Header file cleanup for C++20 header-units

C++20 adds 'header units' as a stepping-stone to modules.  Header
units are regular header-files that have a 'self-contained' property
-- they do not require previously-included headers to provide typedefs
and what not.

This addresses 2 problems discovered when using clang modules (as a
proxy for C++20 header-units).

a) Some headers that pay attention to OPENSSL_NO_STDIO to determine
whether to declare certain FILE*-taking functions do not #include
<stdio.h> themselves, relying on their includer already having done
that.  That breaks the above mentioned encapuslation requirement.
Fixed by conditionally including stdio.h in those headers.  I chose to
always include stdio.h in such headers, even when they included
another such header that transitively included stdio.  That way they
do not rely on an artifact of that intermediate header's behaviour.

b) Some headers have #includes inside 'extern "C" { ... }' regions.
That has a bad code-smell, but GCC and clang have extensions to permit
it with implementation-defined effects.  Clang needs annotation on the
included files to know that they themselves are entirely inside a
similar region.  GCC behavesq as-if there's an extern "C++" region
wrapping the included header (which must therefore wrap its contents
in extern "C", if that is what it wants.  In effect the includer's
extern "C" region is just misleading. I didn't audit all the headers
for this, only those I noticed when addressing #a.

\#a is necessary to build the headers as a set of clang-modules.  #b
is not necessary, but as I mentioned, avoids potentially
implementation-defined behaviour.

Reviewed-by: Todd Short <todd.short@me.com>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18221)
14 files changed
tree: d56f6ec8748baecf686526fa4e0c198c4b28fc50
  1. .github/
  2. apps/
  3. Configurations/
  4. crypto/
  5. demos/
  6. dev/
  7. doc/
  8. engines/
  9. external/
  10. fuzz/
  11. include/
  12. ms/
  13. os-dep/
  14. providers/
  15. ssl/
  16. test/
  17. tools/
  18. util/
  19. VMS/
  20. .gitattributes
  21. .gitignore
  22. .gitmodules
  23. ACKNOWLEDGEMENTS.md
  24. appveyor.yml
  25. AUTHORS.md
  26. build.info
  27. CHANGES.md
  28. config
  29. config.com
  30. configdata.pm.in
  31. Configure
  32. CONTRIBUTING.md
  33. FAQ.md
  34. HACKING.md
  35. INSTALL.md
  36. LICENSE.txt
  37. NEWS.md
  38. NOTES-ANDROID.md
  39. NOTES-DJGPP.md
  40. NOTES-NONSTOP.md
  41. NOTES-PERL.md
  42. NOTES-UNIX.md
  43. NOTES-VALGRIND.md
  44. NOTES-VMS.md
  45. NOTES-WINDOWS.md
  46. README-ENGINES.md
  47. README-FIPS.md
  48. README-PROVIDERS.md
  49. README.md
  50. SUPPORT.md
  51. VERSION.dat
README.md

Welcome to the OpenSSL Project

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OpenSSL is a robust, commercial-grade, full-featured Open Source Toolkit for the Transport Layer Security (TLS) protocol formerly known as the Secure Sockets Layer (SSL) protocol. The protocol implementation is based on a full-strength general purpose cryptographic library, which can also be used stand-alone.

OpenSSL is descended from the SSLeay library developed by Eric A. Young and Tim J. Hudson.

The official Home Page of the OpenSSL Project is www.openssl.org.

Table of Contents

Overview

The OpenSSL toolkit includes:

  • libssl an implementation of all TLS protocol versions up to TLSv1.3 (RFC 8446).

  • libcrypto a full-strength general purpose cryptographic library. It constitutes the basis of the TLS implementation, but can also be used independently.

  • openssl the OpenSSL command line tool, a swiss army knife for cryptographic tasks, testing and analyzing. It can be used for

    • creation of key parameters
    • creation of X.509 certificates, CSRs and CRLs
    • calculation of message digests
    • encryption and decryption
    • SSL/TLS client and server tests
    • handling of S/MIME signed or encrypted mail
    • and more...

Download

For Production Use

Source code tarballs of the official releases can be downloaded from www.openssl.org/source. The OpenSSL project does not distribute the toolkit in binary form.

However, for a large variety of operating systems precompiled versions of the OpenSSL toolkit are available. In particular on Linux and other Unix operating systems it is normally recommended to link against the precompiled shared libraries provided by the distributor or vendor.

For Testing and Development

Although testing and development could in theory also be done using the source tarballs, having a local copy of the git repository with the entire project history gives you much more insight into the code base.

The official OpenSSL Git Repository is located at git.openssl.org. There is a GitHub mirror of the repository at github.com/openssl/openssl, which is updated automatically from the former on every commit.

A local copy of the Git Repository can be obtained by cloning it from the original OpenSSL repository using

git clone git://git.openssl.org/openssl.git

or from the GitHub mirror using

git clone https://github.com/openssl/openssl.git

If you intend to contribute to OpenSSL, either to fix bugs or contribute new features, you need to fork the OpenSSL repository openssl/openssl on GitHub and clone your public fork instead.

git clone https://github.com/yourname/openssl.git

This is necessary, because all development of OpenSSL nowadays is done via GitHub pull requests. For more details, see Contributing.

Build and Install

After obtaining the Source, have a look at the INSTALL file for detailed instructions about building and installing OpenSSL. For some platforms, the installation instructions are amended by a platform specific document.

Specific notes on upgrading to OpenSSL 3.0 from previous versions can be found in the migration_guide(7ossl) manual page.

Documentation

Manual Pages

The manual pages for the master branch and all current stable releases are available online.

Wiki

There is a Wiki at wiki.openssl.org which is currently not very active. It contains a lot of useful information, not all of which is up to date.

License

OpenSSL is licensed under the Apache License 2.0, which means that you are free to get and use it for commercial and non-commercial purposes as long as you fulfill its conditions.

See the LICENSE.txt file for more details.

Support

There are various ways to get in touch. The correct channel depends on your requirement. see the SUPPORT file for more details.

Contributing

If you are interested and willing to contribute to the OpenSSL project, please take a look at the CONTRIBUTING file.

Legalities

A number of nations restrict the use or export of cryptography. If you are potentially subject to such restrictions you should seek legal advice before attempting to develop or distribute cryptographic code.

Copyright

Copyright (c) 1998-2022 The OpenSSL Project

Copyright (c) 1995-1998 Eric A. Young, Tim J. Hudson

All rights reserved.