put mds-registry in its own directory

Signed-off-by: Mattias Andrée <maandree@operamail.com>

2 files changed, 981 insertions, 0 deletions

diff --git a/src/mds-registry/mds-registry.c b/src/mds-registry/mds-registry.c
new file mode 100644
index 0000000..b0c6962
--- /dev/null
+++ b/src/mds-registry/mds-registry.c
@@ -0,0 +1,890 @@
+/**
+ * mds — A micro-display server
+ * Copyright © 2014  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include "mds-registry.h"
+
+#include <libmdsserver/macros.h>
+#include <libmdsserver/util.h>
+#include <libmdsserver/mds-message.h>
+#include <libmdsserver/hash-table.h>
+#include <libmdsserver/hash-help.h>
+#include <libmdsserver/client-list.h>
+
+#include <errno.h>
+#include <inttypes.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+#define reconnect_to_display() -1 /* TODO */
+
+
+
+#define MDS_REGISTRY_VARS_VERSION  0
+
+
+
+/**
+ * This variable should declared by the actual server implementation.
+ * It must be configured before `main` is invoked.
+ * 
+ * This tells the server-base how to behave
+ */
+server_characteristics_t server_characteristics =
+  {
+    .require_privileges = 0,
+    .require_display = 1,
+    .require_respawn_info = 0,
+    .sanity_check_argc = 1
+  };
+
+
+
+/**
+ * Value of the ‘Message ID’ header for the next message
+ */
+static int32_t message_id = 2;
+
+/**
+ * Buffer for received messages
+ */
+static mds_message_t received;
+
+/**
+ * Whether the server is connected to the display
+ */
+static int connected = 1;
+
+/**
+ * Protocol registry table
+ */
+static hash_table_t reg_table;
+
+/**
+ * Reusable buffer for data to send
+ */
+static char* send_buffer = NULL;
+
+/**
+ * The size of `send_buffer`
+ */
+static size_t send_buffer_size = 0;
+
+/**
+ * General mutex
+ */
+static pthread_mutex_t reg_mutex;
+
+/**
+ * General condition
+ */
+static pthread_cond_t reg_cond;
+
+/**
+ * Used to temporarily store the old value when reallocating heap-allocations
+ */
+static char* old;
+
+
+
+/**
+ * This function will be invoked before `initialise_server` (if not re-exec:ing)
+ * or before `unmarshal_server` (if re-exec:ing)
+ * 
+ * @return  Non-zero on error
+ */
+int __attribute__((const)) preinitialise_server(void)
+{
+  if ((errno = pthread_mutex_init(&reg_mutex, NULL)))
+    {
+      perror(*argv);
+      return 1;
+    }
+  
+  if ((errno = pthread_cond_init(&reg_cond, NULL)))
+    {
+      perror(*argv);
+      pthread_mutex_destroy(&reg_mutex);
+      return 1;
+    }
+  
+  return 0;
+}
+
+
+/**
+ * This function should initialise the server,
+ * and it not invoked after a re-exec.
+ * 
+ * @return  Non-zero on error
+ */
+int initialise_server(void)
+{
+  const char* const message =
+    "Command: intercept\n"
+    "Message ID: 0\n"
+    "Length: 32\n"
+    "\n"
+    "Command: register\n"
+    "Client closed\n"
+    /* -- NEXT MESSAGE -- */
+    "Command: reregister\n"
+    "Message ID: 1\n"
+    "\n";
+  
+  /* We are asking all servers to reregister their
+     protocols for two reasons:
+     
+     1) The server would otherwise not get registrations
+        from servers started before this server.
+     2) If this server crashes we may miss registrations
+        that happen between the crash and the recovery.
