question on socket connection

question on socket connection

[Lejanson C. Go]

how do you check if the socket has been disconnected?

Re: question on socket connection

[ronkhu]

  readSet = socketSet;
  if ( select( highestSocketValue + 1, &readSet, NULL, NULL, NULL ) > -1 )
  {
      .
      .
      .
      
      if ( FD_ISSET( mySocket, &readSet ) )
      {
        size = recv( mySocket, message, MAX_MSG_SIZE - 1, 0 );
        if ( size == 0 )
        {
           close( mySocket );
           FD_CLR( mySocket, &socketSet );
        }
        else
        {
           printf( "%s\n", message );
        }
      }
      
      .
      .
      .
      
  }    
  

Re: question on socket connection

[Glynn Clements]

Lejanson C. Go wrote:

> how do you check if the socket has been disconnected?

Try reading from it; if read/recv return zero bytes, it's closed.

-- 
Glynn Clements <glynn.clements@virgin.net>

RE: question on socket connection

[Ranga Reddy M - CTD ,Chennai.]

If the socket is non-blocking mode, I mean if MSG_DONTWAIT send/recv of
flag is set....
If , the other end is no proper socket closing is done (system crash or
power down).
Then how to find the socket connection....?????


-----Original Message-----
From: Glynn Clements [mailto:glynn.clements@virgin.net]
Sent: Monday, May 26, 2003 11:28 AM
To: Lejanson C. Go
Cc: linux-c-programming
Subject: Re: question on socket connection



Lejanson C. Go wrote:

> how do you check if the socket has been disconnected?

Try reading from it; if read/recv return zero bytes, it's closed.

-- 
Glynn Clements <glynn.clements@virgin.net>
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Re: question on socket connection

[ronkhu]

i think
recv() would still return 0 if the remote side of the socket connection 
has disconnected...

if ur using MSG_DONTWAIT... -1 will be returned if there is no data to 
be read...(as well as EGAIN)....
thus, making it possible to differentiate from "no data" from 
"disconnection event"






Ranga Reddy M - CTD ,Chennai. wrote:

>If the socket is non-blocking mode, I mean if MSG_DONTWAIT send/recv of
>flag is set....
>If , the other end is no proper socket closing is done (system crash or
>power down).
>Then how to find the socket connection....?????
>
>
>-----Original Message-----
>From: Glynn Clements [mailto:glynn.clements@virgin.net]
>Sent: Monday, May 26, 2003 11:28 AM
>To: Lejanson C. Go
>Cc: linux-c-programming
>Subject: Re: question on socket connection
>
>
>
>Lejanson C. Go wrote:
>
>  
>
>>how do you check if the socket has been disconnected?
>>    
>>
>
>Try reading from it; if read/recv return zero bytes, it's closed.
>
>  
>

RE: question on socket connection

[Ranga Reddy M - CTD ,Chennai.]

Error -1: because of recv/send fail.
Error EGAIN: this is because of MSG_DONTWAIT.

Client and Server Both are running on different systems.What if client
crashes or powered off.How does the underlaying TCP/IP layer works
here,There is no time for TCP/IP to say socket close to server.

Client does not give any indication of socket close.Then, I think server
will does not know about the status of the client.

I have read the article about the "Nagles allgoritham" . It sets a default
time out of 2 hours. If there is not data on the socket for 2 hrs this will
disconnect the socket.

Is there any way to trace???


-----Original Message-----
From: ronkhu [mailto:ronkhu@ntsp.nec.co.jp]
Sent: Monday, May 26, 2003 1:04 PM
To: linux-c-programming
Subject: Re: question on socket connection


i think
recv() would still return 0 if the remote side of the socket connection 
has disconnected...

if ur using MSG_DONTWAIT... -1 will be returned if there is no data to 
be read...(as well as EGAIN)....
thus, making it possible to differentiate from "no data" from 
"disconnection event"






Ranga Reddy M - CTD ,Chennai. wrote:

>If the socket is non-blocking mode, I mean if MSG_DONTWAIT send/recv of
>flag is set....
>If , the other end is no proper socket closing is done (system crash or
>power down).
>Then how to find the socket connection....?????
>
>
>-----Original Message-----
>From: Glynn Clements [mailto:glynn.clements@virgin.net]
>Sent: Monday, May 26, 2003 11:28 AM
>To: Lejanson C. Go
>Cc: linux-c-programming
>Subject: Re: question on socket connection
>
>
>
>Lejanson C. Go wrote:
>
>  
>
>>how do you check if the socket has been disconnected?
>>    
>>
>
>Try reading from it; if read/recv return zero bytes, it's closed.
>
>  
>



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RE: question on socket connection

[Glynn Clements]

Ranga Reddy M - CTD ,Chennai. wrote:

> Error -1: because of recv/send fail.
> Error EGAIN: this is because of MSG_DONTWAIT.
> 
> Client and Server Both are running on different systems.What if client
> crashes or powered off.How does the underlaying TCP/IP layer works
> here,There is no time for TCP/IP to say socket close to server.

