CONCEPT
        driver hooks

DESCRIPTION
        To allow a greater flexibility of the muds, the gamedrivers
        since 3.2.1 moved several once hardcoded 'underground'
        activities from the driver into the mudlib. This includes for
        example the differences between compat and native mode.

        The hooks are set with the privileged efun set_driver_hook().
        Some of the hooks are mandatory, some not. Most hooks accept
        unbound lambda closures as values, some also lfun closures or
        even strings.
        The hooks are identified by an ordinal number, for which
        symbolic names are defined in /sys/driverhooks.h.

        H_MOVE_OBJECT0
        H_MOVE_OBJECT1
          Mandatory hooks to implement the efun void move_object().
          Hook setting must be an unbound lambda closure:

            void <closure>(object item, object dest)

          Upon call, the hook has to perform the move itself (by using
          set_environment()) and all depending actions (like the calls to
          init() to add actions).

          The difference lies in the binding of the set hook prior to
          the call: the H_MOVE_OBJECT0 closure is bound to the current
          object, the H_MOVE_OBJECT1 to 'item'.
          If both hooks are set, H_MOVE_OBJECT0 is ignored.


        H_LOAD_UIDS
        H_CLONE_UIDS
          Mandatory hooks to determine the uid and euid of loaded or cloned
          objects.  Hook settings can be any closure:

            mixed <load_uids closure> (string objectname)
            mixed <clone_uids closure>(object blueprint, string objectname)

          When an object is newly loaded, the H_LOAD_UIDS hook is
          called with the object name as argument.
          When an object is cloned, the H_CLONE_UIDS hook is called
          with the blueprint object as first and the clone's designated
          name as second argument.
          In both cases the new object already exists, but has 0 uids.

          For the result, the following possibilities exist (<num> is
          a non-zero number, <no-string> is anything but a string):

             "<uid>"                    -> uid = "<uid>", euid = "<uid>"
             ({ "<uid>", "<euid>" })    -> uid = "<uid>", euid = "<euid>"
             ({ "<uid>", <no-string> }) -> uid = "<uid>", euid = 0

          If strict-euids is not active, the following results are
          possible, too:

             <num>                      -> uid = 0, euid = 0
             ({ <num>, "<euid>" })      -> uid = 0, euid = "<euid>"
             ({ <num>, <no-string> })   -> uid = 0, euid = 0


        H_CREATE_SUPER
        H_CREATE_OB
        H_CREATE_CLONE
          Optional hooks to initialize an object after creation.
          Hook setting can be unbound lambda closures, or the name of
          the function to call in the object.

          H_CREATE_SUPER is called for blueprints implicitely loaded
          by inheritance, H_CREATE_OB for explicitely loaded
          blueprints/objects, and H_CREATE_CLONE for cloned objects.

          If the hook is a closure expecting an argument, it is bound
          to the current object and called as

            int <closure> (object obj_to_init)

          If the hook as a closure without arguments, it is bound to
          the object to be initalized and called as

            int <closure> ( void )

          If the result of the call is a non-zero number, it is used
          as the interval to wait before the first reset(), else the default
          interval computed from TIME_TO_RESET is used.

          If the hook is defined as the name of an lfun in the object,
          it is called in the object as

            void <name>(0)

          and any result is ignored.
          In this call the previous_object() is the object initiating
          the load.


        H_RESET
          Optional hook to reset an object.
          Hook setting can be unbound lambda closures, or the name of
          the function to call in the object.

          This hook is called to reset the object after a certain time
          since its creation/last reset.

          If the hook is a closure, it is bound to the object to be
          reset and called with no argument:

            void|int <closure> ( void )

          If the result of the call is a positive number, it is used
          as the interval to wait before the next reset().
          If the result is 0, the default interval computed from
          TIME_TO_RESET is used.
          If the result is a negative number, the object will not be
          reset again, unless directed otherwise by set_next_reset().

