Error: incomplete type when using HMAC_CTX in C++ project

问题:

I am trying to compile this library ndn-cxx in my laptop. I already tried in another computer and it compiled successfully but now i am getting this error and i think its related somhow to openssl. I verify that i have openssl in my laptop using sudo apt-cache search libssl | grep SSL and the result is :

• libssl-ocaml - OCaml bindings for OpenSSL (runtime)
• libssl-ocaml-dev - OCaml bindings for OpenSSL
• libssl0.9.8 - SSL shared libraries
• libsslcommon2 - enterprise messaging system - common SSL libraries
• libsslcommon2-dev - enterprise messaging system - common SSL development files

The error I am getting when trying to compile the library is :

../src/security/transform/hmac-filter.cpp:49:12: error: field ‘m_context’ has incomplete type    HMAC_CTX m_context;             ^  ../src/security/transform/hmac-filter.cpp: In constructor  ‘ndn::security::transform::HmacFilter::Impl::Impl()’: ../src/security/transform/hmac-filter.cpp:35:20: error: ‘m_context’ was not declared in this scope      HMAC_CTX_init(&m_context);                     ^  ../src/security/transform/hmac-filter.cpp:35:29: error: ‘HMAC_CTX_init’ was not declared in this scope      HMAC_CTX_init(&m_context);                              ^  ../src/security/transform/hmac-filter.cpp: In destructor ‘ndn::security::transform::HmacFilter::Impl::~Impl()’: ../src/security/transform/hmac-filter.cpp:40:23: error: ‘m_context’ was not declared in this scope      HMAC_CTX_cleanup(&m_context);                        ^      ../src/security/transform/hmac-filter.cpp:40:32: error: ‘HMAC_CTX_cleanup’ was not declared in this scope      HMAC_CTX_cleanup(&m_context);                                 ^  ../src/security/transform/hmac-filter.cpp: In member function ‘ndn::security::transform::HmacFilter::Impl::operator HMAC_CTX*()’: ../src/security/transform/hmac-filter.cpp:45:13: error: ‘m_context’ was not declared in this scope      return &m_context;              ^  ../src/security/transform/hmac-filter.cpp:46:3: warning: control reaches end of non-void function [-Wreturn-type]    }    ^ 

回答1:

The file that causes the compilation error contains the line #if OPENSSL_VERSION_NUMBER and uses the struct HMAC_CTX in that case. For newer versions of OpenSSL (>1.1.0), it uses HMAX_CTX *. My conclusion is that the waf build tool includes the wrong file to get the OPENSSL_VERSION_NUMBER and consequently compiles as if you are using an older version of OpenSSL, with the struct HMAC_CTX, which is no longer available as such in the newer versions.

You could do grep OPENSSL .waf-tools/openssl.py and analyse the printed lines to see where the different OpenSSL includes come from.

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