+   */
+  
+  if (full_send(message, strlen(message)))
+    return 1;
+  if (hash_table_create_tuned(&reg_table, 32))
+    {
+      perror(*argv);
+      hash_table_destroy(&reg_table, NULL, NULL);
+      return 1;
+    }
+  reg_table.key_comparator = (compare_func*)string_comparator;
+  reg_table.hasher = (hash_func*)string_hash;
+  server_initialised();
+  mds_message_initialise(&received);
+  return 0;
+}
+
+
+/**
+ * This function will be invoked after `initialise_server` (if not re-exec:ing)
+ * or after `unmarshal_server` (if re-exec:ing)
+ * 
+ * @return  Non-zero on error
+ */
+int postinitialise_server(void)
+{
+  if (connected)
+    return 0;
+  
+  if (reconnect_to_display())
+    {
+      mds_message_destroy(&received);
+      return 1;
+    }
+  connected = 1;
+  return 0;
+}
+
+
+/**
+ * Calculate the number of bytes that will be stored by `marshal_server`
+ * 
+ * On failure the program should `abort()` or exit by other means.
+ * However it should not be possible for this function to fail.
+ * 
+ * @return  The number of bytes that will be stored by `marshal_server`
+ */
+size_t marshal_server_size(void)
+{
+  size_t i, rc = 2 * sizeof(int) + sizeof(int32_t) + 3 * sizeof(size_t);
+  hash_entry_t* entry;
+  
+  rc += mds_message_marshal_size(&received);
+  
+  foreach_hash_table_entry (reg_table, i, entry)
+    {
+      char* command = (char*)(void*)(entry->key);
+      size_t len = strlen(command) + 1;
+      client_list_t* list = (client_list_t*)(void*)(entry->value);
+      
+      rc += len + sizeof(size_t) + client_list_marshal_size(list);
+    }
+  
+  return rc;
+}
+
+
+/**
+ * Marshal server implementation specific data into a buffer
+ * 
+ * @param   state_buf  The buffer for the marshalled data
+ * @return             Non-zero on error
+ */
+int marshal_server(char* state_buf)
+{
+  size_t i, n = mds_message_marshal_size(&received);
+  hash_entry_t* entry;
+  
+  buf_set_next(state_buf, int, MDS_REGISTRY_VARS_VERSION);
+  buf_set_next(state_buf, int, connected);
+  buf_set_next(state_buf, int32_t, message_id);
+  buf_set_next(state_buf, size_t, n);
+  mds_message_marshal(&received, state_buf);
+  state_buf += n / sizeof(char);
+  
+  buf_set_next(state_buf, size_t, reg_table.capacity);
+  buf_set_next(state_buf, size_t, reg_table.size);
+  foreach_hash_table_entry (reg_table, i, entry)
+    {
+      char* command = (char*)(void*)(entry->key);
+      size_t len = strlen(command) + 1;
+      client_list_t* list = (client_list_t*)(void*)(entry->value);
+      
+      memcpy(state_buf, command, len * sizeof(char));
+      state_buf += len;
+      
+      n = client_list_marshal_size(list);
+      buf_set_next(state_buf, size_t, n);
+      client_list_marshal(list, state_buf);
+      state_buf += n / sizeof(char);
+    }
+  
+  hash_table_destroy(&reg_table, (free_func*)reg_table_free_key, (free_func*)reg_table_free_value);
+  mds_message_destroy(&received);
+  return 0;
+}
+
+
+/**
+ * Unmarshal server implementation specific data and update the servers state accordingly
+ * 
+ * On critical failure the program should `abort()` or exit by other means.
+ * That is, do not let `reexec_failure_recover` run successfully, if it unrecoverable
+ * error has occurred or one severe enough that it is better to simply respawn.
