path: root/libical/doc/UsingLibical.lyx

#This file was created by <eric> Mon Feb  7 20:19:42 2000
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\layout Title

Using Libical
\layout Author

Eric Busboom (eric@softwarestudio.org)
\layout Date

January 2000
\layout Section

Introduction 
\layout Standard

Libical is an Open Source implementation of the iCalendar protocols and
 protocol data units.
 The iCalendar specification describes how calendar clients can communicate
 with calendar servers for users can store their calendar data and arrange
 meetings with other users.
 
\layout Standard

Libical implements the following specifications and protocols
\layout Standard
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iCal Core
\newline 
2445
\newline 
iTIP
\newline 
2446
\newline 
iMIP
\newline 
2447
\newline 
iRIP
\newline 
draft
\newline 
CAP
\newline 
draft
\layout Standard

(The current version, 0.14, does not implement iRip or CAP.
 ) 
\layout Standard

This documentation assumes that you are familiar with the iCalendar standards
 RFC2445 and RFC2446.
\layout Subsection

The libical project
\layout Standard

This code is under active development.
 If you would like to contribute to the project, you can contact me, Eric
 Busboom, at eric@softwarestudio.org.
 The project has a webpage at
\layout Quote

http://softwarestudio.org/libical/index.html 
\layout Standard

and a mailing list that you can join by sending the following mail:
\layout Code

To: minimalist@softwarestudio.org 
\layout Code

Subject: subscribe libical 
\layout Subsection

License
\layout Standard

The code and datafiles in this distribution are licensed under the Mozilla
 Public License.
 See http://www.mozilla.org/NPL/MPL-1.0.html for a copy of the license.
 Alternately, you may use libical under the terms of the GNU Library General
 Public License.
 See http://www.fsf.org/copyleft/lesser.html for a copy of the LGPL.
\layout Standard

This dual license ensures that the library can be incorporated into both
 proprietary code and GPL'd programs, and will benefit from improvements
 made by programmers in both realms.
 I will only accept changes into my version of the library if they are similarly
 dual-licensed.
\layout Subsection

Purpose & Goals 
\layout Subsection

Document version
\layout Standard

$Id: UsingLibical.lyx,v 1.1 2000/02/17 18:02:36 alves Exp $
\layout Section

Building the Library
\layout Section

Structure 
\layout Standard

The iCal calendar model is based on four types of objects: components, propertie
s, values and parameters.
 
\layout Standard

Properties are the fundamental unit of information in iCal, and they work
 a bit like a hash entry, with a constant key and a variable value.
 Properties may also have modifiers, called parameters.
 In the iCal content line
\layout Code

ORGANIZER;ROLE=CHAIR:MAILTO:mrbig@host.com
\layout Standard

The property name is 
\begin_inset Quotes eld
\end_inset 

ORGANIZER,
\begin_inset Quotes erd
\end_inset 

 the value of the property is 
\begin_inset Quotes eld
\end_inset 

mrbig@host.com
\begin_inset Quotes erd
\end_inset 

 and the 
\begin_inset Quotes eld
\end_inset 

ROLE
\begin_inset Quotes erd
\end_inset 

 parameter specifies that Mr Big is the chair of the meetings associated
 with this property.
 
\layout Standard

Components are groups of properties that represent the core objects of a
 calendar system, such as events or timezones.
 
\layout Standard

The central goal of libical is to parse iTIP data into an internal representatio
n of Components, Properties, Parameters an Values, and to allow the user
 to manipulate the data in various ways
\layout Subsection

Components 
\layout Subsection

Properties 
\layout Subsection

Values 
\layout Subsection

Parameters 
\layout Subsection

Enumerations
\layout Subsection

Types
\layout Subsection

The Parser
\layout Subsection

Restrictions
\layout Subsection

Memory Management
\layout Section

Differences From RFCs 
\layout Standard

Libical has been designed to follow the standards as closely as possible,
 so that the key objects in the standards are also keey objects in the library.
 However, there are a few areas where the specifications are (arguably)
 irregular, and following them exactly would result in an unfriendly interface.
 These deviations make libical easier to use by maintaining a self-similar
 interface.
 
\layout Subsection

Pseudo Components 
\layout Standard

Libical defines components for groups of properties that look and act like
 components, but are not defined as components in the specification.
 XDAYLIGHT and XSTANDARD are notable examples.
 These pseudo components group properties within the VTIMEZONE components.
 XDAYLIGHT starts with 
\begin_inset Quotes eld
\end_inset 

BEGIN:DAYLIGHT
\begin_inset Quotes erd
\end_inset 

 and ends with 
\begin_inset Quotes eld
\end_inset 

END:DAYLIGHT, just like other components, but is not defined as a component
 in RFC2445.
 ( See RFC2445, page 61 ) In Libical, it is a component.
 
