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6be630b9c5
The API contract is more tight than was previously documented -- the returned string must be NUL-terminated, and the supplied buffer includes space for the trailing NUL, so the maximum length that can be read in is reduced. Clarify that the NUL is not included in the returned length, and fix the spelling of "NUL-terminated" in a nearby spot. Adjust punctuation to make a modest improvement to the grammar. Reviewed-by: Matt Caswell <matt@openssl.org> Reviewed-by: Rich Salz <rsalz@openssl.org>
69 lines
2.5 KiB
Plaintext
69 lines
2.5 KiB
Plaintext
=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-1>. 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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The returned string is always NUL-terminated.
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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 NUL-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. The trailing
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NUL is not included in the length returned by BIO_gets().
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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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