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תקשורת באינטרנט

תקשורת באינטרנט. Sockets Programming. Tutorial 8. Contents. Socket programming What is a socket ? Sockets architecture Types of Sockets The Socket system calls Data Transfer Service functions for sockets programming Examples for Client - Server communication STREAM Communication (TCP)

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תקשורת באינטרנט

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  1. תקשורת באינטרנט Sockets Programming Tutorial 8

  2. Contents • Socket programming • What is a socket ? • Sockets architecture • Types of Sockets • The Socket system calls • Data Transfer • Service functions for sockets programming • Examples for Client - Server communication • STREAM Communication (TCP) • DATAGRAM Communication (UDP) • Port reservation • Example

  3. What is a Socket ? • First appeared in 4.1 BSD UNIX 1982. • Sockets: • is an abstraction used as communication endpoints. • is implemented as file descriptor with some state information stored in the socket library.

  4. The Client Server model request reply

  5. Example:UDP Echo • The simplest form of client-server interaction uses unreliable datagram delivery to convey messages from client to server and back. Request sent to a well-known port client server Response sent to the client’s port • The program becomes a • UDP echo client when it allocates • an unused UDP protocol port • Sends a UDP message to the • UDP echo server • Waits for the replay • Reserves the source and destination addresses (IP addresses and ports) • Waits for a datagram to arrive to • the echo port • Returns the datagram to its original • sender

  6. Example: UDP Echo (Cont.) • The example illustrates two important points that are generally true about client-server interaction: • The difference between the lifetime of servers and clients. • The use of reserved and non-reserved port identifiers.

  7. Sockets architecture Application User Socket API Kernel TCP/UDP layer IP (network) layer MAC layer

  8. Type of Sockets • Socket has an associated type that determine the semantic of the communication : • SOCK_STREAM: connection oriented byte stream - TCP • SOCK_DGRAM: unreliable, connectionless communication - UDP • and more

  9. Protocol family for sockets functions • The family specifies the address family: group of protocols with the same address format • Example of address family constants: • AF_INET - IPv4 protocols • AF_INET6 - IPv6 protocols • AF_LOCAL (AF_UNIX) - Unix domain protocols

  10. Data Structures struct sockaddr_in { short int sin_family;/* we use AF_INET */ unsigned short int sin_port;/* port number */ struct in_addr sin_addr; /* comp. address */ unsigned char sin_zero[8]; /* filled with 0s */ }; struct in_addr { u_long s_addr; /* unsigned long */ };

  11. The Socket system calls • The Socket system calls: • intsocket (int family, int type, int protocol) allocate a socket return: a socket descriptor or -1 family: communication domain type: type of socket- SOCK_STREAM, SOCK_DGRAM, SOCK_RAW protocol: particular protocol to use - 0 • intbind (int sd, struct sockaddr *addr, size_t addrlen) Bind a name to a socket return: 0 on success or -1 sd: socket descriptor (from the socket() system call) addr: pointer to the socket address addrlen: socket address length • int connect (int sd, const struct sockaddr *addr, size_t addrlen) Try to connect to a socket (done by the client) return: 0 on success or -1 sd: socket descriptor (from the socket() system call) addr: pointer to the socket address addrlen: socket address length

  12. The Socket system calls (cont) • intlisten (int sd, int backlog) a queue for incoming connections is activated using listen() return: 0 on success or -1 sd: socket descriptor (from the socket() system call) backlog : Maximum queue length of processes waiting for connection • int accept (int sd, struct sockaddr *addr, size_t *addrlen) Wait for a connection request (done by the server) return: new socket descriptor with the properties of sdor -1 in case of failure sd: socket descriptor (from the socket() system call) addr: pointer to the address of the connecting entity addrlen: socket address length • int close (int sd) Close the socket or the connection with the remote host. sd: socket descriptor (from the socket() system call)

  13. Data Transfer - send • intsend (int sd, char *buf, int buf_len) transmit a message to another socket. send() can be used only when the socket is in a connected state. return: the number of bytes that has been delivered or -1 sd: socket descriptor (from the socket() system call) buf: the transmitted message buf_len: the data length of buf • intsendto (int sd, char *buf, int buf_len, conststruct sockaddr *to_addr, size_t to_len) used to transmit data to remote host return: the number of bytes that has been delivered or -1 sd: socket descriptor (from the socket() system call) buf: a pointer to the data location buf_len: the data length to_addr: the socket address of the destination to_len: the “to_addr” structure length