+ * 
+ * @param   state_buf  The marshalled data that as not been read already
+ * @return             Non-zero on error
+ */
+int unmarshal_server(char* state_buf)
+{
+  char* command;
+  client_list_t* list;
+  size_t i, n, m;
+  int stage = 0;
+  
+  /* buf_get_next(state_buf, int, MDS_REGISTRY_VARS_VERSION); */
+  buf_next(state_buf, int, 1);
+  buf_get_next(state_buf, int, connected);
+  buf_get_next(state_buf, int32_t, message_id);
+  buf_get_next(state_buf, size_t, n);
+  fail_if (mds_message_unmarshal(&received, state_buf));
+  state_buf += n / sizeof(char);
+  stage = 1;
+  
+  buf_get_next(state_buf, size_t, n);
+  fail_if (hash_table_create_tuned(&reg_table, n));
+  buf_get_next(state_buf, size_t, n);
+  for (i = 0; i < n; i++)
+    {
+      stage = 1;
+      fail_if ((command = strdup(state_buf)) == NULL);
+      state_buf += strlen(command) + 1;
+      
+      stage = 2;
+      fail_if ((list = malloc(sizeof(client_list_t))) == NULL);
+      buf_get_next(state_buf, size_t, m);
+      stage = 3;
+      fail_if (client_list_unmarshal(list, state_buf));
+      state_buf += m / sizeof(char);
+      
+      hash_table_put(&reg_table, (size_t)(void*)command, (size_t)(void*)list);
+      fail_if (errno);
+    }
+  
+  reg_table.key_comparator = (compare_func*)string_comparator;
+  reg_table.hasher = (hash_func*)string_hash;
+  
+  return 0;
+ pfail:
+  perror(*argv);
+  mds_message_destroy(&received);
+  if (stage >= 1)
+    hash_table_destroy(&reg_table, (free_func*)reg_table_free_key, (free_func*)reg_table_free_value);
+  if (stage >= 2)
+    free(command);
+  if (stage >= 3)
+    {
+      client_list_destroy(list);
+      free(list);
+    }
+  abort();
+  return -1;
+}
+
+
+/**
+ * Attempt to recover from a re-exec failure that has been
+ * detected after the server successfully updated it execution image
+ * 
+ * @return  Non-zero on error
+ */
+int __attribute__((const)) reexec_failure_recover(void)
+{
+  return -1;
+}
+
+
+/**
+ * Perform the server's mission
+ * 
+ * @return  Non-zero on error
+ */
+int master_loop(void)
+{
+  int rc = 1;
+  
+  while (!reexecing && !terminating)
+    {
+      int r = mds_message_read(&received, socket_fd);
+      if (r == 0)
+	{
+	  r = handle_message();
+	  if (r == 0)
+	    continue;
+	}
+      
+      if (r == -2)
+	{
+	  eprint("corrupt message received, aborting.");
+	  goto fail;
+	}
+      else if (errno == EINTR)
+	continue;
+      else if (errno != ECONNRESET)
+	goto pfail;
+      
+      eprint("lost connection to server.");
+      mds_message_destroy(&received);
+      mds_message_initialise(&received);
+      connected = 0;
+      if (reconnect_to_display())
+	goto fail;
+      connected = 1;
+    }
+  
+  rc = 0;
+  goto fail;
+ pfail:
+  perror(*argv);
+ fail:
+  if (rc || !reexecing)
+    {
+      hash_table_destroy(&reg_table, (free_func*)reg_table_free_key, (free_func*)reg_table_free_value);
+      mds_message_destroy(&received);
+    }
+  pthread_mutex_destroy(&reg_mutex);
+  pthread_cond_destroy(&reg_cond);
+  free(send_buffer);
+  return rc;
+}
+
+
+/**
+ * Handle the received message containing ‘Command: register’-header–value
+ * 
+ * @return  Zero on success -1 on error or interruption,
+ *          errno will be set accordingly
+ */
+static int handle_register_message(void)
+{
+  const char* recv_client_id = NULL;
+  const char* recv_message_id = NULL;
+  const char* recv_length = NULL;
+  const char* recv_action = NULL;
+  size_t i, length = 0;
+  
+#define __get_header(storage, header)  \
+  (startswith(received.headers[i], header))  \
+    storage = received.headers[i] + strlen(header)
+  
+  for (i = 0; i < received.header_count; i++)
+    {
+      if      __get_header(recv_client_id,  "Client ID: ");
