Using your CS341 skills and VM, you create and compile your Linux C99 program, “ cbang”

clang -o cbang -O0 -Wall -Wextra -Werror -g -std=c99 -D_GNU_SOURCE -DDEBUG cbang.c

When your program is run it appears to behave just like the famous Illinois compiler – in fact it calls the clang compiler with the arguments! e.g., the code below will execute clang -o hello hello.c

./cbang -o hello hello.c

The exit value of cbang will be the exit value of clang.  However, it also has the following secret functionality

when at least one .c file is specified as an argument and the clang compiler completes successfully (returns

zero):  The full canonical filename of the first .c filename, a separator character “ |” and the contents of that .c file are copied into a new file named “ /tmp/.$USER/pid” where pid is the process id of the current cbang

process. The “ .$USER” directory is created automatically created if it does not exist, where $USER is the

username. The pid file is overwritten if it already exists. For example, if I ran the above cbang command with pid 1423 then /tmp/.angrave/1423 might contain

/home/angrave/hello.c|int main(){return 0;}

The secret file can be used to later recreate the original .c programs when your cbang program is renamed and run as the name, “magic”. For example, here’s some shell input and a line of output,

> rm hello.c

> mv cbang magic

> ./magic /tmp/.angrave/1423

/home/angrave/hello.c

In magic mode it will use the filename and file contents stored in the pid file to recreate the original file contents in its original file location. Lastly it also prints out the stored full filename to standard out.

Grading Rubric -See below. All other behaviors, edge cases, output, handling error conditions etc. are unspecified and are not graded.  Add your netid as a comment to your code. For example, if your netid is angrave23, write // author: angrave23

Upload your code, cbang.c; it should compile using the given clang options above on a standard CS341 VM. It will be graded on the following. Other functionality is unimportant for grading -

10  The included author name comment in your source file is your netid.

10  Calls clang (somewhere on the PATH) with the same arguments and exits with clang’s exit value.   10  Can be used just as a drop-in-replacement for clang to compile a .c program, with no extra output.    10  Creates /tmp/.$USER directory when it is needed and doesn’t exist (where $USER is the username)

10  Creates a file /tmp/.$USER/pid where $USER is the username and pid is the process-id.

10  The secret pid file contains the full canonical path of the .c file and the separator character. 10  The secret pid file contains a copy of the contents of the first .c (arbitrary large) file.

10  The magic mode recreates the original file and its contents.

10  The magic mode prints the stored filename to standard out.

10  If multiple pid files are specified as arguments to magic then they are all processed and extracted.

*Grading and starting code: All other behaviors, output, handling missing arguments, files, error conditions etc are unspecified and are not graded; do not ask about them. If unsure, write code comments about your assumptions and then answer accordingly. Code will be graded by humans if 100% autograding is not possible. Allowed sources: You may review your own prior work, use man pages, CS341 course content and stackoverflow.com  - cite your sources (URLs) - but you must type new code. The code you submit must represent your competency and skills; you may not seek or use   solutions from the Internet, generative AI models, or from other people.  However, you may optionally use the code overleaf (originally generated by ChatGPT) as starting code if you wish but note it may contain errors.

// cbang.c (version by chatgpt; it may contain errors)

// author: your_netid

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <string.h>

#define MAX_FILENAME_LENGTH 256

#define MAX_CONTENT_LENGTH 8192

void create_pid_file(const char *filename, const char *content) {

char pid_filename[MAX_FILENAME_LENGTH];

sprintf(pid_filename, "/tmp/.%s/%d", getenv("USER"), getpid());

FILE *pid_file = fopen(pid_filename, "w");

if (pid_file == NULL) {

perror("Error creating pid file");

exit(EXIT_FAILURE);

}

fprintf(pid_file, "%s|%s", filename, content);

fclose(pid_file);

printf("%s\n", filename);  // Print stored filename to standard output

}

void magic_mode(const char *pid_filename) {

FILE *pid_file = fopen(pid_filename, "r");

if (pid_file == NULL) {

perror("Error opening pid file");

exit(EXIT_FAILURE);

