Resource framework

Description

Applications and libraries often contain binary or textual data that is really part of the application, rather than user data. For instance Gnome::Gtk3::Builder .ui files, splashscreen images, Gnome::Gio::Menu markup XML, CSS files, icons, etc. These are often shipped as files in 'some-data-dir/app-name', or manually included as literal strings in the code.

The Gnome::Gio::Resource API and the glib-compile-resources program provide a convenient and efficient alternative to this which has some nice properties. You maintain the files as normal files, so it is easy to edit them, but during the build the files are combined into a binary bundle.

Resource files can also be marked as compressed. Such files will be included in the resource bundle in a compressed form, but will be automatically uncompressed when the resource is used. This is very useful e.g. for larger text files that are parsed once (or rarely) and then thrown away.

Resource files can also be marked to be preprocessed, by setting the value of the `preprocess` attribute to a comma-separated list of preprocessing options. The only options currently supported are:

• xml-stripblanks which will use the xmllint command to strip ignorable whitespace from the XML file. For this to work, the `XMLLINT` environment variable must be set to the full path to the xmllint executable, or xmllint must be in the `PATH`; otherwise the preprocessing step is skipped.

• to-pixdata which will use the gdk-pixbuf-pixdata command to convert images to the Gnome::Gdk3::Pixdata format, which allows you to create pixbufs directly using the data inside the resource file, rather than an (uncompressed) copy if it. For this, the gdk-pixbuf-pixdata program must be in the PATH, or the GDK_PIXBUF_PIXDATA environment variable must be set to the full path to the gdk-pixbuf-pixdata executable; otherwise the resource compiler will abort.

Resource files will be exported in the N-GResource namespace using the combination of the given `prefix` and the filename from the `file` element. The `alias` attribute can be used to alter the filename to expose them at a different location in the resource namespace. Typically, this is used to include files from a different source directory without exposing the source directory in the resource namespace, as in the example below.

Resource bundles are created by the glib-compile-resources program which takes an XML file that describes the bundle, and a set of files that the XML references. These are combined into a binary resource bundle.

An example resource description:

<?xml version="1.0" encoding="UTF-8"?>
<gresources>
  <gresource prefix="/org/gtk/Example">
    <file>data/splashscreen.png</file>
    <file compressed="true">dialog.ui</file>
    <file preprocess="xml-stripblanks">menumarkup.xml</file>
    <file alias="example.css">data/example.css</file>
  </gresource>
</gresources>

This will create a resource bundle with the following files:

/org/gtk/Example/data/splashscreen.png
/org/gtk/Example/dialog.ui
/org/gtk/Example/menumarkup.xml
/org/gtk/Example/example.css

You can then use glib-compile-resources to compile the XML to a binary bundle that you can load with new(:load).

Once a Gnome::Gio::Resource has been created and registered all the data in it can be accessed globally in the process by using API calls like

g_resources_lookup_data() to get a direct pointer to the data. You can also use URIs like "resource:///org/gtk/Example/data/splashscreen.png" with Gnome::Gio::File to access the resource data.

Some higher-level APIs, such as Gnome::Gtk3::Application, will automatically load resources from certain well-known paths in the resource namespace as a convenience. See the documentation for those APIs for details.

There are two forms of the generated source, the default version uses the compiler support for constructor and destructor functions (where available) to automatically create and register the Gnome::Gio::Resource on startup or library load time. If you pass `--manual-register`, two functions to register/unregister the resource are created instead. This requires an explicit initialization call in your application/library, but it works on all platforms, even on the minor ones where constructors are not supported. (Constructor support is available for at least Win32, Mac OS and Linux.)

Note that resource data can point directly into the data segment of e.g. a library, so if you are unloading libraries during runtime you need to be very careful with keeping around pointers to data from a resource, as this goes away when the library is unloaded. However, in practice this is not generally a problem, since most resource accesses are for your own resources, and resource data is often used once, during parsing, and then released.

When debugging a program or testing a change to an installed version, it is often useful to be able to replace resources in the program or library, without recompiling, for debugging or quick hacking and testing purposes. Since GLib 2.50, it is possible to use the `G_RESOURCE_OVERLAYS` environment variable to selectively overlay resources with replacements from the filesystem. It is a G_SEARCHPATH_SEPARATOR-separated list of substitutions to perform during resource lookups.

