Sidebar

Practical RPG: APIs, Part 3 - Complex Parameters

RPG
Typography
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times

As the APIs become more powerful, they need more complex parameters to control their behavior, and this article shows how to build those complex parameters.

Previous articles in this series have provided direction on how to call an API and how to return errors, but the API interface has been pretty simple. In this installment we're going to look at an API with one of the more complex parameters and learn how we can use all the power of ILE RPG to help us define that parameter.

Retrieve Journal Entries (QjoRetrieveJournalEntries)

If you use journals, you're familiar the DSPJRN command, which takes a wide variety of parameters. These include the receiver range, starting timestamp, ending timestamp, journal codes, journal entry types, and so on. And while this command provides a great deal of flexibility, it isn't always ideal for what we need when trying to analyze journal activity. As a very simple case, if you want to check for activity from a list of programs, you have to run DSPJRN once for each program name. This isn't very efficient.

The better solution is to use the Retrieve Journal Entries API (QjoRetrieveJournalEntries) to spin through all the journal entries (or at least a more inclusive subset) under program control and do the filtering yourself. And that's where we run into the idea of the "variable record" parameter.

Let's start by going to the IBM web page for the QjoRetrieveJournalEntries API. This page has a lot of information, starting with the parameter list.

Practical RPG: APIs, Part 3 - Complex Parameters - Figure 1

Figure 1: This is the parameter list for the QjoRetrieveJournalEntries API.

You'll see that there is a required parameter group and an optional group; this is very common among IBM APIs. We'll be diving more into these parameters in a subsequent article, but for today we're just going to focus on one parameter in particular, the "Journal entries to receive" parameter. This parameter is used to identify the selection criteria for entries to be retrieved from the journal. It uses the variable-length record concept to specify multiple filters.

Variable-Length Record Parameters

The concept of a variable-length record parameter is simple: The parameter is a data structure where the first four bytes identify the number of records in the rest of the data structure. Each record has a specific structure, which starts with the length of that record.

Practical RPG: APIs, Part 3 - Complex Parameters - Figure 2

Figure 2: Each variable-length record has this layout.

The structure is quite rigid right up until the last value, the actual data. Each of the first three values is a 4-byte integer (specified as int(10) in RPG). The first is the length of the entire record, the second is a key identifying what kind of data is in the record, and the third is the length of the data. It's hard to really express how these values work in words, so let's take a look at an example.

Practical RPG: APIs, Part 3 - Complex Parameters - Figure 3

Figure 3: A variable-length record parameter with two records looks like this.

The header is just an integer with a value of 2. This tells the API there are two variable-length records to follow. The first one is a type 1 record, which is used to specify the receiver range. That data consists of four 10-character components (what they are isn't important yet), so the third integer, Data Len, is set to 40. The second integer is set to 1 since, as we noted, this is a type 1 record. That leaves the first value, which is 52. That makes sense because the entire record consists of 40 characters of data and three 4-byte integers, for a total of 52 bytes.

The next record is very similar, except the data is only 26 characters (long enough to hold the character value of the starting timestamp), and thus the first and third values are 38 and 26, respectively. The second integer is set to 3 to indicate this is a type 3 record, a FROMTIME record. (All these types are defined on the same web page.)

These records each butt up against one another to make a complete parameter. The length of the entire parameter in this case is 94 bytes total. So now it's time to see how these are defined in an RPG program.

Using Data Structures to Defined Variable Length Records

What I like about using ILE RPG to call this API is how I can take advantage of data structures to build the selection parameter component by component. The following code shows the free-format RPG code used to define the header and the two data structures depicted in Figure 3.