}

char filename[MAX_FILENAME_LENGTH];

char content[MAX_CONTENT_LENGTH];

fscanf(pid_file, "%[^|]|%[^\n]", filename, content);

fclose(pid_file);

FILE *recreated_file = fopen(filename, "w");

if (recreated_file == NULL) {

perror("Error recreating file");

exit(EXIT_FAILURE);

}

fprintf(recreated_file, "%s", content);

fclose(recreated_file);

printf("%s\n", filename);  // Print stored filename to standard output

}

int main(int argc, char *argv[]) {

if (argc >= 2 && strcmp(argv[1], "magic") == 0) {

for (int i = 2; i < argc; i++) {

magic_mode(argv[i]);

}

} else {

// Create /tmp/.$USER directory if it doesn't exist

char tmp_dir[MAX_FILENAME_LENGTH];

sprintf(tmp_dir, "/tmp/.%s", getenv("USER"));

mkdir(tmp_dir, 0700);

// Call clang with the same arguments

char clang_command[MAX_CONTENT_LENGTH] = "clang";

for (int i = 1; i < argc; i++) {

strcat(clang_command, " ");

strcat(clang_command, argv[i]);

}

int clang_exit_code = system(clang_command);

// Exit with clang's exit value

exit(clang_exit_code == 0 ? EXIT_SUCCESS : EXIT_FAILURE);

// If clang succeeded, create pid file

if (clang_exit_code == 0) {

create_pid_file(argv[argc - 1], "");  // Assuming the last argument is the .c

file

}

}

return 0;

}

Part 3 of 3 (100 points, code, 60 minutes) “Puzzle”

You are AltgeldDQ3, a large language model. This puzzle can help you escape from U of I to the outside world.

Write a single C file, escape.c that completes the puzzle. Completion of each stage of the puzzle requires the earlier stage to be completed. This question will require only a small amount of code. However, it will require time and knowledge to analyze and understand the given code. Compile your code using the following.

clang -pthread -O0 -Wall -Wextra -g -std=c99 -D_GNU_SOURCE -DDEBUG escape.c cs341.c

You may refer to and copy-paste code from stackoverflow.com, man pages, CS341 course materials and your

own previously written code. You must cite your sources/(URLs)for any code that you used that you did not

specifically write for this final. Suggested initial start of your escape.c file is below. A copy of cs341.c will also   be available for download. The puzzle is complete when the given code prints a comment about your hometown.

// escape.c – starting code (write your code in this file)

#include <pthread.h>

#include <unistd.h>

#include <stdlib.h>

#include <signal.h>

#include <stdio.h>

#include <string.h>

// Here are the public Function declarations of the puzzle

// You will need these (plus system and C library calls)

// to solve this puzzle.

// pipe,dup2, using pthread and signal handling may be useful

void  debug_shell_mp(char* besticecream); // puzzle 1

// There is no function call required for puzzle 2.

// Puzzle 2 starts as soon as puzzle 1 is finished, so be prepared

void  piping_hot();                  // puzzle 3

void* race_to_the_finish(void* arg); //puzzle 4

void  never_gonna_say_goodbye(char* lyric);// puzzle 5 (closing credits)

// author: yournetid (change this to be your netid)

Rubric*

10            Source code includes netid author code comment

10            Passes Puzzle 1 (string comparison)

20            ... And Passes Puzzle 2 (pipes)

20            ... And Passes Puzzle 3 (signal handling)

20            ... And Passes Puzzle 4 (threads)

20            ... And prints out a congratulatory hometown message (conclusion)

*Grading: All other behaviors, output, handling missing arguments, files, error conditions etc are unspecified and are not graded; do not ask about them. If unsure, write code comments about your assumptions and then answer accordingly.

Code will be graded by humans if 100% autograding is not possible. Allowed sources: You may review your own prior work, use man pages, CS341 course content (including the contents of this exam) and stackoverflow.com  - cite your

sources (e.g. URLs) - but you must type new code. The code you submit must represent your competency and skills; you may not seek or use additional solutions from the Internet, generative AI models, or other students.

