Signalizace je \u00fazce spjata s na\u0161\u00ed implementac\u00ed soket\u016f, popsanou v n\u00e1sleduj\u00edc\u00ed \u010d\u00e1sti.<\/li>\n<\/ul>\n\nSeznam server\u016f uvnit\u0159 hry a na domovsk\u00e9 str\u00e1nce<\/i><\/p>\nImplementace soket\u016f<\/h1>\n
\nChceme vytvo\u0159it API, kter\u00e9 bude co nejbl\u00ed\u017ee Posix UDP soket\u016fm, abychom minimalizovali pot\u0159ebn\u00e9 zm\u011bny.<\/p>\n
Chceme tak\u00e9 implementovat nezbytn\u00e9 minimum, kter\u00e9 je nutn\u00e9 pro z\u00e1kladn\u00ed v\u00fdm\u011bnu dat p\u0159es s\u00ed\u0165.<\/p>\n
Nap\u0159\u00edklad nepot\u0159ebujeme skute\u010dn\u00e9 sm\u011brov\u00e1n\u00ed: v\u0161echny peer jsou um\u00edst\u011bny v jedn\u00e9 'virtu\u00e1ln\u00ed LAN', kter\u00e1 je spojena s konkr\u00e9tn\u00edm instance datab\u00e1ze Firebase.<\/p>\n
Proto nepot\u0159ebujeme unik\u00e1tn\u00ed IP adresy: pro unik\u00e1tn\u00ed identifikaci peer sta\u010d\u00ed pou\u017e\u00edt unik\u00e1tn\u00ed hodnoty kl\u00ed\u010d\u016f Firebase (podobn\u011b jako dom\u00e9nov\u00e1 jm\u00e9na), a ka\u017ed\u00fd peer m\u00edstn\u011b p\u0159i\u0159azuje 'fale\u0161n\u00e9' IP adresy ka\u017ed\u00e9mu kl\u00ed\u010di, kter\u00fd je t\u0159eba p\u0159ev\u00e9st. To n\u00e1s zcela osvobozuje od pot\u0159eby glob\u00e1ln\u00edho p\u0159id\u011blov\u00e1n\u00ed IP adres, co\u017e je netrivi\u00e1ln\u00ed \u00fakol.<\/p>\n
Zde je minim\u00e1ln\u00ed API, kter\u00e9 mus\u00edme implementovat:<\/p>\n
\/\/ Create and destroy a socket\nint socket();\nint close(int fd);\n\/\/ Bind a socket to a port, and publish it on Firebase\nint bind(int fd, AddrInfo* addr);\n\/\/ Send a packet. This lazily create a WebRTC connection to the \n\/\/ peer when necessary\nint sendto(int fd, uint8_t* buf, int len, const AddrInfo* addr);\n\/\/ Receive the packets destined to this socket\nint recvfrom(int fd, uint8_t* buf, int len, AddrInfo* addr);\n\/\/ Be notified when new packets arrived\nint recvCallback(Callback cb);\n\/\/ Obtain a local ip address for this peer key\nuint32_t resolve(client::String* key);\n\/\/ Get the peer key for this ip\nString* reverseResolve(uint32_t addr);\n\/\/ Get the local peer key\nString* local_key();\n\/\/ Initialize the library with the given Firebase database and \n\/\/ WebRTc connection options\nvoid init(client::FirebaseConfig* fb, client::RTCConfiguration* ice);<\/code><\/pre>\n\nAPI je jednoduch\u00e9 a podob\u00e1 se API Posix soket\u016f, ale m\u00e1 n\u011bkolik d\u016fle\u017eit\u00fdch rozd\u00edl\u016f: registrace zp\u011btn\u00fdch vol\u00e1n\u00ed, p\u0159i\u0159azen\u00ed m\u00edstn\u00edch IP a 'leniv\u00e9' p\u0159ipojen\u00ed<\/strong>.<\/p>\nRegistrace zp\u011btn\u00fdch vol\u00e1n\u00ed<\/h2>\n \nI kdy\u017e p\u016fvodn\u00ed program pou\u017e\u00edv\u00e1 neblokuj\u00edc\u00ed vstup\/v\u00fdstup, pro spu\u0161t\u011bn\u00ed v webov\u00e9m prohl\u00ed\u017ee\u010di je t\u0159eba k\u00f3d refaktorovat.<\/p>\n