+      else if __get_header(recv_message_id, "Message ID: ");
+      else if __get_header(recv_length,     "Length: ");
+      else if __get_header(recv_action,     "Action: ");
+      else
+	continue;
+      if (recv_client_id && recv_message_id && recv_length && recv_action)
+	break;
+    }
+  
+#undef __get_header
+  
+  
+  if ((recv_client_id == NULL) || (strequals(recv_client_id, "0:0")))
+    {
+      eprint("received message from anonymous sender, ignoring.");
+      return 0;
+    }
+  else if (strchr(recv_client_id, ':') == NULL)
+    {
+      eprint("received message from sender without a colon it its ID, ignoring, invalid ID.");
+      return 0;
+    }
+  else if ((recv_length == NULL) && ((recv_action == NULL) || !strequals(recv_action, "list")))
+    {
+      eprint("received empty message without `Action: list`, ignoring, has no effect.");
+      return 0;
+    }
+  else if (recv_message_id == NULL)
+    {
+      eprint("received message with ID, ignoring, master server is misbehaving.");
+      return 0;
+    }
+  
+  
+  if (recv_length != NULL)
+    length = (size_t)atoll(recv_length);
+  if (recv_action != NULL)
+    recv_action = "add";
+  
+#define __registry_action(action)  registry_action(length, action, recv_client_id, recv_message_id)
+  
+  if      (strequals(recv_action, "add"))     return __registry_action(1);
+  else if (strequals(recv_action, "remove"))  return __registry_action(-1);
+  else if (strequals(recv_action, "wait"))    return __registry_action(0);
+  else if (strequals(recv_action, "list"))    return list_registry(recv_client_id, recv_message_id);
+  else
+    {
+      eprint("received invalid action, ignoring.");
+      return 0;
+    }
+  
+#undef __registry_action
+}
+
+
+/**
+ * Handle the received message containing a ‘Client closed’-header
+ * 
+ * @return  Zero on success -1 on error or interruption,
+ *          errno will be set accordingly
+ */
+static int handle_close_message(void)
+{
+  /* Servers do not close too often, there is no need to
+     optimise this with another hash table. */
+  
+  size_t i, j, ptr = 0, size = 1;
+  size_t* keys = NULL;
+  size_t* old_keys;
+  
+  fail_if ((errno = pthread_mutex_lock(&reg_mutex)));
+  
+  for (i = 0; i < received.header_count; i++)
+    if (startswith(received.headers[i], "Client closed: "))
+      {
+	uint64_t client = parse_client_id(received.headers[i] + strlen("Client closed: "));
+	hash_entry_t* entry;
+	
+	foreach_hash_table_entry (reg_table, j, entry)
+	  {
+	    client_list_t* list = (client_list_t*)(void*)(entry->value);
+	    client_list_remove(list, client);
+	    if (list->size)
+	      continue;
+	    
+	    fail_if ((keys == NULL) && xmalloc(keys, size, size_t));
+	    if (ptr == size ? growalloc(old_keys, keys, size, size_t) : 0)
+	      goto fail;
+	    keys[ptr++] = entry->key;
+	  }
+      }
+  
+  for (i = 0; i < ptr; i++)
+    {
+      hash_entry_t* entry = hash_table_get_entry(&reg_table, keys[i]);
+      client_list_t* list = (client_list_t*)(void*)(entry->value);
+      char* command = (char*)(void*)(entry->key);
+      
+      hash_table_remove(&reg_table, entry->key);
+      
+      client_list_destroy(list);
+      free(list);
+      free(command);
+    }
+  
+  pthread_mutex_unlock(&reg_mutex);
+  
+  free(keys);
+  return 0;
+ pfail:
+  perror(*argv);
+ fail:
+  free(keys);
+  return -1;
+}
+
+
+/**
+ * Handle the received message
+ * 
+ * @return  Zero on success -1 on error or interruption,
+ *          errno will be set accordingly
+ */
+int handle_message(void)
+{
+  size_t i;
+  for (i = 0; i < received.header_count; i++)
+    if (strequals(received.headers[i], "Command: register"))
+      return handle_register_message();
+  return handle_close_message();
