CS476/576

Assignment #3

Due Midnight, Wednesday   Nov 23, 2011

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Write a C/UNIX/TCP-Socket programs with the following descriptions:

NAME

gserver – group server:

Creates a frontend process to manage five backend processes for serving gclient processes.

gclient - group client: get service from gserver.

SYNOPSIS

gserver <port>

gclient <host> <port> <1|0>

DESCRIPTION

The Figure below shows an overview of the gserver & gclient:

ê The gclient process:

ü Creates a client socket C to connect to the frontend at (<host> <port>)

ü Creates a server socket S at the same port of the client socket C.

ü Connects C to the frontend and sends either 1 or 0.

§ 1 indicates urgent service (it must get service)

§ 0 indiactes normal service (gets service if there is a free backend process).

ü It receives back either 1 or 0.

§ 1 a backend process will connect to it soon.

§ 0 no backend is available and should exit..

ü After a backend process connects, the gclient:

§ Reads a line from stdin , writes it to the backend process.

§ Receive the echoed line and displays it to the stdout.

§ Terminates if the user type CTRL-D or the backend process closes the connection.

ê The gserver is composed of a frontend process and 5 backend processes.

v The frontend process:

ü Creates a server socket and binds it <port>.

ü Creates five backend processes and connects to each with a pipe.

ü If it receives 0 from a gclient at ((host & port):

§ if there is a free backend process F: send 1 to the gclient & send (host & port) to F.

§ if there is no free backend process, sends 0 to the gclient.

ü If it receives 1 from a gclient

§ send 1 to the gclient

§ find a free backend process F, otherwise select a busy process F to abandon its current client.

§ send (host & port) to F.

v Each backend process:

ü Creates a client socket to connect to any gclient.

ü When it gets a signal from the frontend process it reads the gclient (host & port) from the pipe.

ü Connects to the gclient and offer its echo service (just send back any received line).

ü When the gclient closes the connection, signal the frontend process to change its status from busy to free.

See my implementation is under: /home/cs476/public_html/fall11/assignments/a3/wahab