I am trying to implement basic UDP multicast client and server on Linux. The server, based on a message sent by the client, is supposed to reply with system parameters (kinda like SNMP). Right now, I am testing with a single server. After running client and server on different terminals, I send a 3 character request to the server, but it appears that server is not able to proceed, and just stays suspended there, waiting for client. The codes are given here:
Client:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
#include <sys/time.h>
#include <time.h>
char* createheader(int , int , int , char , int );
#define PORT 15002
#define MAXLINE 10000
char* MULTICAST = "224.0.0.3";
char* myIP = "127.0.0.1";
// Driver code
int main(int argc, char *argv[])
{
char buffer[10000];
char message[10000];
char *msg;
int sockfd, n;
char c = '0';
int req1, req2, req3;
int ctr = 0;
int prev = 0, curr = 0;
char tp = 'Q';
int seq = 0, len;
int yes = 1;
short int resendflag = 0;
struct timeval time1, time2, tv={2,0}; // structures that can take time in seconds and micro seconds.
struct sockaddr_in servaddr;
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_addr.s_addr = inet_addr(MULTICAST);
servaddr.sin_port = htons(PORT);
servaddr.sin_family = AF_INET;
struct in_addr interface_addr;
interface_addr.s_addr = inet_addr(myIP);
// create datagram socket
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, (int*) &yes, sizeof(yes));
if (sockfd < 0) {
perror("Error: socket");
exit(1);
}
/*if(connect(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0)
{
printf("\n Error : Connect Failed \n");
exit(0);
}*/
setsockopt(sockfd,SOL_SOCKET,SO_RCVTIMEO,(char *)&tv,sizeof(struct timeval));
//u_char loop;
//setsockopt(sockfd, IPPROTO_IP, IP_MULTICAST_LOOP, &loop, sizeof(loop));
//Create Tx Header
while(1)
{
prev = seq;
seq++;
printf("\nEnter the 3 request characters, each followed by newline\n");
scanf("%d%d%d", &req1, &req2, &req3);
msg = createheader(req1, req2, req3, tp, seq);
while(c!='\0')
{
c = *(msg+ctr);
//puts(&c);
message[ctr] = c;
ctr++;
}
//printf("\nsize of %d",sizeof(c));
c = '0';
ctr = 0;
//msg = NULL;
// connect to server
// request to send datagram
// connect stores the peers IP and port
sendto(sockfd, message, sizeof(message), 0, (struct sockaddr*)&servaddr, sizeof(servaddr));
puts(message);
// waiting for response
n = recvfrom(sockfd, buffer, sizeof(buffer), 0, (struct sockaddr*)&servaddr, &len);
Portion after this is specific to my application: may be ignored unless you want to test it out.
curr = buffer[4]-'0' + (buffer[5]-'0')*256 + (buffer[6]-'0')*65536 + (buffer[7]-'0')*65536*256;
if (prev == curr || n == -1)
{
resendflag = 1;
while(resendflag)
{
printf("No Response Recieved. Resending...\n");
sendto(sockfd, message, strlen(message), 0, (struct sockaddr*)&servaddr, sizeof(servaddr));
n = recvfrom(sockfd, buffer, sizeof(buffer), 0, (struct sockaddr*)NULL, NULL);
curr = buffer[4]-'0' + (buffer[5]-'0')*256 + (buffer[6]-'0')*65536 + (buffer[7]-'0')*65536*256;
if (prev == curr || n == -1)
{
resendflag = 1;
}
else
{
resendflag = 0;
puts(buffer+12);
}
sleep(1);
}
}
else
puts(buffer+12);
//tp = 'A';
//msg = createheader(req1, req2, req3, tp, seq);
// close the descriptor
}
close(sockfd);
}
char* createheader(int req1, int req2, int req3, char tp, int seq)
{
static char msg1[1000];
int len;
//char req;
msg1[0] = 'A';
msg1[1] = tp;
msg1[3] = '0';
msg1[4] = seq%256+'0';
msg1[5] = (seq/256)%256+'0';
msg1[6] = (seq/65536)%256+'0';
msg1[7] = (seq/(65536*256))%256+'0';
msg1[8] = req1+'0';
msg1[9] = req2+'0';
msg1[10] = req3+'0';
msg1[12] = '\0';
len = strlen(msg1);
msg1[2] = len +'0';
return msg1;
}
And this is the server:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/time.h>
#include <time.h>
#define PORT 15002
#define MAXLINE 10000
char* MULTICAST = "224.0.0.3";
char* myIP = "127.0.0.2";
char* createheader(int , int , int , char , int , int);
char* sysfunc(int , int , int);
// Driver code
int main(int argc, char *argv[])
{
setbuf(stdout, NULL);
printf("lololol5"); //Just some indicators to see the progress
char buffer[10000];
char *message = "Hello Client";
char msg[10000];
char *msg1;
char tp = 'R';
int yes = 1;
int listenfd, len, l=0, seq = 0, req1, req2, req3, i, curr = 0, exc = 0;
const char* syscl= NULL;
int drop;
srand(time(NULL));
FILE* fp;
struct sockaddr_in servaddr, cliaddr;
bzero(&servaddr, sizeof(servaddr));
printf("lololol4");
// Create a UDP Socket
listenfd = socket(AF_INET, SOCK_DGRAM, 0);
if (listenfd < 0) {
perror("socket");
exit(1);
}
if (setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, (int*)&yes, sizeof(yes))<0)
{
perror("socket");
exit(1);
}
printf("lololol3");
servaddr.sin_addr.s_addr = INADDR_ANY;
servaddr.sin_port = htons(PORT);
servaddr.sin_family = AF_INET;
char *ip = inet_ntoa(servaddr.sin_addr);
printf("\nip is %s\n", ip);
// bind server address to socket descriptor
if (bind(listenfd, (struct sockaddr *) &servaddr, sizeof(servaddr)) < 0) {
perror("bind");
exit(1);
}
printf("lololol2");
struct ip_mreq mreq;
mreq.imr_multiaddr.s_addr = inet_addr(MULTICAST);
mreq.imr_interface.s_addr = inet_addr(myIP);
char *ip1 = inet_ntoa(mreq.imr_multiaddr);
printf("\nmulip is %s\n", ip1);
if (setsockopt(listenfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*) &mreq, sizeof(mreq)) < 0)
{
perror("setsockopt");
return 1;
}
while(1)
{
//receive the datagram
len = sizeof(cliaddr);
int n = recvfrom(listenfd, (char*) buffer, sizeof(buffer), 0, (struct sockaddr*)&cliaddr, &len); //receive message from client
As before, application specific portion.
