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Introduction to Sockets Programming in C using TCP/IP

Introduction to Sockets Programming in C using TCP/IP 7
Introduction to Sockets Programming in C using TCP/IP Professor: Panagiota Fatourou TA: Eleftherios Kosmas CSD May 2012‰‰‰‰‰ „„„„„ Introduction Computer Network Host hosts, routers, communication channels Router Hosts run applications Routers forward information Communication Packets: sequence of bytes channel contain control information e.g. destination host Protocol is an agreement meaning of packets structure and size of packets e.g. Hypertext Transfer Protocol (HTTP) CS556 Distributed Systems Tutorial by Eleftherios Kosmas 2‰‰‰‰‰ „)„„„ Protocol Families TCP/IP Several protocols for different problems Protocol Suites or Protocol Families: TCP/IP TCP/IP provides endtoend connectivity specifying how data should be formatted, addressed, transmitted, routed, and received at the destination can be used in the internet and in standalone private networks it is organized into layers CS556 Distributed Systems Tutorial by Eleftherios Kosmas 3TCP/IP FTP, SMTP, … Transport Layer TCP or UDP Network Layer IP Communication Channels image is taken from “http://en.wikipedia.org/wiki/TCP/IPmodel” CS556 Distributed Systems Tutorial by Eleftherios Kosmas 4‰‰ „„„ Internet Protocol (IP) provides a datagram service packets are handled and delivered independently besteffort protocol may loose, reorder or duplicate packets each packet must contain an IP address of its destination CS556 Distributed Systems Tutorial by Eleftherios Kosmas 5‰‰ „„ Addresses IPv4 The 32 bits of an IPv4 address are broken into 4 octets, or 8 bit fields (0255 value in decimal notation). For networks of different size, the first one (for large networks) to three (for small networks) octets can be used to identify the network, while the rest of the octets can be used to identify the node on the network. Range of addresses 724 1.0.0.0 to Class A: 0 Network ID Host ID 127.255.255.255 14 16 128.0.0.0 to Class B: 1 0 Network ID Host ID 191.255.255.255 21 8 192.0.0.0 to Class C: 1 1 0 Network ID Host ID 223.255.255.255 28 224.0.0.0 to Class D (multicast): 1 1 1 0 Multicast address 239.255.255.255 27 240.0.0.0 to Class E (reserved): 1 1 1 1 0 unused 255.255.255.255 CS556 Distributed Systems Tutorial by Eleftherios Kosmas 6Local Area Network Addresses IPv4 CS556 Distributed Systems Tutorial by Eleftherios Kosmas 7„ ‰‰)‰‰‰‰‰‰‰‰ „„„ TCP vs UDP Both use port numbers applicationspecific construct serving as a communication endpoint 16bit unsigned integer, thus ranging from 0 to 65535 to provide endtoend transport UDP: User Datagram Protocol no acknowledgements no retransmissions out of order, duplicates possible connectionless, i.e., app indicates destination for each packet TCP: Transmission Control Protocol reliable bytestream channel (in order, all arrive, no duplicates) similar to file I/O flow control connectionoriented bidirectional CS556 Distributed Systems Tutorial by Eleftherios Kosmas 8„„„ TCP vs UDP TCP is used for services with a large data capacity, and a persistent connection UDP is more commonly used for quick lookups, and single use queryreply actions. Some common examples of TCP and UDP with their default ports: DNS lookup UDP 53 FTP TCP 21 HTTP TCP 80 POP3 TCP 110 Telnet TCP 23 CS556 Distributed Systems Tutorial by Eleftherios Kosmas 9‰ „„„„ Berkley Sockets Universally known as Sockets It is an abstraction through which an application may send and receive data Provide generic access to interprocess communication services e.g. IPX/SPX, Appletalk, TCP/IP Standard API for networking Application Application Socket Socket TCP TCP IP Channel IP Channel IP Router Host Host CS556 Distributed Systems Tutorial by Eleftherios Kosmas 10„„„ ‰‰‰‰‰‰‰ „„„ Sockets Uniquely identified by an internet address an endtoend protocol (e.g. TCP or UDP) a port number Two types of (TCP/IP) sockets Descriptor Table internal data 0 Stream sockets (e.g. uses TCP) structure for file 1 1 provide reliable bytestream service 2 Family: PFINET Datagram sockets (e.g. uses UDP) Service: SOCKSTREAM provide besteffort datagram service LocalIP: RemoteIP: messages up to 65.500 bytes LocalPort: Socket extend the convectional UNIX I/O facilities RemotePort: … file descriptors for network communication extended the read and write system calls CS556 Distributed Systems Tutorial by Eleftherios Kosmas 11Sockets Descriptor references Applications UDP sockets TCP sockets Sockets bound to ports TCP ports 65535 1 2 65535 UDP ports 1 2 TCP UDP IP CS556 Distributed Systems Tutorial by Eleftherios Kosmas 12Socket Programming CS556 Distributed Systems Tutorial by Eleftherios Kosmas 13‰‰‰‰‰ „„ ClientServer communication Server passively waits for and responds to clients passive socket Client initiates the communication must know the address and the port of the server active socket CS556 Distributed Systems Tutorial by Eleftherios Kosmas 14Sockets Procedures CS556 Distributed Systems Tutorial by Eleftherios Kosmas 15Client Server Communication Unix Stream Datagram (e.g. TCP) (e.g. UDP) Server Client Server Client socket() socket() socket() socket() bind() bind() bind() listen() synchronization point accept() connect() recv() send() recvfrom() sendto() send() recv() sendto() recvfrom() close() close() close() close() CS556 Distributed Systems Tutorial by Eleftherios Kosmas 16„„„„„„ ‰‰‰‰‰ „) Socket creation in C: socket() int sockid = socket(family, type, protocol); sockid: socket descriptor, an integer (like a filehandle) family: integer, communication domain, e.g., PFINET, IPv4 protocols, Internet addresses (typically used) PFUNIX, Local communication, File addresses type: communication type SOCKSTREAM reliable, 2way, connectionbased service SOCKDGRAM unreliable, connectionless, messages of maximum length protocol: specifies protocol IPPROTOTCP IPPROTOUDP usually set to 0 (i.e., use default protocol) upon failure returns 1 NOTE: socket call does not specify where data will be coming from, nor where it will be going to – it just creates the interface CS556 Distributed Systems Tutorial by Eleftherios Kosmas 17Client Server Communication Unix Stream Datagram (e.g. TCP) (e.g. UDP) Server Client Server Client socket() socket() socket() socket() bind() bind() bind() listen() synchronization point accept() connect() recv() send() recvfrom() sendto() send() recv() sendto() recvfrom() close() close() close() close() CS556 Distributed Systems Tutorial by Eleftherios Kosmas 18‰‰‰‰ „„„ Socket close in C: close() When finished using a socket, the socket should be closed status = close(sockid); sockid: the file descriptor (socket being closed) status: 0 if successful, 1 if error Closing a socket closes a connection (for stream socket) frees up the port used by the socket CS556 Distributed Systems Tutorial by Eleftherios Kosmas 19„„) Specifying Addresses Socket API defines