To prove it, go to the Run command on your Start button and write the following:
|What You Need|
|Windows 98 or later with IE 4 or later, Wscript, Rebol/View, and a text editor.|
MSDN provides some good information about APPs, but be wary of what you read: You may come away with a misconception about what is required to achieve the most basic implementation of an APP under Windows. For example, one article implies that to write an APP one needs to implement certain interfaces, but APPs are actually very flexible. The basic implementation of an APP under Windows requires only that you make the proper entries in the registry for your protocol and that the handler for your protocol is a valid Windows .exe file. You can see an example at http://msdn.microsoft.com/library/default.asp?url=/workshop/networking/pluggable/overview/appendix_a.asp. The “note” protocol defined in that example opens Notepad, similar to the way the view-source:// protocol can be used to open the .htm source of an HTML file in Notepad. For example, try putting this in your browser: view-source:http://www.devx.com.
I doubt that Notepad implements iinternetprotocol or any related interfaces, as to do so it should be a COM implementation and found at the following registry address HKEY_CLASSES_ROOTPROTOCOLS. Without these related interfaces, in the end all that happens is the protocol address is passed as a string via the command line to your application for analysis.
The W3C provides an incomplete list of addressing schemes, which you can use to search your system to see if these addressing schemes are implemented as APPs. Those that do more than just call over the command line should be found at the HKEY_CLASSES_ROOTPROTOCOLSHandler registry key.
There are many tools that allow you to dynamically load files via the command line, and pass on command lines to files. One example is script interpreters such as Wscript.exe. Here is the sample registry file, which shows how to set a simple WScript as the handler for a protocol called ws-proto.
Windows Registry Editor Version 5.00[HKEY_CLASSES_ROOTws-proto]@=""URL: ws-proto Protocol"""URL Protocol"=""[HKEY_CLASSES_ROOTws-protoshell][HKEY_CLASSES_ROOTws-protoshellopen][HKEY_CLASSES_ROOTws-protoshellopencommand]@="wscript.exe c:\wsproto.js %1"
Here is the protocol that handles the WScript. (Both the registry file and the protocol handler are available in the code download for this article?see left column).
Why Rebol? Because Rebol is particularly good at handling protocols. By implementing a dynamic evaluating protocol in Rebol, I can very easily add functionality to interact with ftp, smtp, http, etc. (These protocols are easily accessible from Rebol using Rebol’s one-liner scripts, e.g. one line of code to read a URL and write the output to a local file.) Rebol can interact with any protocol that can be called via bookmarklet-type behavior, from a link on a web page, from writing in the address bar, from shortcuts, or from most any programming language/environment in the Windows system.
You can download a free, noncommercial version of Rebol from http://www.rebol.com/downloads/view-pro031.zip. It includes a Rebol dialect (sort of a DSL) for graphical interfaces, which I will use to implement a small form in my script. This form will help me decide, by showing the code passed to it, whether to evaluate the code, append it to a local file containing the script fragments I receive, or to edit it and then evaluate it.
It’s time to implement the Rebol script. There are links at various points to the Rebol function dictionary, which provides definitions of built-in Rebol functions to help you along. In the code download for this article there is a registry file called rebsettings.reg, which sets the reb protocol to be evaluated using a script called reb.r. Reb.r is the protocol handler that the registry files point at (see Listing 1). Install Rebol in the default installation folder c:
ebolview. Be advised that the Rebol installation program asks you for information such as your email address, email server etc., which it needs to send and receive mail and for the examples to work.
Once Rebol is installed, you should merge the accompanying .reg file and also install the files in the downloadable sample code (see link in left column) to the c:
ebolview directory. When you’ve done that, open the example.html file in your default browser. Listing 2 shows the contents of the example.html file.
- Callreb() takes a string parameter, which should be a reb:// link, and then uses the browser’s location.href method to navigate to the reb:// link.
- When executed in a link, browseloc() will tell Rebol to browse the page on which the link was executed.
The first link in the HTML page is:
Everything past the reb:// is legal Rebol code. And it does exactly what the link text tells you: It reads a local file, contained in the code download called oldfile.txt and writes a local file called newfile.txt. (Note that the parameters are intentionally opposite their function?this is because of the evaluation order of Rebol syntax). The % before the file names tells Rebol that these are in fact files. When you click on the link you should see something similar to Figure 2:
Pressing Do causes the Rebol interpreter to evaluate the text contained in the
1 + 5
1 + 5 is valid Rebol code so if you press Do the text field should read 6. If you wrote the following in the text area:
1 + 5 > 7
the text field would display false. If your wrote 1 + 5 > 4 it would display true. And if you wrote:
(1 + 5) * 7 + 6
the text field would display 48. You can find more information about Rebol Math at http://www.rebol.com/docs/core23/rebolcore-11.html.
The next link (another Rebol one-liner) is similar to the first one; it reads the address http://www.devx.com and writes it to a local file called text.htm.
You might want to steel yourself before clicking on the third link, it can be a shock if you’re unprepared. It uses the do function to execute a file found at an http address. (This can also be used to execute a file found at an ftp address.) The particular file being executed is called websplitter.r and can be found at http://www.reboltech.com/library/scripts/websplit.r. You can find the text of the file at http://www.reboltech.com/library/html/websplit.html. Clicking this link or pushing the Do button from the sample form opens the Rebol shell, gets an HTML file from Rebol.com, and strips out all the tags. It prints the tags minus the text content to the shell and then the text content minus tags.
