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/****************************************************************************
 * Title       : Bandwidth management
 * File        : mod_bandwidth.c
 * Author      : Yann Stettler (stettler@cohprog.com)
 * Date        : 9 march 2007
 * Version     : 2.1 for Apache 1.3.29+
 *
 * Description :
 *   Provide bandwidth usage limitation either on the whole server or
 *   one a per connection basis based on the size of files, directory
 *   location or remote domain/IP.
 *
 * Revision    : 08/04/97 - "-1" value for LargeFileLimit to disable any
 *                          limits for that kind of files.
 *               01/26/98 - Include in_domain() and in_ip() in this file and
 *                          make them static so it will work with Apache 1.3x
 *               03/29/98 - Change to set bandwidth in VirtualHost directive
 *               07/17/99 - Minor changes to remove warnings at compil time
 *                          
 *                          Allow the use of the network/mask format when
 *                          setting a bandwidth for a remote host/network.
 *                          (Thanks to Sami Kuhmonen for the patch) 
 *
 *                          New directive BandWidthPulse
 *
 *               10/14/00 - Minor bug fixed
 *               12/15/00 - Bug fix when using mmap
 *               08/29/01 - Add a directive to change the data directory
 *                          (Thanks to Awesome Walrus <walrus@amur.ru> )
 *               01/12/03 - Add MaxConnection directive to limit the number
 *                          of simultaneous connections.
 *               03/09/07 - Add byte serving support and other stuff
 *
 ***************************************************************************
 * Copyright (c)1997 Yann Stettler and CohProg SaRL. All rights reserved.
 * Written for the Apache Group by :
 *
 * Yann Stettler
 * stettler@cohprog.com
 * http://www.cohprog.com/
 * http://www.animanga.com/
 *
 * Based on the original default_handler module and on bw_module 0.2 from
 * Etienne BERNARD (eb@via.ecp.fr) at VIA Centrale Reseaux, ECP, France
 * 
 * Many thanks to Colba Net Inc (Montreal) for their sponsoring of 
 * improvements to this module.
 *
 ***************************************************************************/


/*
 * Instruction :
 * -------------
 *
 * Note : this module was writen for Apache 1.3.x and tested on it
 *
 * Installation :
 *
 * 1) Insert the following line at the end of the "Configuration" file :
 *    Module bandwidth_module      mod_bandwidth.o
 *
 * WARNING : This behaviour is not the same between the various main versions
 *           of Apache. Please, read the instruction on our website for the
 *           instructions concerning the latest release : 
 *           http://www.cohprog.com/v3/bandwidth/doc-en.html
 *
 * 2) Run the "Configure" program and re-compile the server with "make".
 *
 * 3) Create the following directories with "rwx" permission to everybody :
 *    (or rwx for the user under which Apache run : Usualy "nobody")
 *    /tmp/apachebw
 *    /tmp/apachebw/link
 *    /tmp/apachebw/master
 *
 *  /==== by Awesome Walrus <walrus@amur.ru> =====================\
 *    Or you may change this name by using BandWidthDataDir global
 *    configuration directive. See below for details.
 *  \==== by Awesome Walrus <walrus@amur.ru> =====================/
 *
 * Note that if any of those directories doesn't exist, or if they can't
 * be accessed by the server, the module is totaly disabled except for
 * logging an error message in the logfile.
 *
 * Be careful that on some systems the content of the /tmp directory
 * is deleted at boot time or every so often by a cronjob. If that the
 * case, either disable this feature or change the location of the
 * directories used by the module in the sources bellow.
 *
 * Server configuration directive :
 * --------------------------------
 *
 *  /==== by Awesome Walrus <walrus@amur.ru> =====================\
 * -  BandWidthDataDir
 *    Syntax  : BandWidthDataDir <directory>
 *    Default : "tmp/apachebw"
 *    Context : server config
 *
 *    Sets the name of the directory used by mod_bandwidth to store
 *    its internal temporary information.
 *    If Apache is running in a chroot(2), this directive must be
 *    set relatively to ServerRoot ("tmp/apachebw").
 *    If Apache is running in an "unsecure" not chroot(2)ed mode,
 *    then the absolute path is needed ("/var/www/tmp/apachebw")
 *  \==== by Awesome Walrus <walrus@amur.ru> =====================/
 *
 * -  BandWidthModule 
 *    Syntax  : BandWidthModule <On|Off>
 *    Default : Off
 *    Context : per server config
 *
 *    Enable or disable totaly the whole module. By default, the module is
 *    disable so it is safe to compile it in the server anyway.
