wolfssl: drop header path hack

The wolfSSL OpenSSL headers reside in `wolfssl/openssl/*.h`.

Before this patch the wolfSSL OpenSSL compatibilty header includes were
shared with the native OpenSSL codepath, and used `openssl/*h`. For
wolfSSL builds this required a hack to append the
`<wolfssl-prefix>/wolfssl` directory to the header search path, to find
the headers.

This patch changes the source to use the correct header references,
allowing to drop the header path hack.

Also fix to use the correct variable to set up the header path in CMake:
`WOLFSSL_INCLUDE_DIRS` (was: `WOLFSSL_INCLUDE_DIR`, without the `S`)

Closes #1439

CMakeLists.txt

@@ -345,7 +345,7 @@ if(CRYPTO_BACKEND STREQUAL "wolfSSL" OR NOT CRYPTO_BACKEND)
   if(WOLFSSL_FOUND)
     set(CRYPTO_BACKEND "wolfSSL")
     set(CRYPTO_BACKEND_DEFINE "LIBSSH2_WOLFSSL")
-    set(CRYPTO_BACKEND_INCLUDE_DIR ${WOLFSSL_INCLUDE_DIR} "${WOLFSSL_INCLUDE_DIR}/wolfssl")
+    set(CRYPTO_BACKEND_INCLUDE_DIR ${WOLFSSL_INCLUDE_DIRS})
     list(APPEND LIBRARIES ${WOLFSSL_LIBRARIES})
     list(APPEND LIBSSH2_PC_LIBS_PRIVATE "-lwolfssl")
     list(APPEND LIBSSH2_PC_REQUIRES_PRIVATE "wolfssl")

acinclude.m4

@@ -866,11 +866,6 @@ m4_case([$1],
 ],
 
 [wolfssl], [
-  if test "${with_libwolfssl_prefix+set}" = set; then
-    CPPFLAGS="$CPPFLAGS${CPPFLAGS:+ }-I${with_libwolfssl_prefix}/include/wolfssl"
-  else
-    AC_MSG_ERROR([When using wolfSSL, must specify prefix with --with-libwolfssl-prefix in order to find OpenSSL compatibility headers.])
-  fi
   LIBSSH2_LIB_HAVE_LINKFLAGS([wolfssl], [], [#include <wolfssl/options.h>], [
     AC_DEFINE(LIBSSH2_WOLFSSL, 1, [Use $1])
     LIBSSH2_PC_REQUIRES_PRIVATE="$LIBSSH2_PC_REQUIRES_PRIVATE${LIBSSH2_PC_REQUIRES_PRIVATE:+,}wolfssl"

src/openssl.h

@@ -48,7 +48,7 @@
 #ifdef LIBSSH2_WOLFSSL
 
 #include <wolfssl/options.h>
-#include <openssl/ecdh.h>
+#include <wolfssl/openssl/ecdh.h>
 
 #if defined(NO_DSA) || defined(HAVE_FIPS)
 #define OPENSSL_NO_DSA
@@ -76,7 +76,23 @@
 /* wolfSSL has no engine framework. */
 #define OPENSSL_NO_ENGINE
 
-#endif /* LIBSSH2_WOLFSSL */
+#include <wolfssl/openssl/opensslconf.h>
+#include <wolfssl/openssl/sha.h>
+#include <wolfssl/openssl/rsa.h>
+#ifndef OPENSSL_NO_DSA
+#include <wolfssl/openssl/dsa.h>
+#endif
+#ifndef OPENSSL_NO_MD5
+#include <wolfssl/openssl/md5.h>
+#endif
+#include <wolfssl/openssl/err.h>
+#include <wolfssl/openssl/evp.h>
+#include <wolfssl/openssl/hmac.h>
+#include <wolfssl/openssl/bn.h>
+#include <wolfssl/openssl/pem.h>
+#include <wolfssl/openssl/rand.h>
+
+#else /* !LIBSSH2_WOLFSSL */
 
 #include <openssl/opensslconf.h>
 #include <openssl/sha.h>
@@ -102,6 +118,8 @@
 #include <openssl/core_names.h>
 #endif
 
+#endif /* LIBSSH2_WOLFSSL */
+
 #if (OPENSSL_VERSION_NUMBER >= 0x10100000L && \
     !defined(LIBRESSL_VERSION_NUMBER)) || defined(LIBSSH2_WOLFSSL) || \
     (defined(LIBRESSL_VERSION_NUMBER) && \