Thread: magic could happen on recvfrom

here's more if you really want to:

Code:

while (checkFullSlots() ||  (!feof(stdin)))
	{
	  /*read data from stdin and fill any empty slots*/
		while (checkEmptySlots() && (!feof(stdin))){
			sigprocmask(SIG_BLOCK, &set , &oset);
			LFS++;
			Frame* frame = (Frame*) calloc(1, sizeof(Frame));
			size = fread(frame->body, 1 , 256, stdin);
			printf("size read to body is %d\n\n", size);
			fwrite(frame->body , 1 , 256 , stdout);
			/*
			if (size != 256){
				printf("Error: Can't read the frame body from stdin %d\n", (int) sizeof(frame->body));
				close(sock_fd);
				exit(1);
			}
			*/
			frame->hdr.type = TYPE_DATA;
			frame->hdr.seq = (SeqNum) LFS;
			if (size == 256)
				frame->hdr.size = 0;
			else
				frame->hdr.size = (u_char) size;

			printf("seq number %d \nsize is %d \n", (int) frame->hdr.seq, (int) size);
			if (feof(stdin)) 
				frame->hdr.flags = FLAG_END;
			
			time_t frame_timeout = time(NULL) + timeout;
			if (insertTimeoutAndFrame(frame, frame_timeout, LFS)){
				perror("Error: Failed inserting frame and timeout into window slot \n");
				exit(1);
			}

			flag = sendto(sock_fd,(void*)frame ,sizeof(Frame),0,(struct sockaddr *)&sockin, sizeof(sockin));
			if (flag == -1)
			{
				perror("Error: Sending frame failed \n");
				close(sock_fd);
				exit(1);
			}
			printf("sending frame with size %d \n", flag);
			sigprocmask(SIG_SETMASK, &oset, NULL);
		}
		
		/*read ACK from socket (recv)*/
	
		
			printf("Trying to receive ACK here!\n");
			Frame *ACK = (Frame*) malloc(sizeof(Frame));
			flag = recvfrom(sock_fd, ACK, sizeof(Frame), 0,  (struct sockaddr *) 0, (socklen_t *) 0);
			if (flag == -1)
			{
				perror("Error: Receiving ACK failed \n");
				close(sock_fd);
				exit(1);
			}
			printf("Receiving ACK for seq %d\n", ACK->hdr.seq);
			sigemptyset(&set);
			sigaddset(&set, SIGALRM);

			sigprocmask(SIG_BLOCK, &set , &oset);
			if ((int) ACK->hdr.seq > LAR){
				int i;
				do {
					printf("emptying slot!\n");
					/*empty slot containing frame LAR*/
					LAR++;
					for (i = 0; i < SWS; i++){
						if (win_slots[i].frame->hdr.seq == LAR){
							free(win_slots[i].frame);
							win_slots[i].frame = NULL;
							win_slots[i].timeout = -1;
						}
					}	
				} while (LAR != ACK->hdr.seq);
			}
			free(ACK);
			printf("ready to send as there's an empty slot available!\n");
			sigprocmask(SIG_SETMASK, &oset, NULL);
		
	}