changelog

最经典的bittorrent协议的实现的源码

            used to download a particular file.
          + Added some option-specific error messages to be displayed
            instead of the help/usage screen when invalid values are
            given on the command line.
     * Peer Handling
          + Peer statistics are maintained if a peer is dropped and later
            reconnects. This can influence unchoking, and the data is
            visible with CTCS.
          + The client is more discerning about choosing to reconnect to
            a lost peer.
          + Peer download rates (the rate at which we download from each
            peer) are now measured more precisely. This should produce
            more accurate unchoking decisions while downloading.
          + Inactive peers (who are interested but don't request any data
            while unchoked) are disconnected when seeding.
          + A newly-interested peer will be unchoked immediately if an
            opening is available.
          + Latency measurement is used to avoid counting errors that are
            likely due to transmission delays. To help with this, latency
            is now also measured when not downloading from a peer. The
            error threshold (tolerance) has also been reduced.
          + Don't count piece hash failures during Initial & Endgame
            modes, since it is likely that the component slices of a
            piece came from multiple peers.
     * Other performance improvements
          + Bandwidth limiting is now based on current (most recent)
            utilization rather than the past 20-second average. This
            should produce smoother loading of the line since we don't
            burst above the limit to make up for a recent slow period.
            Note that average values are still shown in the status line
            (and CTCS) since that is a better representation of the
            overall transfer rates.
          + Data transmission and receiving buffers are now much smaller
            but are still increased as necessary (and now decreased when
            appropriate as well).
          + Some allowance has been made for time to appear to move
            backwards, which could happen due to a system glitch,
            hardware problem, or clock adjustment. This has not been
            extensively tested (and probably won't be) but hadn't been
            reported as a problem either.
          + Timings related to bandwidth management and data transfer
            have been significantly reworked to allow more precise and
            accurate control.
          + Unneeded and bad data is no longer cached and does not cause
            additional piece completion checks.
          + Added additional fdset tracking to reduce processing in the
            checking and handling loops.
          + Other code optimizations not specifically listed here.
     * The Pause functionality is now more useful; it will now stop
       transferring torrent data almost immediately but still interact
       with peers and the tracker.

   Bug Fixes
     * Fixed a potential crash when reassigning a piece to a faster peer.
       While a serious bug, it would likely only show itself on
       memory-contrained systems.
     * Fixed reporting of file completion when using -n, and also with
       CTCS.
     * Ensure that the "completed" event is sent to the tracker during
       the next attempt if contacting the tracker is unsuccessful.
     * The amount of data transferred since the last update, shown in the
       status line, would go berzerk upon becoming a seeder. Some rate
       handling code has been cleaned up and tweaked to fix this.
     * A piece could be incorrectly reported as complete if an error
       occurred reading the piece data for hash verification.
     * Ensure that the client sends the tracker the "completed" event
       upon the next connection if contacting the tracker fails.

   Code Cleanup
     * Moved version number into a new m4 file to make patch distribution
       easier.
     * Changed method of locating and using SSL library and header files
       for SHA1 support. See the INSTALLING file for information about
       how to override this or give a hint to configure about where to
       find the files.
     * Added autoconf checks for integer types that may not be defined on
       some systems.
     * The funny business with cfg_max_slice_size is eliminated since
       request slice size is based on user option rather than a fixed
       request queue size.
     * Moved bandwidth limiting functions from peer.* to peerlist.*
     * Relocated and rewrote get_nl and set_nl.
     * Replaced hard-coded message component length values with
       constants.
     * Formatting adjustments.
     _________________________________________________________________

   Changes for "dnh2.2" Release

   Code Fixes
     * Fixed checking of seed ratio (-E option) to allow fractional
       values.
     * Fixed CTCS interaction when a limit was not specified on the
       command line.
     * Fixed peer reconnect determination.
     * Fixed a request-queue handling error that could cause a crash upon
       becoming a seeder.
     * Fixed creation of metainfo (torrent) file with multiple
       subdirectories.
     * Torrent metainfo is now only printed twice if hash-checking is
       performed.

   Operational Enhancements
     * Errors flushing the cache are now handled more gracefully. (This
       happens when the disk is full.)
     * Added additional seeder detection criteria.
     * Cleaned up parts of the help screen.
     _________________________________________________________________

   Changes for "dnh2.1" Release

   Code Fixes
     * Fixed interaction with CTCS under Linux, resulting in "Operation
       now in progress" errors.
     * Fixed a flaw in optimistic unchoke logic implementation.
     * Fixed problem with return value in _btf_ftruncate() related to my
       update for the vfat issue [btfiles patch].
     * Fixed handling of 301/302 redirect response from the tracker.

