path: root/libical/doc/UsingLibical.lyx

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\layout Title

Using Libical
\layout Author

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

January 2001
\layout Standard


\begin_inset LatexCommand \tableofcontents{}

\end_inset 


\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 so users can store their calendar data and arrange
 meetings with other users.
 
\layout Standard

Libical implements RFC2445, RFC2446 and some of RFC2447 and the CAP draft.
 
\layout Standard

This documentation assumes that you are familiar with the iCalendar standards
 RFC2445 and RFC2446.
 these specifications are online on the CALSCH webpage at:
\layout LyX-Code

http://www.imc.org/ietf-calendar/
\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 LyX-Code

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

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

To: minimalist@softwarestudio.org 
\layout LyX-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

Example Code
\layout Standard

A lot of the documentation for this library is in the form of example code.
 These examples are in the 
\begin_inset Quotes eld
\end_inset 

examples
\begin_inset Quotes erd
\end_inset 

 directory of the distribution.
 Also look in 
\begin_inset Quotes eld
\end_inset 

src/test
\begin_inset Quotes erd
\end_inset 

 for additional annotated examples.
 
\layout Section

Building and Installing the Library
\layout Standard

Libical uses autoconf to generate makefiles.
 It should built with no adjustments on Linux, FreeBSD and Solaris under
 gcc.
 Some version have been successfully been build on MacOS, Solaris, UnixWare,
 And Tru64 UNIX without gcc, but you may run into problems with a particular
 later version.
 
\layout Standard

For a more complete guide to building the library, see the README file in
 the distribution.
 
\layout Standard


\begin_inset Quotes eld
\end_inset 

make install
\begin_inset Quotes erd
\end_inset 

 will install the libraries and header files for three modules: libical,
 libicalss.
 and libicalvcal.
 If you build shared objects, then these files will be installed: 
\layout Itemize

ical.h
\layout Itemize

libical.a
\layout Itemize

libical.so
\layout Itemize

icalss.h
\layout Itemize

libicalss.a
\layout Itemize

libicalss.so
\layout Itemize

icalvcal.h
\layout Itemize

libicalvcal.a
\layout Itemize

libicalvcal.so
\layout Standard

The header files ical.h and icalss.h are combined header files, generated
 by concatenating together all of the header files in src/libical and src/libica
lss respectively.
 
\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 LyX-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.
 Components are delimited by 
\begin_inset Quotes eld
\end_inset 

BEGIN
\begin_inset Quotes erd
\end_inset 

 and 
\begin_inset Quotes eld
\end_inset 

END
\begin_inset Quotes erd
\end_inset 

 tags.
 
\layout Standard
\added_space_bottom 0.3cm 
When a component is sent across a network, if it is un-encrypted, it will
 look something like:
\layout LyX-Code

BEGIN:VCALENDAR
\layout LyX-Code

METHOD:REQUEST
\layout LyX-Code

PRODID: -//hacksw/handcal//NONSGML v1.0//EN
\layout LyX-Code

BEGIN:VEVENT 
\layout LyX-Code

DTSTAMP:19980309T231000Z 
\layout LyX-Code

UID:guid-1.host1.com 
\layout LyX-Code

ORGANIZER;ROLE=CHAIR:MAILTO:mrbig@host.com 
\layout LyX-Code

ATTENDEE;RSVP=TRUE;ROLE=REQ-PARTICIPANT;CUTYPE=GROUP: 
\layout LyX-Code

  MAILTO:employee-A@host.com 
\layout LyX-Code

DESCRIPTION:Project XYZ Review Meeting 
\layout LyX-Code

CATEGORIES:MEETING 
\layout LyX-Code

CLASS:PUBLIC 
\layout LyX-Code

CREATED:19980309T130000Z 
\layout LyX-Code

SUMMARY:XYZ Project Review 
\layout LyX-Code

DTSTART;TZID=US-Eastern:19980312T083000 
\layout LyX-Code

DTEND;TZID=US-Eastern:19980312T093000 
\layout LyX-Code

LOCATION:1CP Conference Room 4350 
\layout LyX-Code

END:VEVENT 
\layout LyX-Code

END:VCALENDAR
\layout Standard

Note that components can be nested; this example has both a VCALENDAR and
 a VEVENT component, one nested inside the other.
 
\layout Standard

The main goal of Libical is to offer a structured, type-safe to create,
 access and manipulate components and their properties, values and parameters.
 
\layout Subsection

Core iCal classes
\layout Standard

Libical is an object-based, data-oriented library.
 There are no real-objects, but the way the routines are named and organized
 results in the same sort of encapsulations and abstraction that are major
 features of Object-Orieted languages.
 Nearly all of the routines in the library are associated with an opaque
 data types and perform some operation on that data type.
 For instnace, a Property is declared as:
\layout LyX-Code

icalproperty *prop;
\layout Standard

Icalproperty is typedef'd to void, so the only way to manipulate it is through
 the accessor routines, all of which have a form similar to:
\layout LyX-Code

char* icalproperty_as_ical_string(icalproperty* prop);
\layout Standard

That is, the name of the 'class' is the first word in the routine name,
 and the first parameter is a pointer to the 'object.'
\layout Standard

Although the library does not actually have classes, we will use those terms
 since the behavior of these associations of data and routines is very similar
 to a class.
 
\layout Subsubsection

Properties
\layout LyX-Code

icalproperty *prop;
\layout Standard

Properties are represented with the icalproperty class and its many 
\begin_inset Quotes eld
\end_inset 

derived
\begin_inset Quotes erd
\end_inset 

 classes with on 
\begin_inset Quotes eld
\end_inset 

derived
\begin_inset Quotes erd
\end_inset 

 class per property type in RFC2445.
 Again, there is no actual inheritance relations, but there are clusters
 of routines that make this term useful.
 A property is a container for a single value and a set of parameters.
 
\layout Subsubsection

Components 
\layout LyX-Code

icalcomponent *comp;
\layout Standard

In libical, components are represented with the icalcomponent class.
 Icalcomponent is a container for a set of other components and properties.
\layout Subsubsection

Values 
\layout LyX-Code

icalvalue *value;
\layout Standard

Values are represented in a similar way to properties; a base class and
 many 
\begin_inset Quotes eld
\end_inset 

derived 
\begin_inset Quotes eld
\end_inset 

 classes.
 A value is essentially a abstract handle on a single fundamental type,
 a structure or a union.
 You probably will never use a value directly, since for most operations
 you can get to its data through the property that holds it.
 