          If the hook is defined as the name of an lfun in the object,
          it is called in the object as

            void <name>(1)

          and any result is ignored.
          In this call the previous_object() is the object initiating
          the reset.
          If the function does not exist, the object won't be reset
          again.


        H_CLEAN_UP
          Optional hook to clean up an object.
          Hook setting can be any closure, or the name of the function
          to call in the object.

          This hook is called for an object if it hasn't been used
          for at least TIME_TO_CLEAN_UP seconds, to give it the
          opportunity to self destruct.

          If the hook is a closure, it is called as

            int <closure>(int ref, object ob)

          with the object's refcount as first argument, and object itself as
          second. Lambda closures are also bound to the object prior to the
          call.

          If the hook is the name of an lfun, it is called in the
          object with its refcount as argument:

            void|int <name>(int ref)

          In both calls, the refcount is constructed as:

            ref = 0: the object is a clone, or a blueprint with
                     replaced program.
            ref = 1: the object is a swapped or unused blueprint.
            ref > 1: the object is a used blueprint with <ref> references.

          The cleanup method has the possibility to destruct the
          object. To survive this time, but try again some time later,
          the call has to result in a non-zero value.

          If the hook specifies a non-existing lfun, or if the call
          returns 0, no further attempt to clean up this object will be done.


        H_COMMAND
          Optional hook to parse and execute commands. If this hook is used,
          it bypasses the normal command parsing done by the driver (including
          the MODIFY_COMMAND and NOTIFY_FAIL hooks).

          The hook is called with two parameters: the command received
          from the living (interactive user or NPC), and the living object
          (the 'command giver') itself. The hook has to return non-0 if the
          command was found and executed, and 0 otherwise.

          At the time the hook is called, query_command() returns the command
          string and this_player() returns the living object. query_verb() and
          query_notify_fail() return 0.

          If the hook is a string, it is the name of an lfun in the command
          giver:

              int <name>(string command, object command_giver)

          If the hook is a closure, it is called as:

              int <closure>(string command, object command_giver)

          Lambda-closures are additionally bound to the command_giver.


        H_MODIFY_COMMAND
          Optional hook to modify commands (both entered or given by a
          call to command()) before the parser sees them (this includes
          special commands like 'status').

          Hook setting can be any closure, the name of the function
          to call in the object, or a mapping.

          For interactives this hook is used only if the interactive
          object has no command modifier already set by the efun
          set_modify_command().

          If the hook is a closure, it is called as

            int|string <closure>(string cmd, object player)

          with the entered command as first, and the command giving
          player as second argument.

          If the hook is a string, it is used as the name of an lfun
          in the command giving player, which is called as

            int|string <name>(string cmd)

          If the hook is a mapping, it is queried with the given
          command as index, and the data retrieved is used (defaults
          to 0 if no data is stored for a given command). If an entry
          is a closure, it is called as

            int|string <closure>(string cmd, object player)

          and the result from the call is used as 'the' result.

          The result is treated equal in all three cases.
          If the result is a string, it is the new command to execute
          instead of the given one. Note that it is not possible to
          make several commands from one this way!
          If the result is a non-zero number, the given command is to
          be ignored. In case of the closure/lfun setting this may
          mean that the closure/lfun already executed it.
          If the result is 0, the originally given command is to be
          used.

          It is possible for the hook to change the command giver
          (this_player()) for the execution of the command. This means that
          even though the commands are execute for the original commandgiver,
          this_player() will return the changed commandgiver.


        H_MODIFY_COMMAND_FNAME
          Mandatory hook specifying the name of the 'modify_command'
          function to call for newly entered commands as result of a
          set_modify_command().

          Hook setting must be a string.

          If set_modify_command() is used for an interactive user, all
          newly entered commands are first passed to the function
          named by this hook.

