gnunet-android

gnunet_mq_lib.h (34882B)

---

 /*
      This file is part of GNUnet.
      Copyright (C) 2012-2016 GNUnet e.V.
 
      GNUnet is free software: you can redistribute it and/or modify it
      under the terms of the GNU Affero General Public License as published
      by the Free Software Foundation, either version 3 of the License,
      or (at your option) any later version.
 
      GNUnet 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
      Affero General Public License for more details.
 
      You should have received a copy of the GNU Affero General Public License
      along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
      SPDX-License-Identifier: AGPL3.0-or-later
  */
 
 #include "gnunet_common.h"
 #if ! defined (__GNUNET_UTIL_LIB_H_INSIDE__)
 #error "Only <gnunet_util_lib.h> can be included directly."
 #endif
 
 
 /**
  * @addtogroup libgnunetutil
  * Multi-function utilities library for GNUnet programs
  * @{
  *
  * @author Florian Dold
  * @author Christian Grothoff
  *
  * @file
  * General-purpose message queue
  *
  * @defgroup mq  MQ library
  * General-purpose message queue
  *
  * @{
  */
 #ifndef GNUNET_MQ_LIB_H
 #define GNUNET_MQ_LIB_H
 
 
 #include "gnunet_scheduler_lib.h"
 
 /**
  * Allocate an envelope, with extra space allocated after the space needed
  * by the message struct.
  * The allocated message will already have the type and size field set.
  *
  * @param mvar variable to store the allocated message in;
  *             must have a header field;
  *             can be NULL
  * @param esize extra space to allocate after the message
  * @param type type of the message
  * @return the MQ message
  */
 #define GNUNET_MQ_msg_extra(mvar, esize, type)                \
         GNUNET_MQ_msg_ (((struct GNUNET_MessageHeader **) &(mvar)), \
                         (esize) + sizeof *(mvar),                   \
                         (type))
 
 /**
  * Allocate a GNUNET_MQ_Envelope.
  * The contained message will already have the type and size field set.
  *
  * @param mvar variable to store the allocated message in;
  *             must have a header field;
  *             can be NULL
  * @param type type of the message
  * @return the allocated envelope
  */
 #define GNUNET_MQ_msg(mvar, type) GNUNET_MQ_msg_extra (mvar, 0, type)
 
 
 /**
  * Allocate a GNUNET_MQ_Envelope, where the message only consists of a header.
  * The allocated message will already have the type and size field set.
  *
  * @param type type of the message
  */
 #define GNUNET_MQ_msg_header(type) \
         GNUNET_MQ_msg_ (NULL, sizeof(struct GNUNET_MessageHeader), type)
 
 
 /**
  * Allocate a GNUNET_MQ_Envelope, where the message only consists of a header and extra space.
  * The allocated message will already have the type and size field set.
  *
  * @param mh pointer that will changed to point at to the allocated message header
  * @param esize extra space to allocate after the message header
  * @param type type of the message
  */
 #define GNUNET_MQ_msg_header_extra(mh, esize, type) \
         GNUNET_MQ_msg_ (&mh, (esize) + sizeof(struct GNUNET_MessageHeader), type \
                         )
 
 
 /**
  * Allocate a GNUNET_MQ_Envelope, and append a payload message after the given
  * message struct.
  *
  * @param mvar pointer to a message struct, will be changed to point at the newly allocated message,
  *        whose size is 'sizeof(*mvar) + ntohs (mh->size)'
  * @param type message type of the allocated message, has no effect on the nested message
  * @param mh message to nest
  * @return a newly allocated 'struct GNUNET_MQ_Envelope *'
  */
 #define GNUNET_MQ_msg_nested_mh(mvar, type, mh)                               \
         ({                                                                          \
     struct GNUNET_MQ_Envelope *_ev;                                           \
     _ev = GNUNET_MQ_msg_nested_mh_ ((struct GNUNET_MessageHeader **) &(mvar), \
                                     sizeof(*(mvar)),                         \
                                     (type),                                   \
                                     (mh));                                    \
     (void) (mvar)->header;  /* type check */                                   \
     _ev;                                                                      \
   })
 
 
 /**
  * Return a pointer to the message at the end of the given message.
  *
  * @param var pointer to a message struct, the type of the expression determines the base size,
  *        the space after the base size is the nested message
  * @return a 'struct GNUNET_MessageHeader *' that points at the nested message of the given message,
  *         or NULL if the given message in @a var does not have any space after the message struct
  */
 #define GNUNET_MQ_extract_nested_mh(var)                               \
         GNUNET_MQ_extract_nested_mh_ ((struct GNUNET_MessageHeader *) (var), \
                                       sizeof(*(var)))
 
