BIO_read_ex, BIO_write_ex, BIO_read, BIO_write, BIO_gets, BIO_get_line, BIO_puts
- BIO I/O functions
#include <openssl/bio.h>
int BIO_read_ex(BIO *b, void *data, size_t dlen, size_t *readbytes);
int BIO_write_ex(BIO *b, const void *data, size_t dlen, size_t *written);
int BIO_read(BIO *b, void *data, int dlen);
int BIO_gets(BIO *b, char *buf, int size);
int BIO_get_line(BIO *b, char *buf, int size);
int BIO_write(BIO *b, const void *data, int dlen);
int BIO_puts(BIO *b, const char *buf);
BIO_read_ex() attempts to read
dlen bytes from BIO
b and
places the data in
data. If any bytes were successfully read then the
number of bytes read is stored in
*readbytes.
BIO_write_ex() attempts to write
dlen bytes from
data to
BIO
b. If successful then the number of bytes written is stored in
*written unless
written is NULL.
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
size-1. 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. The
returned string is always NUL-terminated and the '\n' is preserved if present
in the input data. On binary input there may be NUL characters within the
string; in this case the return value (if nonnegative) may give an incorrect
length.
BIO_get_line() attempts to read from BIO
b a line of data up to
the next '\n' or the maximum length
size-1 is reached and places the
data in
buf. The returned string is always NUL-terminated and the '\n'
is preserved if present in the input data. On binary input there may be NUL
characters within the string; in this case the return value (if nonnegative)
gives the actual length read. For implementing this, unfortunately the data
needs to be read byte-by-byte.
BIO_write() attempts to write
len bytes from
buf to BIO
b.
BIO_puts() attempts to write a NUL-terminated string
buf to BIO
b.
BIO_read_ex() returns 1 if data was successfully read, and 0 otherwise.
BIO_write_ex() returns 1 if no error was encountered writing data, 0
otherwise. Requesting to write 0 bytes is not considered an error.
BIO_write() returns -2 if the "write" operation is not
implemented by the BIO or -1 on other errors. Otherwise it returns the number
of bytes written. This may be 0 if the BIO
b is NULL or
dlen <=
0.
BIO_gets() returns -2 if the "gets" operation is not
implemented by the BIO or -1 on other errors. Otherwise it typically returns
the amount of data read, but depending on the implementation it may return
only the length up to the first NUL character contained in the data read. In
any case the trailing NUL that is added after the data read is not included in
the length returned.
All other 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.
A 0 or -1 return is not necessarily an indication of an error. In particular
when the source/sink is nonblocking 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 "gets" method is not supported by a BIO then
BIO_get_line() can be used. It is also possible to make
BIO_gets() usable even if the "gets" method is not supported
by adding a buffering BIO
BIO_f_buffer(3) to the chain.
BIO_should_retry(3)
BIO_gets() on 1.1.0 and older when called on
BIO_fd() based BIO
did not keep the '\n' at the end of the line in the buffer.
BIO_get_line() was added in OpenSSL 3.0.
BIO_write_ex() returns 1 if the size of the data to write is 0 and the
written parameter of the function can be NULL since OpenSSL 3.0.
Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy in the
file LICENSE in the source distribution or at
<
https://www.openssl.org/source/license.html>.