\layout Standard

There are also pseudo components that are conceptually derived classess
 of VALARM.
 RFC2446 defines what properties may be included in each component, and
 for VALARM, the set of properties it may have depends on the value of the
 ACTION property.
 
\layout Standard

For instance, if a VALARM component has an ACTION property with the value
 of 
\begin_inset Quotes eld
\end_inset 

AUDIO,
\begin_inset Quotes erd
\end_inset 

 the component must also have an 
\begin_inset Quotes eld
\end_inset 

ATTACH
\begin_inset Quotes erd
\end_inset 

 property.
 However, if the ACTION value is 
\begin_inset Quotes eld
\end_inset 

DISPLAY,
\begin_inset Quotes erd
\end_inset 

 the component must have a DESCRIPTION property.
 
\layout Standard

To handle these various, complex restrictions, libical has pseudo components
 for each type of alarm: XAUDIOALARM, XDISPLAYALARM, XEMAILALARM and XPROCEDUREA
LARM.
 
\layout Subsection

Combined Values 
\layout Standard

Many values can take more than one type.
 TRIGGER, for instance, can have a value type of with DURATION or of DATE-TIME.
 These multiple types make it difficult to create routines to return the
 value associated with a property.
 
\layout Standard

It is natural to have interfaces that would return the value of a property,
 but it is cumbersone for a single routine to return multiple types.
 So, in libical, properties that can have multiple types are given a single
 type that is the union of their RFC2445 types.
 For instance, in libical, the value of the TRIGGER property resolves to
 
\noun on 
struct icaltriggertype
\noun default 
.
 This type is a union of a DURATION and a DATE-TIME.
 
\layout Subsection

Multi-Valued Properties
\layout Standard

Some properties, such as CATEGORIES have only one value type, but each CATEGORIE
S property can have multiple value instances.
 This also results in a cumbersome interface -- CATEGORIES accessors would
 have to return a list while all other accessors returned a single value.
 In libical, all properties have a single value, and multi-valued properties
 are broken down into multiple single valued properties during parsing.
 That is, an input line like, 
\layout Code

CATEGORIES: work, home
\layout Standard

becomes in libical's internal representation
\layout Code

CATEGORIES: work
\layout Code

CATEGORIES: home
\layout Standard

Oddly, RFC2445 allows some multi-valued properties ( like FREEBUSY ) to
 exist as both a multi-values property and as multiple single value properties,
 while others ( like CATEGORIES ) can only exist as single multi-valued
 properties.
 This makes the internal representation for CATEGORIES illegal.
 However when you convert a component to a string, the library will collect
 all of the CATEGORIES properties into one.
 
\layout Section

Implementation Limitations 
\layout Section

Using libical
\layout Subsection

Creating Components 
\layout Standard

There are three ways to create components in Libical: creating individual
 objects and assembling them, building entire objects in massive vaargs
 calls, and parsing a text file containing iCalendar data.
 
\layout Subsubsection

Constructor Interfaces 
\layout Standard

Using constructor interfaces, you create each of the objects seperately
 and them assemble them in to components: 
\layout Code

event = icalcomponent_new(ICAL_VEVENT_COMPONENT);
\layout Code

icalcomponent_add_property(event, icalproperty_new_dtstamp(atime) );
\layout Code

icalcomponent_add_property(event,icalproperty_new_uid(strdup("guid-1.host1.com"))
 );
\layout Code

property=icalproperty_new_organizer(strdup("mrbig@host.com")); 
\layout Code

icalproperty_add_parameter(property,icalparameter_new_role(ICAL_ROLE_CHAIR)
 );
\layout Code

icalcomponent_add_property(event,property);
\layout Subsubsection

vaargs Constructors 
\layout Subsubsection

Parsing Text Files 
\layout Subsection

Accessing Components 
\layout Subsubsection

Finding Components 
\layout Subsubsection

Removing Components 
\layout Standard

Removing an element from a list while iterating through the list can cause
 problems, since you will probably be removing the element that the internal
 iterator points to.
 This will result in the iteration loop terminating immediately after removing
 the element.
 To avoid the problem, you will need to step the iterator ahead of the element
 you are going to remove, like this:
\layout Code

for(c = icalcomponent_get_first_component(parent_comp,ICAL_ANY_COMPONENT);
 
\layout Code


\protected_separator 
 
\protected_separator 
 
\protected_separator 
 
\protected_separator 
c != 0; 
\layout Code


\protected_separator 
 
\protected_separator 
 
\protected_separator 
 
\protected_separator 
c = next
\layout Code

{ 
\layout Code


\protected_separator 
 
\protected_separator 
 next = icalcomponent_get_next_component(parent_comp,ICAL_ANY_COMPONENT);
\layout Code