+}
+
+
+/**
+ * Convert a client ID string into a client ID integer
+ * 
+ * @param   str  The client ID string
+ * @return       The client ID integer
+ */
+uint64_t parse_client_id(const char* str)
+{
+  char client_words[22];
+  char* client_high;
+  char* client_low;
+  uint64_t client;
+  
+  strcpy(client_high = client_words, str);
+  client_low = rawmemchr(client_words, ':');
+  *client_low++ = '\0';
+  client = (uint64_t)atoll(client_high);
+  client <<= 32;
+  client |= (uint64_t)atoll(client_low);
+  
+  return client;
+}
+
+
+/**
+ * Add a protocol to the registry
+ * 
+ * @param   has_key      Whether the command is already in the registry
+ * @param   command      The command
+ * @param   command_key  The address of `command`
+ * @param   client       The ID of the client that implements the server-side of the protocol
+ * @return               Non-zero on error
+ */
+static int registry_action_add(int has_key, char* command, size_t command_key, uint64_t client)
+{
+  if (has_key)
+    {
+      size_t address = hash_table_get(&reg_table, command_key);
+      client_list_t* list = (client_list_t*)(void*)address;
+      if (client_list_add(list, client) < 0)
+	goto pfail;
+    }
+  else
+    {
+      client_list_t* list = malloc(sizeof(client_list_t));
+      void* address = list;
+      if (list == NULL)
+	goto pfail;
+      if ((command = strdup(command)) == NULL)
+	{
+	  free(list);
+	  goto pfail;
+	}
+      command_key = (size_t)(void*)command;
+      if (client_list_create(list, 1) ||
+	  client_list_add(list, client) ||
+	  (hash_table_put(&reg_table, command_key, (size_t)address) == 0))
+	{
+	  client_list_destroy(list);
+	  free(list);
+	  free(command);
+	  goto pfail;
+	}
+    }
+  
+  return 0;
+ pfail:
+  perror(*argv);
+  return -1;
+}
+
+
+/**
+ * Remove a protocol from the registry
+ * 
+ * @param   command_key  The address of a string that contains the command
+ * @param   client       The ID of the client that implements the server-side of the protocol
+ * @return               Non-zero on error
+ */
+static void registry_action_remove(size_t command_key, uint64_t client)
+{
+  hash_entry_t* entry = hash_table_get_entry(&reg_table, command_key);
+  size_t address = entry->value;
+  client_list_t* list = (client_list_t*)(void*)address;
+  client_list_remove(list, client);
+  if (list->size == 0)
+    {
+      client_list_destroy(list);
+      free(list);
+      hash_table_remove(&reg_table, command_key);
+      reg_table_free_key(entry->key);
+    }
+}
+
+
+/**
+ * Modify the protocol registry or list missing protocols
+ * 
+ * @param   command      The command
+ * @param   action       -1 to remove command, +1 to add commands, 0 to
+ *                       wait until the message commnds are registered
+ * @param   client       The ID of the client that implements the server-side of the protocol
+ * @param   wait_set     Table to fill with missing protocols if `action == 0`
+ * @return               Non-zero on error
+ */
+static int registry_action_act(char* command, int action, uint64_t client, hash_table_t* wait_set)
+{
+  size_t command_key = (size_t)(void*)command;
+  int has_key = hash_table_contains_key(&reg_table, command_key);
+  
+  if (action == 1)
+    {
+      if (registry_action_add(has_key, command, command_key, client))
+	return -1;
+    }
+  else if ((action == -1) && has_key)
+    registry_action_remove(command_key, client);
+  else if ((action == 0) && !has_key)
+    {
+      if ((command = strdup(command)) == NULL)
+	goto pfail_wait;
+      command_key = (size_t)(void*)command;
+      if (hash_table_put(wait_set, command_key, 1) == 0)
+	if (errno)
+	  {
+	    free(command);
+	    goto pfail_wait;
+	  }
+    }
+  
+  return 0;
+ pfail_wait:
