#This file was created by Mon Feb 7 20:19:42 2000 #LyX 1.0 (C) 1995-1999 Matthias Ettrich and the LyX Team \lyxformat 2.15 \textclass linuxdoc \language default \inputencoding default \fontscheme default \graphics default \paperfontsize default \spacing single \papersize Default \paperpackage a4 \use_geometry 0 \use_amsmath 0 \paperorientation portrait \secnumdepth 3 \tocdepth 3 \paragraph_separation indent \defskip medskip \quotes_language english \quotes_times 2 \papercolumns 1 \papersides 1 \paperpagestyle default \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 \added_space_top 0.3cm \added_space_bottom 0.3cm \align center \LyXTable multicol5 5 2 0 0 -1 -1 -1 -1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 8 1 0 "" "" 8 1 1 "" "" 0 8 1 0 0 0 0 "" "" 0 8 1 0 0 0 0 "" "" 0 8 1 0 0 0 0 "" "" 0 8 1 0 0 0 0 "" "" 0 8 1 0 0 0 0 "" "" 0 8 1 0 0 0 0 "" "" 0 8 1 0 0 0 0 "" "" 0 8 1 0 0 0 0 "" "" 0 8 1 0 0 0 0 "" "" 0 8 1 0 0 0 0 "" "" 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