 
 /**
  * Implementation of the #GNUNET_MQ_extract_nexted_mh macro.
  *
  * @param mh message header to extract nested message header from
  * @param base_size size of the message before the nested message's header appears
  * @return pointer to the nested message, does not copy the message
  *         OR NULL in case of a malformed message.
  */
 const struct GNUNET_MessageHeader *
 GNUNET_MQ_extract_nested_mh_ (const struct GNUNET_MessageHeader *mh,
                               uint16_t base_size);
 
 
 /**
  * Opaque handle to an envelope.
  */
 struct GNUNET_MQ_Envelope;
 
 
 /**
  * Obtain message contained in envelope.
  *
  * @param env the envelope
  * @return message contained in the envelope
  */
 const struct GNUNET_MessageHeader *
 GNUNET_MQ_env_get_msg (const struct GNUNET_MQ_Envelope *env);
 
 
 /**
  * Return next envelope in queue.
  *
  * @param env a queued envelope
  * @return next one, or NULL
  */
 const struct GNUNET_MQ_Envelope *
 GNUNET_MQ_env_next (const struct GNUNET_MQ_Envelope *env);
 
 
 /**
  * Implementation of the #GNUNET_MQ_msg_nested_mh macro.
  *
  * @param mhp pointer to the message header pointer that will be changed to allocate at
  *        the newly allocated space for the message.
  * @param base_size size of the data before the nested message
  * @param type type of the message in the envelope
  * @param nested_mh the message to append to the message after base_size
  */
 struct GNUNET_MQ_Envelope *
 GNUNET_MQ_msg_nested_mh_ (struct GNUNET_MessageHeader **mhp,
                           uint16_t base_size,
                           uint16_t type,
                           const struct GNUNET_MessageHeader *nested_mh);
 
 
 /**
  * Opaque handle to a message queue.
  */
 struct GNUNET_MQ_Handle;
 
 
 /**
  * Error codes for the queue.
  */
 enum GNUNET_MQ_Error
 {
   /**
    * Failed to read message from the network.
    * FIXME: Likely not properly distinguished
    * from TIMEOUT case in the code!
    */
   GNUNET_MQ_ERROR_READ = 1,
 
   /**
    * FIXME: document!
    */
   GNUNET_MQ_ERROR_WRITE = 2,
 
   /**
    * FIXME: document!
    */
   GNUNET_MQ_ERROR_TIMEOUT = 4,
 
   /**
    * We received a message that was malformed and thus
    * could not be passed to its handler.
    */
   GNUNET_MQ_ERROR_MALFORMED = 8,
 
   /**
    * We received a message for which we have no matching
    * handler.
    */
   GNUNET_MQ_ERROR_NO_MATCH = 16
 };
 
 
 /**
  * Per envelope preferences and priorities.
  */
 enum GNUNET_MQ_PriorityPreferences
 {
   /**
    * Lowest priority, i.e. background traffic (e.g. NSE, FS).
    * This is the default!
    */
   GNUNET_MQ_PRIO_BACKGROUND = 0,
 
   /**
    * Best-effort traffic (e.g. CADET relay, DHT)
    */
   GNUNET_MQ_PRIO_BEST_EFFORT = 1,
 
   /**
    * Urgent traffic (local peer, e.g. Conversation).
    */
   GNUNET_MQ_PRIO_URGENT = 2,
 
   /**
    * Highest priority, control traffic (e.g. CORE/CADET KX).
    */
   GNUNET_MQ_PRIO_CRITICAL_CONTROL = 3,
 
   /**
    * Bit mask to apply to extract the priority bits.
    */
   GNUNET_MQ_PRIORITY_MASK = 3,
 
   /**
    * Flag to indicate that unreliable delivery is acceptable.  This
    * means TRANSPORT will not attempt to receive an
    * acknowledgment. CORE will just pass this flag through.  CADET
    * will use unreliable delivery if this flag is set.
    *
    * Note that even without this flag, messages may be lost by
    * TRANSPORT and CORE.
    *
    * Thus, how "strong" the semantics of reliable delivery are depends
    * on the layer!
    */
   GNUNET_MQ_PREF_UNRELIABLE = 16,
 
   /**
    * Flag to indicate that low latency is important.  This flag must
    * generally not be used in combination with
    * #GNUNET_MQ_PREF_CORKING_ALLOWED as it would be a contradiction.
    * When this flags is set, the envelope may skip forward in the
    * queue (depending on priority) and also TRANSPORT should attempt
    * to pick a communicator with particularly low latency.
    */
   GNUNET_MQ_PREF_LOW_LATENCY = 32,
 
