Re: [9fans] adding TCP half-duplex close

[Skip Tavakkolian]

that makes sense. thanks.

On Sat, Feb 4, 2017 at 5:38 AM Charles Forsyth 
wrote:

>
> On 4 February 2017 at 01:56, Skip Tavakkolian 
> wrote:
>
> Shutting down the write-end (i.e. 'shut_wr'), should send FIN, and
> transition to Finwait1.
>
>
> i'd make it a "read" or "write" parameter to the existing "hangup"
> message. older implementations that don't accept the parameter will give an
> error on the request because the current tcp.c doesn't accept a parameter
>

Re: [9fans] adding TCP half-duplex close

[Skip Tavakkolian]

yes, i'm still trying to find a real situation where this would be
critical. i asked go-nuts list for production examples at the same time as
the start of this thread. no answers yet.

On Sat, Feb 4, 2017 at 3:31 AM Charles Forsyth 
wrote:

> it's also funny that the rationale seems to be to pass the same
> conformance test for Go that once had it added to Inferno so it would pass
> a Java test but it was never otherwise used for reasons already given, so I
> took it out again.
>
> On 4 February 2017 at 10:11, Charles Forsyth 
> wrote:
>
> I did once have a use for this in an o/s of mine, in a sort of network
> pipe to servers, but it was so variably implemented by other systems (data
> was flushed, or not) I gave it up as not particularly useful in practice,
> except between two known systems that did what you wanted.
>
> On 4 February 2017 at 09:58, Charles Forsyth 
> wrote:
>
>
> On 4 February 2017 at 01:56, Skip Tavakkolian 
> wrote:
>
> Shutting down the write-end (i.e. 'shut_wr'), should send FIN, and
> transition to Finwait1.
>
>
> i'd make it a "read" or "write" parameter to the existing "hangup"
> message. older implementations that don't accept the parameter will give an
> error on the request because the current tcp.c doesn't accept a parameter
>
>
>
>

Re: [9fans] adding TCP half-duplex close

[Fran. J Ballesteros]

I used half closes to put go chans in the network for my weird chan based 
network
calls. 
But the code works without such feature. 
Being just that, I dont know if it counts. 

> El 5 feb 2017, a las 5:39, Skip Tavakkolian  
> escribió:
> 
> yes, i'm still trying to find a real situation where this would be critical. 
> i asked go-nuts list for production examples at the same time as the start of 
> this thread. no answers yet.
> 
>> On Sat, Feb 4, 2017 at 3:31 AM Charles Forsyth  
>> wrote:
>> it's also funny that the rationale seems to be to pass the same conformance 
>> test for Go that once had it added to Inferno so it would pass a Java test 
>> but it was never otherwise used for reasons already given, so I took it out 
>> again.
>> 
>> On 4 February 2017 at 10:11, Charles Forsyth  
>> wrote:
>> I did once have a use for this in an o/s of mine, in a sort of network pipe 
>> to servers, but it was so variably implemented by other systems (data was 
>> flushed, or not) I gave it up as not particularly useful in practice, except 
>> between two known systems that did what you wanted.
>> 
>> On 4 February 2017 at 09:58, Charles Forsyth  
>> wrote:
>> 
>> On 4 February 2017 at 01:56, Skip Tavakkolian  
>> wrote:
>> Shutting down the write-end (i.e. 'shut_wr'), should send FIN, and 
>> transition to Finwait1.
>> 
>> i'd make it a "read" or "write" parameter to the existing "hangup" message. 
>> older implementations that don't accept the parameter will give an error on 
>> the request because the current tcp.c doesn't accept a parameter
>> 
>> 

Re: [9fans] adding TCP half-duplex close

[Skip Tavakkolian]

cool.

On Fri, Feb 3, 2017 at 10:35 PM Bakul Shah  wrote:

> For the shut_rd case, I think a cleaner impl is to send RST *only* if
> there is pending data (received but not read by the user) or new data is
> received after the read end is closed. At the moment I don't recall what
> BSD does but you don't have to allow draining once the read end is closed.
> Just drain and RST! Any user reads should fail.
>
> I recall having to deal with this in the past while working on a packet
> level network proxy. No access to that code now so the above is from
> memory.
>
>
>
> Sent from my iPad
> On Feb 3, 2017, at 5:56 PM, Skip Tavakkolian 
> wrote:
>
> Has anyone looked into implementing this?  Can anyone comment on the
> details?
>
> For the curious, this is described here:
> https://tools.ietf.org/html/rfc1122#page-87
> Go net package (https://github.com/golang/go/issues/17906).
>
> As I understand it, one would only worry about 'shutdown' if the
> connection is in 'Established' state. It is not clear to me what the state
> should transition to when the read-end is closed (i.e. shut_rd).  Also,
> there doesn't not seem to be consistency between different implementations
> (Windows,Linux, *BSD) on what should happen to what's already in the read
> queue; should it be allowed to drain to the reader or discarded immediately?
>
> Shutting down the write-end (i.e. 'shut_wr'), should send FIN, and
> transition to Finwait1.
>
> I think the correct mechanics to handle this would be to add two new
> messages in tcpctl (/sys/src/9/ip/tcp.c). Then, roughly something like this:
>
> case 'shut_rd' :
>  if (Etablished) {
>   qhangup(rq);
>   send(RST);  // Windows does this and RFC1122 seems to recommend it.
> Linux does not.
>   tcb->rcv.blocked = 1;  // all that's needed?
>   tcb->rcv.wnd = 0;
>   tcpsetstate()  // not sure what it should be or should stay
> Established?
> }
>
> case 'shut_wr':
>   if (Established) {
> qhangup(wq);
> send(FIN)
> tcpsetstate(Finwait_1)
>   }
>
>
>

