Signaliz\u00e1cia je \u00fazko spojen\u00e1 s na\u0161ou implement\u00e1ciou socketov, op\u00edsanou v nasleduj\u00facej \u010dasti.<\/li>\n<\/ul>\n\nZoznam serverov v hre a na domovskej str\u00e1nke<\/i><\/p>\nImplement\u00e1cia socketov<\/h1>\n
\nChceme vytvori\u0165 API, \u010do najbli\u017e\u0161ie k Posix UDP Sockets, aby sme minimalizovali po\u010det potrebn\u00fdch zmien.<\/p>\n
Takisto chceme implementova\u0165 nevyhnutn\u00e9 minimum, potrebn\u00e9 na najjednoduch\u0161iu v\u00fdmenu \u00fadajov v sieti.<\/p>\n
Napr\u00edklad, nepotrebujeme skuto\u010dn\u00e9 smerovanie: v\u0161etky peerov\u00e9 zariadenia s\u00fa v jednej \u201evirtu\u00e1lnej LAN\u201c, spojenej s konkr\u00e9tnym in\u0161tan\u010dn\u00fdm datab\u00e1zov\u00fdm syst\u00e9mom Firebase.<\/p>\n
Preto nepotrebujeme jedine\u010dn\u00e9 IP adresy: na jedine\u010dn\u00fa identifik\u00e1ciu peerov sta\u010d\u00ed pou\u017ei\u0165 jedine\u010dn\u00e9 hodnoty k\u013e\u00fa\u010dov Firebase (podobne ako dom\u00e9nov\u00e9 men\u00e1), a ka\u017ed\u00fd peer lok\u00e1lne prira\u010fuje \u201efalo\u0161n\u00e9\u201c IP adresy ka\u017ed\u00e9mu k\u013e\u00fa\u010du, ktor\u00fd je potrebn\u00e9 previes\u0165. To n\u00e1s \u00faplne zbavuje potreby glob\u00e1lneho prira\u010fovania IP adries, \u010do je netrivi\u00e1lna \u00faloha.<\/p>\n
Tu je minim\u00e1lne API, ktor\u00e9 mus\u00edme implementova\u0165:<\/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 podobn\u00e9 API Posix Sockets, ale m\u00e1 nieko\u013eko d\u00f4le\u017eit\u00fdch rozdielov: registr\u00e1cia sp\u00e4tn\u00fdch volan\u00ed, priradenie lok\u00e1lnych IP a \u201eleniv\u00e1\u201c konektivita<\/strong>.<\/p>\nRegistr\u00e1cia sp\u00e4tn\u00fdch volan\u00ed<\/h2>\n \nAj ke\u010f p\u00f4vodn\u00fd program pou\u017e\u00edva neblokuj\u00faci vstup\/v\u00fdstup, pre spustenie v webovom prehliada\u010di je potrebn\u00e9 k\u00f3d refaktorova\u0165.<\/p>\n
D\u00f4vodom je to, \u017ee slu\u010dka udalost\u00ed v prehliada\u010di je skryt\u00e1 pred programom (\u010di u\u017e je to JavaScript alebo WebAssembly).<\/p>\n
V nat\u00edvnom prostred\u00ed m\u00f4\u017eeme p\u00edsa\u0165 k\u00f3d takto<\/p>\n
while(running) {\n select(...); \/\/ \u010dakajte na I\/O udalosti\n while(true) {\n int r = readfrom(...); \/\/ pokus o \u010d\u00edtanie\n if (r < 0 && errno == EWOULDBLOCK) \/\/ nie s\u00fa k dispoz\u00edcii \u010fal\u0161ie \u00fadaje\n break;\n ...\n }\n ...\n}<\/code><\/pre>\n\nAk je slu\u010dka udalost\u00ed pre n\u00e1s skryt\u00e1, mus\u00edme ju premeni\u0165 na nie\u010do podobn\u00e9:<\/p>\n