   /**
    * Flag to indicate that CORKing is acceptable. This allows the
    * receiver to delay transmission in hope of combining this message
    * with other messages into a larger transmission with less
    * per-message overhead.
    */
   GNUNET_MQ_PREF_CORK_ALLOWED = 64,
 
   /**
    * Flag to indicate that high bandwidth is desired. This flag
    * indicates that the method chosen for transmission should focus on
    * overall goodput.  It rarely makes sense to combine this flag with
    * #GNUNET_MQ_PREF_LOW_LATENCY.
    */
   GNUNET_MQ_PREF_GOODPUT = 128,
 
   /**
    * Flag to indicate that out-of-order delivery is OK.
    */
   GNUNET_MQ_PREF_OUT_OF_ORDER = 256,
 };
 
 
 /**
  * Called when a message has been received.
  *
  * @param cls closure
  * @param msg the received message
  */
 typedef void
 (*GNUNET_MQ_MessageCallback) (
   void *cls,
   const struct GNUNET_MessageHeader *msg);
 
 
 /**
  * Called when a message needs to be validated.
  *
  * @param cls closure
  * @param msg the received message
  * @return #GNUNET_OK if the message is well-formed,
  *         #GNUNET_SYSERR if not
  */
 typedef enum GNUNET_GenericReturnValue
 (*GNUNET_MQ_MessageValidationCallback) (
   void *cls,
   const struct GNUNET_MessageHeader *msg);
 
 
 /**
  * Signature of functions implementing the
  * sending functionality of a message queue.
  *
  * @param mq the message queue
  * @param msg the message to send
  * @param impl_state state of the implementation
  */
 typedef void
 (*GNUNET_MQ_SendImpl) (struct GNUNET_MQ_Handle *mq,
                        const struct GNUNET_MessageHeader *msg,
                        void *impl_state);
 
 
 /**
  * Signature of functions implementing the
  * destruction of a message queue.
  * Implementations must not free @a mq, but should
  * take care of @a impl_state.
  *
  * @param mq the message queue to destroy
  * @param impl_state state of the implementation
  */
 typedef void
 (*GNUNET_MQ_DestroyImpl) (struct GNUNET_MQ_Handle *mq,
                           void *impl_state);
 
 
 /**
  * Implementation function that cancels the currently sent message.
  *
  * @param mq message queue
  * @param impl_state state specific to the implementation
  */
 typedef void
 (*GNUNET_MQ_CancelImpl) (struct GNUNET_MQ_Handle *mq,
                          void *impl_state);
 
 
 /**
  * Generic error handler, called with the appropriate
  * error code and the same closure specified at the creation of
  * the message queue.
  * Not every message queue implementation supports an error handler.
  *
  * @param cls closure
  * @param error error code
  */
 typedef void
 (*GNUNET_MQ_ErrorHandler) (void *cls,
                            enum GNUNET_MQ_Error error);
 
 
 /**
  * Insert @a env into the envelope DLL starting at @a env_head
  * Note that @a env must not be in any MQ while this function
  * is used with DLLs defined outside of the MQ module.  This
  * is just in case some application needs to also manage a
  * FIFO of envelopes independent of MQ itself and wants to
  * reuse the pointers internal to @a env.  Use with caution.
  *
  * @param[in,out] env_head of envelope DLL
  * @param[in,out] env_tail tail of envelope DLL
  * @param[in,out] env element to insert at the tail
  */
 void
 GNUNET_MQ_dll_insert_head (struct GNUNET_MQ_Envelope **env_head,
                            struct GNUNET_MQ_Envelope **env_tail,
                            struct GNUNET_MQ_Envelope *env);
 
 
 /**
  * Insert @a env into the envelope DLL starting at @a env_head
  * Note that @a env must not be in any MQ while this function
  * is used with DLLs defined outside of the MQ module.  This
  * is just in case some application needs to also manage a
  * FIFO of envelopes independent of MQ itself and wants to
  * reuse the pointers internal to @a env.  Use with caution.
  *
  * @param[in,out] env_head of envelope DLL
  * @param[in,out] env_tail tail of envelope DLL
  * @param[in,out] env element to insert at the tail
  */
 void
 GNUNET_MQ_dll_insert_tail (struct GNUNET_MQ_Envelope **env_head,
                            struct GNUNET_MQ_Envelope **env_tail,
                            struct GNUNET_MQ_Envelope *env);
 
