Codechange: refactor the Windows-only DllLoader in a cross-platform LibraryLoader (#11751)

src/os/unix/CMakeLists.txt

@@ -5,6 +5,7 @@ add_files(
 )
 
 add_files(
+    library_loader_unix.cpp
     unix.cpp
     CONDITION UNIX
 )

src/os/unix/library_loader_unix.cpp

@@ -0,0 +1,64 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file library_loader_unix.cpp Implementation of the LibraryLoader for Linux / MacOS */
+
+#include "../../stdafx.h"
+
+#include <dlfcn.h>
+
+#include "../../library_loader.h"
+
+#include "../../safeguards.h"
+
+/* Emscripten cannot dynamically load other files. */
+#if defined(__EMSCRIPTEN__)
+
+void *LibraryLoader::OpenLibrary(const std::string &)
+{
+	this->error = "Dynamic loading is not supported on this platform.";
+	return nullptr;
+}
+
+void LibraryLoader::CloseLibrary()
+{
+}
+
+void *LibraryLoader::GetSymbol(const std::string &)
+{
+	this->error = "Dynamic loading is not supported on this platform.";
+	return nullptr;
+}
+
+#else
+
+void *LibraryLoader::OpenLibrary(const std::string &filename)
+{
+	void *h = dlopen(filename.c_str(), RTLD_NOW | RTLD_LOCAL);
+	if (h == nullptr) {
+		this->error = dlerror();
+	}
+
+	return h;
+}
+
+void LibraryLoader::CloseLibrary()
+{
+	dlclose(this->handle);
+}
+
+void *LibraryLoader::GetSymbol(const std::string &symbol_name)
+{
+	void *p = dlsym(this->handle, symbol_name.c_str());
+	if (p == nullptr) {
+		this->error = dlerror();
+	}
+
+	return p;
+}
+
+#endif /* __EMSCRIPTEN__ */