cctar.c

/* 
https://codingchallenges.substack.com/p/coding-challenge-54-tar

In this coding challenge I will implement some of the functionalities of Unix tar command.

First will be to implement the -t option. Which from the man pages does the following: List archive contents to stdout.  The long option form is --list.

*/
#include <unistd.h> // for getopt
#include <stdio.h> // for FILE
#include <stdlib.h> // for atoi
#include <math.h> // for pow in conversion from octal to decimal

void parse_tarball(FILE *file);
void list_filesizes(FILE *file);
void list_filenames(FILE *file);
int octal_to_decimal(int octal);

int main(int argc, char **argv) {
	int tflag = 0;
	int sflag = 0;
	int opt;
	FILE *tarballf = NULL;
	opterr = 0;

	while ((opt = getopt(argc, argv, "stf:")) != -1) {
		switch(opt) {
			case 't':
				tflag = 1;
				break;
			case 's':
				sflag = 1;
				break;
			case 'f':
				tarballf = fopen(optarg, "rb");
				if (tarballf == NULL) {
					perror("Error opening file");
					return 1;
				}
				break;
			case '?':
				if (optopt == 'f') {
					printf("%s: Option -%c requires an argument.\n",argv[0], optopt);
					return 1;
				}
				printf("Unknown option: %c\n", optopt);
				break;
		}
	}

	if (tarballf == NULL) {
		tarballf = stdin;
	}

	if (tflag == 1) {
		//parse_tarball(tarballf);
		list_filenames(tarballf);
	}

	if (sflag == 1) {
		list_filesizes(tarballf);
	}


	// do some actions then close it
	if (tarballf != stdin) {
		fclose(tarballf);
	}
}

#define BUFF_SIZE 512

void parse_tarball(FILE *file) {
	char buffer[BUFF_SIZE];
	printf("%p\n", file);

	while (!feof(file) && !ferror(file)) {
		size_t bytes_read = fread(buffer, sizeof(*buffer), BUFF_SIZE, file);
		if (bytes_read > 0) {
			for (size_t i = 0; i < bytes_read; i++) {
				printf("%c", buffer[i]);
			}
		}
		else {
			break;
		}
	}
	printf("\n");
}

#define FILENAME_SIZE 100

//
void list_filenames(FILE *file) {
	char buffer[FILENAME_SIZE];

	while (!feof(file) && !ferror(file)) {
		size_t bytes_read = fread(buffer, sizeof(*buffer), BUFF_SIZE, file);
		if (bytes_read > 100) {
			for (size_t i = 0; i < 100; i++) {
				printf("%c", buffer[i]);
			}
			break;
		}
		else {
			break;
		}
	}
	printf("\n");
}

void list_filenames(FILE *file) {
	char buffer[100];
	int padded_size = 0;

	while (!feof(file) && !ferror(file)) {
		size_t bytes_read = fread(buffer, sizeof(*buffer), 100, file);
		if (bytes_read == 0) {
			// We're at the end of the file, so break the loop
			break;
		}
		buffer[100] = '\0'; // Null-terminate the buffer
		printf("%s", buffer);
		int size_octal = atoi(buffer);
		int size_decimal = octal_to_decimal(size_octal);
		padded_size = (size_decimal + 511) / 512 * 512;
		printf("Size in decimal: %d ", size_decimal);
		printf("Padded Size: %d\n", padded_size);
		fseek(file, 512 + padded_size - 11, SEEK_CUR);
	}
}

void list_filesizes(FILE *file) {
	char buffer[12];
	int padded_size = 0;
	fseek(file, 124, SEEK_CUR);

	while (!feof(file) && !ferror(file)) {
		size_t bytes_read = fread(buffer, sizeof(*buffer), 11, file);
		if (bytes_read == 0) {
			// We're at the end of the file, so break the loop
			break;
		}
		buffer[11] = '\0'; // Null-terminate the buffer
		printf("%s", buffer);
		int size_octal = atoi(buffer);
		int size_decimal = octal_to_decimal(size_octal);
		padded_size = (size_decimal + 511) / 512 * 512;
		printf("Size in decimal: %d ", size_decimal);
		printf("Padded Size: %d\n", padded_size);
		fseek(file, 512 + padded_size - 11, SEEK_CUR);
	}
}

int octal_to_decimal(int octal) {
	int decimal = 0;

	int x = 0;
	while (octal > 0)
	{

		// obtaining the right-most digit of num
		int y = octal % 10;

		// Since the right-most digits were previously scanned in the previous step, divide num by 10 to remove them.
		octal /= 10;

		decimal += y * pow(8, x);
		++x;
	}

	return decimal;
}