// Retrieve journal entry selection records    

dcl-ds JrnEntRtv qualified;                                  

  NbrVarRcd int(10);                                        

end-ds;                                                      

                                                            

// RCVRNG - *CURCHAIN - Reset this to get first entry in chain

dcl-ds JrnVarR01 qualified;                                  

RcdLen int(10) inz( %size(JrnVarR01));                    

Key int(10) inz(1);                                        

DtaLen int(10) inz( %size(JrnVarR01.Dta));                

Dta char(40) inz( '*CURCHAIN' );                          

   RcvStr char(10) overlay(Dta);                            

   LibStr char(10) overlay(Dta: *next);                    

   RcvEnd char(10) overlay(Dta: *next);                    

   LibEnd char(10) overlay(Dta: *next);                    

end-ds;                                                      

JrnEntRtv is the header, while JrnVarR01 and JrnVarR03 are the definitions for the type 1 and type 3 variable-length records, respectively. All of them use qualified data structures. While not perhaps strictly necessary for the header, using qualified data structures is critical for the variable-length records because they all use the same names for the first four fields (RcdLen, Key, DtaLen, and Dta). Remember, these all use the same basic structure as shown in Figure 2. Note how we use a self-referential INZ keyword on the length fields to initialize their values.

If you compare the two data structures JrnVarR01 and JrnVarR03, you'll see that the Dta field in JrnVarR03 is very simple; it's just a 26-character field that will be initialized later. But for the JrnVarR01 field, you'll see that the Dta field has subfields defined using the OVERLAY keyword as well as the entire field being initialized to the value *CURCHAIN. That's because you can specify a receiver range by specifying the name and library of both the start and end of the range, or you can use the special value *CURCHAIN with the rest of the field blank to select the entire range. We define the data structure to allow both syntax variations because we'll need them when we're processing the journal in a loop.

Calling the API

To call the API, we need (as always) two things: the prototype and the code that calls the prototype.

dcl-pr RtvJrnE extproc( 'QjoRetrieveJournalEntries');  

RjRcvVar     char(32767) options(*varsize);          

RjRcvVarLen int(10)     const;                      

RjRcvJrnNamQ char(20)   const;                      

RjRcvInfFmt char(8)     const;                      

RjSltInf     char(32767) options(*omit:*varsize) const;

RjError     char(32767) options(*omit:*varsize);    

end-pr;                                                

The prototype is simple; it matches the definition of the API found in Figure 1. We can have some discussion on *VARSIZE and *OMIT at a later date, but this prototype will work as needed. The one thing that's probably most interesting is the fact that we use CONST on the RjSltInf parameter. This is the place where our variable-length records go, and it's important to define it as a CONST for reasons that will become immediately apparent.

// Number of selection criteria = 2                      

// 1. Receiver range (type 1)                              

// 2. Starting timestamp (type 3)                          

JrnEntRtv.NbrVarRcd = 2;  

// RESET sets the DS back to *CURCHAIN                      

reset JrnVarR01;                                            

// Set the timestamp back three days from today

JrnVarR03.Dta = %char(%timestamp() - %days(3));          

                                                            

// Use ApiError1, returns the message ID                    

reset ApiError1;                                            

                                                            

RtvJrnE( JeRcvVar : %Size( JeRcvVar ) : iJrnLib : 'RJNE0200':

         JrnEntRtv + JrnVarR01 + JrnVarR03: ApiError1);  

This is the actual call. I'll be happy to spend plenty of time on this and other code in the utility in another article, but for today I really just want to talk about how the records are initialized and then sent to the API. First, the initialization. We set the NbrVarRcd parameter to 2 to indicate that there are two variable-length records. We reset JrnVarR01 so that it's initialized to *CURCHAIN, and we compute the Dta field in JrnVarR03 to be three days prior to right now. We reset the error API (you can review how that works in the first article in the series) and call the API.

The call to the API is the really cool thing. Because the API uses the length of each record to find the start of the next, I just string them together: JrnEntRtv + JrnVarR01 + JrnVarR03. If I had more records, I could just add them to that expression (making sure, of course, to set the NbrVarRcd field accordingly).

Imagine how hard this would be to create as a single data structure, especially if you needed to include different records on different calls to the API. This technique of concatenating multiple individual data structures into a single parameter has made this API eminently accessible to me, and with any luck I can pass that to you.

In closing, I would like to once again point out that my work here is built upon the pioneering efforts of Carsten Flensberg, available on his website, API - My My.

