tcp socket programming
DESCRIPTION
TCP Socket Programming. What is a socket?. An abstract interface provided to the application programmer File descriptor, allows apps to read/write to the network Allows to processes on remotely connected computers to talk to each other. Two types of sockets. SOCK_STREAM TCP - PowerPoint PPT PresentationTRANSCRIPT
TCP Socket Programming
An abstract interface provided to the application programmer File descriptor, allows apps to read/write to
the network Allows to processes on remotely
connected computers to talk to each other
What is a socket?
SOCK_STREAM TCP connection
oriented, bidirectional
reliable, in-order delivery
Two types of socketsSOCK_DGRAM
UDP no connection unreliable delivery,
no guarantee on the order
can send/receive
CPSC 441 - Application Layer 4
Socket-programming using TCPSocket: a door between application process and end-
end-transport protocol (UDP or TCP)TCP service: reliable transfer of bytes from one
process to another
process
TCP withbuffers,
variables
socket
controlled byapplicationdeveloper
controlled byoperating
system
host orserver
process
TCP withbuffers,
variables
socket
controlled byapplicationdevelopercontrolled byoperatingsystem
host orserver
internet
CPSC 441 - Application Layer 5
Socket programming with TCPClient must contact server server process must first be
running server must have created
socket (door) that welcomes client’s contact
Client contacts server by: creating client-local TCP
socket specifying IP address, port
number of server process When client creates socket:
client TCP establishes connection to server TCP
When contacted by client, server TCP creates new socket for server process to communicate with client allows server to talk
with multiple clients source port numbers
used to distinguish clients
TCP provides reliable, in-order transfer of bytes (“pipe”) between client and server
application viewpoint
TransportLayer
Used to address processes on a host 0-1024 is usually reserved for known service
Ports
FTP Server
Web Server
21 80
NetworkLayer
DLL/Physical
Socket Programming in C
CPSC 441 - Application Layer 7
Socket Programming - Flowsocket()
connect()
send()
recv()
close()
...
socket()
bind()
listen()
accept()
recv()
send()
close()
wait for connection request from next client
Client Server
int s_listen = socket(family, type, protocol); family: AF_INET specifies Ipv4 type: SOCK_STREAM, SOCK_DGRAM protocol: 0 (pseudo, IP ). See /etc/protocols
socket()
bind(s_listen, localAdd, addLength) Server specifies which port and address it will
be listening to s_listen: our listening socket descriptor localAdd: socket address structure addLength: length of localAdd
bind()
struct sockaddr_in {u_char sin_len; // length of addressu_char sin_family; // family of addressu_short sin_port; // protocol port numstruct in_addr sin_addr; // IP Addrchar sin_zero[8]; // set to zero, used for
padding};
Address Structure
Declare address structure struct sockaddr_in sockAdd;
Set family sockAdd.sin_family = AF_INET;
Set IP address (2 ways)//specify address to listen to inet_pton(AF_INET, “127.0.0.1”, &sockAdd.sin_addr.s_addr)//listen to any local address sockAdd.sin_addr.s_addr = htonl(INADDR_ANY)
Set port sockAdd.sin_port = htons(9999);
Address Structure
int status = listen(s_listen, queuelength); status: -1 if error, 0 otherwise s_listen: socket descriptor queuelength: Number of clients that can “wait” for a
connection listen is non-blocking: returns immediately
listen()
int s_new = accept(s_listen, &clientAddress, &addLength); s_new: new socket for communication with client s_listen: the listening socket clientAddress: struct sockaddr, address of client addLength: size of client address structure accept is blocking: waits for connection before returning
accept()
int send(int s_new, const void *buf, int len, int flags);
• s_new – socket descriptor• buf – pointer to buffer• len – size of buffer• flags – can be safely set to 0
int recv(int s_new, void *buf, int len, unsigned int flags);
• similar to send• buf holds the data to be transferred
Talking
fork() is a C system call used to spawn child processes Execution for both child and parent process
continues at the next instruction fork() returns
• 0 if this is the child process• PID (>0) of the child process if this is the parent• <0 if fork() fails
Used to keep listening on socket and talking on another socket
System calls - fork()
Socket Programming in Java
CPSC 441 - Application Layer 17
CPSC 441 - Application Layer 18ou
tToS
erve
r
to network from network
inFr
omS
erve
r
inFr
omU
ser
keyboard monitor
Process
clientSocket
inputstream
inputstream
outputstream
TCPsocket
Clientprocess
client TCP socket
Stream jargon A stream is a sequence
of characters that flow into or out of a process.
An input stream is attached to some input source for the process, e.g., keyboard or socket.
An output stream is attached to an output source, e.g., monitor or socket.
CPSC 441 - Application Layer 19
Example: Java client (TCP)import java.io.*; import java.net.*; class TCPClient {
public static void main(String argv[]) throws Exception { String sentence; String modifiedSentence;
BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in));
Socket clientSocket = new Socket("hostname", 6789);
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
Createinput stream
Create client socket,
connect to serverCreate
output streamattached to socket
CPSC 441 - Application Layer 20
Example: Java client (TCP), cont.
BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
sentence = inFromUser.readLine();
outToServer.writeBytes(sentence + '\n');
modifiedSentence = inFromServer.readLine();
System.out.println("FROM SERVER: " + modifiedSentence);
clientSocket.close(); } }
Createinput stream
attached to socket
Send lineto server
Read linefrom server
CPSC 441 - Application Layer 21
Example: Java server (TCP)import java.io.*; import java.net.*;
class TCPServer {
public static void main(String argv[]) throws Exception { String clientSentence; String capitalizedSentence;
ServerSocket welcomeSocket = new ServerSocket(6789); while(true) { Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
Createwelcoming socket
at port 6789Wait, on welcoming
socket for contactby client
Create inputstream, attached
to socket
CPSC 441 - Application Layer 22
Example: Java server (TCP), cont
DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
clientSentence = inFromClient.readLine();
capitalizedSentence = clientSentence.toUpperCase() + '\n';
outToClient.writeBytes(capitalizedSentence); } } }
Read in linefrom socket
Create outputstream,
attached to socket
Write out lineto socket
End of while loop,loop back and wait foranother client connection
Demo
A simple client – server example:Echo Server
Socket Programming, Dan Rubinstein, http://www1.cs.columbia.edu/~danr/courses/6761/Fall00/intro/6761-1b-sockets.ppt
15-441 Socket Programming, www.cs.cmu.edu/afs/cs/academic/class/15441-f01/www/lectures/lecture03.ppt
Network Programming, Geoff Kuenning, www.cs.hmc.edu/~geoff/classes/hmc.cs105.200701/slides/class21_net2.ppt
Socket Programming, Abhinav Jain, www.cs.purdue.edu/homes/jain8/cs422/pso3.ppt
References