\layout Subsubsection

Parameters 
\layout LyX-Code

icalparameter *param;
\layout Standard

Parameters are represetned in a similar way to properties, except that they
 contain only one value
\layout Subsection

Other elements of libical
\layout Standard

In addition to the core iCal classes, libical has many other types, structures,
 classes that aid in creating and using iCal components.
 
\layout Subsubsection

Enumerations and types
\layout Standard

Libical is strongly typed, so every component, property, parameter, and
 value type has an enumeration, and some have an associated structure or
 union.
 
\layout Subsubsection

The parser
\layout Standard

The libical parser offers a variety of ways to convert RFC2445 text into
 a libical iinsteral component structure.
 the parser can parse blocks of text as a string, or it can parse lin-by-line.
\layout Subsubsection

Error objects
\layout Standard

Libical has a substantial error reporting system for both programming errors
 and component usage errors.
 
\layout Subsubsection

Memory Management
\layout Standard

Since many of libicals interfaces return strings, the library has its own
 memory management system to elimiate the need to free every string returned
 from the libraru.
 
\layout Subsubsection

Storage classes
\layout Standard

The library also offers several classes to store components to flies, memory
 or databases.
 
\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 key 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.
 For instanace, the timezone properties associated with daylight savings
 time 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,this grouping is represented by the
 XDAYLIGHT component.
 Standard iCAL components all start with the letter 
\begin_inset Quotes eld
\end_inset 

V,
\begin_inset Quotes erd
\end_inset 

 while pseudo components start with
\begin_inset Quotes erd
\end_inset 

X.
\begin_inset Quotes erd
\end_inset 


\layout Standard

There are also pseudo components that are conceptually derived classes 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 cumbersome 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
 struct icaltriggertype.
 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 LyX-Code

CATEGORIES: work, home
\layout Standard

becomes in libical's internal representation
\layout LyX-Code

CATEGORIES: work
\layout LyX-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

Using libical
\layout Subsection

Creating Components 
\layout Standard

There are three ways to create components in Libical: 
\layout Itemize

Create individual components, properties and parameters and assemble them
 into structures
\layout Itemize

Build complete components with nested vaargs calls
\layout Itemize

Parse bits of text
\layout Itemize

Parse entire files
\layout Subsubsection

Constructor Interfaces 
\layout Standard

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

icalcomponent *event;
\layout LyX-Code

icalproperty *prop;
\layout LyX-Code

icalparameter *param;
\layout LyX-Code

struct icaltimetype atime;
\layout LyX-Code

\layout LyX-Code

event = icalcomponent_new(ICAL_VEVENT_COMPONENT);
\layout LyX-Code

prop = icalproperty_new_dtstamp(atime); 
\layout LyX-Code

icalcomponent_add_property(event, prop);
\layout LyX-Code

\layout LyX-Code

prop = icalproperty_new_uid(''guid-1.host1.com'') );
\layout LyX-Code

icalcomponent_add_property(event,prop);
\layout LyX-Code

\layout LyX-Code

prop=icalproperty_new_organizer(''mrbig@host.com''); 
\layout LyX-Code

param = icalparameter_new_role(ICAL_ROLE_CHAIR) 
\layout LyX-Code

icalproperty_add_parameter(prop, param);
\layout LyX-Code

\layout LyX-Code

icalcomponent_add_property(event,prop);
\layout Standard

Notice that libical uses a semi-object-oriented style of interface.
 Most things you work with are objects, that are instantiated with a constructor
 that has 
\begin_inset Quotes eld
\end_inset 

new
\begin_inset Quotes erd
\end_inset 

 in the name.
 Also note that, other than the object reference, most structure data is
 passed in to libical routines by value.
 Libical has some complex but very regular memory handling rules.
 These are detailed in section 
\begin_inset LatexCommand \ref{sec:memory}

\end_inset 

.
\layout Standard

If any of the constructors fail, they will return 0.
 If you try to insert 0 into a property or component, or use a zero-valued
 object reference, libical will either silently ignore the error or will
 abort with an error message.
 This behavior is controlled by a compile time flag (ICAL_ERRORS_ARE_FATAL),
 and will abort by default.
 
\layout Subsubsection

vaargs Constructors 
\layout Standard

There is another way to create complex components, which is arguably more
 elegant, if you are not horrified by varargs.
 The varargs constructor interface allows you to create intricate components
 in a single block of code.
 Here is the previous examples in the vaargs style.
 
\layout LyX-Code

    calendar = 
\layout LyX-Code

        icalcomponent_vanew(
\layout LyX-Code

            ICAL_VCALENDAR_COMPONENT,
\layout LyX-Code

            icalproperty_new_version(''2.0''),
\layout LyX-Code

            icalproperty_new_prodid(
\layout LyX-Code

                 ''-//RDU Software//NONSGML HandCal//EN''),
\layout LyX-Code

            icalcomponent_vanew(
\layout LyX-Code

                ICAL_VEVENT_COMPONENT,
\layout LyX-Code

                icalproperty_new_dtstamp(atime),
\layout LyX-Code

                icalproperty_new_uid(''guid-1.host1.com''),
\layout LyX-Code

                icalproperty_vanew_organizer(
\layout LyX-Code

                    ''mrbig@host.com''),
\layout LyX-Code

                    icalparameter_new_role(ICAL_ROLE_CHAIR),
\layout LyX-Code

                    0
\layout LyX-Code

                    ),
\layout LyX-Code

                icalproperty_vanew_attendee(
\layout LyX-Code

                    ''employee-A@host.com'',
\layout LyX-Code

                    icalparameter_new_role(
\layout LyX-Code

                        ICAL_ROLE_REQPARTICIPANT),
\layout LyX-Code

                    icalparameter_new_rsvp(1),
\layout LyX-Code

                    icalparameter_new_cutype(ICAL_CUTYPE_GROUP),
\layout LyX-Code

                    0
\layout LyX-Code

                    ),
\layout LyX-Code

                icalproperty_new_location(
\layout LyX-Code

                   "1CP Conference Room 4350"),
\layout LyX-Code

                0
\layout LyX-Code

                ),
\layout LyX-Code

            0
\layout LyX-Code

            );
\layout Standard

This form is similar to the constructor form , except that the constructors
 have 
\begin_inset Quotes eld
\end_inset 

vanew
\begin_inset Quotes erd
\end_inset 

 instead of 
\begin_inset Quotes eld
\end_inset 

new
\begin_inset Quotes erd
\end_inset 

 in the name.
 The arguments are similar too, except that the component constructor can
 have a list of properties, and the property constructor can have a list
 of parameters.
 Be sure to terminate every list with a '0', or your code will crash, if
 you are lucky.
 