 *
 *    PLEASE, NOTE THAT IF YOU SET A BANDWIDTH LIMIT INSIDE A VIRTUALHOST
 *    BLOCK, YOU ALSO __NEED__ TO PUT THE "BandWidthModule On" DIRECTIVE
 *    INSIDE THAT VIRTUALHOST BLOCK !
 *
 *    IF YOU SET BANDWIDTH LIMITS INSIDE DIRECTORY BLOCKS (OUTSIDE OF
 *    ANY VIRTUALHOST BLOCK), YOU ONLY NEED TO PUT THE "BandWidthModule On"
 *    DIRECTIVE ONCE, OUTSIDE OF ANY VIRTUALHOST OR DIRECTORY BLOCK.
 *
 * -  BandWidthPulse
 *    Syntax  : BandWidthPulse <microseconds>
 *    Default :
 *    Context : per server config
 *
 *    Change the algorithm used to calculate bandwidth and transmit data.
 *    In normal mode (old mode), the module try to transmit data in packets
 *    of 1KB. That mean that if the bandwidth available is of 512B, the
 *    module will transmit 1KB, wait 2 seconds, transmit another 1KB and
 *    so one.
 *
 *    Seting a value with "BandWidthPulse", will change the algorithm so
 *    that the server will always wait the same amount of time between
 *    sending packets but the size of the packets will change.
 *    The value is in microseconds.
 *    For example, if you set "BandWidthPulse 1000000" (1 sec) and the
 *    bandwidth available is of 512B, the sever will transmit 512B,
 *    wait 1 second, transmit 512B and so on.
 *
 *    The advantage is a smother flow of data. The disadvantage is
 *    a bigger overhead of data transmited for packet header.
 *    Setting too small a value (bellow 1/5 of a sec) is not realy
 *    useful and will put more load on the system and generate more
 *    traffic for packet header.
 *
 *    Note also that the operating system may do some buffering on
 *    it's own and so defeat the purpose of setting small values.
 *
 *    This may be very useful on especialy crowded network connection :
 *    In normal mode, several seconds may happen between the sending of
 *    a full packet. This may lead to timeout or people may believe that
 *    the connection is hanging. Seting a value of 1000000 (1 sec) would
 *    guarantee that some data are sent every seconds...
 *
 * Directory / Server / Virtual Server configuration directive :
 * -------------------------------------------------------------
 *
 * -  BandWidth
 *    Syntax  : BandWidth <domain|ip|all> <rate>
 *    Default : none
 *    Context : per directory, .htaccess
 *
 *    Limit the bandwidth for files in this directory and
 *    sub-directories based on the remote host <domain> or
 *    <ip> address or for <all> remote hosts.
 *
 *    Ip addresses may now be specified in the network/mask format.
 *    (Ie: 192.168.0.0/21 )
 *
 *    The <rate> is in Bytes/second.
 *    A <rate> of "0" means no bandwidth limit.
 *
 *    Several BandWidth limits can be set for the same
 *    directory to set different limits for different
 *    hosts. In this case, the order of the "BandWidth"
 *    keywords is important as the module will take the
 *    first entry which matches the client address.
 *
 *    Example :
 *       <Directory /home/www>
 *       BandWidth ecp.fr 0
 *       BandWidth 138.195 0
 *       BandWidth all 1024
 *       </Directory>
 *
 *      This will limit the bandwith for directory /home/www and 
 *      all it's subdirectories to 1024Bytes/sec, except for 
 *      *.ecp.fr or 138.195.*.* where no limit is set.
 *
 * -  LargeFileLimit
 *    Syntax  : LargeFileLimit <filesize> <rate>
 *    Default : none
 *    Context : per directory, .htaccess
 *
 *    Set a maximal <rate> (in bytes/sec) to use when transfering
 *    a file of <filesize> KBytes or more.
 *
 *    Several "LargeFileLimit" can be set for various files sizes
 *    to create range. The rate used for a given file size will be
 *    the one of the matching range.
 *
 *    A <rate> of "0" mean that there isn't any limit based on
 *    the size.