          The function is called as

            int|string <name>(string cmd)

          If the result is a string, it is the new command to execute
          instead of the given one. Note that it is not possible to
          make several commands from one this way!
          If the result is a non-zero number, the given command is to
          be ignored. In case of the closure/lfun setting this may
          mean that the closure/lfun already executed it.
          If the result is 0, the originally given command is to be
          used.

          It is possible for the hook to change the command giver
          (this_player()) for the execution of the command. This means that
          even though the commands are execute for the original commandgiver,
          this_player() will return the changed commandgiver.


        H_NOTIFY_FAIL
          Mandatory hook to issue the default message if an entered
          command couldn't be parsed and no notify_fail() command is
          in effect.
          Hook setting can be a any closure, or a string.

          If set to a string, it is the message returned to the
          player.
          If set to a closure, it is called as

            string <closure>(string entered_command, object cmd_giver)

          and the result is used as failure message. Lambda closures
          are bound to this_player() prior to execution.

          <cmd_giver> is the object which received the command in
          the first place. It is usually identical with this_player(),
          unless the H_MODIFY_COMMAND hook changed it.


        H_SEND_NOTIFY_FAIL
          Optional hook to send the notify fail message, regardless
          of how it was determined, to the player. If the hook is not
          set, the message is delivered using tell_object() internally.
          Hook setting can be a string or a closure.

          If the hook is a string, it is the name of a (possibly static)
          function to call in the current command giver. If the hook
          is a closure, it is the function to be called. Lambda closures
          are bound to the current command giver first.

          The function is called as

            void <function>(string msg, object msgobj, object orig_cmd_giver)

          <msg> is the notify fail message to be delivered.
          <msgobj> is the object which set the message. It is 0 for the
          default message.
          <orig_cmd_giver> is the object for which the original command
          was first received. It is usually identical with the current
          command giver this_player().


        H_NO_IPC_SLOT
          Optional hook specifying the message given to logins
          rejected due to space limitations (MAX_PLAYER).
          Hook setting has to be string.
          If set to 0, the default message "Lpmud is full. Come back
          later." is issued.


        H_INCLUDE_DIRS
          Semi-mandatory hook specifying the directories where <>-type
          include files are searched (this includes ""-includes not
          found as specified).
          Hook setting may be any closure or a string array.
          If not set, only ""-type includes may be used in LPC
          programs.

          If the hook setting is a string array, it has to contain the
          path names of those directories where <>-type includes are
          to be searched. The directories are searched in the order
          they appear in the array. The directory name and the name of
          the actual include file are concatenated, therefore the
          directory names have to end in '/'. Leading slashes may be
          omitted.

          If the setting is a closure, it is called as

            string <closure>(string include_name, string current_file)

          with the name of the desired include file as first, and the
          name of the compiled LPC file as second argument.
          Result has to be the complete path name of the include file
          to use (leading slashes may be omitted).
          If the closure is a lambda closure, it is bound to
          this_object() prior to execution.

          See also: master apply include_file()


        H_AUTO_INCLUDE
          Optional hook specifying a string to be included before
          the source of every compiled LPC object.
          Hook setting can be a string or a closure.

          If the setting is a string, it will be automatically included before
          the source of every compiled LPC object.

          If the setting is a closure, it is called as

            string <closure>(string base_file, string current_file
                            , int sys_include)

          for every file opened by the compiler. <base_file> will be the
          filename of the compiled object, <current_file> the name of a file
          included directly or indirectly by the <base_file>. When the
          <base_file> itself is opened, <current_file> will be 0. For an
          included file, <sys_include> will be TRUE if it is a <>-type
          include.

          If the result is a string, it will be included before the actual
          text of the file.


        H_TELNET_NEG
          Optional hook to specifiy how to perform a single telnet
          negotiation.
          Hook setting may be any closure or a string.
          If not set, most telnet options are rejected (read: only a
          very minimal negotiation takes place).