 
 /**
  * Remove @a env from the envelope DLL starting at @a env_head.
  * Note that @a env must not be in any MQ while this function
  * is used with DLLs defined outside of the MQ module. This
  * is just in case some application needs to also manage a
  * FIFO of envelopes independent of MQ itself and wants to
  * reuse the pointers internal to @a env.  Use with caution.
  *
  * @param[in,out] env_head of envelope DLL
  * @param[in,out] env_tail tail of envelope DLL
  * @param[in,out] env element to remove from the DLL
  */
 void
 GNUNET_MQ_dll_remove (struct GNUNET_MQ_Envelope **env_head,
                       struct GNUNET_MQ_Envelope **env_tail,
                       struct GNUNET_MQ_Envelope *env);
 
 
 /**
  * Copy an array of handlers.
  *
  * Useful if the array has been declared in local memory and needs to be
  * persisted for future use.
  *
  * @param handlers Array of handlers to be copied.
  * @return A newly allocated array of handlers.
  *         Needs to be freed with #GNUNET_free.
  */
 struct GNUNET_MQ_MessageHandler *
 GNUNET_MQ_copy_handlers (const struct GNUNET_MQ_MessageHandler *handlers);
 
 
 /**
  * Copy an array of handlers, appending AGPL handler.
  *
  * Useful if the array has been declared in local memory and needs to be
  * persisted for future use.
  *
  * @param handlers Array of handlers to be copied. Can be NULL (nothing done).
  * @param agpl_handler function to call for AGPL handling
  * @param agpl_cls closure for @a agpl_handler
  * @return A newly allocated array of handlers.
  *         Needs to be freed with #GNUNET_free.
  */
 struct GNUNET_MQ_MessageHandler *
 GNUNET_MQ_copy_handlers2 (const struct GNUNET_MQ_MessageHandler *handlers,
                           GNUNET_MQ_MessageCallback agpl_handler,
                           void *agpl_cls);
 
 
 /**
  * Count the handlers in a handler array.
  *
  * @param handlers Array of handlers to be counted.
  * @return The number of handlers in the array.
  */
 unsigned int
 GNUNET_MQ_count_handlers (const struct GNUNET_MQ_MessageHandler *handlers);
 
 
 /**
  * Message handler for a specific message type.
  */
 struct GNUNET_MQ_MessageHandler
 {
   /**
    * Callback to validate a message of the specified @e type.
    * The closure given to @e mv will be this struct (not @e ctx).
    * Using NULL means only size-validation using
    * @e expected_size.  In this case, @e expected_size must
    * be non-zero.
    */
   GNUNET_MQ_MessageValidationCallback mv;
 
   /**
    * Callback, called every time a new message of
    * the specified @e type has been received.
    * The closure given to @e mv will be this struct (not @e ctx).
    */
   GNUNET_MQ_MessageCallback cb;
 
   /**
    * Closure for @e mv and @e cb.
    */
   void *cls;
 
   /**
    * Type of the message this handler covers, in host byte order.
    */
   uint16_t type;
 
   /**
    * Expected size of messages of this type.  Minimum size of the
    * message if @e mv is non-NULL.  Messages of the given type will be
    * discarded (and the connection closed with an error reported to
    * the application) if they do not have the right size.
    */
   uint16_t expected_size;
 };
 
 
 /**
  * End-marker for the handlers array
  */
 #define GNUNET_MQ_handler_end() \
         {                             \
           NULL, NULL, NULL, 0, 0      \
         }
 
 
 /**
  * Defines a static function @a name which takes as a single argument
  * a message handler for fixed-sized messages of type @a code and with
  * a message type argument of @a str.  Given such an argument, the
  * function @name will return a `struct GNUNET_MQ_MessageHandler`
  * for the given message type.
  *
  * The macro is to be used as follows:
  * <code>
  * struct GNUNET_MessageTest { ... }; // must be fixed size
  * static void
  * handle_test_message (void *cls,
  *                      const struct GNUNET_MessageTest *msg)
  * { ... }
  *
  * struct GNUNET_MQ_MessageHandler handlers[] = {
  *   GNUNET_MQ_hd_fixed_size(test_message,
  *                           GNUNET_MESSAGE_TYPE_TEST,
  *                           struct GNUNET_MessageTest,
  *                           "context"),
  *   GNUNET_MQ_handler_end()
  * };
  *
  * @param name unique basename for the functions
  * @param code message type constant
  * @param str type of the message (a struct)
  * @param ctx context for the callbacks
  */
 #define GNUNET_MQ_hd_fixed_size(name, code, str, ctx)                   \
         ({                                                                    \
     void (*_cb)(void *cls, const str *msg) = &handle_ ## name;           \
     ((struct GNUNET_MQ_MessageHandler){ NULL,                            \
                                         (GNUNET_MQ_MessageCallback) _cb, \
                                         (ctx),                           \
                                         (code),                          \
                                         sizeof(str) });                  \
   })
 