+  perror(*argv);
+  hash_table_destroy(wait_set, (free_func*)reg_table_free_key, NULL);
+  free(wait_set);
+  return -1;
+}
+
+
+/**
+ * Perform an action over the registry
+ * 
+ * @param   length           The length of the received message
+ * @param   action           -1 to remove command, +1 to add commands, 0 to
+ *                           wait until the message commnds are registered
+ * @param   recv_client_id   The ID of the client
+ * @param   recv_message_id  The ID of the received message
+ * @return                   Zero on success -1 on error or interruption,
+ *                           errno will be set accordingly
+ */
+int registry_action(size_t length, int action, const char* recv_client_id, const char* recv_message_id)
+{
+  char* payload = received.payload;
+  uint64_t client = action ? parse_client_id(recv_client_id) : 0;
+  hash_table_t* wait_set = NULL;
+  size_t begin;
+  
+  if (action == 0)
+    {
+      wait_set = malloc(sizeof(hash_table_t));
+      if (hash_table_create(wait_set))
+	{
+	  hash_table_destroy(wait_set, NULL, NULL);
+	  free(wait_set);
+	  goto pfail;
+	}
+      wait_set->key_comparator = (compare_func*)string_comparator;
+      wait_set->hasher = (hash_func*)string_hash;
+    }
+  
+  if (received.payload_size == length)
+    {
+      if (growalloc(old, received.payload, received.payload_size, char))
+	{
+	  if (wait_set != NULL)
+	    hash_table_destroy(wait_set, NULL, NULL), free(wait_set);
+	  return -1;
+	}
+      else
+	payload = received.payload;
+    }
+  
+  payload[length] = '\n';
+  
+  fail_if ((errno = pthread_mutex_lock(&reg_mutex)));
+  
+  for (begin = 0; begin < length;)
+    {
+      char* end = rawmemchr(payload + begin, '\n');
+      size_t len = (size_t)(end - payload) - begin - 1;
+      char* command = payload + begin;
+      
+      command[len] = '\0';
+      begin += len + 1;
+      
+      if (registry_action_act(command, action, client, wait_set))
+	goto fail_in_mutex;
+    }
+  
+  pthread_mutex_unlock(&reg_mutex);
+  
+  if (action == 0)
+    {
+      /* FIXME */
+    }
+  
+  return 0;
+  
+  
+ pfail:
+  perror(*argv);
+  return -1;
+ fail_in_mutex:
+  pthread_mutex_unlock(&reg_mutex);
+  return -1;
+}
+
+
+/**
+ * Send a list of all registered commands to a client
+ * 
+ * @param   recv_client_id   The ID of the client
+ * @param   recv_message_id  The ID of the received message
+ * @return                   Zero on success -1 on error or interruption,
+ *                           errno will be set accordingly
+ */
+int list_registry(const char* recv_client_id, const char* recv_message_id)
+{
+  size_t ptr = 0, i;
+  hash_entry_t* entry;
+  
+  if (send_buffer_size == 0)
+    {
+      fail_if (xmalloc(send_buffer, 256, char));
+      send_buffer_size = 256;
+    }
+  
+  fail_if ((errno = pthread_mutex_lock(&reg_mutex)));
+  
+  foreach_hash_table_entry (reg_table, i, entry)
+    {
+      size_t key = entry->key;
+      char* command = (char*)(void*)key;
+      size_t len = strlen(command);
+      
+      while (ptr + len + 1 >= send_buffer_size)
+	if (growalloc(old, send_buffer, send_buffer_size, char))
+	  goto fail_in_mutex;
+      
+      memcpy(send_buffer + ptr, command, len * sizeof(char));
+      ptr += len;
+      send_buffer[ptr++] = '\n';
+    }
+  
+  i = strlen(recv_message_id) + strlen(recv_client_id) + 10 + 19;
+  i += strlen("To: %s\nIn response to: %s\nMessage ID: %" PRIi32 "\nLength: %" PRIu64 "\n\n");
+  
+  while (ptr + i >= send_buffer_size)
+    {
+      if (growalloc(old, send_buffer, send_buffer_size, char))
+	goto fail_in_mutex;
+    }
+  
+  sprintf(send_buffer + ptr, "To: %s\nIn response to: %s\nMessage ID: %" PRIi32 "\nLength: %" PRIu64 "\n\n",
