--- /dev/null
+! Copyright (C) 2020 John Benediktsson
+! See http://factorcode.org/license.txt for BSD license
+USING: accessors arrays assocs bencode byte-arrays checksums
+checksums.sha combinators fry grouping http.client io io.binary
+io.encodings.binary io.files io.pathnames io.sockets
+io.streams.byte-array kernel literals make math math.bitwise
+math.parser math.ranges namespaces random sequences splitting
+strings urls ;
+
+IN: bittorrent
+
+<<
+CONSTANT: ALPHANUMERIC $[
+ [
+ CHAR: a CHAR: z [a,b] %
+ CHAR: A CHAR: Z [a,b] %
+ CHAR: 0 CHAR: 9 [a,b] %
+ ".-_~" %
+ ] { } make
+]
+
+: random-peer-id ( -- bytes )
+ 20 [ ALPHANUMERIC random ] B{ } replicate-as ;
+>>
+
+SYMBOL: torrent-peer-id
+torrent-peer-id [ random-peer-id ] initialize
+
+SYMBOL: torrent-port
+torrent-port [ 6881 ] initialize
+
+
+! bitfield
+
+: bitfield-index ( n -- j i )
+ 8 /mod 7 swap - ;
+
+: set-bitfield ( elt n bitfield -- )
+ [ bitfield-index rot ] dip -rot
+ '[ _ _ [ set-bit ] [ clear-bit ] if ] change-nth ;
+
+: check-bitfield ( n bitfield -- ? )
+ [ bitfield-index swap ] dip nth bit? ;
+
+
+! http
+
+: http-get-bencode ( url -- obj )
+ <get-request> BV{ } clone [
+ '[ _ push-all ] with-http-request* check-response drop
+ ] keep B{ } like bencode> ;
+
+
+! metainfo
+
+GENERIC: load-metainfo ( obj -- metainfo )
+
+M: url load-metainfo http-get-bencode ;
+
+M: pathname load-metainfo
+ binary [ read-bencode ] with-file-reader ;
+
+M: string load-metainfo
+ dup "http" head? [ >url ] [ <pathname> ] if load-metainfo ;
+
+: info-hash ( metainfo -- hash )
+ "info hash" swap dup '[
+ drop _ "info" of >bencode sha1 checksum-bytes
+ ] cache ;
+
+: announce-url ( metainfo -- url )
+ dup "announce-list" of [ nip first random ] [ "announce" of ] if* ;
+
+: scrape-url ( metainfo -- url/f )
+ announce-url "announce" over path>> subseq? [
+ [ "announce" "scrape" replace ] change-path
+ ] [ drop f ] if ;
+
+
+
+! tracker
+
+: tracker-url ( metainfo -- url )
+ {
+ [ announce-url >url ]
+ [
+ info-hash "info_hash" set-query-param
+ torrent-peer-id get "peer_id" set-query-param
+ torrent-port get "port" set-query-param
+ 0 "uploaded" set-query-param
+ 0 "downloaded" set-query-param
+ 1 "compact" set-query-param
+ ]
+ [
+ { "info" "length" } [ of ] each
+ "left" set-query-param
+ ]
+ } cleave ;
+
+: parse-peer4 ( peerbin -- inet4 )
+ 4 cut [
+ [ number>string ] { } map-as "." join
+ ] dip be> <inet4> ;
+
+: parse-peer4s ( peersbin -- inet4s )
+ dup array? [
+ [ [ "ip" of ] [ "port" of ] bi <inet4> ] map
+ ] [
+ 6 <groups> [ parse-peer4 ] map
+ ] if ;
+
+: parse-peer6 ( peerbin -- inet6 )
+ 16 cut [
+ 2 <groups> [ be> number>string ] map ":" join
+ ] dip be> <inet6> ;
+
+: parse-peer6s ( peersbin -- inet6s )
+ 18 <groups> [ parse-peer6 ] map ;
+
+: load-tracker ( torrent -- response )
+ tracker-url http-get-bencode
+ "peers" over [ parse-peer4s ] change-at ;
+
+: send-event ( torrent event -- response )
+ [ tracker-url ] [ "event" set-query-param ] bi*
+ http-get-bencode ;
+
+
+
+! messages
+
+TUPLE: handshake string reserved info-hash peer-id ;
+
+: <handshake> ( info-hash peer-id -- handshake )
+ handshake new
+ "BitTorrent protocol" >byte-array >>string
+ 8 <byte-array> >>reserved
+ swap >>peer-id
+ swap >>info-hash ;
+
+: read-handshake ( -- handshake/f )
+ read1 [
+ [ 48 + read ] keep cut 8 cut 20 cut handshake boa
+ ] [ f ] if* ;
+
+: write-handshake ( handshake -- )
+ {
+ [ string>> [ length write1 ] [ write ] bi ]
