Skyhigh Policy Code Essentials

Native Object Types

This section describes the built-in object types supported by the MOWGLI interpreter. It does not cover additional object types supported by modules included in Policy Code implementations in Skyhigh products.

Routines

A routine, often referred to as a rule set, is similar to a function or method in many programming languages. It is a section of policy code that groups related logic to accomplish a task.  A ROUTINE does not have a return value. Every line of policy code in a customer’s policy resides within a routine.

Comments

The MOWGLI interpreter allows allows you to include comments in your code by prepending them with//.  Anything after the // is ignored by the interpreter. You can place comments on a separate line or at the end of a line of code.

For example:

// This is a comment and is ignored by the interpreter
NUMBER x = 5  // I can add a comment here explaining why I set the value to 5

MOWGLI does not currently support block comments, or commenting multiple lines of code with a single operator.

IF Statements

You will find IF statements to be extremely prevalent especially in the default policies.  Each rule in the Skyhigh SWG policy is implemented as an IF statement.  Below is the basic syntax of IF statements:

IF (conditional statement) THEN {
    // Conditionally-executed statements go here
}
ELSE IF (conditional statement) THEN {
   // Conditionally-executed statements go here
}
ELSE IF (conditional statement) THEN {
   // Conditionally-executed statements go here
}
ELSE {
   // Conditionally-executed statements go here
}

The IF statement can be followed by any number of ELSE IF statements and, optionally, an unconditional ELSE statement.  If there is only one conditionally-executed command in an IF or ELSE block, then the curly braces are not required.  Also, note that the parentheses around the conditional statements are optional.  

For example:

// Enable progress pages if the User-Agent header starts with "Mozilla"
// Otherwise, enable data trickling.
IF MWG.Request.Headers.Get ("User-Agent").StartsWith("Mozilla") THEN {
    MWG.EnableProgressPage (Skyhigh_Progress_Page_Settings)
} ELSE {
    MWG.EnableDataTrickling(dataTricklingSetting)
}

Dot Notation

MOWGLI uses dot notation that will be familiar to anyone experienced with object‑oriented languages such as Java, Python, or C#. The MOWGLI implementation allows the object before the period to be sent as the first parameter to the function or procedure that appears after the period. This design makes the syntax easier to read.

For example:

NUMBER x = 10
STRING y = "x = " + ToString(x)

This results in the string y equaling "x = 10".  The concatenation of the "x = " string and the value of x requires converting the number x to a STRING or else a type mismatch error occurs.  The ToString(NUMBER) function does this conversion for us. 

Using dot notation, you can rewrite this code as follows:

NUMBER x = 10
STRING y = "x = " + x.ToString()

In the above example, the number x is passed to the ToString(NUMBER) function as the first (and only) parameter.  Because no parameters are listed in the parenthesis, they are optional. You can further simplify the code to:

NUMBER x = 10
STRING y = "x = " + x.ToString

Example 1: Simple Case

The above example is simple because the original code is easy to understand. It shows how the argument before the dot is passed as the first parameter to the function or procedure after the dot. In this case, we used the built‑in ToString function in MOWGLI.

Example 2: Complex Case

Consider a more complex example that shows the real value of this functionality. The argument before the dot is passed as the first parameter to the function or procedure after the dot, just as before. In addition, the dot can separate a function from its namespace. In this example, we use functions not native to MOWGLI but provided by Skyhigh in a policy code module. 

These functions all exist in the MWG namespace, so they are called using MWG.<function_name> as you will see.

STRING original_source = MWG.Get (MWG.Headers (MWG.Request ()), "X-Forwarded-For")

 The above line takes the value of the request header X-Forwarded-For and stores it in a string called original_source. 

The MWG.Request() function returns an MWG.RequestResponse object.  MWG.Headers accepts an MWG.RequestResponse object and returns an MWG.HeaderMap object.  The MWG.Get function accepts both an MWG.HeaderMap and a STRING and returns a STRING. 

Nesting multiple functions can quickly become confusing, but dot notation makes it much easier to follow

STRING original_source = MWG.Request.Headers.Get ("X-Forwarded-For")

This line produces the same result but is easier to read. Declaring the MWGnamespace once applies it to all functions in the command. Dot notation reduces parentheses by passing parameters implicitly. The command runs left to right: MWG.Request() executes first and returns an MWG.RequestResponse object. That object is passed to MWG.Headers(), which returns an MWG.HeaderMap. The MWG.HeaderMap is then passed to MWG.Get(), with "X-Forwarded-For" as the second parameter. The STRING returned by MWG.Get() is assigned to original_source.

Looping

MOWGLI supports two types of loops: fixed‑count loops and FOR loops that iterate through all elements in a VECTOR.  Each type of loop provides two commands to control execution or termination. The BREAK command ends the current loop and exits immediately. The CONTINUE command ends the current iteration and starts the next one, if the loop is not already complete.

NOTE: The iterator (i in this example) must be declared prior to the FOR loop.

Optional Parentheses

There are several situations in MOWGLI code where parentheses can be used but are not required. 

The following are cases where parentheses are optional::

• After a function or procedure called without any arguments (except those passed by dot notation)
• Parentheses are optional around the condition(s) of an IF statement
• Around the parameters of a built-in procedure like CALL
• In a LOOP (NUMBER) statement