CppRestSDK build broken by boost.asio

[NAThompson]

Building off commit 96e7d20 of cpprestsdk and boost.asio commit 95f7e93, CppRestSDK does not compile, due to the following error

                 from /cpprestsdk/Release/src/websockets/client/ws_client_wspp.cpp:14:
/boost/boost/asio/impl/executor.hpp: In instantiation of ‘boost::asio::execution_context& boost::asio::executor::impl< <template-parameter-1-1>, <template-parameter-1-2> >::context() [with Executor = std::reference_wrapper<boost::asio::io_context>; Allocator = std::allocator<void>]’:
/learn_cpprestsdk/cpprestsdk/Release/src/websockets/client/ws_client_wspp.cpp:844:1:   required from here
/boost/boost/asio/impl/executor.hpp:179:22: error: ‘class std::reference_wrapper<boost::asio::io_context>’ has no member named ‘context’
     return executor_.context();
            ~~~~~~~~~~^~~~~~~
/boost/boost/asio/impl/executor.hpp: In instantiation of ‘void boost::asio::executor::impl< <template-parameter-1-1>, <template-parameter-1-2> >::on_work_started() [with Executor = std::reference_wrapper<boost::asio::io_context>; Allocator = std::allocator<void>]’:
/cpprestsdk/Release/src/websockets/client/ws_client_wspp.cpp:844:1:   required from here
/boost/boost/asio/impl/executor.hpp:169:15: error: ‘class std::reference_wrapper<boost::asio::io_context>’ has no member named ‘on_work_started’
     executor_.on_work_started();
     ~~~~~~~~~~^~~~~~~~~~~~~~~

git bisect reveals that the commit in boost.asio which breaks this library is:

 git bisect good
59066d80b26e1d5b83b60d127ee17948d9ae9702 is the first bad commit
commit 59066d80b26e1d5b83b60d127ee17948d9ae9702
Author: Christopher Kohlhoff <[email protected]>
Date:   Sun Feb 17 19:29:45 2019 -1000

    Add custom I/O executor support to I/O objects.
    
    All I/O objects now have an additional Executor template parameter. This
    template parameter defaults to the asio::executor type (the polymorphic
    executor wrapper) but can be used to specify a user-defined executor
    type.
    
    I/O objects' constructors and functions that previously took an
    asio::io_context& now accept either an Executor or a reference to a
    concrete ExecutionContext (such as asio::io_context or
    asio::thread_pool).
    
    One potential point of breakage in existing user code is when reusing an
    I/O object's io_context for constructing another I/O object, as in:
    
        asio::steady_timer my_timer(my_socket.get_executor().context());
    
    To fix this, either construct the second I/O object using the first I/O
    object's executor:
    
        asio::steady_timer my_timer(my_socket.get_executor());
    
    or otherwise explicitly pass the io_context:
    
        asio::steady_timer my_timer(my_io_context);

Forgive me for not knowing if this should be submitted against boost.asio or this repo.

Ubuntu 16.04,

 g++ --version
g++ (Ubuntu 7.4.0-1ubuntu1~18.04.1) 7.4.0

[garethsb]

Root cause is the API change in Boost.Asio, which affects websocketpp (and a gazillion other people). There has been a patch for websocketpp for six months (zaphoyd/websocketpp#814) but although it's been merged to 'develop' branch it hasn't made it into 'master' or a release unfortunately.