+ [ reserved>> write ]
+ [ info-hash>> write ]
+ [ peer-id>> write ]
+ } cleave flush ;
+
+TUPLE: keep-alive ;
+TUPLE: choke ;
+TUPLE: unchoke ;
+TUPLE: interested ;
+TUPLE: not-interested ;
+TUPLE: have index ;
+TUPLE: bitfield bitfield ;
+TUPLE: request index begin length ;
+TUPLE: piece index begin block ;
+TUPLE: cancel index begin length ;
+TUPLE: port port ;
+TUPLE: suggest-piece index ;
+TUPLE: have-all ;
+TUPLE: have-none ;
+TUPLE: reject-request index begin length ;
+TUPLE: allowed-fast index ;
+TUPLE: extended id payload ;
+TUPLE: unknown id payload ;
+
+: read-int ( -- n/f ) 4 read [ be> ] [ f ] if* ;
+
+: parse-message ( bytes -- message/f )
+ unclip {
+ ! Core Protocol
+ { 0 [ drop choke boa ] }
+ { 1 [ drop unchoke boa ] }
+ { 2 [ drop interested boa ] }
+ { 3 [ drop not-interested boa ] }
+ { 4 [ 4 head be> have boa ] }
+ { 5 [ bitfield boa ] }
+ { 6 [ 4 cut 4 cut 4 head [ be> ] tri@ request boa ] }
+ { 7 [ 4 cut 4 cut [ [ be> ] bi@ ] dip piece boa ] }
+ { 8 [ 4 cut 4 cut 4 head [ be> ] tri@ cancel boa ] }
+
+ ! DHT Extension
+ { 9 [ be> port boa ] }
+
+ ! Fast Extensions
+ { 0x0D [ 4 head be> suggest-piece boa ] }
+ { 0x0E [ drop have-all boa ] }
+ { 0x0F [ drop have-none boa ] }
+ { 0x10 [ 4 cut 4 cut 4 head [ be> ] tri@ reject-request boa ] }
+ { 0x11 [ 4 head be> allowed-fast boa ] }
+
+ ! Extension Protocol
+ { 0x14 [ unclip swap extended boa ] }
+
+ ! Hash Transfer Protocol
+ ! { 0x15 [ "HashRequest" ] }
+ ! { 0x16 [ "Hashes" ] }
+ ! { 0x17 [ "HashReject" ] }
+ [ swap unknown boa ]
+ } case ;
+
+: read-message ( -- message )
+ read-int {
+ { f [ f ] }
+ { 0 [ keep-alive boa ] }
+ [ read [ parse-message ] [ f ] if* ]
+ } case ;
+
+: write-int ( n -- ) 4 >be write ;
+
+GENERIC: write-message ( message -- )
+
+M: keep-alive write-message drop 0 write-int ;
+
+M: choke write-message drop 1 write-int 0 write1 ;
+
+M: unchoke write-message drop 1 write-int 1 write1 ;
+
+M: interested write-message drop 1 write-int 2 write1 ;
+
+M: not-interested write-message drop 1 write-int 3 write1 ;
+
+M: have write-message
+ 5 write-int 4 write1 index>> write-int ;
+
+M: bitfield write-message
+ field>> dup length 1 + write-int 5 write1 write ;
+
+M: request write-message
+ [ index>> ] [ begin>> ] [ length>> ] tri
+ 13 write-int 6 write1 [ write-int ] tri@ ;
+
+M: piece write-message
+ [ index>> ] [ offset>> ] [ block>> ] tri
+ dup length 9 + write-int 7 write1
+ [ write-int ] [ write-int ] [ write ] tri* ;
+
+M: cancel write-message
+ [ index>> ] [ offset>> ] [ length>> ] tri
+ 13 write-int 8 write1 [ write-int ] tri@ ;
+
+M: port write-message
+ 5 write-int 9 write1 port>> write-int ;
+
+M: suggest-piece write-message
+ 5 write-int 0x0D write1 index>> write-int ;
+
+M: have-all write-message drop 1 write-int 0x0E write1 ;
+
+M: have-none write-message drop 1 write-int 0x0F write1 ;
+
+M: reject-request write-message
+ [ index>> ] [ begin>> ] [ length>> ] tri
+ 13 write-int 0x10 write1 [ write-int ] tri@ ;
+
+M: allowed-fast write-message
+ 5 write-int 0x11 write1 index>> write-int ;
+
+M: extended write-message
+ [ payload>> ] [ id>> ] bi
+ over length 2 + write-int 0x14 write1 write1 write ;
+
+M: unknown write-message
+ [ payload>> ] [ id>> ] bi
+ over length 1 + write-int write1 write ;
+
+: >message ( bytes -- message )
+ binary [ read-message ] with-byte-reader ;
+
+: message> ( message -- bytes )
+ binary [ write-message ] with-byte-writer ;
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