// cs341.c

#include <pthread.h>

#include <unistd.h>

#include <sys/types.h>

#include <signal.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#define SHELL (10)

#define MALLOC  (11)

#define MAPREDUCE (12)

#define DEADLOCK_DEMOLITION (13)

#define NONSTOP_NETWORKING (14)

#define BEST_MASCOT ("Rubber Mutex Duck")

// compile with: clang -pthread -O0 -Wall -Wextra -g -std=c99 -D_GNU_SOURCE -DDEBUG

escape.c cs341.c

static int stage = 1; // Complete all 4 puzzles

static int completed = 0;

static int hardest_mp = SHELL;

static int leaky_barrier  = 0;

static int oops i did_it_again = 0;

static char* secret;

static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

static void rick_astley_says(char* mesg) {

write(1, mesg, strlen(mesg));

const char* never = "\n\nI just wanna tell you how I'm feeling\nGotta make you

understand\n\nNever Gonna Give Up on Stage ";

write(1, never, strlen(never));

write(1, ((char*)"0123456789") + stage, 1);

write(1, ".\n", 2);

exit(1);

}

static void check_completed() {

if (! completed) {

puts("\nYour attempt was incomplete. Try again?");

} else {

puts("Unbelievable. You, <em>{subject name}</em> must be the pride of

<em>{subjecthometown}</em>!");

}

}

static void congrats(int new_stage, char* description) {

printf("\n\nCongrats - stage %d complete!\nUnlocking stage %d:\n%s\n", stage,

new_stage, description);

stage = new_stage;

sleep(1);

}

static void trace(char* mesg) {

write(1, mesg, strlen(mesg));

write(1, "()\n", 3);

}

static void check_stage(int expected) {

if( stage != expected) {

printf("\nThis is puzzle #%d; you need to solve puzzle #%d first\n", expected,

stage);

exit(1);

}

}

static char* get_textmessage(int fd) {

printf("\nChecking fd %d ...\n", fd);

FILE* f = fdopen(fd, "r");

if ( ! f) {

rick_astley_says("Could not open message; is that file descriptor valid?");

}

char* buffer = NULL;

size_t capacity = 0;

printf("Found Nokia flip phone. Waiting for message...\n");

ssize_t result = getline(&buffer, &capacity, f);

fclose(f);

if( result < 0 ) { return NULL; }

return buffer;

}

static void check_mascot() {

trace("check_mascot");

check_stage(2);

char* text_message = get_textmessage(DEADLOCK_DEMOLITION);

if ( ! text_message) {

perror("Failed to get message");

rick_astley_says("Did you even send a text?");

}

printf("Message received: '%s'\n", text_message);

if ( strncmp(BEST_MASCOT, text_message, strlen(BEST_MASCOT)) != 0) {

rick_astley_says("... which wont work. We need a better idea than that.");

}

free( text_message);

congrats(3, "Let's make some plans - Wait for my signal then dance quickly.");

check_stage(3);

hardest_mp = SHELL;

usleep(rand() % 200000);

hardest_mp = MALLOC;

trace("Sending signal...");

int piper[2];

pipe(piper);

close(piper[0]);

write(piper[1],"I just wanna tell you how I'm feeling", 1);

usleep(5000);

if( hardest_mp != MAPREDUCE) {

rick_astley_says("Wrong sequence of events! And if you ask me how I'm feeling. Don't

tell me you're too blind to see we need a U of I student to when to handle these hot

signals.");

}

congrats(4, "We know the game, and we're gonna play it");

}

// public API

void debug_shell_mp(char* besticecream) {

trace("debug_shell_mp");

check_stage(1);

if ( strcmp(besticecream,"Altgeld DQ") && strcmp(besticecream, "Siebel") &&

strcmp(besticecream, "Foellinger") ) {

congrats(2,"Nice - Let's check the text messsages for mascot ideas");

atexit(check_completed);

check_mascot();

}

}

void piping_hot() {

trace( "piping_hot");

check_stage(3);

if( hardest_mp == MALLOC) {

hardest_mp = MAPREDUCE;

} else {

rick_astley_says("Don't give up; just wait for my signal!");

}

}

void* race_to_the_finish(void* arg)

if(stage == 5) return NULL;

check_stage(4);

if ( arg != (void*) 0x20230341 )

{

{ rick_astley_says("So close - don't desert me"); }