diff --git a/clients/c/cosmopolite.c b/clients/c/cosmopolite.c
index 1c9da9d..4d4348d 100644
--- a/clients/c/cosmopolite.c
+++ b/clients/c/cosmopolite.c
@@ -30,6 +30,17 @@ typedef struct {
   int64_t retry_after;
 } cosmo_transfer;
 
+static json_t *cosmo_find_subscription(cosmo *instance, json_t *subject) {
+  size_t i;
+  json_t *subscription;
+  json_array_foreach(instance->subscriptions, i, subscription) {
+    if (json_equal(json_object_get(subscription, "subject"), subject) == 0) {
+      return subscription;
+    }
+  }
+  return NULL;
+}
+
 static size_t cosmo_read_callback(void *ptr, size_t size, size_t nmemb, void *userp) {
   cosmo_transfer *transfer = userp;
   size_t to_write = min(transfer->send_buf_len, size * nmemb);
@@ -74,13 +85,13 @@ static char *cosmo_build_rpc(const cosmo *instance, const json_t *commands) {
 static bool cosmo_send_http_int(cosmo *instance, cosmo_transfer *transfer) {
   CURLcode res;
  
-  curl_easy_setopt(instance->curl, CURLOPT_POSTFIELDSIZE, transfer->send_buf_len);
-  curl_easy_setopt(instance->curl, CURLOPT_READDATA, transfer);
-  curl_easy_setopt(instance->curl, CURLOPT_WRITEDATA, transfer);
-  curl_easy_setopt(instance->curl, CURLOPT_HEADERDATA, transfer);
+  assert(!curl_easy_setopt(instance->curl, CURLOPT_POSTFIELDSIZE, transfer->send_buf_len));
+  assert(!curl_easy_setopt(instance->curl, CURLOPT_READDATA, transfer));
+  assert(!curl_easy_setopt(instance->curl, CURLOPT_WRITEDATA, transfer));
+  assert(!curl_easy_setopt(instance->curl, CURLOPT_HEADERDATA, transfer));
   res = curl_easy_perform(instance->curl);
 
-  if (res != CURLE_OK) {
+  if (res) {
     fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res));
     return false;
   }
@@ -256,7 +267,7 @@ json_t *cosmo_subject(const char *name, const char *readable_only_by, const char
   return ret;
 }
 
-void cosmo_subscribe(cosmo *instance, const json_t *subject, const json_int_t messages, const json_int_t last_id) {
+void cosmo_subscribe(cosmo *instance, json_t *subject, const json_int_t messages, const json_int_t last_id) {
   json_t *arguments = json_pack("{sO}", "subject", subject);
   if (messages) {
     json_object_set_new(arguments, "messages", json_integer(messages));
@@ -264,9 +275,30 @@ void cosmo_subscribe(cosmo *instance, const json_t *subject, const json_int_t me
   if (last_id) {
     json_object_set_new(arguments, "last_id", json_integer(last_id));
   }
+
+  assert(!pthread_mutex_lock(&instance->lock));
+  json_t *subscription = cosmo_find_subscription(instance, subject);
+  if (!subscription) {
+    json_array_append_new(instance->subscriptions, json_pack("{sOs[]s[]}", "subject", subject, "messages", "pins"));
+  }
+  assert(!pthread_mutex_unlock(&instance->lock));
+
   cosmo_send_command(instance, cosmo_command("subscribe", arguments));
 }
 