 *
 *    A <rate> of "-1" mean that there isn't any limit for that type
 *    of file. It's override even a BandWidth limit. I found this usefull
 *    to give priority to very small files (html pages, very small pictures)
 *    while seting limits for larger files... (users with their video files
 *    can go to hell ! :)
 *
 *    Example :
 *    If the following limits are set :
 *       LargeFileLimit 200 3072
 *       LargeFileLimit 1024 2048
 *
 *       That's mean that a file of less than 200KBytes won't be
 *       limited based on his size. A file with a size between
 *       200KBytes (included) and 1023Kbytes (included) will be
 *       limited to 3072Bytes/sec and a file of 1024Kbytes or more
 *       will be limited to 2048Bytes/sec.
 *
 * -  MinBandWidth
 *    Syntax  : MinBandWidth <domain|ip|all> <rate>
 *    Default : all 256
 *    Context : per directory, .htaccess
 *
 *    Set a minimal bandwidth to use for transfering data. This
 *    over-ride both BandWidth and LargeFileLimit rules as well
 *    as the calculated rate based on the number of connections.
 *
 *    The first argument is used in the same way as the first
 *    argument of BandWidth.
 *
 *    <rate> is in bytes per second.
 *
 *    A rate of "0" explicitly means to use the default minimal
 *    value (256 Bytes/sec).
 *
 *    A rate of "-1" means that the minimal rate is equal to the
 *    actual rate defined by BandWidth and LargeFileLimit.
 *    In fact, that means that the final rate won't depend
 *    of the number of connections but only on what was defined.
 *
 *    Example :
 *    If BandWidth is set to "3072" (3KBytes/sec) and MinBandWidth
 *    is set to "1024" (1KBytes/sec) that means :
 *       - if there is one connection, the file will be transfered
 *         at 3072 Bytes/sec.
 *       - if there is two connections, each files will be transfered
 *         at 1536 Bytes/sec. 
 *       - if there is three or more connections, each files will be
 *         transfered at 1024 Bytes/sec. (Minimal of 1024 Bytes/sec).
 *
 *    If MinBandWidth is set to "-1" that means :
 *       - if there is one connection, the file will be transfered
 *         at 3072 Bytes/sec.
 *       - if there is two or more connections, each files will be
 *         transfered at 3072 Bytes/sec. In effect, the rate doesn't
 *         depend anymore on the number of connections but only on
 *         the configuration values.
 *
 *    Note that the total transfer rate will never exceed your physical
 *    bandwidth limitation.
 *
 * Note : If both a "BandWidth" and a "LargeFileLimit" limit apply,
 *        the lowest one will be used. (But never lower than the
 *        "MinBandWidth" rate)
 *
 *        If both a virtual server limit is defined and another
 *        apply for a directory under this virtual server, the
 *        directory limit will over-ride it.
 *
 *        If a limit is defined outside a Directory or VirtualHost
 *        directive, it will act as default on a per virtual server
 *        basis. (Ie: each virtual server will have that limit,
 *        _independantly_ of the other servers)
 *
 * -  MaxConnection
 *    Syntax  : MaxConnection <connections>
 *    Default : 0 (illimited)
 *    Context : per directory, .htaccess 
 *
 *    Restrict the number of maximum simultanous connections. If the
 *    limit is reached, new connections will be rejected.
 "
 *    A value of 0 mean that there isn't any limits.
 *
 * Implementation notes :
 * ----------------------
 * 
 * 1) This module isn't called when serving a cgi-script. In this
 *    case, it's the functions in mod_cgi.c that handle the connection.
 *
 *    That's not a bug : I didn't want to change the cgi_module and
 *    I was too lazy to do it anyway.
 *
 * 2) The rate of data transmission is only calculated. It isn't
 *    measured. Which mean that this module calculates the final
 *    rate that should apply for a file and simply divides this
 *    number by the number of actual connections subject to the
 *    same "per directory" directives.
 * 
 * 3) On the "+" side, the module regulate the speed taking
 *    into account the actual time that was needed to send the
 *    data. Which also mean that if data are read by the client
 *    at a slowest rate than the limit, no time will be lost and
 *    data will be sent as fast as the client can read them (but
 *    no faster than the limited rate :) ...
 *
 * 4) Some kind of buffering is done as side effect. Data are
 *    sent in packet of 1024 Bytes which seems a good value
 *    for TCP/IP.
 *    If another packet size is wanted, change the value of
 *    "#define PACKET" in the codes bellow.
 *
 * 5) The default value for MinBandWidth is defined by :
 *    "#define MIN_BW_DEFAULT" (in Bytes/sec)
 *
 * 6) Don't define "BWDEBUG" for a production server :
 *    this would log a _lot_ of useless informations for
 *    debuging purpose.
 *
 */

