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\quotes_language english
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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
