Forward declaration error when migrating code from openssl 1.0.1 to 1.1.0

Question

I have a codebase that was moved from openssl 1.0.1 to 1.1.0. One Project in it is producing errors when compiling. Some parts do compile without error but I stumbled upon forward declaration errors:

Foo/BarDH.cpp:37:28: error: member access into incomplete type 'dh_st'
        nRes = BN_bn2bin( key->pub_key, &keyout[0] );
                                  ^
/usr/local/sysroot/usr/local/include/openssl/ossl_typ.h:104:16: note: forward declaration of 'dh_st'
typedef struct dh_st DH;

This is how files are included:

BarDH.cpp:

#include BarDH.hpp
[...]

BarDH.hpp:

#include <openssl/bn.h>
#include <openssl/dh.h>
#include <openssl/ec.h>
[...]
class BarDH{
    BarDH(void);
    virtual ~BarDH(void);

    enum
    {
     MAX_PUBKEY_SIZE = 2048 / 8
    };
    DH* key;
};

Did anything change in how one is supposed to include files form openssl 1.0.1 to 1.1.0 or can anyone see what's going on here? Thank you!

Answer 1

OpenSSL 1.1.0 made most structures opaque, so you are no longer allowed to directly access the members of the DH struct. Use DH_get0_pub_key(key) to get hold of the pub_key value instead of key->pub_key on line 37 of BarDH.cpp

https://www.openssl.org/docs/man1.1.1/man3/DH_get0_pub_key.html