auto cb = []() { \/\/ toto sa zavol\u00e1, ke\u010f s\u00fa nov\u00e9 \u00fadaje k dispoz\u00edcii\n while(true) {\n int r = readfrom(...); \/\/ pokus o \u010d\u00edtanie\n if (r < 0 && errno == EWOULDBLOCK) \/\/ nie s\u00fa k dispoz\u00edcii \u010fal\u0161ie \u00fadaje\n break;\n ...\n }\n ...\n};\nrecvCallback(cb); \/\/ registr\u00e1cia sp\u00e4tn\u00e9ho volania<\/code><\/pre>\n<\/p>\n
Priradenie lok\u00e1lnych IP<\/h2>\n \nIdentifik\u00e1tory uzlov v na\u0161ej \u2018sieti\u2019 nie s\u00fa IP adresy, ale Firebase k\u013e\u00fa\u010de (to s\u00fa re\u0165azce, ktor\u00e9 vyzeraj\u00fa takto: -LmEC50PYZLCiCP-vqde<\/code> ).<\/p>\nJe to pohodln\u00e9, preto\u017ee nepotrebujeme mechanizmus na priradenie IP a kontrolu ich jedine\u010dnosti (ako aj ich likvid\u00e1ciu po odpojen\u00ed klienta), ale ve\u013emi \u010dasto je potrebn\u00e9 identifikova\u0165 peer pod\u013ea \u010d\u00edselnej hodnoty.<\/p>\n
Na tento \u00fa\u010del sa pou\u017e\u00edvaj\u00fa funkcie resolve<\/code> a reverseResolve<\/code>: aplik\u00e1cia z\u00edska re\u0165azcov\u00fa hodnotu k\u013e\u00fa\u010da (cez vstup pou\u017e\u00edvate\u013ea alebo cez majstrovsk\u00fd server) a m\u00f4\u017ee ju previes\u0165 na IP adresu na vn\u00fatorn\u00e9 pou\u017eitie. Zvy\u0161ok API pre jednoduchos\u0165 tie\u017e z\u00edska t\u00fato hodnotu namiesto re\u0165azca.<\/p>\nJe to podobn\u00e9 ako DNS vyh\u013ead\u00e1vanie, ale vykon\u00e1va sa lok\u00e1lne u klienta.<\/p>\n
To znamen\u00e1, \u017ee IP adresy nem\u00f4\u017eu by\u0165 zdie\u013ean\u00e9 medzi r\u00f4znymi klientmi, a ak potrebujeme nejak\u00fd glob\u00e1lny identifik\u00e1tor, bude ho potrebn\u00e9 generova\u0165 in\u00fdm sp\u00f4sobom.<\/p>\n
Leniv\u00e9 pripojenie<\/h2>\n \nUDP nevy\u017eaduje pripojenie, ale, ako sme videli, sk\u00f4r ako za\u010dneme pren\u00e1\u0161a\u0165 \u00fadaje medzi dvoma peerami, WebRTC vy\u017eaduje dlh\u00fd proces pripojenia.<\/p>\n
Ak chceme zabezpe\u010di\u0165 rovnak\u00fa \u00farove\u0148 abstrakcie, (sendto<\/code>\/recvfrom<\/code> s \u013eubovo\u013en\u00fdmi peerami bez predch\u00e1dzaj\u00faceho pripojenia), mus\u00edme vykona\u0165 \u201eleniv\u00e9\u201c (oneskoren\u00e9) pripojenie v r\u00e1mci API.<\/p>\nToto je to, \u010do sa deje pri be\u017enej v\u00fdmene \u00fadajov medzi \u201eserverom\u201c a \u201eklientom\u201c v pr\u00edpade pou\u017eitia UDP, a \u010do by mala na\u0161a kni\u017enica vykon\u00e1va\u0165:<\/p>\n
