Add GET_CLIPBOARD device event

Add the first device event, used to forward the device clipboard to the
computer.

app/src/device_event.c

@@ -0,0 +1,48 @@
+#include "device_event.h"
+
+#include <string.h>
+#include <SDL2/SDL_assert.h>
+
+#include "buffer_util.h"
+#include "log.h"
+
+ssize_t
+device_event_deserialize(const unsigned char *buf, size_t len,
+                         struct device_event *event) {
+    if (len < 3) {
+        // at least type + empty string length
+        return 0; // not available
+    }
+
+    event->type = buf[0];
+    switch (event->type) {
+        case DEVICE_EVENT_TYPE_GET_CLIPBOARD: {
+            uint16_t clipboard_len = buffer_read16be(&buf[1]);
+            if (clipboard_len > len - 3) {
+                return 0; // not available
+            }
+            char *text = SDL_malloc(clipboard_len + 1);
+            if (!text) {
+                LOGW("Could not allocate text for clipboard");
+                return -1;
+            }
+            if (clipboard_len) {
+                memcpy(text, &buf[3], clipboard_len);
+            }
+            text[clipboard_len] = '\0';
+
+            event->clipboard_event.text = text;
+            return 3 + clipboard_len;
+        }
+        default:
+            LOGW("Unsupported device event type: %d", (int) event->type);
+            return -1; // error, we cannot recover
+    }
+}
+
+void
+device_event_destroy(struct device_event *event) {
+    if (event->type == DEVICE_EVENT_TYPE_GET_CLIPBOARD) {
+        SDL_free(event->clipboard_event.text);
+    }
+}

app/src/device_event.h

@@ -0,0 +1,33 @@
+#ifndef DEVICEEVENT_H
+#define DEVICEEVENT_H
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <unistd.h>
+
+#define DEVICE_EVENT_QUEUE_SIZE 64
+#define DEVICE_EVENT_TEXT_MAX_LENGTH 4093
+#define DEVICE_EVENT_SERIALIZED_MAX_SIZE (3 + DEVICE_EVENT_TEXT_MAX_LENGTH)
+
+enum device_event_type {
+    DEVICE_EVENT_TYPE_GET_CLIPBOARD,
+};
+
+struct device_event {
+    enum device_event_type type;
+    union {
+        struct {
+            char *text; // owned, to be freed by SDL_free()
+        } clipboard_event;
+    };
+};
+
+// return the number of bytes consumed (0 for no event available, -1 on error)
+ssize_t
+device_event_deserialize(const unsigned char *buf, size_t len,
+                         struct device_event *event);
+
+void
+device_event_destroy(struct device_event *event);
+
+#endif