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February 3, 2022 18:28
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// src https://www.cs.cmu.edu/afs/cs/academic/class/15213-f99/www/class26/tcpserver.c | |
// modified to show the impact of bind(2) v listen(2) on tcp connection as visible by netstat -atp | |
/* | |
* tcpserver.c - A simple TCP echo server | |
* usage: tcpserver <port> | |
*/ | |
#include <stdio.h> | |
#include <unistd.h> | |
#include <stdlib.h> | |
#include <string.h> | |
#include <netdb.h> | |
#include <sys/types.h> | |
#include <sys/socket.h> | |
#include <netinet/in.h> | |
#include <arpa/inet.h> | |
#define BUFSIZE 1024 | |
#if 0 | |
/* | |
* Structs exported from in.h | |
*/ | |
/* Internet address */ | |
struct in_addr { | |
unsigned int s_addr; | |
}; | |
/* Internet style socket address */ | |
struct sockaddr_in { | |
unsigned short int sin_family; /* Address family */ | |
unsigned short int sin_port; /* Port number */ | |
struct in_addr sin_addr; /* IP address */ | |
unsigned char sin_zero[...]; /* Pad to size of 'struct sockaddr' */ | |
}; | |
/* | |
* Struct exported from netdb.h | |
*/ | |
/* Domain name service (DNS) host entry */ | |
struct hostent { | |
char *h_name; /* official name of host */ | |
char **h_aliases; /* alias list */ | |
int h_addrtype; /* host address type */ | |
int h_length; /* length of address */ | |
char **h_addr_list; /* list of addresses */ | |
} | |
#endif | |
/* | |
* error - wrapper for perror | |
*/ | |
void error(char *msg) { | |
perror(msg); | |
exit(1); | |
} | |
int main(int argc, char **argv) { | |
int parentfd; /* parent socket */ | |
int childfd; /* child socket */ | |
int portno; /* port to listen on */ | |
int clientlen; /* byte size of client's address */ | |
struct sockaddr_in serveraddr; /* server's addr */ | |
struct sockaddr_in clientaddr; /* client addr */ | |
struct hostent *hostp; /* client host info */ | |
char buf[BUFSIZE]; /* message buffer */ | |
char *hostaddrp; /* dotted decimal host addr string */ | |
int optval; /* flag value for setsockopt */ | |
int n; /* message byte size */ | |
/* | |
* check command line arguments | |
*/ | |
if (argc != 2) { | |
fprintf(stderr, "usage: %s <port>\n", argv[0]); | |
exit(1); | |
} | |
portno = atoi(argv[1]); | |
/* | |
* socket: create the parent socket | |
*/ | |
parentfd = socket(AF_INET, SOCK_STREAM, 0); | |
if (parentfd < 0) | |
error("ERROR opening socket"); | |
/* setsockopt: Handy debugging trick that lets | |
* us rerun the server immediately after we kill it; | |
* otherwise we have to wait about 20 secs. | |
* Eliminates "ERROR on binding: Address already in use" error. | |
*/ | |
/* | |
optval = 1; | |
setsockopt(parentfd, SOL_SOCKET, SO_REUSEADDR, | |
(const void *)&optval , sizeof(int)); | |
*/ | |
/* | |
* build the server's Internet address | |
*/ | |
bzero((char *) &serveraddr, sizeof(serveraddr)); | |
/* this is an Internet address */ | |
serveraddr.sin_family = AF_INET; | |
/* let the system figure out our IP address */ | |
serveraddr.sin_addr.s_addr = htonl(INADDR_ANY); | |
/* this is the port we will listen on */ | |
serveraddr.sin_port = htons((unsigned short)portno); | |
/* | |
* bind: associate the parent socket with a port | |
*/ | |
if (bind(parentfd, (struct sockaddr *) &serveraddr, | |
sizeof(serveraddr)) < 0) | |
error("ERROR on binding"); | |
// wait here | |
int dummy = getchar( ); | |
/* | |
* listen: make this socket ready to accept connection requests | |
*/ | |
if (listen(parentfd, 5) < 0) /* allow 5 requests to queue up */ | |
error("ERROR on listen"); | |
/* | |
* main loop: wait for a connection request, echo input line, | |
* then close connection. | |
*/ | |
clientlen = sizeof(clientaddr); | |
while (1) { | |
/* | |
* accept: wait for a connection request | |
*/ | |
childfd = accept(parentfd, (struct sockaddr *) &clientaddr, &clientlen); | |
if (childfd < 0) | |
error("ERROR on accept"); | |
/* | |
* gethostbyaddr: determine who sent the message | |
*/ | |
hostp = gethostbyaddr((const char *)&clientaddr.sin_addr.s_addr, | |
sizeof(clientaddr.sin_addr.s_addr), AF_INET); | |
if (hostp == NULL) | |
error("ERROR on gethostbyaddr"); | |
hostaddrp = inet_ntoa(clientaddr.sin_addr); | |
if (hostaddrp == NULL) | |
error("ERROR on inet_ntoa\n"); | |
printf("server established connection with %s (%s)\n", | |
hostp->h_name, hostaddrp); | |
/* | |
* read: read input string from the client | |
*/ | |
bzero(buf, BUFSIZE); | |
n = read(childfd, buf, BUFSIZE); | |
if (n < 0) | |
error("ERROR reading from socket"); | |
printf("server received %d bytes: %s", n, buf); | |
/* | |
* write: echo the input string back to the client | |
*/ | |
n = write(childfd, buf, strlen(buf)); | |
if (n < 0) | |
error("ERROR writing to socket"); | |
close(childfd); | |
} | |
} |
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