The socket won't be "closed" until the other end is rebooted or
powered up and sends a RST, or (if SO_KEEPALIVE is used) until the
kernel times out the connection.

> Client does not give any indication of socket close.Then, I think server
> will does not know about the status of the client.

Correct. If you don't get a response, there's no way to tell whether
that's due to a transient network fault, or because the other end has
crashed or is powered off.

> I have read the article about the "Nagles allgoritham" . It sets a default
> time out of 2 hours. If there is not data on the socket for 2 hrs this will
> disconnect the socket.

No. The "Nagle algorithm" is for coalescing many small writes into
fewer, larger packets.

TCP keep-alive is something else; it involves sending occasional
zero-byte packets when the connection would otherwise be idle in order
to detect whether the remote end is still functioning.

> Is there any way to trace???

I don't understand that question.

-- 
Glynn Clements <glynn.clements@virgin.net>

Re: question on socket connection

[ronkhu]

hmmm..
have u tried using select()?
instead of  invoking recv() on a socket that has no data? (in this case, 
u dont have to use MSG_DONTWAIT)

I dont know about the underlying TCP/IP mechanism.....
but recv() will still return -1  when the remote side of the socket 
closes... or when the application making use of that socket crashes for 
that matter....





Ranga Reddy M - CTD ,Chennai. wrote:

>Error -1: because of recv/send fail.
>Error EGAIN: this is because of MSG_DONTWAIT.
>
>Client and Server Both are running on different systems.What if client
>crashes or powered off.How does the underlaying TCP/IP layer works
>here,There is no time for TCP/IP to say socket close to server.
>
>Client does not give any indication of socket close.Then, I think server
>will does not know about the status of the client.
>
>I have read the article about the "Nagles allgoritham" . It sets a default
>time out of 2 hours. If there is not data on the socket for 2 hrs this will
>disconnect the socket.
>
>Is there any way to trace???
>
>
>-----Original Message-----
>From: ronkhu [mailto:ronkhu@ntsp.nec.co.jp]
>Sent: Monday, May 26, 2003 1:04 PM
>To: linux-c-programming
>Subject: Re: question on socket connection
>
>
>i think
>recv() would still return 0 if the remote side of the socket connection 
>has disconnected...
>
>if ur using MSG_DONTWAIT... -1 will be returned if there is no data to 
>be read...(as well as EGAIN)....
>thus, making it possible to differentiate from "no data" from 
>"disconnection event"
>
>
>
>
>
>
>Ranga Reddy M - CTD ,Chennai. wrote:
>
>  
>
>>If the socket is non-blocking mode, I mean if MSG_DONTWAIT send/recv of
>>flag is set....
>>If , the other end is no proper socket closing is done (system crash or
>>power down).
>>Then how to find the socket connection....?????
>>
>>
>>-----Original Message-----
>>From: Glynn Clements [mailto:glynn.clements@virgin.net]
>>Sent: Monday, May 26, 2003 11:28 AM
>>To: Lejanson C. Go
>>Cc: linux-c-programming
>>Subject: Re: question on socket connection
>>
>>
>>
>>Lejanson C. Go wrote:
>>
>> 
>>
>>    
>>
>>>how do you check if the socket has been disconnected?
>>>   
>>>
>>>      
>>>
>>Try reading from it; if read/recv return zero bytes, it's closed.
>>
>> 
>>
>>    
>>
>
>
>
>-
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>-
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>
>
>  
>

RE: question on socket connection

[Ranga Reddy M - CTD ,Chennai.]

Now Iam puting alarm (SIGALRM) on the reader side if There is no
data/response for some time,(according to my application manipulation).Iam
disconnecting the client connection.

In the above design client application is implented like that each 5 min or
(according to my application manipulation) will send a "KEEP ALIVE request
to the server". With this request Iam updating the client connection in the
server.

According to me this is OK, but Iam wasting the network bandwidth and if by
mistake this packet is lost then server disconnects the client connection.

Can any one give me a idea.

