WinSock. What Is Sockets What Is Windows Sockets What Are Its Benefits Architecture of Windows Sockets Network Application Mechanics

Transcription

1 WinSock What Is Sockets What Is Windows Sockets What Are Its Benefits Architecture of Windows Sockets Network Application Mechanics

2 What Is Sockets Standard API (Application Programming Interface) for Network Programming OS: UNIX Language: C Standards: Berkeley Sockets System V Transport Layer Interface (TLI)

3 What Is Standard

4 What Is Windows Sockets WinSock Standard Windows Sockets API (WSA) for Windows Network Programming OS: Microsoft Windows/NT Language: C Variants: Java, BCB, VB,...

5 What Are Its Benefits Open Standard Binary Compatibility Source Code Portability Dynamic Linking

6 DLL (Dynamic Link Library) call draw(...) int draw(...) Program A main memory Program A call draw(...) call draw(...) duplicated Program B call draw(...) int draw(...) Program B DLL int draw(...)

7 DLL Code sharing (Memory saving) only one copy of the DLL code in memory Modularization to change the DLL without changing the application, or vice versa Compatible application binary interface (ABI) to allow portability of executables, not just source code

8 Architecture of Windows Sockets telnet ftp browser other applications Windows Sockets API Windows Sockets Dynamic Link Library (WINSOCK.DLL/WSOCK32.DLL/WS2-32.DLL) TCP/IP DECNet Appletalk SPX/IPX Multiple Protocol Stack Driver (ODI, Packer Driver, NDIS) Network Interface (Ethernet, Token Ring, Serial, etc.) Transmission Media

9 Network Application Mechanics Client-Server Model Association Network Program Sketch

10 Client-Server Mode (file server) (printer server) (client)

11 Association current CLIENT to know each other SERVER data

12 Association with Multiple Outlets CLIENT CLIENT SERVER CLIENT CLIENT

13 Elements of Association Protocol Client IP Address Client Port Number Server IP Address Server Port Number

14 Client-Server Association Client Port Number Server Port Number CLIENT Client IP Address Protocol Server IP Address SERVER

15 Network Program Sketch Open a socket Name the socket Associate with another socket Send and receive between sockets Close the socket

16 Step1: Open A Socket WinSock #include <winsock.h> SOCKET PASCAL FAR socket (int family, int type, int protocol); Berkeley Socket #include <sys/types.h> #include <sys/socket.h> int socket (int family, int type, int protocol);

17 Return Value WinSock success: a value called a socket descriptor failure: INVALID_SOCKET Berkeley Socket success: a socket descriptor failure: < 0

18 Address Family AF_INET PF_INET Internet protocols AF_UNIX PF_UNIX UNIX internal protocols AF_NS PF_NS Xerox NS protocols AF_IMPLINK PF_IMPLINK IMP link layer AF_IPX PF_IPX IPX/SPX AF_APPLETALK PF_APPLETALK Appletalk

19 Type SOCK_STREAM SOCK_DGRAM SOCK_RAW SOCK_SEQPACKET SOCK_RDM stream socket datagram socket raw socket sequenced packet socket reliably delivered message socket

20 Family And Type AF_UNIX AF_INET AF_NS SOCK_STREAM Yes TCP SPP SOCK_DGRAM Yes UDP IDP SOCK_RAW IP Yes SOCK_SEQPACKET SPP

21 #include <netinet/in.h> /* for IPPROTO_xxx */ #include <netns/ns.h> /* for NSPROTO_xxx */ Protocol family type protocol comment AF_INET SOCK_DGRAM IPPROTO_UDP UDP AF_INET SOCK_STREAM IPPROTO_TCP TCP AF_INET SOCK_RAW IPPROTO_ICMP ICMP AF_INET SOCK_RAW IPPROTO_RAW (raw) AF_NS SOCK_STREAM NSPROTO_SPP SPP AF_NS SOCK_SEQPACKET NSPROTO_SPP SPP AF_NS SOCK_RAW NSPROTO_ERROR error protocol AF_NS SOCK_RAW NSPROTO_RAW (raw)

22 Association After socket() Elements Client Server Protocol set set Client IP Address not yet not yet Client Port Number not yet not yet Server IP Address not yet not yet Server Port Number not yet not yet

23 Step2: Name The Socket WinSock #include <winsock.h> int PASCAL FAR bind (SOCKET sockfd, struct sockaddr FAR *addr, int addrlen); Berkeley Socket #include <sys/types.h> #include <sys/socket.h> int bind (int sockfd, struct sockaddr *addr, int addrlen); addrlen: sizeof(struct sockaddr)

24 Return Value WinSock success: 0 failure: SOCKET_ERROR Berkeley Socket success: 0 failure: < 0

25 Client Socket Name Is Optional A server must name its socket to allow the client to find it on the network. A client is not required to name its socket, but neither is it restricted from naming it. On a TCP socket, the protocol stack implicitly names the socket when connect() is called. On a UDP socket, the protocol stack implicitly names the socket when connect() or sendto() is called.

