perf: improve XML deserialization speed

7 files changed, 857 insertions, 447 deletions

diff --git a/src/command.rs b/src/command.rs
index c7ada95..2ba92ea 100644
--- a/src/command.rs
+++ b/src/command.rs
@@ -1,5 +1,14 @@
 //! OpenGL command.
-use crate::xml::element::{Elements, FromElements};
+use quick_xml::events::BytesStart;
+
+use crate::deserialization::{
+    Deserialize,
+    DeserializeWithFn,
+    Deserializer,
+    DeserializerError,
+    IgnoreEnd,
+    ResultExt,
+};
 
 /// A command.
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -38,25 +47,21 @@ impl Command
     }
 }
 
-impl FromElements for Command
+impl Deserialize for Command
 {
     type Error = Error;
 
-    fn from_elements(
-        elements: &crate::xml::element::Elements,
+    fn deserialize<TDeserializer: Deserializer>(
+        start: &BytesStart,
+        deserializer: &mut TDeserializer,
     ) -> Result<Self, Self::Error>
     {
-        let proto_element = elements
-            .get_first_tagged_element("proto")
-            .ok_or(Self::Error::MissingPrototype)?;
+        let prototype = deserializer.de_tag::<Prototype>("proto", IgnoreEnd::No)?;
 
-        let prototype = Prototype::from_elements(proto_element.child_elements())?;
+        let parameters = deserializer.de_tag_list::<Parameter>("param")?;
 
-        let parameters = elements
-            .get_all_tagged_elements_with_name("param")
-            .into_iter()
-            .map(|param_element| Parameter::from_elements(param_element.child_elements()))
-            .collect::<Result<Vec<_>, _>>()?;
+        deserializer
+            .skip_to_tag_end(std::str::from_utf8(start.name().as_ref()).unwrap())?;
 
         Ok(Self {
             prototype,
@@ -80,6 +85,10 @@ pub enum Error
     /// Invalid parameter.
     #[error("Invalid parameter")]
     InvalidParameter(#[from] ParameterError),
+
+    /// Deserialization failed.
+    #[error("Deserialization failed")]
+    DeserializationFailed(#[from] DeserializerError),
 }
 
 /// A command prototype.
@@ -116,23 +125,22 @@ impl Prototype
     }
 }
 
-impl FromElements for Prototype
+impl Deserialize for Prototype
 {
     type Error = PrototypeError;
 
-    fn from_elements(
-        elements: &crate::xml::element::Elements,
+    fn deserialize<TDeserializer: Deserializer>(
+        _start: &BytesStart,
+        deserializer: &mut TDeserializer,
     ) -> Result<Self, Self::Error>
     {
-        let name = elements
-            .get_first_tagged_element("name")
-            .ok_or(Self::Error::MissingName)?
-            .child_elements()
-            .get_first_text_element()
-            .cloned()
-            .unwrap_or_default();
+        let return_type = deserialize_type::<PrototypeError>(deserializer)?;
 
-        let return_type = find_type(elements);
+        let name = deserializer.de_tag_with::<_, _, DeserializeWithFn<_, _, _>>(
+            "name",
+            IgnoreEnd::No,
+            |_, deserializer| deserializer.de_text(),
+        )?;
 
         Ok(Self { name, return_type })
     }
@@ -145,6 +153,14 @@ pub enum PrototypeError
     /// No 'name' element was found.
     #[error("No 'name' element was found")]
     MissingName,
+
+    /// No return type was found.
+    #[error("No return type was found")]
+    MissingReturnType,
+
+    /// Deserialization failed.
+    #[error("Deserialization failed")]
+    DeserializationFailed(#[from] DeserializerError),
 }
 
 /// A command parameter.
@@ -181,21 +197,22 @@ impl Parameter
     }
 }
 
-impl FromElements for Parameter
+impl Deserialize for Parameter
 {
     type Error = ParameterError;
 
-    fn from_elements(elements: &Elements) -> Result<Self, Self::Error>
+    fn deserialize<TDeserializer: Deserializer>(
+        _start: &BytesStart,
+        deserializer: &mut TDeserializer,
+    ) -> Result<Self, Self::Error>
     {
-        let name = elements
-            .get_first_tagged_element("name")
-            .ok_or(Self::Error::MissingName)?
-            .child_elements()
-            .get_first_text_element()
-            .cloned()
-            .unwrap_or_default();
+        let ty = deserialize_type::<ParameterError>(deserializer)?;
 
-        let ty = find_type(elements);
+        let name = deserializer.de_tag_with::<_, _, DeserializeWithFn<_, _, _>>(
+            "name",
+            IgnoreEnd::No,
+            |_, deserializer| deserializer.de_text(),
+        )?;
 
         Ok(Self { name, ty })
     }
@@ -208,46 +225,47 @@ pub enum ParameterError
     /// No 'name' element was found.
     #[error("No 'name' element was found")]
     MissingName,
+
+    /// Deserialization failed.
+    #[error("Deserialization failed")]
+    DeserializationFailed(#[from] DeserializerError),
 }
 
