Thoughts, stories and ideas.

#include <stdio.h> /* for printf() and fprintf() */
#include <sys/socket.h> /* for socket(), bind(), sendto() and recvfrom() */
#include <arpa/inet.h> /* for sockaddr_in and inet_ntoa() */
#include <string.h> /* for memset() */
#include <unistd.h> /* for close() */
#include <fcntl.h>
int main(int argc, char *argv[]) {
	if (argc != 3) {
		printf("Usage:\n%s <IP Address> <File Name>\n", argv[0]);
		return 1;
	}
	int serverSock;
	struct sockaddr_in serverAddr;
	char *fileName, buffer[100];
	if ((serverSock = socket(AF_INET, SOCK_STREAM, 0)) < 0)
		printf("socket() failed.\n");
	memset(&serverAddr, 0, sizeof(serverAddr));
	serverAddr.sin_family = AF_INET;
	serverAddr.sin_addr.s_addr = inet_addr(argv[1]);
	serverAddr.sin_port = htons(1234);
	connect(serverSock, (struct sockaddr *) &serverAddr, sizeof(serverAddr));
	printf("Connecting to server:  %s\n", argv[1]);
	send(serverSock, argv[2], strlen(argv[2]), 0);
	fileName = argv[2];
	strcat(fileName, ".bak\0");
	int file = open(fileName, O_RDWR | O_CREAT);
	int transferSize = 0, recvLen;
	while ((recvLen = recv(serverSock, buffer, 50, 0)) != 0) {
		write(file, buffer, recvLen);
		transferSize += recvLen;
	}
	close(file);
	printf("File received\n");
	printf("%d BYTES received, and stored in %s\n", transferSize, fileName);
	return 0;
}

#include <stdio.h> /* for printf() and fprintf() */
#include <sys/socket.h> /* for socket(), sendto() and recvfrom() */
#include <arpa/inet.h> /* for sockaddr_in and inet_addr() */
#include <stdlib.h> /* for atoi() and exit() */
#include <string.h> /* for memset() */
#include <unistd.h> /* for close() */
#define ECHOMAX 255 /* Longest string to echo */
int main(int argc, char *argv[]) {
	int sock; /* Socket descriptor */
	struct sockaddr_in echoServAddr; /* Echo server address */
//	struct sockaddr_in fromAddr; /* Source address of echo */
	unsigned short echoServPort; /* Echo server port */
//	unsigned int fromSize; /* In-out of address size for recvfrom() */
	char *servIP; /* IP address of server */
	char *echoString; /* String to send to echo server */
//	char echoBuffer[ECHOMAX + 1]; /* Buffer for receiving echoed string */
	size_t echoStringLen; /* Length of string to echo */
//	int respStringLen; /* Length of received response */
	if (argc < 3) { /* Test for correct number of arguments */
		printf("Usage: %s <Server IP> <Echo Word>\n", argv[0]);
		exit(1);
	}
	servIP = argv[1]; /* First arg: server IP address (dotted quad) */
	echoServPort = 56325;
	/* Create a datagram/UDP socket */
	if ((sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
		printf("socket() failed.\n");
	/* Construct the server address structure */
	memset(&echoServAddr, 0, sizeof(echoServAddr));/*Zero out structure*/
	echoServAddr.sin_family = AF_INET; /* Internet addr family */
	echoServAddr.sin_addr.s_addr = inet_addr(servIP);/*Server IP address*/
	echoServAddr.sin_port = htons(echoServPort); /* Server port */
	for (int i = 2; i < argc; i++) {
		echoString = argv[i]; /* Second arg: string to echo */
		if ((echoStringLen = strlen(echoString)) > ECHOMAX) /* Check input length */
			printf("Echo word too long.\n");
		/* Send the string to the server */
		if (sendto(sock, echoString, echoStringLen, 0, (struct sockaddr *) &echoServAddr, sizeof(echoServAddr)) != echoStringLen)
			printf("sendto() sent a different number of bytes than expected.\n");
		printf("sending data to '%s'\n", servIP);
	}
//	/* Recv a response */
//	fromSize = sizeof(fromAddr);
//	if ((respStringLen = recvfrom(sock, echoBuffer, ECHOMAX, 0, (struct sockaddr *) &fromAddr, &fromSize)) != echoStringLen)
//		printf("recvfrom() failed\n");
//
//	if (echoServAddr.sin_addr.s_addr != fromAddr.sin_addr.s_addr) {
//		printf("Error: received a packet from unknown source.\n");
//		exit(1);
//	}
//	/* null-terminate the received data */
//	echoBuffer[respStringLen] = '\0';
//	printf("Received: %s\n", echoBuffer);/*Print the echoed message*/
	close(sock);
	return 0;
}

#include <stdio.h>
#include <netdb.h>
#include <arpa/inet.h>
int main(int argc, char *argv[]) {
	struct hostent *h;
	long addr;
	if (argc != 2) {
		printf("Usage:\n%s sample.com\nor\n%s 8.8.8.8\n", argv[0], argv[0]);
		return 1;
	}
	if (inet_addr(argv[1]) != -1) {
		addr = inet_addr(argv[1]);
		if ((h = gethostbyaddr((char *) &addr, sizeof(addr), AF_INET)) == NULL) {
			printf("gethostbyaddr error for address: %s\n", argv[1]);
			return 1;
		}
	} else {
		if ((h = gethostbyname(argv[1])) == NULL) {
			printf("gethostbyname error for name: %s\n", argv[1]);
			return 1;
		}
	}
	printf("Looking information for host: %s\n", argv[1]);
	printf("Official Name: %s\n", h->h_name);
	while ((h->h_aliases)[0])
		printf("Host aliases: %s\n", *h->h_aliases++);
	while ((h->h_addr_list)[0])
		printf("IP address: %s\n", inet_ntoa(*(struct in_addr *) *h->h_addr_list++));
	return 0;
}

#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
int main() {
	char buf[10];
	int fd1, fd2;
	if ((fd1 = open("test1", O_RDWR | O_APPEND)) == -1) {
		printf("Error in opening-1\n");
		return 1;
	}
	if ((fd2 = open("test2", O_RDONLY)) == -1) {
		printf("Error in opening-2\n");
		return 1;
	}
	while ((read(fd2, buf, 1)) != 0) {
		write(fd1, buf, 1);
	}
	close(fd1);
	close(fd2);
	return 0;
}