a generic data type for addresses: struct sockaddr unsigned short safamily; / Address family (e.g. AFINET) / char sadata14; / Familyspecific address information / Particular form of the sockaddr used for TCP/IP addresses: struct inaddr unsigned long saddr; / Internet address (32 bits) / struct sockaddrin unsigned short sinfamily; / Internet protocol (AFINET) / unsigned short sinport; / Address port (16 bits) / struct inaddr sinaddr; / Internet address (32 bits) / char sinzero8; / Not used / Important: sockaddrin can be casted to a sockaddr CS556 Distributed Systems Tutorial by Eleftherios Kosmas 20Client Server Communication Unix Stream Datagram (e.g. TCP) (e.g. UDP) Server Client Server Client socket() socket() socket() socket() bind() bind() bind() listen() synchronization point accept() connect() recv() send() recvfrom() sendto() send() recv() sendto() recvfrom() close() close() close() close() CS556 Distributed Systems Tutorial by Eleftherios Kosmas 21„ ‰‰‰‰ „„ Assign address to socket: bind() associates and reserves a port for use by the socket int status = bind(sockid, addrport, size); sockid: integer, socket descriptor addrport: struct sockaddr, the (IP) address and port of the machine for TCP/IP server, internet address is usually set to INADDRANY, i.e., chooses any incoming interface size: the size (in bytes) of the addrport structure status: upon failure 1 is returned CS556 Distributed Systems Tutorial by Eleftherios Kosmas 22bind() Example with TCP int sockid; struct sockaddrin addrport; sockid = socket(PFINET, SOCKSTREAM, 0); addrport.sinfamily = AFINET; addrport.sinport = htons(5100); addrport.sinaddr.saddr = htonl(INADDRANY); if(bind(sockid, (struct sockaddr ) addrport, sizeof(addrport))= 1) … CS556 Distributed Systems Tutorial by Eleftherios Kosmas 23‰‰‰‰ „„„ Skipping the bind() bind can be skipped for both types of sockets Datagram socket: if only sending, no need to bind. The OS finds a port each time the socket sends a packet if receiving, need to bind Stream socket: destination determined during connection setup don’t need to know port sending from (during connection setup, receiving end is informed of port) CS556 Distributed Systems Tutorial by Eleftherios Kosmas 24Client Server Communication Unix Stream Datagram (e.g. TCP) (e.g. UDP) Server Client Server Client socket() socket() socket() socket() bind() bind() bind() listen() synchronization point accept() connect() recv() send() recvfrom() sendto() send() recv() sendto() recvfrom() close() close() close() close() CS556 Distributed Systems Tutorial by Eleftherios Kosmas 25‰‰‰‰‰ „„„„ Assign address to socket: bind() Instructs TCP protocol implementation to listen for connections int status = listen(sockid, queueLimit); sockid: integer, socket descriptor queuelen: integer, of active participants that can “wait” for a connection status: 0 if listening, 1 if error listen() is nonblocking: returns immediately The listening socket (sockid) is never used for sending and receiving is used by the server only as a way to get new sockets CS556 Distributed Systems Tutorial by Eleftherios Kosmas 26Client Server Communication Unix Stream Datagram (e.g. TCP) (e.g. UDP) Server Client Server Client socket() socket() socket() socket() bind() bind() bind() listen() synchronization point accept() connect() recv() send() recvfrom() sendto() send() recv() sendto() recvfrom() close() close() close() close() CS556 Distributed Systems Tutorial by Eleftherios Kosmas 27‰‰‰‰ „„„ Establish Connection: connect() The client establishes a connection with the server by calling connect() int status = connect(sockid, foreignAddr, addrlen); sockid: integer, socket to be used in connection foreignAddr: struct sockaddr: address of the passive participant addrlen: integer, sizeof(name) status: 0 if successful connect, 1 otherwise connect() is blocking CS556 Distributed Systems Tutorial by Eleftherios Kosmas 28„„„ ‰‰‰‰‰‰ „„„ Incoming Connection: accept() The server gets a socket for an incoming client connection by calling accept() int s = accept(sockid, clientAddr, addrLen); s: integer, the new socket (used for datatransfer) sockid: integer, the orig. socket (being listened on) clientAddr: struct sockaddr, address of the active participant filled in upon return addrLen: sizeof(clientAddr): value/result parameter must be set appropriately before call adjusted upon return accept() is blocking: waits for connection before returning dequeues the next connection on the queue for socket (sockid) CS556 Distributed Systems Tutorial by Eleftherios Kosmas 29Client Server Communication Unix Stream Datagram (e.g. TCP) (e.g. UDP) Server Client Server Client socket() socket() socket() socket() bind() bind() bind() listen() synchronization point accept() connect() recv() send() recvfrom() sendto() send() recv() sendto() recvfrom() close() close() close() close() CS556 Distributed Systems Tutorial by Eleftherios Kosmas 30‰‰‰‰‰‰‰‰‰ „„„ Exchanging data with stream socket int count = send(sockid, msg, msgLen, flags); msg: const void, message to be transmitted msgLen: integer, length of message (in bytes) to transmit flags: integer, special options, usually just 0 count: bytes transmitted (1 if error) int count = recv(sockid, recvBuf, bufLen, flags); recvBuf: void, stores received bytes bufLen: bytes received flags: integer, special options, usually just 0 count: bytes received (1 if error) Calls are blocking returns only after data is sent / received CS556 Distributed Systems Tutorial by Eleftherios Kosmas 31‰‰‰‰‰‰‰ „„„ Exchanging data with datagram socket int count = sendto(sockid, msg, msgLen, flags, foreignAddr, addrlen); msg, msgLen, flags, count: same with send() foreignAddr: struct sockaddr, address of the destination addrLen: sizeof(foreignAddr) int count = recvfrom(sockid, recvBuf, bufLen, flags,clientAddr, addrlen); recvBuf, bufLen, flags, count: same with recv() clientAddr: struct sockaddr, address of the client addrLen: sizeof(clientAddr) Calls are blocking returns only after data is sent / received CS556 Distributed Systems Tutorial by Eleftherios Kosmas 32„„ Example Echo A client communicates with an “echo” server The server simply echoes whatever it receives back to the client CS556 Distributed Systems Tutorial by Eleftherios Kosmas 33Example Echo using stream socket The server starts by getting ready to receive client connections… Client Server 1. Create a TCP socket 1. Create a TCP socket 2. Establish connection 2. Assign a port to socket 3. Communicate 3. Set socket to listen 4. Close the connection 4. Repeatedly: a. Accept new connection b. Communicate c. Close the connection CS556 Distributed Systems Tutorial by Eleftherios Kosmas 34Example Echo using stream socket / Create socket for incoming connections / if ((servSock = socket(PFINET, SOCKSTREAM, IPPROTOTCP)) 0) DieWithError("socket() failed"); Client Server 1. Create a TCP socket 1. Create a TCP socket 2. Establish connection 2. Assign