Implement keyboard/mouse control

To control the device from the computer:
 - retrieve mouse and keyboard SDL events;
 - convert them to Android events;
 - serialize them;
 - send them on the same socket used by the video stream (but in the
 opposite direction);
 - deserialize the events on the Android side;
 - inject them using the InputManager.

app/tests/test_control_event_queue.c

@@ -0,0 +1,94 @@
+#include <assert.h>
+
+#include "controlevent.h"
+
+static void test_control_event_queue_empty() {
+    struct control_event_queue queue;
+    SDL_bool init_ok = control_event_queue_init(&queue);
+    assert(init_ok);
+
+    assert(control_event_queue_is_empty(&queue));
+
+    struct control_event dummy_event;
+    SDL_bool push_ok = control_event_queue_push(&queue, &dummy_event);
+    assert(push_ok);
+    assert(!control_event_queue_is_empty(&queue));
+
+    SDL_bool take_ok = control_event_queue_take(&queue, &dummy_event);
+    assert(take_ok);
+    assert(control_event_queue_is_empty(&queue));
+
+    SDL_bool take_empty_ok = control_event_queue_take(&queue, &dummy_event);
+    assert(!take_empty_ok); // the queue is empty
+
+    control_event_queue_destroy(&queue);
+}
+
+static void test_control_event_queue_full() {
+    struct control_event_queue queue;
+    SDL_bool init_ok = control_event_queue_init(&queue);
+    assert(init_ok);
+
+    assert(!control_event_queue_is_full(&queue));
+
+    struct control_event dummy_event;
+    // fill the queue
+    while (control_event_queue_push(&queue, &dummy_event));
+
+    SDL_bool take_ok = control_event_queue_take(&queue, &dummy_event);
+    assert(take_ok);
+    assert(!control_event_queue_is_full(&queue));
+
+    control_event_queue_destroy(&queue);
+}
+
+static void test_control_event_queue_push_take() {
+    struct control_event_queue queue;
+    SDL_bool init_ok = control_event_queue_init(&queue);
+    assert(init_ok);
+
+    struct control_event event = {
+        .type = CONTROL_EVENT_TYPE_KEYCODE,
+        .keycode_event = {
+            .action = AKEY_EVENT_ACTION_DOWN,
+            .keycode = AKEYCODE_ENTER,
+            .metastate = AMETA_CTRL_LEFT_ON | AMETA_CTRL_ON,
+        },
+    };
+
+    SDL_bool push1_ok = control_event_queue_push(&queue, &event);
+    assert(push1_ok);
+
+    event = (struct control_event) {
+        .type = CONTROL_EVENT_TYPE_TEXT,
+        .text_event = {
+            .text = "abc",
+        },
+    };
+
+    SDL_bool push2_ok = control_event_queue_push(&queue, &event);
+    assert(push2_ok);
+
+    // overwrite event
+    SDL_bool take1_ok = control_event_queue_take(&queue, &event);
+    assert(take1_ok);
+    assert(event.type == CONTROL_EVENT_TYPE_KEYCODE);
+    assert(event.keycode_event.action == AKEY_EVENT_ACTION_DOWN);
+    assert(event.keycode_event.keycode == AKEYCODE_ENTER);
+    assert(event.keycode_event.metastate == (AMETA_CTRL_LEFT_ON | AMETA_CTRL_ON));
+
+    // overwrite event
+    SDL_bool take2_ok = control_event_queue_take(&queue, &event);
+    assert(take2_ok);
+    assert(event.type == CONTROL_EVENT_TYPE_TEXT);
+    assert(!strcmp(event.text_event.text, "abc"));
+
+    control_event_queue_destroy(&queue);
+}
+
+int main() {
+    test_control_event_queue_empty();
+    test_control_event_queue_full();
+    test_control_event_queue_push_take();
+    return 0;
+}