-fn find_type(elements: &Elements) -> String
+fn deserialize_type<Err>(deserializer: &mut impl Deserializer) -> Result<String, Err>
+where
+    Err: From<DeserializerError>,
 {
-    let text_type_parts = elements
-        .get_all_text_elements()
-        .into_iter()
-        .map(|text_type_part| text_type_part.trim())
-        .filter(|text_type_part| !text_type_part.is_empty())
-        .collect::<Vec<_>>();
+    let type_before = deserializer.de_text().try_event()?;
 
-    let opt_ptype_text = get_ptype_text(elements);
+    let type_ptype = deserializer
+        .de_tag_with::<_, _, DeserializeWithFn<_, _, _>>(
+            "ptype",
+            IgnoreEnd::No,
+            |_, deserializer| deserializer.de_text(),
+        )
+        .try_event()?;
 
-    opt_ptype_text.map_or_else(
-        || join_space_strs(text_type_parts.iter()),
-        |ptype_text| {
-            let Some(first_part) = text_type_parts.first() else {
-                return ptype_text.clone();
-            };
+    let type_after = deserializer.de_text().try_event()?;
 
-            let before = if *first_part == "const" { "const " } else { "" };
+    let type_before_after = [type_before.clone(), type_after.clone()]
+        .into_iter()
+        .flatten();
 
-            let after_start_index = usize::from(*first_part == "const");
+    Ok(type_ptype.map_or_else(
+        || join_space_strs(type_before_after),
+        |ptype_text| {
+            let before = type_before
+                .map(|before| format!("{before} "))
+                .unwrap_or_default();
 
             format!(
-                "{before}{ptype_text} {}",
-                text_type_parts
-                    .get(after_start_index..)
-                    .map(|parts| join_space_strs(parts.iter()))
+                "{before}{ptype_text}{}",
+                type_after
+                    .map(|after| format!(" {after}"))
                     .unwrap_or_default()
             )
         },
-    )
-}
-
-fn get_ptype_text(elements: &Elements) -> Option<&String>
-{
-    let ptype_element = elements.get_first_tagged_element("ptype")?;
-
-    ptype_element.child_elements().get_first_text_element()
+    ))
 }
 
