TweetFollow Us on Twitter

CGI Programming with REALbasic and Apache

Volume Number: 20 (2004)
Issue Number: 6
Column Tag: Programming

CGI Programming with REALbasic and Apache

by Mark Choate

With the recent release of REALbasic 5.5, RB has become an excellent tool to use for web development. The most recent version sports improved networking features and support for XML (including XSLT and Xquery), plus the ability to compile command-line applications, called console applications in REALbasic. Perhaps most interesting is the ability to compile applications for use on Windows and Linux, in addition to Macintosh platforms.

Traditionally, Mac web servers communicated with CGI applications through Apple events. This doesn't work with Apache, however, so a CGI application needs to be able to be able to receive information from the server in the normal CGI way - through environment variables. This article illustrates the steps necessary to implement this in REALbasic. One important thing to note: since many of the features that enable CGI programming in REALbasic are new, the current release (5.5.1) has some bugs, which I have had to work around. Some may be fixed by the time this article is released, but hopefully this will save you some time for those that have not been fixed.

The first step will be to review CGI programming for those who aren't familiar with it. CGI stands for the common gateway interface. It's called an interface because it provides the means for Apache (or any web server that supports CGI) to execute scripts and applications on the host machine of a web server. When a user types a URL into his or her web browser, that URL often represents the location of an HTML file that the server just picks up and sends back to the browser. In a CGI program, the URL represents a script or a program that gets executed. The output of the program then gets sent back to the user. In order to provide security, Apache allows the administrator to configure which directories allow CGI programs to be executed. On OS X the cgi-bin directory is here:

/Library/WebServer/CGI-Executables

This article assumes that you haven't made any changes to the default Apache configuration that comes with OS X. The configuration file that Apache uses is available at /etc/ httpd/http.conf. If you have never modified this file, now is not a good time to start - but you shouldn't need to. It's worth taking a look at it just to make sure that CGI is set up properly. My httpd.conf file has this, about 2/3 of the way through the document:

    # ScriptAlias: This controls which directories contain server scripts.
    # ScriptAliases are essentially the same as Aliases, except that
    # documents in the realname directory are treated as applications and
    # run by the server when requested rather than as documents sent to the client.
    # The same rules about trailing "/" apply to ScriptAlias directives as to
    # Alias.
    #
    ScriptAlias /cgi-bin/ "/Library/WebServer/CGI-Executables/"

The last line indicates two things. "/cgi-bin/" is going to be part of the URL for the CGI application - something like: http://localhost/cgi-bin/ plus the name of your script. The second path is the absolute path for this directory on the server. For this example, we'll be placing our REALbasic CGI program in this directory. Sometimes you'll see CGI scripts that end with a ".cgi" extension, but we won't need to use that - in fact, you should avoid using any extensions because it will mess things up. Other scripting languages, like perl and Python, usually reside on the web server as text files that are executed by an interpreter. Apache uses extensions to map an interpreter to a particular file. Since REALbasic is a compiled program, it doesn't need an interpreter and it's better just to leave the extension off. It also provides for a much nicer URL, which is important, too.

Now we can start work on the program. The easiest way to work is to save the project in the CGI-Executables directory. This is because you'll need to compile the application in order to test it with Apache, and it's easier to just compile it and leave it there to test than it would be to compile it and copy it to the CGI directory.

In RB, a console application is one that does not have a graphical interface - it runs on the command line. In order to create a console application, simply create a new project in REALbasic 5.5+, and select the "Console Application" template. Once that is done, RB will provide you with the shell of an application with one class called "App".


Figure 1. Starting a new console application in REALbasic.

There are two default events in a console application - "UnhandledException" and "Run". The "Run" event is triggered when the program is launched - in the case of a CGI application, it is triggered when a user requests it by typing the application's URL in her web browser.


Figure 2. Blank console application project.

Now is a good time to select the FILE a Build Settings... menu and configure the application. Select "Build for OS X" (this program has only been tested on OS X, although it should work on other platforms as well. Click on the top popup menu on the page, and select "Mac OS Settings". The only thing to change here is the name - be sure to give it a name without an extension and without spaces or punctuation. In this example, I've chosen the name "CGI", which is short and easy to type into a browser window.

Once that is done, it's time to write some code.

Since console applications do not have a graphical interface, they have to be able to input data and output data in some other fashion. For programs that are executed on the command line, this is typically referred to as "Standard Input" and "Standard Output" respectively. With a REALbasic console application, the command "INPUT" represents (you guessed it) standard input. "PRINT" sends data to standard output. In addition to standard input and output, CGI applications also make use of environment variables that are set by the web server. In order to access environment variables, you need the system object, which includes the method: System.EnvironmentVariable(), which returns the value for the environment variable that is passed to it. In the current version (5.5.1) there is a bug that causes REALbasic to crash if you try to access a variable that does not exist. This places some real limitations on what you can do, but it is supposed to be fixed in 5.5.2.

The console application "App" class is where the action is. It has two events: "Run", and "UnhandledException". The "Run" event is triggered when the application is invoked by the web server, so it is in the "Run" event that we put the main part of our code. I also created a "request" object, which is created when the "Run" method is executed. It is a sub class of Dictionary and it is used to hold the data that is passed to the CGI application from Apache. It also executes a "Write" method, that sends data back to the client browser.

The "Run" method should look like this:

App.Run
#pragma disableBackgroundTasks 
  
request = new request
  
request.value("SERVER_SOFTWARE") = system.environmentVariable("SERVER_SOFTWARE")
request.value("SERVER_NAME") = system.environmentVariable("SERVER_NAME")
    
request.value("REQUEST_METHOD") = system.environmentVariable("REQUEST_METHOD")
    
request.value("QUERY_STRING") = system.environmentVariable("QUERY_STRING")
request.value("REMOTE_ADDR") = system.environmentVariable("REMOTE_ADDR")
    
request.getQueryString
request.handleRequest

Background tasks are disabled because Apache doesn't work well with them. If you don't disable them, every time you do a loop, or execute anything that triggers a new thread or background task, the application crashes mercilessly.

In this example, I have only gathered the minimal environment variables necessary to execute the program, because of the bug mentioned earlier. One notable environment variable missing is "HTTP_COOKIE", which is very useful if you use cookies, which provide a way to track a visitor to the site. A complete list of variables is included in the sample script, but commented out.

The two variables that matter most to use are "REQUEST_METHOD" and "QUERY_STRING". There are several kinds of requests a web server can accept. The two that concern us are "Post" requests and "Get" requests. The distinction between the two in actual practice is virtually non-existent, except that it changes the way that form data is passed to the CGI program.

Any time you fill out a form on a web page, either to log in or make a purchase, the information that you enter needs to be transferred to the server so that it can take some appropriate action. When you create a form in HTML, you have the option of selecting the request method you want to use - either "Get" or "Post". If you choose "Get", then the data from the form is encoded and sent across as part of the URL. If you use "Post", then the data is sent to the CGI program as standard input. Here is an example of a "Get" request URL:

http://localhost/cgi-bin/test?cat=dog

The first step in processing a CGI request is to find out what kind of request it is, and process it accordingly. In the request class, I have implemented the following method:

App.request.getQueryString
#pragma disableBackgroundTasks // Throws an error during the loop
  
  Dim query_string, field, key, value As String
  Dim x As Integer
  
  query = New Dictionary
//If the REQUEST_METHOD is a "post", then get the string from standard input, 
   otherwise get it from QUERY_STRING
  If me.hasKey("REQUEST_METHOD") then
    if me.value("REQUEST_METHOD") = "POST" Then
      query_string = Input
    Else
      query_string = System.EnvironmentVariable("QUERY_STRING")
    End If
  end if
  
  if query_string <> "" then
    //parse the query string
    For x = 1 to CountFields(query_string, "&")
      field = NthField(query_string, "&", x)
      key = NthField(field, "=", 1)
      value = NthField(field, "=", 2)
      value = ReplaceAll(value, "+", " ")
      value = DecodeURLComponent(value)
      query.value(key) = value
    Next
  end if
  

The method creates a new dictionary to hold the values of the query (the data from the form). If the request method is a "Post", then the method grabs the string from standard input. If it is a "Get", then it grabs it from the environment variable "QUERY_STRING". Beyond that, everything else is the same and the string is parsed and the dictionary values are set.