a port to socket 3. Communicate 3. Set socket to listen 4. Close the connection 4. Repeatedly: a. Accept new connection b. Communicate c. Close the connection CS556 Distributed Systems Tutorial by Eleftherios Kosmas 35Example Echo using stream socket echoServAddr.sinfamily = AFINET; / Internet address family / echoServAddr.sinaddr.saddr = htonl(INADDRANY); / Any incoming interface / echoServAddr.sinport = htons(echoServPort); / Local port / if (bind(servSock, (struct sockaddr ) echoServAddr, sizeof(echoServAddr)) 0) DieWithError("bind() failed"); Client Server 1. Create a TCP socket 1. Create a TCP socket 2. Establish connection 2. Assign a port to socket 3. Communicate 3. Set socket to listen 4. Close the connection 4. Repeatedly: a. Accept new connection b. Communicate c. Close the connection CS556 Distributed Systems Tutorial by Eleftherios Kosmas 36Example Echo using stream socket / Mark the socket so it will listen for incoming connections / if (listen(servSock, MAXPENDING) 0) DieWithError("listen() failed"); Client Server 1. Create a TCP socket 1. Create a TCP socket 2. Establish connection 2. Assign a port to socket 3. Communicate 3. Set socket to listen 4. Close the connection 4. Repeatedly: a. Accept new connection b. Communicate c. Close the connection CS556 Distributed Systems Tutorial by Eleftherios Kosmas 37Example Echo using stream socket for (;;) / Run forever / clntLen = sizeof(echoClntAddr); if ((clientSock=accept(servSock,(struct sockaddr )echoClntAddr,clntLen))0) DieWithError("accept() failed"); ... Client Server 1. Create a TCP socket 1. Create a TCP socket 2. Establish connection 2. Assign a port to socket 3. Communicate 3. Set socket to listen 4. Close the connection 4. Repeatedly: a. Accept new connection b. Communicate c. Close the connection CS556 Distributed Systems Tutorial by Eleftherios Kosmas 38Example Echo using stream socket Server is now blocked waiting for connection from a client … A client decides to talk to the server Client Server 1. Create a TCP socket 1. Create a TCP socket 2. Establish connection 2. Assign a port to socket 3. Communicate 3. Set socket to listen 4. Close the connection 4. Repeatedly: a. Accept new connection b. Communicate c. Close the connection CS556 Distributed Systems Tutorial by Eleftherios Kosmas 39Example Echo using stream socket / Create a reliable, stream socket using TCP / if ((clientSock = socket(PFINET, SOCKSTREAM, IPPROTOTCP)) 0) DieWithError("socket() failed"); Client Server 1. Create a TCP socket 1. Create a TCP socket 2. Establish connection 2. Assign a port to socket 3. Communicate 3. Set socket to listen 4. Close the connection 4. Repeatedly: a. Accept new connection b. Communicate c. Close the connection CS556 Distributed Systems Tutorial by Eleftherios Kosmas 40Example Echo using stream socket echoServAddr.sinfamily = AFINET; / Internet address family / echoServAddr.sinaddr.saddr = inetaddr(echoservIP); / Server IP address/ echoServAddr.sinport = htons(echoServPort); / Server port / if (connect(clientSock, (struct sockaddr ) echoServAddr, sizeof(echoServAddr)) 0) DieWithError("connect() failed"); Client Server 1. Create a TCP socket 1. Create a TCP socket 2. Establish connection 2. Assign a port to socket 3. Communicate 3. Set socket to listen 4. Close the connection 4. Repeatedly: a. Accept new connection b. Communicate c. Close the connection CS556 Distributed Systems Tutorial by Eleftherios Kosmas 41Example Echo using stream socket Server’s accept procedure in now unblocked and returns client’s socket for (;;) / Run forever / clntLen = sizeof(echoClntAddr); if ((clientSock=accept(servSock,(struct sockaddr )echoClntAddr,clntLen))0) DieWithError("accept() failed"); ... Client Server 1. Create a TCP socket 1. Create a TCP socket 2. Establish connection 2. Assign a port to socket 3. Communicate 3. Set socket to listen 4. Close the connection 4. Repeatedly: a. Accept new connection b. Communicate c. Close the connection CS556 Distributed Systems Tutorial by Eleftherios Kosmas 42Example Echo using stream socket echoStringLen = strlen(echoString); / Determine input length / / Send the string to the server / if (send(clientSock, echoString, echoStringLen, 0) = echoStringLen) DieWithError("send() sent a different number of bytes than expected"); Client Server 1. Create a TCP socket 1. Create a TCP socket 2. Establish connection 2. Assign a port to socket 3. Communicate 3. Set socket to listen 4. Close the connection 4. Repeatedly: a. Accept new connection b. Communicate c. Close the connection CS556 Distributed Systems Tutorial by Eleftherios Kosmas 43Example Echo using stream socket / Receive message from client / if ((recvMsgSize = recv(clntSocket, echoBuffer, RCVBUFSIZE, 0)) 0) DieWithError("recv() failed"); / Send received string and receive again until end of transmission / while (recvMsgSize 0) / zero indicates end of transmission / if (send(clientSocket, echobuffer, recvMsgSize, 0) = recvMsgSize) DieWithError(“send() failed”); if ((recvMsgSize = recv(clientSocket, echoBuffer, RECVBUFSIZE, 0)) 0) DieWithError(“recv() failed”); Client Server 1. Create a TCP socket 1. Create a TCP socket 2. Establish connection 2. Assign a port to socket 3. Communicate 3. Set socket to listen 4. Close the connection 4. Repeatedly: a. Accept new connection b. Communicate c. Close the connection CS556 Distributed Systems Tutorial by Eleftherios Kosmas 44Example Echo using stream socket Similarly, the client receives the data from the server Client Server 1. Create a TCP socket 1. Create a TCP socket 2. Establish connection 2. Assign a port to socket 3. Communicate 3. Set socket to listen 4. Close the connection 4. Repeatedly: a. Accept new connection b. Communicate c. Close the connection CS556 Distributed Systems Tutorial by Eleftherios Kosmas 45Example Echo using stream socket close(clientSock); close(clientSock); Client Server 1. Create a TCP socket 1. Create a TCP socket 2. Establish connection 2. Assign a port to socket 3. Communicate 3. Set socket to listen 4. Close the connection 4. Repeatedly: a. Accept new connection b. Communicate c. Close the connection CS556 Distributed Systems Tutorial by Eleftherios Kosmas 46Example Echo using stream socket Server is now blocked waiting for connection from a client … Client Server 1. Create a TCP socket 1. Create a TCP socket 2. Establish connection 2. Assign a port to socket 3. Communicate 3. Set socket to listen 4. Close the connection 4. Repeatedly: a. Accept new connection b. Communicate c. Close the connection CS556 Distributed Systems Tutorial by Eleftherios Kosmas 47ƒ Example Echo using datagram socket / Create socket for sending/receiving datagrams / if ((servSock = socket(PFINET, SOCKDGRAM, IPPROTOUDP)) 0) DieWithError("socket() failed"); / Create a datagram/UDP socket / if ((clientSock = socket(PFINET, SOCKDGRAM, IPPROTOUDP)) 0) DieWithError("socket() failed"); Client Server 1. Create a UDP socket 1. Create