JSON Module

Andrei Dragus

   OpenSIPS Solutions

Edited by

Andrei Dragus

   Copyright © 2009 Voice Sistem SRL
   Revision History
   Revision $Revision: 8740 $ $Date$
     __________________________________________________________

   Table of Contents

   1. Admin Guide

        1.1. Overview
        1.2. Dependencies

              1.2.1. OpenSIPS Modules
              1.2.2. External Libraries or Applications

        1.3. Exported Parameters
        1.4. Exported Variables

              1.4.1. Variable lifetime
              1.4.2. Accessing the $json(id) variable
              1.4.3. Returned values from $json(id)
              1.4.4. Operators for the $json(id) variable

        1.5. Exported Functions

              1.5.1. json_link("$json(dest_id)",
                      "$json(source_id)")

   List of Examples

   1.1. Accessing the $json variable
   1.2. Iterating through an array using variables
   1.3. Appending integers to arrays
   1.4. Deleting the last element in an array
   1.5. Adding a string value to a json object
   1.6. Initializing an array
   1.7. Setting a boolean or null value
   1.8. Adding a json to another json
   1.9. Creating a reference
   1.10. [LOGICAL ERROR] Creating a circular reference

Chapter 1. Admin Guide

1.1. Overview

   This module introduces a new type of variable that provides
   both serialization and de-serialization from JSON format.

   The variable provides ways to access objects and arrays to
   add,replace or delete values from the script.

   The correct approach is to consider a json object as a
   hashtable ( you can put (key;value) pairs, and you can delete
   and get values by key) and a json array as an array ( you can
   append, delete and replace values).

   Since the JSON format can have objects inside other objects you
   can have multiple nested hashtables or arrays and you can
   access these using paths.

1.2. Dependencies

1.2.1. OpenSIPS Modules

   This module does not depend on other modules.

1.2.2. External Libraries or Applications

     * libjson The libjson C library can be downloaded from:
       http://oss.metaparadigm.com/json-c/

1.3. Exported Parameters

   The module does not export any parameters.

1.4. Exported Variables

   This module exports the $json(id) variable.

   The json variable provides methods to access fields in json
   objects and indexes in json arrays.

1.4.1. Variable lifetime

   The json variables will be available to the process that
   created them from the moment they were initialized. They will
   not reset per message or per transaction. If you want to use
   the on a per message basis you should initialize them each
   time.

1.4.2. Accessing the $json(id) variable

   The grammar that describes the id is:

   id = name(identifier)*

   identifier = key | index

   key = /string | /$var

   index = [integer] | [$var] | []

   The "[]" index represents appending to the array. It should
   only be used when trying to set a value and not when trying to
   get one.

   Negative indexes can be used to access an array starting from
   the end. So "[-1]" signifies the last element.

   IMPORTANT: The id strictly complies to this grammar. You should
   be careful when using spaces because they will NOT be ignored.
   This was done to allow keys that contain spaces.

   Variables can be used as indexes or keys. Variables that will
   be used as indexes must contain integer values. Variables that
   will be used as keys should contain string values.

   Trying to get a value from a non-existing path (key or value)
   will return the NULL value and notice messages will be placed
   in the log describing the value of the json and the path used.

   Trying to replace or insert a value in a non-existing path will
   cause an error in setting the value and notice messages will be
   printed in the log describing the value of the json and the
   path used

   Example 1.1. Accessing the $json variable
...
$json(obj1/key) = "value"; #replace or insert the (key,value)
                           #pair into the json object;

$json(matrix1[1][2]) = 1;  #replace the element at index 2 in the elemen
t
                           #at index 1 in an array

xlog("$json(name/key1[0][-1]/key2)"); # a more complex example

...

   Example 1.2. Iterating through an array using variables
...

$json(ar1) := "[1,2,3,4]";

$var(i) = 0;

while( $json(ar1[$var(i)]) )
{

        #print each value
        xlog("Found:[$json(ar1[$var(i)])]\n");

        #increment each value
        $json(ar1[$var(i)])  = $json(ar1[$var(i)]) + 1 ;

        $var(i) = $var(i) + 1;

}


...

