udpechoclt.c

利用UDP client向server 发送信息

/* A sample program of echo client based on UDP. */

#include <stdio.h> /* for printf() and fprintf() */
#include <sys/socket.h> /* for socket(), connect(), 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 */
//void DieWithError(char *errorMessage); /* External error handling function */

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 */
	int echoStringLen; /* Length of string to echo */
	int respStringLen; /* Length of received response */

    int j;
	char *s=argv[2];
	servIP = argv[1]; /* First arg: server IP address (dotted quad) */
	for( j=0; j< (argc - 3); j++){
     strcpy(s, argv[j+3]);}
    echoString= s;

	echoString = s; /* Second arg: string to echo */
	if ((echoStringLen = strlen(echoString)) > ECHOMAX) /* Check input length */
		//DieWithError("Echo word too long");
		printf("Echo word too long.\n");
	//if (argc == 4)
		echoServPort = atoi(argv[argc-1]); /* Use given port, if any */
//	else
	//	echoServPort = 7; /* 7 is the well-known port for the echo service */
		
     

	/* Create a datagram/UDP socket */
	if ((sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0)
		//DieWithError("socket() failed");
		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 */
	/* Send the string to the server */
	if (sendto(sock, echoString, echoStringLen, 0, (struct sockaddr *)
			&echoServAddr, sizeof(echoServAddr)) != echoStringLen)
		//DieWithError("sendto() sent a different number of bytes than expected");
		printf("sendto() sent a different number of bytes than expected.\n");
	/* Recv a response */
	fromSize = sizeof(fromAddr);
	if ((respStringLen = recvfrom(sock, echoBuffer, ECHOMAX, 0,
			(struct sockaddr *) &fromAddr, &fromSize)) != echoStringLen)
		//DieWithError("recvfrom() failed");
		printf("recvfrom() failed\n");
		
	if (echoServAddr.sin_addr.s_addr != fromAddr.sin_addr.s_addr)
	{
		fprintf(stderr,"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 arg */
	close(sock);
	exit(0);
}