Sockets(Programming(CS144(Review(Session(1(April(4,(2008(Ben(Nham(Announcements(• New(classroom(for(lecture(– 200‐034,(MW(4:15‐5:30(• Simple(client(assignment(due(Wednesday,(4/9(• Use(newsgroup(for(general(quesNons(– su.class.cs144(– Refresh(your(newsgroup(list(from(the(server(if(you(can’t(find(it(Simple(Client(Overview(• Opens(TCP(socket(to(other(host(– Does(DNS(lookup(if(necessary(• Reads(request(from(command(line,(appending("\r\n",(and(sends(it(through(the(socket(• Echoes(response(to(stdout(• Demo:(Sending(HTTP(request(to(SCS(homepage(– ./sc(www.scs.stanford.edu(80("GET(/"(Sockets(and(TCP/IP(• In(TCP/IP:(– Endpoint(has(unique((TCP(port,(IP(address)(pair(– ConnecNon(between(two(endpoints(is(idenNfied(by(the(pair([(IP,(port)src,((IP,(port)dst](• All(Unix(I/O(streams(are(referenced(by(descriptors((– Socket(maps(a(descriptor(to(an(endpoint(– ConnecNng(sockets(allows(us(to(connect(endpoints(and(do(I/O(Process( Process(ApplicaNon(TCP/UDP(Transport(IP(Network(Hardware(Interface(Link(Sockets(API(IP(Address(Port( Port(Port(sd( sd(sd(Socket(API(for(Client(int$socket(int$domain,$int$type,$int$protocol)$• Returns(a(descriptor(associated(with(a(new(endpoint(int$bind(int$sd,$struct$sockaddr$*addr,$$u_int$addr_len)$• Set(addr/port(of(endpoint(for(socket(descriptor(sd(• OpNonal(for(client((lets(the(kernel(choose(some(available(port(with(the(default(IP(address)(int$connect(int$sd,$struct$sockaddr$*addr,$$u_int$addr_len)$• Connect(to(desNnaNon(address(+(port(endpoint(int$send(int$sd,$void$*buf,$int$len,$int$flags)$int$recv(int$sd,$void$*buf,$int$len,$int$flags)$• Two‐way(communicaNon(int$shutdown(int$sd,$int$how)$• ParNal(or(complete(connecNon(teardown(socket(bind(connect(send/recv(shutdown(Sockets(API(for(Server(int$socket(int,$int,$int)$int$bind(int,$struct$sockaddr$*,$u_int)$int$listen(int$sd,$int$backlog)$• Wait(for(a(client(to(connect(to(this(port(int$accept(int$sd,$struct$sockaddr$*addr,$u_int$*addr_len)$• Accept(connecNon,(returning(a(new(descriptor(for(this((IP,(port)src(–((IP,(port)dst(pair(int$send(int,$void$*,$int)$int$recv(int,$void$*,$int)$int$shutdown(int,$int)$socket(bind(send/recv(shutdown(listen(accept(Typical(Request‐Response(Client‐Server(Pair(socket(bind(connect(send/recv(socket(bind(send/recv(shutdown( shutdown(listen(accept(Client(Server("Can(I(connect?"("Yes.(Can(I(connect?"(Request:("GET(/"(One(side(starts(shutdown("Yes."(Typical(Request‐Response(Client‐Server(Pair(socket(bind(connect(send/recv(socket(bind(send/recv(shutdown( shutdown(listen(accept(Client(Server(SYN(SYN/ACK(Request:("GET(/"(One(side(starts(shutdown(ACK(Example(DayNme(Server(• See(the(posted(dayNme.c(• Problems(– Doesn’t(check(return(values(of(system(calls(• You(should(check(the(return(value(and(use(perror()(or(fpring(stderr,(strerror(errno))(to(print(out(an(informaNve(error(message(– Doesn’t(handle(mulNple(clients(simultaneously(– Problems(with(re‐using(the(same(port((use(setsockopt—covered(in(next(review(session)(Main(Structures(• Generic(socket(address($ struct$sockaddr${$$$u_short$sa_family;$$ $$char$sa_data[14];$$ };$• TCP/UDP(+(IPv4(specific(address(–(convenience(parallel(struct(for(sockaddr($ struct$sockaddr_in${$$ $$u_short$sa_family;$$$$$$$//$usually$AF_INET$$ $$u_short$sin_port;$$ $$struct$in_addr$sin_addr;$//$see$below$$ $$char$sin_zero[8];$$$$$$$$//$zero$out$$ };$• IP(Address(($ struct$in_addr${$$ $$u_long$s_addr;$$$$$$$$$$$//$Network$byte$order$$ };$$Next(two(slides(by(Clay(Collier(Useful(FuncNons(struct$hostent$*gethostbyname(const$char$*name)$• Converts(domain(names(and(dojed‐quad(IP(addresses(into(numerical(IP(addresses(via(DNS(struct$servent$*getservbyname(const$char$*name,$const$char$*proto)$• Query(/etc/services(to(find(expected(protocol(and(port(for(a(service(• Example:(getservbyname("hjp",(NULL)(to(find(it(resides(on(tcp(port(80(getsockname(...),$getpeername(...)$$• Gets(IP(address(and(port(for(source/desNnaNon(More(Notes(• ParNal(sends(and(receives(– Receive(might(not(return(with(all(the(bytes(requested(• Endian(issues(– All(shorts/ints(going(over(the(wire(must(be(encoded(using(htons/htonl(– All(shorts/ints(being(read(from(the(wire(must(be(decoded(using(ntohs/ntohl(– Why(don’t(we(have(to(worry(about(endianness(for(text?(For(arbitrary(binary(data?(Grading(• No(set(rubric(yet(• Mostly(funcNonality(– Test(yourself(by(sending((for(example)(hjp(requests(• Some(style(points(– Don’t(write(everything(in(main(– Handle(parNal(receives(and(other(edge(cases(– Check(return(values(of(system(calls(Resources(• IPC(tutorial(• Man(pages(• Outside(references(– Beej’s(Sockets(Tutorial:((hjp://beej.us/guide/bgnet/(– Unix%Network%Programming(by(Stevens(• Newsgroup(•
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