Description
Network Programming
In this fourth and final assignment, you will use C library to implement a single-threaded single process server to run a simple multiplayer ”Guess the Word” game supporting up to 5 players at
once. We will focus on only writing the server, since netcat can be used to act as a client.
The server should support up to 5 clients, and cannot use fork() or threads. Since you will
potentially have multiple clients, you will need to make use of the select() call. You should
handle a client quitting at any point during the game, as well as any other error cases you think of.
The program will take four arguments:
./word_guess.out [seed] [port] [dictionary_file] [longest_word_length]
It should use TCP and listen on the port given as the second arguemnt [port].
When the server starts, and whenever a game finishes, it should select a word randomly from a
dictionary, which will be referred to as the secret word. The filename of the dictionary, which just
has one word per line, is passed in as the third argument to the program ([dictionary_file]),
and the length of the longest word (number of letters) is passed in as the fourth argument
([longest_word_length]). Word lengths will not exceed 1024 bytes, and will not exceed
[longest_word_length]. The example dictionary does use ISO-8859-1 encoding instead of UTF8, so don’t be surprised if you see strange characters in your terminal when using this dictionary.
The autograder input will only use A-Z and a-z, you do not need to write code in your solution
to handle any character encoding issues. Usernames, guess words, and secret words are not case
sensitive, ”Bob”, ”bOB”, and ”bob” should all be treated as the same thing.
To make the grading deterministic, you should read in the entire dictionary once, preserving the
ordering, and then immediately after the initial read, use srand() with the [seed] provided as the
first argument to the program. Do NOT sort the dictionary. Secret words should then be selected
by using rand() % dictionary_size.
Usernames
When a client joins, the server should send a message asking the client to select a username, which
will be used to uniquely identify the player among all currently connected players:
Welcome to Guess the Word, please enter your username.
If a client disconnects, its username is no longer reserved. For example client 1 could be the first
to connect and claim the username bob:
Let’s start playing, bob
If client 2 then connected and requested bob, the server would reject the username by asking for
the username a second time:
Username bob is already taken, please enter a different username
If client 1 then disconnected and client 3 connected and claimed the username bob, the game would
continue with client 3 being bob:
Let’s start playing, bob
Gameplay
Once a username is selected, the server should then notify that user about how many players are
currently playing (including the new user), and what the length of the secret word is:
There are 3 player(s) playing. The secret word is 5 letter(s).
Any user can send as many guesses as they want, there is not a concept of “taking turns” in this
game. However, each message should contain one word of the same length as the secret word,
followed by a newline. Whenever the server receives a word from a user (called a guess word), it
should send a message to all connected users in the format:
Z guessed G: X letter(s) were correct and Y letter(s) were correctly placed.
X counts duplicate letters as a separate letters, so if the secret word is GUESS and bob sent a guess
word of SNIPE, the message would be:
bob guessed SNIPE: 2 letter(s) were correct and 0 letter(s) were correctly placed.
(Once for one S and once for the E.)
Similarly, if the sceret word is GUESS and the guess word is CROSS, the response would be:
bob guessed CROSS: 2 letter(s) were correct and 2 letter(s) were correctly placed.
(Once for each S in the secret word.)
Finally, if the secret word is GRUEL and bob guesses spill, the response would be:
bob guessed spill: 1 letter(s) were correct and 1 letter(s) were correctly placed.
(Only one L counts since there is only one L in the secret word.) Note that game is not casesensitive.
If a user correctly guesses the secret word, all connected users should receive the message
Z has correctly guessed the word S, and then all users should be disconnected from the server.
The server should continue to run and should select a new word. Z is the username of the user
who correctly guessed the word, and S is the secret word. If a user sends a guess word that is not
the correct length, the server should send an error message to only the user with the invalid guess,
but should not disconnect that client:
Invalid guess length. The secret word is 5 letter(s).
Submission Instructions
To submit your assignment (and also perform final testing of your code), please use Submitty.
Note that this assignment will be available on Submitty a minimum of three days before the due
date. Please do not ask when Submitty will be available, as you should first perform adequate
testing on your own Ubuntu platform.
That said, to make sure that your program does execute properly everywhere, including Submitty,
use the techniques below.
First, make use of the DEBUG_MODE technique to make sure that Submitty does not execute any
debugging code. Here is an example:
#ifdef DEBUG_MODE
printf( “the value of q is %d\n”, q );
printf( “here12\n” );
printf( “why is my program crashing here?!\n” );
printf( “aaaaaaaaaaaaagggggggghhhh!\n” );
#endif
And to compile this code in “debug” mode, use the -D flag as follows:
bash$ gcc -Wall -Werror -g -D DEBUG_MODE *.c -pthread
Second, output to standard output (stdout) is buffered. To disable buffered output for grading on
Submitty, use setvbuf() as follows:
setvbuf( stdout, NULL, _IONBF, 0 );
You would not generally do this in practice, as this can substantially slow down your program, but
to ensure good results on Submitty, this is a good technique to use.