D\u016fvodem je, \u017ee cyklus ud\u00e1lost\u00ed v prohl\u00ed\u017ee\u010di je skryt p\u0159ed programem (a\u0165 u\u017e se jedn\u00e1 o JavaScript nebo WebAssembly).<\/p>\n
V nativn\u00edm prost\u0159ed\u00ed m\u016f\u017eeme ps\u00e1t k\u00f3d t\u00edmto zp\u016fsobem<\/p>\n
while(running) {\n select(...); \/\/ \u010dekejte na I\/O ud\u00e1losti\n while(true) {\n int r = readfrom(...); \/\/ pokus o \u010dten\u00ed\n if (r < 0 && errno == EWOULDBLOCK) \/\/ \u017e\u00e1dn\u00e1 dal\u0161\u00ed data k dispozici\n break;\n ...\n }\n ...\n}<\/code><\/pre>\n\nPokud je cyklus ud\u00e1lost\u00ed pro n\u00e1s skryt\u00fd, mus\u00edme ho p\u0159ev\u00e9st na n\u011bco podobn\u00e9ho:<\/p>\n
auto cb = []() { \/\/ toto bude vol\u00e1no, kdy\u017e jsou nov\u00e1 data k dispozici\n while(true) {\n int r = readfrom(...); \/\/ pokus o \u010dten\u00ed\n if (r < 0 && errno == EWOULDBLOCK) \/\/ \u017e\u00e1dn\u00e1 dal\u0161\u00ed data k dispozici\n break;\n ...\n }\n ...\n};\nrecvCallback(cb); \/\/ registrace zp\u011btn\u00e9ho vol\u00e1n\u00ed<\/code><\/pre>\n<\/p>\n
P\u0159i\u0159azen\u00ed m\u00edstn\u00edch IP<\/h2>\n \nIdentifik\u00e1tory uzl\u016f v na\u0161\u00ed \"s\u00edti\" nejsou IP adresy, ale kl\u00ed\u010de Firebase (jsou to \u0159et\u011bzce, kter\u00e9 vypadaj\u00ed takto: -LmEC50PYZLCiCP-vqde<\/code> ).<\/p>\nJe to pohodln\u00e9, proto\u017ee nepot\u0159ebujeme mechanismus pro p\u0159i\u0159azen\u00ed IP a kontrolu jejich jedine\u010dnosti (ani jejich likvidaci po odpojen\u00ed klienta), ale \u010dasto je nutn\u00e9 identifikovat peer pomoc\u00ed \u010d\u00edseln\u00e9 hodnoty.<\/p>\n
Pr\u00e1v\u011b k tomu se pou\u017e\u00edvaj\u00ed funkce resolve<\/code> a reverseResolve<\/code>: aplikace n\u011bjak\u00fdm zp\u016fsobem z\u00edsk\u00e1v\u00e1 \u0159et\u011bzcovou hodnotu kl\u00ed\u010de (prost\u0159ednictv\u00edm vstupu u\u017eivatele nebo p\u0159es master server) a m\u016f\u017ee ji p\u0159ev\u00e9st na IP adresu pro intern\u00ed pou\u017eit\u00ed. Zbytek API tak\u00e9 pro jednoduchost dost\u00e1v\u00e1 m\u00edsto \u0159et\u011bzce tuto hodnotu.<\/p>\nJe to podobn\u00e9 jako DNS dotaz, jen se prov\u00e1d\u00ed lok\u00e1ln\u011b u klienta.<\/p>\n
To znamen\u00e1, \u017ee IP adresy nemohou b\u00fdt sd\u00edleny mezi r\u016fzn\u00fdmi klienty, a pokud je pot\u0159eba n\u011bjak\u00fd glob\u00e1ln\u00ed identifik\u00e1tor, mus\u00ed b\u00fdt generov\u00e1n jin\u00fdm zp\u016fsobem.<\/p>\n
Lazy connection<\/h2>\n \nUDP nepot\u0159ebuje p\u0159ipojen\u00ed, ale, jak jsme vid\u011bli, p\u0159ed zah\u00e1jen\u00edm p\u0159enosu dat mezi dv\u011bma peer, WebRTC vy\u017eaduje dlouh\u00fd proces p\u0159ipojen\u00ed.<\/p>\n
Pokud chceme zajistit stejnou \u00farove\u0148 abstrakce, (sendto<\/code>\/recvfrom<\/code> s libovoln\u00fdmi peery bez p\u0159edchoz\u00edho p\u0159ipojen\u00ed), mus\u00edme prov\u00e9st \"l\u00edn\u00e9\" (odlo\u017een\u00e9) p\u0159ipojen\u00ed uvnit\u0159 API.<\/p>\nTo, co se d\u011bje p\u0159i b\u011b\u017en\u00e9 v\u00fdm\u011bn\u011b dat mezi \"serverem\" a \"klientem\" v p\u0159\u00edpad\u011b pou\u017eit\u00ed UDP, a co by m\u011bla na\u0161e knihovna vykon\u00e1vat:<\/p>\n