1.4.3.  Returned values from $json(id)

   If the value specified by the id is an integer it will be
   returned as an integer value.

   If the value specified by the id is a string it will be
   returned as a string.

   If the value specified by the id is any other type of json (
   null, boolean, object, array ) the serialized version of the
   object will be returned as a string value. Using this and the
   ":=" operator you can duplicate json objects and put them in
   other json objects ( for string or integer you may use the "="
   operator).

   If the id does not exist a NULL value will be returned.

1.4.4.  Operators for the $json(id) variable

   There are 2 operators available for this variable.

1.4.4.1.  The "=" operator

   This will cause the value to be taken as is and be added to the
   json object ( e.g. string value or integer value ).

   Setting a value to NULL will cause it to be deleted.

   Example 1.3. Appending integers to arrays
...
$json(array1[]) = 1;
...

   Example 1.4. Deleting the last element in an array
...
$json(array1[-1]) = NULL;
...

   Example 1.5. Adding a string value to a json object
...
$json(object1/some_key) = "some_value";
...

1.4.4.2.  The ":=" operator

   This will cause the value to be taken and interpreted as a json
   object ( e.g. this operator should be used to parse json inputs
   ).

   Example 1.6. Initializing an array
...
$json(array1) := "[]";
...

   Example 1.7. Setting a boolean or null value
...
$json(array1[]) := "null";
$json(array1[]) := "true";
$json(array1[]) := "false";
...

   Example 1.8. Adding a json to another json
...

$json(array) := "[1,2,3]";
$json(object) := "{}";
$json(object/array) := $json(array) ;

...

1.5. Exported Functions

1.5.1.  json_link("$json(dest_id)", "$json(source_id)")

   This function can be used to link json objects together. This
   will work simillar to setting a value to an object, the only
   difference is that the second object is not copied, only a
   reference is created.

   Changes to any of the objects will be visible in both of them.

   You can use this method either to create references so each
   time you access the field you don't have to go through the full
   path (for speed efficiency and shorter code), or if you have an
   object that must be added to many other objects and you don't
   want to copy it each time (space and speed efficiency).

   You can think of this object exactly as a reference in an
   object-oriented language. Modifying fields referenced by the
   variable will cause modifications in all the objects, BUT
   modifying the variable itsef will not cause any changes to
   other objects.

   WARNING: You should be carefull when using references. If you
   accidentally create a circular reference and try to get the
   value from the object you will crash OPENSIPS.

   Example 1.9. Creating a reference
...

$json(b) := "[{},{},{}]";

json_link("$json(stub)","$json(b[0])");

$json(stub/ana) = "are"; #add to the stub
$json(stub/ar) := "[]";
$json(stub/ar[]) = 1;
$json(stub/ar[]) = 2;
$json(stub/ar[]) = 3;

$json(b[0]/ar[0]) = NULL; # delete from the original object

xlog("\nTest link :\n$json(stub)\n$json(b)\n\n");

/*Output:

Test link :
{ "ana": "are", "ar": [ 2, 3 ] }
[ { "ana": "are", "ar": [ 2, 3 ] }, { }, { } ]

*/

$json(stub) = NULL; #delete the stub, no change will happen to the sourc
e


xlog("\nTest link :\n$json(stub)\n$json(b)\n\n");

/* Output:

Test link :
<null>
[ { "ana": "are", "ar": [ 2, 3 ] }, { }, { } ]

*/





...

   Example 1.10. [LOGICAL ERROR] Creating a circular reference
...

$json(b) := "[1]";

/* NEVER do this, it is meant only to show where problems might occur  *
/
json_link("$json(b[0])","$json(b)"); # replace 1 with a reference to b

xlog("\nTest link :\n$json(stub)\n$json(b)\n\n");

/* this will cause OPENSIPS to crash because it will continuously try
 to get b, then b[0], then b ... */


...
