diff --git a/clients/c/cosmopolite.c b/clients/c/cosmopolite.c
index d378dd9..d797824 100644
--- a/clients/c/cosmopolite.c
+++ b/clients/c/cosmopolite.c
@@ -161,9 +161,12 @@ static void cosmo_handle_message(cosmo *instance, json_t *event) {
       break;
     }
   }
-  printf("new message: %lld\n", id);
   json_array_insert(messages, insert_after + 1, event);
   assert(!pthread_mutex_unlock(&instance->lock));
+
+  if (instance->callbacks.message) {
+    instance->callbacks.message(event);
+  }
 }
 
 static void cosmo_handle_event(cosmo *instance, json_t *event) {
@@ -417,7 +420,7 @@ json_t *cosmo_get_last_message(cosmo *instance, json_t *subject) {
   return ret;
 }
 
-cosmo *cosmo_create(const char *base_url, const char *client_id) {
+cosmo *cosmo_create(const char *base_url, const char *client_id, const cosmo_callbacks *callbacks) {
   curl_global_init(CURL_GLOBAL_DEFAULT);
   srandomdev();
 
@@ -427,6 +430,8 @@ cosmo *cosmo_create(const char *base_url, const char *client_id) {
   strcpy(instance->client_id, client_id);
   cosmo_uuid(instance->instance_id);
 
+  memcpy(&instance->callbacks, callbacks, sizeof(instance->callbacks));
+
   assert(!pthread_mutex_init(&instance->lock, NULL));
   assert(!pthread_cond_init(&instance->cond, NULL));
 
diff --git a/clients/c/cosmopolite.h b/clients/c/cosmopolite.h
index 8b612eb..5086089 100644
--- a/clients/c/cosmopolite.h
+++ b/clients/c/cosmopolite.h
@@ -8,9 +8,14 @@
 
 #define COSMO_UUID_SIZE 37
 
+typedef struct {
+  void (*message)(const json_t *);
+} cosmo_callbacks;
+
 typedef struct {
   char client_id[COSMO_UUID_SIZE];
   char instance_id[COSMO_UUID_SIZE];
+  cosmo_callbacks callbacks;
 
   pthread_mutex_t lock;
   pthread_cond_t cond;
@@ -26,7 +31,7 @@ typedef struct {
 
 void cosmo_uuid(char *uuid);
 
-cosmo *cosmo_create(const char *base_url, const char *client_id);
+cosmo *cosmo_create(const char *base_url, const char *client_id, const cosmo_callbacks *callbacks);
 void cosmo_shutdown(cosmo *instance);
 
 const char *cosmo_current_profile(cosmo *instance);
diff --git a/clients/c/test.c b/clients/c/test.c
index 2339383..ca40b08 100644
--- a/clients/c/test.c
+++ b/clients/c/test.c
@@ -2,19 +2,23 @@
 
 #include "cosmopolite.h"
 
+void on_message(const json_t *message) {
+  printf("new message: %lld\n", json_integer_value(json_object_get(message, "id")));
+}
+
 int main(int argc, char *argv[]) {
   char client_id[COSMO_UUID_SIZE];
   cosmo_uuid(client_id);
-  cosmo *instance = cosmo_create("https://playground.cosmopolite.org/cosmopolite", client_id);
+
+  cosmo_callbacks callbacks = {
+    .message = on_message
+  };
+
+  cosmo *instance = cosmo_create("https://playground.cosmopolite.org/cosmopolite", client_id, &callbacks);
   json_t *subject = cosmo_subject("foobar", NULL, NULL);
   cosmo_subscribe(instance, subject, -1, 0);
-  json_t *message = json_string("test from C");
-  cosmo_send_message(instance, subject, message);
-  json_decref(message);
   json_decref(subject);
-  sleep(5);
-  printf("profile: %s\n", cosmo_current_profile(instance));
-  sleep(120);
+  sleep(20);
   cosmo_shutdown(instance);
 
   return 0;