 
 /**
  * Defines a static function @a name which takes two arguments and a
  * context-pointer for validating and handling variable-sized messages
  * of type @a code and with a message type argument of @a str.  Given
  * such arguments, the function @name will return a `struct
  * GNUNET_MQ_MessageHandler` for the given message type.
  *
  * The macro is to be used as follows:
  * <code>
  * struct GNUNET_MessageTest { ... }; // can be variable size
  * static int
  * check_test (void *cls,
  *             const struct GNUNET_MessageTest *msg)
  * {
  *   const char *ctx = cls;
  *   GNUNET_assert (0 == strcmp ("context", ctx));
  *   // ...
  * }
  * static void
  * handle_test (void *cls,
  *              const struct GNUNET_MessageTest *msg)
  * {
  *   const char *ctx = cls;
  *   GNUNET_assert (0 == strcmp ("context", ctx));
  *   // ...
  * }
  *
  * struct GNUNET_MQ_MessageHandler handlers[] = {
  *   GNUNET_MQ_hd_var_size(test_message,
  *                         GNUNET_MESSAGE_TYPE_TEST,
  *                         struct GNUNET_MessageTest,
  *                         "context"),
  *   GNUNET_MQ_handler_end()
  * };
  * </code>
  *
  * @param name unique basename for the functions
  * @param code message type constant
  * @param str type of the message (a struct)
  * @param ctx context for the callbacks
  */
 #define GNUNET_MQ_hd_var_size(name, code, str, ctx)                          \
         __extension__ ({                                                            \
     int (*_mv)(void *cls, const str *msg) = &check_ ## name;                  \
     void (*_cb)(void *cls, const str *msg) = &handle_ ## name;                \
     ((struct GNUNET_MQ_MessageHandler){ (GNUNET_MQ_MessageValidationCallback) \
                                         _mv,                                \
                                         (GNUNET_MQ_MessageCallback) _cb,      \
                                         (ctx),                                \
                                         (code),                               \
                                         sizeof(str) });                       \
   })
 
 
 /**
  * Insert code for a "check_" function that verifies that
  * a given variable-length message received over the network
  * is followed by a 0-terminated string.  If the message @a m
  * is not followed by a 0-terminated string, an error is logged
  * and the function is returned with #GNUNET_NO.
  *
  * @param an IPC message with proper type to determine
  *  the size, starting with a `struct GNUNET_MessageHeader`
  */
 #define GNUNET_MQ_check_zero_termination(m)                       \
         {                                                               \
           const char *str = (const char *) &m[1];                       \
           const struct GNUNET_MessageHeader *hdr =                      \
             (const struct GNUNET_MessageHeader *) m;                    \
           uint16_t slen = ntohs (hdr->size) - sizeof(*m);              \
           if ((0 == slen) || (memchr (str, 0, slen) != &str[slen - 1])) \
           {                                                             \
             GNUNET_break (0);                                           \
             return GNUNET_NO;                                           \
           }                                                             \
         }
 
 
 /**
  * Insert code for a "check_" function that verifies that
  * a given variable-length message received over the network
  * is followed by another variable-length message that fits
  * exactly with the given size.  If the message @a m
  * is not followed by another `struct GNUNET_MessageHeader`
  * with a size that adds up to the total size, an error is logged
  * and the function is returned with #GNUNET_NO.
  *
  * @param an IPC message with proper type to determine
  *  the size, starting with a `struct GNUNET_MessageHeader`
  */
 #define GNUNET_MQ_check_boxed_message(m)                 \
         {                                                      \
           const struct GNUNET_MessageHeader *inbox =           \
             (const struct GNUNET_MessageHeader *) &m[1];       \
           const struct GNUNET_MessageHeader *hdr =             \
             (const struct GNUNET_MessageHeader *) m;           \
           uint16_t slen = ntohs (hdr->size) - sizeof(*m);     \
           if ((slen < sizeof(struct GNUNET_MessageHeader)) || \
               (slen != ntohs (inbox->size)))                   \
           {                                                    \
             GNUNET_break (0);                                  \
             return GNUNET_NO;                                  \
           }                                                    \
         }
 
