Merge from vendor branch OPENSSL:
[dragonfly.git] / secure / lib / libcrypto / man / BIO_read.3
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124.\" ========================================================================
125.\"
126.IX Title "BIO_read 3"
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127.TH BIO_read 3 "2007-10-24" "0.9.8g" "OpenSSL"
128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
984263bc 132.SH "NAME"
74dab6c2 133BIO_read, BIO_write, BIO_gets, BIO_puts \- BIO I/O functions
984263bc 134.SH "SYNOPSIS"
8b0cefbb 135.IX Header "SYNOPSIS"
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136.Vb 1
137\& #include <openssl/bio.h>
2eaa1526 138\&
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139\& int BIO_read(BIO *b, void *buf, int len);
140\& int BIO_gets(BIO *b,char *buf, int size);
141\& int BIO_write(BIO *b, const void *buf, int len);
142\& int BIO_puts(BIO *b,const char *buf);
143.Ve
144.SH "DESCRIPTION"
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145.IX Header "DESCRIPTION"
146\&\fIBIO_read()\fR attempts to read \fBlen\fR bytes from \s-1BIO\s0 \fBb\fR and places
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147the data in \fBbuf\fR.
148.PP
8b0cefbb 149\&\fIBIO_gets()\fR performs the BIOs \*(L"gets\*(R" operation and places the data
984263bc 150in \fBbuf\fR. Usually this operation will attempt to read a line of data
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151from the \s-1BIO\s0 of maximum length \fBlen\fR. There are exceptions to this
152however, for example \fIBIO_gets()\fR on a digest \s-1BIO\s0 will calculate and
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153return the digest and other BIOs may not support \fIBIO_gets()\fR at all.
154.PP
8b0cefbb 155\&\fIBIO_write()\fR attempts to write \fBlen\fR bytes from \fBbuf\fR to \s-1BIO\s0 \fBb\fR.
984263bc 156.PP
8b0cefbb 157\&\fIBIO_puts()\fR attempts to write a null terminated string \fBbuf\fR to \s-1BIO\s0 \fBb\fR
984263bc 158.SH "RETURN VALUES"
8b0cefbb 159.IX Header "RETURN VALUES"
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160All these functions return either the amount of data successfully read or
161written (if the return value is positive) or that no data was successfully
162read or written if the result is 0 or \-1. If the return value is \-2 then
8b0cefbb 163the operation is not implemented in the specific \s-1BIO\s0 type.
984263bc 164.SH "NOTES"
8b0cefbb 165.IX Header "NOTES"
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166A 0 or \-1 return is not necessarily an indication of an error. In
167particular when the source/sink is non-blocking or of a certain type
168it may merely be an indication that no data is currently available and that
169the application should retry the operation later.
170.PP
171One technique sometimes used with blocking sockets is to use a system call
172(such as \fIselect()\fR, \fIpoll()\fR or equivalent) to determine when data is available
173and then call \fIread()\fR to read the data. The equivalent with BIOs (that is call
8b0cefbb 174\&\fIselect()\fR on the underlying I/O structure and then call \fIBIO_read()\fR to
984263bc 175read the data) should \fBnot\fR be used because a single call to \fIBIO_read()\fR
8b0cefbb 176can cause several reads (and writes in the case of \s-1SSL\s0 BIOs) on the underlying
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177I/O structure and may block as a result. Instead \fIselect()\fR (or equivalent)
178should be combined with non blocking I/O so successive reads will request
179a retry instead of blocking.
180.PP
8b0cefbb 181See \fIBIO_should_retry\fR\|(3) for details of how to
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182determine the cause of a retry and other I/O issues.
183.PP
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184If the \fIBIO_gets()\fR function is not supported by a \s-1BIO\s0 then it possible to
185work around this by adding a buffering \s-1BIO\s0 \fIBIO_f_buffer\fR\|(3)
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186to the chain.
187.SH "SEE ALSO"
74dab6c2 188.IX Header "SEE ALSO"
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189\&\fIBIO_should_retry\fR\|(3)
190.PP
191\&\s-1TBA\s0