26 sockaddr Structure #include <sys/socket.h> struct sockaddr { u_short sa_family; /* address family: AF_xxx */ char sa_data[14]; /* host address for general purpose */ };

27 #include <netinet/in.h> struct in_addr { }; sockaddr_in Structure u_long s_addr; /* 32-bit IP address in network order */ struct { }; sockaddr_in short sin_family; /* address family: PF_INET */ u_short sin_port; /* 16-bit port number in network order */ struct in_addr sin_addr; /* 32-bit IP address in network order */ char sin_zero[8]; /* not used */

28 Port Numbers Reserved for well-known services (e.g., FTP) 1024 Reserved for IANA (Internet Assigned Numbers Authority) Typical range for user-defined services System dependent (new services or system services)

29 Get Legal Port Number Motivation Without knowing which port is available Porting in different system How? Set port number 0 and then call bind() to get an available port number

30 Set Local IP Address Motivation Without knowing what IP address the host has Porting in different system How? Set IP address INADDR_ANY and call bind() to assign the local IP address automatically

31 Network Byte Ordering vs. Host Byte Ordering 0x7531 big endian network byte order little endian host byte order on Intel processors byte nibble in the memory

32 Problem With Byte Ordering PortNumber = 0x7531; interpret in network byte order unknown port number 0x host byte order in the memory send

33 Byte Ordering Functions u_short PASCAL FAR htons (u_short hostshort); u_short PASCAL FAR ntohs (u_short netshort); u_long PASCAL FAR ntohl (u_long netlong); u_long PASCAL FAR htonl (u_long hostlong);

34 Example struct sockaddr_in serveraddr; serveraddr.sin_family=af_inet; serveraddr.sin_addr.s_addr=htonl(inaddr_any); serveraddr.sin_port=0; if(bind(serversock, (struct sockaddr *)&serveraddr, sizeof(serveraddr))) { puts("server: bind() error."); close(serversock); exit(1); }

35 Example (continued) int serverlen; serverlen=sizeof(serveraddr); if(getsockname(serversock, (struct sockaddr *)&serveraddr, &serverlen)) { puts("server: getsockname() error."); close(serversock); exit(1); } printf("server: Port Number is %d\n", ntohs(serveraddr.sin_port));

36 Association After bind() Elements Client Server Protocol set set Client IP Address set not yet Client Port Number set not yet Server IP Address not yet set Server Port Number not yet set

37 Step 3: Associate With Another Socket Server prepares for an association A datagram (UDP) server does not do anything to prepare to associate with a client, since it creates an association when it receives data. Client initiates the association Server completes the association

38 Step 3.1: TCP Server Prepares WinSock For An Association int PASCAL FAR listen (SOCKET sockfd, int backlog); Berkeley Socket int listen (int sockfd, int backlog); backlog: the number of incoming connection requests you want the stack to queue

39 Return Value WinSock success: 0 failure: SOCKET_ERROR Berkeley Socket success: 0 failure: < 0

40 Step 3.2: Client Initiates The WinSock Association #include <winsock.h> int PASCAL FAR connect (SOCKET sockfd, struct sockaddr FAR *serveraddr, int addrlen); Berkeley Socket #include <sys/types.h> #include <sys/socket.h> int connect (int sockfd, struct sockaddr *serveraddr, int addrlen);

41 Return Value WinSock success: 0 failure: SOCKET_ERROR Berkeley Socket success: 0 failure: < 0

42 Association Initialization By UDP Clients Is Optional The advantage to using sendto() is that the target of each datagram can be changed. Function connect() can be called to establish the remote target when the UDP socket will send to the same remote address for the life of the socket, and/or a filter is needed to be set on that socket for receiving only datagrams from the named destination address

43 Step 3.3: TCP Server Completes The Association WinSock #include <winsock.h> SOCKET PASCAL FAR accept (SOCKET sockfd, struct sockaddr FAR *clientaddr, int FAR *addrlen); Berkeley Socket #include <sys/types.h> #include <sys/socket.h> int accept (int sockfd, struct sockaddr *clientaddr, int *addrlen);

44 Return Value WinSock success: a socket descriptor failure: INVALID_SOCKET (not SOCKET_ERROR) Berkeley Socket success: a socket descriptor failure: < 0

45 Client Socket vs. Server Socket Client 1 cs=socket() Client 2 cs=socket() Server ss=socket() connect(cs,...) connect(cs,...) cs1=accept(ss,...) cs2=accept(ss,...) send(cs,...) recv(cs,...) send(cs,...) recv(cs,...) send(cs1,...) recv(cs1,...) send(cs2,...) recv(cs2,...)

