add Lazy struct to prevent parsing unneeded objects (that may error)

pdf-rs · Mar 15, 2024 · 28c9200 · 28c9200
1 parent bf26151
commit 28c9200
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Showing 4 changed files with 32 additions and 5 deletions.
diff --git a/examples/src/bin/form.rs b/examples/src/bin/form.rs
@@ -43,7 +43,8 @@ fn run() -> Result<(), PdfError> {
     let resources = file.create(resources)?;
 
     let page0 = file.get_page(0).unwrap();
-    for annot in &page0.annotations {
+    let annots = page0.annotations.load(&file.resolver()).expect("can't load annotations");
+    for annot in &annots {
         if let Some(ref a) = annot.appearance_streams {
             let normal = file.resolver().get(a.normal);
             if let Ok(normal) = normal {

diff --git a/pdf/src/build.rs b/pdf/src/build.rs
@@ -132,7 +132,7 @@ impl CatalogBuilder {
                 lgi: page.lgi,
                 vp: page.vp,
                 other: page.other,
-                annotations: vec![]
+                annotations: Default::default(),
             };
             update.fulfill(promise, PagesNode::Leaf(page))?;
         }

diff --git a/pdf/src/object/mod.rs b/pdf/src/object/mod.rs
@@ -430,6 +430,32 @@ impl<T> PartialEq for MaybeRef<T> {
 }
 impl<T> Eq for MaybeRef<T> {}
 
+#[derive(Debug, Clone, DataSize)]
+pub struct Lazy<T> {
+    primitive: Primitive,
+    _marker: PhantomData<T>
+}
+impl<T: Object> Lazy<T> {
+    pub fn load(&self, resolve: &impl Resolve) -> Result<T> {
+        T::from_primitive(self.primitive.clone(), resolve)
+    }
+}
+impl<T: Object> Object for Lazy<T> {
+    fn from_primitive(p: Primitive, _: &impl Resolve) -> Result<Self> {
+        Ok(Self { primitive: p, _marker: PhantomData })
+    }
+}
+impl<T: ObjectWrite> ObjectWrite for Lazy<T> {
+    fn to_primitive(&self, update: &mut impl Updater) -> Result<Primitive> {
+        Ok(self.primitive.clone())
+    }
+}
+impl<T> Default for Lazy<T> {
+    fn default() -> Self {
+        Lazy { primitive: Primitive::Null, _marker: PhantomData }
+    }
+}
+
 //////////////////////////////////////
 // Object for Primitives & other types
 //////////////////////////////////////

diff --git a/pdf/src/object/types.rs b/pdf/src/object/types.rs
@@ -294,8 +294,8 @@ pub struct Page {
     #[pdf(key="VP")]
     pub vp:         Option<Primitive>,
 
-    #[pdf(key="Annots", default="vec![]")]
-    pub annotations: Vec<MaybeRef<Annot>>,
+    #[pdf(key="Annots")]
+    pub annotations: Lazy<Vec<MaybeRef<Annot>>>,
 
     #[pdf(other)]
     pub other: Dictionary,
@@ -326,7 +326,7 @@ impl Page {
             lgi:        None,
             vp:         None,
             other: Dictionary::new(),
-            annotations: vec![]
+            annotations: Default::default(),
         }
     }
     pub fn media_box(&self) -> Result<Rectangle> {