\layout Subsubsection

Parsing Text
\layout Standard

Several routines are available for generating objects from text.
 For properties, use:
\layout LyX-Code

icalproperty* p;
\layout LyX-Code

p = icalproperty_new_from_string("DTSTART:19970101T120000Z
\backslash 
n");
\layout Standard

For parameters, use:
\layout LyX-Code

icalparameter *param
\layout LyX-Code

param = icalparameter_new_from_string("PARTSTAT=ACCEPTED");
\layout Standard

The final way to create components will probably be the most common; you
 can create components from RFC2445 compliant text.
 If you have the string in memory, use
\layout LyX-Code

icalcomponent* icalcomponent_new_from_string(char* str);
\layout Standard

If the string contains only one component, the routine will return the component
 in libical form.
 If the string contains multiple components, the multiple components will
 be returned as the children of an ICAL_XROOT_COMPONENT component.
 This routine is identical to ( and actually uses ) icalparser_parse_string(char
* str).
\layout Standard

Parsing a whole string may seem wasteful if you want to pull a large component
 off of the network or from a file; you may prefer to parse the component
 line by line.
 This is possible too by using:
\layout LyX-Code

icalparser* icalparser_new(); 
\layout LyX-Code

void icalparser_free(icalparser* parser);
\layout LyX-Code

icalparser_get_line(parser,read_stream);
\layout LyX-Code

icalparser_add_line(parser,line);
\layout LyX-Code

icalparser_set_gen_data(parser,stream)
\layout Standard

These routines will construct a parser object to which you can add lines
 of input and retrieve any components that the parser creates from the input.
 These routines work by specifing an adaptor routine to get string data
 from a source.
 For an example:
\layout LyX-Code

char* read_stream(char *s, size_t size, void *d) 
\layout LyX-Code

{ 
\layout LyX-Code

  char *c = fgets(s,size, (FILE*)d);
\layout LyX-Code

  return c;
\layout LyX-Code

}
\layout LyX-Code

main() {
\layout LyX-Code

  char* line; 
\layout LyX-Code

  icalcomponent *c; 
\layout LyX-Code

  icalparser *parser = icalparser_new();
\layout LyX-Code

  FILE* stream = fopen(argv[1],"r");
\layout LyX-Code

  icalparser_set_gen_data(parser,stream);
\layout LyX-Code

  do{ 
\layout LyX-Code

    line = icalparser_get_line(parser,read_stream); 
\layout LyX-Code

    c = icalparser_add_line(parser,line);
\layout LyX-Code

    if (c != 0){ 
\layout LyX-Code

     printf("%s",icalcomponent_as_ical_string(c));     
\layout LyX-Code

     icalparser_claim(parser); 
\layout LyX-Code

     printf("
\backslash 
n---------------
\backslash 
n"); 
\layout LyX-Code

     icalcomponent_free(c); 
\layout LyX-Code

   }
\layout LyX-Code

   if (line != 0)
\layout LyX-Code

     icalmemory_free_buffer(line);
\layout LyX-Code

  } while ( line != 0);
\layout LyX-Code

}
\layout Standard

The parser object parameterizes the routine used to get input lines with
 icalparser_set_gen_data() and
\emph on 
 
\emph default 
icalparser_get_line().
 In this example, the routine read_stream() will fetch the next line from
 a stream, with the stream passed in as the void* parameter d.
 The parser calls read_stream() from icalparser_get_line(), but it also
 needs to know what stream to use.
 This is set by the call to icalparser_set_gen_data().
 By using a different routine for read_stream or passing in different data
 with icalparser_set_gen_data, you can connect to any data source.
 
\layout Standard

Using the same mechanism, other implementations could read from memory buffers,
 sockets or other interfaces.
 
\layout Standard

Since the example code is a very common way to use the parser, there is
 a convenience routine;
\layout LyX-Code

icalcomponent* icalparser_parse(icalparser *parser, 
\layout LyX-Code

               char* (*line_gen_func)(char *s, size_t size,  void* d))
\layout Standard

To use this routine, you still must construct the parser object and pass
 in a reference to a line reading routine.
 If the parser can create a single component from the input, it will return
 a pointer to the newly constructed component.
 If the parser can construct multiple components from the input, it will
 return a reference to an XROOT component ( of type ICAL_XROOT_COMPONENT.)
 This XROOT component will hold all of the components constructed from the
 input as children.
 
\layout Subsection

Accessing Components 
\layout Standard

Given a reference to a component, you probably will want to access the propertie
s, parameters and values inside.
 Libical interfaces let you find sub-components, add and remove sub-components,
 and do the same three operations on properties.
 
\layout Subsubsection

Finding Components 
\layout Standard

To find a sub-component of a component, use: 
\layout LyX-Code

icalcomponent* icalcomponent_get_first_component(
\layout LyX-Code

                                   icalcomponent* component, 
\layout LyX-Code

                                   icalcomponent_kind kind);
\layout Standard

This routine will return a reference to the first component of the type
 'kind.' The key kind values, listed in icalenums.h are: 
\layout LyX-Code

ICAL_ANY_COMPONENT
\layout LyX-Code

ICAL_VEVENT_COMPONENT
\layout LyX-Code

ICAL_VTODO_COMPONENT
\layout LyX-Code

ICAL_VJOURNAL_COMPONENT
\layout LyX-Code

ICAL_VCALENDAR_COMPONENT 
\layout LyX-Code

ICAL_VFREEBUSY_COMPONENT
\layout LyX-Code

ICAL_VALARM_COMPONENT
\layout Standard

These are only the most common components; there are many more listed in
 icalenums.h.
\layout Standard

As you might guess, if there is more than one subcomponent of the type you
 have chosen, this routine will return only the first.
 to get at the others, you need to iterate through the component.
 
