network programming using internet sockets wu xuanxuan lai xinyu 吴璇璇 赖新宇...
TRANSCRIPT
Agenda
• Basic Socket Programming– Understanding Sockets– Socket API– Structs and Data Handling– A simple example
• Assignment• References
Basic Socket Programming• What is a Socket– Definition 1:• A door between application process and end-end
transport protocol(TCP/UDP)
– Definition 2:• A way to speak to other programs using standard UNIX
file descriptors.
– Definition 3:• An endpoint in communication
• Definition 1: a door between application process and end-end transport protocol (TCP/UDP)
Basic Socket Programming Understanding Sockets- Definition 1
Basic Socket Programming Understanding Sockets-Definition1
controlled byapp developer
Controlled by OS
You write sockets programs without knowing how the lower levels‘ protocols works!
loosely-coupled
Basic Socket Programming Understanding Sockets- Definition1
Socket API: (1) choice of transport protocol; (2) ability to fix a few parameters• Two types of transport service via Internet socket
API: – Stream Sockets (connection-oriented )
• They use TCP (Transmission Control Protocol) protocol– Reliable stream
– Datagram Sockets (connectionless)• They use UDP (User Datagram Protocol) protocol
– Unreliable datagram
• Definition2: a way to speak to other programs using standard Unix file descriptors.
Basic Socket Programming Understanding Sockets- Definition 2
• Socket Programmingint sockfd; /*socket descriptor*/sockfd= socket( AF_INET, SOCK_STREAM, 0);read( sockfd, … );
• File Operationchar buf[100];int fd; /*file descriptor*/fd= open(“foo", O_RDONLY);read( fd, buf, num_bytes);
Basic Socket Programming Understanding Sockets- Definition2
• Definition3: merely an endpoint in communication.
Basic Socket Programming Understanding Sockets- Definition 3
Basic Socket Programming Understanding Sockets- Definition 3
– IP ： User needs to know the IP ADDRESS of the server.– Port number: On the server, many processes are
running. We want to “talk” to the right one.
• The knowledge of the IP addresses and the Port Number define uniquely a communication endpoint.
Basic Socket Programming Socket API-TCP Model
Basic Socket Programming Socket API-UDP Model
Server:No bind() and accept().Client:No connect().
Basic Socket Programming Socket API-socket()
• socket() -Get the File Descriptor! – The first step is to require the OS to reserve one
“descriptor” for the communication channel.int sockfd = socket(AF_INET, socket_type, 0);/*socket_type=SOCK_STREAM|SOCK_DGRAM*//*AF_INET means we use IP (version 4)*//*0 is for IP (not ICMP or others)*/
/*return a socket descriptor or -1 when error*/Protocol Family Symbolic NameTCP/IP Internet AF_INETXerox NS AF_NSIntra-host Unix AF_UNIXDEC DNA AF_DECNET
Service Type symbolic namedatagram (UDP) SOCK_DGRAMreliable, in order (TCP) SOCK_STREAMraw socket SOCK_RAW
If(sockfd < 0)perror(“can’t create socket");
Basic Socket Programming Socket API-bind()
• bind()-What IP address and port am I on? struct sockaddr_in servaddr;bind(sockfd, (struct sockaddr *) &servaddr, sizeof(servaddr));
Note:–Only the server need to call this API;–The type of the second parameter should be sockaddr while we often use sockaddr_in in the program——Type Conversation
• close(sockfd); – frees up any memory associated with the socket
• shutdown(sockfd, how);/* how = 0 -> disable receptions *//* how = 1 -> disable transmission *//* how = 2 -> the same as close() */
Basic Socket Programming Socket API-close(),shutdown()
Basic Socket Programming TCP API(SERVER)-listen()
• listen()-Who will call me?
listen(sockfd, req_no);• req_no: specifies the maximum number of client connections
that the kernel will queue for this listening descriptor.
• accept()-Thank you for calling port 3490.int new_sd, sockfd, size;struct sockaddr remote_addr;new_sd = accept(sockfd, &remote_addr, &size);
– If the queue is empty, the process will be blocked.– If so, accept() returns a NEW SOCKET DESCRIPTOR ! – the old socket descriptor (sockfd) is still queuing request from the
network !– So, if we want to communicate with the client, we MUST use new_sd.– new_sd is a socket ready for the communication– It is suggested that handle new_sd in a child process or a thread.
Basic Socket Programming TCP API(SERVER)-accept()
Basic Socket Programming TCP API(CLIENT)-connect()
• connect()-Hey, you! int sockfd; connect(sockfd, (sockaddr*) &servaddr,
sizeof(servaddr) );
– On the client side, bind is done automatically– The local IP address is the one provided by default – A port “randomly” assigned by the operating system is good.– So, we put in servaddr the information on the server and try to
connect to it.– Finish three-way handshake
Basic Socket Programming TCP API-send() , recv()
• send() and recv() -Talk to me, baby!int send(int sockfd, const void *msg, int len, int
flags); int recv(int sockfd, void *buf, int len, unsigned int
flags);
char *msg = “Hi, baby!";char buffer[SOME_SIZE];int len, nset, nrecv;..
len = strlen(msg);nset= send(sockfd, msg, len, 0);.nrecv = recv(sockfd, &buffer, len, flags)
Basic Socket Programming TCP API-read() , write()
• read() and write() –more choices• read() = recv(*, *, *, 0)• write() = send(*, *, *, 0)• Programmers are familiar with, similar to file operations
• recv() and send()• explicit meaning
Basic Socket Programming UDP API-sendto() , recvfrom()
• sendto() and recvfrom() int sendto(int sockfd, const void *msg, int len, unsigned
int flags, const struct sockaddr *to, int tolen);int recvfrom(int sockfd, void *buf,int len,unsigned int
flags, struct sockaddr *from, int *fromlen)
– Send directly without handshake – The first four parameters are the same with send/recv– to/from is a pointer to a struct sockaddr which contains the
destination IP address and port.
