BIO_read.pod revision 291721 
1=pod
2
3=head1 NAME
4
5BIO_read, BIO_write, BIO_gets, BIO_puts - BIO I/O functions
6
7=head1 SYNOPSIS
8
9 #include <openssl/bio.h>
10
11 int	BIO_read(BIO *b, void *buf, int len);
12 int	BIO_gets(BIO *b, char *buf, int size);
13 int	BIO_write(BIO *b, const void *buf, int len);
14 int	BIO_puts(BIO *b, const char *buf);
15
16=head1 DESCRIPTION
17
18BIO_read() attempts to read B<len> bytes from BIO B<b> and places
19the data in B<buf>.
20
21BIO_gets() performs the BIOs "gets" operation and places the data
22in B<buf>. Usually this operation will attempt to read a line of data
23from the BIO of maximum length B<len>. There are exceptions to this
24however, for example BIO_gets() on a digest BIO will calculate and
25return the digest and other BIOs may not support BIO_gets() at all.
26
27BIO_write() attempts to write B<len> bytes from B<buf> to BIO B<b>.
28
29BIO_puts() attempts to write a null terminated string B<buf> to BIO B<b>.
30
31=head1 RETURN VALUES
32
33All these functions return either the amount of data successfully read or
34written (if the return value is positive) or that no data was successfully
35read or written if the result is 0 or -1. If the return value is -2 then
36the operation is not implemented in the specific BIO type.
37
38=head1 NOTES
39
40A 0 or -1 return is not necessarily an indication of an error. In
41particular when the source/sink is non-blocking or of a certain type
42it may merely be an indication that no data is currently available and that
43the application should retry the operation later.
44
45One technique sometimes used with blocking sockets is to use a system call
46(such as select(), poll() or equivalent) to determine when data is available
47and then call read() to read the data. The equivalent with BIOs (that is call
48select() on the underlying I/O structure and then call BIO_read() to
49read the data) should B<not> be used because a single call to BIO_read()
50can cause several reads (and writes in the case of SSL BIOs) on the underlying
51I/O structure and may block as a result. Instead select() (or equivalent)
52should be combined with non blocking I/O so successive reads will request
53a retry instead of blocking.
54
55See L<BIO_should_retry(3)|BIO_should_retry(3)> for details of how to
56determine the cause of a retry and other I/O issues.
57
58If the BIO_gets() function is not supported by a BIO then it possible to
59work around this by adding a buffering BIO L<BIO_f_buffer(3)|BIO_f_buffer(3)>
60to the chain.
61
62=head1 SEE ALSO
63
64L<BIO_should_retry(3)|BIO_should_retry(3)>
65
66TBA
67