A substitution has the form

/org/gtk/libgtk=/home/desrt/gtk-overlay

The part before the `=` is the resource subpath for which the overlay applies. The part after is a filesystem path which contains files and subdirectories as you would like to be loaded as resources with the equivalent names.

In the example above, if an application tried to load a resource with the resource path `/org/gtk/libgtk/ui/gtkdialog.ui` then N-GResource would check the filesystem path `/home/desrt/gtk-overlay/ui/gtkdialog.ui`. If a file was found there, it would be used instead. This is an overlay, not an outright replacement, which means that if a file is not found at that path, the built-in version will be used instead. Whiteouts are not currently supported.

Substitutions must start with a slash, and must not contain a trailing slash before the '='. The path after the slash should ideally be absolute, but this is not strictly required. It is possible to overlay the location of a single resource with an individual file.

Synopsis

Declaration

unit class Gnome::Gio::Resource;
also is Gnome::GObject::Boxed;

Types

class N-GResource

Native object to hold a resource bundle

Methods

new

:load

Loads a binary resource bundle and creates a Gnome::Gio::Resource representation of it, allowing you to query it for data.

If you want to use this resource in the global resource namespace you need to register it with register().

If filename is empty or the data in it is corrupt, an exception is thrown with a message about the reason.

multi method new ( :load! )

:native-object

Create a Resource object using a native object from elsewhere. See also Gnome::N::TopLevelClassSupport.

multi method new ( N-GObject :$native-object! )

g_resource_ref

Atomically increments the reference count of resource by one. This function is MT-safe and may be called from any thread.

Returns: The passed in N-GResource

Since: 2.32

method g_resource_ref ( --> N-GResource )

g_resource_unref

Atomically decrements the reference count of resource by one. If the reference count drops to 0, all memory allocated by the resource is released. This function is MT-safe and may be called from any thread.

Since: 2.32

method g_resource_unref ( )

enumerate-children

Returns all the names of children at the specified $path in the resource.

If $path is invalid or does not exist in the Gnome::Gio::Resource, G-RESOURCE-ERROR-NOT-FOUND will be returned.

Returns: a List

method enumerate-children ( Str $path --> List )

• Str $path; A pathname inside the resource

The returned list contains;

• Gnome::Glib::Error; a error object. When $path is invalid or does not exist in the resource, this object is valid and the message will show the reason.

• Array; when there are children at the specified path, they will be stored in this array. Note that there might be a bug in the C-library. Whatever (correct) path is used, there are no children returned.

error-quark

Gets the Gnome::Gio::Resource Error Quark.

Returns: a GQuark

method error-quark ( --> UInt )

get-info

Looks for a file at the specified path in the set of globally registered resources and if found returns information about it.

lookup-flags controls the behaviour of the lookup.

Returns: True if the file was found. False if there were errors

method get-info ( Str $path, GResourceLookupFlags $lookup_flags, UInt $size, UInt $flags, N-GError $error --> Int )

• Str $path; A pathname inside the resource

• GResourceLookupFlags $lookup_flags; A GResourceLookupFlags

• UInt $size; (out) (optional): a location to place the length of the contents of the file, or undefined if the length is not needed

• UInt $flags; (out) (optional): a location to place the GResourceFlags about the file, or undefined if the flags are not needed

• N-GError $error; return location for a GError, or undefined

lookup-data

Looks for a file at the specified path in the set of globally registered resources and returns a GBytes that lets you directly access the data in memory.

The data is always followed by a zero byte, so you can safely use the data as a C string. However, that byte is not included in the size of the GBytes.

For uncompressed resource files this is a pointer directly into the resource bundle, which is typically in some readonly data section in the program binary. For compressed files we allocate memory on the heap and automatically uncompress the data.

lookup-flags controls the behaviour of the lookup.

Returns: (transfer full): GBytes or undefined on error. Free the returned object with g-bytes-unref()

method lookup-data ( Str $path, GResourceLookupFlags $lookup_flags, N-GError $error --> N-GObject )

• Str $path; A pathname inside the resource

• GResourceLookupFlags $lookup_flags; A GResourceLookupFlags

• N-GError $error; return location for a GError, or undefined

register

Registers the resource with the process-global set of resources. Once a resource is registered the files in it can be accessed with the global resource lookup functions like lookup-data().

method register ( )

unregister

Unregisters the resource from the process-global set of resources.

method unregister ( )

g-static-resource-fini

Finalized a N-GResource initialized by g-static-resource-init().

This is normally used by code generated by [glib-compile-resources][glib-compile-resources] and is not typically used by other code.

method g-static-resource-fini ( GStaticResource $static_resource )

• GStaticResource $static_resource; pointer to a static GStaticResource

g-static-resource-get-resource

Gets the N-GResource that was registered by a call to g-static-resource-init().

This is normally used by code generated by [glib-compile-resources][glib-compile-resources] and is not typically used by other code.

Returns: (transfer none): a Gnome::Gio::Resource

method g-static-resource-get-resource ( GStaticResource $static_resource --> N-GResource )

• GStaticResource $static_resource; pointer to a static GStaticResource

g-static-resource-init

Initializes a N-GResource from static data using a GStaticResource.

This is normally used by code generated by [glib-compile-resources][glib-compile-resources] and is not typically used by other code.

method g-static-resource-init ( GStaticResource $static_resource )

• GStaticResource $static_resource; pointer to a static GStaticResource

get-info

Looks for a file at the specified path in the resource and if found returns information about it.

lookup-flags controls the behaviour of the lookup.

Returns: True if the file was found. False if there were errors

method get-info ( Str $path, GResourceLookupFlags $lookup_flags, UInt $size, UInt $flags, N-GError $error --> Int )

• Str $path; A pathname inside the resource

• GResourceLookupFlags $lookup_flags; A GResourceLookupFlags

• UInt $size; (out) (optional): a location to place the length of the contents of the file, or undefined if the length is not needed

• UInt $flags; (out) (optional): a location to place the flags about the file, or undefined if the length is not needed

• N-GError $error; return location for a GError, or undefined

load

Loads a binary resource bundle and creates a Gnome::Gio::Resource representation of it, allowing you to query it for data.

If you want to use this resource in the global resource namespace you need to register it with register().

If filename is empty or the data in it is corrupt, G-RESOURCE-ERROR-INTERNAL will be returned. If filename doesn’t exist, or there is an error in reading it, an error from g-mapped-file-new() will be returned.

Returns: (transfer full): a new Gnome::Gio::Resource, or undefined on error

method load ( Str $filename, N-GError $error --> N-GResource )

• Str $filename; (type filename): the path of a filename to load, in the GLib filename encoding

• N-GError $error; return location for a GError, or undefined

lookup-data

Looks for a file at the specified path in the resource and returns a GBytes that lets you directly access the data in memory.

The data is always followed by a zero byte, so you can safely use the data as a C string. However, that byte is not included in the size of the GBytes.

For uncompressed resource files this is a pointer directly into the resource bundle, which is typically in some readonly data section in the program binary. For compressed files we allocate memory on the heap and automatically uncompress the data.

lookup-flags controls the behaviour of the lookup.

Returns: (transfer full): GBytes or undefined on error. Free the returned object with g-bytes-unref()

method lookup-data ( Str $path, GResourceLookupFlags $lookup_flags, N-GError $error --> N-GObject )

• Str $path; A pathname inside the resource

• GResourceLookupFlags $lookup_flags; A GResourceLookupFlags

• N-GError $error; return location for a GError, or undefined

open-stream

Looks for a file at the specified path in the resource and returns a GInputStream that lets you read the data.

lookup-flags controls the behaviour of the lookup.

Returns: (transfer full): GInputStream or undefined on error. Free the returned object with g-object-unref()

method open-stream ( Str $path, GResourceLookupFlags $lookup_flags, N-GError $error --> GInputStream )

• Str $path; A pathname inside the resource

• GResourceLookupFlags $lookup_flags; A GResourceLookupFlags

• N-GError $error; return location for a GError, or undefined

_g_resource_new_from_data

Creates a N-GResource from a reference to the binary resource bundle. This will keep a reference to data while the resource lives, so the data should not be modified or freed.

If you want to use this resource in the global resource namespace you need to register it with register().

Note: data must be backed by memory that is at least pointer aligned. Otherwise this function will internally create a copy of the memory since GLib 2.56, or in older versions fail and exit the process.

If data is empty or corrupt, G-RESOURCE-ERROR-INTERNAL will be returned.

Returns: (transfer full): a new Gnome::Gio::Resource, or undefined on error

method _g_resource_new_from_data ( N-GObject $data, N-GError $error --> N-GResource )

• N-GObject $data; A GBytes

• N-GError $error; return location for a GError, or undefined