02
Sat, Nov
2 New Articles
  1. You are here:  
  2. Home
  3. Programming
  4. Programming - Other
  5. General
  6. iSockets for Web Services

iSockets for Web Services

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

With the advent of V5R4, RPG IV can be used to do basic parsing of XML natively. The new XML-INTO opcode, while not strictly intuitive, can easily be used to extract pieces of data from XML.

So where do you get XML? One place is from Web services. But just what is a Web service? Before we look at that, let's review a primary candidate for a Web services routine: shipment tracking.

Let's assume you need to get the tracking information for a package you've shipped. You go to the shipper's Web site and enter the tracking number, and the package delivery status is displayed. This is accomplished though the Web site via a CGI script (or program) that generates the tracking information and writes it out to a Web page.

What if you could get that tracking information into your RPG IV program? That way, you could give your customer service people the ability to report to your customers the current location of their orders.

Web services can be anything, but fundamentally they are CGI programs that return data in a known format. Rather than behaving like typical CGI programs and returning data formatted with HTML, Web services routines return data in other formats. Typically, this means XML, but it can be any defined format.

Accessing a Web services routine with RPG IV can be complicated. Consider that when you're online via a Web browser, the browser reads and renders CGI program responses, and simulating a browser in RPG IV, for example, can be challenging.

To call Web service routines, you need to use either a service program of routines that makes doing HTTP calls easier or TCP/IP and sockets programming APIs.

The free iSockets service program allows you to easily call CGI and Web services from within RPG IV. In fact, it was created specifically for this purpose.

The iSockets routines that simplify calls to Web Services are PostURLData and GetURLData. The PostURLData procedure uses the CGI POST method to send the request, whereas the GetURLData procedure uses the CGI GET method to send the request. Other than that, they are similar. Most Web services require you to use POST or GET and fail if you use the wrong one. So make sure you know which method your Web service requires.

To illustrate a call to a Web service routine, I found a Web service that converts Celsius to Fahrenheit. You pass in degrees Celsius, and it returns degrees Fahrenheit. For example, if you send it 36 degrees Celsius, it'll return the following data:


97 

If you look at the above XML, you'll notice that buried in that mess is the number 97, which is the converted degrees in Fahrenheit.

The element named "short" identifies the converted value. The namespace is not really relevant to anything, so we can ignore it.

To retrieve this information into our own RPG IV program, we need to call the iSockets PostURLData procedure and specify the Web services program. Here's an example:

      /copy ISOCKETS/QCPYSRC,ISOCKETS
     D szDomain        S            128A   Varying 
     D                                     Inz('www.w3schools.com')
     D WebService      S            128A   Varying 
     D                                     Inz('/webservices/tempconvert.asmx+
     D                                          /CelsiusToFahrenheit')
     D szFormData      S             64A   Varying 
     D                                     Inz('Celsius=')
     D nCelsius        S             10I 0 Inz(36)
     D szHtml          S           4096A
                  
     C                   eval      szFormData = szFormData + %char(nCelsius)
     C                   eval      nBytes=PostUrldata(szDomain:
     C                                        szWebService : szFormData :
     C                                        %addr(szHtml) : %size(szHtml))

The above program calls a Web services program on www.w3schools.com and passes 'Celsius=36' to the Web services program. Upon completion of the process, the field named szHtml contains the response data from the Web services program. This includes any HTTP response headers.

Normally, HTTP response headers are discarded once you verify that you received the proper response. (If something else is returned, you have to decide what you want to do about it.) iSockets includes the ParseHttpReply procedure to detect the HTTP response header and return the location of the actual data you need to use in your RPG IV program.

The following code adds this capability to the previous example:

     D nBytes          S             10I 0 
     D nDataPos        S             10I 0 
     D nLen            S             10I 0 
     D nCelsius        S             10I 0 Inz(36)
     D nFahren         S             10I 0 
     C                   if         nBytes > 0
     C                   eval       nDataPos = ParseHTTPReply(pHTML:nBytes)
     C                   eval       nLen = nBytes-(nDataPos-1)
     C                   callp      Joblog(%subst(szHtml:nDataPos:nLen))
     C                   endif

      **  If compiling on V5R4, then we can use XML-INTO to parse
      **  the XML response.
      /IF DEFINED(*V5R4M0)
     C                   XML-INTO   nFahren %xml(%subst(szHtml:nDataPos: nLen):
     C                                       'path=short allowextra=yes')
     C                   callp      joblog('%s Fahrenheit is %s Celsius':
     C                                      %char(nFahren) : %char(nCelsius))
      /ENDIF

Upon completion of the XML-INTO opcode, the nFahren variable contains the value 97, which is extracted from the returned XML. Note the 'path=short' option on the %XML built-in function of the XML-INTO opcode. This option indicates which XML element should be extracted. Since this Web server returns the tag that contains the returned degrees value, that is the element we need to extract. If we had not specified 'path=short', then %XML would default to the element name nFahren (same as the return value name). Also, since this Web service returns a namespace element, we need to include the 'allowextra=yes' option; otherwise, we would get a runtime error as %XML attempts to copy the value of the namespace to a variable that we haven't specified.