\layout Subsubsection

Iterating Through Components
\layout Standard

Iteration requires a second routine to get the next subcomponent after the
 first:
\layout LyX-Code

icalcomponent* icalcomponent_get_next_component(
\layout LyX-Code

               icalcomponent* component, 
\layout LyX-Code

               icalcomponent_kind kind);
\layout Standard

With the 'first' and 'next' routines, you can create a for loop to iterate
 through all of a components subcomponents
\layout LyX-Code

  for(c = icalcomponent_get_first_component(comp,ICAL_ANY_COMPONENT); 
\layout LyX-Code

         c != 0; 
\layout LyX-Code

 c = icalcomponent_get_next_component(comp,ICAL_ANY_COMPONENT))
\layout LyX-Code

{ 
\layout LyX-Code

      do_something(c);
\layout LyX-Code

}
\layout Standard

This code bit wil iterate through all of the subcomponents in 'comp' but
 you can select a specific type of component by changing ICAL_ANY_COMPONENT
 to another component type.
\layout Subsubsection

Using Component Iterators
\layout Standard

The iteration model in the previous section requires the component to keep
 the state of the iteration.
 So, you could not use this model to perform a sorting operations, since
 you'd need two iterators and there is only space for one.
 If you ever call icalcomponent_get_first_component() when an iteration
 is in progress, the pointer will be reset to the beginning.
 
\layout Standard

To solve this problem, there are also external iterators for components.
 The routines associated with these external iterators are: 
\layout LyX-Code

icalcompiter icalcomponent_begin_component(icalcomponent* component, icalcompone
nt_kind kind);
\layout LyX-Code

icalcompiter icalcomponent_end_component(icalcomponent* component, icalcomponent
_kind kind);
\layout LyX-Code

icalcomponent* icalcompiter_next(icalcompiter* i); 
\layout LyX-Code

icalcomponent* icalcompiter_prior(icalcompiter* i); 
\layout LyX-Code

icalcomponent* icalcompiter_deref(icalcompiter* i);
\layout Standard

The _begin_() and _end_() routines return a new iterator that points to
 the beginning and ending of the list of subcomponent for the given component,
 and the kind argument works like the kind argument for internal iterators.
 
\layout Standard

After creating an iterators, use _next_() and _prior_() to step forward
 and backward through the list and get the component that the iterator points
 to, and use _deref() to return the component that the iterator points to
 without moving the iterator.
 All routines will return 0 when they move to point off the end of the list.
 
\layout Standard

Here is an example of a loop using these routines: 
\layout LyX-Code

for(
\layout LyX-Code

   i = icalcomponent_begin_component(impl->cluster,ICAL_ANY_COMPONENT);
 
\layout LyX-Code

   icalcompiter_deref(&i)!= 0; 
\layout LyX-Code

   icalcompiter_next(&i)
\layout LyX-Code

) { 
\layout LyX-Code

      icalcomponent *this = icalcompiter_deref(&i);
\layout LyX-Code

}
\layout Subsubsection

Removing Components 
\layout Standard

Removing an element from a list while iterating through the list with the
 internal iterators can cause problems, since you will probably be removing
 the element that the internal iterator points to.
 The _remove() routine will keep the iterator valid by moving it to the
 next component, but in a normal loop, this will result in two advances
 per iteration, and you will remove only every other component.
  To avoid the problem, you will need to step the iterator ahead of the
 element you are going to remove, like this:
\layout LyX-Code

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

       c != 0; 
\layout LyX-Code

       c = next
\layout LyX-Code

{     
\layout LyX-Code

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

    icalcomponent_remove_component(parent_comp,c); 
\layout LyX-Code

}
\layout Standard

Another way to remove components is to rely on the side effect of icalcomponent_
remove_component: if component iterator in the parent component is pointing
 to the child that will be removed, it will move the iterator to the component
 after the child.
 The following code will exploit this behavior: 
\layout LyX-Code

icalcomponent_get_first_component(parent_comp,ICAL_VEVENT_COMPONENT);
\layout LyX-Code

while((c=icalcomponent_get_current_component(c)) != 0 ){ 
\layout LyX-Code

   if(icalcomponent_isa(c) == ICAL_VEVENT_COMPONENT){ 
\layout LyX-Code

      icalcomponent_remove_component(parent_comp,inner);
\layout LyX-Code

   } else { 
\layout LyX-Code

      icalcomponent_get_next_component(parent_comp,ICAL_VEVENT_COMPONENT);
 
\layout LyX-Code

   } 
\layout LyX-Code

}
\layout Subsubsection

Working with properties and parameters
\layout Standard

Finding, iterating and removing properties works the same as it does for
 components, using the property-specific or parameter-specific interfaces:
 
\layout LyX-Code

icalproperty* icalcomponent_get_first_property(
\layout LyX-Code

     icalcomponent* component, 
\layout LyX-Code

     icalproperty_kind kind); 
\layout LyX-Code

icalproperty* icalcomponent_get_next_property(
\layout LyX-Code

     icalcomponent* component, 
\layout LyX-Code

     icalproperty_kind kind);
\layout LyX-Code

void icalcomponent_add_property(
\layout LyX-Code

     icalcomponent* component, 
\layout LyX-Code

     icalproperty* property);
\layout LyX-Code

void icalcomponent_remove_property(
\layout LyX-Code

     icalcomponent* component, 
\layout LyX-Code

     icalproperty* property);
\layout Standard

For parameters:
\layout LyX-Code

icalparameter* icalproperty_get_first_parameter(
\layout LyX-Code

     icalproperty* prop, 
\layout LyX-Code

     icalparameter_kind kind); 
\layout LyX-Code

icalparameter* icalproperty_get_next_parameter(
\layout LyX-Code

     icalproperty* prop, 
\layout LyX-Code

     icalparameter_kind kind);
\layout LyX-Code

void icalproperty_add_parameter(
\layout LyX-Code

     icalproperty* prop,
\layout LyX-Code

     icalparameter* parameter);
\layout LyX-Code

void icalproperty_remove_parameter(
\layout LyX-Code

     icalproperty* prop, 
\layout LyX-Code

     icalparameter_kind kind);
\layout Standard

Note that since there should be only one parameter of each type in a property,
 you will rarely need to use icalparameter_get_nect_paameter.
\layout Subsubsection

Working with values
\layout Standard

Values are typically part of a property, although they can exist on their
 own.
 You can manipulate them either as part of the property or independently.
\layout Standard

The most common way to work with values to is to manipulate them from they
 properties that contain them.
 This involves fewer routine calls and intermediate variables than working
 with them independently, and it is type-safe.
 
