fixes #735 Configuring ZeroTier for a unified build is too hard

This changes the code to make use of a different project we have
created (libzerotiercore) that is "CMake clean". This should make
using and configuring this code *much* better.  It may also have the
benefit of making this configuration work better for Windows systems.

2 files changed, 17 insertions, 31 deletions

diff --git a/src/transport/zerotier/CMakeLists.txt b/src/transport/zerotier/CMakeLists.txt
index 8ca78f0f..d8dbb566 100644
--- a/src/transport/zerotier/CMakeLists.txt
+++ b/src/transport/zerotier/CMakeLists.txt
@@ -10,43 +10,29 @@
 
 # ZeroTier protocol
 
-set (NNG_TRANSPORT_ZEROTIER_SOURCE "" CACHE PATH "Location of ZeroTier source tree.")
-mark_as_advanced(NNG_TRANSPORT_ZEROTIER_SOURCE)
-
 if (NNG_TRANSPORT_ZEROTIER)
 
-    # We use the libzerotiercore.a library, which is unfortunately a C++ object
-    # even though it exposes only public C symbols.  It would be extremely
-    # helpful if libzerotiercore didn't make us carry the whole C++ runtime
-    # behind us.  The user must specify the location of the ZeroTier source
-    # tree (dev branch for now, and already compiled please) by setting the
-    # NNG_ZEROTIER_SOURCE macro.
-    # NB: This needs to be the zerotierone tree, not the libzt library.
-    # This is because we don't access the API, but instead use the low
-    # level zerotiercore functionality directly.
+    # The zerotiercore project will have been found at the top level
+    # of the package.  This is necessary because import libraries cannot
+    # percolate back to the parent tree.
+
     # NB: As we wind up linking libzerotiercore.a into the application,
     # this means that your application will *also* need to either be licensed
     # under the GPLv3, or you will need to have a commercial license from
     # ZeroTier permitting its use elsewhere.
-    
-    enable_language(CXX)
-    find_library(NNG_LIBZTCORE zerotiercore PATHS ${NNG_TRANSPORT_ZEROTIER_SOURCE})
-    if (NNG_LIBZTCORE)
-        set(CMAKE_REQUIRED_INCLUDES ${NNG_TRANSPORT_ZEROTIER_SOURCE}/include)
-        message(STATUS "C++ ${CMAKE_CXX_IMPLICIT_LINK_LIBRARIES}")
-        set(CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES} ${NNG_LIBZTCORE} ${CMAKE_CXX_IMPLICIT_LINK_LIBRARIES})
-        set(NNG_REQUIRED_LIBRARIES ${NNG_REQUIRED_LIBRARIES} ${NNG_LIBZTCORE} ${CMAKE_CXX_IMPLICIT_LINK_LIBRARIES} PARENT_SCOPE)
-        set(NNG_REQUIRED_INCLUDES ${NNG_REQUIRED_INCLUDES} ${NNG_TRANSPORT_ZEROTIER_SOURCE}/include PARENT_SCOPE)
-        nng_check_sym(ZT_Node_join ZeroTierOne.h HAVE_ZTCORE)
-    endif()
-    if (NOT HAVE_ZTCORE)
-        message (FATAL_ERROR "Cannot find ZeroTier components")
-    endif()
-    message(STATUS "Found ZeroTier at ${NNG_LIBZTCORE}")
+
+    message(WARNING "
+        ************************************************************
+        Linking against zerotiercore changes license terms (GPLv3).
+        Consult a lawyer and the license files for details.
+        ************************************************************")
+
+    set(NNG_REQUIRED_LIBRARIES ${NNG_REQUIRED_LIBRARIES} zerotiercore::zerotiercore)
+    set(NNG_REQUIRED_LIBRARIES ${NNG_REQUIRED_LIBRARIES} PARENT_SCOPE)
 
     set(ZT_SOURCES transport/zerotier/zerotier.c transport/zerotier/zerotier.h)
     set(ZT_HEADERS transport/zerotier/zerotier.h)
-endif()
 
-set(NNG_SOURCES ${NNG_SOURCES} ${ZT_SOURCES} PARENT_SCOPE)
-set(NNG_HEADERS ${NNG_HEADERS} ${ZT_HEADERS} PARENT_SCOPE)
+    set(NNG_SOURCES ${NNG_SOURCES} ${ZT_SOURCES} PARENT_SCOPE)
+    set(NNG_HEADERS ${NNG_HEADERS} ${ZT_HEADERS} PARENT_SCOPE)
+endif()
diff --git a/src/transport/zerotier/zerotier.c b/src/transport/zerotier/zerotier.c
index 1fc128b7..0cd83ee7 100644
--- a/src/transport/zerotier/zerotier.c
+++ b/src/transport/zerotier/zerotier.c
@@ -16,7 +16,7 @@
 #include "core/nng_impl.h"
 #include "zerotier.h"
 
-#include <ZeroTierOne.h>
+#include <zerotiercore/ZeroTierOne.h>
 
 // ZeroTier Transport.  This sits on the ZeroTier L2 network, which itself
 // is implemented on top of UDP.  This requires the 3rd party