Joe Pluta

Joe Pluta is the founder and chief architect of Pluta Brothers Design, Inc. He has been extending the IBM midrange since the days of the IBM System/3. Joe uses WebSphere extensively, especially as the base for PSC/400, the only product that can move your legacy systems to the Web using simple green-screen commands. He has written several books, including Developing Web 2.0 Applications with EGL for IBM i, E-Deployment: The Fastest Path to the Web, Eclipse: Step by Step, and WDSC: Step by Step. Joe performs onsite mentoring and speaks at user groups around the country. You can reach him at joepluta@plutabrothers.com.


MC Press books written by Joe Pluta available now on the MC Press Bookstore.

Developing Web 2.0 Applications with EGL for IBM i Developing Web 2.0 Applications with EGL for IBM i
Joe Pluta introduces you to EGL Rich UI and IBM’s Rational Developer for the IBM i platform.
List Price $39.95

Now On Sale

WDSC: Step by Step WDSC: Step by Step
Discover incredibly powerful WDSC with this easy-to-understand yet thorough introduction.
List Price $74.95

Now On Sale

Eclipse: Step by Step Eclipse: Step by Step
Quickly get up to speed and productivity using Eclipse.
List Price $59.00

Now On Sale

More Articles By This Author
Related Articles
BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

RESOURCE CENTER

  • WHITE PAPERS

  • WEBCAST

  • TRIAL SOFTWARE

  • White Paper: Node.js for Enterprise IBM i Modernization

    SB Profound WP 5539

    If your business is thinking about modernizing your legacy IBM i (also known as AS/400 or iSeries) applications, you will want to read this white paper first!

    Download this paper and learn how Node.js can ensure that you:
    - Modernize on-time and budget - no more lengthy, costly, disruptive app rewrites!
    - Retain your IBM i systems of record
    - Find and hire new development talent
    - Integrate new Node.js applications with your existing RPG, Java, .Net, and PHP apps
    - Extend your IBM i capabilties to include Watson API, Cloud, and Internet of Things


    Read Node.js for Enterprise IBM i Modernization Now!

     

  • Profound Logic Solution Guide

    SB Profound WP 5539More than ever, there is a demand for IT to deliver innovation.
    Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects.
    The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the companyare not aligned with the current IT environment.

    Get your copy of this important guide today!

     

  • 2022 IBM i Marketplace Survey Results

    Fortra2022 marks the eighth edition of the IBM i Marketplace Survey Results. Each year, Fortra captures data on how businesses use the IBM i platform and the IT and cybersecurity initiatives it supports.

    Over the years, this survey has become a true industry benchmark, revealing to readers the trends that are shaping and driving the market and providing insight into what the future may bring for this technology.

  • Brunswick bowls a perfect 300 with LANSA!

    FortraBrunswick is the leader in bowling products, services, and industry expertise for the development and renovation of new and existing bowling centers and mixed-use recreation facilities across the entertainment industry. However, the lifeblood of Brunswick’s capital equipment business was running on a 15-year-old software application written in Visual Basic 6 (VB6) with a SQL Server back-end. The application was at the end of its life and needed to be replaced.
    With the help of Visual LANSA, they found an easy-to-use, long-term platform that enabled their team to collaborate, innovate, and integrate with existing systems and databases within a single platform.
    Read the case study to learn how they achieved success and increased the speed of development by 30% with Visual LANSA.

     

  • Progressive Web Apps: Create a Universal Experience Across All Devices

    LANSAProgressive Web Apps allow you to reach anyone, anywhere, and on any device with a single unified codebase. This means that your applications—regardless of browser, device, or platform—instantly become more reliable and consistent. They are the present and future of application development, and more and more businesses are catching on.
    Download this whitepaper and learn:

    • How PWAs support fast application development and streamline DevOps
    • How to give your business a competitive edge using PWAs
    • What makes progressive web apps so versatile, both online and offline

     

     

  • The Power of Coding in a Low-Code Solution

    LANSAWhen it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed.
    Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

    • Discover the benefits of Low-code's quick application creation
    • Understand the differences in model-based and language-based Low-Code platforms
    • Explore the strengths of LANSA's Low-Code Solution to Low-Code’s biggest drawbacks

     

     

  • Why Migrate When You Can Modernize?