 fn join_space_strs<Strings, StrItem>(strings: Strings) -> String
@@ -261,3 +279,420 @@ where
         .collect::<Vec<_>>()
         .join(" ")
 }
+
+#[cfg(test)]
+mod tests
+{
+    use pretty_assertions::assert_str_eq;
+    use quick_xml::events::Event;
+    use ridicule::mock;
+    use ridicule::predicate::{always, eq, function};
+
+    use super::*;
+
+    mock! {
+        MockDeserializer {}
+
+        impl Deserializer for MockDeserializer {
+            fn de_tag<De: Deserialize>(
+                &mut self,
+                tag_name: &str,
+                ignore_end: IgnoreEnd,
+            ) -> Result<De, DeserializerError>;
+
+            fn de_tag_with<Output, Err, DeserializeFn>(
+                &mut self,
+                tag_name: &str,
+                ignore_end: IgnoreEnd,
+                deserialize: DeserializeFn,
+            ) -> Result<Output, DeserializerError>
+            where
+                Err: std::error::Error + Send + Sync + 'static,
+                DeserializeFn: FnOnce(&BytesStart, &mut MockDeserializer) -> Result<Output, Err>;
+
+            fn de_tag_list<De: Deserialize>(
+                &mut self,
+                tag_name: &str
+            ) -> Result<Vec<De>, DeserializerError>;
+
+            fn de_text(&mut self) -> Result<String, DeserializerError>;
+
+            fn skip_to_tag_start(&mut self, tag_name: &str) -> Result<(), DeserializerError>;
+
+            fn skip_to_tag_end(&mut self, tag_name: &str) -> Result<(), DeserializerError>;
+        }
+    }
+
+    #[test]
+    fn deserialize_prototype_works_with_ptype()
+    {
+        let mut mock_deserializer = MockDeserializer::new();
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| {
+                Err(DeserializerError::UnexpectedEvent {
+                    expected_event_name: "text".to_string(),
+                    found_event: Event::Start(BytesStart::new("ptype")),
+                })
+            })
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("GLuint".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_tag_with::<String, DeserializerError, DeserializeWithFn<_, _, _>>()
+            .with(
+                eq("ptype"),
+                function(|ignore_end| matches!(ignore_end, IgnoreEnd::No)),
+                always(),
+            )
+            .returning(|deserializer, tag_name, _, func| {
+                func(&BytesStart::new(tag_name), deserializer)
+            })
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| {
+                Err(DeserializerError::UnexpectedEvent {
+                    expected_event_name: "text".to_string(),
+                    found_event: Event::Start(BytesStart::new("name")),
+                })
+            })
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("glDoComplicatedThing".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_tag_with::<String, DeserializerError, DeserializeWithFn<_, _, _>>()
+            .with(
+                eq("name"),
+                function(|ignore_end| matches!(ignore_end, IgnoreEnd::No)),
+                always(),
+            )
+            .returning(|deserializer, tag_name, _, func| {
+                func(&BytesStart::new(tag_name), deserializer)
+            })
+            .times(1);
+
+        let prototype =
+            Prototype::deserialize(&BytesStart::new("proto"), &mut mock_deserializer)
+                .expect("Expected Ok");
+
+        assert_str_eq!(prototype.name, "glDoComplicatedThing");
+        assert_str_eq!(prototype.return_type, "GLuint");
+    }
+
+    #[test]
+    fn deserialize_prototype_works_with_text()
+    {
+        let mut mock_deserializer = MockDeserializer::new();
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("void".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_tag_with::<String, DeserializerError, DeserializeWithFn<_, _, _>>()
+            .with(
+                eq("ptype"),
+                function(|ignore_end| matches!(ignore_end, IgnoreEnd::No)),
+                always(),
+            )
+            .returning(|_, _, _, _| {
+                Err(DeserializerError::UnexpectedEvent {
+                    expected_event_name: "start".to_string(),
+                    found_event: Event::Start(BytesStart::new("name")),
+                })
+            })
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| {
+                Err(DeserializerError::UnexpectedEvent {
+                    expected_event_name: "text".to_string(),
+                    found_event: Event::Start(BytesStart::new("name")),
+                })
+            })
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("glDoSomeThing".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_tag_with::<String, DeserializerError, DeserializeWithFn<_, _, _>>()
+            .with(
+                eq("name"),
+                function(|ignore_end| matches!(ignore_end, IgnoreEnd::No)),
+                always(),
+            )
+            .returning(|deserializer, tag_name, _, func| {
+                func(&BytesStart::new(tag_name), deserializer)
+            })
+            .times(1);
+
+        let prototype =
+            Prototype::deserialize(&BytesStart::new("proto"), &mut mock_deserializer)
+                .expect("Expected Ok");
+
+        assert_str_eq!(prototype.name, "glDoSomeThing");
+        assert_str_eq!(prototype.return_type, "void");
+    }
+
+    #[test]
+    fn deserialize_parameter_works_with_ptype_only()
+    {
+        let mut mock_deserializer = MockDeserializer::new();