 
 /**
  * Call the message message handler that was registered
  * for the type of the given message in the given @a handlers list.
  *
  * This function is indented to be used for the implementation
  * of message queues.
  *
  * @param handlers a set of handlers
  * @param mh message to dispatch
  * @return #GNUNET_OK on success, #GNUNET_NO if no handler matched,
  *         #GNUNET_SYSERR if message was rejected by check function
  */
 enum GNUNET_GenericReturnValue
 GNUNET_MQ_handle_message (const struct GNUNET_MQ_MessageHandler *handlers,
                           const struct GNUNET_MessageHeader *mh);
 
 
 /**
  * Create a new envelope.
  *
  * @param mhp message header to store the allocated message header in, can be NULL
  * @param size size of the message to allocate
  * @param type type of the message, will be set in the allocated message
  * @return the allocated MQ message
  */
 struct GNUNET_MQ_Envelope *
 GNUNET_MQ_msg_ (struct GNUNET_MessageHeader **mhp,
                 uint16_t size,
                 uint16_t type);
 
 
 /**
  * Create a new envelope by copying an existing message.
  *
  * @param hdr header of the message to copy
  * @return envelope containing @a hdr
  */
 struct GNUNET_MQ_Envelope *
 GNUNET_MQ_msg_copy (const struct GNUNET_MessageHeader *hdr);
 
 
 /**
  * Discard the message queue message, free all
  * allocated resources. Must be called in the event
  * that a message is created but should not actually be sent.
  *
  * @param mqm the message to discard
  */
 void
 GNUNET_MQ_discard (struct GNUNET_MQ_Envelope *mqm);
 
 
 /**
  * Function to obtain the current envelope
  * from within #GNUNET_MQ_SendImpl implementations.
  *
  * @param mq message queue to interrogate
  * @return the current envelope
  */
 struct GNUNET_MQ_Envelope *
 GNUNET_MQ_get_current_envelope (struct GNUNET_MQ_Handle *mq);
 
 
 /**
  * Function to copy an envelope.  The envelope must not yet
  * be in any queue or have any options or callbacks set.
  *
  * @param env envelope to copy
  * @return copy of @a env
  */
 struct GNUNET_MQ_Envelope *
 GNUNET_MQ_env_copy (struct GNUNET_MQ_Envelope *env);
 
 
 /**
  * Function to obtain the last envelope in the queue.
  *
  * @param mq message queue to interrogate
  * @return the last envelope in the queue
  */
 struct GNUNET_MQ_Envelope *
 GNUNET_MQ_get_last_envelope (struct GNUNET_MQ_Handle *mq);
 
 
 /**
  * Set application-specific options for this envelope.
  * Overrides the options set for the queue with
  * #GNUNET_MQ_set_options() for this message only.
  *
  * @param env message to set options for
  * @param pp priority and preferences to set for @a env
  */
 void
 GNUNET_MQ_env_set_options (struct GNUNET_MQ_Envelope *env,
                            enum GNUNET_MQ_PriorityPreferences pp);
 
 
 /**
  * Get performance preferences set for this envelope.
  *
  * @param env message to set options for
  * @return priority and preferences to use
  */
 enum GNUNET_MQ_PriorityPreferences
 GNUNET_MQ_env_get_options (struct GNUNET_MQ_Envelope *env);
 
 
 /**
  * Combine performance preferences set for different
  * envelopes that are being combined into one larger envelope.
  *
  * @param p1 one set of preferences
  * @param p2 second set of preferences
  * @return combined priority and preferences to use
  */
 enum GNUNET_MQ_PriorityPreferences
 GNUNET_MQ_env_combine_options (enum GNUNET_MQ_PriorityPreferences p1,
                                enum GNUNET_MQ_PriorityPreferences p2);
 
 
 /**
  * Remove the first envelope that has not yet been sent from the message
  * queue and return it.
  *
  * @param mq queue to remove envelope from
  * @return NULL if queue is empty (or has no envelope that is not under transmission)
  */
 struct GNUNET_MQ_Envelope *
 GNUNET_MQ_unsent_head (struct GNUNET_MQ_Handle *mq);
 
 
 /**
  * Set application-specific options for this queue.
  *
  * @param mq message queue to set options for
  * @param pp priority and preferences to use by default
  */
 void
 GNUNET_MQ_set_options (struct GNUNET_MQ_Handle *mq,
                        enum GNUNET_MQ_PriorityPreferences pp);
 