\nServer vol\u00e1 bind()<\/code>, aby informoval opera\u010dn\u00fd syst\u00e9m, \u017ee chce prij\u00edma\u0165 pakety na zadan\u00fd port.<\/li>\n<\/ul>\n\nNamiesto toho zverejn\u00edme otvoren\u00fd port vo Firebase pod k\u013e\u00fa\u010dom servera a budeme po\u010d\u00fava\u0165 udalosti v jeho podstromu.<\/p>\n
\nServer vol\u00e1 recvfrom()<\/code>, prij\u00edmaj\u00faci na tento port pakety poch\u00e1dzaj\u00face od ak\u00e9hoko\u013evek hostite\u013ea.<\/li>\n<\/ul>\n\nV na\u0161om pr\u00edpade je potrebn\u00e9 kontrolova\u0165 prich\u00e1dzaj\u00facu frontu paketov, ktor\u00e9 boli odoslan\u00e9 na tento port.<\/p>\n
Ka\u017ed\u00fd port m\u00e1 svoju vlastn\u00fa frontu, a prid\u00e1vame na za\u010diatok d\u00e1tagramov WebRTC p\u00f4vodn\u00e9 a cie\u013eov\u00e9 porty, aby sme vedeli, do ktorej fronty presmerova\u0165 nov\u00fd paket pri jeho pr\u00edchode.<\/p>\n
Volanie je neblo\u010dka, tak\u017ee ak nie s\u00fa pakety, jednoducho vr\u00e1time -1 a nastav\u00edme errno=EWOULDBLOCK<\/code>.<\/p>\n\nKlient z\u00edska extern\u00fdmi prostriedkami IP a port servera a vol\u00e1 sendto()<\/code>. Tie\u017e pritom prebieha vn\u00fatorn\u00e9 volanie bind()<\/code>, tak\u017ee nasleduj\u00faci recvfrom()<\/code> z\u00edska odpove\u010f bez explicitn\u00e9ho vykonania bind.<\/li>\n<\/ul>\n\nV na\u0161om pr\u00edpade klient extern\u00fdm sp\u00f4sobom z\u00edskava re\u0165azov\u00fd k\u013e\u00fa\u010d a pou\u017e\u00edva funkciu resolve()<\/code> na z\u00edskanie IP adresy.<\/p>\nV tejto f\u00e1ze za\u010d\u00edname \u201epodanie ruky\u201c WebRTC, ak sa dva peer e\u0161te navz\u00e1jom nespojili. Pripojenia na r\u00f4zne porty jedn\u00e9ho peer pou\u017e\u00edvaj\u00fa rovnak\u00fd DataChannel WebRTC.<\/p>\n
Taktie\u017e vykon\u00e1vame nepriamy bind()<\/code>, aby server mohol obnovi\u0165 pripojenie v nasleduj\u00facom sendto()<\/code> v pr\u00edpade, \u017ee sa z nejak\u00e9ho d\u00f4vodu uzavrie.<\/p>\nServer je informovan\u00fd o pripojen\u00ed klienta, ke\u010f klient zapisuje svoj SDP offer pod inform\u00e1ciou o porte servera vo Firebase, a server tam odpoved\u00e1 svoj\u00edm odpovedom.<\/p>\n
\nNa ni\u017e\u0161ie uvedenom sch\u00e9me je uk\u00e1\u017eka prenosu spr\u00e1v pre sch\u00e9mu soketov a prenos prv\u00e9ho spr\u00e1vy od klienta k serveru:<\/p>\n
\u00dapln\u00e1 sch\u00e9ma f\u00e1zy pripojenia medzi klientom a serverom<\/i><\/p>\nZ\u00e1ver<\/h1>\n
\nAk ste do\u010d\u00edtali a\u017e do konca, pravdepodobne v\u00e1s zauj\u00edma pozrie\u0165 sa na te\u00f3riu v praxi. Hru si m\u00f4\u017eete zahra\u0165 na teeworlds.leaningtech.com<\/a><\/noindex>, vysk\u00fa\u0161ajte!<\/p>\n