#This file was created by <eric> Mon Feb 7 20:19:42 2000
#LyX 1.0 (C) 1995-1999 Matthias Ettrich and the LyX Team
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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