 
 /**
  * Obtain the current length of the message queue.
  *
  * @param mq queue to inspect
  * @return number of queued, non-transmitted messages
  */
 unsigned int
 GNUNET_MQ_get_length (struct GNUNET_MQ_Handle *mq);
 
 
 /**
  * Send a message with the given message queue.
  * May only be called once per message.
  *
  * @param mq message queue
  * @param ev the envelope with the message to send.
  */
 void
 GNUNET_MQ_send (struct GNUNET_MQ_Handle *mq,
                 struct GNUNET_MQ_Envelope *ev);
 
 
 /**
  * Send a copy of a message with the given message queue.
  * Can be called repeatedly on the same envelope.
  *
  * @param mq message queue
  * @param ev the envelope with the message to send.
  */
 void
 GNUNET_MQ_send_copy (struct GNUNET_MQ_Handle *mq,
                      const struct GNUNET_MQ_Envelope *ev);
 
 
 /**
  * Cancel sending the message. Message must have been sent with
  * #GNUNET_MQ_send before.  May not be called after the notify sent
  * callback has been called
  *
  * @param ev queued envelope to cancel
  */
 void
 GNUNET_MQ_send_cancel (struct GNUNET_MQ_Envelope *ev);
 
 
 /**
  * Associate the assoc_data in @a mq with a unique request id.
  *
  * @param mq message queue, id will be unique for the queue
  * @param assoc_data to associate
  */
 uint32_t
 GNUNET_MQ_assoc_add (struct GNUNET_MQ_Handle *mq,
                      void *assoc_data);
 
 
 /**
  * Get the data associated with a @a request_id in a queue
  *
  * @param mq the message queue with the association
  * @param request_id the request id we are interested in
  * @return the associated data
  */
 void *
 GNUNET_MQ_assoc_get (struct GNUNET_MQ_Handle *mq,
                      uint32_t request_id);
 
 
 /**
  * Remove the association for a @a request_id
  *
  * @param mq the message queue with the association
  * @param request_id the request id we want to remove
  * @return the associated data
  */
 void *
 GNUNET_MQ_assoc_remove (struct GNUNET_MQ_Handle *mq,
                         uint32_t request_id);
 
 
 /**
  * Create a message queue for the specified handlers.
  *
  * @param send function the implements sending messages
  * @param destroy function that implements destroying the queue
  * @param cancel function that implements canceling a message
  * @param impl_state for the queue, passed to @a send, @a destroy and @a cancel
  * @param handlers array of message handlers
  * @param error_handler handler for read and write errors
  * @param cls closure for message handlers and error handler
  * @return a new message queue
  */
 struct GNUNET_MQ_Handle *
 GNUNET_MQ_queue_for_callbacks (GNUNET_MQ_SendImpl send,
                                GNUNET_MQ_DestroyImpl destroy,
                                GNUNET_MQ_CancelImpl cancel,
                                void *impl_state,
                                const struct GNUNET_MQ_MessageHandler *handlers,
                                GNUNET_MQ_ErrorHandler error_handler,
                                void *cls);
 
 
 /**
  * Change the closure argument in all of the `handlers` of the
  * @a mq.
  *
  * @param mq to modify
  * @param handlers_cls new closure to use
  */
 void
 GNUNET_MQ_set_handlers_closure (struct GNUNET_MQ_Handle *mq,
                                 void *handlers_cls);
 
 
 /**
  * Call a callback once the envelope has been sent, that is,
  * sending it can not be canceled anymore.
  * There can be only one notify sent callback per envelope.
  *
  * @param ev message to call the notify callback for
  * @param cb the notify callback
  * @param cb_cls closure for the callback
  */
 void
 GNUNET_MQ_notify_sent (struct GNUNET_MQ_Envelope *ev,
                        GNUNET_SCHEDULER_TaskCallback cb,
                        void *cb_cls);
 
 
 /**
  * Destroy the message queue.
  *
  * @param mq message queue to destroy
  */
 void
 GNUNET_MQ_destroy (struct GNUNET_MQ_Handle *mq);
 
 
 /**
  * Handle we return for callbacks registered to be
  * notified when #GNUNET_MQ_destroy() is called on a queue.
  */
 struct GNUNET_MQ_DestroyNotificationHandle;
 
 
 /**
  * Register function to be called whenever @a mq is being
  * destroyed.
  *
  * @param mq message queue to watch
  * @param cb function to call on @a mq destruction
  * @param cb_cls closure for @a cb
  * @return handle for #GNUNET_MQ_destroy_notify_cancel().
  */
 struct GNUNET_MQ_DestroyNotificationHandle *
 GNUNET_MQ_destroy_notify (struct GNUNET_MQ_Handle *mq,
                           GNUNET_SCHEDULER_TaskCallback cb,
                           void *cb_cls);
 