          The hook is called whenever the driver receives a demand for
          option negotiation for:

            SB:               Suboption negotiation
            TELOPT_LINEMODE:  linemode
            TELOPT_NAWS:      window size
            TELOPT_TTYPE:     terminal type
            TELOPT_TM:        timing mark
            TELOPT_NEWENV:    remote environment variables
            TELOPT_ENVIRON:   remote environment variables
            TELOPT_XDISPLOC:  remote X display address
            TELOPT_TSPEED:    terminal speed
            TELOPT_BINARY:    binary data, needed for non-ASCII charsets
            TELOPT_EOR:       TinyFugue prompt marker (together with EOR)

            TELOPT_COMPRESS:  Mud Compression Protocol
            TELOPT_COMPRESS2: Mud Compression Protocol
            TELOPT_MSP:       Mud Sound Protocol
            TELOPT_MXP:       Mud Extension Protocol

          The hook has then to perform the negotiation using the efun
          binary_message().

          Alternatively, if H_NOECHO is set, this hook is called
          for all telnet data received.

          If the setting is a string, it used as name of an lfun to
          call in this_player():

            void|mixed <name>(int action, int option [, int * opts ] )

          Similar, if the setting is a closure, it is called as:

            void|mixed <closure>(int action, int option [, int * opts ] )

          with unbound lambda-closures being bound to this_player()
          prior to execution.

          The hook is called for a 'DO/DONT/WILL/WONT <opt>' with the action
          (DO/DONT/...) as the first, and <opt> as the second argument.

          If the driver receives the sequence

            IAC SB <opt> <opts>...

          followed by IAC SB/SE,  the hook is called with 'SB' as first
          argument, <opt> as second, and <opts> as an array of integers as
          third argument.


        H_NOECHO
          Optional hook to specifiy how to perform the telnet actions
          to switch the echo mode (used for e.g. password input_to()s).
          Hook setting may be any closure or a string.
          If not set, a default handling is performed.

          If the setting is a string, it used as name of an lfun to
          call in the intercative <user>:

            void <name>(int flag, object user)

          where <flag> is the echo-flag passed to the input_to()
          statement.
          Similar, if the setting is a closure, it is called as:

            void <closure>(int flag, object user)

          with unbound lambda-closures being bound to this_player()
          prior to execution.

          When set, the hook is called whenever the driver needs to
          change the echo mode, thus you can negotiate about things
          that are coupled with it, like LINEMODE or
          character-at-a-time.

          IMPORTANT: If this hook is used, the control of all telnet
          negotiation is transferred to the mudlib: all incoming negotiations
          are passed to H_TELNET_NEG, and the sending of no-echo negotiations
          is handled by this hook.


        H_ERQ_STOP
          Optional hook to notify the mudlib about the termination of
          the erq demon.
          Hook setting may be any closure.

          The closure is called without arguments:

            void <closure>()

          and may do whatever it likes to clean-up after the erq.


HISTORY
        H_NOTIFY_FAIL recevied the new 'command_giver' argument in 3.2.7.
        The hooks concept was introduced in 3.2.1
        The hook for moving was introduced in 3.2.1@1
        The hook for clean up was introduced in 3.2.1@34
        The hook for modifying commands was introduced in 3.2.1@51,
            the evaluation of mapping as hooks was extended in 3.2.1@54.
            The lfun called as result of set_modify_command() was
            'hooked' in 3.2.1@109.
        The hooks for notify_fail and full muds were introduced in 3.2.1@55.
        The hook for include dirs was introduced in 3.2.1@57.
        The hook for telnet negotiation was introduced in 3.2.1@60.
        The hooks for no-echo negotiation and erq-lossage notification
            were introduced in 3.2.1@85.
        H_COMMAND was introduced in 3.2.7.
        H_SEND_NOTIFY_FAIL and H_AUTO_INCLUDE were introduced in 3.2.9.

SEE ALSO
        native(C), set_driver_hook(E)
