Task 34 (2nd sol).c

// github.com/andy489

#include <stdlib.h>
#include <err.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>

void clo(const int olderrno, ssize_t fd1, ssize_t fd2, ssize_t fd3, ssize_t fd4){
	if(fd1 != -1) close(fd1);
	if(fd2 != -1) close(fd2);
	if(fd3 != -1) close(fd3);
	if(fd4 != -1) close(fd4);
	errno = olderrno;
}

int main(int argc, char **argv){
	if(argc != 5)
		errx(1, "Invalid number of arguments. Usage: %s <f1.dat> <f1.idx> <f2.dat> <f2.idx>", argv[0]);

	char *dat1 = argv[1], *idx1 = argv[2], *dat2 = argv[3], *idx2 = argv[4];

	struct stat st;
	if(stat(idx1, &st) == -1)
		err(2, "error while stat file %s", idx1);

	struct window{
   		uint16_t displacement;
		uint8_t len;
		uint8_t free;
	} __attribute__((packed)) fmt1, fmt2;
	//printf("size of struct: %lu\n", sizeof(fmt));

	if(!(st.st_mode & S_IRUSR))
		errx(3, "file %s is not readable", idx1);	
	
	if(st.st_size % sizeof(fmt1) != 0)
		errx(4, "file %s is corrupted", idx1);

	ssize_t fd1 = open(dat1, O_RDONLY);
	if(fd1 == -1)
		err(5, "error while opening file %s", dat1);
	
	ssize_t fd2 = open(idx1, O_RDONLY);
	if(fd2 == -1){
		clo(errno, fd1, -1, -1, -1);
		err(6, "error while opening file %s", idx1);
	}

	ssize_t fd3 = open(dat2, O_CREAT | O_RDWR |O_TRUNC, 0644);
	if(fd3 == -1){
		clo(errno, fd1, fd2, -1, -1);
		err(7, "error while opening file %s", dat2);
	}

	ssize_t fd4 = open(idx2, O_CREAT | O_RDWR | O_TRUNC, 0644);
	if(fd4 == -1){
		clo(errno, fd1, fd2, fd3, -1);
		err(8, "error while opening file %s", idx2);
	}

	fmt2.displacement = 0;
	fmt2.len = 0;
	fmt2.free = 0;

	ssize_t rd2 = -1, rd1 = -1;
	while((rd2 = read(fd2, &fmt1, sizeof(fmt1))) == sizeof(fmt1)){
		uint16_t d = fmt1.displacement;
		uint8_t l = fmt1.len;
		
		off_t ls = lseek(fd1, d, SEEK_SET);
		if(ls == -1){
			clo(errno, fd1, fd2, fd3, fd4);
			err(9, "error while lseek file %s", dat1);
		}
		char buf;
		uint8_t cnt = 0, flag_Capital = 0;
		while((rd1 = read(fd1, &buf, sizeof(buf))) == sizeof(buf)){
			++cnt;
			if (flag_Capital == 0){
				if(buf > 'Z' || buf < 'A') {
					break;
				} else { 
					flag_Capital = 1;
				}
			}
			ssize_t wr1 = write(fd3, &buf, sizeof(buf));
			if(wr1 == -1){
				clo(errno, fd1, fd2, fd3, fd4);
				err(10, "error while writing into file %s", dat2);
			}
			if(cnt == l) break;
		}
		if(flag_Capital){

			// constructing fmt2 for writing to d2.idx file
			fmt2.len = l;
			
			ssize_t wr2 = write(fd4, &fmt2, sizeof(fmt2));
			if(wr2 == -1){
				clo(errno, fd1, fd2, fd3, fd4);
				err(11, "error while writing into file %s", idx2);
			}
			fmt2.displacement = fmt2.displacement + l;
		}
	}
	if(rd2 == -1){
		clo(errno, fd1, fd2, fd3, fd4);
		err(12, "error while reading from file %s", dat1);
	}
	clo(0, fd1, fd2, fd3, fd4);
	exit(0);
}