Struct gio::Resource

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pub struct Resource { /* private fields */ }
Expand description

Applications and libraries often contain binary or textual data that is really part of the application, rather than user data. For instance GtkBuilder .ui files, splashscreen images, Menu markup XML, CSS files, icons, etc. These are often shipped as files in $datadir/appname, or manually included as literal strings in the code.

The GResource 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’s easy to edit them, but during the build the files are combined into a binary bundle that is linked into the executable. This means that loading the resource files are efficient (as they are already in memory, shared with other instances) and simple (no need to check for things like I/O errors or locate the files in the filesystem). It also makes it easier to create relocatable applications.

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 (deprecated since gdk-pixbuf 2.32) which will use the gdk-pixbuf-pixdata command to convert images to the GdkPixdata format, which allows you to create pixbufs directly using the data inside the resource file, rather than an (uncompressed) copy of 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. to-pixdata has been deprecated since gdk-pixbuf 2.32, as GResource supports embedding modern image formats just as well. Instead of using it, embed a PNG or SVG file in your GResource.

  • json-stripblanks which will use the json-glib-format command to strip ignorable whitespace from the JSON file. For this to work, the JSON_GLIB_FORMAT environment variable must be set to the full path to the json-glib-format executable, or it must be in the PATH; otherwise the preprocessing step is skipped. In addition, at least version 1.6 of json-glib-format is required.

Resource files will be exported in the 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

Note that all resources in the process share the same namespace, so use Java-style path prefixes (like in the above example) to avoid conflicts.

You can then use glib-compile-resources to compile the XML to a binary bundle that you can load with load(). However, it’s more common to use the --generate-source and --generate-header arguments to create a source file and header to link directly into your application. This will generate get_resource(), register_resource() and unregister_resource() functions, prefixed by the --c-name argument passed to glib-compile-resources. get_resource() returns the generated GResource object. The register and unregister functions register the resource so its files can be accessed using resources_lookup_data().

Once a GResource has been created and registered all the data in it can be accessed globally in the process by using API calls like resources_open_stream() to stream the data or 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 File to access the resource data.

Some higher-level APIs, such as GtkApplication, 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 GResource 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.

§Overlays

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. It is ignored when running in a setuid process.

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 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.

Implementations§

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impl Resource

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pub fn from_data(data: &Bytes) -> Result<Resource, Error>

Creates a 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 g_resources_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, ResourceError::Internal will be returned.

§data

A #GBytes

§Returns

a new #GResource, or None on error

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impl Resource

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pub fn as_ptr(&self) -> *mut GResource

Return the inner pointer to the underlying C value.

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pub unsafe fn from_glib_ptr_borrow<'a>(ptr: *const *const GResource) -> &'a Self

Borrows the underlying C value.

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impl Resource

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pub fn enumerate_children( &self, path: &str, lookup_flags: ResourceLookupFlags ) -> Result<Vec<GString>, Error>

Returns all the names of children at the specified @path in the resource. The return result is a None terminated list of strings which should be released with g_strfreev().

If @path is invalid or does not exist in the #GResource, ResourceError::NotFound will be returned.

@lookup_flags controls the behaviour of the lookup.

§path

A pathname inside the resource

§lookup_flags

A #GResourceLookupFlags

§Returns

an array of constant strings

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pub fn info( &self, path: &str, lookup_flags: ResourceLookupFlags ) -> Result<(usize, u32), Error>

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.

§path

A pathname inside the resource

§lookup_flags

A #GResourceLookupFlags

§Returns

true if the file was found. false if there were errors

§size

a location to place the length of the contents of the file, or None if the length is not needed

§flags

a location to place the flags about the file, or None if the length is not needed

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pub fn lookup_data( &self, path: &str, lookup_flags: ResourceLookupFlags ) -> Result<Bytes, Error>

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.