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| {
+                Err(DeserializerError::UnexpectedEvent {
+                    expected_event_name: "text".to_string(),
+                    found_event: Event::Start(BytesStart::new("ptype")),
+                })
+            })
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("GLenum".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_tag_with::<String, DeserializerError, DeserializeWithFn<_, _, _>>()
+            .with(
+                eq("ptype"),
+                function(|ignore_end| matches!(ignore_end, IgnoreEnd::No)),
+                always(),
+            )
+            .returning(|deserializer, tag_name, _, func| {
+                func(&BytesStart::new(tag_name), deserializer)
+            })
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| {
+                Err(DeserializerError::UnexpectedEvent {
+                    expected_event_name: "text".to_string(),
+                    found_event: Event::Start(BytesStart::new("name")),
+                })
+            })
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("value".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_tag_with::<String, DeserializerError, DeserializeWithFn<_, _, _>>()
+            .with(
+                eq("name"),
+                function(|ignore_end| matches!(ignore_end, IgnoreEnd::No)),
+                always(),
+            )
+            .returning(|deserializer, tag_name, _, func| {
+                func(&BytesStart::new(tag_name), deserializer)
+            })
+            .times(1);
+
+        let parameter =
+            Parameter::deserialize(&BytesStart::new("param"), &mut mock_deserializer)
+                .expect("Expected Ok");
+
+        assert_str_eq!(parameter.name, "value");
+        assert_str_eq!(parameter.ty, "GLenum");
+    }
+
+    #[test]
+    fn deserialize_parameter_works_with_ptype_and_text_after()
+    {
+        let mut mock_deserializer = MockDeserializer::new();
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| {
+                Err(DeserializerError::UnexpectedEvent {
+                    expected_event_name: "text".to_string(),
+                    found_event: Event::Start(BytesStart::new("ptype")),
+                })
+            })
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("GLchar".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_tag_with::<String, DeserializerError, DeserializeWithFn<_, _, _>>()
+            .with(
+                eq("ptype"),
+                function(|ignore_end| matches!(ignore_end, IgnoreEnd::No)),
+                always(),
+            )
+            .returning(|deserializer, tag_name, _, func| {
+                func(&BytesStart::new(tag_name), deserializer)
+            })
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("*".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("source".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_tag_with::<String, DeserializerError, DeserializeWithFn<_, _, _>>()
+            .with(
+                eq("name"),
+                function(|ignore_end| matches!(ignore_end, IgnoreEnd::No)),
+                always(),
+            )
+            .returning(|deserializer, tag_name, _, func| {
+                func(&BytesStart::new(tag_name), deserializer)
+            })
+            .times(1);
+
+        let parameter =
+            Parameter::deserialize(&BytesStart::new("param"), &mut mock_deserializer)
+                .expect("Expected Ok");
+
+        assert_str_eq!(parameter.name, "source");
+        assert_str_eq!(parameter.ty, "GLchar *");
+    }
+
+    #[test]
+    fn deserialize_parameter_works_with_ptype_and_text_before_and_after()
+    {
+        let mut mock_deserializer = MockDeserializer::new();
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("const".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("GLchar".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_tag_with::<String, DeserializerError, DeserializeWithFn<_, _, _>>()
+            .with(
+                eq("ptype"),
+                function(|ignore_end| matches!(ignore_end, IgnoreEnd::No)),
+                always(),
+            )
+            .returning(|deserializer, tag_name, _, func| {
+                func(&BytesStart::new(tag_name), deserializer)
+            })
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("*".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("name".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_tag_with::<String, DeserializerError, DeserializeWithFn<_, _, _>>()
+            .with(
+                eq("name"),
+                function(|ignore_end| matches!(ignore_end, IgnoreEnd::No)),
+                always(),
+            )
+            .returning(|deserializer, tag_name, _, func| {
+                func(&BytesStart::new(tag_name), deserializer)
+            })
+            .times(1);
+
+        let parameter =
+            Parameter::deserialize(&BytesStart::new("param"), &mut mock_deserializer)
+                .expect("Expected Ok");
+
+        assert_str_eq!(parameter.name, "name");
+        assert_str_eq!(parameter.ty, "const GLchar *");
+    }
+
+    #[test]
+    fn deserialize_parameter_works_with_text()
+    {
+        let mut mock_deserializer = MockDeserializer::new();
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("void *".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_tag_with::<String, DeserializerError, DeserializeWithFn<_, _, _>>()
+            .with(
