[doc] Document that a BIO pair may need 2-pass read to retrieve all bytes due to ring buffer

[space88man]

Version

master

Description

When a BIO pair has known NN bytes available from (wolfSSL_BIO_pending) it may still need two-pass wolfSSL_BIO_read to get all bytes due to ring buffer, i.e, the first read may be short, then the 2nd read will get the remainder.

This is an implementation detail as wolfSSL_BIO_BIO_read uses wolfSSL_BIO_nread0 under the cover and does not perform wrap around (i.e it does only 1 x XMEMCPY).

This is different behaviour from OpenSSL where the BIO_read on a BIO pair will do wrap around.
(The OpenSSL nread behaviour is the same as wolfSSL's nread behaviour). OpenSSL uses two implementations - a BIO_read that does wrap around(and provides all bytes in one pass) and a BIO_nread that does not do wrap around.

[julek-wolfssl]

Thank you for your report. I opened a pull request that solves your issue at #7169. Please try it and let us know your feedback.

[space88man]

Great - LGTM.

Thank you for your report. I opened a pull request that solves your issue at #7169. Please try it and let us know your feedback.