From b51c6c769385214eaf2d88ae18360270c62f2c78 Mon Sep 17 00:00:00 2001
From: Maciej Mrozowski <reavertm@gmail.com>
Date: Thu, 26 May 2016 02:24:19 +0200
Subject: [PATCH] Add SYSTEM_UDNS CMake option. Remove spurious EXPAT_LIBRARIES
 linking when using bundled expat.

---
 3rdparty/CMakeLists.txt     |  2 +-
 CMakeLists.txt              | 19 ++++++++++++-----
 CMakeModules/FindUdns.cmake | 42 +++++++++++++++++++++++++++++++++++++
 simgear/CMakeLists.txt      | 11 +++++++++-
 4 files changed, 67 insertions(+), 7 deletions(-)
 create mode 100644 CMakeModules/FindUdns.cmake

diff --git a/3rdparty/CMakeLists.txt b/3rdparty/CMakeLists.txt
index e9b52823..a03a82d0 100644
--- a/3rdparty/CMakeLists.txt
+++ b/3rdparty/CMakeLists.txt
@@ -4,6 +4,6 @@ endif()
 
 add_subdirectory(utf8)
 
-if (ENABLE_DNS)
+if (ENABLE_DNS AND NOT SYSTEM_UDNS)
 	add_subdirectory(udns)
 endif()
diff --git a/CMakeLists.txt b/CMakeLists.txt
index ff0586a2..76774923 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -114,12 +114,14 @@ endif()
 
 if (NOT MSVC)
 option(SIMGEAR_SHARED   "Set to ON to build SimGear as a shared library/framework" OFF)
-option(SYSTEM_EXPAT     "Set to ON to build SimGear using the system libExpat" OFF)
+option(SYSTEM_EXPAT     "Set to ON to build SimGear using the system expat library" OFF)
+option(SYSTEM_UDNS      "Set to ON to build SimGear using the system udns library" OFF)
 else()
 # Building SimGear DLLs is currently not supported for MSVC.
 set(SIMGEAR_SHARED OFF)
-# Using a system expat is currently not supported for MSVC - it would require shared simgear (DLL).
+# Using external 3rd party libraries is currently not supported for MSVC - it would require shared simgear (DLL).
 set(SYSTEM_EXPAT OFF)
+set(SYSTEM_UDNS OFF)
 endif()
 
 option(SIMGEAR_HEADLESS "Set to ON to build SimGear without GUI/graphics support" OFF)
@@ -424,9 +426,16 @@ endif()
 install (FILES ${PROJECT_BINARY_DIR}/simgear/simgear_config.h  DESTINATION include/simgear/)
 
 include_directories(3rdparty/utf8/source)
-if (ENABLE_DNS)
-    message(STATUS "DNS resolver: ENABLED")
-    include_directories(3rdparty/udns)
+
+if(ENABLE_DNS)
+    if(SYSTEM_UDNS)
+        message(STATUS "Requested to use system udns library, forcing SIMGEAR_SHARED to true")
+        set(SIMGEAR_SHARED ON)
+        find_package(Udns REQUIRED)
+    else()
+        message(STATUS "DNS resolver: ENABLED")
+        include_directories(3rdparty/udns)
+    endif()
 else()
     message(STATUS "DNS resolver: DISABLED")
 endif()
diff --git a/CMakeModules/FindUdns.cmake b/CMakeModules/FindUdns.cmake
new file mode 100644
index 00000000..a4363610
--- /dev/null
+++ b/CMakeModules/FindUdns.cmake
@@ -0,0 +1,42 @@
+# - Try to find UDNS library
+# Once done this will define
+#
+#  UDNS_FOUND - system has UDNS
+#  UDNS_INCLUDE_DIRS - the UDNS include directory
+#  UDNS_LIBRARIES - Link these to use UDNS
+#  UDNS_DEFINITIONS - Compiler switches required for using UDNS
+#
+#  Copyright (c) 2016 Maciej Mrozowski <reavertm@gmail.com>
+#
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE_1_0.txt or copy at
+# http://www.boost.org/LICENSE_1_0.txt)
+
+
+if (UDN_LIBRARIES AND UDN_INCLUDE_DIRS)
+  # in cache already
+  set(UDNS_FOUND TRUE)
+else ()
+  set(UDNS_DEFINITIONS "")
+
+  find_path(UDNS_INCLUDE_DIRS NAMES udns.h)
+  find_library(UDNS_LIBRARIES NAMES udns)
+
+  if (UDNS_INCLUDE_DIRS AND UDNS_LIBRARIES)
+    set(UDNS_FOUND TRUE)
+  endif ()
+
+  if (UDNS_FOUND)
+    if (NOT Udns_FIND_QUIETLY)
+      message(STATUS "Found UDNS: ${UDNS_LIBRARIES}")
+    endif ()
+  else ()
+    if (Udns_FIND_REQUIRED)
+      message(FATAL_ERROR "Could not find UDNS")
+    endif ()
+  endif ()
+
+  # show the UDNS_INCLUDE_DIRS and UDNS_LIBRARIES variables only in the advanced view
+  mark_as_advanced(UDNS_INCLUDE_DIRS UDNS_LIBRARIES)
+
+endif ()
diff --git a/simgear/CMakeLists.txt b/simgear/CMakeLists.txt
index 59768334..516ea6cd 100644
--- a/simgear/CMakeLists.txt
+++ b/simgear/CMakeLists.txt
@@ -128,11 +128,20 @@ target_link_libraries(SimGearCore
     ${ZLIB_LIBRARY}
     ${RT_LIBRARY}
     ${DL_LIBRARY}
-    ${EXPAT_LIBRARIES}
     ${CMAKE_THREAD_LIBS_INIT}
     ${COCOA_LIBRARY}
     ${CURL_LIBRARIES})
 
+if(SYSTEM_EXPAT)
+    target_link_libraries(SimGearCore
+        ${EXPAT_LIBRARIES})
+endif()
+
+if(ENABLE_DNS AND SYSTEM_UDNS)
+    target_link_libraries(SimGearCore
+        ${UDNS_LIBRARIES})
+endif()
+
 if(NOT SIMGEAR_HEADLESS)
     target_link_libraries(SimGearScene
         SimGearCore
-- 
2.39.5