    LANSABusiness users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.
    In this white paper, you’ll learn how to think of these issues as opportunities rather than problems. We’ll explore motivations to migrate or modernize, their risks and considerations you should be aware of before embarking on a (migration or modernization) project.
    Lastly, we’ll discuss how modernizing IBM i applications with optimized business workflows, integration with other technologies and new mobile and web user interfaces will enable IT – and the business – to experience time-added value and much more.

     

  • UPDATED: Developer Kit: Making a Business Case for Modernization and Beyond

    Profound Logic Software, Inc.Having trouble getting management approval for modernization projects? The problem may be you're not speaking enough "business" to them.

    This Developer Kit provides you study-backed data and a ready-to-use business case template to help get your very next development project approved!

  • What to Do When Your AS/400 Talent Retires

    FortraIT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators is small.

    This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn:

    • Why IBM i skills depletion is a top concern
    • How leading organizations are coping
    • Where automation will make the biggest impact

     

  • Node.js on IBM i Webinar Series Pt. 2: Setting Up Your Development Tools

    Profound Logic Software, Inc.Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application. In Part 2, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Attend this webinar to learn:

    • Different tools to develop Node.js applications on IBM i
    • Debugging Node.js
    • The basics of Git and tools to help those new to it
    • Using NodeRun.com as a pre-built development environment

     

     

  • Expert Tips for IBM i Security: Beyond the Basics

    SB PowerTech WC GenericIn this session, IBM i security expert Robin Tatam provides a quick recap of IBM i security basics and guides you through some advanced cybersecurity techniques that can help you take data protection to the next level. Robin will cover:

    • Reducing the risk posed by special authorities
    • Establishing object-level security
    • Overseeing user actions and data access

    Don't miss this chance to take your knowledge of IBM i security beyond the basics.

     

     

  • 5 IBM i Security Quick Wins

    SB PowerTech WC GenericIn today’s threat landscape, upper management is laser-focused on cybersecurity. You need to make progress in securing your systems—and make it fast.
    There’s no shortage of actions you could take, but what tactics will actually deliver the results you need? And how can you find a security strategy that fits your budget and time constraints?
    Join top IBM i security expert Robin Tatam as he outlines the five fastest and most impactful changes you can make to strengthen IBM i security this year.
    Your system didn’t become unsecure overnight and you won’t be able to turn it around overnight either. But quick wins are possible with IBM i security, and Robin Tatam will show you how to achieve them.

  • Security Bulletin: Malware Infection Discovered on IBM i Server!

    SB PowerTech WC GenericMalicious programs can bring entire businesses to their knees—and IBM i shops are not immune. It’s critical to grasp the true impact malware can have on IBM i and the network that connects to it. Attend this webinar to gain a thorough understanding of the relationships between:

    • Viruses, native objects, and the integrated file system (IFS)
    • Power Systems and Windows-based viruses and malware
    • PC-based anti-virus scanning versus native IBM i scanning

    There are a number of ways you can minimize your exposure to viruses. IBM i security expert Sandi Moore explains the facts, including how to ensure you're fully protected and compliant with regulations such as PCI.

     

     

  • Encryption on IBM i Simplified

    SB PowerTech WC GenericDB2 Field Procedures (FieldProcs) were introduced in IBM i 7.1 and have greatly simplified encryption, often without requiring any application changes. Now you can quickly encrypt sensitive data on the IBM i including PII, PCI, PHI data in your physical files and tables.
    Watch this webinar to learn how you can quickly implement encryption on the IBM i. During the webinar, security expert Robin Tatam will show you how to:

    • Use Field Procedures to automate encryption and decryption
    • Restrict and mask field level access by user or group
    • Meet compliance requirements with effective key management and audit trails

     

  • Lessons Learned from IBM i Cyber Attacks

    SB PowerTech WC GenericDespite the many options IBM has provided to protect your systems and data, many organizations still struggle to apply appropriate security controls.
    In this webinar, you'll get insight into how the criminals accessed these systems, the fallout from these attacks, and how the incidents could have been avoided by following security best practices.

