.\" $OpenBSD: BIO_read.3,v 1.8 2018/03/27 17:35:50 schwarze Exp $ .\" OpenSSL 99d63d46 Oct 26 13:56:48 2016 -0400 .\" .\" This file was written by Dr. Stephen Henson . .\" Copyright (c) 2000, 2016 The OpenSSL Project. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" 3. All advertising materials mentioning features or use of this .\" software must display the following acknowledgment: .\" "This product includes software developed by the OpenSSL Project .\" for use in the OpenSSL Toolkit. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: March 27 2018 $ .Dt BIO_READ 3 .Os .Sh NAME .Nm BIO_read , .Nm BIO_gets , .Nm BIO_write , .Nm BIO_puts .Nd BIO I/O functions .Sh SYNOPSIS .In openssl/bio.h .Ft int .Fo BIO_read .Fa "BIO *b" .Fa "void *buf" .Fa "int len" .Fc .Ft int .Fo BIO_gets .Fa "BIO *b" .Fa "char *buf" .Fa "int size" .Fc .Ft int .Fo BIO_write .Fa "BIO *b" .Fa "const void *buf" .Fa "int len" .Fc .Ft int .Fo BIO_puts .Fa "BIO *b" .Fa "const char *buf" .Fc .Sh DESCRIPTION .Fn BIO_read attempts to read .Fa len bytes from BIO .Fa b and places the data in .Fa buf . .Pp .Fn BIO_gets performs the BIOs "gets" operation and places the data in .Fa buf . Usually this operation will attempt to read a line of data from the BIO of maximum length .Fa len No - 1 . There are exceptions to this however, for example .Fn BIO_gets on a digest BIO will calculate and return the digest and other BIOs may not support .Fn BIO_gets at all. The returned string is always NUL-terminated. .Pp .Fn BIO_write attempts to write .Fa len bytes from .Fa buf to BIO .Fa b . .Pp .Fn BIO_puts attempts to write a null terminated string .Fa buf to BIO .Fa b . .Pp One technique sometimes used with blocking sockets is to use a system call (such as .Xr select 2 , .Xr poll 2 or equivalent) to determine when data is available and then call .Xr read 2 to read the data. The equivalent with BIOs (that is call .Xr select 2 on the underlying I/O structure and then call .Fn BIO_read to read the data) should .Em not be used because a single call to .Fn BIO_read can cause several reads (and writes in the case of SSL BIOs) on the underlying I/O structure and may block as a result. Instead .Xr select 2 (or equivalent) should be combined with non-blocking I/O so successive reads will request a retry instead of blocking. .Pp See .Xr BIO_should_retry 3 for details of how to determine the cause of a retry and other I/O issues. .Pp If the .Fn BIO_gets function is not supported by a BIO then it is possible to work around this by adding a buffering BIO .Xr BIO_f_buffer 3 to the chain. .Sh RETURN VALUES All these functions return either the amount of data successfully read or written (if the return value is positive) or that no data was successfully read or written if the result is 0 or -1. If the return value is -2, then the operation is not implemented in the specific BIO type. The trailing NUL is not included in the length returned by .Fn BIO_gets . .Pp A 0 or -1 return is not necessarily an indication of an error. In particular when the source/sink is non-blocking or of a certain type it may merely be an indication that no data is currently available and that the application should retry the operation later. .Sh SEE ALSO .Xr BIO_meth_new 3 , .Xr BIO_new 3 , .Xr BIO_should_retry 3 .Sh HISTORY .Fn BIO_read , .Fn BIO_gets , .Fn BIO_write , and .Fn BIO_puts first appeared in SSLeay 0.6.0 and have been available since .Ox 2.4 .