Initial Commit

openssl-1.0.2f/doc/crypto/BIO_read.pod

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+=pod
+
+=head1 NAME
+
+BIO_read, BIO_write, BIO_gets, BIO_puts - BIO I/O functions
+
+=head1 SYNOPSIS
+
+ #include <openssl/bio.h>
+
+ int	BIO_read(BIO *b, void *buf, int len);
+ int	BIO_gets(BIO *b, char *buf, int size);
+ int	BIO_write(BIO *b, const void *buf, int len);
+ int	BIO_puts(BIO *b, const char *buf);
+
+=head1 DESCRIPTION
+
+BIO_read() attempts to read B<len> bytes from BIO B<b> and places
+the data in B<buf>.
+
+BIO_gets() performs the BIOs "gets" operation and places the data
+in B<buf>. Usually this operation will attempt to read a line of data
+from the BIO of maximum length B<len>. There are exceptions to this
+however, for example BIO_gets() on a digest BIO will calculate and
+return the digest and other BIOs may not support BIO_gets() at all.
+
+BIO_write() attempts to write B<len> bytes from B<buf> to BIO B<b>.
+
+BIO_puts() attempts to write a null terminated string B<buf> to BIO B<b>.
+
+=head1 RETURN VALUES
+
+All these functions return either the amount of data successfully read or
+written (if the return value is positive) or that no data was successfully
+read or written if the result is 0 or -1. If the return value is -2 then
+the operation is not implemented in the specific BIO type.
+
+=head1 NOTES
+
+A 0 or -1 return is not necessarily an indication of an error. In
+particular when the source/sink is non-blocking or of a certain type
+it may merely be an indication that no data is currently available and that
+the application should retry the operation later.
+
+One technique sometimes used with blocking sockets is to use a system call
+(such as select(), poll() or equivalent) to determine when data is available
+and then call read() to read the data. The equivalent with BIOs (that is call
+select() on the underlying I/O structure and then call BIO_read() to
+read the data) should B<not> be used because a single call to BIO_read()
+can cause several reads (and writes in the case of SSL BIOs) on the underlying
+I/O structure and may block as a result. Instead select() (or equivalent)
+should be combined with non blocking I/O so successive reads will request
+a retry instead of blocking.
+
+See L<BIO_should_retry(3)|BIO_should_retry(3)> for details of how to
+determine the cause of a retry and other I/O issues.
+
+If the BIO_gets() function is not supported by a BIO then it possible to
+work around this by adding a buffering BIO L<BIO_f_buffer(3)|BIO_f_buffer(3)>
+to the chain.
+
+=head1 SEE ALSO
+
+L<BIO_should_retry(3)|BIO_should_retry(3)>
+
+TBA