\protected_separator 
 
\protected_separator 
 icalcomponent_remove_component(parent_comp,c); 
\layout Code

}
\layout Subsubsection

Finding Properties 
\layout Subsubsection

Removing Properties 
\layout Subsubsection

Getting Values 
\layout Subsubsection

Setting Values 
\layout Subsubsection

Getting Parameters
\layout Subsubsection

Setting Parameters 
\layout Subsubsection

Removing Parameters 
\layout Subsubsection

Checking Component Validity
\layout Subsection

Storing Objects
\layout Standard

The libical distribution inclues a seperate library, libicalss, that allows
 you to store iCal component data to disk in a variety of ways.
 This library is documented seperately.
 
\layout Subsection

Memory Management 
\layout Standard

Libical relies heavily on dynamic allocation for both the core objects and
 for the strings used to hold values.
 Some of this memory the library caller owns and must free, and some of
 the memory is managed by the library.
 Here is a summary of the memory rules.
 
\layout Description

1) If the function name has "new" in it, the caller gets control of the
 memory.
 ( such as icalcomponent_new(), or icalproperty_new_clone() ) 
\layout Description

2) If you got the memory from a routine with new in it, you must call the
 corresponding *_free routine to free the memory.
 ( Use icalcomponent_free() to free objects created with icalcomponent_new())
 
\layout Description

3) If the function name has "add" in it, the caller is transfering control
 of the memory to the routine.
 ( icalproperty_add_parameter() )
\layout Description

4) If the function name has "remove" in it, the caller passes in a pointer
 to an object and after the call returns, the caller owns the object.
 So, before you call icalcomponent_remove_property(comp,foo), you do not
 own "foo" and after the call returns, you do.
 
\layout Description

5) If the routine returns a string, libical owns the memory and will put
 it on a ring buffer to reclaim later.
 You'd better strdup() it if you want to keep it, and you don't have to
 delete it.
 
\layout Subsection

Error Handling
\layout Standard

icalerror_errno.
 Return values.
 #defines.
 icalerror_stop_here
\layout Subsubsection

Return values
\layout Subsubsection

icalerrno
\layout Subsubsection

Component errors
\layout Subsection

Naming Standard
\layout Standard

Structures that you access with the 
\begin_inset Quotes eld
\end_inset 

struct
\begin_inset Quotes erd
\end_inset 

 keyword, such as 
\begin_inset Quotes eld
\end_inset 

struct icaltimetype
\begin_inset Quotes erd
\end_inset 

 are things that you are allowed to see inside and poke at.
 
\layout Standard

Structures that you access though a typedef, such as 
\begin_inset Quotes eld
\end_inset 

icalcomponent
\begin_inset Quotes erd
\end_inset 

 are things where all of the data is hidden.
 
\layout Standard

Component names that start with 
\begin_inset Quotes eld
\end_inset 

V
\begin_inset Quotes erd
\end_inset 

 are part of RFC 2445 or another iCal standard.
 Component names that start with 
\begin_inset Quotes eld
\end_inset 

X
\begin_inset Quotes erd
\end_inset 

 are also part of the spec, but they are not actually components in the
 spec.
 However, they look and act like components, so they are components in libical.
 Names that start with 
\begin_inset Quotes eld
\end_inset 

XLIC
\begin_inset Quotes erd
\end_inset 

 or 
\begin_inset Quotes eld
\end_inset 

X-LIC
\begin_inset Quotes erd
\end_inset 

 are not part of any iCal spec.
 They are used internally by libical.
 
\layout Standard

Enums that identify a component, property, value or parameter end with 
\begin_inset Quotes eld
\end_inset 

_COMPONENT,
\begin_inset Quotes erd
\end_inset 

 
\begin_inset Quotes eld
\end_inset 

_PROPERTY,
\begin_inset Quotes erd
\end_inset 

 
\begin_inset Quotes eld
\end_inset 

_VALUE,
\begin_inset Quotes erd
\end_inset 

 or 
\begin_inset Quotes eld
\end_inset 

_PAAMETER
\begin_inset Quotes erd
\end_inset 

s
\layout Standard

Enums that identify a parameter value have the name of the parameter as
 the second word.
 For instance: ICAL_ROLE_REQPARTICIPANT or ICAL_PARTSTAT_ACCEPTED.
\layout Standard

The enums for the parts of a recurarance rule and request statuses are irregular.
 
\layout Section

Useful Recipies
\layout Standard

Iteration
\layout Standard

Copying components.
 Remember that you must clone or remove an object before putting in on anothr
 list.
 
\layout Standard

Finding compliance errors
\layout Section

Performance
\layout Standard

Checking restrictions is computationally expensive
\layout Section

Hacks and Bugs
\the_end