\layout Standard

For each property, there are a _get_ and a _set_ routine that access the
 internal value.
 For instanace, for the UID property, the routines are: 
\layout LyX-Code

void icalproperty_set_uid(icalproperty* prop, const char* v)
\layout LyX-Code

const char* icalproperty_get_uid(icalproperty* prop)
\layout Standard

For multi-valued properties, like ATTACH, the value type is usually a struct
 or union that holds both possible types.
 
\layout Standard

If you want to work with the underlying value object, you can get and set
 it with:
\layout LyX-Code

icalvalue* icalproperty_get_value (icalproperty* prop)
\layout LyX-Code

void icalproperty_set_value(icalproperty* prop, icalvalue* value);
\layout Standard

Icalproperty_get_value() will return a reference that you can manipulate
 with other icalvalue routines.
 Most of the time, you will have to know what the type of the value is.
 For instance, if you know that the value is a DATETIME type, you can manipulate
 it with: 
\layout LyX-Code

struct icaltimetype icalvalue_get_datetime(icalvalue* value); 
\layout LyX-Code

void icalvalue_set_datetime(icalvalue* value, struct icaltimetype v);
\layout Standard

When working with an extension property or value (and X-PROPERTY or a property
 that has the parameter VALUE=x-name ) the value type is always a string.
 To get and set the value, use: 
\layout LyX-Code

void icalproperty_set_x(icalproperty* prop, char* v); 
\layout LyX-Code

char* icalproperty_get_x(icalproperty* prop);
\layout Standard

All X properties have the type of ICAL_X_PROPERTY, so you will need these
 routines to get and set the name of the property:
\layout LyX-Code

char* icalproperty_get_x_name(icalproperty* prop)
\layout LyX-Code

void icalproperty_set_x_name(icalproperty* prop, char* name);
\layout Subsubsection

Checking Component Validity
\layout Standard

RFC 2446 defines rules for what properties must exist in a component to
 be used for transferring scheduling data.
 Most of these rules relate to the existence of properties relative to the
 METHOD property, which declares what operation a remote receiver should
 use to process a component.
 For instance, if the METHOD is REQUEST and the component is a VEVENT, the
 sender is probably asking the receiver to join in a meeting.
 In this case, RFC2446 says that the component must specify a start time
 (DTSTART) and list the receiver as an attendee (ATTENDEE).
 
\layout Standard

Libical can check these restrictions with the routine:
\layout LyX-Code

int icalrestriction_check(icalcomponent* comp);
\layout Standard

This routine returns 0 if the component does not pass RFC2446 restrictions,
 or if the component is malformed.
 The component you pass in 
\emph on 
must
\emph default 
 be a VCALENDAR, with one or more children, like the examples in RFC2446.
 
\layout Standard

When this routine runs, it will insert new properties into the component
 to indicate any errors it finds.
 See section 6.5.3, X-LIC-ERROR for more information about these error properties.
 
\layout Subsubsection

Converting Components to Text
\layout Standard

To create an RFC2445 compliant text representation of an object, use one
 of the *_as_ical_string() routines:
\layout LyX-Code

char* icalcomponent_as_ical_string (icalcomponent* component)
\layout LyX-Code

char* icalproperty_as_ical_string (icalproperty* property)
\layout LyX-Code

char* icalparameter_as_ical_string (icalparameter* parameter)
\layout LyX-Code

char* icalvalue_as_ical_string (icalvalue* value)
\layout Standard

In most cases, you will only use icalcomponent_as_ical_string (), since
 it will cascade and convert all of the parameters, properties and values
 that are attached to the root component.
\layout Standard

Icalproperty_as_ical_string() will terminate each line with the RFC2445
 specified line terminator 
\begin_inset Quotes eld
\end_inset 


\backslash 

\backslash 
n
\begin_inset Quotes erd
\end_inset 

 However, if you compile with the symbol ICAL_UNIX_NEWLINE undefined, (
 it is defined by default) it will terminate lines with 
\begin_inset Quotes eld
\end_inset 


\backslash 

\backslash 
n
\backslash 

\backslash 
r
\begin_inset Quotes erd
\end_inset 


\layout Standard

Remember that the string returned by these routines is owned by the library,
 and will eventually be re-written.
 You should copy it if you want to preserve it.
 
\layout Subsection

Time
\layout Subsubsection

Time structure
\layout Standard

LIbical defines it's own time structure for storing all dates and times.
 It would have been nice to re-use the C library's 
\emph on 
struct tm, 
\emph default 
but that structure does not differentiate between dates and times, and between
 local time and UTC.
 The libical structure is:
\layout LyX-Code

struct icaltimetype { 
\layout LyX-Code

  int year; 
\layout LyX-Code

  int month; 
\layout LyX-Code

  int day; 
\layout LyX-Code

  int hour; 
\layout LyX-Code

  int minute; 
\layout LyX-Code

  int second;
\layout LyX-Code

  int is_utc; /* 1-> time is in UTC timezone */
\layout LyX-Code

  int is_date; /* 1 -> interpret this as date.
 */ }; 
\layout Standard

The year, month, day, hour, minute and second fields hold the broken-out
 time values.
 The is_utc field distinguishes between times in UTC and a local time zone.
 The is_date field indicates if the time should be interpreted only as a
 date.
 If it is a date, the hour, minute and second fields are assumed to be zero,
 regardless of their actual vaules.
 
\layout Subsubsection

Creating time structures
\layout Standard

There are several ways to create a new icaltimetype structure: 
\layout LyX-Code

struct icaltimetype icaltime_from_string(const char* str);
\layout LyX-Code

struct icaltimetype icaltime_from_timet(time_t v, int is_date);
\layout LyX-Code

\layout Standard

Icaltime_from_string takes any RFC2445 compliant time string: 
\layout LyX-Code

struct icaltimetype tt = icaltime_from_string("19970101T103000");
\layout Standard

Icaltime_from_timet takes a timet value, representing seconds past the POSIX
 epoch, and a flag to indicate if the time is a date.
 Dates have an identical structure to a time, but the time portion ( hours,
 minuts and seconds ) is always 00:00:00.
 Dates act differently in sorting an comparision, and they have a different
 string representation in RFC2445.
 
