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Data handler for a 2 part tcp request

Question asked by KishoreThadani on Aug 13, 2015
Latest reply on Feb 22, 2017 by Balamuruganravir

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I am trying to write a data handler for tcp request.

This tcp request(s) is generated by triggering a SOAP request in the front end.

The format of the tcp Requests is:

4ByteHeader(which specifies the length of data payload) followed by DataPayload

The way the 2 part Request comes in is:

1st part (Request): 4ByteHeader

2nd part (a new Request): Followed by the data payload.

In the vs that I have created, in the first tcp listen step which contains the header, I do nothing and trigger the tcp Respond step. This particular action generates an error response (in the original SOAP request which is the front end request that generates the entire tcp requests that I am trying to write a handler for). I also observe that, the subsequent tcp request that contains the data payload comes in next, and it is processed successfully with the proper response, but this response becomes completely mute in the original SOAP transacation, since it already generated the error response resulting from the handling of the first part 4byteheader tcp portion.

Any tips and/or help will be appreciated on how to process/handle the first tcp header part which can be totally ignored and move straight to processing the 2nd tcp data payload part.

Josh_Hendrick

Aug 13, 2015 6:21 PM

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Have you written a custom TCP Delimiter along with your DPH? The TCP Delimiter is what helps DevTest to identify the start/end of a payload. If you have a 4 byte header which should be ignored, you could create your delimiter to remove/ignore the first four bytes of the message. If you create a custom delimiter, it should appear in the list of TCP delimiters for you to choose from. I can send you a sample TCP Delimiter if you are not familiar with them.

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Josh_Hendrick Aug 13, 2015 6:21 PM
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Have you written a custom TCP Delimiter along with your DPH? The TCP Delimiter is what helps DevTest to identify the start/end of a payload. If you have a 4 byte header which should be ignored, you could create your delimiter to remove/ignore the first four bytes of the message. If you create a custom delimiter, it should appear in the list of TCP delimiters for you to choose from. I can send you a sample TCP Delimiter if you are not familiar with them.
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- KishoreThadani @ Josh_Hendrick on Aug 13, 2015 6:46 PM
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  Josh, thanks for your response. I have not created a custom TCP delimeter.
  There is actually no delimeter that seperates the 4 byte header from the data payload.
  This is a sample of how the input tcp record looks:
  
  0024field1<0x1C>field2<0x1C>field3<0x1C>field4
  
  where 0024 is the 4 byte header record which indicates the total length of data payload
  and <0x1C> is the field delimeter in hex format.
  
  What I have observed is the following:
  
  In the 1st tcp request, only 0024 arrives.
  My virtual model listens to this data, figures out that this is the header (through script assertion), and I directly trigger the TCP/IP Respond step,
  However, the SOAP Request comes back with a Read timeout error message.
  Then the 2nd part data payload comes in as a new Request, the virtual model processes this Request with a proper tcp response.
  However, this part is completely ignored due to the error response already generated by SOAP in the 1st part.
  
  Given this scenario, do you think your suggestion would help my case?
  
  Thanks again
  
  Kishore
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  - Josh_Hendrick @ KishoreThadani on Aug 13, 2015 6:51 PM
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    Hi Kishore,
    
    If your messages are coming in as two separate requests, the delimiter may not be what you need. Once you figure out that the data is the header through your scripted assertion, instead of triggering the respond step perhaps you need to simply loop back to the listen step so that you don't send a response for the incoming header portion. Then when you receive the 2nd part of the data payload you could trigger the respond step as normal. Does that make sense?
    