+void cosmo_unsubscribe(cosmo *instance, json_t *subject) {
+  assert(!pthread_mutex_lock(&instance->lock));
+  size_t i;
+  json_t *subscription;
+  json_array_foreach(instance->subscriptions, i, subscription) {
+    if (json_equal(json_object_get(subscription, "subject"), subject) == 0) {
+      json_array_remove(instance->subscriptions, i);
+      break;
+    }
+  }
+  assert(!pthread_mutex_unlock(&instance->lock));
+}
+
 void cosmo_send_message(cosmo *instance, const json_t *subject, json_t *message) {
   char sender_message_id[COSMO_UUID_SIZE];
   cosmo_uuid(sender_message_id);
@@ -296,18 +328,23 @@ cosmo *cosmo_create(const char *base_url, const char *client_id) {
   assert(instance->curl);
   char api_url[strlen(base_url) + 5];
   sprintf(api_url, "%s/api", base_url);
-  curl_easy_setopt(instance->curl, CURLOPT_URL, api_url);
-  curl_easy_setopt(instance->curl, CURLOPT_PROTOCOLS, CURLPROTO_HTTPS);
-  curl_easy_setopt(instance->curl, CURLOPT_REDIR_PROTOCOLS, CURLPROTO_HTTPS);
-  curl_easy_setopt(instance->curl, CURLOPT_SSL_CIPHER_LIST, "ECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH");
-  curl_easy_setopt(instance->curl, CURLOPT_TIMEOUT, COSMO_CHECK_SECONDS);
-  curl_easy_setopt(instance->curl, CURLOPT_POST, 1L);
-  curl_easy_setopt(instance->curl, CURLOPT_READFUNCTION, cosmo_read_callback);
-  curl_easy_setopt(instance->curl, CURLOPT_WRITEFUNCTION, cosmo_write_callback);
-  curl_easy_setopt(instance->curl, CURLOPT_HEADERFUNCTION, cosmo_header_callback);
+  assert(!curl_easy_setopt(instance->curl, CURLOPT_URL, api_url));
+  assert(!curl_easy_setopt(instance->curl, CURLOPT_PROTOCOLS, CURLPROTO_HTTPS));
+  assert(!curl_easy_setopt(instance->curl, CURLOPT_REDIR_PROTOCOLS, CURLPROTO_HTTPS));
+  assert(!curl_easy_setopt(instance->curl, CURLOPT_SSL_CIPHER_LIST, "ECDH+AESGCM:EDH+AESGCM:AES256+EECDH:AES256+EDH"));
+  assert(!curl_easy_setopt(instance->curl, CURLOPT_TIMEOUT, COSMO_CHECK_SECONDS));
+  assert(!curl_easy_setopt(instance->curl, CURLOPT_POST, 1L));
+  assert(!curl_easy_setopt(instance->curl, CURLOPT_READFUNCTION, cosmo_read_callback));
+  assert(!curl_easy_setopt(instance->curl, CURLOPT_WRITEFUNCTION, cosmo_write_callback));
+  assert(!curl_easy_setopt(instance->curl, CURLOPT_HEADERFUNCTION, cosmo_header_callback));
 
   instance->shutdown = false;
+  instance->profile = NULL;
   instance->command_queue = json_array();
+  assert(instance->command_queue);
+  instance->subscriptions = json_array();
+  assert(instance->subscriptions);
+  instance->next_delay_ms = 0;
 
   assert(!pthread_create(&instance->thread, NULL, cosmo_thread_main, instance));
   return instance;
@@ -324,6 +361,7 @@ void cosmo_shutdown(cosmo *instance) {
   assert(!pthread_mutex_destroy(&instance->lock));
   assert(!pthread_cond_destroy(&instance->cond));
   json_decref(instance->command_queue);
+  json_decref(instance->subscriptions);
   free(instance->profile);
   curl_easy_cleanup(instance->curl);
 
diff --git a/clients/c/cosmopolite.h b/clients/c/cosmopolite.h
index 980a0a0..9677fdb 100644
--- a/clients/c/cosmopolite.h
+++ b/clients/c/cosmopolite.h
@@ -15,10 +15,10 @@ typedef struct {
   pthread_mutex_t lock;
   pthread_cond_t cond;
   bool shutdown;
-  json_t *command_queue;
-  uint64_t next_delay_ms;
-
   char *profile;
+  json_t *command_queue;
+  json_t *subscriptions;
+  uint64_t next_delay_ms;
 
   pthread_t thread;
   CURL *curl;
@@ -32,11 +32,11 @@ void cosmo_shutdown(cosmo *instance);
 const char *cosmo_current_profile(cosmo *instance);
 
 json_t *cosmo_subject(const char *name, const char *readable_only_by, const char *writeable_only_by);
-void cosmo_subscribe(cosmo *instance, const json_t *subject, const json_int_t messages, const json_int_t last_id);
+void cosmo_subscribe(cosmo *instance, json_t *subject, const json_int_t messages, const json_int_t last_id);
+void cosmo_unsubscribe(cosmo *instance, json_t *subject);
 void cosmo_send_message(cosmo *instance, const json_t *subject, json_t *message);
 
 // TODO
-void cosmo_unsubscribe(cosmo *instance, const json_t *subject);
 json_t *cosmo_get_messages(cosmo *instance, const json_t *subject);
 json_t *cosmo_get_last_message(cosmo *instance, const json_t *subject);
 json_t *cosmo_get_pins(cosmo *instance, const json_t *subject);