Use system rapidjson, fall back to bundled.

Currently the `rapidjson` headers are hard-coded into
`davix_gcloud_utils.cpp` in a way that makes it difficult to use
external/system provided rapidjson headers rather than the bundled ones.

This commit uses `find_package` to look for an external instance of
rapidjson, falling back to the bundled version in `src/libs/rapidjson`
if that search fails. In either case, it sets up the variable
`RAPIDJSON_INCLUDE_DIRS` pointing to the location of the headers and
adds this to the list of `DAVIX_INTERNAL_INCLUDES` to allow the location
to be included during compilation (via `-I${RAPIDJSON_INCLUDE_DIRS}`).
Finally, it modifies the `#include` in `davix_gcloud_utils.cpp` to
support a generic location.

CMakeLists.txt

@@ -97,6 +97,13 @@ set(NE_HAVE_SSL 1)
 
 add_subdirectory(deps)
 
+find_package(RapidJSON QUIET)
+if(${RapidJSON_FOUND})
+  set(RAPIDJSON_INCLUDE_DIRS ${RapidJSON_INCLUDE_DIRS})
+else()
+  message(STATUS "Using bundled RapidJSON")
+  set(RAPIDJSON_INCLUDE_DIRS ${CMAKE_CURRENT_SOURCE_DIR}/src/libs)
+endif()
 
 #libuuid
 if(NOT APPLE)

src/CMakeLists.txt

@@ -84,6 +84,7 @@ set(DAVIX_SOURCES
 set(DAVIX_INTERNAL_INCLUDES
   ${OPENSSL_INCLUDE_DIR}
   ${LIBXML2_INCLUDE_DIR}
+  ${RAPIDJSON_INCLUDE_DIRS}
   ${PROJECT_SOURCE_DIR}/deps
   ${PROJECT_SOURCE_DIR}/src
   ${CMAKE_CURRENT_BINARY_DIR}

src/utils/davix_gcloud_utils.cpp

@@ -23,7 +23,7 @@
 #include <libs/alibxx/crypto/hmacsha.hpp>
 #include <libs/alibxx/crypto/base64.hpp>
 #include <fstream>
-#include <libs/rapidjson/document.h>
+#include <rapidjson/document.h>
 #include <sstream>
 
 #define SSTR(message) static_cast<std::ostringstream&>(std::ostringstream().flush() << message).str()