d900a015b5
Reviewed-by: Rich Salz <rsalz@openssl.org> Reviewed-by: Richard Levitte <levitte@openssl.org>
66 lines
2.3 KiB
Text
66 lines
2.3 KiB
Text
=pod
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=head1 NAME
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BIO_read, BIO_write, BIO_gets, BIO_puts - BIO I/O functions
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=head1 SYNOPSIS
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#include <openssl/bio.h>
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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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=head1 DESCRIPTION
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BIO_read() attempts to read B<len> bytes from BIO B<b> and places
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the data in B<buf>.
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BIO_gets() performs the BIOs "gets" operation and places the data
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in B<buf>. Usually this operation will attempt to read a line of data
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from the BIO of maximum length B<len>. There are exceptions to this
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however, for example BIO_gets() on a digest BIO will calculate and
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return the digest and other BIOs may not support BIO_gets() at all.
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BIO_write() attempts to write B<len> bytes from B<buf> to BIO B<b>.
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BIO_puts() attempts to write a null terminated string B<buf> to BIO B<b>.
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=head1 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 BIO type.
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=head1 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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One technique sometimes used with blocking sockets is to use a system call
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(such as select(), poll() or equivalent) to determine when data is available
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and then call read() to read the data. The equivalent with BIOs (that is call
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select() on the underlying I/O structure and then call BIO_read() to
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read the data) should B<not> be used because a single call to BIO_read()
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can cause several reads (and writes in the case of SSL BIOs) on the underlying
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I/O structure and may block as a result. Instead select() (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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See L<BIO_should_retry(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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If the BIO_gets() function is not supported by a BIO then it possible to
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work around this by adding a buffering BIO L<BIO_f_buffer(3)>
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to the chain.
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=head1 SEE ALSO
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L<BIO_should_retry(3)>
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TBA
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