+                eq("ptype"),
+                function(|ignore_end| matches!(ignore_end, IgnoreEnd::No)),
+                always(),
+            )
+            .returning(|_, _, _, _| {
+                Err(DeserializerError::UnexpectedEvent {
+                    expected_event_name: "start".to_string(),
+                    found_event: Event::Start(BytesStart::new("name")),
+                })
+            })
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| {
+                Err(DeserializerError::UnexpectedEvent {
+                    expected_event_name: "text".to_string(),
+                    found_event: Event::Start(BytesStart::new("name")),
+                })
+            })
+            .times(1);
+
+        mock_deserializer
+            .expect_de_text()
+            .returning(|_| Ok("pixels".to_string()))
+            .times(1);
+
+        mock_deserializer
+            .expect_de_tag_with::<String, DeserializerError, DeserializeWithFn<_, _, _>>()
+            .with(
+                eq("name"),
+                function(|ignore_end| matches!(ignore_end, IgnoreEnd::No)),
+                always(),
+            )
+            .returning(|deserializer, tag_name, _, func| {
+                func(&BytesStart::new(tag_name), deserializer)
+            })
+            .times(1);
+
+        let parameter =
+            Parameter::deserialize(&BytesStart::new("param"), &mut mock_deserializer)
+                .expect("Expected Ok");
+
+        assert_str_eq!(parameter.name, "pixels");
+        assert_str_eq!(parameter.ty, "void *");
+    }
+}
diff --git a/src/deserialization/buffer_deserializer.rs b/src/deserialization/buffer_deserializer.rs
new file mode 100644
index 0000000..652e1ff
--- /dev/null
+++ b/src/deserialization/buffer_deserializer.rs
@@ -0,0 +1,210 @@
+use std::any::type_name;
+use std::error::Error;
+use std::io::BufRead;
+
+use quick_xml::events::{BytesStart, Event};
+use quick_xml::Reader;
+
+use crate::deserialization::{
+    Deserialize,
+    Deserializer,
+    DeserializerError,
+    IgnoreEnd,
+    WrappedDeserializeError,
+};
+
+macro_rules! read_event {
+    ($self: ident) => {{
+        let event = if let Some(leftover_event) = $self.leftover_event.take() {
+            leftover_event
+        } else {
+            $self.reader.read_event_into(&mut $self.buf)?.into_owned()
+        };
+
+        if let Event::Eof = &event {
+            return Err(DeserializerError::UnexpectedEndOfFile);
+        }
+
+        event
+    }};
+}
+
+pub struct BufferDeserializer<Source>
+{
+    reader: Reader<Source>,
+    leftover_event: Option<Event<'static>>,
+    buf: Vec<u8>,
+}
+
+impl<Source> BufferDeserializer<Source>
+where
+    Source: BufRead,
+{
+    pub fn new(source: Source) -> Self
+    {
+        let mut reader = Reader::from_reader(source);
+
+        reader.trim_text(true);
+        reader.expand_empty_elements(true);
+
+        Self {
+            reader,
+            leftover_event: None,
+            buf: Vec::new(),
+        }
+    }
+}
+
+impl<Source> Deserializer for BufferDeserializer<Source>
+where
+    Source: BufRead,
+{
+    fn de_tag<De: Deserialize>(
+        &mut self,
+        tag_name: &str,
+        ignore_end: IgnoreEnd,
+    ) -> Result<De, DeserializerError>
+    {
+        self.de_tag_with(tag_name, ignore_end, De::deserialize)
+    }
+
+    fn de_tag_with<Output, Err, DeserializeFn>(
+        &mut self,
+        tag_name: &str,
+        ignore_end: IgnoreEnd,
+        deserialize: DeserializeFn,
+    ) -> Result<Output, DeserializerError>
+    where
+        Err: Error + Send + Sync + 'static,
+        DeserializeFn: FnOnce(&BytesStart, &mut Self) -> Result<Output, Err>,
+    {
+        let deserialized = match read_event!(self) {
+            Event::Start(start) if start.name().as_ref() == tag_name.as_bytes() => {
+                deserialize(&start, self).map_err(|err| {
+                    DeserializerError::DeserializeFailed(
+                        type_name::<Output>(),
+                        WrappedDeserializeError::new(err),
+                    )
+                })?
+            }
+            event => {
+                self.leftover_event = Some(event.clone().into_owned());
+
+                return Err(DeserializerError::UnexpectedEvent {
+                    expected_event_name: format!("start({tag_name})"),
+                    found_event: event,
+                });
+            }
+        };
+
+        if let IgnoreEnd::No = ignore_end {
+            self.read_end_event(tag_name)?;
+        }
+
+        Ok(deserialized)
+    }
+
+    fn de_tag_list<De: Deserialize>(
+        &mut self,
+        tag_name: &str,
+    ) -> Result<Vec<De>, DeserializerError>
+    {
+        let mut deserialized_items = Vec::new();
+
+        loop {
+            let start = match read_event!(self) {
+                Event::Start(start) if start.name().as_ref() == tag_name.as_bytes() => {
+                    start
+                }
+                Event::Comment(_) => {
+                    continue;
+                }
+                event => {
+                    self.leftover_event = Some(event.into_owned());
+                    break;
+                }
+            };
+
+            let deserialized = De::deserialize(&start, self).map_err(|err| {
+                DeserializerError::DeserializeFailed(
+                    type_name::<De>(),
+                    WrappedDeserializeError::new(err),
+                )
+            })?;
+
+            self.read_end_event(tag_name)?;