a UDP socket 2. Assign a port to socket 2. Assign a port to socket 3. Communicate 3. Repeatedly Communicate 4. Close the socket CS556 Distributed Systems Tutorial by Eleftherios Kosmas 48ƒ Example Echo using datagram socket echoServAddr.sinfamily = AFINET; / Internet address family / echoServAddr.sinaddr.saddr = htonl(INADDRANY); / Any incoming interface / echoServAddr.sinport = htons(echoServPort); / Local port / if (bind(servSock, (struct sockaddr ) echoServAddr, sizeof(echoServAddr)) 0) DieWithError("bind() failed"); echoClientAddr.sinfamily = AFINET; / Internet address family / echoClientAddr.sinaddr.saddr = htonl(INADDRANY); / Any incoming interface / echoClientAddr.sinport = htons(echoClientPort); / Local port / if(bind(clientSock,(struct sockaddr )echoClientAddr,sizeof(echoClientAddr))0) DieWithError("connect() failed"); Client Server 1. Create a UDP socket 1. Create a UDP socket 2. Assign a port to socket 2. Assign a port to socket 3. Communicate 3. Repeatedly Communicate 4. Close the socket CS556 Distributed Systems Tutorial by Eleftherios Kosmas 49ƒ Example Echo using datagram socket echoServAddr.sinfamily = AFINET; / Internet address family / echoServAddr.sinaddr.saddr = inetaddr(echoservIP); / Server IP address/ echoServAddr.sinport = htons(echoServPort); / Server port / echoStringLen = strlen(echoString); / Determine input length / / Send the string to the server / if (sendto( clientSock, echoString, echoStringLen, 0, (struct sockaddr ) echoServAddr, sizeof(echoServAddr)) = echoStringLen) DieWithError("send() sent a different number of bytes than expected"); Client Server 1. Create a UDP socket 1. Create a UDP socket 2. Assign a port to socket 2. Assign a port to socket 3. Communicate 3. Repeatedly Communicate 4. Close the socket CS556 Distributed Systems Tutorial by Eleftherios Kosmas 50ƒ Example Echo using datagram socket for (;;) / Run forever / clientAddrLen = sizeof(echoClientAddr) / Set the size of the inout parameter / /Block until receive message from client/ if ((recvMsgSize = recvfrom(servSock, echoBuffer, ECHOMAX, 0), (struct sockaddr ) echoClientAddr, sizeof(echoClientAddr))) 0) DieWithError(“recvfrom() failed"); if (sendto(servSock, echobuffer, recvMsgSize, 0, (struct sockaddr ) echoClientAddr, sizeof(echoClientAddr)) = recvMsgSize) DieWithError(“send() failed”); Client Server 1. Create a UDP socket 1. Create a UDP socket 2. Assign a port to socket 2. Assign a port to socket 3. Communicate 3. Repeatedly Communicate 4. Close the socket CS556 Distributed Systems Tutorial by Eleftherios Kosmas 51ƒ Example Echo using datagram socket Similarly, the client receives the data from the server Client Server 1. Create a UDP socket 1. Create a UDP socket 2. Assign a port to socket 2. Assign a port to socket 3. Communicate 3. Repeatedly Communicate 4. Close the socket CS556 Distributed Systems Tutorial by Eleftherios Kosmas 52ƒ Example Echo using datagram socket close(clientSock); Client Server 1. Create a UDP socket 1. Create a UDP socket 2. Assign a port to socket 2. Assign a port to socket 3. Communicate 3. Repeatedly Communicate 4. Close the socket CS556 Distributed Systems Tutorial by Eleftherios Kosmas 53Client Server Communication Unix Stream Datagram (e.g. TCP) (e.g. UDP) Server Client Server Client socket() socket() socket() socket() bind() bind() bind() listen() synchronization point accept() connect() recv() send() recvfrom() sendto() send() recv() sendto() recvfrom() close() close() close() close() CS556 Distributed Systems Tutorial by Eleftherios Kosmas 54‰ „„„ Constructing Messages Encoding Data Client wants to send two integers x and y to server st 1 Solution: Character Encoding e.g. ASCII the same representation is used to print or display them to screen allows sending arbitrarily large numbers (at least in principle) e.g. x = 17,998,720 and y = 47,034,615 49 55 57 57 56 55 50 48 32 52 55 48 51 52 54 49 53 32 1 7 9 9 8 7 2 0 4 7 0 3 4 6 1 5 sprintf(msgBuffer, “d d ”, x, y); send(clientSocket, strlen(msgBuffer), 0); CS556 Distributed Systems Tutorial by Eleftherios Kosmas 55„„ ‰‰‰'' „'„ Constructing Messages Encoding Data Pitfalls the second delimiter is required otherwise the server will not be able to separate it from whatever it follows msgBuffer must be large enough strlen counts only the bytes of the message not the null at the end of the string This solution is not efficient each digit can be represented using 4 bits, instead of one byte it is inconvenient to manipulate numbers nd 2 Solution: Sending the values of x and y CS556 Distributed Systems Tutorial by Eleftherios Kosmas 56„„ ‰) „ Constructing Messages Encoding Data nd 2 Solution: Sending the values of x and y pitfall: native integer format a protocol is used how many bits are used for each integer what type of encoding is used (e.g. two’s complement, sign/magnitude, unsigned) st 1 Implementation typedef struct int x,y; msgStruct; … msgStruct.x = x; msgStruct.y = y; send(clientSock, msgStruct, sizeof(msgStruct), 0); nd 2 Implementation nd 2 implementation send(clientSock, x, sizeof(x)), 0); send(clientSock, y, sizeof(y)), 0); works in any case CS556 Distributed Systems Tutorial by Eleftherios Kosmas 57‰‰  „ ˆ Constructing Messages Byte Ordering Address and port are stored as integers ushort sinport; (16 bit) inaddr sinaddr; (32 bit) Problem: different machines / OS’s use different word orderings • littleendian: lower bytes first • bigendian: higher bytes first these machines may communicate with one another over the network BigEndian LittleEndian 12.40.119.128 machine machine 128.119.40.12 128 119 40 12 128 119 40 12 CS556 Distributed Systems Tutorial by Eleftherios Kosmas 58„„ Constructing Messages Byte Ordering BigEndian: LittleEndian: CS556 Distributed Systems Tutorial by Eleftherios Kosmas 59ntohl „„ ˆˆ „„ „„ Constructing Messages Byte Ordering Solution: Network Byte Ordering Host ByteOrdering: the byte ordering used by a host (big or little) Network ByteOrdering: the byte ordering used by the network – always bigendian ulong htonl(ulong x); ulong ntohl(ulong x); ushort htons(ushort x); ushort ntohs(ushort x); On bigendian machines, these routines do nothing On littleendian machines, they reverse the byte order BigEndian LittleEndian 128.119.40.12 12 40 119 128 128 119 40 12 machine machine 128.119.40.12 128 119 40 12 128 119 40 12 CS556 Distributed Systems Tutorial by Eleftherios Kosmas 60 htonlConstructing Messages Byte Ordering Example Client unsigned short clientPort, message; unsigned int messageLenth; servPort = 1111; message = htons(clientPort); messageLength = sizeof(message); if (sendto( clientSock, message, messageLength, 0, (struct sockaddr ) echoServAddr, sizeof(echoServAddr)) = messageLength) DieWithError("send() sent a different number of bytes than expected"); Server unsigned short clientPort, rcvBuffer; unsigned int recvMsgSize ; if ( recvfrom(servSock, rcvBuffer, sizeof(unsigned int), 0), (struct sockaddr ) echoClientAddr, sizeof(echoClientAddr)) 0) DieWithError(“recvfrom() failed"); clientPort = ntohs(rcvBuffer); printf (“Client’s port: d”, clientPort); CS556 Distributed Systems Tutorial by Eleftherios Kosmas 61Æ ‰‰‰‰ „„„„„ Constructing Messages Alignment and Padding consider the following 12 byte structure typedef struct int x; short x2; int y; short y2; msgStruct; After compilation it will be a 14 byte structure Why Alignment Remember the following rules: data structures are maximally aligned, according to the size of the largest native integer other multibyte fields are aligned to their size, e.g., a fourbyte integer’s address will be divisible by four x x2 y y2 x x2 y y2 pad 4 bytes 2 bytes 4 bytes 2 bytes 4 bytes 2 bytes 2 bytes 4 bytes 2 bytes This can be avoided typedef struct typedef struct int x; int x; include padding to data structure short x2; int y; char pad2; short x2; reorder fields int y; short y2; short y2; msgStruct; msgStruct; CS556 Distributed Systems Tutorial by Eleftherios Kosmas 62‰‰‰ „„„„ Constructing Messages Framing and Parsing Framing is the problem of formatting the information so that the receiver can parse messages Parse means to locate the beginning and the end of message This is easy if the fields have fixed sizes e.g., msgStruct For textstring representations is harder Solution: use of appropriate delimiters caution is needed since a call of recv may return the messages sent by multiple calls of send CS556 Distributed Systems Tutorial by Eleftherios Kosmas 63‰‰‰‰‰‰ „„„ Socket Options getsockopt and setsockopt allow socket options values to be queried and set, respectively int getsockopt (sockid, level, optName, optVal, optLen); sockid: integer, socket descriptor level: integer, the layers of the protocol stack (socket, TCP, IP) optName: integer, option optVal: pointer to a buffer; upon return it contains the value of the specified option optLen: integer, inout parameter it returns 1 if an error occured int setsockopt (sockid, level, optName, optVal, optLen); optLen is now only an input parameter CS556 Distributed Systems Tutorial by Eleftherios Kosmas 64Socket Options Table„ Socket Options Example Fetch and then double the current number of bytes in the socket’s receive buffer int rcvBufferSize; int sockOptSize; … / Retrieve and print the default buffer size / sockOptSize = sizeof(recvBuffSize); if (getsockopt(sock, SOLSOCKET, SORCVBUF, rcvBufferSize, sockOptSize) 0) DieWithError(“getsockopt() failed”); printf(“Initial Receive Buffer Size: d\n”, rcvBufferSize); / Double the buffer size / recvBufferSize = 2; / Set the buffer size to new value / if (setsockopt(sock, SOLSOCKET, SORCVBUF, rcvBufferSize, sizeof(rcvBufferSize)) 0) DieWithError(“getsockopt() failed”); CS556 Distributed Systems Tutorial by Eleftherios Kosmas 66„ ‰‰‰‰‰‰‰‰ „„„ Dealing with blocking calls Many of the functions we saw block (by default) until a certain event accept: until a connection comes in connect: until the connection is established recv, recvfrom: until a packet (of data) is received what if a packet is lost (in datagram socket) send: until data are pushed into socket’s buffer sendto: until data are given to the network subsystem For simple programs, blocking is convenient What about more complex programs multiple connections simultaneous sends and receives simultaneously doing nonnetworking processing CS556 Distributed Systems Tutorial by Eleftherios Kosmas 67„„„ Dealing with blocking calls Nonblocking Sockets Asynchronous I/O Timeouts CS556 Distributed Systems Tutorial by Eleftherios Kosmas 68‰‰‰‰)‰‰ „„„ Nonblocking Sockets If an operation can be completed immediately, success is returned; otherwise, a failure is returned (usually 1) errno is properly set, to distinguish this (blocking) failure from other (EINPROGRESS for connect, EWOULDBLOCK for the other) st 1 Solution: int fcntl (sockid, command, argument); sockid: integer, socket descriptor command: integer, the operation to be performed (FGETFL, FSETFL) argument: long, e.g. ONONBLOCK fcntl (sockid, FSETFL, ONONBLOCK); nd 2 Solution: flags parameter of send, recv, sendto, recvfrom MSGDONTWAIT not supported by all implementations CS556 Distributed Systems Tutorial by Eleftherios Kosmas 69„„ ‰‰‰‰‰‰‰ „„„„„ Signals Provide a mechanism for operating system to notify processes that certain events occur e.g., the user typed the “interrupt” character, or a timer expired signals are delivered asynchronously upon signal delivery to program it may be ignored, the process is never aware of it the program is forcefully terminated by the OS a signalhandling routine, specified by the program, is executed this happens in a different thread the signal is blocked, until the program takes action to allow its delivery each process (or thread) has a corresponding mask Each signal has a default behavior e.g. SIGINT (i.e., Ctrl+C) causes termination it can be changed using sigaction() Signals can be nested (i.e., while one is being handled another is delivered) CS556 Distributed Systems Tutorial by Eleftherios Kosmas 70‰‰‰ „„ ‰‰‰‰ „ Signals int sigaction(whichSignal, newAction, oldAction); whichSignal: integer newAction: struct sigaction, defines the new behavior oldAction: struct sigaction, if not NULL, then previous behavior is copied it returns 0 on success, 1 otherwise struct sigaction void (sahandler)(int); / Signal handler / sigsett samask; / Signals to be blocked during handler execution / int saflags; / Flags to modify default behavior / ; sahandler determines which of the first three possibilities occurs when signal is delivered, i.e., it is not masked SIGIGN, SIGDFL, address of a function samask specifies the signals to be blocked while handling whichSignal whichSignal is always blocked it is implemented as a set of boolean flags int sigemptyset (sigsett set); / unset all the flags / int sigfullset (sigsett set); / set all the flags / int sigaddset(sigsett set, int whichSignal); / set individual flag / int sigdelset(sigsett set, int whichSignal); / unset individual flag / CS556 Distributed Systems Tutorial by Eleftherios Kosmas 71Signals Example include stdio.h include signal.h include unistd.h void DieWithError(char errorMessage); void InterruptSignalHandler(int signalType); int main (int argc, char argv) struct sigaction handler; / Signal handler specification structure / handler.sahandler = InterruptSignalHandler; / Set handler function / if (sigfillset(handler.samask) 0) / Create mask that masks all signals / DieWithError (“sigfillset() failed”); handler.saflags = 0; if (sigaction(SIGINT,handler, 0) 0) / Set signal handling for interrupt signals / DieWithError (“sigaction() failed”); for(;;) pause(); / Suspend program until signal received / exit(0); void InterruptHandler (int signalType) printf (“Interrupt received. Exiting program.