printf("\nHi\n");
puts(buffer); //display message
printf("\n");
curr = buffer[4]-'0' + (buffer[5]-'0')*256 + (buffer[6]-'0')*65536 + (buffer[7]-'0')*65536*256;//acquire client seq. no
req1 = buffer[8]; req2 = buffer[9]; req3 = buffer[10];//extract request bytes
syscl = sysfunc(req1-48, req2-48, req3-48); //Function call to get system corresponding system command string
l = 12; //After 12 bytes of header
puts(syscl);
if (strcmp(syscl, "\nInvalid Command...\n\0"))
{
system(syscl); //The system call with the string gotten
fp = fopen("sysstat.txt","r"); //Open the file where system output is written
while(!feof(fp))
{
msg[l] = fgetc(fp); //write file into an array
l++;
}
fclose(fp);
msg[l] = '\0'; //Append string with end of text char
}
else
{
char c1 = '0';
while(c1 != '\0')
{
c1 = *(syscl+l-12); //write file into an array
//printf("\n %c", msg[l]);
msg[l] = c1;
l++;
}
}
msg1 = createheader(req1, req2, req3, tp, curr, l); //Create Header
for (i=0; i<12; i++)
{
msg[i] = *(msg1+i);
}
drop = rand()%10+1; //to simulate dropped packets
if (drop > 2) //Drop with a given prob (i.e (x-1)/10)
{
sendto(listenfd, &msg, MAXLINE, 0,(struct sockaddr*)&cliaddr, sizeof(cliaddr));
puts(msg);
}
l = 0;
}
}
char* createheader(int req1, int req2, int req3, char tp, int seq, int len) //header
{
static char msg1[10000];
//int len;
//char req;
msg1[0] = '$'; //Start Char
msg1[1] = tp; //Type of req.
//msg1[3] = '0';
msg1[4] = seq%256+'0'; //4-7: seq no in little endian
msg1[5] = (seq/256)%256+'0';
msg1[6] = (seq/65536)%256+'0';
msg1[7] = (seq/(65536*256))%256+'0';
msg1[8] = req1;
msg1[9] = req2;
msg1[10] = req3;
msg1[11] = '0';//Reserved Byte, Also for alignment
//len = strlen(msg1);
msg1[2] = (len +'0')%256+'0'; //2-3:Length in lil' endian
msg1[3] = ((len+'0')/256)%256+'0';
return msg1;
}
char* sysfunc(int req1, int req2, int req3)
{
static char syscl[100];
//printf("\ncomm %d\n", req2);
//printf("\ncomm %d\n", req3);
switch (req2)
{
case 1: //Hardware
{
switch (req3)
{
case 1: strcpy(syscl, "lscpu > sysstat.txt\0"); //CPU
break;
case 2: strcpy(syscl, "lsmem > sysstat.txt\0"); //Memoru=y
break;
case 3: strcpy(syscl, "lsblk > sysstat.txt\0"); //HDDs
break;
case 4: strcpy(syscl, "lspci > sysstat.txt\0"); //PCI Add-Ons
break;
default: strcpy(syscl, "\nInvalid Command...\n\0"); //Default
break;
}
}
break;
case 2: //OS
{
switch (req3)
{
case 1: strcpy(syscl, "hostname > sysstat.txt\0");//Hostname
break;
case 2: strcpy(syscl, "hostnamectl > sysstat.txt\0");//OS and Kernel
break;
case 3: strcpy(syscl, "uptime > sysstat.txt\0");//Uptime
break;
default: strcpy(syscl, "\nInvalid Command...\n\0");
break;
}
}
break;
case 3: //Network
{
switch (req3)
{
case 1: strcpy(syscl, "ip link show > sysstat.txt\0");//Ifs
break;
case 2: strcpy(syscl, "ifconfig | grep ether > sysstat.txt\0");//Ethernet
break;
case 3: strcpy(syscl, "ifconfig > sysstat.txt\0");//IP
break;
case 4: strcpy(syscl, "route -n > sysstat.txt\0");//Routing Table
break;
default: strcpy(syscl, "\nInvalid Command...\n\0");
break;
}
}
break;
default: strcpy(syscl, "\nInvalid Command...\n\0");
break;
}
return syscl;
}
Have been at it for 2 days. Unable to figure out where I went wrong. Since the server is showing no reaction, I am assuming there is something wrong in the initial portions (recvfrom on the server side) and therefore have split the code in such a way. Sorry if I have made some obvious noob mistakes.
