192 lines
6.4 KiB
Groff
192 lines
6.4 KiB
Groff
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.\" ========================================================================
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.\"
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.IX Title "BIO_read 3"
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.TH BIO_read 3 "2014-08-06" "1.0.1i" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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BIO_read, BIO_write, BIO_gets, BIO_puts \- BIO I/O functions
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/bio.h>
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\&
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\& int BIO_read(BIO *b, void *buf, int len);
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\& int BIO_gets(BIO *b,char *buf, int size);
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\& int BIO_write(BIO *b, const void *buf, int len);
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\& int BIO_puts(BIO *b,const char *buf);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\fIBIO_read()\fR attempts to read \fBlen\fR bytes from \s-1BIO\s0 \fBb\fR and places
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the data in \fBbuf\fR.
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.PP
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\&\fIBIO_gets()\fR performs the BIOs \*(L"gets\*(R" operation and places the data
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in \fBbuf\fR. Usually this operation will attempt to read a line of data
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from the \s-1BIO\s0 of maximum length \fBlen\fR. There are exceptions to this
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however, for example \fIBIO_gets()\fR on a digest \s-1BIO\s0 will calculate and
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return the digest and other BIOs may not support \fIBIO_gets()\fR at all.
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.PP
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\&\fIBIO_write()\fR attempts to write \fBlen\fR bytes from \fBbuf\fR to \s-1BIO\s0 \fBb\fR.
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.PP
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\&\fIBIO_puts()\fR attempts to write a null terminated string \fBbuf\fR to \s-1BIO\s0 \fBb\fR
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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All these functions return either the amount of data successfully read or
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written (if the return value is positive) or that no data was successfully
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read or written if the result is 0 or \-1. If the return value is \-2 then
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the operation is not implemented in the specific \s-1BIO\s0 type.
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.SH "NOTES"
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.IX Header "NOTES"
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A 0 or \-1 return is not necessarily an indication of an error. In
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particular when the source/sink is non-blocking or of a certain type
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it may merely be an indication that no data is currently available and that
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the application should retry the operation later.
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.PP
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One technique sometimes used with blocking sockets is to use a system call
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(such as \fIselect()\fR, \fIpoll()\fR or equivalent) to determine when data is available
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and then call \fIread()\fR to read the data. The equivalent with BIOs (that is call
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\&\fIselect()\fR on the underlying I/O structure and then call \fIBIO_read()\fR to
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read the data) should \fBnot\fR be used because a single call to \fIBIO_read()\fR
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can cause several reads (and writes in the case of \s-1SSL\s0 BIOs) on the underlying
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I/O structure and may block as a result. Instead \fIselect()\fR (or equivalent)
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should be combined with non blocking I/O so successive reads will request
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a retry instead of blocking.
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.PP
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See \fIBIO_should_retry\fR\|(3) for details of how to
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determine the cause of a retry and other I/O issues.
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.PP
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If the \fIBIO_gets()\fR function is not supported by a \s-1BIO\s0 then it possible to
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work around this by adding a buffering \s-1BIO\s0 \fIBIO_f_buffer\fR\|(3)
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to the chain.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\fIBIO_should_retry\fR\|(3)
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.PP
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\&\s-1TBA\s0
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