Author: Eric Busboom [email protected]
Date: January 2001
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.
Libical implements multiple RFC calendar standards.
This documentation assumes that you are familiar with the iCalendar standards RFC5545 and RFC5546. These specifications are available at the IETF Tools website:
This code is under active development. If you would like to contribute to the project, visit https://libical.github.io/libical/.
The code and datafiles in this distribution are licensed under the Mozilla Public License version 2.0. See https://www.mozilla.org/MPL for a copy of the license. Alternately, you may use libical under the terms of the GNU Lesser General Public License, version 2.1. See https://www.gnu.org/licenses/lgpl-2.1.html for a copy of the LGPL.
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. We (the libical developers) will only accept changes to this library if they are similarly dual-licensed.
A lot of the documentation for this library is in the form of example
code. These examples are in the examples/ directory of the distribution.
Also look in src/test/ for additional annotated examples.
Libical uses CMake to generate makefiles. It should build with no adjustments on Linux,
MacOS and Windows using gcc, clang and Microsoft Visual. Please report build problems
to the Libical issue tracker.
For a more complete guide to building the library, see the Install.txt file
in the distribution.
The iCalendar data model is based on four types of objects: components, properties, values and parameters.
Properties are the fundamental unit of information in iCalendar, 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
ORGANIZER;ROLE=CHAIR:MAILTO:[email protected]The property name is ORGANIZER, the value of the property is [email protected]
and the ROLE parameter specifies that Mr Big is the chair of the
meetings associated with this property.
Components are groups of properties that represent the core objects
of a calendar system, such as events or timezones. Components are
delimited by BEGIN and END tags.
When a component is sent across a network, if it is un-encrypted, it will look something like:
BEGIN:VCALENDAR
METHOD:REQUEST
PRODID: -//hacksw/handcal//NONSGML v1.0//EN
BEGIN:VEVENT
DTSTAMP:19980309T231000Z
UID:guid-1.host1.com
ORGANIZER;ROLE=CHAIR:MAILTO:[email protected]
ATTENDEE;RSVP=TRUE;ROLE=REQ-PARTICIPANT;CUTYPE=GROUP:
MAILTO:[email protected]
DESCRIPTION:Project XYZ Review Meeting
CATEGORIES:MEETING
CLASS:PUBLIC
CREATED:19980309T130000Z
SUMMARY:XYZ Project Review
DTSTART;TZID=US-Eastern:19980312T083000
DTEND;TZID=US-Eastern:19980312T093000
LOCATION:1CP Conference Room 4350
END:VEVENT
END:VCALENDARNote that components can be nested; this example has both a VCALENDAR and a VEVENT component, one nested inside the other.
Libical is an object-based, data-oriented library. Nearly all of the routines in the library are associated with an opaque data types and perform some operation on that data type. 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.
Properties are represented with the icalproperty class and its many
"derived" classes with one "derived" class per property type in RFC5545.
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.
In libical, components are represented with the icalcomponent class.
icalcomponent is a container for a set of other components and properties.
Values are represented in a similar way to properties; a base class and many "derived " classes. A value is essentially an abstract handle on a single fundamental type, a structure or a union.
Parameters are represented in a similar way to properties, except that they contain only one value.
In addition to the core iCal classes, libical has many other types, structures, and classes that aid in creating and using iCal components.
Libical is strongly typed, so every component, property, parameter, and value type has an enumeration, and some have an associated structure or union.
The libical parser offers a variety of ways to convert RFC5545 text into a libical internal component structure. The parser can parse blocks of text as a string, or it can parse line-by-line.
Libical has a substantial error reporting system for both programming errors and component usage errors.
Since many of libical's interfaces return strings, the library has its own memory management system to eliminate the need to free every string returned from the library. See Memory Management.
The library also offers several classes to store components to files, memory or databases.
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.
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 instance, the
timezone properties associated with daylight savings time starts with
BEGIN:DAYLIGHT and ends with END:DAYLIGHT, just like other components,
but is not defined as a component in RFC5545 (see section 3.6.5)
In libical, this grouping is represented by the XDAYLIGHT component.
Standard iCal components all start with the letter "V," while pseudo
components start with "X."