  14. Data Transfer - receive • intrecv (int sd, char *buf, int buf_len) Obtain data from the socket. Used only when the socket is in a connected state. return: the number of bytes at the obtain input or -1 sd: socket descriptor (from the socket() system call) buf: the address of buffer holding the received data buf_len: the buffer length • intrecvfrom (int sd, char *buf, int bub_len, struct sockaddr *from_addr, int from_len) Obtain data from the socket. return: the number of bytes at the obtain input or -1 sd: socket descriptor (from the socket() system call) buf: the address of buffer holding the received data buf_len: the buffer length from_addr: the socket address of the transmitter from_len: the “from_addr” structure length

  15. Service functions for sockets programming • Byte ordering • short htons(short) - convert 16-bit value from host to network • long htonl(long) - convert 32-bit value from host to network • short ntohs(short) - convert 16-bit value from network to host • long ntohl(long) - convert 32-bit value from network to host • Deal with IP address • ina.sin_addr.s_addr = inet_addr("132.68.1.8") • returns the address in Network Byte Order already. • DNS • int gethostname(char* name, int namelen) return local host name • struct hostent *gethostbyname(char* name) use to get computer address by the name. • struct hostent *gethostbyaddr(char *addrp, int len, int type)

  16. Stream Sockets TCP Client TCP Server sd = socket(…) bind(sd,port) connect(sd,dest) send(sd,…) recv(sd,…) close(sd) sd = socket(…) bind(sd,port) listen(sd) new_sd = accept(sd) recv(new_sd,…) send(new_sd,…) close(new_sd,...)

  17. Datagram Sockets UDP Server UDP Client sd = socket(…) bind(sd,port) recvfrom(sd,…) sendto(sd,…) sd = socket(…) sendto(sd,…) recvfrom(sd,…) close(sd)

  18. Port reservation • Ports 0 through 1023 are reserved. • Other ports are used by system for assignment to clients.

  19. Example (UDP Client) // This program sends UDP packets to the given address #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <stdio.h> #define SERVER_ADDR "127.0.0.1" #define SERVER_PORT 5555 void error(char *str) { printf("\n%s", str); exit(0); } int main(int argc, char *argv[]) { char message[100], message2[10]; int sockfd, res; struct sockaddr_in client_addr, server_addr; int i, mesNum; printf("\nClient is running..."); if (argc < 2) error("\nYou should supply parameter: the number of messages to send");

  20. Example (UDP Client) // Opening socket if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) error("Could not open socket"); // Sending a message to the server bzero((char*) &server_addr, sizeof(server_addr)); server_addr.sin_family = AF_INET; server_addr.sin_addr.s_addr = inet_addr(SERVER_ADDR); server_addr.sin_port = htons(SERVER_PORT); mesNum = atoi(argv[1]); if (mesNum == 0) error("\nIllegal parameter"); for (i=0; i<mesNum; i++) { strcpy(message, "Test message: "); sprintf(message2, "%d", i+mesNum); strcat(message, message2); res = sendto(sockfd, message, strlen(message)+1, 0, (struct sockaddr*)&server_addr, sizeof(server_addr)); printf("\nClient sent %d bytes", res); } }

  21. Example (UDP Server) // This program receives UDP packets #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <stdio.h> #define SERVER_PORT 5555 #define MAX_MESSAGE_SIZE 100 void error(char *str) { printf("\n%s", str); exit(0); } int main() { char message[MAX_MESSAGE_SIZE]; int sockfd, res; struct sockaddr_in client_addr, server_addr; int addr_len; printf("\nServer is running..."); fflush(stdout);

  22. Example (UDP Server) // Opening socket if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) error("Could not open socket"); // Bind local ip and process addresses bzero((char*) &server_addr, sizeof(server_addr)); server_addr.sin_family = AF_INET; server_addr.sin_addr.s_addr = htonl(INADDR_ANY); server_addr.sin_port = htons(SERVER_PORT); if (bind(sockfd, (struct sockaddr*)&server_addr, sizeof(server_addr)) < 0) error("Could not bind to the socket"); while (1) { // Receiving a message from the client addr_len = sizeof(client_addr); res = recvfrom(sockfd, message, MAX_MESSAGE_SIZE, 0, (struct sockaddr*)&client_addr, &addr_len); printf("\nServer received %d bytes", res); printf("\n%s", message); fflush(stdout); } }

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