 /**
  * Cancel registration from #GNUNET_MQ_destroy_notify().
  *
  * @param dnh handle for registration to cancel
  */
 void
 GNUNET_MQ_destroy_notify_cancel (
   struct GNUNET_MQ_DestroyNotificationHandle *dnh);
 
 
 /**
  * Call the message message handler that was registered
  * for the type of the given message in the given message queue.
  *
  * This function is intended to be used for the implementation
  * of message queues.
  *
  * @param mq message queue with the handlers
  * @param mh message to dispatch
  */
 void
 GNUNET_MQ_inject_message (struct GNUNET_MQ_Handle *mq,
                           const struct GNUNET_MessageHeader *mh);
 
 
 /**
  * Call the error handler of a message queue with the given
  * error code.  If there is no error handler, log a warning.
  *
  * This function is intended to be used for the implementation
  * of message queues.
  *
  * @param mq message queue
  * @param error the error type
  */
 void
 GNUNET_MQ_inject_error (struct GNUNET_MQ_Handle *mq,
                         enum GNUNET_MQ_Error error);
 
 
 /**
  * Call the send implementation for the next queued message, if any.
  * Calls the send notification for the current message unless
  * #GNUNET_MQ_impl_send_in_flight was called for this envelope.
  *
  * Only useful for implementing message queues, results in undefined
  * behavior if not used carefully.
  *
  * @param mq message queue to send the next message with
  */
 void
 GNUNET_MQ_impl_send_continue (struct GNUNET_MQ_Handle *mq);
 
 
 /**
  * Call the send notification for the current message, but do not
  * try to send the next message until #gnunet_mq_impl_send_continue
  * is called.
  *
  * Only useful for implementing message queues, results in undefined
  * behavior if not used carefully.
  *
  * @param mq message queue to send the next message with
  */
 void
 GNUNET_MQ_impl_send_in_flight (struct GNUNET_MQ_Handle *mq);
 
 
 /**
  * Get the implementation state associated with the
  * message queue.
  *
  * While the GNUNET_MQ_Impl* callbacks receive the
  * implementation state, continuations that are scheduled
  * by the implementation function often only have one closure
  * argument, with this function it is possible to get at the
  * implementation state when only passing the `struct GNUNET_MQ_Handle`
  * as closure.
  *
  * @param mq message queue with the current message
  * @return message to send, never NULL
  */
 void *
 GNUNET_MQ_impl_state (struct GNUNET_MQ_Handle *mq);
 
 
 /**
  * Get the message that should currently be sent.
  * Fails if there is no current message.
  * Only useful for implementing message queues,
  * results in undefined behavior if not used carefully.
  *
  * @param mq message queue with the current message
  * @return message to send, never NULL
  */
 const struct GNUNET_MessageHeader *
 GNUNET_MQ_impl_current (struct GNUNET_MQ_Handle *mq);
 
 
 /**
  * Enum defining all known preference categories.
  *
  * @deprecated will be replaced by `enum GNUNET_MQ_PriorityPreference`
  */
 enum GNUNET_MQ_PreferenceKind
 {
   /**
    * No preference was expressed.
    */
   GNUNET_MQ_PREFERENCE_NONE = 0,
 
   /**
    * The preferred transmission for this envelope focuses on
    * maximizing bandwidth.
    */
   GNUNET_MQ_PREFERENCE_BANDWIDTH = 1,
 
   /**
    * The preferred transmission for this envelope foces on
    * minimizing latency.
    */
   GNUNET_MQ_PREFERENCE_LATENCY = 2,
 
   /**
    * The preferred transmission for this envelope foces on
    * reliability.
    */
   GNUNET_MQ_PREFERENCE_RELIABILITY = 3
 
 /**
  * Number of preference values allowed.
  */
 #define GNUNET_MQ_PREFERENCE_COUNT 4
 };
 
 
 /**
  * Convert an `enum GNUNET_MQ_PreferenceType` to a string
  *
  * @param type the preference type
  * @return a string or NULL if invalid
  *
  * @deprecated will be replaced by `enum GNUNET_MQ_PriorityPreference`
  */
 const char *
 GNUNET_MQ_preference_to_string (enum GNUNET_MQ_PreferenceKind type);
 
 
 #endif
 
 /** @} */ /* end of group mq */
 
 /** @} */ /* end of group addition */