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Can the accept() be used after using one successful connect() with the same TCP port ?

Can the accept() be used after using one successful connect() with the same TCP port ?

Post by Louie Ch » Tue, 18 Mar 2003 15:16:54



Dear sir/madam,

I am using the glibc under the Linux platform.

Does anyone know if I can use the functions "listen() & accept()"
after one successful TCP connection with the function "connect" ?
Please refer to the following concept codes !!

int sockfd, new_connect_fd;

sockfd = socket(domain, type, protocol);
connect(sockfd, sockaddr, addrlen);                     <--- connect() and connection
successful !
listen(sockfd, backlog);
new_connect_fd =  accept(sockfd, sockaddr, addrlen);    <--- Can the
accept() be used after using connect() ?

Thanks for your help !

Best Regards. Louie

 
 
 
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Can the accept() be used after using one successful connect() with the same TCP port ?

Post by Michael Fu » Tue, 18 Mar 2003 23:31:53



> I am using the glibc under the Linux platform.

> Does anyone know if I can use the functions "listen() & accept()"
> after one successful TCP connection with the function "connect" ?
> Please refer to the following concept codes !!

> int sockfd, new_connect_fd;

> sockfd = socket(domain, type, protocol);
> connect(sockfd, sockaddr, addrlen);                        <--- connect() and connection
> successful !
> listen(sockfd, backlog);
> new_connect_fd =  accept(sockfd, sockaddr, addrlen);       <--- Can the
> accept() be used after using connect() ?

Experimentation is a great way to learn.  Rather than ask if something
can be done, try it yourself and see if it can be done.

Be sure to add error checking to your code so you'll know if the
function calls succeeded or failed, and if they failed, why they
failed.

--
Michael Fuhr
http://www.fuhr.org/~mfuhr/

 
 
 
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Can the accept() be used after using one successful connect() with the same TCP port ?

Post by Road Runner New » Wed, 19 Mar 2003 09:33:12


Connect is not used with accept - returns a socket after it has received
data.  use accept with bind, and listen.



> > I am using the glibc under the Linux platform.

> > Does anyone know if I can use the functions "listen() & accept()"
> > after one successful TCP connection with the function "connect" ?
> > Please refer to the following concept codes !!

> > int sockfd, new_connect_fd;

> > sockfd = socket(domain, type, protocol);
> > connect(sockfd, sockaddr, addrlen); <--- connect() and connection
> > successful !
> > listen(sockfd, backlog);
> > new_connect_fd =  accept(sockfd, sockaddr, addrlen); <--- Can the
> > accept() be used after using connect() ?

> Experimentation is a great way to learn.  Rather than ask if something
> can be done, try it yourself and see if it can be done.

> Be sure to add error checking to your code so you'll know if the
> function calls succeeded or failed, and if they failed, why they
> failed.

> --
> Michael Fuhr
> http://www.fuhr.org/~mfuhr/

 
 
 
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Can the accept() be used after using one successful connect() with the same TCP port ?

Post by j.. » Thu, 20 Mar 2003 00:22:54



> Dear sir/madam,

> I am using the glibc under the Linux platform.

> Does anyone know if I can use the functions "listen() & accept()"
> after one successful TCP connection with the function "connect" ?
> Please refer to the following concept codes !!

> int sockfd, new_connect_fd;

> sockfd = socket(domain, type, protocol);
> connect(sockfd, sockaddr, addrlen); <--- connect() and connection
> successful !
> listen(sockfd, backlog);
> new_connect_fd =  accept(sockfd, sockaddr, addrlen);       <--- Can the
> accept() be used after using connect() ?

You're mixing apples and oranges. A listening socket can't be used for
anything but accepting connections. It's not connected to anything.

A connected socket is, well, connected. You can't use it as a
listening socket.

If you're serious about network programming, get this book:

http://www.amazon.com/exec/obidos/ASIN/013490012X/qid=1048000908/sr=2...

 
 
 
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Can the accept() be used after using one successful connect() with the same TCP port ?

Post by Irfan Bond » Thu, 20 Mar 2003 09:02:28



> Dear sir/madam,

> I am using the glibc under the Linux platform.

> Does anyone know if I can use the functions "listen() & accept()"
> after one successful TCP connection with the function "connect" ?
> Please refer to the following concept codes !!

> int sockfd, new_connect_fd;

> sockfd = socket(domain, type, protocol);
> connect(sockfd, sockaddr, addrlen);                        <--- connect() and connection
> successful !
> listen(sockfd, backlog);
> new_connect_fd =  accept(sockfd, sockaddr, addrlen);       <--- Can the
> accept() be used after using connect() ?

> Thanks for your help !

> Best Regards. Louie

Server Side Calls : socket, bind, listen, accept.

Client Side Calls : Socket, connect

Then client side or Server side can use recv, send to send or receive
data from the other peer.

You don't want to mix client side and server side calls.

In TCP case anyways the fd that u get can  be used for bidirectional
communication anyways.

So Client and server can both receive and send data.
Irfan.

 
 
 
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Can the accept() be used after using one successful connect() with the same TCP port ?

Post by Alexander Kotelniko » Fri, 21 Mar 2003 02:03:32


>>>>> On Tue, 18 Mar 2003 15:22:54 GMT


j>

Quote:>> Dear sir/madam,

>> I am using the glibc under the Linux platform.

>> Does anyone know if I can use the functions "listen() & accept()"
>> after one successful TCP connection with the function "connect" ?
>> Please refer to the following concept codes !!

