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[dragonfly.git] / secure / lib / libcrypto / man / BIO_read.3
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138.\" ======================================================================
139.\"
140.IX Title "BIO_read 3"
141.TH BIO_read 3 "0.9.7a" "2003-02-19" "OpenSSL"
142.UC
143.SH "NAME"
144BIO_read, BIO_write, BIO_gets, BIO_puts \- \s-1BIO\s0 I/O functions
145.SH "SYNOPSIS"
146.IX Header "SYNOPSIS"
147.Vb 1
148\& #include <openssl/bio.h>
149.Ve
150.Vb 4
151\& int BIO_read(BIO *b, void *buf, int len);
152\& int BIO_gets(BIO *b,char *buf, int size);
153\& int BIO_write(BIO *b, const void *buf, int len);
154\& int BIO_puts(BIO *b,const char *buf);
155.Ve
156.SH "DESCRIPTION"
157.IX Header "DESCRIPTION"
158\&\fIBIO_read()\fR attempts to read \fBlen\fR bytes from \s-1BIO\s0 \fBb\fR and places
159the data in \fBbuf\fR.
160.PP
161\&\fIBIO_gets()\fR performs the BIOs \*(L"gets\*(R" operation and places the data
162in \fBbuf\fR. Usually this operation will attempt to read a line of data
163from the \s-1BIO\s0 of maximum length \fBlen\fR. There are exceptions to this
164however, for example \fIBIO_gets()\fR on a digest \s-1BIO\s0 will calculate and
165return the digest and other BIOs may not support \fIBIO_gets()\fR at all.
166.PP
167\&\fIBIO_write()\fR attempts to write \fBlen\fR bytes from \fBbuf\fR to \s-1BIO\s0 \fBb\fR.
168.PP
169\&\fIBIO_puts()\fR attempts to write a null terminated string \fBbuf\fR to \s-1BIO\s0 \fBb\fR
170.SH "RETURN VALUES"
171.IX Header "RETURN VALUES"
172All these functions return either the amount of data successfully read or
173written (if the return value is positive) or that no data was successfully
174read or written if the result is 0 or \-1. If the return value is \-2 then
175the operation is not implemented in the specific \s-1BIO\s0 type.
176.SH "NOTES"
177.IX Header "NOTES"
178A 0 or \-1 return is not necessarily an indication of an error. In
179particular when the source/sink is non-blocking or of a certain type
180it may merely be an indication that no data is currently available and that
181the application should retry the operation later.
182.PP
183One technique sometimes used with blocking sockets is to use a system call
184(such as \fIselect()\fR, \fIpoll()\fR or equivalent) to determine when data is available
185and then call \fIread()\fR to read the data. The equivalent with BIOs (that is call
186\&\fIselect()\fR on the underlying I/O structure and then call \fIBIO_read()\fR to
187read the data) should \fBnot\fR be used because a single call to \fIBIO_read()\fR
188can cause several reads (and writes in the case of \s-1SSL\s0 BIOs) on the underlying
189I/O structure and may block as a result. Instead \fIselect()\fR (or equivalent)
190should be combined with non blocking I/O so successive reads will request
191a retry instead of blocking.
192.PP
193See BIO_should_retry(3) for details of how to
194determine the cause of a retry and other I/O issues.
195.PP
196If the \fIBIO_gets()\fR function is not supported by a \s-1BIO\s0 then it possible to
197work around this by adding a buffering \s-1BIO\s0 BIO_f_buffer(3)
198to the chain.
199.SH "SEE ALSO"
200.IX Header "SEE ALSO"
201BIO_should_retry(3)
202.PP
203\&\s-1TBA\s0