\n); exit(1); CS556 Distributed Systems Tutorial by Eleftherios Kosmas 72‰ '„ Asynchronous I/O Nonblocking sockets require “polling” With asynchronous I/O the operating system informs the program when a socket call is completed the SIGIO signal is delivered to the process, when some I/Orelated event occurs on the socket Three steps: / i. inform the system of the desired disposition of the signal / struct sigaction handler; handler.sahandler = SIGIOHandler; if (sigfillset(handler.samask) 0) DiewithError(“…”); handler.saflags = 0; if (sigaction(SIGIO, handler, 0) 0) DieWithError(“…”); / ii. ensure that signals related to the socket will be delivered to this process / if (fcntl(sock, FSETOWN, getpid()) 0) DieWithError(); / iii. mark the socket as being primed for asynchronous I/O / if (fcntl(sock, FSETFL, ONONBLOCK FASYNC) 0) DieWithError(); CS556 Distributed Systems Tutorial by Eleftherios Kosmas 73„„ ‰‰‰‰ „„„ Timeouts Using asynchronous I/O the operating system informs the program for the occurrence of an I/O related event what happens if a UPD packet is lost We may need to know if something doesn’t happen after some time unsigned int alarm (unsigned int secs); starts a timer that expires after the specified number of seconds (secs) returns the number of seconds remaining until any previously scheduled alarm was due to be delivered, or zero if there was no previously scheduled alarm process receives SIGALARM signal when timer expires and errno is set to EINTR CS556 Distributed Systems Tutorial by Eleftherios Kosmas 74Asynchronous I/O Example / Inform the system of the desired disposition of the signal / struct sigaction myAction; myAction.sahandler = CatchAlarm; if (sigfillset(myAction.samask) 0) DiewithError(“…”); myAction.saflags = 0; if (sigaction(SIGALARM, handler, 0) 0) DieWithError(“…”); / Set alarm / alarm(TIMEOUTSECS); / Call blocking receive / if (recvfrom(sock, echoBuffer, ECHOMAX, 0, … ) 0) if (errno = EINTR) … /Alarm went off / else DieWithError(“recvfrom() failed”); CS556 Distributed Systems Tutorial by Eleftherios Kosmas 75‰‰ „„' Iterative Stream Socket Server Handles one client at a time Additional clients can connect while one is being served connections are established they are able to send requests but, the server will respond after it finishes with the first client Works well if each client required a small, bounded amount of work by the server otherwise, the clients experience long delays CS556 Distributed Systems Tutorial by Eleftherios Kosmas 76Iterative Server Example: echo using stream socket include stdio.h / for printf() and fprintf() / include sys/socket.h / for socket(), bind(), connect(), recv() and send() / include arpa/inet.h / for sockaddrin and inetntoa() / include stdlib.h / for atoi() and exit() / include string.h / for memset() / include unistd.h / for close() / define MAXPENDING 5 / Maximum outstanding connection requests / void DieWithError(char errorMessage); / Error handling function / void HandleTCPClient(int clntSocket); / TCP client handling function / int main(int argc, char argv) int servSock; / Socket descriptor for server / int clntSock; / Socket descriptor for client / struct sockaddrin echoServAddr; / Local address / struct sockaddrin echoClntAddr; / Client address / unsigned short echoServPort; / Server port / unsigned int clntLen; / Length of client address data structure / if (argc = 2) / Test for correct number of arguments / fprintf(stderr, "Usage: s Server Port\n", argv0); exit(1); echoServPort = atoi(argv1); / First arg: local port / / Create socket for incoming connections / if ((servSock = socket(PFINET, SOCKSTREAM, IPPROTOTCP)) 0) DieWithError("socket() failed"); ... CS556 Distributed Systems Tutorial by Eleftherios Kosmas 77Iterative Server Example: echo using stream socket ... / Construct local address structure / memset(echoServAddr, 0, sizeof(echoServAddr)); / Zero out structure / echoServAddr.sinfamily = AFINET; / Internet address family / echoServAddr.sinaddr.saddr = htonl(INADDRANY); / Any incoming interface / echoServAddr.sinport = htons(echoServPort); / Local port / / Bind to the local address / if (bind(servSock, (struct sockaddr ) echoServAddr, sizeof(echoServAddr)) 0) DieWithError("bind() failed"); / Mark the socket so it will listen for incoming connections / if (listen(servSock, MAXPENDING) 0) DieWithError("listen() failed"); for (;;) / Run forever / / Set the size of the inout parameter / clntLen = sizeof(echoClntAddr); / Wait for a client to connect / if ((clntSock = accept(servSock, (struct sockaddr ) echoClntAddr, clntLen)) 0) DieWithError("accept() failed"); / clntSock is connected to a client / printf("Handling client s\n", inetntoa(echoClntAddr.sinaddr)); HandleTCPClient(clntSock); / NOT REACHED / CS556 Distributed Systems Tutorial by Eleftherios Kosmas 78Iterative Server Example: echo using stream socket define RCVBUFSIZE 32 / Size of receive buffer / void HandleTCPClient(int clntSocket) char echoBufferRCVBUFSIZE; / Buffer for echo string / int recvMsgSize; / Size of received message / / Receive message from client / if ((recvMsgSize = recv(clntSocket, echoBuffer, RCVBUFSIZE, 0)) 0) DieWithError("recv() failed"); / Send received string and receive again until end of transmission / while (recvMsgSize 0) / zero indicates end of transmission / / Echo message back to client / if (send(clntSocket, echoBuffer, recvMsgSize, 0) = recvMsgSize) DieWithError("send() failed"); / See if there is more data to receive / if ((recvMsgSize = recv(clntSocket, echoBuffer, RCVBUFSIZE, 0)) 0) DieWithError("recv() failed"); close(clntSocket); / Close client socket / CS556 Distributed Systems Tutorial by Eleftherios Kosmas 79‰‰‰‰ „„ Multitasking PerClient Process For each client connection request, a new process is created to handle the communication int fork(); a new process is created, identical to the calling process, except for its process ID and the return value it receives from fork() returns 0 to child process, and the process ID of the new child to parent Caution: when a child process terminates, it does not automatically disappears use waitpid() to parent in order to “harvest” zombies CS556 Distributed Systems Tutorial by Eleftherios Kosmas 80Multitasking PerClient Process Example: echo using stream socket include sys/wait.h / for waitpid() / int main(int argc, char argv) int servSock; / Socket descriptor for server / int clntSock; / Socket descriptor for client / unsigned short echoServPort; / Server port / pidt processID; / Process ID from fork()/ unsigned int childProcCount = 0; / Number of child processes / if (argc = 2) / Test for correct number of arguments / fprintf(stderr, "Usage: s Server Port\n", argv0); exit(1); echoServPort = atoi(argv1); / First arg: local port / servSock = CreateTCPServerSocket(echoServPort); for (;;) / Run forever / clntSock = AcceptTCPConnection(servSock); if ((processID = fork()) 0) DieWithError (“fork() failed”); / Fork child process / else if (processID = 0) / This is the child process / close(servSock); / child closes listening socket / HandleTCPClient(clntSock); exit(0); / child process terminates / close(clntSock); / parent closes child socket / childProcCount++; / Increment number of outstanding child processes / ... CS556 Distributed Systems Tutorial by Eleftherios Kosmas 81Multitasking PerClient Process Example: echo using stream socket ... while (childProcCount) / Clean up all zombies / processID = waitpid((pidt) 1, NULL, WHOANG); / Nonblocking wait / if (processID 0) DieWithError (“...”); else if (processID == 0) break; / No zombie to wait / else childProcCount; / Cleaned up after a child / / NOT REACHED / CS556 Distributed Systems Tutorial by Eleftherios Kosmas 82‰‰ ' Multitasking PerClient Thread Forking a new process is expensive duplicate the entire state (memory, stack, file/socket descriptors, …) Threads decrease this cost by allowing multitasking within the same process threads share the same address space (code and data) An example is provided using POSIX Threads CS556 Distributed Systems Tutorial by Eleftherios Kosmas 83Multitasking PerClient Thread Example: echo using stream socket include pthread.h / for POSIX threads / void ThreadMain(void arg) / Main program of a thread / struct ThreadArgs / Structure of arguments to pass to client thread / int clntSock; / socket descriptor for client / ; int main(int argc, char argv) int servSock; / Socket descriptor for server / int clntSock; / Socket descriptor for client / unsigned short echoServPort; / Server port / pthreadt threadID; / Thread ID from pthreadcreate()/ struct ThreadArgs threadArgs; / Pointer to argument structure for thread / if (argc = 2) / Test for correct number of arguments / fprintf(stderr, "Usage: s Server Port\n", argv0); exit(1); echoServPort = atoi(argv1); / First arg: local port / servSock = CreateTCPServerSocket(echoServPort); for (;;) / Run forever / clntSock = AcceptTCPConnection(servSock); / Create separate memory for client argument / if ((threadArgs = (struct ThreadArgs ) malloc(sizeof(struct ThreadArgs)))) == NULL) DieWithError(“…”); threadArgs clntSock = clntSock; / Create client thread / if (pthreadcreate (threadID, NULL, ThreadMain, (void ) threadArgs) = 0) DieWithError(“…”); / NOT REACHED / CS556 Distributed Systems Tutorial by Eleftherios Kosmas 84Multitasking PerClient Thread Example: echo using stream socket void ThreadMain(void threadArgs) int clntSock; / Socket descriptor for client connection / pthreaddetach(pthreadself()); / Guarantees that thread resources are deallocated upon return / / Extract socket file descriptor from argument / clntSock = ((struct ThreadArgs ) threadArgs) clntSock; free(threadArgs); / Deallocate memory for argument / HandleTCPClient(clntSock); return (NULL); CS556 Distributed Systems Tutorial by Eleftherios Kosmas 85„„ ‰‰‰‰‰‰ „„„ Multitasking Constrained Both process and thread incurs overhead creation, scheduling and context switching As their numbers increases this overhead increases after some point it would be better if a client was blocked Solution: Constrained multitasking. The server: begins, creating, binding and listening to a socket creates a number of processes, each loops forever and accept connections from the same socket when a connection is established the client socket descriptor is returned to only one process the other remain blocked CS556 Distributed Systems Tutorial by Eleftherios Kosmas 86Multitasking Constrained Example: echo using stream socket void ProcessMain(int servSock); / Main program of process / int main(int argc, char argv) int servSock; / Socket descriptor for server/ unsigned short echoServPort; / Server port / pidt processID; / Process ID / unsigned int processLimit; / Number of child processes to create / unsigned int processCt; / Process counter / if (argc = 3) / Test for correct number of arguments / fprintf(stderr,"Usage: s SERVER PORT FORK LIMIT\n", argv0); exit(1); echoServPort = atoi(argv1); / First arg: local port / processLimit = atoi(argv2); / Second arg: number of child processes / servSock = CreateTCPServerSocket(echoServPort); for (processCt=0; processCt processLimit; processCt++) if ((processID = fork()) 0) DieWithError("fork() failed"); / Fork child process / else if (processID == 0) ProcessMain(servSock); / If this is the child process / exit(0); / The children will carry on / void ProcessMain(int servSock) int clntSock; / Socket descriptor for client connection / for (;;) / Run forever / clntSock = AcceptTCPConnection(servSock); printf("with child process: d\n", (unsigned int) getpid()); HandleTCPClient(clntSock); CS556 Distributed Systems Tutorial by Eleftherios Kosmas 87' ‰‰‰‰‰ „„„„ Multiplexing So far, we have dealt with a single I/O channel We may need to cope with multiple I/O channels e.g., supporting the echo service over multiple ports Problem: from which socket the server should accept connections or receive messages it can be solved using nonblocking sockets but it requires polling Solution: select() specifies a list of descriptors to check for pending I/O operations blocks until one of the descriptors is ready returns which descriptors are ready CS556 Distributed Systems Tutorial by Eleftherios Kosmas 88Æ ‰‰‰‰‰ „ Multiplexing int select (maxDescPlus1, readDescs, writeDescs, exceptionDescs, timeout); maxDescsPlus1: integer, hint of the maximum number of descriptors readDescs: fdset, checked for immediate input availability writeDescs: fdset, checked for the ability to immediately write data exceptionDescs: fdset, checked for pending exceptions timeout: struct timeval, how long it blocks (NULL forever) returns the total number of ready descriptors, 1 in case of error changes the descriptor lists so that only the corresponding positions are set int FDZERO (fdset descriptorVector); / removes all descriptors from vector / int FDCLR (int descriptor, fdset descriptorVector); / remove descriptor from vector / int FDSET (int descriptor, fdset descriptorVector); / add descriptor to vector / int FDISSET (int descriptor, fdset descriptorVector); / vector membership check / struct timeval timet tvsec; / seconds / timet tvusec; / microseconds / ; CS556 Distributed Systems Tutorial by Eleftherios Kosmas 89Multiplexing Example: echo using stream socket include sys/time.h / for struct timeval / int main(int argc, char argv) int servSock; / Socket descriptors for server / int maxDescriptor; / Maximum socket descriptor value / fdset sockSet; / Set of socket descriptors for select() / long timeout; / Timeout value given on commandline / struct timeval selTimeout; / Timeout for select() / int running = 1; / 1 if server should be running; 0 otherwise / int noPorts; / Number of port specified on commandline / int port; / Looping variable for ports / unsigned short portNo; / Actual port number / if (argc 3) / Test for correct number of arguments / fprintf(stderr, "Usage: s Timeout (secs.) Port 1 ...