There are also pseudo components that are conceptually derived classes
of VALARM. RFC5546 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.
For instance, if a VALARM component has an ACTION property with the
value of AUDIO, the component must also have an ATTACH property.
However, if the ACTION value is DISPLAY, the component must have
a DESCRIPTION property.
To handle these various, complex restrictions, libical has pseudo components
for each type of alarm: XAUDIOALARM, XDISPLAYALARM, XEMAILALARM and
XPROCEDUREALARM.
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.
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 RFC5545 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.
Some properties, such as CATEGORIES have only one value type, but each
CATEGORIES 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,
CATEGORIES: work, homebecomes in libical's internal representation
CATEGORIES: work
CATEGORIES: homeOddly, RFC5545 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.
There are three ways to create components in Libical:
- creating individual objects and assembling them,
- building entire objects in massive vargs calls,
- parsing a text file containing iCalendar data.
Using constructor interfaces, you create each of the objects separately and then assemble them in to components:
icalcomponent *event;
icalproperty *prop;
icalparameter *param;
struct icaltimetype atime;
// create new VEVENT component
event = icalcomponent_new(ICAL_VEVENT_COMPONENT);
// add DTSTAMP property to the event
prop = icalproperty_new_dtstamp(atime);
icalcomponent_add_property(event, prop);
// add UID property to the event
prop = icalproperty_new_uid("guid-1.example.com");
icalcomponent_add_property(event, prop);
// add ORGANIZER (with ROLE=CHAIR) to the event
prop = icalproperty_new_organizer("[email protected]");
param = icalparameter_new_role(ICAL_ROLE_CHAIR);
icalproperty_add_parameter(prop, param);
icalcomponent_add_property(event, prop);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 "new" 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 Memory Management.
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.
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.
icalcomponent *calendar;
struct icaltimetype atime;
calendar =
icalcomponent_vanew(
ICAL_VCALENDAR_COMPONENT,
icalproperty_new_version("2.0"),
icalproperty_new_prodid(
"-//RDU Software//NONSGML HandCal//EN"),
icalcomponent_vanew(
ICAL_VEVENT_COMPONENT,
icalproperty_new_dtstamp(atime),
icalproperty_new_uid("guid-1.host1.com"),
icalproperty_vanew_organizer(
"[email protected]",
icalparameter_new_role(ICAL_ROLE_CHAIR),
(void *)0),
icalproperty_vanew_attendee(
"[email protected]",
icalparameter_new_role(
ICAL_ROLE_REQPARTICIPANT),
icalparameter_new_rsvp(1),
icalparameter_new_cutype(ICAL_CUTYPE_GROUP),
(void *)0),
icalproperty_new_location(
"1CP Conference Room 4350"),
(void *)0),
(void *)0);This form is similar to the constructor form, except that the constructors
have vanew instead of new 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 NULL (or a (void 0), or your code
will crash, if you are lucky. The reason you can't use 0 itself is that
depending on what platform you are on, sizeof(int) ≠ sizeof(void *).
The final way to create components will probably be the most common; you can create components from RFC5545 compliant text. If you have the string in memory, use
icalcomponent* icalparser_parse_string(char* str);If the string contains only one component, the parser 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.
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:
icalparser* icalparser_new();
void icalparser_free(
icalparser* parser);
icalparser_get_line(
icalparser *parser,
char* (*read_stream)(char *s, size_t size, void *d));
icalparser_add_line(
icalparser *parser,
char *line);
icalparser_set_gen_data(
icalparser *parser,
void *data);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 specifying an adaptor routine to get string data from a source. For example:
char* read_stream(char *s, size_t size, void *d)
{
return fgets(s, size, (FILE*)d);
}
int main(int argc, char *argv[])
{
char *line;
icalcomponent *component;
icalparser *parser = icalparser_new();
// open file (first command-line argument)
FILE* stream = fopen(argv[1], "r");
// associate the FILE with the parser so that read_stream
// will have access to it
icalparser_set_gen_data(parser, stream);
do {
// read the file, line-by-line, and parse the data
line = icalparser_get_line(parser, read_stream);
component = icalparser_add_line(parser, line);
// if icalparser has finished parsing a component,
// it will return it
if (component != 0) {
// print the parsed component
printf("%s", icalcomponent_as_ical_string(component));
icalparser_clean(parser);
printf("\n---------------\n");
icalcomponent_free(component);
}
} while (line != 0);
return 0;
}The parser object parametrizes the routine used to get input lines
with icalparser_set_gen_data()and 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.
Using the same mechanism, other implementations could read from memory buffers, sockets or other interfaces.
Since the example code is a very common way to use the parser, there is a convenience routine;
icalcomponent* icalparser_parse(
icalparser *parser,
char* (*line_gen_func)(char *s, size_t size, void *d));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.
char* read_stream(char *s, size_t size, void *d)
{
return fgets(s, size, (FILE*)d);
}
int main(int argc, char *argv[])
{
char* line;
icalcomponent *component;
icalparser *parser = icalparser_new();
// open file (first command-line argument)
FILE* stream = fopen(argv[1], "r");
// associate the FILE with the parser so that read_stream
// will have access to it
icalparser_set_gen_data(parser, stream);
// parse the opened file
component = icalparser_parse(parser, read_stream);
if (component != 0) {
// print the parsed component
printf("%s", icalcomponent_as_ical_string(component));
icalcomponent_free(component);
}
icalparser_free(parser);
return 0;
}Given a reference to a component, you probably will want to access the properties, parameters and values inside. Libical interfaces let you find sub-component, add and remove sub-components, and do the same three operations on properties.
To find a sub-component of a component, use:
icalcomponent* icalcomponent_get_first_component(
icalcomponent* component,
icalcomponent_kind kind);This routine will return a reference to the first component of the
type kind. The key kind values, listed in icalenums.h are:
ICAL_ANY_COMPONENTICAL_VEVENT_COMPONENTICAL_VTODO_COMPONENTICAL_VJOURNAL_COMPONENTICAL_VCALENDAR_COMPONENTICAL_VFREEBUSY_COMPONENTICAL_VALARM_COMPONENT
These are only the most common components; there are many more listed in icalenums.h.
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.
Iteration requires a second routine to get the next subcomponent after the first:
icalcomponent* icalcomponent_get_next_component(
icalcomponent* component,
icalcomponent_kind kind);With the 'first' and 'next' routines, you can create a for loop to iterate through all of a components subcomponents
icalcomponent *c;
for(c = icalcomponent_get_first_component(comp, ICAL_ANY_COMPONENT);
c != 0;
c = icalcomponent_get_next_component(comp, ICAL_ANY_COMPONENT))
{
do_something(c);
}This code bit will 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.
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.
To solve this problem, there are also external iterators for components. The routines associated with these external iterators are:
icalcompiter icalcomponent_begin_component(
icalcomponent* component,
icalcomponent_kind kind);
icalcompiter icalcomponent_end_component(
icalcomponent* component,
icalcomponent_kind kind);
icalcomponent* icalcompiter_next(
icalcompiter* i);
icalcomponent* icalcompiter_prior(
icalcompiter* i);
icalcomponent* icalcompiter_deref(
icalcompiter* i);The *_begin_*() and *_end_*() routines return a new iterator that points
to the beginning and end of the list of subcomponent for the given
component, and the kind argument works like the kind argument for
internal iterators.
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.
Here is an example of a loop using these routines:
for(i = icalcomponent_begin_component(impl->cluster, ICAL_ANY_COMPONENT);
icalcompiter_deref(&i)!= 0;
icalcompiter_next(&i))
{
icalcomponent *this = icalcompiter_deref(&i);
}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:
for(c = icalcomponent_get_first_component(parent_comp, ICAL_ANY_COMPONENT);
c != 0;
c = next)
{
next = icalcomponent_get_next_component(parent_comp, ICAL_ANY_COMPONENT);
icalcomponent_remove_component(parent_comp,c);
}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:
icalcomponent_get_first_component(parent_comp,ICAL_VEVENT_COMPONENT);
while((c=icalcomponent_get_current_component(c)) != 0){
if(icalcomponent_isa(c) == ICAL_VEVENT_COMPONENT){
icalcomponent_remove_component(parent_comp,inner);
} else {
icalcomponent_get_next_component(parent_comp,ICAL_VEVENT_COMPONENT);
}
}Finding, iterating and removing properties works the same as it does for components, using the property-specific or parameter-specific interfaces:
icalproperty* icalcomponent_get_first_property(
icalcomponent* component,
icalproperty_kind kind);
icalproperty* icalcomponent_get_next_property(
icalcomponent* component,
icalproperty_kind kind);
void icalcomponent_add_property(
icalcomponent* component,
icalproperty* property);
void icalcomponent_remove_property(
icalcomponent* component,
icalproperty* property);For parameters:
icalparameter* icalproperty_get_first_parameter(
icalproperty* prop,
icalparameter_kind kind);
icalparameter* icalproperty_get_next_parameter(
icalproperty* prop,
icalparameter_kind kind);
void icalproperty_add_parameter(
icalproperty* prop,
icalparameter* parameter);
void icalproperty_remove_parameter_by_kind(
icalproperty* prop,
icalparameter_kind kind);Note that since there should be only one parameter of each type in
a property, you will rarely need to use icalparameter_get_next_parameter().
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.
The most common way to work with values to is to manipulate them from the properties that contain them. This involves fewer routine calls and intermediate variables than working with them independently, and it is type-safe.
For each property, there are a _get_() and a _set_() routine that
accesses the internal value. For instanace, for the UID property, the
routines are:
void icalproperty_set_uid(
icalproperty* prop,
const char* v);
const char* icalproperty_get_uid(
icalproperty* prop);For multi-valued properties, like ATTACH, the value type is usually
a struct or union that holds both possible types.
If you want to work with the underlying value object, you can get and set it with:
icalvalue* icalproperty_get_value(
icalproperty* prop);
void icalproperty_set_value(
icalproperty* prop,
icalvalue* value);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:
struct icaltimetype icalvalue_get_datetime(
icalvalue* value);
void icalvalue_set_datetime(
icalvalue* value,
struct icaltimetype v);Some complex value types, such as ATTACH and RECUR, are passed by reference
rather than by value. For example, when using icalvalue_get_recur(), you
receive a reference to the internal state of the value object. Conversely, when
setting these values, the value object retains a reference to the original
object instead of creating a copy.
Caution: Manipulating this referenced object will also modify the owning value object.
Be mindful of the memory management for these objects, which is managed through reference counting. For more details, see Memory Management.
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:
void icalproperty_set_x(
icalproperty* prop,
char* v);
char* icalproperty_get_x(
icalproperty* prop);
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:
char* icalproperty_get_x_name(
icalproperty* prop)
void icalproperty_set_x_name(
icalproperty* prop,
char* name);RFC5546 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, RFC5546 says that the component must specify
a start time (DTSTART) and list the receiver as an attendee
(ATTENDEE).
Libical can check these restrictions with the routine:
int icalrestriction_check(icalcomponent* comp);This routine returns 0 if the component does not pass RFC5546 restrictions,
or if the component is malformed. The component you pass in must be
a VCALENDAR, with one or more children, like the examples in RFC5546.
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.
5.2.8 Converting Components to Text
To create an RFC5545 compliant text representation of an object, use
one of the *_as_ical_string() routines:
char* icalcomponent_as_ical_string(icalcomponent* component)
char* icalproperty_as_ical_string(icalproperty* property)
char* icalparameter_as_ical_string(icalparameter* parameter)
char* icalvalue_as_ical_string(icalvalue* value)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.
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.
Libical defines its own time structure for storing all dates and times.
It would have been nice to reuse the C library's struct tm, but that
structure does not differentiate between dates and times, and between
local time and UTC. The libical structure is:
struct icaltimetype {
int year;
int month;
int day;
int hour;
int minute;
int second;
int is_utc; /* 1-> time is in UTC timezone */
int is_date; /* 1 -> interpret this as date. */
};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 values.
There are several ways to create a new icaltimetype structure:
struct icaltimetype icaltime_from_string(
const char* str);
struct icaltimetype icaltime_from_timet_with_zone(
icaltime_t v,
int is_date,
icaltimezone* zone);icaltime_from_string() takes any RFC5545 compliant time string:
struct icaltimetype tt = icaltime_from_string("19970101T103000");icaltime_from_timet_with_zone() takes a icaltime_t value, representing seconds past
the POSIX epoch, a flag to indicate if the time is a date, and a time zone.
Dates have an identical structure to a time, but the time portion (hours,
minutes and seconds) is always 00:00:00. Dates act differently in
sorting and comparison, and they have a different string representation
in RFC5545.
The null time value is used to indicate that the data in the structure
is not a valid time.
struct icaltimetype icaltime_null_time(void);
int icaltime_is_null_time(struct icaltimetype t);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.
struct icaltimetype icaltime_normalize(struct icaltimetype t);Normalizing allows you to do arithmetic operations on time values.
struct icaltimetype tt = icaltime_from_string("19970101T103000");
tt.days +=3
tt.second += 70;
tt = icaltime_normalize(tt);There are several routines to get the day of the week or month, etc, from a time structure.
short icaltime_day_of_year(
struct icaltimetype t);
struct icaltimetype icaltime_from_day_of_year(
short doy,
short year);
short icaltime_day_of_week(
struct icaltimetype t);
short icaltime_start_doy_week(
struct icaltimetype t,
int fdow);
short icaltime_week_number(
short day_of_month,
short month,
short year);
short icaltime_days_in_month(
short month,
short year);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.
struct icaltimetype icaltime_from_timet_with_zone(
icaltime_t v,
int is_date,
icaltimezone* zone);
icaltime_t icaltime_as_timet(
struct icaltimetype);The compare routine works exactly like strcmp(), but on time structures.
int icaltime_compare(
struct icaltimetype a,
struct icaltimetype b);The following routines convert between UTC and a named timezone. The
tzid field must be a timezone name from the Olsen database, such as
America/Los_Angeles.
The utc_offset routine returns the offset of the named time zone from
UTC, in seconds.
The tt parameter in the following routines indicates the date on which
the conversion should be made. The 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.
int icaltime_utc_offset(
struct icaltimetype tt,
char* tzid);
int icaltime_local_utc_offset();
struct icaltimetype icaltime_as_utc(
struct icaltimetype tt,
char* tzid);
struct icaltimetype icaltime_as_zone(
struct icaltimetype tt,
char* tzid);
struct icaltimetype icaltime_as_local(
struct icaltimetype tt);The libical distribution includes a separate library, libicalss, that allows you to store iCal component data to disk in a variety of ways.
The file storage routines are organized in an inheritance hierarchy 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 classes, for storage to a heap or a mysql database for example, could be added in the future.
All of the icalset derived classes have the same interface:
icaldirset* icaldirset_new(
const char* path);
void icaldirset_free(
icaldirset* store);
const char* icaldirset_path(
icaldirset* store);
void icaldirset_mark(
icaldirset* store);
icalerrorenum icaldirset_commit(
icaldirset* store);
icalerrorenum icaldirset_add_component(
icaldirset* store,
icalcomponent* comp);
icalerrorenum icaldirset_remove_component(
icaldirset* store,
icalcomponent* comp);
int icaldirset_count_components(
icaldirset* store,
icalcomponent_kind kind);
icalerrorenum icaldirset_select(
icaldirset* store,
icalcomponent* gauge);
void icaldirset_clear(
icaldirset* store);
icalcomponent* icaldirset_fetch(
icaldirset* store,
const char* uid);
int icaldirset_has_uid(
icaldirset* store,
const char* uid);
icalcomponent* icaldirset_fetch_match(
icaldirset* set,
icalcomponent *c);
icalerrorenum icaldirset_modify(
icaldirset* store,
icalcomponent *oldc,
icalcomponent *newc);
icalcomponent* icaldirset_get_current_component(
icaldirset* store);
icalcomponent* icaldirset_get_first_component(
icaldirset* store);
icalcomponent* icaldirset_get_next_component(
icaldirset* store);You can create a new set from either the base class or the direved class. From the base class use one of:
icalset* icalset_new_file(const char* path);
icalset* icalset_new_dir(const char* path);
icalset* icalset_new_heap(void);
icalset* icalset_new_mysql(const char* path);You can also create a new set based on the derived class, For instance, with icalfileset:
icalfileset* icalfileset_new(
const char* path);
icalfileset* icalfileset_new_open(
const char* path,
int flags,
int mode);icalset_new_file() is identical to icalfileset_new(). Both routines will
open an existing file for reading and writing, or create a new file
if it does not exist. icalfileset_new_open() takes the same arguments
as the open() system routine and behaves in the same way.
The icalset and icalfileset objects are somewhat interchangeable -- you
can use an icalfileset* as an argument to any of the icalset routines.
The following examples will all use icalfileset routines; using the other icalset derived classes will be similar.
To add components to a set, use:
icalerrorenum icalfileset_add_component(
icalfileset* cluster,
icalcomponent* child);The fileset keeps an in-memory copy of the components, and this set must be written back to the file occasionally. There are two routines to manage this:
void icalfileset_mark(icalfileset* cluster);
icalerrorenum icalfileset_commit(icalfileset* cluster);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.
To iterate through the components in a set, use:
icalcomponent* icalfileset_get_first_component(icalfileset* cluster);
icalcomponent* icalfileset_get_next_component(icalfileset* cluster);
icalcomponent* icalfileset_get_current_component (icalfileset* cluster);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:
icalgauge* icalgauge_new_from_sql(const char* sql);Then, you can add the gauge to the set with :
icalerrorenum icalfileset_select(
icalfileset* store,
icalgauge* gauge);Here is an example that puts all of these routines together:
void test_fileset()
{
icalfileset *fs;
icalcomponent *c;
int i;
char *path = "test_fileset.ics";
icalgauge *g = icalgauge_new_from_sql(
"SELECT * FROM VEVENT WHERE DTSTART > '20000103T120000Z' AND
DTSTART <= '20000106T120000Z'");
fs = icalfileset_new(path);
for (i = 0; i!= 10; i++){
c = make_component(i); /* Make a new component where DTSTART has month of i */
icalfileset_add_component(fs,c);
}
icalfileset_commit(fs); /* Write to disk */
icalfileset_select(fs,g); /* Set the gauge to filter components */
for (c = icalfileset_get_first_component(fs);
c != 0;
c = icalfileset_get_next_component(fs))
{
struct icaltimetype t = icalcomponent_get_dtstart(c);
printf("%s\n",icaltime_as_ctime(t));
}
icalfileset_free(fs);
}There are several other routines in the icalset interface, but they not fully implemented yet.
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.
-
If the function name has "new" in it (such as
icalcomponent_new(), oricalproperty_new_from_string()), the caller gets control of the memory. The caller also gets control over an object that is cloned via a function that ends with "_clone" (likeicalcomponent_clone()) -
If you got the memory from a routine with "clone" or "new" in it, you must call the corresponding
*_free()routine to free the memory, for example useicalcomponent_free()to free objects created withicalcomponent_new()oricalcomponent_clone(). The only exception to this rule are objects that implement reference counting (i.e.icalattachandicalrecurrencetype), which are deallocated via*_unref()functions. Learn more in the next section. -
If the function name has "add" in it, the caller is transferring control of the memory to the routine, for example the function
icalproperty_add_parameter() -
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. -
If the routine returns a string and its name does NOT end in
_r, libical owns the memory and will put it on a ring buffer to reclaim later. For example,icalcomponent_as_ical_string(). You betterstrdup()it if you want to keep it, and you don't have to delete it. -
If the routine returns a string and its name does end in
_r, the caller gets control of the memory and is responsible for freeing it. For example,icalcomponent_as_ical_string_r()does the same thing asicalcomponent_as_ical_string(), except you now have control of the string buffer it returns.
Some special types are managed using reference counting, in particular:
icalattachstruct icalrecurrencetype
Just as any other object they are allocated using any of the *_new*() functions, e.g.
icalrecurrencetype_new_from_string()icalattach_new_from_data()
When an object is returned by one of these constructor functions, its reference counter is set to 1.
The reference counter can be modified using:
*_ref()– to increase the counter.*_unref()– to decrease the counter.
The object is automatically deallocated when the reference counter reaches 0.
No explicit *_free() functions exist for these types.
When such objects are passed to functions as arguments, it is the task of the function being called to manage the reference counter, not of the caller. If a pointer to an object is returned by a function other than the constructor functions, it is the task of the calling function rather than of the returning function to manage the reference counter.
Libical has several error handling mechanisms for the various types of programming, semantic and syntactic errors you may encounter.
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.
5.6.2 icalerrno
Most routines will set the global error value icalerrno on errors.
This variable is an enumeration; permissible values can be found in
libical/icalerror.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:
-
ICAL_BADARG_ERROR: One of the arguments to a routine was bad. Typically for a null pointer. -
ICAL_NEWFAILED_ERROR: Anew()ormalloc()failed. -
ICAL_MALFORMEDDATA_ERROR: An input string was not in the correct format -
ICAL_PARSE_ERROR: The parser failed to parse an incoming component -
ICAL_INTERNAL_ERROR: Largely equivalent to an assert -
ICAL_FILE_ERROR: A file operation failed. Check errno for more detail. -
ICAL_ALLOCATION_ERROR: ? -
ICAL_USAGE_ERROR: ? -
ICAL_NO_ERROR: No error -
ICAL_MULTIPLEINCLUSION_ERROR: ? -
ICAL_TIMEDOUT_ERROR: For CSTP and acquiring locks -
ICAL_UNKNOWN_ERROR: ?
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 RFC5546 (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:
X-LIC-ERROR;X-LIC-ERRORTYPE=INVALID_ITIP :Failed iTIP restrictions
for property DTSTART.
Expected 1 instances of the property and got 0This error resulted from a call to icalrestriction_check(), which discovered
that the component does not have a DTSTART property, as required by
RFC5545.
There are a few routines to manipulate error properties:
| Routine | Purpose |
|---|---|
void icalrestriction_check() |
Check a component against RFC5546 and insert error properties to indicate non compliance |
int icalcomponent_count_errors() |
Return the number of error properties in a component |
void icalcomponent_strip_errors() |
Remove all error properties in a component |
void icalcomponent_convert_errors() |
Convert some error properties into REQUESTS-STATUS properties to indicate the inability to process the component as an iTIP request |
The types of errors are listed in icalerror.h. They are:
ICAL_XLICERRORTYPE_COMPONENTPARSEERRORICAL_XLICERRORTYPE_PARAMETERVALUEPARSEERRORICAL_XLICERRORTYPE_PARAMETERNAMEPARSEERRORICAL_XLICERRORTYPE_PROPERTYPARSEERRORICAL_XLICERRORTYPE_VALUEPARSEERRORICAL_XLICERRORTYPE_UNKVCALPROPICAL_XLICERRORTYPE_INVALIDITIP
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.
icalcomponent_convert_errors() converts some of the error properties
in a component into REQUEST-STATUS properties that indicate a failure.
As of libical version 0.18, this routine only converts 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.
If icalerror_get_errors_are_fatal() returns 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.
Initially, icalerror_get_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_get_errors_are_fatal() is also set to 1 by default.
You can change the compiled-in ICAL_ERRORS_ARE_FATAL behavior at runtime
by calling icalerror_set_errors_are_fatal(0) (i.e, errors are not fatal)
or icalerror_set_errors_are_fatal(1) (i.e, errors are fatal).
Structures that you access with the "struct" keyword, such as struct icaltimetype are things that you are allowed to see inside and poke
at.
Structures that you access though a typedef, such as icalcomponent
are things where all of the data is hidden.
Component names that start with "V" are part of RFC5545 or another
iCal standard. Component names that start with "X" 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 XLIC or X-LIC are not part of any iCal spec.
They are used internally by libical.
Enums that identify a component, property, value or parameter end with
_COMPONENT, _PROPERTY, _VALUE, or _PARAMETER"
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.
The enums for the parts of a recurrence rule and request statuses are irregular.
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 "HACK."
struct icaltimetype
{
int year;
int month;
int day;
int hour;
int minute;
int second;
int is_utc;
int is_date;
const char* zone;
};