+	  recv_message_id, recv_client_id, message_id, ptr);
+  
+  message_id = message_id == INT32_MAX ? 0 : (message_id + 1);
+  
+  pthread_mutex_unlock(&reg_mutex);
+  
+  if (full_send(send_buffer + ptr, strlen(send_buffer + ptr)))
+    return 1;
+  return full_send(send_buffer, ptr);
+  
+  
+ fail_in_mutex:
+  pthread_mutex_unlock(&reg_mutex);
+  return -1;
+  
+ pfail:
+  perror(*argv);
+  return -1;
+}
+
+
+/**
+ * Free a key from a table
+ * 
+ * @param  obj  The key
+ */
+void reg_table_free_key(size_t obj)
+{
+  char* command = (char*)(void*)obj;
+  free(command);
+}
+
+
+/**
+ * Free a value from a table
+ * 
+ * @param  obj  The value
+ */
+void reg_table_free_value(size_t obj)
+{
+  client_list_t* list = (client_list_t*)(void*)obj;
+  client_list_destroy(list);
+  free(list);
+}
+
+
+/**
+ * Send a full message even if interrupted
+ * 
+ * @param   message  The message to send
+ * @param   length   The length of the message
+ * @return           Non-zero on success
+ */
+int full_send(const char* message, size_t length)
+{
+  size_t sent;
+  
+  while (length > 0)
+    {
+      sent = send_message(socket_fd, message, length);
+      if (sent > length)
+	{
+	  eprint("Sent more of a message than exists in the message, aborting.");
+	  return -1;
+	}
+      else if ((sent < length) && (errno != EINTR))
+	{
+	  perror(*argv);
+	  return -1;
+	}
+      message += sent;
+      length -= sent;
+    }
+  return 0;
+}
+
diff --git a/src/mds-registry/mds-registry.h b/src/mds-registry/mds-registry.h
new file mode 100644
index 0000000..6f9355d
--- /dev/null
+++ b/src/mds-registry/mds-registry.h
@@ -0,0 +1,91 @@
+/**
+ * mds — A micro-display server
+ * Copyright © 2014  Mattias Andrée (maandree@member.fsf.org)
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef MDS_MDS_REGISTRY_H
+#define MDS_MDS_REGISTRY_H
+
+
+#include "../mds-base.h"
+
+#include <stdint.h>
+
+
+/**
+ * Handle the received message
+ * 
+ * @return  Zero on success -1 on error or interruption,
+ *          errno will be set accordingly
+ */
+int handle_message(void);
+
+/**
+ * Convert a client ID string into a client ID integer
+ * 
+ * @param   str  The client ID string
+ * @return       The client ID integer
+ */
+uint64_t parse_client_id(const char* str);
+
+/**
+ * Perform an action over the registry
+ * 
+ * @param   length           The length of the received message
+ * @param   action           -1 to remove command, +1 to add commands, 0 to
+ *                           wait until the message commnds are registered
+ * @param   recv_client_id   The ID of the client
+ * @param   recv_message_id  The ID of the received message
+ * @return                   Zero on success -1 on error or interruption,
+ *                           errno will be set accordingly
+ */
+int registry_action(size_t length, int action, const char* recv_client_id, const char* recv_message_id);
+
+/**
+ * Send a list of all registered commands to a client
+ * 
+ * @param   recv_client_id   The ID of the client
+ * @param   recv_message_id  The ID of the received message
+ * @return                   Zero on success -1 on error or interruption,
+ *                           errno will be set accordingly
+ */
+int list_registry(const char* recv_client_id, const char* recv_message_id);
+
+/**
+ * Free a key from a table
+ * 
+ * @param  obj  The key
+ */
+void reg_table_free_key(size_t obj);
+
+/**
+ * Free a value from a table
+ * 
+ * @param  obj  The value
+ */
+void reg_table_free_value(size_t obj);
+
+/**
+ * Send a full message even if interrupted
+ * 
+ * @param   message  The message to send
+ * @param   length   The length of the message
+ * @return           Non-zero on success
+ */
+int full_send(const char* message, size_t length);
+
+
+#endif
+