Using IBM WebSphere MQ message property APIs in ILE RPG
The old way and the way forward
Traditionally, to communicate with a JMS application (say, a web service running in IBM WebSphere Application Server), one would need to use an RFH2 header. This is cumbersome, especially in RPG. The RFH2 headers consist of a set of fixed header fields followed by an arbitrary number of data structures, each containing a length field and a buffer containing XML data that defines the properties. Generating an RFH2 header is not too hard. Just include the copy file, cmqrfh2g, in to your data structure and define as many lengths and data pairs as needed for the number of folders you need to set (properties in different folders must be sent in different pairs). For more freedom and to eliminate sending extra blanks from the fixed length fields, you can also build a buffer dynamically. The real trouble comes in trying to read the properties, which requires parsing an RFH2 header sent by another application. Although RPG is perfectly capable of parsing varying length headers with an arbitrary number of varying length fields, it is much better suited to fixed-length, record-like data.
The other issue with using RFH2 headers in RPG (really any ILE language) is that the XML data must be in Unicode. RPG has the benefit here of supporting UTF-16 natively. Unless you're only dealing with other RPG applications, though, most likely any RFH2 headers you get from other applications will be in UTF-8, since that is the default for Linux, Windows, and Java. This means that your are pretty much guaranteed to have to deal with iconv, which is always a pain.
With the release of WebSphere MQ 7.0, MQ gained new API calls that greatly decrease the amount of work needed to interact with message properties and remove the need to generate or parse RFH2 headers. These are:
MQSETMP– Set a message property
MQDLTMP– Delete a message property
MQINQMP– Inquire about a message property
Along with these APIs, other APIs were added to aid in the use of the message property APIs:
MQCRTMH– Create a message handle
MQDLTMH– Delete a message handle
MQBUFMH– Convert a message buffer into a message handle
MQMHBUF– Convert a message handle into a message buffer
The key to the new message property APIs is a message handle. A message
MQHMSG) is a 64-bit identifier and is used to allow
an application to refer to the properties of a message, similar to how an
MQHCONN is used to refer to a connection to a queue manager
MQHOBJ is used to refer to a topic or queue. The first
step in using these new message property APIs is to create a message
dcl-s Hmsg int(20); dcl-ds MQCMHO Qualified; /copy CMQCMHOG end-ds; MQCRTMH(HConn : MQCMHO : HMsg : CompletionCode : Reason);
You declare two variables,
HMsg as a 64-bit integer and an
MQCMHO (Create Message Handle Options) structure. Then, you
MQCRTMH to generate our message handle. Assuming that
0, you now have a message
handle with which you can use the new message property APIs.
To see how to use
MQSETMP to set a message property, let's
first look at the parameters of
Example 1: MQSETMP procedure definition from CMQG
DMQSETMP PR EXTPROC('MQSETMP') D* Connection handle D HCONN 10I 0 VALUE D* Message handle D HMSG 20I 0 VALUE D* Options that control the action of MQSETMP (MQSMPO) D SETOPT 20A D* Property name (MQCHARV) D PRNAME 32A D* Property descriptor (MQPD) D PRPDSC 24A D* Property data type D TYPE 10I 0 VALUE D* Length of the Value area D VALLEN 10I 0 VALUE D* Property value D VALUE * VALUE D* Completion code D CMPCOD 10I 0 D* Reason code qualifying CompCode D REASON 10I 0
For the purposes of this exercise, using the default values for
MQPD are fine. For more information
on these parameters, refer to the WebSphere MQ Information Center.
Let's define some variables to use
dcl-ds PropName Qualified; /copy QMCHRVG end-ds; dcl-s PropertyName varchar(40); dcl-s PropertyValue varchar(40); dcl-ds MQPD Qualified; /copy CMQPDG end-ds; dcl-ds MQSMPO Qualified; /copy CMQSMPOG end-ds;
In this example, we will define the usr.format property to inform the receiving application that the message is XML data. First, set up the property name.
PropertyName = 'format'; PropertyValue = 'xml'; PropName.VCHRP = %ADDR(PropertyName : *DATA); PropName.VCHRL = %LEN(PropertyName);
Note: If you do not qualify a property name, it will default to the 'usr' folder.
Then, you just need to call
MQSETMP, specifying all the
MQSETMP(HConn : HMsg : MQSMPO : PropName : MQPD : TYPSTR : %LEN(PropertyValue) : %ADDR(PropertyValue : *DATA) : CompletionCode : Reason);
At this point, you've created a message handle and set the
usr.format property to
xml, but what message has
received this property? The answer is that you haven't actually set this
property on an actual message yet. All you've done is allocated a message
handle that refers to an area of storage within WebSphere MQ which holds
the message properties. When you put a message, you can tell WebSphere MQ
to add those properties to the message you are putting. The only thing you
must do for this to happen is to set the message handle field to the
message handle you got from
MQCRTMH and tell WebSphere MQ
that you are using a version 3
MQPMO (so that WebSphere MQ
knows that the message handle field is defined).
MQPMO.PMVER = PMVER3; MQPMO.PMOMH = Hmsg;
Now, just do an
MQPUT like normal and the message properties
will be added to the message. Under the covers, WebSphere MQ will read the
properties from the message handle and generate the RFH2 header for you.
You can easily verify that everything worked by using IBM WebSphere MQ
Explorer or the
WRKMQMQ system command. MQ Explorer is an
Eclipse-based graphical tool that enables you to explore and configure all
WebSphere MQ objects and resources from your Microsoft® Windows®
or Linux® PC. It is included with the MQ server installation and is
also available separately in the MS0T SupportPac. To view in MQ Explorer, expand the queue manager
and click Queues. You can then right-click the queue and
click Browse Messages. Find the message in the list to
inspect and right-click it and then click Properties.
When you select Named Properties in the left pane you can
see the properties as shown in Figure 1.
Figure 1: MQ Explorer
MQSETMP, which makes it easier to set message properties,
there is also
MQINQMP to retrieve the value of a specific
message property or even use wildcards to fetch the value of multiple
properties. A prototype is shown in Example 2.
Example 2: MQINQMP procedure definition from CMQG
DMQINQMP PR EXTPROC('MQINQMP') D* Connection handle D HCONN 10I 0 VALUE D* Message handle D HMSG 20I 0 VALUE D* Options that control the action of MQINQMP (MQIMPO) D INQOPT 72A D* Property name (MQCHARV) D PRNAME 32A D* Property descriptor (MQPD) D PRPDSC 24A D* Property data type D TYPE 10I 0 D* Length in bytes of the Value area D VALLEN 10I 0 VALUE D* Property value D VALUE * VALUE D* Length of the property value D DATLEN 10I 0 D* Completion code D CMPCOD 10I 0 D* Reason code qualifying CompCode D REASON 10I 0
The only real difference from
MQSETMP is that you use an
MQIMPO instead of
MQINQMP, you first create a message handle like above
and pass it in the
MQGMO. The only other trick you need is to
tell WebSphere MQ that you want the message properties returned in the
message handle and not in an RFH2 header.
MQGMO.GMVER = GMVER4; MQGMO.GMMH = Hmsg; MQGMO.GMOPT += GMPRIH; // return message properties in handle MQIMPO.IPOPT = IPINQN + // iterate over properties IPCTYP + // convert type if necessary IPCVAL; // convert value into native CCSID PropQuery = 'usr.%'; PropName.VCHRP = %ADDR(PropQuery : *DATA); PropName.VCHRL = %LEN(PropQuery); MQIMPO.IPRETNAMCHRP = %ADDR(PropertyName : *DATA); MQIMPO.IPRETNAMVSBS = PropNameMax; MQINQMP(HConn : HMsg : MQIMPO : PropName : MQPD : PropertyType : PropValueMax : %ADDR(PropertyValue : *DATA) : ActPropLength : CompletionCode : Reason); %LEN(PropertyValue) = ActPropLength; %LEN(PropertyName) = MQIMPO.IPRETNAMCHRL;
Here, you use the query of
usr.% to retrieve all the
properties in the
usr folder. After the call to
PropertyName contains the name of the
first user property found and
PropertyValue contains its
value. After you have processed this property, you can call
MQINQMP again to retrieve the next property that matched the
query. Eventually, there will be no more properties and WebSphere MQ will
set a completion code of 1 and a reason code 2471
With the advent of the new message property functions in WebSphere MQ 7.0, it is now much easier to deal with message properties within ILE applications. No longer does an application need to handle parsing RFH2 headers, deal with XML, or deal with character conversion using iconv to get or set message properties. This article has shown how to make use of these new APIs in your applications. Full examples can be found in the AMQ3IQM4 and AMQ3STM4 samples included with WebSphere MQ 7.1. These samples are also included in WebSphere MQ 18.104.22.168 and later fix packs.
- Find more information about Message Properties, MQSETMP, and MQINQMP in the WebSphere MQ Information Center.
- SupportPac MS0T download
- IBM i developerWorks forum