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DOC: document in more detail what a BIO_read_ex() via BIO_f_buffer() does

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The BIO_f_buffer() documentation tells in enough detail how it affects
BIO_gets(), but not how it affects BIO_read_ex().  This change
remedies that.

Fixes #10859

Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10890)
This commit is contained in:
Richard Levitte 2020-01-19 03:19:31 +01:00
parent 9ea5924174
commit 9a4fd80ee0
1 changed files with 14 additions and 4 deletions
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18
doc/man3/BIO_f_buffer.pod
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@ -49,10 +49,20 @@ is expanded.
These functions, other than BIO_f_buffer(), are implemented as macros.
Buffering BIOs implement BIO_gets() by using BIO_read_ex() operations on the
next BIO in the chain. By prepending a buffering BIO to a chain it is therefore
possible to provide BIO_gets() functionality if the following BIOs do not
support it (for example SSL BIOs).
Buffering BIOs implement BIO_read_ex() and BIO_gets() by using
BIO_read_ex() operations on the next BIO in the chain and storing the
result in an internal buffer, from which bytes are given back to the
caller as appropriate for the call; a BIO_gets() is guaranteed to give
the caller a whole line, and BIO_read_ex() is guaranteed to give the
caller the number of bytes it asks for, unless there's an error or end
of communication is reached in the next BIO. By prepending a
buffering BIO to a chain it is therefore possible to provide
BIO_gets() or exact size BIO_read_ex() functionality if the following
BIOs do not support it.
Do not add more than one BIO_f_buffer() to a BIO chain. The result of
doing so will force a full read of the size of the internal buffer of
the top BIO_f_buffer(), which is 4 KiB at a minimum.
Data is only written to the next BIO in the chain when the write buffer fills
or when BIO_flush() is called. It is therefore important to call BIO_flush()