+
+            deserialized_items.push(deserialized);
+        }
+
+        Ok(deserialized_items)
+    }
+
+    fn de_text(&mut self) -> Result<String, DeserializerError>
+    {
+        let text = match read_event!(self) {
+            Event::Text(text) => Ok(text),
+            event => {
+                self.leftover_event = Some(event.clone().into_owned());
+
+                Err(DeserializerError::UnexpectedEvent {
+                    expected_event_name: "text".to_string(),
+                    found_event: event,
+                })
+            }
+        }?
+        .unescape()?;
+
+        Ok(text.to_string())
+    }
+
+    fn skip_to_tag_start(&mut self, tag_name: &str) -> Result<(), DeserializerError>
+    {
+        loop {
+            match read_event!(self) {
+                Event::Start(start) if start.name().as_ref() == tag_name.as_bytes() => {
+                    self.leftover_event = Some(Event::Start(start).into_owned());
+
+                    break;
+                }
+                _ => {}
+            }
+        }
+
+        Ok(())
+    }
+
+    fn skip_to_tag_end(&mut self, tag_name: &str) -> Result<(), DeserializerError>
+    {
+        loop {
+            match read_event!(self) {
+                Event::End(end) if end.name().as_ref() == tag_name.as_bytes() => {
+                    self.leftover_event = Some(Event::End(end).into_owned());
+
+                    return Ok(());
+                }
+                _ => {}
+            }
+        }
+    }
+}
+
+impl<Source> BufferDeserializer<Source>
+where
+    Source: BufRead,
+{
+    fn read_end_event(&mut self, tag_name: &str) -> Result<(), DeserializerError>
+    {
+        let event = read_event!(self);
+
+        if matches!(&event, Event::End(end) if end.name().as_ref() == tag_name.as_bytes())
+        {
+            return Ok(());
+        }
+
+        Err(DeserializerError::UnexpectedEvent {
+            expected_event_name: "end".to_string(),
+            found_event: event.into_owned(),
+        })
+    }
+}
diff --git a/src/deserialization/mod.rs b/src/deserialization/mod.rs
new file mode 100644
index 0000000..fa25e4b
--- /dev/null
+++ b/src/deserialization/mod.rs
@@ -0,0 +1,124 @@
+use std::error::Error;
+use std::ops::Deref;
+
+use quick_xml::events::{BytesStart, Event};
+
+pub mod buffer_deserializer;
+
+pub trait Deserialize: Sized
+{
+    type Error: Error + Send + Sync + 'static;
+
+    fn deserialize<TDeserializer: Deserializer>(
+        start: &BytesStart,
+        deserializer: &mut TDeserializer,
+    ) -> Result<Self, Self::Error>;
+}
+
+pub trait Deserializer
+{
+    fn de_tag<De: Deserialize>(
+        &mut self,
+        tag_name: &str,
+        ignore_end: IgnoreEnd,
+    ) -> Result<De, DeserializerError>;
+
+    fn de_tag_with<Output, Err, DeserializeFn>(
+        &mut self,
+        tag_name: &str,
+        ignore_end: IgnoreEnd,
+        deserialize: DeserializeFn,
+    ) -> Result<Output, DeserializerError>
+    where
+        Err: Error + Send + Sync + 'static,
+        DeserializeFn: FnOnce(&BytesStart, &mut Self) -> Result<Output, Err>;
+
+    fn de_tag_list<De: Deserialize>(
+        &mut self,
+        tag_name: &str,
+    ) -> Result<Vec<De>, DeserializerError>;
+
+    fn de_text(&mut self) -> Result<String, DeserializerError>;
+
+    fn skip_to_tag_start(&mut self, tag_name: &str) -> Result<(), DeserializerError>;
+
+    fn skip_to_tag_end(&mut self, tag_name: &str) -> Result<(), DeserializerError>;
+}
+
+pub enum IgnoreEnd
+{
+    Yes,
+    No,
+}
+
+/// Function pointer type passable to [`Deserializer::de_tag_with`].
+pub type DeserializeWithFn<Output, Err, Deserializer> =
+    fn(&BytesStart, &mut Deserializer) -> Result<Output, Err>;
+
+#[derive(Debug, thiserror::Error)]
+pub enum DeserializerError
+{
+    #[error("Failed to read")]
+    ReadFailed(#[from] quick_xml::Error),
+
+    #[error("Failed to deserialize {0}")]
+    DeserializeFailed(&'static str, #[source] WrappedDeserializeError),
+
+    #[error("Expected {expected_event_name} event. Found {found_event:?}")]
+    UnexpectedEvent
+    {
+        expected_event_name: String,
+        found_event: Event<'static>,
+    },
+
+    #[error("Unexpected end of file")]
+    UnexpectedEndOfFile,
+}
+
+#[derive(Debug, thiserror::Error)]
+#[error(transparent)]
+pub struct WrappedDeserializeError(Box<dyn Error + Send + Sync>);
+
+impl WrappedDeserializeError
+{
+    fn new<Err: Error + Send + Sync + 'static>(err: Err) -> Self
+    {
+        Self(Box::new(err))
+    }
+}
+
+impl Deref for WrappedDeserializeError
+{
+    type Target = dyn Error;
+
+    fn deref(&self) -> &Self::Target
+    {
+        self.0.as_ref()
+    }
+}
+
+pub trait ResultExt<Value>
+{
+    fn try_event(self) -> Result<Option<Value>, DeserializerError>;
+}
+
+impl<Value> ResultExt<Value> for Result<Value, DeserializerError>
+{
+    fn try_event(self) -> Result<Option<Value>, DeserializerError>
+    {
+        self.map_or_else(
+            |err| {
+                if let DeserializerError::UnexpectedEvent {
+                    expected_event_name: _,
+                    found_event: _,
+                } = err
+                {
+                    return Ok(None);
+                }
+
+                Err(err)
+            },
+            |value| Ok(Some(value)),
+        )
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index c305ae3..f3bbc54 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -24,20 +24,24 @@
 use std::fs::File;
 use std::io::Read;
 
+use quick_xml::events::BytesStart;
+
 use crate::command::{Command, Error as CommandError};
-use crate::xml::element::{Element, Elements, FromElements};
-use crate::xml::parser::{Error as ParserError, Parser};
+use crate::deserialization::buffer_deserializer::BufferDeserializer;
+use crate::deserialization::{Deserialize, Deserializer, DeserializerError, IgnoreEnd};
 
 pub mod command;
 
-mod xml;
+mod deserialization;
 
+/// XML.
 #[cfg(feature = "include-xml")]
 const GL_REGISTRY_XML: &[u8] = include_bytes!("../OpenGL-Registry/xml/gl.xml");
 
 const REGISTRY_TAG_NAME: &str = "registry";
 
 /// Representation of the OpenGL registry.
+#[derive(Debug, PartialEq, Eq)]
 pub struct Registry
 {
     commands: Vec<Command>,
@@ -62,15 +66,12 @@ impl Registry
     /// Returns `Err` if parsing fails in any way.
     pub fn retrieve_from_bytes(xml_bytes: &[u8]) -> Result<Registry, RegistryError>
     {
-        let mut parser = Parser::new(xml_bytes);
-
-        let elements = parser.parse().map_err(ParsingError)?;
+        let mut deserializer = BufferDeserializer::new(xml_bytes);
 
-        let registry_element = elements
-            .get_first_tagged_element(REGISTRY_TAG_NAME)
-            .ok_or(RegistryError::MissingRegistryElement)?;
+        deserializer.skip_to_tag_start(REGISTRY_TAG_NAME)?;
 
-        let registry = Registry::from_elements(registry_element.child_elements())?;
+        let registry =
+            deserializer.de_tag::<Registry>(REGISTRY_TAG_NAME, IgnoreEnd::Yes)?;
 
         Ok(registry)
     }
@@ -110,35 +111,21 @@ impl Registry
     }
 }
 
-impl FromElements for Registry
+impl Deserialize for Registry
 {
     type Error = RegistryError;
 
-    fn from_elements(elements: &Elements) -> Result<Self, Self::Error>
+    fn deserialize<TDeserializer: Deserializer>(
+        _start: &BytesStart,
+        deserializer: &mut TDeserializer,
+    ) -> Result<Self, Self::Error>
     {
-        let commands_element = elements
-            .get_first_tagged_element("commands")
-            .ok_or(Self::Error::MissingCommandsElement)?;
-
-        let command_elements =
-            commands_element
-                .child_elements()
-                .into_iter()
-                .filter_map(|element| match element {
-                    Element::Tagged(tagged_element)
-                        if tagged_element.name() == "command" =>
-                    {
-                        Some(tagged_element)
-                    }
-                    _ => None,
-                });
-
-        let commands = command_elements
-            .into_iter()
-            .map(|command_element| {
-                Command::from_elements(command_element.child_elements())
-            })
-            .collect::<Result<Vec<_>, _>>()?;
+        deserializer.skip_to_tag_start("commands")?;
+
+        let commands =
+            deserializer.de_tag_with("commands", IgnoreEnd::No, |_, deserializer| {
+                deserializer.de_tag_list::<Command>("command")
+            })?;
 
         Ok(Self { commands })
     }
@@ -160,16 +147,11 @@ pub enum RegistryError
     #[error("Invalid command")]
     InvalidCommand(#[from] CommandError),
 
-    /// Parsing failed.
-    #[error("Parsing failed")]
-    ParsingFailed(#[from] ParsingError),
-
     /// I/O failed.
     #[error("I/O failed")]
     IOFailed(#[from] std::io::Error),
-}
 
-/// Parsing error.
-#[derive(Debug, thiserror::Error)]
-#[error(transparent)]
-pub struct ParsingError(#[from] ParserError);
+    /// Deserialization failed.
+    #[error("Deserialization failed")]
+    DeserializationFailed(#[from] DeserializerError),
+}
diff --git a/src/xml/element.rs b/src/xml/element.rs
deleted file mode 100644
index f469480..0000000
--- a/src/xml/element.rs
+++ /dev/null
@@ -1,144 +0,0 @@
-#[derive(Debug, PartialEq, Eq)]
-pub struct Elements
-{
-    elements: Vec<Element>,
-}
-
-impl Elements
-{
-    pub fn get_first_tagged_element(&self, tag_name: &str) -> Option<&Tagged>
-    {
-        self.elements.iter().find_map(|element| match element {
-            Element::Tagged(tagged_element) if tagged_element.name == tag_name => {
-                Some(tagged_element)
-            }
-            _ => None,
-        })
-    }
-
-    pub fn get_all_tagged_elements_with_name(&self, tag_name: &str) -> Vec<&Tagged>
-    {
-        self.elements
-            .iter()
-            .filter_map(|element| match element {
-                Element::Tagged(tagged_element) if tagged_element.name == tag_name => {
-                    Some(tagged_element)
-                }
-                _ => None,
-            })
-            .collect()
-    }
-
-    pub fn get_first_text_element(&self) -> Option<&String>
-    {
-        self.elements.iter().find_map(|element| match element {
-            Element::Text(text) => Some(text),
-            _ => None,
-        })
-    }
-
-    pub fn get_all_text_elements(&self) -> Vec<&String>
-    {
-        self.elements
-            .iter()
-            .filter_map(|element| match element {
-                Element::Text(text) => Some(text),
-                _ => None,
-            })
-            .collect()
-    }
-
-    pub fn has_tagged_element(&self, tag_name: &str) -> bool
-    {
-        self.elements.iter().any(|element| {
-            matches!(
-                element,
-                Element::Tagged(tagged_element) if tagged_element.name == tag_name
-            )
-        })
-    }
-}
-
-impl<IntoIter: IntoIterator<Item = Element>> From<IntoIter> for Elements
-{
-    fn from(into_iter: IntoIter) -> Self
-    {
-        Self {
-            elements: into_iter.into_iter().collect(),
-        }
-    }
-}
-
-impl<'elements> IntoIterator for &'elements Elements
-{
-    type IntoIter = Iter<'elements>;
-    type Item = &'elements Element;
-
-    fn into_iter(self) -> Self::IntoIter
-    {
-        Self::IntoIter {
-            elements: self.elements.iter(),
-        }
-    }
-}
-
-pub struct Iter<'elements>
-{
-    elements: std::slice::Iter<'elements, Element>,
-}
-
-impl<'elements> Iterator for Iter<'elements>
-{
-    type Item = &'elements Element;
-
-    fn next(&mut self) -> Option<Self::Item>
-    {
-        self.elements.next()
-    }
-}
-
-#[derive(Debug, PartialEq, Eq)]
-pub enum Element
-{
-    Tagged(Tagged),
-    Text(String),
-    Comment(String),
-}
-
-#[derive(Debug, PartialEq, Eq)]
-pub struct Tagged
-{
-    name: String,
-    child_elements: Elements,
-}
-
-impl Tagged
-{
-    pub fn new<Name, ChildElements>(name: &Name, child_elements: ChildElements) -> Self
-    where
-        Name: ToString,
-        ChildElements: Into<Elements>,
-    {
-        Self {
-            name: name.to_string(),
-            child_elements: child_elements.into(),
-        }
-    }
-
-    pub fn name(&self) -> &str
-    {
-        &self.name
-    }
-
-    pub fn child_elements(&self) -> &Elements
-    {
-        &self.child_elements
-    }
-}
-
-pub trait FromElements: Sized
-{
-    type Error;
-
-    fn from_elements(elements: &Elements) -> Result<Self, Self::Error>;
-}
diff --git a/src/xml/mod.rs b/src/xml/mod.rs
deleted file mode 100644
index 12368c3..0000000
--- a/src/xml/mod.rs
+++ /dev/null
@@ -1,2 +0,0 @@
-pub mod element;
-pub mod parser;
diff --git a/src/xml/parser.rs b/src/xml/parser.rs
deleted file mode 100644
index d152a6e..0000000
--- a/src/xml/parser.rs
+++ /dev/null
@@ -1,195 +0,0 @@
-use std::io::BufRead;
-
-use quick_xml::events::{BytesStart, BytesText, Event};
-use quick_xml::Reader;
-
-use crate::xml::element::{Element, Elements, Tagged};
-
-/// XML parser.
-pub struct Parser<Source>
-{
-    reader: Reader<Source>,
-}
-
-impl<Source: BufRead> Parser<Source>
-{
-    pub fn new(src: Source) -> Self
-    {
-        Self {
-            reader: Reader::from_reader(src),
-        }
-    }
-
-    pub fn parse(&mut self) -> Result<Elements, Error>
-    {
-        let mut buf = Vec::new();
-
-        let mut elements = Vec::new();
-
-        loop {
-            let event = self.reader.read_event_into(&mut buf)?;
-
-            let element = match self.handle_event(event)? {
-                EventHandlingResult::Element(element) => element,
-                EventHandlingResult::Event(_) => {
-                    continue;
-                }
-                EventHandlingResult::End => {
-                    break;
-                }
-            };
-
-            elements.push(element);
-        }
-
-        Ok(elements.into())
-    }
-
-    fn parse_text(text: &BytesText) -> Result<String, Error>
-    {
-        String::from_utf8(text.to_vec()).map_err(|_| Error::TextNotUTF8)
-    }
-
-    fn parse_tagged(&mut self, start: &BytesStart) -> Result<Element, Error>
-    {
-        let mut child_elements = Vec::new();
-
-        let mut buf = Vec::new();
-
-        loop {
-            let event = self.reader.read_event_into(&mut buf)?;
-
-            match event {
-                Event::End(end) if end.name() == start.name() => {
-                    break;
-                }
-                event => match self.handle_event(event)? {
-                    EventHandlingResult::Element(element) => {
-                        child_elements.push(element);
-                    }
-                    EventHandlingResult::End => {
-                        return Err(Error::UnexpectedEndOfFile);
-                    }
-                    EventHandlingResult::Event(_) => {}
-                },
-            }
-        }
-
-        Ok(Element::Tagged(Tagged::new(
-            &String::from_utf8(start.name().as_ref().to_vec())
-                .map_err(|_| Error::TagNameNotUTF8)?,
-            child_elements,
-        )))
-    }
-
-    fn handle_event<'a>(
-        &'a mut self,
-        event: Event<'a>,
-    ) -> Result<EventHandlingResult, Error>
-    {
-        match event {
-            Event::Text(text) => Ok(EventHandlingResult::Element(Element::Text(
-                Self::parse_text(&text)?,
-            ))),
-            Event::Start(start) => {
-                Ok(EventHandlingResult::Element(self.parse_tagged(&start)?))
-            }
-            Event::End(_) => Err(Error::UnexpectedTagEnd),
-            Event::Eof => Ok(EventHandlingResult::End),
-            Event::Comment(comment_text) => Ok(EventHandlingResult::Element(
-                Element::Comment(Self::parse_text(&comment_text)?),
-            )),
-            event => Ok(EventHandlingResult::Event(event)),
-        }
-    }
-}
-
-#[derive(Debug, thiserror::Error)]
-pub enum Error
-{
-    #[error(transparent)]
-    QuickXMLFailed(#[from] quick_xml::Error),
-
-    #[error("Text is not UTF-8")]
-    TextNotUTF8,
-
-    #[error("Tag name is not UTF-8")]
-    TagNameNotUTF8,
-
-    #[error("Unexpectedly found the end of a tag")]
-    UnexpectedTagEnd,
-
-    #[error("Unexpected end of file")]
-    UnexpectedEndOfFile,
-}
-
-enum EventHandlingResult<'event>
-{
-    Element(Element),
-    Event(Event<'event>),
-    End,
-}
-
-#[cfg(test)]
-mod tests
-{
-    use pretty_assertions::assert_eq;
-
-    use super::*;
-
-    #[test]
-    fn can_parse()
-    {
-        let mut parser = Parser::new("<foo>Hello there</foo>".as_bytes());
-
-        assert_eq!(
-            parser.parse().expect("Expected Ok"),
-            Elements::from(vec![Element::Tagged(Tagged::new(
-                &"foo",
-                vec![Element::Text("Hello there".to_string())]
-            ))])
-        );
-
-        let mut parser = Parser::new("<foo><bar>123</bar> Hello</foo>".as_bytes());
-
-        assert_eq!(
-            parser.parse().expect("Expected Ok"),
-            Elements::from(vec![Element::Tagged(Tagged::new(
-                &"foo",
-                vec![
-                    Element::Tagged(Tagged::new(
-                        &"bar",
-                        Elements::from(vec![Element::Text("123".to_string())])
-                    )),
-                    Element::Text(" Hello".to_string())
-                ]
-            ))])
-        );
-
-        let mut parser = Parser::new("".as_bytes());
-
-        assert_eq!(
-            parser.parse().expect("Expected Ok"),
-            Elements::from(Vec::new())
-        );
-
-        let mut parser = Parser::new(
-            "<foo><!--XML is awful-->Hello there<bar>123</bar></foo>".as_bytes(),
-        );
-
-        assert_eq!(
-            parser.parse().expect("Expected Ok"),
-            Elements::from(vec![Element::Tagged(Tagged::new(
-                &"foo",
-                vec![
-                    Element::Comment("XML is awful".to_string()),
-                    Element::Text("Hello there".to_string()),
-                    Element::Tagged(Tagged::new(
-                        &"bar",
-                        vec![Element::Text("123".to_string())]
-                    )),
-                ]
-            ))])
-        );
-    }
-}