    Josh
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    - KishoreThadani @ Josh_Hendrick on Aug 13, 2015 6:56 PM
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      I definitely tried what you suggested earlier. However, in that case (looping back to the TCP listen step), it completely ignores the 2nd part of tcp request which contains the data payload. The data payload never gets its turn in the listen step. The tcp listen step is waiting for a brand new set of request.
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      - Kenneth_Avery @ KishoreThadani on Aug 13, 2015 8:03 PM
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        Kishore,
        
        You question is very confusing to me, because of a mention of SOAP, as well as TCP. If I understand correctly, I think you are describing a case where you submit a SOAP request to a middle tier, which in turns generates a TCP request to your virtual service (meaning that the virtual service never deals with the SOAP directly). If that is the case, it will make things easier. Josh is correct in stating that you need to use the appropriate delimiter (or create your own). If every request message is exactly the same length, try the fixed length delimiter. Otherwise, you need one that can parse the first four bytes, and determine the actual number of total bytes for the listen step to receive from the input socket before allowing the processing to continue.
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        KishoreThadani @ Kenneth_Avery on Aug 13, 2015 8:13 PM
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        Hi Ken,
        
        You are correct in your statement: "you submit a SOAP request to a middle tier, which in turns generates a TCP request to your virtual service (meaning that the virtual service never deals with the SOAP directly."
        
        For further clarification, if you could read down below this Discussion chain/thread, I have given a sample of the input data and how it gets broken up as a 2 part request. After reading this part, Josh felt that usage of tcp delimeter would not help much.
        
        Let me know if you have any other ideas.
        
        Thanks
        
        Kishore
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        Kenneth_Avery @ KishoreThadani on Aug 13, 2015 8:17 PM
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        I miss things in emails frequently, but I did actually read the entire thread, and do believe that using the correct TCP delimiter would solve your issue. As I mentioned, whatever current delimiter you are using is deciding that the header by itself is a "complete request". This isn't accurate, and needs to be corrected.
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- Balamuruganravir @ Josh_Hendrick on Feb 22, 2017 10:30 AM
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  Hi Josh,
  Can you please share the sample TCP Delimiter.We are also looking for the reference to create the custom delimiter for 6 byte header.
  Email: balamuruganravir@gmail.com
  
  Thanks,
  Balamurugan.
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Josh_Hendrick Aug 13, 2015 8:17 PM
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Kishore - after reading your last response, my initial thought was most likely correct. You will need a delimiter defined as Ken mentioned above. This will tell DevTest how to determine the start and end of a message. It appears that is not happening correctly as is stands currently which is why you are seeing two separate messages pass through your VSM when it should likely be a single request.
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- KishoreThadani @ Josh_Hendrick on Aug 13, 2015 8:49 PM
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  Thank you Ken and Josh. I think you are both correct!
  
  I did try out with one record wherein the last 2 character will be constant for that operation. And it did treat it as a single TCP request.
  However, for other operations that will be supported by the same virtual model, it will not be constant.
  But, atleast, we have narrowed down and are closer to a resolution.
  
  If you could share some sample of custom TCP delimeter, I would really appreciate it.
  
  Thank you so much!!
  
  Kishore
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  - Lenn Thompson @ KishoreThadani on Aug 18, 2015 5:32 PM
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    Kishore -- was your problem solved?
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    - KishoreThadani @ Lenn Thompson on Aug 18, 2015 5:44 PM
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      Yes, the problem was solved using tcp delimeter in the Request. Thanks to all for your tips/feedback/solution. Really appreciate it!
      Great and helpful community. Glad to be a part of it.
      
      Kishore
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JayantChatterjee62134974 Aug 13, 2015 8:57 PM
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Do not use any out of the box TCP delimiters. Use the DRDA protocol/listener. This TCP listener reads the complete message body irrespective of format/ delimiters.
Once you get the complete message, use the scriptable data protocol handler and extract the body as a string. And then you can read the header as well as the body. I have implemented atleast 4-5 TCP services this way.

Sample code:

import com.itko.util.ParameterList;
ParameterList args = lisa_vse_request.getArguments();
String message = lisa_vse_request.getBodyText();

// use string subset to extract first 4 characters of header
// use string subset to extract rest of message

String[] reqt = message.substring(4);

// Set operation and arguments as shown below
lisa_vse_request.setOperation("couponConsumption");

args.setParameterValue("Value1","argument1_value");
args.setParameterValue("Value2","argument2_value");
lisa_vse_request.setArguments(args);
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Data handler for a 2 part tcp request

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