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| deepu4u |
 Posted: Wed Aug 01, 2007 10:58 pm Post subject: Does mq support header extension mechanism |
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Apprentice
Joined: 20 Jun 2005
Posts: 37
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Hi all,
I want to specify some user defined properties as part of header ( not as a part of payload) of mq message. Is there a way to specify the user defined properties as part of MQMD header?
thanks |
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| Vitor |
| Posted: Wed Aug 01, 2007 11:58 pm Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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No, the MQMD is a fixed format, but if you add an RFH2 header to the message you can put anything you want (within reason) within the header's usr folder.
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| deepu4u |
| Posted: Thu Aug 02, 2007 1:09 am Post subject: |
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Apprentice
Joined: 20 Jun 2005
Posts: 37
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Hi Vitor,
Thanks for the reply.
Then a question arise that how would the application which would be consuming this message would know that the payload contains the RFH2 header. |
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| Vitor |
| Posted: Thu Aug 02, 2007 1:12 am Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| deepu4u wrote: |
| Then a question arise that how would the application which would be consuming this message would know that the payload contains the RFH2 header. |
Because (as laid out in the Application Programming Reference) the MQMD would indicate this fact.
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| jefflowrey |
| Posted: Thu Aug 02, 2007 3:23 am Post subject: |
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Grand Poobah
Joined: 16 Oct 2002
Posts: 19981
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In addition to the MQRFH/MQRFH2 headers, MQ allows you to put any number of headers after the MQMD, in any order, where the header can be anything you want it to be.
So you can string multiple MQRFH2 headers after the MQMD, followed by an MQCIH header, followed by a custom header. If one had gone slightly insane, perhaps.
Using a single MQRFH2 header, as suggested by Vitor, has several advantages. It's predefined and "well-known". It works very nicely with JMS and XMS. It's flexible and can hold all your data.
Headers are constructed sort of like HTTP Headers. Each header is separated from the next portion of the message by a blank line. All headers other than the MQMD are included in the message body. The Format field of the current header tells you what the next part of the message will be.
So the MQMD could indicate that the format is MQFMT_MQRFH2. OR MQFMT_STRING. Or some string constant that identified your custom header.
And the Format field of the MQRFH2 could indicate that the next piece is MQFMT_STRING, or MQRFH2, or etc.
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| deepu4u |
| Posted: Thu Aug 02, 2007 3:56 am Post subject: |
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Apprentice
Joined: 20 Jun 2005
Posts: 37
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Thank you all for your reply.
I'll use RFH2 header to supply custom application header. |
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| bruce2359 |
| Posted: Thu Aug 02, 2007 6:13 am Post subject: |
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Guest
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| There are a variety of unused fields in the Message Descriptor (MQMD) that are available to the programmer for passing along additional information that can't be included in the application data payload. MsgId and CorrelId are two examples, if they are not used by your applications. |
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| Vitor |
| Posted: Thu Aug 02, 2007 6:25 am Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
Posts: 26093
Location: Texas, USA
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| bruce2359 wrote: |
| MsgId and CorrelId are two examples, if they are not used by your applications. |
Errrmmmmmmm......................... 
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| jefflowrey |
| Posted: Thu Aug 02, 2007 6:31 am Post subject: |
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Grand Poobah
Joined: 16 Oct 2002
Posts: 19981
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| bruce2359 wrote: |
| There are a variety of unused fields in the Message Descriptor (MQMD) that are available to the programmer for passing along additional information that can't be included in the application data payload. MsgId and CorrelId are two examples, if they are not used by your applications. |
And the minute one writes one application that uses any field in the MQMD for business purposes, one has to ensure that every application that might possibly touch the messages (now or in the future) is aware that the MQMD is being used for business purposes.
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| bruce2359 |
| Posted: Thu Aug 02, 2007 6:41 am Post subject: |
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Guest
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| Quote: |
| Is there a way to specify the user defined properties as part of MQMD header? |
The simple answer to the original post is yes. The complicated answer is either no or it depends.  |
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| jefflowrey |
| Posted: Thu Aug 02, 2007 6:53 am Post subject: |
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Grand Poobah
Joined: 16 Oct 2002
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| bruce2359 wrote: |
| Quote: |
| Is there a way to specify the user defined properties as part of MQMD header? |
The simple answer to the original post is yes. The complicated answer is either no or it depends. |
The simple answer to the original post is NO.
The complicated answer is "You can do it, if you really know what you're doing".
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| Vitor |
| Posted: Thu Aug 02, 2007 7:10 am Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
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Location: Texas, USA
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| jefflowrey wrote: |
| The complicated answer is "You can do it, if you really know what you're doing". |
And if you're storing business data in the id fields, you better know exactly what you're doing! 
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| fjb_saper |
| Posted: Thu Aug 02, 2007 8:25 pm Post subject: |
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Grand High Poobah
Joined: 18 Nov 2003
Posts: 20756
Location: LI,NY
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| Vitor wrote: |
| jefflowrey wrote: |
| The complicated answer is "You can do it, if you really know what you're doing". |
And if you're storing business data in the id fields, you better know exactly what you're doing! |
I'd say you don't know what you're doing any more because you're breaking a number of concepts and patterns that MQ was built upon like anonymous identifier, uniqueness of the identifier etc...
But then that's just me ranting... 
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| Vitor |
| Posted: Thu Aug 02, 2007 11:18 pm Post subject: |
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Grand High Poobah
Joined: 11 Nov 2005
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Location: Texas, USA
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| fjb_saper wrote: |
| Vitor wrote: |
| jefflowrey wrote: |
| The complicated answer is "You can do it, if you really know what you're doing". |
And if you're storing business data in the id fields, you better know exactly what you're doing! |
I'd say you don't know what you're doing any more because you're breaking a number of concepts and patterns that MQ was built upon like anonymous identifier, uniqueness of the identifier etc...
But then that's just me ranting... |
Exactly - you do this, you better know what you're doing. The MQ equivalent of a parachute jump with a bedsheet instead of a parachute. You may make it to the ground alive but it's not likely and it's going to hurt... 
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| bruce2359 |
| Posted: Fri Aug 03, 2007 9:40 am Post subject: |
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Guest
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Uh, oh. Hyperbola alert!
Yes, in all things we should know what we're doing. One of several possible solutions was what I was offering with 'spare' fields in the MD.
If you can't change the application data payload (for whatever reason: contractual, being my favorite), yet need to send it and some other data along with it from point A to point B, there are always alternatives. I'm not all that fond of the one I suggested; but it's been done, it works, and it's pretty straight-forward.
This scenario violates best practices; but there are corpses of best practices littering all our collective floors. After all these years, and all these miles, someone out there is still testing in production, for example. |
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