man BIO O

BIO(7ossl)                          OpenSSL                         BIO(7ossl)

NAME
       bio - Basic I/O abstraction

SYNOPSIS
        #include <openssl/bio.h> 

DESCRIPTION
       A BIO is an I/O abstraction, it hides many of the underlying I/O
       details from an application. If an application uses a BIO for its I/O
       it can transparently handle SSL connections, unencrypted network
       connections and file I/O.

       There are two types of BIO, a source/sink BIO and a filter BIO.

       As its name implies a source/sink BIO is a source and/or sink of data,
       examples include a socket BIO and a file BIO.

       A filter BIO takes data from one BIO and passes it through to another,
       or the application. The data may be left unmodified (for example a
       message digest BIO) or translated (for example an encryption BIO). The
       effect of a filter BIO may change according to the I/O operation it is
       performing: for example an encryption BIO will encrypt data if it is
       being written to and decrypt data if it is being read from.

       BIOs can be joined together to form a chain (a single BIO is a chain
       with one component). A chain normally consists of one source/sink BIO
       and one or more filter BIOs. Data read from or written to the first BIO
       then traverses the chain to the end (normally a source/sink BIO).

       Some BIOs (such as memory BIOs) can be used immediately after calling
       BIO_new(). Others (such as file BIOs) need some additional
       initialization, and frequently a utility function exists to create and
       initialize such BIOs.

       If BIO_free() is called on a BIO chain it will only free one BIO
       resulting in a memory leak.

       Calling BIO_free_all() on a single BIO has the same effect as calling
       BIO_free() on it other than the discarded return value.

       Normally the type argument is supplied by a function which returns a
       pointer to a BIO_METHOD. There is a naming convention for such
       functions: a source/sink BIO typically starts with BIO_s_ and a filter
       BIO with BIO_f_.

   TCP Fast Open
       TCP Fast Open (RFC7413), abbreviated "TFO", is supported by the BIO
       interface since OpenSSL 3.2. TFO is supported in the following
       operating systems:

       o   Linux kernel 3.13 and later, where TFO is enabled by default.

       o   Linux kernel 4.11 and later, using TCP_FASTOPEN_CONNECT.

       o   FreeBSD 10.3 to 11.4, supports server TFO only.

       o   FreeBSD 12.0 and later, supports both client and server TFO.

       o   macOS 10.14 and later.

       Each operating system has a slightly different API for TFO. Please
       refer to the operating systems' API documentation when using sockets
       directly.

EXAMPLES
       Create a memory BIO:

        BIO *mem = BIO_new(BIO_s_mem());

SEE ALSO
       BIO_ctrl(3), BIO_f_base64(3), BIO_f_buffer(3), BIO_f_cipher(3),
       BIO_f_md(3), BIO_f_null(3), BIO_f_ssl(3), BIO_f_readbuffer(3),
       BIO_find_type(3), BIO_get_conn_mode(3), BIO_new(3),
       BIO_new_bio_pair(3), BIO_push(3), BIO_read_ex(3), BIO_s_accept(3),
       BIO_s_bio(3), BIO_s_connect(3), BIO_s_fd(3), BIO_s_file(3),
       BIO_s_mem(3), BIO_s_null(3), BIO_s_socket(3), BIO_set_callback(3),
       BIO_set_conn_mode(3), BIO_set_tfo(3), BIO_set_tfo_accept(3),
       BIO_should_retry(3)

COPYRIGHT
       Copyright 2000-2022 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>.

3.2.2                             2025-01-29                        BIO(7ossl)
O(3pm)                 Perl Programmers Reference Guide                 O(3pm)

NAME
       O - Generic interface to Perl Compiler backends

SYNOPSIS
               perl -MO=[-q,]Backend[,OPTIONS] foo.pl

DESCRIPTION
       This is the module that is used as a frontend to the Perl Compiler.

       If you pass the "-q" option to the module, then the STDOUT filehandle
       will be redirected into the variable $O::BEGIN_output during
       compilation.  This has the effect that any output printed to STDOUT by
       BEGIN blocks or use'd modules will be stored in this variable rather
       than printed. It's useful with those backends which produce output
       themselves ("Deparse", "Concise" etc), so that their output is not
       confused with that generated by the code being compiled.

       The "-qq" option behaves like "-q", except that it also closes STDERR
       after deparsing has finished. This suppresses the "Syntax OK" message
       normally produced by perl.

CONVENTIONS
       Most compiler backends use the following conventions: OPTIONS consists
       of a comma-separated list of words (no white-space).  The "-v" option
       usually puts the backend into verbose mode.  The "-ofile" option
       generates output to file instead of stdout. The "-D" option followed by
       various letters turns on various internal debugging flags. See the
       documentation for the desired backend (named "B::Backend" for the
       example above) to find out about that backend.

IMPLEMENTATION
       This section is only necessary for those who want to write a compiler
       backend module that can be used via this module.

       The command-line mentioned in the SYNOPSIS section corresponds to the
       Perl code

           use O ("Backend", OPTIONS);

       The "O::import" function loads the appropriate "B::Backend" module and
       calls its "compile" function, passing it OPTIONS. That function is
       expected to return a sub reference which we'll call CALLBACK. Next, the
       "compile-only" flag is switched on (equivalent to the command-line
       option "-c") and a CHECK block is registered which calls CALLBACK. Thus
       the main Perl program mentioned on the command-line is read in, parsed
       and compiled into internal syntax tree form. Since the "-c" flag is
       set, the program does not start running (excepting BEGIN blocks of
       course) but the CALLBACK function registered by the compiler backend is
       called.

       In summary, a compiler backend module should be called "B::Foo" for
       some foo and live in the appropriate directory for that name.  It
       should define a function called "compile". When the user types

           perl -MO=Foo,OPTIONS foo.pl

       that function is called and is passed those OPTIONS (split on commas).
       It should return a sub ref to the main compilation function.  After the
       user's program is loaded and parsed, that returned sub ref is invoked
       which can then go ahead and do the compilation, usually by making use
       of the "B" module's functionality.

BUGS
       The "-q" and "-qq" options don't work correctly if perl isn't compiled
       with PerlIO support : STDOUT will be closed instead of being redirected
       to $O::BEGIN_output.

AUTHOR
       Malcolm Beattie, "mbeattie@sable.ox.ac.uk"

perl v5.32.1                      2025-07-03                            O(3pm)