\layout Subsubsection

Time manipulating routines
\layout Standard

The null time value is used to indicate that the data in the structure is
 not a valid time.
\layout LyX-Code

struct icaltimetype icaltime_null_time(void);
\layout LyX-Code

int icaltime_is_null_time(struct icaltimetype t);
\layout Standard

It is sensible for the broken-out time fields to contain values that are
 not permitted in an ISO compliant time string.
 For instance, the seconds field can hold values greater than 59, and the
 hours field can hold values larger than 24.
 The excessive values will be rolled over into the next larger field when
 the structure is normalized.
 
\layout LyX-Code

struct icaltimetype icaltime_normalize(struct icaltimetype t);
\layout Standard

Normalizing allows you to do arithmetic operations on time values.
 
\layout LyX-Code

struct icaltimetype tt = icaltime_from_string(
\begin_inset Quotes eld
\end_inset 

19970101T103000
\begin_inset Quotes erd
\end_inset 

);
\layout LyX-Code

tt.days +=3 
\layout LyX-Code

tt.second += 70;
\layout LyX-Code

tt = icaltime_normalize(tt);
\layout Standard

There are several routines to get the day of the week or month, etc, from
 a time structure.
\layout LyX-Code

short icaltime_day_of_year(struct icaltimetype t); 
\layout LyX-Code

struct icaltimetype icaltime_from_day_of_year(short doy, short year);
\layout LyX-Code

short icaltime_day_of_week(struct icaltimetype t); 
\layout LyX-Code

short icaltime_start_doy_of_week(struct icaltimetype t);
\layout LyX-Code

short icaltime_week_number(short day_of_month, short month, short year);
\layout LyX-Code

struct icaltimetype icaltime_from_week_number(short week_number, short year);
\layout LyX-Code

short icaltime_days_in_month(short month,short year);
\layout Standard

Two routines convert time structures to and from the number of seconds since
 the POSIX epoch.
 The is_date field indicates whether or not the hour, minute and second
 fields should be used in the conversion.
\layout LyX-Code

struct icaltimetype icaltime_from_timet(time_t v, int is_date); 
\layout LyX-Code

time_t icaltime_as_timet(struct icaltimetype);
\layout Standard

The compare routine works exactly like strcmp, but on time structures.
 
\layout LyX-Code

int icaltime_compare(struct icaltimetype a,struct icaltimetype b);
\layout Standard

The following routines convert between UTC and a named timezone.
 The tzid field must be a timezone name from the Olsen database, such as
 
\begin_inset Quotes eld
\end_inset 

America/Los_Angeles.
\begin_inset Quotes erd
\end_inset 

 
\layout Standard

The utc_offset routine returns the offset of the named time zone from UTC,
 in seconds.
 
\layout Standard

The tt parameter in the following routines indicates the date on which the
 conversion should be made.
 The tt parameter is necessary because timezones have many different rules
 for when daylight savings time is used, and these rules can change over
 time.
 So, for a single timezone one year may have daylight savings time on March
 15, but for other years March 15 may be standard time, and some years may
 have standard time all year.
 
\layout LyX-Code

int icaltime_utc_offset(struct icaltimetype tt, char* tzid);
\layout LyX-Code

int icaltime_local_utc_offset();
\layout LyX-Code

struct icaltimetype icaltime_as_utc(struct icaltimetype tt,char* tzid);
\layout LyX-Code

struct icaltimetype icaltime_as_zone(struct icaltimetype tt,char* tzid);
\layout LyX-Code

struct icaltimetype icaltime_as_local(struct icaltimetype tt);
\layout Subsection

Storing Objects
\layout Standard

The libical distribution includes a separate library, libicalss, that allows
 you to store iCal component data to disk in a variety of ways.
 This library also includes code to implement the CSTP protocol of CAP and
 has some routines for deciphering incomming messages.
 
\layout Standard

The file storage routines are organized in an inheritance heirarchy that
 is rooted in icalset, with the derived class icalfileset and icaldirset.
 Icalfileset stores components to a file, while icaldirset stores components
 to multiple files, one per month based on DTSTAMP.
 Other storages classess, for storage to a heap or a mysql database are
 planned for the future.
 
\layout Standard

All of the icalset derived classes have the same interface: 
\layout LyX-Code

\layout LyX-Code

icaldirset* icaldirset_new(const char* path);
\layout LyX-Code

void icaldirset_free(icaldirset* store);
\layout LyX-Code

const char* icaldirset_path(icaldirset* store);
\layout LyX-Code

void icaldirset_mark(icaldirset* store);
\layout LyX-Code

icalerrorenum icaldirset_commit(icaldirset* store); 
\layout LyX-Code

icalerrorenum icaldirset_add_component(icaldirset* store, icalcomponent*
 comp);
\layout LyX-Code

icalerrorenum icaldirset_remove_component(icaldirset* store, icalcomponent*
 comp);
\layout LyX-Code

int icaldirset_count_components(icaldirset* store, icalcomponent_kind kind);
\layout LyX-Code

icalerrorenum icaldirset_select(icaldirset* store, icalcomponent* gauge);
\layout LyX-Code

void icaldirset_clear(icaldirset* store);
\layout LyX-Code

icalcomponent* icaldirset_fetch(icaldirset* store, const char* uid);
\layout LyX-Code

int icaldirset_has_uid(icaldirset* store, const char* uid);
\layout LyX-Code

icalcomponent* icaldirset_fetch_match(icaldirset* set, icalcomponent *c);
\layout LyX-Code

icalerrorenum icaldirset_modify(icaldirset* store, icalcomponent *oldc,
 icalcomponent *newc);
\layout LyX-Code

icalcomponent* icaldirset_get_current_component(icaldirset* store);
\layout LyX-Code

icalcomponent* icaldirset_get_first_component(icaldirset* store);
\layout LyX-Code

icalcomponent* icaldirset_get_next_component(icaldirset* store);
\layout Subsubsection

Creating a new set
\layout Standard

You can create a new set from either the base class or the direved class.
 From the base class use one of:
\layout LyX-Code

icalset* icalset_new_file(const char* path); 
\layout LyX-Code

icalset* icalset_new_dir(const char* path); 
\layout LyX-Code

icalset* icalset_new_heap(void); 
\layout LyX-Code

icalset* icalset_new_mysql(const char* path);
\layout Standard

You can also create a new set based on the derived class, For instance,
 with icalfileset: 
\layout LyX-Code

icalfileset* icalfileset_new(const char* path);
\layout LyX-Code

icalfileset* icalfileset_new_open(const char* path, int flags, mode_t mode);
\layout Standard

Icaset_new_file is identical to icalfileset_new.
 BOth routines will open an existing file for readinga and writing, or create
 a new file if it does not exist.
 Icalfilset_new_open takes the same arguments as the open() system routine
 and behaves in the same way.
 
