build: use the system provided c-ares if found

e.g. buildroot has logic to build c-ares,
so if pkg_check_modules can find a suitable version,
then use that one if -DFLB_PREFER_SYSTEM_LIBS=Yes.

Note that the CheckIncludeFiles include for wasm is added,
since that was done by c-ares otherwise.

Signed-off-by: Thomas Devoogdt <[email protected]>

CMakeLists.txt

@@ -581,16 +581,27 @@ else()
 endif()
 
 # C-Ares (DNS library)
-FLB_OPTION(CARES_STATIC      ON)
-FLB_OPTION(CARES_SHARED      OFF)
-FLB_OPTION(CARES_INSTALL     OFF)
-FLB_OPTION(CARES_BUILD_TESTS OFF)
-FLB_OPTION(CARES_BUILD_TOOLS OFF)
-if (FLB_SYSTEM_MACOS)
-  # macOS SDK always has <arpa/nameser.h>.
-  FLB_DEFINITION(CARES_HAVE_ARPA_NAMESER_H)
+if(FLB_PREFER_SYSTEM_LIBS)
+  find_package(PkgConfig)
+  pkg_check_modules(CARES libcares>=1.0.0)
+endif()
+if(CARES_FOUND)
+  include_directories(${CARES_INCLUDE_DIRS})
+  link_directories(${CARES_LIBRARY_DIRS})
+else()
+  FLB_OPTION(CARES_STATIC      ON)
+  FLB_OPTION(CARES_SHARED      OFF)
+  FLB_OPTION(CARES_INSTALL     OFF)
+  FLB_OPTION(CARES_BUILD_TESTS OFF)
+  FLB_OPTION(CARES_BUILD_TOOLS OFF)
+  if (FLB_SYSTEM_MACOS)
+    # macOS SDK always has <arpa/nameser.h>.
+    FLB_DEFINITION(CARES_HAVE_ARPA_NAMESER_H)
+  endif()
+  add_subdirectory(${FLB_PATH_LIB_CARES})# EXCLUDE_FROM_ALL)
+
+  set(CARES_LIBRARIES "c-ares")
 endif()
-add_subdirectory(${FLB_PATH_LIB_CARES})# EXCLUDE_FROM_ALL)
 
 # Chunk I/O
 FLB_OPTION(CIO_LIB_STATIC  ON)
@@ -660,6 +671,7 @@ if(FLB_WASM)
           _Atomic int a;
           return 0;
        }" FLB_HAVE_STDATOMIC_H)
+    include(CheckIncludeFiles)
     check_include_files(stdatomic.h FLB_HAVE_STDATOMIC_H)
     if (FLB_HAVE_STDATOMIC_H)
       enable_language (ASM)

src/CMakeLists.txt

@@ -371,7 +371,7 @@ set(FLB_DEPS
   ${FLB_PLUGINS}
   ${FLB_PROXY_PLUGINS}
   ${extra_libs}
-  c-ares
+  ${CARES_LIBRARIES}
   snappy-c
   lwrb
   ${NGHTTP2_LIBRARIES}