Re: [9fans] adding TCP half-duplex close

[Bakul Shah]

I think shutdown(sock, SHU_RD) is mainly to let the sender generate an SIGPIPE 
signal in case it has sent data on a closed direction of a connection. But I 
think this is only for completeness. Almost always you’d use close(sock). At 
least I have not found a usecase when I’d want to shutdown the read-end but 
continue sending on write-end. 

> On Feb 4, 2017, at 8:39 PM, Skip Tavakkolian  
> wrote:
> 
> yes, i'm still trying to find a real situation where this would be critical. 
> i asked go-nuts list for production examples at the same time as the start of 
> this thread. no answers yet.
> 
> On Sat, Feb 4, 2017 at 3:31 AM Charles Forsyth  > wrote:
> it's also funny that the rationale seems to be to pass the same conformance 
> test for Go that once had it added to Inferno so it would pass a Java test 
> but it was never otherwise used for reasons already given, so I took it out 
> again.
> 
> On 4 February 2017 at 10:11, Charles Forsyth  > wrote:
> I did once have a use for this in an o/s of mine, in a sort of network pipe 
> to servers, but it was so variably implemented by other systems (data was 
> flushed, or not) I gave it up as not particularly useful in practice, except 
> between two known systems that did what you wanted.
> 
> On 4 February 2017 at 09:58, Charles Forsyth  > wrote:
> 
> On 4 February 2017 at 01:56, Skip Tavakkolian  > wrote:
> Shutting down the write-end (i.e. 'shut_wr'), should send FIN, and transition 
> to Finwait1.
> 
> i'd make it a "read" or "write" parameter to the existing "hangup" message. 
> older implementations that don't accept the parameter will give an error on 
> the request because the current tcp.c doesn't accept a parameter
> 
> 

Re: [9fans] adding TCP half-duplex close

[Charles Forsyth]

On 4 February 2017 at 01:56, Skip Tavakkolian 
wrote:

> Shutting down the write-end (i.e. 'shut_wr'), should send FIN, and
> transition to Finwait1.


i'd make it a "read" or "write" parameter to the existing "hangup" message.
older implementations that don't accept the parameter will give an error on
the request because the current tcp.c doesn't accept a parameter

Re: [9fans] adding TCP half-duplex close

[Charles Forsyth]

I did once have a use for this in an o/s of mine, in a sort of network pipe
to servers, but it was so variably implemented by other systems (data was
flushed, or not) I gave it up as not particularly useful in practice,
except between two known systems that did what you wanted.

On 4 February 2017 at 09:58, Charles Forsyth 
wrote:

>
> On 4 February 2017 at 01:56, Skip Tavakkolian 
> wrote:
>
>> Shutting down the write-end (i.e. 'shut_wr'), should send FIN, and
>> transition to Finwait1.
>
>
> i'd make it a "read" or "write" parameter to the existing "hangup"
> message. older implementations that don't accept the parameter will give an
> error on the request because the current tcp.c doesn't accept a parameter
>

Re: [9fans] adding TCP half-duplex close

[Charles Forsyth]

it's also funny that the rationale seems to be to pass the same conformance
test for Go that once had it added to Inferno so it would pass a Java test
but it was never otherwise used for reasons already given, so I took it out
again.

On 4 February 2017 at 10:11, Charles Forsyth 
wrote:

> I did once have a use for this in an o/s of mine, in a sort of network
> pipe to servers, but it was so variably implemented by other systems (data
> was flushed, or not) I gave it up as not particularly useful in practice,
> except between two known systems that did what you wanted.
>
> On 4 February 2017 at 09:58, Charles Forsyth 
> wrote:
>
>>
>> On 4 February 2017 at 01:56, Skip Tavakkolian > > wrote:
>>
>>> Shutting down the write-end (i.e. 'shut_wr'), should send FIN, and
>>> transition to Finwait1.
>>
>>
>> i'd make it a "read" or "write" parameter to the existing "hangup"
>> message. older implementations that don't accept the parameter will give an
>> error on the request because the current tcp.c doesn't accept a parameter
>>
>
>