EECS340 Recitation 1: Very helpful to your project

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EECS340 Recitation 1 Very helpful to your
project

• Hongyu Gao

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If youre not

• Burke Fetscher, Jedidiah McClurg, Beibei Lin,
  Xitao Wen, Gopi Vajravelu, Taiyo Sogawa, Galiya
  Ibrgimova, Andrew Lee, Cary Lee, Brad Weinberger,
  Jonathan Chan, Daniel Lieberman, Xin Zhao, or
  Weixian Wen
• Email to networkingta_at_gmail.com

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If you have not

• Joined the newsgroup,
• Use your favorite email client (thunderbird,
  outlook, etc. )
• Add a newsgroup account
• Server name news.cs.northwestern.edu
• Select newsgroup cs.340

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If you have not

• Turned in homework1,

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Roadmap

• How to do socket programming?
• How to use hints from project 1?

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Socket programming
Goal learn how to build client/server
application that communicate using sockets

• Socket API
• introduced in BSD4.1 UNIX, 1981
• explicitly created, used, released by apps
• client/server paradigm
• two types of transport service via socket API
• unreliable datagram
• reliable, byte stream-oriented

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Socket programming
Goal learn how to build client/server
application that communicate using sockets

• Socket API
• introduced in BSD4.1 UNIX, 1981
• explicitly created, used, released by apps
• client/server paradigm
• two types of transport service via socket API
• unreliable datagram
• reliable, byte stream-oriented

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source
message
application transport network link physical
segment
datagram
frame
switch
destination
application transport network link physical
router
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source
application
sockets
Something (that I cont care) in between
destination
application
sockets
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Socket programming

• Server always listens (waits)
• To some socket (port) that welcomes clients
  contact
• Usually 80, 8000, 8080 for HTTP server
• Its always a client that initiates contact
• Contact the socket (port) that the server is
  listening on

• Server side (When contacted by client)
• Accept the connection (automatically create a new
  socket)
• Communicate with client through the new socket
  (different than the socket that its listening on)

• Client side
• Create client-local TCP socket
• specify IP address, port number of server process
• Establish connection to server

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Server high level view
Corresponding functions (parameters
omitted) socket(SOCK_STREAM) bind() listen()
//block accept() recv(), send() close()
Create a socket
Bind the socket with port
Listen for connections
Accept new client connections
Read/write to client connections
Shutdown connection
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Client high level view
Corresponding functions (parameters
omitted) socket(SOCK_STREAM) connect() send()
recv() close()
Create a socket
Connect to server
Send HTTP request
Receive HTTP response
Shutdown connection
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A piece of real code (client or server?)

• int connect_ socket( char hostname, int port)
• int sock
• struct sockaddr_in sin
• struct hostent host
• sock socket( AF_ INET, SOCK_ STREAM, 0)
• if (sock -1)
• return sock
• host gethostbyname( hostname)
• if (host NULL)
• close( sock)
• return -1
• memset ( sin, 0, sizeof( sin))
• sin. sin_ family AF_ INET
• sin. sin_ port htons( port)
• sin. sin_ addr. s_ addr ( unsigned long )
  host-gt h_ addr_ list 0
• if (connect( sock, (struct sockaddr ) sin,
  sizeof( sin)) ! 0)
• close (sock)
• return -1

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Another piece of real code
int make_ listen_ socket( int port) struct
sockaddr_ in sin int sock sock socket( AF_
INET, SOCK_ STREAM, 0) if (sock lt 0) return
-1 memset( sin, 0, sizeof( sin)) sin. sin_
family AF_ INET sin. sin_ addr. s_ addr
htonl( INADDR_ ANY) sin. sin_ port htons(
port) if (bind( sock, (struct sockaddr ) sin,
sizeof( sin)) lt 0) return -1 return sock
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Client-server interaction
TCP Server
socket()
bind()
Well-known port
TCP Client
listen()
Socket()
accept()
blocks until connection from client
connect()
Connection establishment
Data(request)
write()
read()
process request
Data(reply)
write()
read()
close()
End-of-file notification
read()
close()
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Standard socket vs Minet
Standard function call Minet function call
socket() minet_socket()
bind() minet_bind()
listen() minet_listen()
accept() minet_accept()
recv() minet_read()
send() minet_write()
close() minet_close()
connect() minet_connect()
select() minet_select()
man every function to get help on how to use it
exactly!
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Dealing with blocking calls

• Many functions block
• accept(), connect(), recvfrom()
• Consider the following case
• The server accepts a client, and blocks on
  receiving the HTTP request
• Another client tries to initiate a connection

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How to handle multiple connections

• Create multi-process or multi-threaded code
• Not covered
• I/O multiplexing using polling
• Not covered
• I/O multiplexing using select ()

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I/O Multiplexing Select (1)

• select()
• Wait on multiple file descriptors/sockets and
  timeout
• Return when any file descriptor
• is ready to be read or written, or
• Indicate an error, or
• timeout exceeded
• How to solve the blocking problem?
• select() among the listening socket and all the
  opened connection

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I/O Multiplexing Select (2)

• int select(int nfds, fd_set readfds, fd_set
  writefds, fd_set exceptfds, struct timeval
  timeout)
• Use FD_CLR(), FD_ISSET(), FD_SET(), and FD_ZERO()
  to manipulate the file descriptor lists
• man select and get all the help that is needed

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Roadmap

• How to do socket programming?
• How to use hints from project 1?

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Read comments in the file

• In client.cc, from line 53
• / create socket /
• // Do DNS lookup
• / Hint use gethostbyname() /
• / set address /
• / connect socket /
• / send request /

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See the behavior of correct implementations

• /home/hga202/EECS340/netclass-execs/http_client
• /home/hga202/EECS340/netclass-execs/http_server1
• /home/hga202/EECS340/netclass-execs/http_server2
• /home/hga202/EECS340/netclass-execs/http_server3