   Operational Enhancements
     * Attempt to reconnect to successful peers that disconnect
       unexpectedly, if possible.
     * Changed the unchoke choice algorithm when seeding. The new method
       is based on page 4 of the paper "Rarest First and Choke Algorithms
       Are Enough" by Arnaud Legout et al. An exception is that CTorrent
       chooses new unchokes using its original method (based on wait
       time) rather than randomly.
       See [1]the paper for details.
     _________________________________________________________________

   Changes for "dnh2" Release

   Patches
     * The following patches or their functionality are incorporated:
       1380164 [dnh1.2]
       1357832 [invert] (included in dnh1.2)
       1352866 [dnh1.1]
       1266767 [passkey2]
       1239547 [dnh1]
       1170457 [standalone-sha1] Added as a fallback case in configure if
       OpenSSL is not found. To force it to be used, define
       USE_STANDALONE_SHA1 in config.h (after running configure).
       1164454 [ip]
       1119610 [vfat] This bug appears to be linux-specific; I've tried
       to handle it in a more general way that may apply to similar
       situations on other platforms and filesystems, but I have limited
       capability to test this.
       1067196 [lfs] This is the large-file support that many have asked
       for.

   Optimization
     * Use fewer calls to random() by shifting the previously unused
       bits.
     * Time() calls have been greatly reduced; a global timestamp
       variable "now" is set once per main loop iteration and referenced
       in functions that need a timestamp (except the caching I/O
       routines which were left alone).
     * Overall current bandwidth rates are now computed only once per
       main loop and referenced in any routines that evaluate or control
       bandwidth.
     * Avoid flushing peer output buffers except in SendModule. This
       allows for some consolidation of messages to reduce network
       overhead.

   Code Fixes
     * Fixed use of cfg_req_queue_length to be the actual queue size
       (queue was half of this value).
     * Fixed: "peer is" verbose output could fubar the terminal.
     * Formatting: Replaced indentation tabs with spaces for consistency.

   Operational Enhancements
     * Improved piece selection methods to include rarity as a factor.
       This is not strictly "rarest-first", as we do not make a
       comprehensive effort to find the "rarest" piece or rank pieces by
       rarity. Rather, we use a more efficient compromise and try to find
       the set of pieces that have "trade value" (another peer needs
       them) and make a random choice from that set. Here is the current
       preference order used in each mode:
       Trade Value is defined as:
         1. Piece that only this peer has (not considering other
            seeders), that a peer in which we're interested needs.
         2. Piece that not every peer in which we're interested has.
         3. Piece that only this peer has (not considering other
            seeders).
         4. Piece that not every peer has.
       Normal Mode
         1. Piece we tried to get from another peer but stopped due to
            choking or lost connection. (We have part of the piece
            already.)
         2. Piece most recently acquired by the peer (possibly/probably
            rare).
         3. Piece with trade value.
         4. Any piece not yet requested.
       Initial-piece Mode
         1. Piece with trade value which is already in progress.
         2. Piece with trade value that more than one peer has.
         3. Piece with trade value.
         4. Any piece not yet requested.
       Endgame Mode
         1. Piece with trade value which is already in progress, of which
            we have the least amount.
         2. Piece already in progress of which we have the least amount.
     * Advanced request queueing system.
          + Instead of requesting all of the slices for a piece at one
            time, we now measure latency to the peer and send requests
            based on how long it takes the data to arrive. This avoids
            wasting upload banwidth by having too many outstanding
            requests: If we get choked or lose the connection, the extra
            requests were wasted; in initial or endgame modes, more
            requests would have to be cancelled when we completed the
            piece.
          + A new piece will be queued for download when there is space
            in the queue and we've requested the slices that have been
            queued already. We also don't wait for the current piece to
            complete before sending requests for a new piece. This helps
            to maintain a continuous flow of data in the download
            pipeline.
          + When duplicating a request in initial or endgame mode, slices
            that have already been requested are queued last.
     * Don't send HAVE messages to seeders (to save UL bandwidth).
          + Since we maintain interested state, and know the peer is a
            seeder, we'll do the right thing when we become a seeder.
          + Not sending HAVE to all peers (leechers) that already have
            the piece is a bad idea IMO. If everyone takes the same
            attitude, none of us will know when another becomes a seeder
            and connections will remain open/occupied.
          + We do send a HAVE to seeders upon completing our first piece
            so that we don't continue to appear empty.
     * Endgame strategy is used in get1file mode to complete the file.
     * Queue management:
          + Don't accept requests from choked peers.
          + Discard peer's reponse_q when we choke them.
          + Don't send cancels when we get choked (according to spec &
            discussions).
          + Don't put full piece queues in pending.
          + Move closing peer's request queue to pending instead of
            discarding it.
     * Prefer uploading to or downloading from a peer after we skip them
       due to bandwidth limiting. This is done via the g_next_up and
       g_defer_up global variables in peer.cpp (for UL; s/up/dn for the
       DL versions). The peerlist Sort() function and peer "click"
       variables have been removed since they are not needed with this
       feature.

   Options & Features
     * The -c option now reports file completion status.
          + As a side effect the metainfo details are printed twice. This
            allows you to view the torrent contents while pieces are
            being verified.
          + Total percentage completion is also added to the output.
     * "-E" option to seed to a specified UL:DL ratio. Seeding will stop
       when this ratio or the timeout (-e) is reached. If CTorrent starts
       as a seeder, the ratio is interpreted as UL:[torrent size].
     * If "-e 0" is specified (explicitly) and -E is used, there will be