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BIO_read.3

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.\" ========================================================================
.\"
.IX Title "BIO_read 3"
.TH BIO_read 3 "2019-12-20" "1.0.2u" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH "NAME"
BIO_read, BIO_write, BIO_gets, BIO_puts \- BIO I/O functions
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/bio.h>
\&
\& int    BIO_read(BIO *b, void *buf, int len);
\& int    BIO_gets(BIO *b, char *buf, int size);
\& int    BIO_write(BIO *b, const void *buf, int len);
\& int    BIO_puts(BIO *b, const char *buf);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fBBIO_read()\fR attempts to read \fBlen\fR bytes from \s-1BIO\s0 \fBb\fR and places
the data in \fBbuf\fR.
.PP
\&\fBBIO_gets()\fR performs the BIOs \*(L"gets\*(R" operation and places the data
in \fBbuf\fR. Usually this operation will attempt to read a line of data
from the \s-1BIO\s0 of maximum length \fBlen\fR. There are exceptions to this
however, for example \fBBIO_gets()\fR on a digest \s-1BIO\s0 will calculate and
return the digest and other BIOs may not support \fBBIO_gets()\fR at all.
.PP
\&\fBBIO_write()\fR attempts to write \fBlen\fR bytes from \fBbuf\fR to \s-1BIO\s0 \fBb\fR.
.PP
\&\fBBIO_puts()\fR attempts to write a null terminated string \fBbuf\fR to \s-1BIO\s0 \fBb\fR.
.SH "RETURN VALUES"
.IX Header "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 \s-1BIO\s0 type.
.SH "NOTES"
.IX Header "NOTES"
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.
.PP
One technique sometimes used with blocking sockets is to use a system call
(such as \fBselect()\fR, \fBpoll()\fR or equivalent) to determine when data is available
and then call \fBread()\fR to read the data. The equivalent with BIOs (that is call
\&\fBselect()\fR on the underlying I/O structure and then call \fBBIO_read()\fR to
read the data) should \fBnot\fR be used because a single call to \fBBIO_read()\fR
can cause several reads (and writes in the case of \s-1SSL\s0 BIOs) on the underlying
I/O structure and may block as a result. Instead \fBselect()\fR (or equivalent)
should be combined with non blocking I/O so successive reads will request
a retry instead of blocking.
.PP
See \fBBIO_should_retry\fR\|(3) for details of how to
determine the cause of a retry and other I/O issues.
.PP
If the \fBBIO_gets()\fR function is not supported by a \s-1BIO\s0 then it possible to
work around this by adding a buffering \s-1BIO\s0 \fBBIO_f_buffer\fR\|(3)
to the chain.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBBIO_should_retry\fR\|(3)
.PP
\&\s-1TBA\s0

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