\layout Standard

The icalset and icalfilset objects are somewhat interchangable -- you can
 use an icalfileset* as an argument to any of the icalset routines.
\layout Standard

The following examples will all use icalfileset routines; using the other
 icalset derived classess will be similar.
 
\layout Subsubsection

Adding, Finding and Removing Components 
\layout Standard

To add components to a set, use: 
\layout LyX-Code

icalerrorenum icalfileset_add_component(icalfileset* cluster, icalcomponent*
 child);
\layout Standard

The fileset keeps an inmemory copy of the components, and this set must
 be written back to the file ocassionally.
 There are two routines to manage this: 
\layout LyX-Code

void icalfileset_mark(icalfileset* cluster); 
\layout LyX-Code

icalerrorenum icalfileset_commit(icalfileset* cluster);
\layout Standard

Icalfileset_mark indicates that the in-memory components have changed.
 Calling the _add_component routine will call _mark automatically, but you
 may need to call it yourself if you have made a change to an existing component.
 The _commit routine writes the data base to disk, but only if it is marked.
 The _commit routine is called automatically when the icalfileset is freed.
 
\layout Standard

To iterate through the components in a set, use: 
\layout LyX-Code

icalcomponent* icalfileset_get_first_component(icalfileset* cluster); 
\layout LyX-Code

icalcomponent* icalfileset_get_next_component(icalfileset* cluster);
\layout LyX-Code

icalcomponent* icalfileset_get_current_component (icalfileset* cluster);
  
\layout Standard

These routines work like the corresponding routines from icalcomponent,
 except that their output is filtered through a gauge.
 A gauge is a test for the properties within a components; only components
 that pass the test are returned.
 A gauge can be constructed from a MINSQL string with:
\layout LyX-Code

icalgauge* icalgauge_new_from_sql(char* sql);
\layout Standard

Then, you can add the gauge to the set with : 
\layout LyX-Code

icalerrorenum icalfileset_select(icalfileset* store, icalgauge* gauge);
\layout Standard

Here is an example that puts all of these routines together: 
\layout LyX-Code


\latex no_latex 
void test_fileset()
\layout LyX-Code


\latex no_latex 
{
\layout LyX-Code


\latex no_latex 
    icalfileset *fs;
\layout LyX-Code


\latex no_latex 
    icalcomponent *c;
\layout LyX-Code


\latex no_latex 
    int i;
\layout LyX-Code


\latex no_latex 
    char *path = "test_fileset.ics";
\layout LyX-Code


\latex no_latex 
    icalgauge  *g = icalgauge_new_from_sql(
\layout LyX-Code


\latex no_latex 
        "SELECT * FROM VEVENT WHERE DTSTART > '20000103T120000Z' AND DTSTART
 <= '20000106T120000Z'");
\layout LyX-Code


\latex no_latex 
 
\layout LyX-Code

    
\latex no_latex 
fs = icalfileset_new(path);
\layout LyX-Code

  
\layout LyX-Code

    
\latex no_latex 
for (i = 0; i!= 10; i++){
\layout LyX-Code


\latex no_latex 
        c = make_component(i);
\latex default 
 /* Make a new component where DTSTART has month of i */
\layout LyX-Code


\latex no_latex 
        icalfileset_add_component(fs,c);
\layout LyX-Code


\latex no_latex 
    }
\layout LyX-Code

\layout LyX-Code


\latex no_latex 
    icalfileset_commit(fs);
\latex default 
 /* Write to disk */
\layout LyX-Code

\layout LyX-Code


\latex no_latex 
    icalfileset_select(fs,g);
\latex default 
 /* Set the gauge to filter components */
\layout LyX-Code


\latex no_latex 
 
\layout LyX-Code


\latex no_latex 
    for (c = icalfileset_get_first_component(fs);
\layout LyX-Code


\latex no_latex 
         c != 0;
\layout LyX-Code


\latex no_latex 
         c = icalfileset_get_next_component(fs)){
\layout LyX-Code


\latex no_latex 
        struct icaltimetype t = icalcomponent_get_dtstart(c);
\layout LyX-Code


\latex no_latex 
 
\layout LyX-Code


\latex no_latex 
        printf("%s
\backslash 
n",icaltime_as_ctime(t));
\layout LyX-Code


\latex no_latex 
    }
\layout LyX-Code

    
\latex no_latex 
icalfileset_free(fs);
\layout LyX-Code


\latex no_latex 
}
\layout Subsubsection

Other routines
\layout Standard

There are several other routines in the icalset interface, but they not
 fully implemented yet.
 
\layout Subsection


\begin_inset LatexCommand \label{sec:memory}

\end_inset 

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 transferring 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.
 For example, icalcomponent_as_ical_string().
 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

Libical has several error handling mechanisms for the various types of programmi
ng, semantic and syntactic errors you may encounter.
\layout Subsubsection

Return values
\layout Standard

Many library routines signal errors through their return values.
 All routines that return a pointer, such as icalcomponent_new(), will return
 0 ( zero ) on a fatal error.
 Some routines will return a value of enum icalerrorenum.
 
