From 9a4fd80ee0ad1833879b6a55c9c4673eeb8446a3 Mon Sep 17 00:00:00 2001 From: Richard Levitte Date: Sun, 19 Jan 2020 03:19:31 +0100 Subject: [PATCH] DOC: document in more detail what a BIO_read_ex() via BIO_f_buffer() does 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 (Merged from https://github.com/openssl/openssl/pull/10890) --- doc/man3/BIO_f_buffer.pod | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/doc/man3/BIO_f_buffer.pod b/doc/man3/BIO_f_buffer.pod index 6009b479e5..ec3f04d731 100644 --- a/doc/man3/BIO_f_buffer.pod +++ b/doc/man3/BIO_f_buffer.pod @@ -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() -- 2.25.1