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Add a note about Nagle's algorithm on the SSL_connect man page

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Fixes #4237

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Ben Kaduk <kaduk@mit.edu>
(Merged from https://github.com/openssl/openssl/pull/6143)
This commit is contained in:
Matt Caswell 2018-05-01 11:46:58 +01:00
parent aebd0e5ca1
commit 6299c7a402
1 changed files with 15 additions and 0 deletions
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15
doc/man3/SSL_connect.pod
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@ -35,6 +35,21 @@ nothing is to be done, but select() can be used to check for the required
condition. When using a buffering BIO, like a BIO pair, data must be written
into or retrieved out of the BIO before being able to continue.
Many systems implement Nagle's algorithm by default which means that it will
buffer outgoing TCP data if a TCP packet has already been sent for which no
corresponding ACK has been received yet from the peer. This can have performance
impacts after a successful TLSv1.3 handshake or a successful TLSv1.2 (or below)
resumption handshake, because the last peer to communicate in the handshake is
the client. If the client is also the first to send application data (as is
typical for many protocols) then this data could be buffered until an ACK has
been received for the final handshake message.
The B<TCP_NODELAY> socket option is often available to disable Nagle's
algorithm. If an application opts to disable Nagle's algorithm consideration
should be given to turning it back on again later if appropriate. The helper
function BIO_set_tcp_ndelay() can be used to turn on or off the B<TCP_NODELAY>
option.
=head1 RETURN VALUES
The following return values can occur: