path: root/libical/doc/UsingLibical.lyx

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\layout Title

Using Libical
\layout Author

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

November 2000
\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 for users can store their calendar data and arrange
 meetings with other users.
 
\layout Standard

Libical implements RFC2445 and RFC2446.
 Eventually, it will also implement iRIP and CAP.
 
\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 Verbatim

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 Verbatim

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

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

To: minimalist@softwarestudio.org 
\layout Verbatim

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 more annotated examples.
 
\layout Section

Building the Library
\layout Standard

Libical uses autoconf to generate makefiles, although it uses none of the
 autoconf flags to influence the compilation.
 It should built with no adjustments on Linux, FreeBSD and Solaris under
 gcc.
 Some version have been successfully been build on MacOS, Solaris and UnixWare
 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 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 Verbatim

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 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 Verbatim

BEGIN:VEVENT 
\layout Verbatim

DTSTAMP:19980309T231000Z 
\layout Verbatim

UID:guid-1.host1.com 
\layout Verbatim

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

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

  MAILTO:employee-A@host.com 
\layout Verbatim

DESCRIPTION:Project XYZ Review Meeting 
\layout Verbatim

CATEGORIES:MEETING 
\layout Verbatim

CLASS:PUBLIC 
\layout Verbatim

CREATED:19980309T130000Z 
\layout Verbatim

SUMMARY:XYZ Project Review 
\layout Verbatim

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

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

LOCATION:1CP Conference Room 4350 
\layout Verbatim

END:VEVENT 
\layout Subsection

Core iCal classes
\layout Subsubsection

Components 
\layout Subsubsection

Properties 
\layout Subsubsection

Values 
\layout Subsubsection

Parameters 
\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
\layout Subsubsection

Types
\layout Subsubsection

The parser
\layout Subsubsection

Restrictions
\layout Subsubsection

Error objects
\layout Subsubsection

Memory Management
\layout Subsubsection

Storage classes
\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.
 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 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 Verbatim

CATEGORIES: work, home
\layout Standard

becomes in libical's internal representation
\layout Verbatim

CATEGORIES: work
\layout Verbatim

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

icalcomponent *event;
\layout Code

icalproperty *prop;
\layout Code

icalparameter *param;
\layout Code

struct icaltimetype atime;
\layout Code

event = icalcomponent_new(ICAL_VEVENT_COMPONENT);
\layout Code

prop = icalproperty_new_dtstamp(atime) ;
\layout Code

icalcomponent_add_property(event, prop);
\layout Code

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

icalcomponent_add_property(event,prop);
\layout Code

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

param = icalparameter_new_role(ICAL_ROLE_CHAIR) 
\layout Code

icalproperty_add_parameter(prop, param);
\layout Code

icalcomponent_add_property(event,prop);
\layout Standard

While we are on this example, you should 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 arguable more
 elegant, if you are not horrified by varargs.
 The varargs constructor interface all you to create intricate components
 in a single block of text.
 
\layout Verbatim

    calendar = 
\layout Verbatim

        icalcomponent_vanew(
\layout Verbatim

            ICAL_VCALENDAR_COMPONENT,
\layout Verbatim

            icalproperty_new_version("2.0"),
\layout Verbatim

            icalproperty_new_prodid(
\layout Verbatim

                 "-//RDU Software//NONSGML HandCal//EN"),
\layout Verbatim

            icalcomponent_vanew(
\layout Verbatim

                ICAL_VEVENT_COMPONENT,
\layout Verbatim

                icalproperty_new_dtstamp(atime),
\layout Verbatim

                icalproperty_new_uid("guid-1.host1.com"),
\layout Verbatim

                icalproperty_vanew_organizer(
\layout Verbatim

                    "mrbig@host.com"),
\layout Verbatim

                    icalparameter_new_role(ICAL_ROLE_CHAIR),
\layout Verbatim

                    0
\layout Verbatim

                    ),
\layout Verbatim

                icalproperty_vanew_attendee(
\layout Verbatim

                    "employee-A@host.com",
\layout Verbatim

                    icalparameter_new_role(
\layout Verbatim

                        ICAL_ROLE_REQPARTICIPANT),
\layout Verbatim

                    icalparameter_new_rsvp(1),
\layout Verbatim

                    icalparameter_new_cutype(ICAL_CUTYPE_GROUP),
\layout Verbatim

                    0
\layout Verbatim

                    ),
\layout Verbatim

                icalproperty_new_location(
\layout Verbatim

                   "1CP Conference Room 4350"),
\layout Verbatim

                0
\layout Verbatim

                ),
\layout Verbatim

            0
\layout Verbatim

            );
\layout Standard

This form is similar to the regular constructor, except that they 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 contstructor can
 have a list of properties, and the property constructor can have a list
 or parameters.
 Be sure to terminate every list with a '0', or your code will crash, if
 you are lucky.
 
\layout Subsubsection

Parsing Text Files 
\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 Verbatim

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

This may seem wasteful if you want to pull a large component off of the
 network; you may prefer to parse the component line by line.
 This is possible too by using:
\layout Verbatim

icalparser* icalparser_new(); 
\layout Verbatim

void icalparser_free(icalparser* parser);
\layout Verbatim

icalparser_get_line(parser,read_stream);
\layout Verbatim

icalparser_add_line(parser,line);
\layout Verbatim

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.
 For an example:
\layout Verbatim

char* read_stream(char *s, size_t size, void *d) 
\layout Verbatim

{ 
\layout Verbatim

  char *c = fgets(s,size, (FILE*)d);
\layout Verbatim

  return c;
\layout Verbatim

}
\layout Verbatim

main() {
\layout Verbatim

  char* line; 
\layout Verbatim

  icalcomponent *c; 
\layout Verbatim

  icalparser *parser = icalparser_new();
\layout Verbatim

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

  icalparser_set_gen_data(parser,stream);
\layout Verbatim

  do{ 
\layout Verbatim

    line = icalparser_get_line(parser,read_stream); 
\layout Verbatim

    c = icalparser_add_line(parser,line);
\layout Verbatim

    if (c != 0){ 
\layout Verbatim

     printf("%s",icalcomponent_as_ical_string(c));     
\layout Verbatim

     icalparser_claim(parser); 
\layout Verbatim

     printf("
\backslash 
n---------------
\backslash 
n"); 
\layout Verbatim

     icalcomponent_free(c); 
\layout Verbatim

   }
\layout Verbatim

  } while ( line != 0);
\layout Verbatim

}
\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().
 
\layout Standard

Using the same mechanism, other implmentations 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 convienience routine;
\layout Verbatim

icalcomponent* icalparser_parse(icalparser *parser, 
\layout Verbatim

               char* (*line_gen_func)(char *s, size_t sise,  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 cmponents 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.
 See section 6.2.2 for how to iterate through the child components.
 
\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 interface let you find sub-component, 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 Verbatim

icalcomponent* icalcomponent_get_first_component(
\layout Verbatim

                                   icalcomponent* component, 
\layout Verbatim

                                   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 Verbatim

ICAL_ANY_COMPONENT
\layout Verbatim

ICAL_VEVENT_COMPONENT
\layout Verbatim

ICAL_VTODO_COMPONENT
\layout Verbatim

ICAL_VJOURNAL_COMPONENT
\layout Verbatim

ICAL_VCALENDAR_COMPONENT 
\layout Verbatim

ICAL_VFREEBUSY_COMPONENT
\layout Verbatim

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

Interating Through Components
\layout Standard

Iteration requires a second routine to get the next subcomponent after the
 first:
\layout Verbatim

icalcomponent* icalcomponent_get_next_component(
\layout Verbatim

               icalcomponent* component, 
\layout Verbatim

               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 Verbatim

  for(c = icalcomponent_get_first_component(comp,ICAL_ANY_COMPONENT); 
\layout Verbatim

         c != 0; 
\layout Verbatim

 c = icalcomponent_get_next_component(comp,ICAL_ANY_COMPONENT))
\layout Verbatim

{ 
\layout Verbatim

      do_something(c);
\layout Verbatim

}
\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() which 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 Verbatim

icalcompiter icalcomponent_begin_component(icalcomponent* component, icalcompone
nt_kind kind);
\layout Verbatim

icalcompiter icalcomponent_end_component(icalcomponent* component, icalcomponent
_kind kind);
\layout Verbatim

icalcomponent* icalcompiter_next(icalcompiter* i); 
\layout Verbatim

icalcomponent* icalcompiter_prior(icalcompiter* i); 
\layout Verbatim

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

The _begin_() and _end_() routines return a new iterator that points to
 the begining 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 Verbatim

for(
\layout Verbatim

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

   icalcompiter_deref(&i)!= 0; 
\layout Verbatim

   icalcompiter_next(&i)
\layout Verbatim

) { 
\layout Verbatim

      icalcomponent *this = icalcompiter_deref(&i);
\layout Verbatim

}
\layout Subsubsection

Removing Components 
\layout Standard

Libical component have internal iterators, so you can only have one iteration
 over a component at a time.
 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.
 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 Verbatim

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

       c != 0; 
\layout Verbatim

       c = next
\layout Verbatim

{     
\layout Verbatim

    next = icalcomponent_get_next_component(parent_comp,ICAL_ANY_COMPONENT);
\layout Verbatim

    icalcomponent_remove_component(parent_comp,c); 
\layout Verbatim

}
\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 Verbatim

icalcomponent_get_first_component(parent_comp,ICAL_VEVENT_COMPONENT);
\layout Verbatim

while((c=icalcomponent_get_current_component(c)) != 0 ){ 
\layout Verbatim

   if(icalcomponent_isa(c) == ICAL_VEVENT_COMPONENT){ 
\layout Verbatim

      icalcomponent_remove_component(parent_comp,inner);
\layout Verbatim

   } else { 
\layout Verbatim

      icalcomponent_get_next_component(parent_comp,ICAL_VEVENT_COMPONENT);
 
\layout Verbatim

   } 
\layout Verbatim

}
\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 Verbatim

icalproperty* icalcomponent_get_first_property(
\layout Verbatim

     icalcomponent* component, 
\layout Verbatim

     icalproperty_kind kind); 
\layout Verbatim

icalproperty* icalcomponent_get_next_property(
\layout Verbatim

     icalcomponent* component, 
\layout Verbatim

     icalproperty_kind kind);
\layout Verbatim

void icalcomponent_add_property(
\layout Verbatim

     icalcomponent* component, 
\layout Verbatim

     icalproperty* property);
\layout Verbatim

void icalcomponent_remove_property(
\layout Verbatim

     icalcomponent* component, 
\layout Verbatim

     icalproperty* property);
\layout Verbatim

icalparameter* icalproperty_get_first_parameter(
\layout Verbatim

     icalproperty* prop, 
\layout Verbatim

     icalparameter_kind kind); 
\layout Verbatim

icalparameter* icalproperty_get_next_parameter(
\layout Verbatim

     icalproperty* prop, 
\layout Verbatim

     icalparameter_kind kind);
\layout Verbatim

void icalproperty_add_parameter(
\layout Verbatim

     icalproperty* prop,
\layout Verbatim

     icalparameter* parameter);
\layout Verbatim

void icalproperty_remove_parameter(
\layout Verbatim

     icalproperty* prop, 
\layout Verbatim

     icalparameter_kind kind);
\layout Subsubsection

Working with values
\layout Standard

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

The most common way to work with values to is to maniplate 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 instnace, for the UID property, the routines are: 
\layout Verbatim

void icalproperty_set_uid(icalproperty* prop, const char* v)
\layout Verbatim

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

For multivalued 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 Verbatim

icalvalue* icalproperty_get_value (icalproperty* prop)
\layout Verbatim

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

Icalproperty_get_value() will return a reference that you can manipluate
 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 manipluate
 it with: 
\layout Verbatim

struct icaltimetype icalvalue_get_datetime(icalvalue* value); 
\layout Verbatim

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 Verbatim

void icalproperty_set_x(icalproperty* prop, char* v); 
\layout Verbatim

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

Working with parameters
\layout Subsubsection

Checking Component Validity
\layout Standard

RFC 2446 defines rules for what properties must exist in a component to
 be used for transfering scheduling data.
 Most of these rules relate to the existence of properties relative to the
 METHOD property, which declares what operation a remote reciever 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 reciever to join in a meeting.
 In this case, RFC2446 says that the component must specify a start time
 (DTSTART) and list the reciever as an attendee (ATTENDEE).
 
\layout Standard

Libical can check these restrictions with the routine:
\layout Verbatim

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 representtion of an object, use one
 of the *_as_ical_string() routines:
\layout Verbatim

char* icalcomponent_as_ical_string (icalcomponent* component)
\layout Verbatim

char* icalproperty_as_ical_string (icalproperty* property)
\layout Verbatim

char* icalparameter_as_ical_string (icalparameter* parameter)
\layout Verbatim

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 
r
\backslash 
n
\begin_inset Quotes erd
\end_inset 

 However, if you compile with the symbol ICAL_UNIX_NEWLINE defined, it will
 terminate lines with 
\begin_inset Quotes eld
\end_inset 


\backslash 
n
\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 Verbatim

struct icaltimetype { 
\layout Verbatim

  int year; 
\layout Verbatim

  int month; 
\layout Verbatim

  int day; 
\layout Verbatim

  int hour; 
\layout Verbatim

  int minute; 
\layout Verbatim

  int second;
\layout Verbatim

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

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

The year, month, day, hour, minute and second fields how the broken-out
 time values.
 The is_utc field distinguishes between times UTC and a local time zone.
 The is_date field indicates if the intra-day fields hold valid data.
 
\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 Verbatim

struct icaltimetype icaltime_null_time(void);
\layout Verbatim

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 Verbatim

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

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

short icaltime_day_of_year(struct icaltimetype t); 
\layout Verbatim

struct icaltimetype icaltime_from_day_of_year(short doy, short year);
\layout Verbatim

short icaltime_day_of_week(struct icaltimetype t); 
\layout Verbatim

short icaltime_start_doy_of_week(struct icaltimetype t);
\layout Verbatim

short icaltime_week_number(short day_of_month, short month, short year);
\layout Verbatim

struct icaltimetype icaltime_from_week_number(short week_number, short year);
\layout Verbatim

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 wether or not the hour, minute and second fields
 should be used in the conversion, and is_utc indicates if the value should
 be converted to a local time or a UTC time, using the operating system
 suppled notion of the local timezone.
 
\layout Verbatim

struct icaltimetype icaltime_from_timet(time_t v, int is_date, int is_utc);
 
\layout Verbatim

time_t icaltime_as_timet(struct icaltimetype);
\layout Standard

The compare routine works exactly like strcmp, but on time structures.
 
\layout Verbatim

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 parmeter in the fonllowing 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 Verbatim

int icaltime_utc_offset(struct icaltimetype tt, char* tzid)
\layout Verbatim

struct icaltimetype icaltime_as_utc(struct icaltimetype tt,char* tzid);
\layout Verbatim

struct icaltimetype icaltime_as_zone(struct icaltimetype tt,char* tzid);
\layout Verbatim

\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.
 ( & currently, not at all.
 ) 
\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 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

Libical has several error handling mechanisms for the varioustypes of programmin
g, 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; permissable 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
\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 requirments 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 Verbatim

X-LIC-ERROR;X-LIC-ERRORTYPE=INVALID_ITIP :Failed iTIP restrictions for property
 DTSTART.
 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
1 0 0 0
0 1 1 0
1 0 0 0
0 1 1 0
1 1 0 0
0 1 1 0
1 1 0 0
0 1 1 0
0 1 1 0
2 1 0 "" ""
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 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 Verbatim

ICAL_XLICERRORTYPE_COMPONENTPARSEERROR
\layout Verbatim

ICAL_XLICERRORTYPE_PARAMETERVALUEPARSEERROR
\layout Verbatim

ICAL_XLICERRORTYPE_PARAMETERNAMEPARSEERROR 
\layout Verbatim

ICAL_XLICERRORTYPE_PROPERTYPARSEERROR
\layout Verbatim

ICAL_XLICERRORTYPE_VALUEPARSEERROR
\layout Verbatim

ICAL_XLICERRORTYPE_UNKVCALPROP
\layout Verbatim

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 ina
 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 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

Useful Recipies
\layout Standard

Iteration
\layout Standard

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

Finding compliance errors
\layout Section

Performance
\layout Standard

Checking restrictions is computationally expensive.
\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 propbably be changed.
 These are marked with the comment string 
\begin_inset Quotes eld
\end_inset 

HACK.
\begin_inset Quotes erd
\end_inset 


\the_end