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BIO_read(3)                         OpenSSL                        BIO_read(3)

NAME
       BIO_read, BIO_write, BIO_gets, BIO_puts - BIO I/O functions
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);
DESCRIPTION
       BIO_read() attempts to read len bytes from BIO b and places the data in
       buf.
       BIO_gets() performs the BIOs "gets" operation and places the data in
       buf. Usually this operation will attempt to read a line of data from
       the BIO of maximum length 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 len bytes from buf to BIO b.
       BIO_puts() attempts to write a null terminated string buf to BIO b.
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.
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 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 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 BIO_f_buffer(3) to the
       chain.
SEE ALSO
       BIO_should_retry(3)
       TBA

1.0.2k                            2017-01-26                       BIO_read(3)