This is just a taste of how RPG IV can use iSockets to easily access Web services and process the results using XML-INTO.

Bob Cozzi is a programmer/consultant, writer/author, and software developer of the RPG xTools, a popular add-on subprocedure library for RPG IV. His book The Modern RPG Language has been the most widely used RPG programming book for nearly two decades. He, along with others, speaks at and runs the highly-popular RPG World conference for RPG programmers.

BOB COZZI

Bob Cozzi is a programmer/consultant, writer/author, and software developer. His popular RPG xTools add-on subprocedure library for RPG IV is fast becoming a standard with RPG developers. His book The Modern RPG Language has been the most widely used RPG programming book for more than a decade. He, along with others, speaks at and produces the highly popular RPG World conference for RPG programmers.

MC Press books written by Robert Cozzi available now on the MC Press Bookstore.

RPG TnT RPG TnT
Get this jam-packed resource of quick, easy-to-implement RPG tips!
List Price $65.00

Now On Sale

The Modern RPG IV Language The Modern RPG IV Language
 Cozzi on everything RPG! What more could you want?
List Price $99.95

Now On Sale
BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

$

Book Reviews

Resource Center

  • SB Profound WC 5536 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. You can find Part 1 here. In Part 2 of our free Node.js Webinar Series, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Brian will briefly discuss the different tools available, and demonstrate his preferred setup for Node development on IBM i or any platform. Attend this webinar to learn:

  • 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 company are not aligned with the current IT environment.

  • SB HelpSystems ROBOT Generic IBM announced the E1080 servers using the latest Power10 processor in September 2021. The most powerful processor from IBM to date, Power10 is designed to handle the demands of doing business in today’s high-tech atmosphere, including running cloud applications, supporting big data, and managing AI workloads. But what does Power10 mean for your data center? In this recorded webinar, IBMers Dan Sundt and Dylan Boday join IBM Power Champion Tom Huntington for a discussion on why Power10 technology is the right strategic investment if you run IBM i, AIX, or Linux. In this action-packed hour, Tom will share trends from the IBM i and AIX user communities while Dan and Dylan dive into the tech specs for key hardware, including:

  • Magic MarkTRY 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. Make sure your data survives when catastrophe hits. Request your trial now!  Request Now.

  • SB HelpSystems ROBOT GenericForms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.

  • SB HelpSystems ROBOT GenericIT security is a top priority for businesses around the world, but most IBM i pros don’t know where to begin—and most cybersecurity experts don’t know IBM i. In this session, Robin Tatam explores the business impact of lax IBM i security, the top vulnerabilities putting IBM i at risk, and the steps you can take to protect your organization. If you’re looking to avoid unexpected downtime or corrupted data, you don’t want to miss this session.

  • SB HelpSystems ROBOT GenericCan you trust all of your users all of the time? A typical end user receives 16 malicious emails each month, but only 17 percent of these phishing campaigns are reported to IT. Once an attack is underway, most organizations won’t discover the breach until six months later. A staggering amount of damage can occur in that time. Despite these risks, 93 percent of organizations are leaving their IBM i systems vulnerable to cybercrime. In this on-demand webinar, IBM i security experts Robin Tatam and Sandi Moore will reveal:

  • FORTRA Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) 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:

  • FORTRAManaging messages on your IBM i can be more than a full-time job if you have to do it manually. Messages need a response and resources must be monitored—often over multiple systems and across platforms. 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:

  • FORTRAThe thought of printing, distributing, and storing iSeries reports manually may reduce you to tears. Paper and labor costs associated with report generation can spiral out of control. Mountains of paper threaten to swamp your files. Robot 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:

  • FORTRAFor over 30 years, Robot has been a leader in systems management for IBM i. With batch job creation and scheduling at its core, the Robot Job Scheduling Solution reduces the opportunity for human error and helps you maintain service levels, automating even the biggest, most complex runbooks. Manage your job schedule with the Robot Job Scheduling Solution. Key features include:

  • LANSA Business 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.

  • 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:

  • LANSASupply Chain is becoming increasingly complex and unpredictable. From raw materials for manufacturing to food supply chains, the journey from source to production to delivery to consumers is marred with inefficiencies, manual processes, shortages, recalls, counterfeits, and scandals. In this webinar, we discuss how:

  • The MC Resource Centers bring you the widest selection of white papers, trial software, and on-demand webcasts for you to choose from. >> Review the list of White Papers, Trial Software or On-Demand Webcast at the MC Press Resource Center. >> Add the items to yru Cart and complet he checkout process and submit

  • Profound Logic 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.

  • SB Profound WC 5536Join us for this hour-long webcast that will explore:

  • Fortra IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? 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: