ccxxd.c

/* This challenge is to build your own version of xxd. Xxd is a Unix command line tool to create hexdumps and to convert a hexdump back into it’s binary form.

ccxxd files.tar
pass a file to the utility. we gotta open this file in read mode and start reading. 
 
*/
#include <unistd.h> // for getopts
#include <stdio.h>
#include <ctype.h> // for isprint function
#include <stdlib.h> // atoi

FILE *open_file_ro_mode(const char *filename);
void print_hex(unsigned char *buffer, size_t num_read, unsigned char col_size, unsigned char group_size);
void print_ascii(unsigned char *buffer, size_t num_read);
void hex_dump_loop(FILE *file, unsigned char col_size, unsigned char group_size, int len_octets);

int main(int argc, char **argv) {
	int opt;
	int col_size = 16;
	int group_size = 16;
	// default size for dumping the whole file
	int len_octets = 0;
	
	while ((opt = getopt(argc, argv, "c:g:l:")) != -1) {
		switch (opt) {
		case 'c':
			col_size = atoi(optarg);
			if (col_size < 1 || col_size > 30) {
				printf("Warning: column size should be between 1 and 30. Using default column size 16.\n");
				col_size = 16;
			}
			break;
		case 'g':
			group_size = atoi(optarg);
			if (group_size < 1 || group_size > 30) {
				printf("Warning: group size should be between 1 and 30. Using default group size 16.\n");
				group_size = 16;
			}
			break;
		case 'l':
			len_octets = atoi(optarg);
			if (len_octets < 1) {
				printf("Warning: length should be a positive number. Using default size of infinite.\n");
				len_octets = 0;
			}
			break;
		case '?':
			printf("Unknown option: %c\n", optopt);
			break;
		}
	}

	if (optind >= argc) {
		printf("Please provide a filename to the hexdump utility as an argument.\n");
		return 1;
	}

	printf("Hex dumping the file: %s...\n", argv[optind]);
	FILE *fp = open_file_ro_mode(argv[optind]);
	hex_dump_loop(fp, col_size, group_size, len_octets);
	fclose(fp);
	return 0;
}

FILE *open_file_ro_mode(const char *filename) {
	FILE *file_to_dump = fopen(filename, "rb");
	if (file_to_dump == NULL) {
		printf("Error opening the file: %s\n", filename);
		return NULL;
	}
	return file_to_dump;
}

void print_hex(unsigned char *buffer, size_t num_read, unsigned char col_size, unsigned char group_size) {
	for (size_t i = 0; i < col_size; i++) {
		if (i < num_read) {
			printf("%02x", buffer[i]);
			if ((i+1) % group_size == 0) {
				printf(" ");
			}
		}
		else {
			if (i % group_size == group_size - 1) {
				printf("  ");
			} else {
				printf("   ");
			}
		}
	}
	printf(" ");
}

void print_ascii(unsigned char *buffer, size_t num_read) {
	for (size_t i = 0; i < num_read; i++) {
		if (isprint(buffer[i])) {
			printf("%c", buffer[i]);
		}
		else {
			printf(".");
		}
	}
	printf("\n");
}

void hex_dump_loop(FILE *file, unsigned char col_size, unsigned char group_size, int len_octets) {
	unsigned char buffer[col_size];
	size_t total_read = 0;

	while (!feof(file) && !ferror(file)) {
		size_t bytes_to_read = col_size;
		if (len_octets > 0 && total_read + bytes_to_read > len_octets) {
			bytes_to_read = len_octets - total_read;
		}
		
		size_t num_read = fread(buffer, sizeof(*buffer), bytes_to_read, file);
		total_read += num_read;
		printf("%08zx: ", total_read - num_read);

		print_hex(buffer, num_read, col_size, group_size);
		print_ascii(buffer, num_read);
		
		if (len_octets > 0 && total_read >= len_octets) {
            break;
        }
	}
}