diff --git a/clients/c/test.c b/clients/c/test.c
index a8b77a7..87629de 100644
--- a/clients/c/test.c
+++ b/clients/c/test.c
@@ -11,13 +11,12 @@
 #include <uuid/uuid.h>
 
 #define COSMO_UUID_SIZE 37
-#define COSMO_CLIENT_ID_SIZE COSMO_UUID_SIZE
 #define COSMO_CHECK_SECONDS 10
 
 #define min(a, b) ((a) < (b) ? (a) : (b))
 
 typedef struct {
-  char client_id[COSMO_CLIENT_ID_SIZE];
+  char client_id[COSMO_UUID_SIZE];
   char instance_id[COSMO_UUID_SIZE];
 
   pthread_mutex_t lock;
@@ -36,12 +35,6 @@ typedef struct {
   size_t recv_buf_len;
 } cosmo_transfer;
 
-static void cosmo_generate_uuid(char *uuid) {
-  uuid_t uu;
-  uuid_generate(uu);
-  uuid_unparse_lower(uu, uuid);
-}
-
 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);
@@ -102,7 +95,7 @@ static bool cosmo_send_http_int(cosmo *instance, cosmo_transfer *transfer, CURL
   return true;
 }
 
-// Takes ownership of request
+// Takes ownership of request.
 static char *cosmo_send_http(cosmo *instance, char *request) {
   CURL *curl = curl_easy_init();
   assert(curl);
@@ -121,12 +114,13 @@ static char *cosmo_send_http(cosmo *instance, char *request) {
   return ret ? transfer.recv_buf : NULL;
 }
 
-static void cosmo_send_rpc(cosmo *instance, json_t *commands) {
+// Takes ownership of commands.
+static json_t *cosmo_send_rpc(cosmo *instance, json_t *commands) {
   char *request = cosmo_build_rpc(instance, commands);
 
   char *response = cosmo_send_http(instance, request);
   if (!response) {
-    return;
+    return commands;
   }
 
   json_error_t error;
@@ -134,12 +128,39 @@ static void cosmo_send_rpc(cosmo *instance, json_t *commands) {
   if (!received) {
     fprintf(stderr, "json_loads() failed: %s (json: \"%s\")\n", error.text, response);
     free(response);
-    return;
+    return commands;
   }
   printf("response: %s\n", response);
   free(response);
 
+  json_t *command_responses = json_object_get(received, "responses");
+  if (!command_responses) {
+    fprintf(stderr, "response lacks \"responses\" key\n");
+    return commands;
+  }
+
+  json_t *to_retry = json_array();
+  size_t index;
+  json_t *command;
+  json_array_foreach(commands, index, command) {
+    json_t *command_response = json_array_get(command_responses, index);
+    json_t *result = json_object_get(command_response, "result");
+    if (!result) {
+      fprintf(stderr, "response lacks \"result\" key\n");
+      json_array_append(to_retry, command);
+      continue;
+    }
+    if (!strcmp(json_string_value(result), "retry")) {
+      json_array_append(to_retry, command);
+      continue;
+    }
+    // Other result code.
+  }
+
+  json_decref(commands);
   json_decref(received);
+
+  return to_retry;
 }
 
 static void *cosmo_thread_main(void *arg) {
@@ -150,9 +171,13 @@ static void *cosmo_thread_main(void *arg) {
     while (json_array_size(instance->command_queue)) {
       json_t *commands = instance->command_queue;
       instance->command_queue = json_array();
+
       assert(!pthread_mutex_unlock(&instance->lock));
-      cosmo_send_rpc(instance, commands);
+      json_t *to_retry = cosmo_send_rpc(instance, commands);
       assert(!pthread_mutex_lock(&instance->lock));
+
+      json_array_extend(instance->command_queue, to_retry);
+      json_decref(to_retry);
     }
     assert(!pthread_cond_wait(&instance->cond, &instance->lock));
   }
@@ -177,8 +202,10 @@ static json_t *cosmo_command(char *name, json_t *arguments) {
 
 // Public interface below
 
-void cosmo_generate_client_id(char *client_id) {
-  cosmo_generate_uuid(client_id);
+void cosmo_generate_uuid(char *uuid) {
+  uuid_t uu;
+  uuid_generate(uu);
+  uuid_unparse_lower(uu, uuid);
 }
 
 json_t *cosmo_subject(char *name, char *readable_only_by, char *writeable_only_by) {
@@ -235,8 +262,8 @@ void cosmo_destroy(cosmo *instance) {
 
 
 int main(int argc, char *argv[]) {
-  char client_id[COSMO_CLIENT_ID_SIZE];
-  cosmo_generate_client_id(client_id);
+  char client_id[COSMO_UUID_SIZE];
+  cosmo_generate_uuid(client_id);
   cosmo *instance = cosmo_create(client_id);
   json_t *subject = cosmo_subject("foobar", NULL, NULL);
   cosmo_subscribe(instance, subject, -1, 0);