first try on adding linux support.

linux/CMakeLists.txt

@@ -0,0 +1,26 @@
+cmake_minimum_required(VERSION 3.10)
+set(PROJECT_NAME "argon2_ffi")
+project(${PROJECT_NAME} LANGUAGES CXX)
+
+set(PLUGIN_NAME "${PROJECT_NAME}_plugin")
+
+add_library(${PLUGIN_NAME} SHARED
+  "${PLUGIN_NAME}.cc"
+  
+  ../ios/Classes/argon2_ffi.c
+
+  ../ios/Classes/argon2src/argon2.c
+  ../ios/Classes/argon2src/core.c
+  ../ios/Classes/argon2src/encoding.c
+  ../ios/Classes/argon2src/genkat.c
+  ../ios/Classes/argon2src/ref.c
+  ../ios/Classes/argon2src/thread.c
+  ../ios/Classes/argon2src/blake2/blake2b.c
+)
+apply_standard_settings(${PLUGIN_NAME})
+set_target_properties(${PLUGIN_NAME} PROPERTIES
+  CXX_VISIBILITY_PRESET hidden)
+target_compile_definitions(${PLUGIN_NAME} PRIVATE FLUTTER_PLUGIN_IMPL)
+target_include_directories(${PLUGIN_NAME} INTERFACE
+  "${CMAKE_CURRENT_SOURCE_DIR}/include")
+target_link_libraries(${PLUGIN_NAME} PRIVATE flutter flutter_wrapper_plugin)

linux/argon2_ffi_plugin.cc

@@ -0,0 +1,78 @@
+#include "include/argon2_ffi_plugin.h"
+
+#include <flutter/method_channel.h>
+#include <flutter/plugin_registrar_glfw.h>
+#include <flutter/standard_method_codec.h>
+#include <sys/utsname.h>
+
+#include <map>
+#include <memory>
+#include <sstream>
+
+namespace {
+
+class Argon2FfiPlugin : public flutter::Plugin {
+ public:
+  static void RegisterWithRegistrar(flutter::PluginRegistrarGlfw *registrar);
+
+  Argon2FfiPlugin();
+
+  virtual ~Argon2FfiPlugin();
+
+ private:
+  // Called when a method is called on this plugin's channel from Dart.
+  void HandleMethodCall(
+      const flutter::MethodCall<flutter::EncodableValue> &method_call,
+      std::unique_ptr<flutter::MethodResult<flutter::EncodableValue>> result);
+};
+
+// static
+void Argon2FfiPlugin::RegisterWithRegistrar(
+    flutter::PluginRegistrarGlfw *registrar) {
+  auto channel =
+      std::make_unique<flutter::MethodChannel<flutter::EncodableValue>>(
+          registrar->messenger(), "argon2_ffi",
+          &flutter::StandardMethodCodec::GetInstance());
+  auto plugin = std::make_unique<Argon2FfiPlugin>();
+
+  channel->SetMethodCallHandler(
+      [plugin_pointer = plugin.get()](const auto &call, auto result) {
+        plugin_pointer->HandleMethodCall(call, std::move(result));
+      });
+
+  registrar->AddPlugin(std::move(plugin));
+}
+
+Argon2FfiPlugin::Argon2FfiPlugin() {}
+
+Argon2FfiPlugin::~Argon2FfiPlugin() {}
+
+void Argon2FfiPlugin::HandleMethodCall(
+    const flutter::MethodCall<flutter::EncodableValue> &method_call,
+    std::unique_ptr<flutter::MethodResult<flutter::EncodableValue>> result) {
+  // Replace "getPlatformVersion" check with your plugin's method.
+  // See:
+  // https://github.com/flutter/engine/tree/master/shell/platform/common/cpp/client_wrapper/include/flutter
+  // and
+  // https://github.com/flutter/engine/tree/master/shell/platform/glfw/client_wrapper/include/flutter
+  // for the relevant Flutter APIs.
+  if (method_call.method_name().compare("getPlatformVersion") == 0) {
+    struct utsname uname_data = {};
+    uname(&uname_data);
+    std::ostringstream version_stream;
+    version_stream << "Linux " << uname_data.version;
+    flutter::EncodableValue response(version_stream.str());
+    result->Success(&response);
+  } else {
+    result->NotImplemented();
+  }
+}
+
+}  // namespace
+
+void Argon2FfiPluginRegisterWithRegistrar(
+    FlutterDesktopPluginRegistrarRef registrar) {
+  Argon2FfiPlugin::RegisterWithRegistrar(
+      flutter::PluginRegistrarManager::GetInstance()
+          ->GetRegistrar<flutter::PluginRegistrarGlfw>(registrar));
+}

linux/include/argon2_ffi_plugin.h

@@ -0,0 +1,23 @@
+#ifndef FLUTTER_PLUGIN_ARGON2_FFI_PLUGIN_H_
+#define FLUTTER_PLUGIN_ARGON2_FFI_PLUGIN_H_
+
+#include <flutter_plugin_registrar.h>
+
+#ifdef FLUTTER_PLUGIN_IMPL
+#define FLUTTER_PLUGIN_EXPORT __attribute__((visibility("default")))
+#else
+#define FLUTTER_PLUGIN_EXPORT
+#endif
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+FLUTTER_PLUGIN_EXPORT void Argon2FfiPluginRegisterWithRegistrar(
+    FlutterDesktopPluginRegistrarRef registrar);
+
+#if defined(__cplusplus)
+}  // extern "C"
+#endif
+
+#endif  // FLUTTER_PLUGIN_ARGON2_FFI_PLUGIN_H_

pubspec.yaml

@@ -41,6 +41,8 @@ flutter:
         pluginClass: Argon2FfiPlugin
       macos:
         pluginClass: Argon2FfiPlugin
+      linux:
+        pluginClass: Argon2FfiPlugin
 
   # To add assets to your plugin package, add an assets section, like this:
   # assets: