Added reliability layer documentation

Signed-off-by: Adriaan de Jong <dejong@fox-it.com>
Acked-by: James Yonan <james@openvpn.net>
Signed-off-by: David Sommerseth <dazo@users.sourceforge.net>

1 files changed, 381 insertions, 64 deletions

diff --git a/reliable.h b/reliable.h
index 9cf8eec..086761f 100644
--- a/reliable.h
+++ b/reliable.h
@@ -22,11 +22,13 @@
  *  59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  */
 
-/*
- * This routines implement a reliability layer on top of UDP,
- * so that TLS can be run over UDP.
+
+/**
+ * @file
+ * Reliability Layer module header file.
  */
 
+
 #if defined(USE_CRYPTO) && defined(USE_SSL)
 
 #ifndef RELIABLE_H
@@ -38,48 +40,35 @@
 #include "session_id.h"
 #include "mtu.h"
 
+/** @addtogroup reliable
+ *  @{ */
+
+
 #define EXPONENTIAL_BACKOFF
 
-#define RELIABLE_ACK_SIZE 8
+#define RELIABLE_ACK_SIZE 8     /**< The maximum number of packet IDs
+                                 *   waiting to be acknowledged which can
+                                 *   be stored in one \c reliable_ack
+                                 *   structure. */
+
+#define RELIABLE_CAPACITY 8	/**< The maximum number of packets that
+                                 *   the reliability layer for one VPN
+                                 *   tunnel in one direction can store. */
 
+/**
+ * The acknowledgment structure in which packet IDs are stored for later
+ * acknowledgment.
+ */
 struct reliable_ack
 {
   int len;
   packet_id_type packet_id[RELIABLE_ACK_SIZE];
 };
 
-/* no active buffers? */
-static inline bool
-reliable_ack_empty (struct reliable_ack *ack)
-{
-  return !ack->len;
-}
-
-/* get a packet_id from buf */
-bool reliable_ack_read_packet_id (struct buffer *buf, packet_id_type *pid);
-
-/* acknowledge a packet_id by adding it to a struct reliable_ack */
-bool reliable_ack_acknowledge_packet_id (struct reliable_ack *ack, packet_id_type pid);
-
-/* read a packet ID acknowledgement record from buf */
-bool reliable_ack_read (struct reliable_ack *ack,
-			struct buffer *buf, const struct session_id *sid);
-
-/* write a packet ID acknowledgement record to buf */
-bool reliable_ack_write (struct reliable_ack *ack,
-			 struct buffer *buf,
-			 const struct session_id *sid, int max, bool prepend);
-
-/* print a reliable ACK record coming off the wire */
-const char *reliable_ack_print (struct buffer *buf, bool verbose, struct gc_arena *gc);
-
-/* add to extra_frame the maximum number of bytes we will need for reliable_ack_write */
-void reliable_ack_adjust_frame_parameters (struct frame* frame, int max);
-
-void reliable_ack_debug_print (const struct reliable_ack *ack, char *desc);
-
-#define RELIABLE_CAPACITY 8
-
+/**
+ * The structure in which the reliability layer stores a single incoming
+ * or outgoing packet.
+ */
 struct reliable_entry
 {
   bool active;
@@ -90,6 +79,10 @@ struct reliable_entry
   struct buffer buf;
 };
 
+/**
+ * The reliability layer storage structure for one VPN tunnel's control
+ * channel in one direction.
+ */
 struct reliable
 {
   int size;
@@ -100,64 +93,388 @@ struct reliable
   struct reliable_entry array[RELIABLE_CAPACITY];
 };
 
-void reliable_debug_print (const struct reliable *rel, char *desc);
 
-/* set sending timeout (after this time we send again until ACK) */
-static inline void
-reliable_set_timeout (struct reliable *rel, interval_t timeout)
+/**************************************************************************/
+/** @name Functions for processing incoming acknowledgments
+ *  @{ */
+
+/**
+ * Read an acknowledgment record from a received packet.
+ *
+ * This function reads the packet ID acknowledgment record from the packet
+ * contained in \a buf.  If the record contains acknowledgments, these are
+ * stored in \a ack.  This function also compares the packet's session ID
+ * with the expected session ID \a sid, which should be equal.
+ *
+ * @param ack The acknowledgment structure in which received
+ *     acknowledgments are to be stored.
+ * @param buf The buffer containing the packet.
+ * @param sid The expected session ID to compare to the session ID in
+ *     the packet.
+ *
+ * @return
+ * @li True, if processing was successful.
+ * @li False, if an error occurs during processing.
+ */
+bool reliable_ack_read (struct reliable_ack *ack,
+			struct buffer *buf, const struct session_id *sid);
+
+/**
+ * Remove acknowledged packets from a reliable structure.
+ *
+ * @param rel The reliable structure storing sent packets.
+ * @param ack The acknowledgment structure containing received
+ *     acknowledgments.
+ */
+void reliable_send_purge (struct reliable *rel, struct reliable_ack *ack);
+
+/** @} name Functions for processing incoming acknowledgments */
+
+
+/**************************************************************************/
+/** @name Functions for processing outgoing acknowledgments
+ *  @{ */
+
+/**
+ * Check whether an acknowledgment structure contains any
+ *     packet IDs to be acknowledged.
+ *
+ * @param ack The acknowledgment structure to check.
+ *
+ * @return
+ * @li True, if the acknowledgment structure is empty.
+ * @li False, if there are packet IDs to be acknowledged.
+ */
+static inline bool
+reliable_ack_empty (struct reliable_ack *ack)
 {
-  rel->initial_timeout = timeout;
+  return !ack->len;
 }
 
+/**
+ * Write a packet ID acknowledgment record to a buffer.
+ *
+ * @param ack The acknowledgment structure containing packet IDs to be
+ *     acknowledged.
+ * @param buf The buffer into which the acknowledgment record will be
+ *     written.
+ * @param sid The session ID of the VPN tunnel associated with the
+ *     packet IDs to be acknowledged.
+ * @param max The maximum number of acknowledgments to be written in
+ *     the record.
+ * @param prepend If true, prepend the acknowledgment record in the
+ *     buffer; if false, write into the buffer's current position.
+ *
+ * @return
+ * @li True, if processing was successful.
+ * @li False, if an error occurs during processing.
+ */
+bool reliable_ack_write (struct reliable_ack *ack,
+			 struct buffer *buf,
+			 const struct session_id *sid, int max, bool prepend);
+
+/** @} name Functions for processing outgoing acknowledgments */
+
+
+/**************************************************************************/
+/** @name Functions for initialization and cleanup
+ *  @{ */
+
+/**
+ * Initialize a reliable structure.
+ *
+ * @param rel The reliable structure to initialize.
+ * @param buf_size The size of the buffers in which packets will be
+ *     stored.
+ * @param offset The size of reserved space at the beginning of the
+ *     buffers to allow efficient header prepending.
+ * @param array_size The number of packets that this reliable
+ *     structure can store simultaneously.
+ * @param hold description
+ */
 void reliable_init (struct reliable *rel, int buf_size, int offset, int array_size, bool hold);
 
+/**
+ * Free allocated memory associated with a reliable structure.
+ *
+ * @param rel The reliable structured to clean up.
+ */
 void reliable_free (struct reliable *rel);
 
-/* no active buffers? */
-bool reliable_empty (const struct reliable *rel);
+/* add to extra_frame the maximum number of bytes we will need for reliable_ack_write */
+void reliable_ack_adjust_frame_parameters (struct frame* frame, int max);
 
-/* in how many seconds should we wake up to check for timeout */
-interval_t reliable_send_timeout (const struct reliable *rel);
+/** @} name Functions for initialization and cleanup */
 
-/* del acknowledged items from send buf */
-void reliable_send_purge (struct reliable *rel, struct reliable_ack *ack);
 
-/* true if at least one free buffer available */
+/**************************************************************************/
+/** @name Functions for inserting incoming packets
+ *  @{ */
+
+/**
+ * Check whether a reliable structure has any free buffers
+ *     available for use.
+ *
+ * @param rel The reliable structure to check.
+ *
+ * @return
+ * @li True, if at least one buffer is available for use.
+ * @li False, if all the buffers are active.
+ */
 bool reliable_can_get (const struct reliable *rel);
 
-/* make sure that incoming packet ID isn't a replay */
+/**
+ * Check that a received packet's ID is not a replay.
+ *
+ * @param rel The reliable structure for handling this VPN tunnel's
+ *     received packets.
+ * @param id The packet ID of the received packet.
+ *
+ * @return
+ * @li True, if the packet ID is not a replay.
+ * @li False, if the packet ID is a replay.
+ */
 bool reliable_not_replay (const struct reliable *rel, packet_id_type id);
 
-/* make sure that incoming packet ID won't deadlock the receive buffer */
+/**
+ * Check that a received packet's ID can safely be stored in
+ *     the reliable structure's processing window.
+ *
+ * This function checks the difference between the received packet's ID
+ * and the lowest non-acknowledged packet ID in the given reliable
+ * structure.  If that difference is larger than the total number of
+ * packets which can be stored, then this packet cannot be stored safely,
+ * because the reliable structure could possibly fill up without leaving
+ * room for all intervening packets.  In that case, this received packet
+ * could break the reliable structure's sequentiality, and must therefore
+ * be discarded.
+ *
+ * @param rel The reliable structure for handling this VPN tunnel's
+ *     received packets.
+ * @param id The packet ID of the received packet.
+ *
+ * @return
+ * @li True, if the packet can safely be stored.
+ * @li False, if the packet does not fit safely in the reliable
+ *     structure's processing window.
+ */
 bool reliable_wont_break_sequentiality (const struct reliable *rel, packet_id_type id);
 
-/* grab a free buffer */
+/**
+ * Read the packet ID of a received packet.
+ *
+ * @param buf The buffer containing the received packet.
+ * @param pid A pointer where the packet's packet ID will be written.
+ *
+ * @return
+ * @li True, if processing was successful.
+ * @li False, if an error occurs during processing.
+ */
+bool reliable_ack_read_packet_id (struct buffer *buf, packet_id_type *pid);
+
+/**
+ * Get the buffer of a free %reliable entry in which to store a
+ *     packet.
+ *
+ * @param rel The reliable structure in which to search for a free
+ *     entry.
+ *
+ * @return A pointer to a buffer of a free entry in the \a rel
+ *     reliable structure.  If there are no free entries available, this
+ *     function returns NULL.
+ */
 struct buffer *reliable_get_buf (struct reliable *rel);
 
-/* grab a free buffer, fail if buffer clogged by unacknowledged low packet IDs */
-struct buffer *reliable_get_buf_output_sequenced (struct reliable *rel);
+/**
+ * Mark the %reliable entry associated with the given buffer as active
+ * incoming.
+ *
+ * @param rel The reliable structure associated with this packet.
+ * @param buf The buffer into which the packet has been copied.
+ * @param pid The packet's packet ID.
+ * @param opcode The packet's opcode.
+ */
+void reliable_mark_active_incoming (struct reliable *rel, struct buffer *buf,
+				    packet_id_type pid, int opcode);
+
+/**
+ * Record a packet ID for later acknowledgment.
+ *
+ * @param ack The acknowledgment structure which stores this VPN
+ *     tunnel's packet IDs for later acknowledgment.
+ * @param pid The packet ID of the received packet which should be
+ *     acknowledged.
+ *
+ * @return
+ * @li True, if the packet ID was added to \a ack.
+ * @li False, if the packet ID was already present in \a ack or \a ack
+ *     has no free space to store any more packet IDs.
+ */
+bool reliable_ack_acknowledge_packet_id (struct reliable_ack *ack, packet_id_type pid);
+
+/** @} name Functions for inserting incoming packets */
 
-/* get active buffer for next sequentially increasing key ID */
+
+/**************************************************************************/
+/** @name Functions for extracting incoming packets
+ *  @{ */
+
+/**
+ * Get the buffer of the next sequential and active entry.
+ *
+ * @param rel The reliable structure from which to retrieve the
+ *     buffer.
+ *
+ * @return A pointer to the buffer of the entry with the next
+ *     sequential key ID.  If no such entry is present, this function
+ *     returns NULL.
+ */
 struct buffer *reliable_get_buf_sequenced (struct reliable *rel);
 
-/* return true if reliable_send would return a non-NULL result */
+/**
+ * Remove an entry from a reliable structure.
+ *
+ * @param rel The reliable structure associated with the given buffer.
+ * @param buf The buffer of the reliable entry which is to be removed.
+ * @param inc_pid If true, the reliable structure's packet ID counter
+ *     will be incremented.
+ */
+void reliable_mark_deleted (struct reliable *rel, struct buffer *buf, bool inc_pid);
+
+/** @} name Functions for extracting incoming packets */
+
+
+/**************************************************************************/
+/** @name Functions for inserting outgoing packets
+ *  @{ */
+
+/**
+ * Get the buffer of free reliable entry and check whether the
+ *     outgoing acknowledgment sequence is still okay.
+ *
+ * @param rel The reliable structure in which to search for a free
+ *     entry.
+ *
+ * @return A pointer to a buffer of a free entry in the \a rel
+ *     reliable structure.  If there are no free entries available, this
+ *     function returns NULL.  If the outgoing acknowledgment sequence is
+ *     broken, this function also returns NULL.
+ */
+struct buffer *reliable_get_buf_output_sequenced (struct reliable *rel);
+
+/**
+ * Mark the reliable entry associated with the given buffer as
+ *     active outgoing.
+ *
+ * @param rel The reliable structure for handling this VPN tunnel's
+ *     outgoing packets.
+ * @param buf The buffer previously returned by \c
+ *     reliable_get_buf_output_sequenced() into which the packet has been
+ *     copied.
+ * @param opcode The packet's opcode.
+ */
+void reliable_mark_active_outgoing (struct reliable *rel, struct buffer *buf, int opcode);
+
+/** @} name Functions for inserting outgoing packets */
+
+
+/**************************************************************************/
+/** @name Functions for extracting outgoing packets
+ *  @{ */
+
+/**
+ * Check whether a reliable structure has any active entries
+ *     ready to be (re)sent.
+ *
+ * @param rel The reliable structure to check.
+ *
+ * @return
+ * @li True, if there are active entries ready to be (re)sent
+ *     president.
+ * @li False, if there are no active entries, or the active entries
+ *     are not yet ready for resending.
+ */
 bool reliable_can_send (const struct reliable *rel);
 
-/* return next buffer to send to remote */
+/**
+ * Get the next packet to send to the remote peer.
+ *
+ * This function looks for the active entry ready for (re)sending with the
+ * lowest packet ID, and returns the buffer associated with it.  This
+ * function also resets the timeout after which that entry will become
+ * ready for resending again.
+ *
+ * @param rel The reliable structure to check.
+ * @param opcode A pointer to an integer in which this function will
+ *     store the opcode of the next packet to be sent.
+ *
+ * @return A pointer to the buffer of the next entry to be sent, or
+ *     NULL if there are no entries ready for (re)sending present in the
+ *     reliable structure.  If a valid pointer is returned, then \a opcode
+ *     will point to the opcode of that packet.
+ */
 struct buffer *reliable_send (struct reliable *rel, int *opcode);
 
-/* schedule all pending packets for immediate retransmit */
+/** @} name Functions for extracting outgoing packets */
+
+
+/**************************************************************************/
+/** @name Miscellaneous functions
+ *  @{ */
+
+/**
+ * Check whether a reliable structure is empty.
+ *
+ * @param rel The reliable structure to check.
+ *
+ * @return
+ * @li True, if there are no active entries in the given reliable
+ *     structure.
+ * @li False, if there is at least one active entry present.
+ */
+bool reliable_empty (const struct reliable *rel);
+
+/**
+ * Determined how many seconds until the earliest resend should
+ *     be attempted.
+ *
+ * @param rel The reliable structured to check.
+ *
+ * @return The interval in seconds until the earliest resend attempt
+ *     of the outgoing packets stored in the \a rel reliable structure. If
+ *     the next time for attempting resending of one or more packets has
+ *     already passed, this function will return 0.
+ */
+interval_t reliable_send_timeout (const struct reliable *rel);
+
+/**
+ * Reschedule all entries of a reliable structure to be ready
+ *     for (re)sending immediately.
+ *
+ * @param rel The reliable structure of which the entries should be
+ *     modified.
+ */
 void reliable_schedule_now (struct reliable *rel);
 
-/* enable an incoming buffer previously returned by a get function as active */
-void reliable_mark_active_incoming (struct reliable *rel, struct buffer *buf,
-				    packet_id_type pid, int opcode);
+void reliable_debug_print (const struct reliable *rel, char *desc);
 
-/* enable an outgoing buffer previously returned by a get function as active. */
-void reliable_mark_active_outgoing (struct reliable *rel, struct buffer *buf, int opcode);
+/* set sending timeout (after this time we send again until ACK) */
+static inline void
+reliable_set_timeout (struct reliable *rel, interval_t timeout)
+{
+  rel->initial_timeout = timeout;
+}
+
+/* print a reliable ACK record coming off the wire */
+const char *reliable_ack_print (struct buffer *buf, bool verbose, struct gc_arena *gc);
+
+void reliable_ack_debug_print (const struct reliable_ack *ack, char *desc);
+
+/** @} name Miscellaneous functions */
+
+
+/** @} addtogroup reliable */
 
-/* delete a buffer previously activated by reliable_mark_active() */
-void reliable_mark_deleted (struct reliable *rel, struct buffer *buf, bool inc_pid);
 
 #endif /* RELIABLE_H */
 #endif /* USE_CRYPTO && USE_SSL */