Parity as a library (#8412)

* Parity as a library

* Fix concerns

* Allow using a null on_client_restart_cb

* Fix more concerns

* Test the C library in test.sh

* Reduce CMake version to 3.5

* Move the clib test before cargo test

* Add println in test

parity-clib-example/CMakeLists.txt

@@ -0,0 +1,19 @@
+cmake_minimum_required(VERSION 3.5)
+include(ExternalProject)
+
+include_directories("${CMAKE_SOURCE_DIR}/../parity-clib")
+
+add_executable(parity-example main.cpp)
+
+ExternalProject_Add(
+    libparity
+    DOWNLOAD_COMMAND ""
+    CONFIGURE_COMMAND ""
+    BUILD_COMMAND ""
+    COMMAND cargo build -p parity-clib      # Note: use --release in a real project
+    BINARY_DIR "${CMAKE_SOURCE_DIR}/../target"
+    INSTALL_COMMAND ""
+    LOG_BUILD ON)
+
+add_dependencies(parity-example libparity)
+target_link_libraries(parity-example "${CMAKE_SOURCE_DIR}/../target/debug/libparity.so")

parity-clib-example/main.cpp

@@ -0,0 +1,28 @@
+#include <cstddef>
+#include <unistd.h>
+#include <parity.h>
+
+void on_restart(void*, const char*, size_t) {}
+
+int main() {
+    ParityParams cfg = { 0 };
+    cfg.on_client_restart_cb = on_restart;
+
+    const char* args[] = {"--light"};
+    size_t str_lens[] = {7};
+    if (parity_config_from_cli(args, str_lens, 1, &cfg.configuration) != 0) {
+        return 1;
+    }
+
+    void* parity;
+    if (parity_start(&cfg, &parity) != 0) {
+        return 1;
+    }
+
+    sleep(5);
+    if (parity != NULL) {
+        parity_destroy(parity);
+    }
+
+    return 0;
+}