get 91in one go the more opportunity we have to parallelise the processing. As noted 92above when setting B<max_pipelines> to a value greater than one, B<read_ahead> 93is automatically set. The B<read_ahead> parameter causes OpenSSL to attempt to 94read as much data into the read buffer as the network can provide and will fit 95into the buffer. Without this set data is read into the read buffer one record 96at a time. The more data that can be read, the more opportunity there is for 97parallelising the processing at the cost of increased memory overhead per 98connection. Setting B<read_ahead> can impact the behaviour of the SSL_pending() 99function (see L<SSL_pending(3)>). In addition the default size of the internal 100read buffer is multiplied by the number of pipelines available to ensure that we 101can read multiple records in one go. This can therefore have a significant 102impact on memory usage. 103 104The SSL_CTX_set_default_read_buffer_len() and SSL_set_default_read_buffer_len() 105functions control the size of the read buffer that will be used. The B<len> 106parameter sets the size of the buffer. The value will only be used if it is 107greater than the default that would have been used anyway. The normal default 108value depends on a number of factors but it will be at least 109SSL3_RT_MAX_PLAIN_LENGTH + SSL3_RT_MAX_ENCRYPTED_OVERHEAD (16704) bytes. 110 111SSL_CTX_set_tlsext_max_fragment_length() sets the default maximum fragment 112length negotiation mode via value B<mode> to B<ctx>. 113This setting affects only SSL instances created after this function is called. 114It affects the client-side as only its side may initiate this extension use. 115 116SSL_set_tlsext_max_fragment_length() sets the maximum fragment length 117negotiation mode via value B<mode> to B<ssl>. 118This setting will be used during a handshake when extensions are exchanged 119between client and server. 120So it only affects SSL sessions created after this function is called. 121It affects the client-side as only its side may initiate this extension use. 122 123SSL_SESSION_get_max_fragment_length() gets the maximum fragment length 124negotiated in B<session>. 125 126=head1 RETURN VALUES 127 128All non-void functions return 1 on success and 0 on failure. 129 130=head1 NOTES 131 132The Maximum Fragment Length extension support is optional on the server side. 133If the server does not support this extension then 134SSL_SESSION_get_max_fragment_length() will return: 135TLSEXT_max_fragment_length_DISABLED. 136 137The following modes are available: 138 139=over 4 140 141=item TLSEXT_max_fragment_length_DISABLED 142 143Disables Maximum Fragment Length Negotiation (default). 144 145=item TLSEXT_max_fragment_length_512 146 147Sets Maximum Fragment Length to 512 bytes. 148 149=item TLSEXT_max_fragment_length_1024 150 151Sets Maximum Fragment Length to 1024. 152 153=item TLSEXT_max_fragment_length_2048 154 155Sets Maximum Fragment Length to 2048. 156 157=item TLSEXT_max_fragment_length_4096 158 159Sets Maximum Fragment Length to 4096. 160 161=back 162 163With the exception of SSL_CTX_set_default_read_buffer_len() 164SSL_set_default_read_buffer_len(), SSL_CTX_set_tlsext_max_fragment_length(), 165SSL_set_tlsext_max_fragment_length() and SSL_SESSION_get_max_fragment_length() 166all these functions are implemented using macros. 167 168=head1 SEE ALSO 169 170L<ssl(7)>, 171L<SSL_CTX_set_read_ahead(3)>, L<SSL_pending(3)> 172 173=head1 HISTORY 174 175The SSL_CTX_set_max_pipelines(), SSL_set_max_pipelines(), 176SSL_CTX_set_split_send_fragment(), SSL_set_split_send_fragment(), 177SSL_CTX_set_default_read_buffer_len() and SSL_set_default_read_buffer_len() 178functions were added in OpenSSL 1.1.0. 179 180The SSL_CTX_set_tlsext_max_fragment_length(), SSL_set_tlsext_max_fragment_length() 181and SSL_SESSION_get_max_fragment_length() functions were added in OpenSSL 1.1.1. 182 183=head1 COPYRIGHT 184 185Copyright 2016-2023 The OpenSSL Project Authors. All Rights Reserved. 186 187Licensed under the Apache License 2.0 (the "License"). You may not use 188this file except in compliance with the License. You can obtain a copy 189in the file LICENSE in the source distribution or at 190L<https://www.openssl.org/source/license.html>. 191 192=cut 193