\layout Subsubsection

icalerrno
\layout Standard

Most routines will set the global error value icalerrno on errors.
 This variable is an enumeration; permissible values can be found in libical/ica
lerror.h.
 If the routine returns an enum icalerrorenum, then the return value will
 be the same as icalerrno.
 You can use icalerror_strerror() to get a string that describes the error.
 The enumerations are:
\layout Standard
\added_space_top 0.3cm \added_space_bottom 0.3cm \align center \LyXTable
multicol5
12 2 0 0 -1 -1 -1 -1
1 1 0 0
1 0 0 0
1 0 0 0
1 0 0 0
1 0 0 0
1 0 0 0
1 0 0 0
1 0 0 0
1 0 0 0
1 0 0 0
1 0 0 0
1 1 0 0
2 1 0 "" ""
2 1 1 "" ""
0 8 1 0 0 0 0 "" ""
0 8 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""


\newline 

\newline 
ICAL_BADARG_ERROR
\newline 
One of the argument to a routine was bad.
 Typically for a null pointer.
\newline 
ICAL_NEWFAILED_ERROR
\newline 
A new() or malloc() failed
\newline 
ICAL_MALFORMEDDATA_ERROR
\newline 
An input string was not in the correct format
\newline 
ICAL_PARSE_ERROR
\newline 
the parser failed to parse an incomming component
\newline 
ICAL_INTERNAL_ERROR 
\newline 
Largely equivalent to an assert; it indicates a bug in the libical code
\newline 
ICAL_FILE_ERROR
\newline 
A file operation failed.
 Check errno for more detai
\newline 
ICAL_ALLOCATION_ERROR
\newline 

\newline 
ICAL_NO_ERROR
\newline 
No error has occured
\newline 
ICAL_TIMEDOUT_ERROR
\newline 
Failed to acquire a lock on a file, or the CSTP protocol timed out.
 
\newline 
ICAL_MULTIPLEINCLUSION_ERROR 
\newline 

\newline 
ICAL_UNKNOWN_ERROR
\newline 

\layout Subsubsection

X-LIC-ERROR and X-LIC-INVALID-COMPONENT
\layout Standard

The library handles semantic and syntactic errors in components by inserting
 errors properties into the components.
 If the parser cannot parse incoming text ( a syntactic error ) or if the
 icalrestriction_check() routine indicates that the component does not meet
 the requirements of RFC2446 ( a semantic error) the library will insert
 properties of the type X-LIC-ERROR to describe the error.
 Here is an example of the error property: 
\layout LyX-Code

X-LIC-ERROR;X-LIC-ERRORTYPE=INVALID_ITIP :Failed iTIP restrictions for property
 DTSTART.
 
\layout LyX-Code

Expected 1 instances of the property and got 0 
\layout Standard

This error resulted from a call to icalrestriction_check(), which discovered
 that the component does not have a DTSTART property, as required by RFC2445.
 
\layout Standard

There are a few routines to manipulate error properties:
\layout Standard
\LyXTable
multicol5
10 2 0 0 -1 -1 -1 -1
1 1 0 0
0 0 0 0
0 1 1 0
0 0 0 0
0 1 1 0
0 1 0 0
0 1 1 0
0 1 0 0
0 1 1 0
0 1 1 0
2 1 1 "" ""
2 1 1 "3in" ""
0 2 1 1 0 0 0 "" ""
0 8 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 1 0 1 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 1 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 1 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 1 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 1 1 0 1 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 1 1 0 1 "" ""
0 2 1 0 0 0 0 "" ""
0 2 1 1 0 0 1 "" ""

Routine
\newline 
Purpose
\newline 
void icalrestriction_check()
\newline 
Check a component against RFC2446 and insert
\newline 

\newline 
error properties to indicate non compliance
\newline 
int icalcomponent_count_errors()
\newline 
Return the number of error properties 
\newline 

\newline 
in a component
\newline 
void icalcomponent_strip_errors()
\newline 
Remove all error properties in as
\newline 

\newline 
component
\newline 
void icalcomponent_convert_errors()
\newline 
Convert some error properties into 
\newline 

\newline 
REQUESTS-STATUS proprties to indicate the inability to 
\newline 

\newline 
process the component as an iTIP request.
 
\layout Standard

The types of errors are listed in icalerror.h.
 They are:
\layout LyX-Code

ICAL_XLICERRORTYPE_COMPONENTPARSEERROR
\layout LyX-Code

ICAL_XLICERRORTYPE_PARAMETERVALUEPARSEERROR
\layout LyX-Code

ICAL_XLICERRORTYPE_PARAMETERNAMEPARSEERROR 
\layout LyX-Code

ICAL_XLICERRORTYPE_PROPERTYPARSEERROR
\layout LyX-Code

ICAL_XLICERRORTYPE_VALUEPARSEERROR
\layout LyX-Code

ICAL_XLICERRORTYPE_UNKVCALPROP
\layout LyX-Code

ICAL_XLICERRORTYPE_INVALIDITIP
\layout Standard

The libical parser will generate the error that end in PARSEERROR when it
 encounters garbage in the input steam.
 ICAL_XLICERRORTYPE_INVALIDITIP is inserted by icalrestriction_check(),
 and ICAL_XLICERRORTYPE_UNKVCALPROP is generated by icalvcal_convert() when
 it encounters a vCal property that it cannot convert or does not know about.
 
\layout Standard

Icalcomponent_convert_errors() converts some of the error properties in
 a component into REQUEST-STATUS properties that indicate a failure.
 As of libical version0.18, this routine only convert *PARSEERROR errors
 and it always generates a 3.x ( failure ) code.
 This makes it more of a good idea than a really useful bit of code.
 
\layout Subsubsection

ICAL_ERRORS_ARE_FATAL and icalerror_errors_are_fatal
\layout Standard

If the global variable icalerror_errors_are_fatal is set to 1, then any
 error condition will cause the program to abort.
 The abort occurs in icalerror_set_errno(), and is done with an assert(0)
 if NDEBUG is undefined, and with icalerror_crash_here if NDEBUG is defined.
 The default value of icalerror_errors_are_fatal is 1 when ICAL_ERRORS_ARE_FATAL
 is defined, and 0 otherwise.
 Since ICAL_ERRORS_ARE_FATAL is defined by default, icalerror_errors_are_fatal
 is also defined by default.
 
\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 

_PARAMETER
\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

Hacks and Bugs
\layout Standard

There are a lot of hacks in the library -- bits of code that I am not proud
 of and should probably be changed.
 These are marked with the comment string 
\begin_inset Quotes eld
\end_inset 

HACK.
\begin_inset Quotes erd
\end_inset 


\the_end