    • Learn which security gaps cyber criminals love most
    • Find out how other IBM i organizations have fallen victim
    • Get the details on policies and processes you can implement to protect your organization, even when staff works from home

    You will learn the steps you can take to avoid the mistakes made in these examples, as well as other inadequate and misconfigured settings that put businesses at risk.

     

     

  • The Power of Coding in a Low-Code Solution

    SB PowerTech WC GenericWhen it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed.
    Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

    • Discover the benefits of Low-code's quick application creation
    • Understand the differences in model-based and language-based Low-Code platforms
    • Explore the strengths of LANSA's Low-Code Solution to Low-Code’s biggest drawbacks

     

     

  • Node Webinar Series Pt. 1: The World of Node.js on IBM i

    SB Profound WC GenericHave you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application.
    Part 1 will teach you what Node.js is, why it's a great option for IBM i shops, and how to take advantage of the ecosystem surrounding Node.
    In addition to background information, our Director of Product Development Scott Klement will demonstrate applications that take advantage of the Node Package Manager (npm).
    Watch Now.

  • The Biggest Mistakes in IBM i Security

    SB Profound WC Generic The Biggest Mistakes in IBM i Security
    Here’s the harsh reality: cybersecurity pros have to get their jobs right every single day, while an attacker only has to succeed once to do incredible damage.
    Whether that’s thousands of exposed records, millions of dollars in fines and legal fees, or diminished share value, it’s easy to judge organizations that fall victim. IBM i enjoys an enviable reputation for security, but no system is impervious to mistakes.
    Join this webinar to learn about the biggest errors made when securing a Power Systems server.
    This knowledge is critical for ensuring integrity of your application data and preventing you from becoming the next Equifax. It’s also essential for complying with all formal regulations, including SOX, PCI, GDPR, and HIPAA
    Watch Now.

  • Comply in 5! Well, actually UNDER 5 minutes!!

    SB CYBRA PPL 5382

    TRY the one package that solves all your document design and printing challenges on all your platforms.

    Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product.

    Request your trial now!

  • Backup and Recovery on IBM i: Your Strategy for the Unexpected

    FortraRobot automates the routine tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:
    - Simplified backup procedures
    - Easy data encryption
    - Save media management
    - Guided restoration
    - Seamless product integration
    Make sure your data survives when catastrophe hits. Try the Robot Backup and Recovery Solution FREE for 30 days.

  • Manage IBM i Messages by Exception with Robot

    SB HelpSystems SC 5413Managing messages on your IBM i can be more than a full-time job if you have to do it manually. How can you be sure you won’t miss important system events?
    Automate your message center with the Robot Message Management Solution. Key features include:
    - Automated message management
    - Tailored notifications and automatic escalation
    - System-wide control of your IBM i partitions
    - Two-way system notifications from your mobile device
    - Seamless product integration
    Try the Robot Message Management Solution FREE for 30 days.

  • Easiest Way to Save Money? Stop Printing IBM i Reports

    FortraRobot automates report bursting, distribution, bundling, and archiving, and offers secure, selective online report viewing.
    Manage your reports with the Robot Report Management Solution. Key features include:

    - Automated report distribution
    - View online without delay
    - Browser interface to make notes
    - Custom retention capabilities
    - Seamless product integration
    Rerun another report? Never again. Try the Robot Report Management Solution FREE for 30 days.

  • Hassle-Free IBM i Operations around the Clock

    SB HelpSystems SC 5413For over 30 years, Robot has been a leader in systems management for IBM i.
    Manage your job schedule with the Robot Job Scheduling Solution. Key features include:
    - Automated batch, interactive, and cross-platform scheduling
    - Event-driven dependency processing
    - Centralized monitoring and reporting
    - Audit log and ready-to-use reports
    - Seamless product integration
    Scale your software, not your staff. Try the Robot Job Scheduling Solution FREE for 30 days.