Problems Returning an HTTP 200 Ok Message

[Gabriel Genellina]

En Thu, 10 Jul 2008 18:10:46 -0300, Guy Davidson <GDavidson7 at gmail.com>  
escribi�:

> On Jul 10, 12:38 pm, samwyse <samw... at gmail.com> wrote:
>> On Jul 10, 1:50 pm, Guy Davidson <GDavids... at gmail.com> wrote:
>>
>> > My code (attached below) us supposed to read an HTTP Post message
>> > coming from a power meter, parse it, and return a proper HTTP 200 Ok
>> > message. The problem is that the socket fails to send the entire
>> > message as one message, creating a fragmented message which the power
>> > meter then fails to read and accept.
>>
>> From your description, I get the feeling that your power meter has a
>> broken network stack, and you're trying to program around it.  You
>> need to repair the meter.
>
> The meter sends HTTP Post messages, and expects, as a reply, an HTTP
> 200/Ok message.
>
> I try to send the following message, using the socket.send() command:
>
> 'HTTP/1.1 200 OK\r\nDate: Thu, 10 July 2008 14:07:50 GMT\r\nServer:
> Apache/2.2.8 (Fedora)\r\nX-Powered-By: PHP/5.2.4\r\nContent-Length: 4\r
> \nConnection: close\r\nContent-Type: text/html; charset=UTF-8\r\n\r
> \n[0]\n'
>
> However, when I snoop on the packets in wireshark, here's what I see:
>
> HTTP/1.1 200 Ok:
>
> HTTP/1.1 200 OK
> Date: Wed, 09 July 2008 14:55:50 GMT
> Server: Apache/2.2.8 (Fedora)
> X-Powered-By:
>
> Continuation or non-HTTP traffic:
>
> PHP/5.2.4
> Content-Length: 4
> Connection: close
> Content-Type: text/html; charset=UTF-8
>
> [0]
>
> It splits into two packages, which the meter can't read, and the
> communication breaks down there.
>
> Any ideas?

As Guy Davidson has already pointed out, this is a problem in the meter  
TCP implementation, and you should ask the vendor to fix it. (Anyway,  
looks like "somewhere" there is a buffer size of 100 bytes or so, very  
small).

As a workaround, try to shorten your HTTP response; I guess the Server and  
X-Powered-By headers are not required; the Date probably isn't either; and  
if all your responses are like "[0]" a simple "Content-Type: text/plain"  
may suffice (the meter might just ignore it, anyway).

-- 
Gabriel Genellina