– tolen/fromlen, can simply be set to sizeof(struct sockaddr).
Basic Socket Programming Structs and Data Handling-IP address• IP Address
– Every host has a unique IP Address– 32bits
• Three forms– hostname (string) e.g. localhost– dotted decimal(string) e.g. 192.168.2.1– binary(u_long)
• Dealing with theminet_addr() : dotted decimal to binarygethostbyname() : hostname to binary
e.g. servaddr.sin_addr.s_addr =inet_addr(“59.67.33.68");
Basic Socket Programming Structs and Data Handling-Port
• Port– 1-255 reserved for standard services– 21 ftp– 23 telnet– 25 SMTP– 80 HTTP– 1-1023 Available only to priviledged users – 1024-4999 Usuable by system and user processes– 5000- Usuable by user processes only
Basic Socket Programming Structs and Data Handling-struct sock_addr • struct sockaddr ： This structure holds socket address
information for many types of sockets:
• struct sockaddr { unsigned short sa_family; // address family, AF_xxx char sa_data[14]; // 14 bytes of protocol
address };
• sockaddr is the structure with the addresses and the ports. We put IP address and the Port in sa_data[14].
Not convenient to deal with?
Basic Socket Programming Structs and Data Handling-struct sockaddr_in
• struct sockaddr_in ： To deal with sockaddr, programmers created a structure: struct sockaddr_in ("in" for "Internet".)
• struct sockaddr_in { short int sin_family; // Address family unsigned short int sin_port; // Port number struct in_addr sin_addr; // Internet address unsigned char sin_zero[8]; // Same size as struct sockaddr
}; • struct in_addr{
/* 32-byte IP Address *./
in_addr_t s_addr; };
We can work with sockaddr_in and cast it to sockaddr.
struct sockaddr_in servaddr;bind(sockfd, (struct sockaddr *) &servaddr, sizeof(servaddr));
Basic Socket Programming Structs and Data Handling
• Convert the Natives! • Know this:
– there are two byte orderings• most significant byte first-“Network Byte Order” (NBO). • or least significant byte first-"Host Byte Order” (HBO).
– htons() host to network short– htonl() host to network long– ntohs() network to host short– ntohl() network to host long
• e.g. servaddr.sin_addr.s_addr = htonl(INADDR_ANY); /*IP address of
localhost*/servaddr.sin_port = htons(13);
Basic Socket Programming Structs and Data Handling
• And here's a sample, while packing a struct sockaddr_in /* an Internet endpoint address*/ struct sockaddr_in my_addr;
my_addr.sin_family = AF_INET; /* host byte order */ my_addr.sin_port = htons(MYPORT); /* short, NBO*/ my_addr.sin_addr.s_addr = inet_addr("132.241.5.10");
bzero(&(my_addr.sin_zero)); /* zero the rest of the struct */
Basic Socket Programming a simple example-TCP server
Basic Socket Programming a simple example-TCP client
Basic Socket Programminga simple example- Result
• P2P Principle
login search share logout
ping download
P2P Server
Peer ClientPeer Client
Programming Assignment
Assignment
• Phase1: Establishing Client-Server Communications (Mandatory; 60 points)
• Phase2: Establishing Peer-Peer Communications (Mandatory; 40 points Optional; 20 points)
Phase1: Establishing Client-Server Communications -- Mandatory
• 1) Authenticate with the server (provide a username and encrypted password)
• 2) Send a list of files to the server that you wish to share with other users
• 3) Submit a search query to the server for a file you wish to download
• 4) Receive the search results, parse them, and output them to the user
• 5) Log out
Phase1: Authenticate
• Protocol packetpacket head is 4 bytes!
Phase1: Share
• Protocol packet:
Phase1: Search
• Protocol packet:
Phase1: Logout
• Protocol packet:
Phase2: Establishing Peer-Peer Communications
• 1) Add functionality to send "ping" messages over UDP and listen for echo responses, in order to estimate the round trip time to another peer. --Mandatory
• 2) Add functionality to respond to ping messages from other peers.-- Mandatory
• 3) Add functionality to connect to another peer and download a file.
• 4) Add functionality to make your peer a file server, so that other peers may connect and download files from you.
Phase2: Ping
• Send UDP Ping Message.• Protocol packet:
Do not guarantee delivery of packets!
Use timeout control—select()
Phase2: Peer-Peer Communications
• Protocol packet: No need password!
Phase2: Peer-Peer Communications (cont...)
• Protocol packet:
Requirement
• Program Correctness and Functionality: 60%
• Code design & Program Structure: 10%
• Documentation: 30%
Deadline
• Mandatory : April 27
• Optional: May 7
• Submit to: [email protected]
• For more detail: detailed requirements.pdf
References
• Warren W. Gay , “Linux Socket Programming by Example”• Beej's Guide to Network Programming Using Internet Sockets• Douglas E. Comer, David L. Stevens, “Internetworking With
TCP/IP Vol III”
Thank you!