§path

A pathname inside the resource

§lookup_flags

A #GResourceLookupFlags

§Returns

#GBytes or None on error. Free the returned object with g_bytes_unref()

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pub fn open_stream( &self, path: &str, lookup_flags: ResourceLookupFlags ) -> Result<InputStream, Error>

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.

§path

A pathname inside the resource

§lookup_flags

A #GResourceLookupFlags

§Returns

#GInputStream or None on error. Free the returned object with g_object_unref()

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pub fn load(filename: impl AsRef<Path>) -> Result<Resource, Error>

Loads a binary resource bundle and creates a #GResource 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 g_resources_register().

If @filename is empty or the data in it is corrupt, ResourceError::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.

§filename

the path of a filename to load, in the GLib filename encoding

§Returns

a new #GResource, or None on error

Trait Implementations§

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impl Clone for Resource

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fn clone(&self) -> Self

Returns a copy of the value. Read more
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fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more
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impl Debug for Resource

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl From<Resource> for Value

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fn from(s: Resource) -> Self

Converts to this type from the input type.
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impl HasParamSpec for Resource

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type ParamSpec = ParamSpecBoxed

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type SetValue = Resource

Preferred value to be used as setter for the associated ParamSpec.
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type BuilderFn = fn(_: &str) -> ParamSpecBoxedBuilder<'_, Resource>

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fn param_spec_builder() -> Self::BuilderFn

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impl Hash for Resource

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fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher. Read more
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fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
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impl Ord for Resource

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fn cmp(&self, other: &Resource) -> Ordering

This method returns an Ordering between self and other. Read more
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fn max(self, other: Self) -> Self
where Self: Sized,

Compares and returns the maximum of two values. Read more
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fn min(self, other: Self) -> Self
where Self: Sized,

Compares and returns the minimum of two values. Read more
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fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized + PartialOrd,

Restrict a value to a certain interval. Read more
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impl PartialEq for Resource

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fn eq(&self, other: &Resource) -> bool

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl PartialOrd for Resource

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fn partial_cmp(&self, other: &Resource) -> Option<Ordering>

This method returns an ordering between self and other values if one exists. Read more
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fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator. Read more
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fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more
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fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator. Read more
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fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more
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impl StaticType for Resource

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fn static_type() -> Type

Returns the type identifier of Self.
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impl Eq for Resource

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impl StructuralPartialEq for Resource

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T> FromGlibContainerAsVec<<T as GlibPtrDefault>::GlibType, *const GList> for T

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impl<T> FromGlibContainerAsVec<<T as GlibPtrDefault>::GlibType, *const GSList> for T

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impl<T> FromGlibContainerAsVec<<T as GlibPtrDefault>::GlibType, *mut GList> for T

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impl<T> FromGlibContainerAsVec<<T as GlibPtrDefault>::GlibType, *mut GPtrArray> for T

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impl<T> FromGlibContainerAsVec<<T as GlibPtrDefault>::GlibType, *mut GSList> for T

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impl<T> FromGlibPtrArrayContainerAsVec<<T as GlibPtrDefault>::GlibType, *const GList> for T

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impl<T> FromGlibPtrArrayContainerAsVec<<T as GlibPtrDefault>::GlibType, *const GPtrArray> for T

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impl<T> FromGlibPtrArrayContainerAsVec<<T as GlibPtrDefault>::GlibType, *const GSList> for T

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impl<T> FromGlibPtrArrayContainerAsVec<<T as GlibPtrDefault>::GlibType, *mut GList> for T

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impl<T> FromGlibPtrArrayContainerAsVec<<T as GlibPtrDefault>::GlibType, *mut GPtrArray> for T

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impl<T> FromGlibPtrArrayContainerAsVec<<T as GlibPtrDefault>::GlibType, *mut GSList> for T

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T> Property for T
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type Value = T

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Ensures that the type has been registered with the type system.
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type Owned = T

The resulting type after obtaining ownership.
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Creates owned data from borrowed data, usually by cloning. Read more
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Uses borrowed data to replace owned data, usually by cloning. Read more
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Performs the conversion.
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