\n", argv0); exit(1); timeout = atol(argv1); / First arg: Timeout / noPorts = argc 2; / Number of ports is argument count minus 2 / servSock = (int ) malloc(noPorts sizeof(int)); / Allocate list of sockets for incoming connections / maxDescriptor = 1; / Initialize maxDescriptor for use by select() / for (port = 0; port noPorts; port++) / Create list of ports and sockets to handle ports / portNo = atoi(argvport + 2); / Add port to port list. Skip first two arguments / servSockport = CreateTCPServerSocket(portNo); / Create port socket / if (servSockport maxDescriptor) / Determine if new descriptor is the largest / maxDescriptor = servSockport; ... CS556 Distributed Systems Tutorial by Eleftherios Kosmas 90Multiplexing Example: echo using stream socket printf("Starting server: Hit return to shutdown\n"); while (running) / Zero socket descriptor vector and set for server sockets / / This must be reset every time select() is called / FDZERO(sockSet); FDSET(STDINFILENO, sockSet); / Add keyboard to descriptor vector / for (port = 0; port noPorts; port++) FDSET(servSockport, sockSet); / Timeout specification / / This must be reset every time select() is called / selTimeout.tvsec = timeout; / timeout (secs.) / selTimeout.tvusec = 0; / 0 microseconds / / Suspend program until descriptor is ready or timeout / if (select(maxDescriptor + 1, sockSet, NULL, NULL, selTimeout) == 0) printf("No echo requests for ld secs...Server still alive\n", timeout); else if (FDISSET(0, sockSet)) / Check keyboard / printf("Shutting down server\n"); getchar(); running = 0; for (port = 0; port noPorts; port++) if (FDISSET(servSockport, sockSet)) printf("Request on port d: ", port); HandleTCPClient(AcceptTCPConnection(servSockport)); for (port = 0; port noPorts; port++) close(servSockport); / Close sockets / free(servSock); / Free list of sockets / exit(0); CS556 Distributed Systems Tutorial by Eleftherios Kosmas 91„„„ ‰'‰‰) „„„„ Multiple Recipients So far, all sockets have dealt with unicast communication i.e., an onetoone communication, where one copy (“uni”) of the data is sent (“cast”) what if we want to send data to multiple recipients st 1 Solution: unicast a copy of the data to each recipient inefficient, e.g., consider we are connected to the internet through a 3Mbps line a video server sends 1Mbps streams then, server can support only three clients simultaneously nd 2 Solution: using network support broadcast, all the hosts of the network receive the message multicast, a message is sent to some subset of the host for IP: only UDP sockets are allowed to broadcast and multicast CS556 Distributed Systems Tutorial by Eleftherios Kosmas 92‰‰‰‰‰ „„„„ Multiple Recipients Broadcast Only the IP address changes Local broadcast: to address 255.255.255.255 send the message to every host on the same broadcast network not forwarded by the routers Directed broadcast: for network identifier 169.125 (i.e., with subnet mask 255.255.0.0) the directed broadcast address is 169.125.255.255 No networkwide broadcast address is available why In order to use broadcast the options of socket must change: int broadcastPermission = 1; setsockopt(sock, SOLSOCKET, SOBROADCAST, (void) broadcastPermission, sizeof(broadcastPermission)); CS556 Distributed Systems Tutorial by Eleftherios Kosmas 93‰ „„„ Multiple Recipients Multicast Using class D addresses range from 224.0.0.0 to 239.255.255.255 hosts send multicast requests for specific addresses a multicast group is formed we need to set TTL (timetolive), to limit the number of hops using sockopt() no need to change the options of socket CS556 Distributed Systems Tutorial by Eleftherios Kosmas 94‰‰‰‰‰ „„„ Useful Functions int atoi(const char nptr); converts the initial portion of the string pointed to by nptr to int int inetaton(const char cp, struct inaddr inp); converts the Internet host address cp from the IPv4 numbersand dots notation into binary form (in network byte order) stores it in the structure that inp points to. it returns nonzero if the address is valid, and 0 if not char inetntoa(struct inaddr in); converts the Internet host address in, given in network byte order, to a string in IPv4 dotteddecimal notation typedef uint32t inaddrt; struct inaddr inaddrt saddr; ; CS556 Distributed Systems Tutorial by Eleftherios Kosmas 95‰‰‰‰ „„ Useful Functions int getpeername(int sockfd, struct sockaddr addr, socklent addrlen); returns the address (IP and port) of the peer connected to the socket sockfd, in the buffer pointed to by addr 0 is returned on success; 1 otherwise int getsockname(int sockfd, struct sockaddr addr, socklent addrlen); returns the current address to which the socket sockfd is bound, in the buffer pointed to by addr 0 is returned on success; 1 otherwise CS556 Distributed Systems Tutorial by Eleftherios Kosmas 96‰‰‰ „„ Domain Name Service struct hostent gethostbyname(const char name); returns a structure of type hostent for the given host name name is a hostname, or an IPv4 address in standard dot notation e.g. gethostbyname(“www.csd.uoc.gr”); struct hostent gethostbyaddr(const void addr, socklent len, int type); returns a structure of type hostent for the given host address addr of length len and address type type struct hostent char hname; / official name of host / char haliases; / alias list (strings) / int haddrtype; / host address type (AFINET) / int hlength; / length of address / char haddrlist; / list of addresses (binary in network byte order) / define haddr haddrlist0 / for backward compatibility / CS556 Distributed Systems Tutorial by Eleftherios Kosmas 97‰‰‰ „„ Domain Name Service struct servent getservbyname(const char name, const char proto); returns a servent structure for the entry from the database that matches the service name using protocol proto. if proto is NULL, any protocol will be matched. e.g. getservbyname(“echo”, “tcp”) ; struct servent getservbyport(int port, const char proto); returns a servent structure for the entry from the database that matches the service name using port port struct servent char sname; / official service name / char saliases; / list of alternate names (strings)/ int sport; / service port number / char sproto; / protocol to use (“tcp” or “udp”)/ CS556 Distributed Systems Tutorial by Eleftherios Kosmas 98„„ Compiling and Executing include the required header files Example: milo:/CS556/sockets gcc o TCPEchoServer TCPEchoServer.c DieWithError.c HandleTCPClient.c milo:/CS556/sockets gcc o TCPEchoClient TCPEchoClient.c DieWithError.c milo:/CS556/sockets TCPEchoServer 3451 1 6273 milo:/CS556/sockets TCPEchoClient 0.0.0.0 hello 3451 Handling client 127.0.0.1 Received: hello milo:/CS556/sockets ps PID TTY TIME CMD 5128 pts/9 00:00:00 tcsh 6273 pts/9 00:00:00 TCPEchoServer 6279 pts/9 00:00:00 ps milo:/CS556/sockets kill 6273 milo:/CS556/sockets 1 Terminated TCPEchoServer 3451 milo:/CS556/sockets CS556 Distributed Systems Tutorial by Eleftherios Kosmas 99The End Questions CS556 Distributed Systems Tutorial by Eleftherios Kosmas 100
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