Transcript Network Programming Using Internet Sockets

Network Programming Using
Internet Sockets
Wu Xuanxuan Lai Xinyu
吴璇璇 赖新宇
[email protected]
[email protected]
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
Basic Socket Programming
Understanding Sockets- Definition 1
• Definition 1: a door between application
process and end-end transport protocol
(TCP/UDP)
Basic Socket Programming
Understanding Sockets-Definition1
loosely-coupled
controlled by
app developer
Controlled by OS
You write sockets programs without knowing
how the lower levels‘ protocols works!
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
Basic Socket Programming
Understanding Sockets- Definition 2
• Definition2: a way to speak to other programs
using standard Unix file descriptors.
Basic Socket Programming
Understanding Sockets- Definition2
• Socket Programming
int sockfd; /*socket descriptor*/
sockfd= socket( AF_INET, SOCK_STREAM, 0);
read( sockfd, … );
• File Operation
char buf[100];
int fd;
/*file descriptor*/
fd= open(“foo", O_RDONLY);
read( fd, buf, num_bytes);
Basic Socket Programming
Understanding Sockets- Definition 3
• Definition3: merely an endpoint in
communication.
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
TCP/IP Internet
Xerox NS
Intra-host
DEC DNA
Symbolic Name
AF_INET
AF_NS
Unix AF_UNIX
AF_DECNET
Service Type
datagram (UDP)
reliable, in order (TCP)
raw socket
If(sockfd < 0)
perror(“can’t create socket");
symbolic name
SOCK_DGRAM
SOCK_STREAM
SOCK_RAW
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
Basic Socket Programming
Socket API-close(),shutdown()
• 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
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.
Basic Socket Programming
TCP API(SERVER)-accept()
• 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(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 them
inet_addr() : dotted decimal to binary
gethostbyname() : 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
21
23
25
80
1-1023
1024-4999
5000-
reserved for standard services
ftp
telnet
SMTP
HTTP
Available only to priviledged users
Usuable by system and user processes
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 Programming
a simple example- Result
Programming Assignment
• P2P Principle
P2P Server
login
share
Peer Client
search
logout
ping
download
Peer Client
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 packet
packet 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!