Added cffi/* module for third-party advanced modules

resources/custom_modules/cffi_example/.gitignore

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+.cache/

resources/custom_modules/cffi_example/README.md

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+# C FFI module
+
+A C FFI module is a dynamic library that exposes standard C functions and
+constants, that Waybar can load and execute to create custom advanced widgets.
+
+Most language can implement the required functions and constants (C, C++, Rust,
+Go, Python, ...), meaning you can develop custom modules using your language of
+choice, as long as there's GTK bindings.
+
+# Usage
+
+## Building this module
+
+```bash
+meson setup build
+meson compile -C build
+```
+
+## Load the module
+
+Edit your waybar config:
+```json
+{
+	// ...
+	"modules-center": [
+		// ...
+		"cffi/c_example"
+	],
+	// ...
+	"cffi/c_example": {
+		// Path to the compiled dynamic library file
+		"module_path": "resources/custom_modules/cffi_example/build/wb_cffi_example.so"
+	}
+}
+```

resources/custom_modules/cffi_example/main.c

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+
+#include "waybar_cffi_module.h"
+
+typedef struct {
+  GtkContainer* root;
+  GtkBox* container;
+  GtkButton* button;
+} Instance;
+
+// This static variable is shared between all instances of this module
+static int instance_count = 0;
+
+void onclicked(GtkButton* button) {
+  char text[256];
+  snprintf(text, 256, "Dice throw result: %d", rand() % 6 + 1);
+  gtk_button_set_label(button, text);
+}
+
+// You must
+const size_t wbcffi_version = 1;
+
+void* wbcffi_init(GtkContainer* root, const struct wbcffi_config_entry* config_entries,
+                  size_t config_entries_len) {
+  printf("cffi_example: init config:\n");
+  for (size_t i = 0; i < config_entries_len; i++) {
+    printf("  %s = %s\n", config_entries[i].key, config_entries[i].value);
+  }
+
+  // Allocate the instance object
+  Instance* inst = malloc(sizeof(Instance));
+  inst->root = root;
+
+  // Add a container for displaying the next widgets
+  inst->container = GTK_BOX(gtk_box_new(GTK_ORIENTATION_HORIZONTAL, 5));
+  gtk_container_add(GTK_CONTAINER(inst->root), GTK_WIDGET(inst->container));
+
+  // Add a label
+  GtkLabel* label = GTK_LABEL(gtk_label_new("[Example C FFI Module:"));
+  gtk_container_add(GTK_CONTAINER(inst->container), GTK_WIDGET(label));
+
+  // Add a button
+  inst->button = GTK_BUTTON(gtk_button_new_with_label("click me !"));
+  g_signal_connect(inst->button, "clicked", G_CALLBACK(onclicked), NULL);
+  gtk_container_add(GTK_CONTAINER(inst->container), GTK_WIDGET(inst->button));
+
+  // Add a label
+  label = GTK_LABEL(gtk_label_new("]"));
+  gtk_container_add(GTK_CONTAINER(inst->container), GTK_WIDGET(label));
+
+  // Return instance object
+  printf("cffi_example inst=%p: init success ! (%d total instances)\n", inst, ++instance_count);
+  return inst;
+}
+void wbcffi_deinit(void* instance) {
+  printf("cffi_example inst=%p: free memory\n", instance);
+  free(instance);
+}
+void wbcffi_refresh(void* instance, int signal) {
+  printf("cffi_example inst=%p: Received refresh signal %d\n", instance, signal);
+}
+void wbcffi_doaction(void* instance, const char* name) {
+  printf("cffi_example inst=%p: doAction(%s)\n", instance, name);
+}

resources/custom_modules/cffi_example/meson.build

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+project(
+    'waybar_cffi_example', 'c',
+    version: '0.1.0',
+    license: 'MIT',
+)
+
+shared_library('wb_cffi_example',
+    ['main.c'],
+    dependencies: [
+        dependency('gtk+-3.0', version : ['>=3.22.0'])
+    ],
+    name_prefix: ''
+)

resources/custom_modules/cffi_example/waybar_cffi_module.h

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+#pragma once
+
+#include <gtk/gtk.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/// Waybar ABI version. 1 is the latest version
+extern const size_t wbcffi_version;
+
+/// Config key-value pair
+struct wbcffi_config_entry {
+  /// Entry key
+  const char* key;
+  /// Entry value as string. JSON object and arrays are serialized.
+  const char* value;
+};
+
+/// Module init/new function, called on module instantiation
+///
+/// MANDATORY CFFI function
+///
+/// @param root_widget        Root GTK widget instantiated by Waybar
+/// @param config_entries     Flat representation of the module JSON config. The data only available
+///                           during wbcffi_init call.
+/// @param config_entries_len Number of entries in `config_entries`
+///
+/// @return A untyped pointer to module data, NULL if the module failed to load.
+void* wbcffi_init(GtkContainer* root_widget, const struct wbcffi_config_entry* config_entries,
+                  size_t config_entries_len);
+
+/// Module deinit/delete function, called when Waybar is closed or when the module is removed
+///
+/// MANDATORY CFFI function
+///
+/// @param instance Module instance data (as returned by `wbcffi_init`)
+void wbcffi_deinit(void* instance);
+
+/// When Waybar receives a POSIX signal, it forwards the signal to each module, calling this
+/// function
+///
+/// Optional CFFI function
+///
+/// @param instance Module instance data (as returned by `wbcffi_init`)
+/// @param signal Signal ID
+void wbcffi_refresh(void* instance, int signal);
+
+///
+/// Optional CFFI function
+///
+/// @param instance Module instance data (as returned by `wbcffi_init`)
+/// @param name Action name
+void wbcffi_doaction(void* instance, const char* name);
+
+#ifdef __cplusplus
+}
+#endif