Introduce <botan/boost_compat.h> as feature flag

doc/api_ref/tls.rst

@@ -1191,7 +1191,13 @@ TLS Stream
 
 :cpp:class:`TLS::Stream` offers a Boost.Asio compatible wrapper around :cpp:class:`TLS::Client` and :cpp:class:`TLS::Server`.
 It can be used as an alternative to Boost.Asio's `ssl::stream <https://www.boost.org/doc/libs/1_66_0/doc/html/boost_asio/reference/ssl__stream.html>`_ with minor adjustments to the using code.
-It offers the following interface:
+
+To use the asio stream wrapper, a relatively recent version of boost is required.
+Include ``botan/boost_compat.h`` and check that ``BOTAN_FOUND_COMPATIBLE_BOOST_VERSION``
+is defined before including ``botan/asio_stream.h`` to be ensure compatibility at
+compile time of your application.
+
+The asio Stream offers the following interface:
 
 .. cpp:class:: template <class StreamLayer, class ChannelT> TLS::Stream
 

src/examples/tls_stream_client.cpp

@@ -1,14 +1,17 @@
 #include <iostream>
 
-#include <botan/asio_stream.h>
-#include <botan/auto_rng.h>
-#include <botan/certstor_system.h>
-#include <botan/tls.h>
+#include <botan/boost_compat.h>
+#if defined(BOTAN_FOUND_COMPATIBLE_BOOST_VERSION)
 
-#include <boost/asio.hpp>
-#include <boost/beast.hpp>
-#include <boost/bind.hpp>
-#include <utility>
+   #include <botan/asio_stream.h>
+   #include <botan/auto_rng.h>
+   #include <botan/certstor_system.h>
+   #include <botan/tls.h>
+
+   #include <boost/asio.hpp>
+   #include <boost/beast.hpp>
+   #include <boost/bind.hpp>
+   #include <utility>
 
 namespace http = boost::beast::http;
 namespace ap = boost::asio::placeholders;
@@ -113,3 +116,12 @@ int main() {
 
    return 0;
 }
+
+#else
+
+int main() {
+   std::cout << "Your boost version is too old, sorry.\n";
+   return 1;
+}
+
+#endif

src/lib/tls/asio/asio_async_ops.h

@@ -9,10 +9,8 @@
 #ifndef BOTAN_ASIO_ASYNC_OPS_H_
 #define BOTAN_ASIO_ASYNC_OPS_H_
 
-#include <botan/types.h>
-
-#include <boost/version.hpp>
-#if BOOST_VERSION >= 107300
+#include <botan/boost_compat.h>
+#if defined(BOTAN_FOUND_COMPATIBLE_BOOST_VERSION)
 
    #include <botan/asio_error.h>
 
@@ -305,5 +303,5 @@ class AsyncHandshakeOperation : public AsyncBase<Handler, typename Stream::execu
 
    #include <boost/asio/unyield.hpp>
 
-#endif  // BOOST_VERSION
+#endif
 #endif  // BOTAN_ASIO_ASYNC_OPS_H_

src/lib/tls/asio/asio_context.h

@@ -9,10 +9,8 @@
 #ifndef BOTAN_ASIO_TLS_CONTEXT_H_
 #define BOTAN_ASIO_TLS_CONTEXT_H_
 
-#include <botan/types.h>
-
-#include <boost/version.hpp>
-#if BOOST_VERSION >= 107300
+#include <botan/boost_compat.h>
+#if defined(BOTAN_FOUND_COMPATIBLE_BOOST_VERSION)
 
    #include <functional>
 
@@ -99,5 +97,5 @@ class Context {
 
 }  // namespace Botan::TLS
 
-#endif  // BOOST_VERSION
+#endif
 #endif  // BOTAN_ASIO_TLS_CONTEXT_H_

src/lib/tls/asio/asio_error.h

@@ -9,10 +9,8 @@
 #ifndef BOTAN_ASIO_ERROR_H_
 #define BOTAN_ASIO_ERROR_H_
 
-#include <botan/types.h>
-
-#include <boost/version.hpp>
-#if BOOST_VERSION >= 107300
+#include <botan/boost_compat.h>
+#if defined(BOTAN_FOUND_COMPATIBLE_BOOST_VERSION)
 
    #include <boost/system/system_error.hpp>
 
@@ -122,5 +120,5 @@ struct is_error_code_enum<Botan::ErrorType> {
 
 }  // namespace boost::system
 
-#endif  // BOOST_VERSION
+#endif
 #endif  // BOTAN_ASIO_ERROR_H_

src/lib/tls/asio/asio_stream.h

@@ -10,12 +10,10 @@
 #ifndef BOTAN_ASIO_STREAM_H_
 #define BOTAN_ASIO_STREAM_H_
 
-#include <botan/types.h>
-
-#include <boost/version.hpp>
-
-// First version of boost asio that is prepared to use C++20 concepts
-#if BOOST_VERSION >= 107300
+#include <botan/boost_compat.h>
+#if !defined(BOTAN_FOUND_COMPATIBLE_BOOST_VERSION)
+   #error Available boost headers are too old for the boost asio stream.
+#else
 
    #include <botan/asio_async_ops.h>
    #include <botan/asio_context.h>
@@ -800,5 +798,5 @@ class Stream {
 
 }  // namespace Botan::TLS
 
-#endif  // BOOST_VERSION
+#endif
 #endif  // BOTAN_ASIO_STREAM_H_

src/lib/utils/boost/boost_compat.h

@@ -0,0 +1,47 @@
+/*
+* Checks compatibility between the existing headers of Botan and boost
+* (C) 2023 Jack Lloyd
+*     2023 René Meusel - Rohde & Schwarz Cybersecurity
+*
+* Botan is released under the Simplified BSD License (see license.txt)
+*/
+
+#ifndef BOTAN_BOOST_COMPAT_H_
+#define BOTAN_BOOST_COMPAT_H_
+
+#include <botan/build.h>
+
+#if defined(BOTAN_HAS_BOOST_ASIO)
+
+   #include <boost/version.hpp>
+
+   /** @brief minimum supported boost version for the TLS ASIO wrapper
+    *
+    *  BOOST_VERSION % 100 is the patch level
+    *  BOOST_VERSION / 100 % 1000 is the minor version
+    *  BOOST_VERSION / 100000 is the major version
+    *
+    * Botan may still work with older versions of boost. Though, the asio TLS
+    * wrapper won't work with versions older than the one specified below.
+    *
+    * Also note the changelog with rationales for the required versions:
+    *
+    * until Botan 3.2.0
+    *   1.66.0 - first version to be compatible with Networking TS (N4656) and boost::beast
+    *
+    * as of Botan 3.3.0
+    *   1.73.0 - first version supporting the C++20 concepts syntax
+    */
+   #define BOTAN_MINIMUM_SUPPORTED_BOOST_VERSION 107300
+
+   #if BOOST_VERSION >= BOTAN_MINIMUM_SUPPORTED_BOOST_VERSION
+
+      /**
+       * Indicates that the local boost and botan headers are compatible.
+       */
+      #define BOTAN_FOUND_COMPATIBLE_BOOST_VERSION 1
+
+   #endif
+
+#endif
+#endif

src/lib/utils/boost/info.txt

@@ -8,6 +8,10 @@ name -> "Boost"
 
 load_on vendor
 
+<header:public>
+boost_compat.h
+</header:public>
+
 <libs>
 linux -> rt
 mingw -> ws2_32

src/tests/test_tls_stream_integration.cpp

@@ -11,8 +11,8 @@
 
 #if defined(BOTAN_HAS_TLS) && defined(BOTAN_HAS_TLS_ASIO_STREAM) && defined(BOTAN_TARGET_OS_HAS_THREADS)
 
-   #include <boost/version.hpp>
-   #if BOOST_VERSION >= 107300
+   #include <botan/boost_compat.h>
+   #if defined(BOTAN_FOUND_COMPATIBLE_BOOST_VERSION)
 
       #include <functional>
       #include <memory>
@@ -835,5 +835,5 @@ BOTAN_REGISTER_TEST("tls", "tls_stream_integration", Tls_Stream_Integration_Test
 
 }  // namespace Botan_Tests
 
-   #endif  // BOOST_VERSION
-#endif     // BOTAN_HAS_TLS && BOTAN_HAS_BOOST_ASIO
+   #endif
+#endif  // BOTAN_HAS_TLS && BOTAN_HAS_BOOST_ASIO

src/tests/unit_asio_stream.cpp

@@ -10,12 +10,12 @@
 
 #if defined(BOTAN_HAS_TLS) && defined(BOTAN_HAS_TLS_ASIO_STREAM)
 
-   #include <botan/asio_stream.h>
-   #include <botan/tls_callbacks.h>
-   #include <botan/tls_session_manager_noop.h>
+   #include <botan/boost_compat.h>
+   #if defined(BOTAN_FOUND_COMPATIBLE_BOOST_VERSION)
 
-   #include <boost/version.hpp>
-   #if BOOST_VERSION >= 107300
+      #include <botan/asio_stream.h>
+      #include <botan/tls_callbacks.h>
+      #include <botan/tls_session_manager_noop.h>
 
       #include <boost/beast/_experimental/test/stream.hpp>
       #include <boost/bind.hpp>
@@ -736,5 +736,5 @@ BOTAN_REGISTER_TEST("tls", "tls_asio_stream", Asio_Stream_Tests);
 
 }  // namespace Botan_Tests
 
-   #endif  // BOOST_VERSION
-#endif     // BOTAN_HAS_TLS && BOTAN_HAS_BOOST_ASIO
+   #endif
+#endif  // BOTAN_HAS_TLS && BOTAN_HAS_TLS_ASIO_STREAM