258 lines
9.1 KiB
Groff
258 lines
9.1 KiB
Groff
.\" $NetBSD: BIO_should_retry.3,v 1.1 2001/04/12 10:45:36 itojun Exp $
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.\" ======================================================================
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.\"
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.IX Title "BIO_should_retry 3"
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.TH BIO_should_retry 3 "0.9.6a" "2001-04-12" "OpenSSL"
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.UC
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.SH "NAME"
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BIO_should_retry, BIO_should_read, BIO_should_write,
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BIO_should_io_special, BIO_retry_type, BIO_should_retry,
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BIO_get_retry_BIO, BIO_get_retry_reason \- \s-1BIO\s0 retry functions
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.SH "LIBRARY"
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libcrypto, -lcrypto
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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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.Ve
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.Vb 5
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\& #define BIO_should_read(a) ((a)->flags & BIO_FLAGS_READ)
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\& #define BIO_should_write(a) ((a)->flags & BIO_FLAGS_WRITE)
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\& #define BIO_should_io_special(a) ((a)->flags & BIO_FLAGS_IO_SPECIAL)
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\& #define BIO_retry_type(a) ((a)->flags & BIO_FLAGS_RWS)
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\& #define BIO_should_retry(a) ((a)->flags & BIO_FLAGS_SHOULD_RETRY)
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.Ve
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.Vb 5
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\& #define BIO_FLAGS_READ 0x01
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\& #define BIO_FLAGS_WRITE 0x02
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\& #define BIO_FLAGS_IO_SPECIAL 0x04
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\& #define BIO_FLAGS_RWS (BIO_FLAGS_READ|BIO_FLAGS_WRITE|BIO_FLAGS_IO_SPECIAL)
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\& #define BIO_FLAGS_SHOULD_RETRY 0x08
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.Ve
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.Vb 2
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\& BIO * BIO_get_retry_BIO(BIO *bio, int *reason);
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\& int BIO_get_retry_reason(BIO *bio);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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These functions determine why a \s-1BIO\s0 is not able to read or write data.
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They will typically be called after a failed \fIBIO_read()\fR or \fIBIO_write()\fR
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call.
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.PP
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\&\fIBIO_should_retry()\fR is true if the call that produced this condition
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should then be retried at a later time.
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.PP
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If \fIBIO_should_retry()\fR is false then the cause is an error condition.
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.PP
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\&\fIBIO_should_read()\fR is true if the cause of the condition is that a \s-1BIO\s0
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needs to read data.
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.PP
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\&\fIBIO_should_write()\fR is true if the cause of the condition is that a \s-1BIO\s0
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needs to read data.
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.PP
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\&\fIBIO_should_io_special()\fR is true if some \*(L"special\*(R" condition, that is a
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reason other than reading or writing is the cause of the condition.
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.PP
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\&\fIBIO_get_retry_reason()\fR returns a mask of the cause of a retry condition
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consisting of the values \fB\s-1BIO_FLAGS_READ\s0\fR, \fB\s-1BIO_FLAGS_WRITE\s0\fR,
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\&\fB\s-1BIO_FLAGS_IO_SPECIAL\s0\fR though current \s-1BIO\s0 types will only set one of
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these.
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.PP
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\&\fIBIO_get_retry_BIO()\fR determines the precise reason for the special
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condition, it returns the \s-1BIO\s0 that caused this condition and if
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\&\fBreason\fR is not \s-1NULL\s0 it contains the reason code. The meaning of
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the reason code and the action that should be taken depends on
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the type of \s-1BIO\s0 that resulted in this condition.
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.PP
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\&\fIBIO_get_retry_reason()\fR returns the reason for a special condition if
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passed the relevant \s-1BIO\s0, for example as returned by \fIBIO_get_retry_BIO()\fR.
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.SH "NOTES"
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.IX Header "NOTES"
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If \fIBIO_should_retry()\fR returns false then the precise \*(L"error condition\*(R"
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depends on the \s-1BIO\s0 type that caused it and the return code of the \s-1BIO\s0
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operation. For example if a call to \fIBIO_read()\fR on a socket \s-1BIO\s0 returns
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0 and \fIBIO_should_retry()\fR is false then the cause will be that the
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connection closed. A similar condition on a file \s-1BIO\s0 will mean that it
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has reached \s-1EOF\s0. Some \s-1BIO\s0 types may place additional information on
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the error queue. For more details see the individual \s-1BIO\s0 type manual
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pages.
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.PP
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If the underlying I/O structure is in a blocking mode almost all current
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\&\s-1BIO\s0 types will not request a retry, because the underlying I/O
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calls will not. If the application knows that the \s-1BIO\s0 type will never
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signal a retry then it need not call \fIBIO_should_retry()\fR after a failed
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\&\s-1BIO\s0 I/O call. This is typically done with file BIOs.
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.PP
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\&\s-1SSL\s0 BIOs are the only current exception to this rule: they can request a
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retry even if the underlying I/O structure is blocking, if a handshake
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occurs during a call to \fIBIO_read()\fR. An application can retry the failed
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call immediately or avoid this situation by setting \s-1SSL_MODE_AUTO_RETRY\s0
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on the underlying \s-1SSL\s0 structure.
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.PP
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While an application may retry a failed non blocking call immediately
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this is likely to be very inefficient because the call will fail
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repeatedly until data can be processed or is available. An application
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will normally wait until the necessary condition is satisfied. How
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this is done depends on the underlying I/O structure.
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.PP
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For example if the cause is ultimately a socket and \fIBIO_should_read()\fR
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is true then a call to \fIselect()\fR may be made to wait until data is
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available and then retry the \s-1BIO\s0 operation. By combining the retry
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conditions of several non blocking BIOs in a single \fIselect()\fR call
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it is possible to service several BIOs in a single thread, though
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the performance may be poor if \s-1SSL\s0 BIOs are present because long delays
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can occur during the initial handshake process.
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.PP
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It is possible for a \s-1BIO\s0 to block indefinitely if the underlying I/O
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structure cannot process or return any data. This depends on the behaviour of
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the platforms I/O functions. This is often not desirable: one solution
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is to use non blocking I/O and use a timeout on the \fIselect()\fR (or
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equivalent) call.
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.SH "BUGS"
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.IX Header "BUGS"
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The OpenSSL \s-1ASN1\s0 functions cannot gracefully deal with non blocking I/O:
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that is they cannot retry after a partial read or write. This is usually
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worked around by only passing the relevant data to \s-1ASN1\s0 functions when
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the entire structure can be read or written.
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\s-1TBA\s0
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