>> int sockfd, new_connect_fd;

>> sockfd = socket(domain, type, protocol);
>> connect(sockfd, sockaddr, addrlen); <--- connect() and connection
>> successful !
>> listen(sockfd, backlog);
>> new_connect_fd =  accept(sockfd, sockaddr, addrlen);   <--- Can the
>> accept() be used after using connect() ?

j>
j> You're mixing apples and oranges. A listening socket can't be used for
j> anything but accepting connections. It's not connected to anything.

You are wrong. Look at TCP state diagram. Simultaneous open is allowed
in TCP, and Stevens writes about it in UNPv1 TCP Connection
Establishment and Termination

--
Alexander Kotelnikov
Saint-Petersburg, Russia

 
 
 
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Can the accept() be used after using one successful connect() with the same TCP port ?

Post by Valentin Nechaye » Fri, 21 Mar 2003 02:45:39



>>> sockfd = socket(domain, type, protocol);
>>> connect(sockfd, sockaddr, addrlen); <--- connect() and connection
>>> successful !
>>> listen(sockfd, backlog);
>>> new_connect_fd =  accept(sockfd, sockaddr, addrlen);       <--- Can the
>>> accept() be used after using connect() ?

j>> You're mixing apples and oranges. A listening socket can't be used for
j>> anything but accepting connections. It's not connected to anything.
AK> You are wrong. Look at TCP state diagram. Simultaneous open is allowed
AK> in TCP, and Stevens writes about it in UNPv1 TCP Connection
AK> Establishment and Termination

I think you mixed *sockets* and *ports*. BSD sockets don't allow socket
to switch to listening state after connect(), and don't allow to do
connect on socket which is listening. This has no common with TCP states,
TCP ports (as numbers in per-host addressing space), TCP by itself, and
simultaneous opening of a port using different sockets (which may require
SO_REUSEADDR and SO_REUSEPORT).

-netch-

 
 
 
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Can the accept() be used after using one successful connect() with the same TCP port ?

Post by j.. » Fri, 21 Mar 2003 03:46:49



> >>>>> On Tue, 18 Mar 2003 15:22:54 GMT

> j>

> >> Dear sir/madam,

> >> I am using the glibc under the Linux platform.

> >> Does anyone know if I can use the functions "listen() & accept()"
> >> after one successful TCP connection with the function "connect" ?
> >> Please refer to the following concept codes !!

> >> int sockfd, new_connect_fd;

> >> sockfd = socket(domain, type, protocol);
> >> connect(sockfd, sockaddr, addrlen); <--- connect() and connection
> >> successful !
> >> listen(sockfd, backlog);
> >> new_connect_fd =  accept(sockfd, sockaddr, addrlen);      <--- Can the
> >> accept() be used after using connect() ?
> j>
> j> You're mixing apples and oranges. A listening socket can't be
> j> used for anything but accepting connections. It's not connected
> j> to anything.

> You are wrong. Look at TCP state diagram. Simultaneous open is
> allowed in TCP, and Stevens writes about it in UNPv1 TCP Connection
> Establishment and Termination

A simultaneous open is when two applications send a SYN to each other
at about the same time, such that the segments pass each other on the
wire, and are received by each side before any ACK is. It doesn't have
anything to do with the socket API.
 
 
 
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Can the accept() be used after using one successful connect() with the same TCP port ?

Post by Alexander Kotelniko » Fri, 21 Mar 2003 04:24:23


>>>>> On Wed, 19 Mar 2003 19:45:39 +0200

VN>

>>>> sockfd = socket(domain, type, protocol);
>>>> connect(sockfd, sockaddr, addrlen); <--- connect() and connection
>>>> successful !
>>>> listen(sockfd, backlog);
>>>> new_connect_fd =  accept(sockfd, sockaddr, addrlen);   <--- Can the
>>>> accept() be used after using connect() ?

j> You're mixing apples and oranges. A listening socket can't be used for
j> anything but accepting connections. It's not connected to anything.
AK> You are wrong. Look at TCP state diagram. Simultaneous open is allowed
AK> in TCP, and Stevens writes about it in UNPv1 TCP Connection
AK> Establishment and Termination
VN>
VN> I think you mixed *sockets* and *ports*. BSD sockets don't allow socket
VN> to switch to listening state after connect(), and don't allow to do
VN> connect on socket which is listening. This has no common with TCP states,
VN> TCP ports (as numbers in per-host addressing space), TCP by itself, and
VN> simultaneous opening of a port using different sockets (which may require
VN> SO_REUSEADDR and SO_REUSEPORT).

Oops, I was wrong, but in another way. I remembered that there is a
branch from LISTEN to SYN_SEND in TCP state diagram (and from SYN_SENT
we can achieve simultaneous open), but I had not remembered that it is
used not on OPEN, but on SEND, so this really can not occur with BSD
sockets.

Sorry for misinformation,
--
Alexander Kotelnikov
Saint-Petersburg, Russia

 
 
 
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Can the accept() be used after using one successful connect() with the same TCP port ?

Post by Valentin Nechaye » Fri, 21 Mar 2003 04:47:30



> You're mixing apples and oranges. A listening socket can't be used for
> anything but accepting connections. It's not connected to anything.
> A connected socket is, well, connected. You can't use it as a
> listening socket.

It was possible in some versions of network stack in Linux 2.2 branch.
In it one could do delisten() (which was implemented hackerly, as another
socket call with incorrect parameters combination) to close listening
and then reopen it; and one could do disconnecting (closing of connection)
keeping socket bound to some port. Idea of this was to keep binding to
low port (which requires root) after dropping root privilege (or even
specific capability) and keeping possibility to open or close listening
and/or connection in arbitrary moments. But this died in the next version.

-netch-

 
 
 
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