Thanks
------
Ranga

-----Original Message-----
From: Glynn Clements [mailto:glynn.clements@virgin.net]
Sent: Monday, May 26, 2003 1:58 PM
To: Ranga Reddy M - CTD ,Chennai.
Cc: ronkhu@ntsp.nec.co.jp; linux-c-programming
Subject: RE: question on socket connection



Ranga Reddy M - CTD ,Chennai. wrote:

> Error -1: because of recv/send fail.
> Error EGAIN: this is because of MSG_DONTWAIT.
> 
> Client and Server Both are running on different systems.What if client
> crashes or powered off.How does the underlaying TCP/IP layer works
> here,There is no time for TCP/IP to say socket close to server.

The socket won't be "closed" until the other end is rebooted or
powered up and sends a RST, or (if SO_KEEPALIVE is used) until the
kernel times out the connection.

> Client does not give any indication of socket close.Then, I think server
> will does not know about the status of the client.

Correct. If you don't get a response, there's no way to tell whether
that's due to a transient network fault, or because the other end has
crashed or is powered off.

> I have read the article about the "Nagles allgoritham" . It sets a default
> time out of 2 hours. If there is not data on the socket for 2 hrs this
will
> disconnect the socket.

No. The "Nagle algorithm" is for coalescing many small writes into
fewer, larger packets.

TCP keep-alive is something else; it involves sending occasional
zero-byte packets when the connection would otherwise be idle in order
to detect whether the remote end is still functioning.

> Is there any way to trace???

I don't understand that question.

-- 
Glynn Clements <glynn.clements@virgin.net>

Re: question on socket connection

[John T. Williams]

send a keep alive packet every minute, and only have the server disconnect
if 10 in a row are missing.




Or cause your server respond to keep_alive packets. This way the client
knows if the server received it or not and can resend if it doesn't get the
appropriate response withing an given time period.



Unless bandwidth is at an unusual premium, I don't think you need to worry
about Keep_alive packets waisting bandwidth. TCP/IP waist plenty of
bandwidth; far more then any reasonable sized keep_alive packet could.



----- Original Message ----- 
From: "Ranga Reddy M - CTD ,Chennai." <rangareddym@ctd.hcltech.com>
To: "Glynn Clements" <glynn.clements@virgin.net>; "Ranga Reddy M - CTD
,Chennai." <rangareddym@ctd.hcltech.com>
Cc: <ronkhu@ntsp.nec.co.jp>; "linux-c-programming"
<linux-c-programming@vger.kernel.org>
Sent: Monday, May 26, 2003 4:44 AM
Subject: RE: question on socket connection


>
> Now Iam puting alarm (SIGALRM) on the reader side if There is no
> data/response for some time,(according to my application manipulation).Iam
> disconnecting the client connection.
>
> In the above design client application is implented like that each 5 min
or
> (according to my application manipulation) will send a "KEEP ALIVE request
> to the server". With this request Iam updating the client connection in
the
> server.
>
> According to me this is OK, but Iam wasting the network bandwidth and if
by
> mistake this packet is lost then server disconnects the client connection.
>
> Can any one give me a idea.
>
> Thanks
> ------
> Ranga
>
> -----Original Message-----
> From: Glynn Clements [mailto:glynn.clements@virgin.net]
> Sent: Monday, May 26, 2003 1:58 PM
> To: Ranga Reddy M - CTD ,Chennai.
> Cc: ronkhu@ntsp.nec.co.jp; linux-c-programming
> Subject: RE: question on socket connection
>
>
>
> Ranga Reddy M - CTD ,Chennai. wrote:
>
> > Error -1: because of recv/send fail.
> > Error EGAIN: this is because of MSG_DONTWAIT.
> >
> > Client and Server Both are running on different systems.What if client
> > crashes or powered off.How does the underlaying TCP/IP layer works
> > here,There is no time for TCP/IP to say socket close to server.
>
> The socket won't be "closed" until the other end is rebooted or
> powered up and sends a RST, or (if SO_KEEPALIVE is used) until the
> kernel times out the connection.
>
> > Client does not give any indication of socket close.Then, I think server
> > will does not know about the status of the client.
>
> Correct. If you don't get a response, there's no way to tell whether
> that's due to a transient network fault, or because the other end has
> crashed or is powered off.
>
> > I have read the article about the "Nagles allgoritham" . It sets a
default
> > time out of 2 hours. If there is not data on the socket for 2 hrs this
> will
> > disconnect the socket.
>
> No. The "Nagle algorithm" is for coalescing many small writes into
> fewer, larger packets.
>
> TCP keep-alive is something else; it involves sending occasional
> zero-byte packets when the connection would otherwise be idle in order
> to detect whether the remote end is still functioning.
>
> > Is there any way to trace???
>
> I don't understand that question.
>
> -- 
> Glynn Clements <glynn.clements@virgin.net>
> -
> To unsubscribe from this list: send the line "unsubscribe
linux-c-programming" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html