We now have a request object that contains all the needed values from the request, plus the query parsed into a dictionary. Normally, this would be sent to some method that would provide a response based upon the content of the query. For our example, we'll just send back to the client all the information stored in the request object.

To send data back to the client, we need to send some header information followed by an HTML string.

App.request.write
#pragma disableBackgroundTasks
  // simple write method that returns the data in the request.
  dim output as string
  dim html as string
  dim requestString, queryString as string  
  dim x,y as integer 
  
  // set the value for "Content-type", followed by a blank line
  output = "Content-type: text/html" + chr(13) + chr(10) + chr(13) + chr(10)
  
  // create the html string 
  html = "<html><head><title>TestOutput</title></head><body>"
  
  y = me.count
  for x = 0 to y-1
    requestString = requestString + me.key(x) + ": " + me.value(me.key(x)) + "<br />"
  next
  
  y = me.query.count
  for x = 0 to y-1
    queryString = queryString + me.query.key(x) + ": " + me.query.value(me.query.key(x)) + "<br />"
  next
  
  html = html + requestString + queryString + "</body></html>"
  
  output = output + html
  
  print output

If you placed the application in the /Library/WebServer/CGI-Executables directory, and set the application name as "CGI", then you should be able to access the script from the following URL:

Localhost/cgi-bin/CGI/CGI

You should be able to paste it in the browser, hit return, and then get back a list of the variables. If you want to test the query string, then enter a URL like the following:

Localhost/cgi-bin/CGI/CGI?key=value


Figure 3. Results of CGI application.

You now have a good starting point for writing CGI programs in REALbasic for Apache. One thing you'll notice, especially if you have a lot of traffic on your site, is that CGI can be slow at times. The reason for this is that the program has to be started up with each request, which produces a lot of overhead. The downside to RB is that it produces large executable files - about 1.3 MB for this simple CGI program, so the particular solution is best limited to low-traffic sites. Because of this, there have been a variety of CGI workarounds that speed up the process. They way they work is that instead of invoking the program each time it is requested, the program stays resident in memory and handles the requests as they come in. This is usually accomplished with an Apache plug-in. This is an interesting approach that can be used with REALbasic as well - and you don't need to rely on console programming.

I developed an RB application that worked with an Apache plug-in called "mod_scgi". Mod_scgi works by taking the data that Apache would normally send as environment variables to a CGI program, and instead sends it as a block of data over a TCP connection. Using REALbasic's networking abilities, you can create a SocketServer that creates a pool of TCPSockets that listen on the appropriate port, gets the data when it is available, parses it and acts on it just like a CGI program. As soon as the individual socket is done, instead of exiting, it returns to listening on the port for the next request. This creates a huge performance boost, and is a tactic that should be considered if you expect a lot of traffic to your site.

The original (and best) guide to CGI from the inventor's of Mosaic, NCSA:

http://hoohoo.ncsa.uiuc.edu/cgi/


Mark Choate

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

TechTool Pro 9.5.1 - Hard drive and syst...
TechTool Pro has long been one of the foremost utilities for keeping your Mac running smoothly and efficiently. With the release of version 9, it has become more proficient than ever. TechTool... Read more
Jamf Pro 9.99.0 - Powerful sysadmin/ente...
Jamf Pro (formerly Casper Suite) is the EMM tool that delights IT pros and the users they support by delivering on the promise of unified endpoint management for Apple devices. At Jamf, connecting... Read more
VueScan 9.5.78 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
Adobe Lightroom 6.10.1 - Import, develop...
Adobe Lightroom is available as part of Adobe Creative Cloud for as little as $9.99/month bundled with Photoshop CC as part of the photography package. Lightroom 6 is also available for purchase as a... Read more
iPhoto Library Manager 4.2.7 - Manage mu...
iPhoto Library Manager allows you to organize your photos among multiple iPhoto libraries, rather than having to store all of your photos in one giant library. You can browse the photos in all your... Read more
Smultron 9.4 - Easy-to-use, powerful tex...
Smultron 9 is an elegant and powerful text editor that is easy to use. Use it to create or edit any text document. Everything from a web page, a note or a script to any single piece of text or code.... Read more
TextSoap 8.4 - Automate tedious text doc...
TextSoap can automatically remove unwanted characters, fix up messed up carriage returns, and do pretty much anything else that we can think of to text. Save time and effort. Be more productive. Stop... Read more
Merlin Project 4.2.3 - $349.00
Merlin Project is the leading professional project management software for OS X. If you plan complex projects on your Mac, you won’t get far with a simple list of tasks. Good planning raises... Read more
QuarkXPress 13.0.0.0 - Desktop publishin...
QuarkXPress 2017 is the new version that raises the bar for design and productivity. With non-destructive graphics and image editing directly within your layout, you no longer have to choose between... Read more
Path Finder 7.5 - Powerful, award-winnin...
Path Finder makes you a master of file management. Take full control over your file system. Save your time: compare and synchronize folders, view hidden files, use Dual Pane and full keyboard... Read more

Latest Forum Discussions

See All

Zombie Gunship Survival Beginner's...
The much anticipated Zombie Gunship Survival is here. In this latest entry in the Zombie Gunship franchise, you're tasked with supporting ground troops and protecting your base from the zombie horde. There's a lot of rich base building fun, and... | Read more »
Mordheim: Warband Skirmish (Games)
Mordheim: Warband Skirmish 1.2.2 Device: iOS Universal Category: Games Price: $3.99, Version: 1.2.2 (iTunes) Description: Explore the ruins of the City of Mordheim, clash with other scavenging warbands and collect Wyrdstone -... | Read more »
Mordheim: Warband Skirmish brings tablet...
Legendary Games has just launched Mordheim: Warband Skirmish, a new turn-based action game for iOS and Android. | Read more »
Magikarp Jump splashes onto Android worl...
If you're tired ofPokémon GObut still want something to satisfy your mobilePokémon fix,Magikarp Jumpmay just do the trick. It's out now on Android devices the world over. While it looks like a simple arcade jumper, there's quite a bit more to it... | Read more »
Purrfectly charming open-world RPG Cat Q...
Cat Quest, an expansive open-world RPG from former Koei-Tecmo developers, got a new gameplay trailer today. The video showcases the combat and exploration features of this feline-themed RPG. Cat puns abound as you travel across a large map in a... | Read more »
Jaipur: A Card Game of Duels (Games)
Jaipur: A Card Game of Duels 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: ** WARNING: iPad 2, iPad Mini 1 & iPhone 4S are NOT compatible. ** *** Special Launch Price for a limited... | Read more »
Subdivision Infinity (Games)
Subdivision Infinity 1.03 Device: iOS Universal Category: Games Price: $2.99, Version: 1.03 (iTunes) Description: Launch sale! 40% Off! Subdivision Infinity is an immersive and pulse pounding sci-fi 3D space shooter. https://www.... | Read more »
Clash of Clans' gets a huge new upd...
Clash of Clans just got a massive new update, and that's not hyperbole. The update easily tacks on a whole new game's worth of content to the hit base building game. In the update, that mysterious boat on the edge of the map has been repaired and... | Read more »
Thimbleweed Park officially headed to iO...
Welp, it's official. Thimbleweed Park will be getting a mobile version. After lots of wondering and speculation, the developers confirmed it today. Thimbleweed Park will be available on both iOS and Android sometime in the near future. There's no... | Read more »
Pokémon GO might be getting legendaries...
The long-awaited legendary Pokémon may soon be coming to Pokémon GO at long last. Data miners have already discovered that the legendary birds, Articuno, Moltres, and Zapdos are already in the game, it’s just a matter of time. [Read more] | Read more »

Price Scanner via MacPrices.net

Huawei Unveils New ‘Business-Styled’ MateBook...
Huawei has introduced a trio of new MateBook laptops, expanding its mobile portfolio and building on its success in delivering attractive and powerful high-end devices. The company claims the HUAWEI... Read more
Deal! Gold 12-inch 1.2GHz Retina MacBook for...
Amazon has the 2016 Gold 12″ 1.2GHz Retina MacBook (MLHF2LL/A) on sale for $350 off MSRP for a limited time. Shipping is free: - 12″ 1.2GHz Gold Retina MacBook: $1249.99 $350 off MSRP We expect this... Read more
13-inch 2.0GHz MacBook Pros on sale for $100...
B&H has the non-Touch Bar 13″ 2.0GHz MacBook Pros in stock today and on sale for $100 off MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: - 13″ 2.0GHz MacBook Pro Space... Read more
15-inch 2.2GHz Retina MacBook Pro, Apple refu...
Apple has Certified Refurbished 2015 15″ 2.2GHz Retina MacBook Pros available for $1699. That’s $300 off MSRP, and it’s the lowest price available for a 15″ MacBook Pro. An Apple one-year warranty is... Read more
Apple refurbished 9-inch and 12-inch iPad Pro...
Apple has Certified Refurbished 9″ and 12″ Apple iPad Pros available for up to $160 off the cost of new iPads. An Apple one-year warranty is included with each model, and shipping is free: - 32GB 9″... Read more
Apple Certified Refurbished iMacs available f...
Apple has Certified Refurbished 2015 21″ & 27″ iMacs available for up to $350 off MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are available: - 21″ 3.... Read more
Sale! 15-inch 2.6GHz Silver Touch Bar MacBook...
DataVision has the 15″ 2.6GHz Silver Touch Bar MacBook Pro (MLW72LL/A) on sale for $2199 including free shipping. Their price is $200 off MSRP, and it’s the lowest price available for this model (... Read more
A Kaby Lake Processor Upgrade For The MacBook...
Now they tell me! Well, actually Apple hasn’t said anything official on the subject, but last week Bloomberg News’s Mark Gurman and Alex Webb cited unnamed “people familiar with the matter”... Read more
Kodak’s Camera-First Smartphone EKTRA Launche...
The Eastman Kodak Company and Bullitt Group have announced the availability of a U.S. GSM version of the KODAK EKTRA Smartphone. The U.S. launch coincides with a software update addressing requests... Read more
Apple Launches App Development Curriculum for...
Apple today launched a new app development curriculum designed for students who want to pursue careers in the fast-growing app economy. The curriculum is available as a free download today from Apple... Read more

Jobs Board

Data Engineer - *Apple* Media Products - Ap...
Changing the world is all in a day's work at Apple . If you love innovation, here's your chance to make a career of it. You'll work hard. But the job comes with more Read more
*Apple* Store Leader Program - Apple, Inc (U...
…Summary Learn and grow as you explore the art of leadership at the Apple Store. You'll master our retail business inside and out through training, hands-on Read more
*Apple* Integration Specialist - A3 Solution...
Apple Integration Specialist Contract-To-HireWe are searching for dedicated, well-experienced and energetic individuals for an information technology corporation Read more
Sr. Software Engineer, *Apple* Online Store...
Changing the world is all in a day's work at Apple . If you love innovation, here's your chance to make a career of it. You'll work hard. But the job comes with more Read more
Senior Engineering Project Manager, *Apple*...
Changing the world is all in a day's work at Apple . If you love innovation, here's your chance to make a career of it. You'll work hard. But the job comes with more Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.