The next link sets the value of two Rebol variables, string and webpage, to ‘microsoft’ and the content at http://www.yahoo.com, respectively. If the string ‘microsoft’ is found anywhere on the Web page, then the shell opens and the code prints the contents of the Web page to it:
Rebol has numerous ways to deal with strings and putting them in curly brackets?as shown above with Microsoft?works from many different interfaces.
The following are examples of building a reb: link with insertPrompt() using user input:
So clicking on one of the links displays the prompt: “Please write your email address here.” When you do the code calls the reb:// protocol and you will either receive an e-mail with the text “hello from reb protocol” in the body, or the HTML of the page www.rebol.com as text.
Finally, to write a local file containing the contents of a file located on an ftp site, you can use the following link:
That’s enough simple examples. Here’s a brief explanation of the sample reb.r code (see Listing 1). First, reb.ra parses the input to a separate executable script from the protocol body. The following two lines perform the separation:
argsstring: to-string system/script/argsparsestring: remove/part argsstring 6
System/script is an object that applies to the script argument passed in (think of it as the Rebol DOM). One subsidiary object of system/script is args, which contains the command line arguments. The word argsstring turns this object into a string value. The word parsestring then removes the first six characters of the argsstring string. Remove is a Rebol function.
|Author’s Note: Rebol calls these variables “words.” In Rebol, a word may or may not be a variable, depending on how it is used.|
Next there’s a little problem with command arguments that originate in browser address bars: The URL ends with a forward slash (/). The slash can cause some real problems, so you need to remove it, using this code:
if #"/" = last parsestring [ remove back tail parsestring]
This checks if the last of parsestring is the character “/”; if so, it executes the code inside the square brackets, called a block in Rebol. It also removes the last character of parsestring by going to the end and moving one character backward. One of the goals of Rebol’s design was to make it more like a natural language, which I think has succeeded, although at some points the grammatical methods of verb inflexion quite maddening can be. ;)
Next I set the value of the word filename to be %reb-protoLog.txt. This is the name of the log file where the script saves the protocol body when you save.
Now a look at the code that creates the form. As I stated earlier Rebol/View includes a dialect for creating GUIs. (Read more about the View dialect.) You call this dialect with the code:
Everything within the square brackets gets evaluated as being code in the View dialect.
The next three lines should be pretty clear:
vh2 "result:" f1: area parsestring returnf2: field
The code creates a headline (think of it as being analogous to the h2 tag in HTML) with the text “result:” beneath that is an area, analogous to an HTML
Next:button "Save"[write/append filename join newline join now join ":" join newline
join f1/text join newline "_________________________"]
The form has a button with the text value “Save.” When you click on it the Rebol code in the block associated with the button gets evaluated. This code could have been written in a cleaner manner, but doing so might have been more confusing for someone unfamiliar with Rebol. Basically all the preceding code does is write or append a text value to the file %reb-protoLog.txt that I associated with the word filename earlier. The code builds up the text value written to the file by concatenating other values together. Concatenation is handled via the word join.
The Save button code concatenates linefeeds/carriage returns (made by the word newline), the present date/time (made by the word now) followed by a colon followed by the text in the area F1, which, will be the same as the text passed in the protocol body if the user does not edit it first. Finally, the code appends another newline and a line “________________________” to break up various log entries.
Next: button "Do" [ clear f2/texterr: error? try[returnstring: to-string do f1/text]either err = true[append f2/text "No string output returned" show f2][append f2/text returnstring show f2]]
Another button with the text “Do,” causes the application to execute code sent to it. The first thing the button code does is clear any text already in the F2 field. This is necessary in case a user edits the value of F1 several times, as in the calculator examples. The word err evaluates f1/text as well as checking if there is an error. By breaking the preceding code down you can get a better feel for the way Rebol evaluates code:
This code evaluates the string in the F1 area as Rebol code. The word to-string before the ‘do’ line (see above) attempts to turn the result of that evaluation into a string (‘do’ does not return a value unless the operation it evaluates returns a value). This whole process is associated with a word? returnstring?wrapped within a simple error-checking process.
Next it checks to see if an error occurred with the line:
either err = true
If an error occured, then Rebol executes the first block, right next to the true, if no error occurred then Rebol evaluates the second block. The first block writes “No string output returned” to F2. If the second block gets evaluated then the process of evaluating whatever was in F1 did return a value, and the code writes that value to F2 using the word holding that value?returnstring.
button "quit" [quit]
This last bit of code should be self-explanatory. When a user clicks on the quit button the code inside the block evaluates the quit function.
If this article inspires you to learn more about Rebol, please check out the related resources in the left column. One of these is an advanced article about writing protocols in Rebol. The techniques presented there, combined with those presented here, will let you implement many protocols that are still missing in the Windows system with relative ease.
|Author’s Note: The author wishes to thank Gabrielle Santilli, Gregg Irwin, Carl Read, and others from the Rebol List for their help.|