[ale] connect()

[Chris Fowler]

Stephan,


He is some test code that works like a champ!


I'm sure I need the option to reuse but this code works on Linux.  Now it will need to be tested on our embedded platform.  Thanks for the help.

I also verified I could read data from the remote machine.  I pulled this code direclty from Beej's guide.  I needed a fast solution to test the concept.

Thanks,
Chris


----- test.c ----


#include <string.h> 
#include <sys/types.h> 
#include <sys/socket.h> 
#include <netinet/in.h> 
#include <stdio.h> 


#define THISPORT 3001 
#define DEST_IP "160.77.63.112" 
#define DEST_PORT 23 


void 
main(void) 
{ 
        int sockfd; 
        int status; 
        struct sockaddr_in my_addr; 
        struct sockaddr_in dest_addr; 


        sockfd = socket(AF_INET, SOCK_STREAM, 0); 


        my_addr.sin_family = AF_INET; 
        my_addr.sin_port = htons(THISPORT); 
        my_addr.sin_addr.s_addr = inet_addr("160.77.63.112"); 
        memset(&(my_addr.sin_zero), '\0', 8); 


        status = bind(sockfd, (struct sockaddr *) &my_addr, sizeof(struct sockaddr)); 
        if (status == -1) 
        { 
                perror("bind()"); 
                exit(1); 
        } 


        printf("Bound to %d\n", THISPORT); 
        fflush(stdout); 
        
        dest_addr.sin_family = AF_INET; 
        dest_addr.sin_port = htons(DEST_PORT); 
        dest_addr.sin_addr.s_addr = inet_addr("160.77.63.112"); 
        memset(&(dest_addr.sin_zero), '\0', 8); 


        status = connect(sockfd, (struct sockaddr *)&dest_addr, sizeof(struct sockaddr)); 


        if (status == -1) 
        { 
                perror("connect()"); 
                exit(1); 
        } 


        sleep(100);  


        
} 


  


-----Original Message-----
From: Stephan Uphoff
To: Chris Fowler
Cc: ups at tree.com
Sent: 8/1/01 8:24 PM
Subject: Re: [ale] connect() 


--SNIP--
> 
> I do think the above should work.  Do you see any problems?
> 
> Thanks,
> Chris
> 


Only if you do the  socket,bind,connect stuff in a loop
binding to the same local port and to the same remote port.


In this case you are in deep trouble.


Even after a close of the socket the mapping 
<localPort,localIP <=> remotePort,remoteIP> might 
hang around for a certain time. 
Your socket is closed but the kernel is still busy with the
protocol to close the connection
(see TCP protocol state machine closing states)


First Problem:
---------------


This will prevent you from binding to it.
( Especially on Solaris)
setsockopt() with SO_REUSEADDR should fix the problem.



Second Problem:
---------------


Even after the bind the old mapping <lp,li,rp,ri> is still there.
Now you get an error on the connect()
(EADDRNOTAVAIL)


If you try again and again you will eventually succeed ...


--------------------------


You are buying yourself a lot of trouble ....
This is also a way less traveled so you might just run into some
implementation bugs/features in the TCP stacks.


good luck


        Stephan