minix/common/lib/libprop/prop_ingest.3

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.Dd January 21, 2008
.Dt PROP_INGEST 3
.Os
.Sh NAME
.Nm prop_ingest_context_alloc ,
.Nm prop_ingest_context_free ,
.Nm prop_ingest_context_error ,
.Nm prop_ingest_context_type ,
.Nm prop_ingest_context_key ,
.Nm prop_ingest_context_private ,
.Nm prop_dictionary_ingest
.Nd Ingest a dictionary into an arbitrary binary format
.Sh SYNOPSIS
.In prop/proplib.h
.Ft prop_ingest_context_t
.Fn prop_ingest_context_alloc "void *private"
.Ft void
.Fn prop_ingest_context_free "prop_ingest_context_t ctx"
.Ft prop_ingest_error_t
.Fn prop_ingest_context_error "prop_ingest_context_t ctx"
.Ft prop_type_t
.Fn prop_ingest_context_type "prop_ingest_context_t ctx"
.Ft const char *
.Fn prop_ingest_context_key "prop_ingest_context_t ctx"
.Ft void *
.Fn prop_ingest_context_private "prop_ingest_context_t ctx"
.Ft bool
.Fn prop_dictionary_ingest "prop_dictionary_t dict" \
    "const prop_ingest_table_entry rules[]" \
    "prop_ingest_context_t ctx"
.Pp
.Ft typedef bool
.Fn (*prop_ingest_handler_t) "prop_ingest_context_t" "prop_object_t"
.Sh DESCRIPTION
The
.Nm prop_dictionary_ingest
function provides a convenient way to convert a property list into
an arbitrary binary format or to extract values from dictionaries in a
way that is convenient to an application
.Pq for configuration files, for example .
.Pp
.Nm prop_dictionary_ingest
is driven by a table of rules provided by the application.
Each rule consists of three items:
.Bl -bullet
.It
A C string containing a key to be looked up in the dictionary.
.It
The expected property type of the object associated with the key
(or
.Dv PROP_TYPE_UNKNOWN
to specify that any type is allowed).
.It
A callback function of type
.Dv prop_ingest_handler_t
that will perform the translation for the application.
.El
.Pp
The table is constructed using a series of macros as follows:
.Bd -literal
static const prop_ingest_table_entry ingest_rules[] = {
	PROP_INGEST("file-name", PROP_TYPE_STRING, ingest_filename),
	PROP_INGEST("count", PROP_TYPE_NUMBER, ingest_count),
	PROP_INGEST_OPTIONAL("required", PROP_TYPE_BOOL, ingest_required),
	PROP_INGEST_OPTIONAL("extra", PROP_TYPE_UNKNOWN, ingest_extra),
	PROP_INGEST_END
};
.Ed
.Pp
The
.Dv PROP_INGEST
macro specifies that the key is required to be present in the dictionary.
The
.Dv PROP_INGEST_OPTIONAL
macro specifies that the presence of the key in the dictionary is optional.
The
.Dv PROP_INGEST_END
macro marks the end of the rules table.
.Pp
In each case,
.Nm prop_dictionary_ingest
looks up the rule's key in the dictionary.
If an object is present in the dictionary at that key, its type is checked
against the type specified in the rule.
A type specification of
.Dv PROP_TYPE_UNKNOWN
allows the object to be of any type.
If the object does not exist and the rule is not marked as optional, then
an error is returned.
Otherwise, the handler specified in the rule is invoked with the ingest
context and the object
(or
.Dv NULL
if the key does not exist in the dictionary).
The handler should return
.Dv false
if the value of the object is invalid to indicate failure and
.Dv true
otherwise.
.Pp
The ingest context contains several pieces of information that are
useful during the ingest process.
The context also provides specific error information should the ingest
fail.
.Bl -tag -width "xxxxx"
.It Fn prop_ingest_context_alloc "void *private"
Allocate an ingest context.
The argument
.Fa private
may be used to pass application-specific context to the ingest handlers.
Note that an ingest context can be re-used to perform multiple ingests.
Returns
.Dv NULL
on failure.
.It Fn prop_ingest_context_free "prop_ingest_context_t ctx"
Free an ingest context.
.It Fn prop_ingest_context_error "prop_ingest_context_t ctx"
Returns the code indicating the error encountered during ingest.
The following error codes are defined:
.Pp
.Bl -tag -width "PROP_INGEST_ERROR_HANDLER_FAILED" -compact
.It Dv PROP_INGEST_ERROR_NO_ERROR
No error was encountered during ingest.
.It Dv PROP_INGEST_ERROR_NO_KEY
A non-optional key was not found in the dictionary.
.It Dv PROP_INGEST_ERROR_WRONG_TYPE
An object in the dictionary was not the same type specified in the rules.
.It Dv PROP_INGEST_ERROR_HANDLER_FAILED
An object's handler returned
.Dv false .
.El
.Pp
.It Fn prop_ingest_context_type "prop_ingest_context_t ctx"
Returns the type of the last object visited during an ingest.
When called by an ingest handler, it returns the type of the object
currently being processed.
.It Fn prop_ingest_context_key "prop_ingest_context_t ctx"
Returns the last dictionary key looked up during an ingest.
When called by an ingest handler, it returns the dictionary key corresponding
to the object currently being processed.
.It Fn prop_ingest_context_private "prop_ingest_context_t ctx"
Returns the private data set when the context was allocated with
.Fn prop_ingest_context_alloc .
.El
.Sh SEE ALSO
.Xr prop_dictionary 3 ,
.Xr proplib 3
.Sh HISTORY
The
.Nm proplib
property container object library first appeared in
.Nx 4.0 .