46 Step 4: Send And Receive With WinSock int PASCAL FAR send (SOCKET sockfd, const char FAR *buf, int len, int flags); int PASCAL FAR sendto (SOCKET sockfd, const char FAR *buf, int len, int flags, struct sockaddr FAR *to, int addrlen); int PASCAL FAR recv (SOCKET sockfd, char FAR *buf, int len, int flags); int PASCAL FAR recvfrom (SOCKET sockfd, char FAR *buf, int len, int flags, struct sockaddr FAR *from, int *addrlen);

47 Step 4: Send And Receive With Berkeley Socket int send (int sockfd, char *buf, int len, int flags); int sendto (int sockfd, char *buf, int len, int flags, struct sockaddr *to, int addrlen); int recv (int sockfd, char *buf, int len, int flags); int recvfrom (int sockfd, char *buf, int len, int flags, struct sockaddr *from, int *addrlen);

48 Return Value For send() / sendto() WinSock success: the number of bytes sent on success failure: SOCKET_ERROR Berkeley Socket success: the number of bytes sent on success failure: < 0

49 WinSock Return Value For recv() / recvfrom() success: the number of bytes received failure: SOCKET_ERROR Berkeley Socket success: the number of bytes received failure: < 0 A return value with 0 indicates the other side has finished data transmission.

50 Socket s Read / Write Client 1 cs=socket() Client 2 cs=socket() Server ss=socket() connect(cs,...) connect(cs,...) cs1=accept(ss,...) cs2=accept(ss,...) send(cs,...) recv(cs,...) send(cs,...) recv(cs,...) send(cs1,...) recv(cs1,...) send(cs2,...) recv(cs2,...)

51 Flags Flags for send() / sendto() MSG_OOB MSG_DONTROUTE Flags for recv() / recvfrom() MSG_OOB MSG_PEEK to find out how much data is available for reading without removing received data from the protocol stack s buffers

52 Step 5: Close The Socket WinSock int PASCAL FAR closesocket (SOCKET sockfd); Berkeley Socket int close (int sockfd);

53 Return Value WinSock success: 0 failure: SOCKET_ERROR Berkeley Socket success: 0 failure: < 0

54 Client 1 Close Sockets Client 2 Server cs=socket() cs=socket() ss=socket() connect(cs,...) connect(cs,...) cs1=accept(ss,...) cs2=accept(ss,...) send(cs,...) recv(cs,...) send(cs,...) recv(cs,...) send(cs1,...) recv(cs1,...) send(cs2,...) recv(cs2,...)

55 Partial Close WinSock int PASCAL FAR shutdown (SOCKET sockfd, int howto); Berkeley Socket int shutdown (int sockfd, int howto); howto: flag that indicates the behavior

56 Return Value WinSock success: 0 failure: SOCKET_ERROR Berkeley Socket success: 0 failure: < 0

57 howto 0 (not recommended due to many problems) receives are disallowed (lower layer protocols are not affected) 1 (graceful close) sends are disallowed (a TCP FIN is sent to remote socket) 2 both sends and receives are disallowed (a TCP FIN is sent to remote socket)

58 TCP Network Applications client socket() initialize sockaddr_in structure connect() send() / recv() server socket() initialize sockaddr_in structure bind() listen() accept() recv() / send() closesocket() closesocket() closesocket()

59 UDP Network Applications 1 client socket() initialize sockaddr_in structure connect() send() / sendto() recv() / recvfrom() closesocket() server socket() initialize sockaddr_in structure bind() recvfrom() sendto() closesocket()

60 UDP Network Applications 2 client socket() initialize sockaddr_in structure server socket() initialize sockaddr_in structure bind() sendto() recvfrom() closesocket() recvfrom() sendto() closesocket()

61 Startup And Cleanup In WinSock Every WinSock application must initialize the WinSock DLL before it begins operation and notify the DLL to cleanup when it has done. A WinSock DLL needs to know when every process comes and goes so it can allocate and deallocate process-specific resources.

62 WSAStartup() int PASCAL FAR WSAStartup (WORD wversionrequired, LPWSADATA lpwsadata); Return Value success: 0 failure: an error value (not SOCKET_ERROR)

63 WinSock Version wversionrequired: the major.minor version number The LSB is the major version, and the MSB is the minor version (revision number). version 1.1: 0x0101 version 2.0: 0x0002

64 WSAData typedef struct WSAData { WORD wversion; WORD whighversion; char szdescription[wsadescription_len+1]; char szsystemstatus[wsasys_status_len+1]; long imaxsockets; long imaxudpdg; char FAR *lpvendorinfo; } WSADATA;

65 Members In WSADATA wversion the version of the Windows Sockets specification that the Windows Sockets DLL expects the caller to use whighversion the highest version of the Windows Sockets specification that this DLL can support szdescription a null-terminated string into which a WinSock vendor can put any description

66 Members In WSADATA szsystemstatus a null-terminated string into which the WinSock DLL copies relevant status or configuration information imaxsockets the maximum number of sockets a single process can potentially open imaxudpdg the size in bytes of the largest UDP datagram that can be sent or received by the WinSock implementation

67 Members In WSADATA lpvendorinfo a far pointer to vendor-specific data structure

68 WSACleanup() int PASCAL FAR WSACleanup (void); Return Value success: 0 failure: SOCKET_ERROR

69 Error Reporting int PASCAL FAR WSAGetLastError (void); to return the error value which is reset only when the next WinSock function fails

70 Some Error Values bind() WSAEADDRINUSE(10048) listen() WSAEMFILE(10024) connect() WSAECONNREFUSED(10061) WSAEADDRINUSE(10048) send() WSAENOTCONN(10057) WSAEMSGSIZE(10040) closesocket() WSAENOTSOCK(10038)