扯谈网络编程之自己实现ping

64 bytes from 192.168.1.1: icmp_seq=1 ttl=64 time=6.28 ms

#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <errno.h>
#include <netinet/ip.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/time.h>

unsigned short csum(unsigned short *ptr, int nbytes) {
	register long sum;
	unsigned short oddbyte;
	register short answer;

	sum = 0;
	while (nbytes > 1) {
		sum += *ptr++;
		nbytes -= 2;
	}
	if (nbytes == 1) {
		oddbyte = 0;
		*((u_char*) &oddbyte) = *(u_char*) ptr;
		sum += oddbyte;
	}

	sum = (sum >> 16) + (sum & 0xffff);
	sum = sum + (sum >> 16);
	answer = (short) ~sum;

	return (answer);
}

inline double countMs(timeval before, timeval after){
	return (after.tv_sec - before.tv_sec)*1000 + (after.tv_usec - before.tv_usec)/1000.0;
}

#pragma pack(1)
struct EchoPacket {
	u_int8_t type;
	u_int8_t code;
	u_int16_t checksum;
	u_int16_t identifier;
	u_int16_t sequence;
	timeval timestamp;
	char data[40];   //sizeof(EchoPacket) == 64
};
#pragma pack()

void ping(in_addr_t source, in_addr_t destination) {
	static int sequence = 1;
	static int pid = getpid();
	static int ipId = 0;

	char sendBuf[sizeof(iphdr) + sizeof(EchoPacket)] = { 0 };

	struct iphdr* ipHeader = (iphdr*)sendBuf;
	ipHeader->version = 4;
	ipHeader->ihl = 5;

	ipHeader->tos = 0;
	ipHeader->tot_len = htons(sizeof(sendBuf));

	ipHeader->id = htons(ipId++);
	ipHeader->frag_off = htons(0x4000);  //set Flags: don't fragment

	ipHeader->ttl = 64;
	ipHeader->protocol = IPPROTO_ICMP;
	ipHeader->check = 0;
	ipHeader->saddr = source;
	ipHeader->daddr = destination;

	ipHeader->check = csum((unsigned short*)ipHeader, ipHeader->ihl * 2);

	EchoPacket* echoRequest = (EchoPacket*)(sendBuf + sizeof(iphdr));
	echoRequest->type = 8;
	echoRequest->code = 0;
	echoRequest->checksum = 0;
	echoRequest->identifier = htons(pid);
	echoRequest->sequence = htons(sequence++);
	gettimeofday(&(echoRequest->timestamp), NULL);
	u_int16_t ccsum = csum((unsigned short*)echoRequest, sizeof(sendBuf) - sizeof(iphdr));

	echoRequest->checksum = ccsum;

	struct sockaddr_in sin;
	sin.sin_family = AF_INET;
	sin.sin_port = htons(0);
	sin.sin_addr.s_addr = destination;

	int s = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
	if (s == -1) {
		perror("socket");
		return;
	}

	//IP_HDRINCL to tell the kernel that headers are included in the packet
	if (setsockopt(s, IPPROTO_IP, IP_HDRINCL, "1",sizeof("1")) < 0) {
		perror("Error setting IP_HDRINCL");
		exit(0);
	}

	sendto(s, sendBuf, sizeof(sendBuf), 0, (struct sockaddr *) &sin, sizeof(sin));

	char responseBuf[sizeof(iphdr) + sizeof(EchoPacket)] = {0};

	struct sockaddr_in receiveAddress;
	socklen_t len = sizeof(receiveAddress);
	int reveiveSize = recvfrom(s, (void*)responseBuf, sizeof(responseBuf), 0, (struct sockaddr *) &receiveAddress, &len);

	if(reveiveSize == sizeof(responseBuf)){
		EchoPacket* echoResponse = (EchoPacket*) (responseBuf + sizeof(iphdr));
		//TODO check identifier == pid ?
		if(echoResponse->type == 0){
			struct timeval tv;
			gettimeofday(&tv, NULL);

			in_addr tempAddr;
			tempAddr.s_addr = destination;
			printf("%d bytes from %s : icmp_seq=%d ttl=%d time=%.2f ms\n",
					sizeof(EchoPacket),
					inet_ntoa(tempAddr),
					ntohs(echoResponse->sequence),
					((iphdr*)responseBuf)->ttl,
					countMs(echoResponse->timestamp, tv));
		}else{
			printf("response error, type:%d\n", echoResponse->type);
		}
	}else{
		printf("error, response size != request size.\n");
	}

	close(s);
}

int main(void) {
	in_addr_t source = inet_addr("192.168.1.100");
	in_addr_t destination = inet_addr("192.168.1.1");
	for(;;){
		ping(source, destination);
		sleep(1);
	}

	return 0;
}