\nServer zavol\u00e1 bind()<\/code>, aby ozn\u00e1mil opera\u010dn\u00edmu syst\u00e9mu, \u017ee chce p\u0159ij\u00edmat pakety na ur\u010den\u00e9m portu.<\/li>\n<\/ul>\n\nM\u00edsto toho zve\u0159ejn\u00edme otev\u0159en\u00fd port v Firebase pod kl\u00ed\u010dem serveru a budeme poslouchat ud\u00e1losti v jeho podstromu.<\/p>\n
\nServer zavol\u00e1 recvfrom()<\/code>, p\u0159ij\u00edmat na tento port pakety p\u0159ich\u00e1zej\u00edc\u00ed od jak\u00e9hokoli hostitele.<\/li>\n<\/ul>\n\nV na\u0161em p\u0159\u00edpad\u011b je t\u0159eba kontrolovat p\u0159\u00edchoz\u00ed frontu paket\u016f odeslan\u00fdch do tohoto portu.<\/p>\n
Ka\u017ed\u00fd port m\u00e1 svou vlastn\u00ed frontu a na za\u010d\u00e1tek datagram\u016f WebRTC p\u0159id\u00e1v\u00e1me zdrojov\u00e9 a c\u00edlov\u00e9 porty, abychom v\u011bd\u011bli, do kter\u00e9 fronty p\u0159esm\u011brovat nov\u00fd paket p\u0159i jeho p\u0159\u00edjmu.<\/p>\n
Zavol\u00e1n\u00ed je neblokuj\u00edc\u00ed, tak\u017ee pokud nejsou \u017e\u00e1dn\u00e9 pakety, jednodu\u0161e vr\u00e1t\u00edme -1 a nastav\u00edme errno=EWOULDBLOCK<\/code>.<\/p>\n\nKlient z\u00edsk\u00e1v\u00e1 IP a port serveru n\u011bjak\u00fdmi extern\u00edmi prost\u0159edky a vol\u00e1 sendto()<\/code>. Tak\u00e9 se p\u0159itom prov\u00e1d\u00ed intern\u00ed vol\u00e1n\u00ed bind()<\/code>, tak\u017ee n\u00e1sledn\u00fd recvfrom()<\/code> dostane odpov\u011b\u010f bez explicitn\u00edho proveden\u00ed bind.<\/li>\n<\/ul>\n\nV na\u0161em p\u0159\u00edpad\u011b klient extern\u011b z\u00edsk\u00e1v\u00e1 \u0159et\u011bzcov\u00fd kl\u00ed\u010d a pou\u017e\u00edv\u00e1 funkci resolve()<\/code> k z\u00edsk\u00e1n\u00ed IP adresy.<\/p>\nV tomto kroku zahajujeme \u201eruce se pod\u00e1vaj\u00edc\u00ed\u201c WebRTC, pokud dva peer je\u0161t\u011b nejsou spojeni mezi sebou. P\u0159ipojen\u00ed k r\u016fzn\u00fdm port\u016fm jednoho peer pou\u017e\u00edv\u00e1 stejn\u00fd DataChannel WebRTC.<\/p>\n
Tak\u00e9 prov\u00e1d\u00edme nep\u0159\u00edm\u00e9 bind()<\/code>, aby server mohl obnovit p\u0159ipojen\u00ed v n\u00e1sleduj\u00edc\u00edm sendto()<\/code> v p\u0159\u00edpad\u011b, \u017ee bylo z n\u011bjak\u00e9ho d\u016fvodu uzav\u0159eno.<\/p>\nServer je informov\u00e1n o p\u0159ipojen\u00ed klienta, kdy\u017e klient zapisuje sv\u016fj SDP nab\u00eddku pod informac\u00ed o portu serveru do Firebase, a server zde tak\u00e9 odpov\u00edd\u00e1 svou odpov\u011bd\u00ed.<\/p>\n
\nNa n\u00ed\u017ee uveden\u00e9m sch\u00e9matu je uveden p\u0159\u00edklad pohybu zpr\u00e1v pro sch\u00e9ma socket\u016f a p\u0159ed\u00e1n\u00ed prvn\u00ed zpr\u00e1vy od klienta k serveru:<\/p>\n
Cel\u00e9 sch\u00e9ma f\u00e1ze p\u0159ipojen\u00ed mezi klientem a serverem<\/i><\/p>\nZ\u00e1v\u011br<\/h1>\n
\nPokud jste do\u010detli a\u017e do konce, asi v\u00e1s zaj\u00edm\u00e1 pod\u00edvat se na teorii v akci. Hru si m\u016f\u017eete zahr\u00e1t na teeworlds.leaningtech.com<\/a><\/noindex>, zkuste to!<\/p>\n