Check available rrdtool API version

See oetiker/rrdtool-1.x@b76e3c5

Fix #8

CMakeLists.txt

@@ -1,14 +1,36 @@
 cmake_minimum_required(VERSION 3.15)
 project(${SKBUILD_PROJECT_NAME} VERSION ${SKBUILD_PROJECT_VERSION} LANGUAGES C)
 
+include(CheckCSourceCompiles)
+
 set(CMAKE_C_STANDARD 99)
 
+function(check_mutable_argv)
+    set(CMAKE_REQUIRED_LIBRARIES PkgConfig::LIBRRD)
+    check_c_source_compiles(
+        "
+        #include <rrd.h>
+
+        int main() {
+            (void)rrd_graph_v(0, (char**)NULL);
+            return 0;
+        }
+        "
+        LIBRRD_HAS_MUTABLE_ARGV)
+    unset(CMAKE_REQUIRED_LIBRARIES)
+endfunction()
+
 find_package(Python REQUIRED COMPONENTS Interpreter Development.Module)
 find_package(PkgConfig REQUIRED)
 pkg_check_modules(LIBRRD REQUIRED IMPORTED_TARGET librrd)
 
+check_mutable_argv()
+
 python_add_library(rrd MODULE c_src/rrd.c WITH_SOABI)
 target_link_libraries(rrd PRIVATE PkgConfig::LIBRRD)
+if(LIBRRD_HAS_MUTABLE_ARGV)
+    target_compile_definitions(rrd PRIVATE LIBRRD_HAS_MUTABLE_ARGV)
+endif()
 set_property(TARGET rrd PROPERTY INTERPROCEDURAL_OPTIMIZATION True)
 
 install(TARGETS rrd DESTINATION collectd_rest)

c_src/rrd.c

@@ -95,12 +95,18 @@ static int rrd_parse_arguments(char* command) {
 
 static PyObject*
 rrd_render(PyObject* self, PyObject* args) {
+#ifdef LIBRRD_HAS_MUTABLE_ARGV // before rrdtool 1.9.0
+	typedef char* arg_t;
+#else
+	typedef const char* arg_t;
+#endif // LIBRRD_HAS_MUTABLE_ARGV
+
 	PyObject* ret = NULL;
 
 	int    i;
 	char*  it;
 	int    argc;
-	char** argv;
+	arg_t* argv;
 	char*  format;
 	char*  command;
 	int    command_argc;
@@ -129,7 +135,7 @@ rrd_render(PyObject* self, PyObject* args) {
 	}
 	command_argc = rrd_parse_arguments(command_args);
 
-	argv = PyMem_New(char*, 3 + 1 + command_argc + 1);
+	argv = PyMem_New(arg_t, 3 + 1 + command_argc + 1);
 	if (argv == NULL) {
 		PyErr_SetString(PyExc_MemoryError, "PyMem_New: Out of memory");
 		goto err_PyMem_New;