Linjun Ouyang
8963381321

What you have done in the assignment:
Simulate the social network recommendation (distributed) system
where clients take (country, userId) as input, which is sent to main server via TCP.
Main server can support multiple clients.
Main server decides whether [country] exists, and forward query to corresponding backend server via UDP.
Backend server generates recommendation based on common neighbors, and reply to main server by UDP.
Main server forwards the reply to client, and client displays the result.
Repeat this process until ctrl+c is pressed.

Files:
client: 
1. take user input (country, id), send query to main server by TCP, 
2. receive reply from main server and display reply
main server:
1. ask backend servers for (country, server) mapping.
2. listen to client queries by TCP, check whether country exists.
3. Forward query to backend servers by UDP, and receive result from backend
serverA, serverB:
1. process data files consisting of countries and users, represent it as graph (using adjacency list)
2. listen to queries from main server, generates recommendation based on common neighbors,
and reply back to main server through UDP
makefile:
commands to compile, run, and clean.

message format:
------
Backend server A/B
Booting up (Only while starting):
The server A/B is up and running using UDP on port <server A/B port number>

Sending the country list that contains in “data1/2.txt” to Main Server:
The server A/B has sent a country list to Main Server

For friends searching, upon receiving the input query: 
The server A/B has received request for finding possiblefriends of User <user ID> in <Country Name>

If we could not find this user ID in this country, send “not found” back to Main Server: 
User <user ID> does not show up in <Country Name>
The server A/B has sent “User <user ID> not found” to Main Server

If we find this user ID in this country, searching possible friends for this user and send result(s) back to Main Server:
The server A/B is searching possible friends for User <userID> ...
Here are the results: User<user ID1>, User<user ID2>...
The server A/B has sent the result(s) to Main Server
------
Main server:
Booting up(only while starting): 
The Main server is up and running.

Upon receiving the country list from server A/B: 
The Main server has received the country list from server A/B using UDP over port <Main server UDP port number>

List the results of which country serverA/serverB is responsible for: 
Server A
<Country Name 1>
<Country Name 2>

Server B
<Country Name 1>
<Country Name 2>

Upon receiving the input from the client: 
The Main server has received the request on User <userID> in <Country Name> from client<client ID> using TCP over port <Main server TCP port number>

If the input country name could not be found, send the error message to the client: 
<Country Name> does not show up in server A&B
The Main Server has sent “Country Name: Not found” to the client using TCP over port <Main server TCP portnumber>

If the input country name could be <Country Name> shows up in server A/B found, decide which server contains related information 
about the input userID and send a request to serverA/B:
<Country Name> shows up in server A/B
The Main Server has sent request from User <user ID> to server A/B using UDP over port <Main server UDP port number>

If we could find this user ID in the graph, 
the Main Server will receive the searching results from serverA/B and send them to client1/2:
The Main server has received searching result of User <userID> from server<A/B>
The Main Server has sent searching result(s) to client using TCP over port <Main Server TCP port number>

If we could not find this user ID in the graph, send the error message back to client:
The Main server has received “User ID: Not found” from server <A/B>
The Main Server has sent error to client using TCP over <Main Server UDP port number>
------
Client
Booting up(only while starting):
The client is up and running

asking for input:
Please enter the User ID:
Please enter the Country Name:

After sending User ID to Main Server:
The client has sent User<user ID> and <Country Name> to Main Server using TCP

If input country not found:
<Country Name> not found

If input User ID not found:
User<user ID> not found

If input User ID and country can be found:
The client has received results from Main Server:
User<user ID1>, User<user ID2> is/are possible friend(s)of User<user ID> in <Country Name>
------

idiosyncrasy: none

Reused code:
https://beej.us/guide/bgnet/html/
code in Client-Server Background:
A Simple Stream Server
A Simple Stream Client
Datagram Sockets