Split out namespace aware reader to a struct that manage the internal namespaces buffer

Changelog.md

@@ -27,6 +27,17 @@
   the XML declared encoding and always use UTF-8
 - [#416]: Add `borrow()` methods in all event structs which allows to get
   a borrowed version of any event
+- [#437]: Split out namespace reading functionality to a dedicated `NsReader`, namely:
+  |Old function in `Reader`|New function in `NsReader`
+  |------------------------|--------------------------
+  |                        |`read_event` -- borrow from input
+  |                        |`read_resolved_event` -- borrow from input
+  |                        |`read_event_into`
+  |`read_namespaced_event` |`read_resolved_event_into`
+  |                        |`resolve`
+  |`event_namespace`       |`resolve_element`
+  |`attribute_namespace`   |`resolve_attribute`
+
 
 ### Bug Fixes
 
@@ -167,6 +178,7 @@
 [#418]: https://github.com/tafia/quick-xml/pull/418
 [#421]: https://github.com/tafia/quick-xml/pull/421
 [#423]: https://github.com/tafia/quick-xml/pull/423
+[#437]: https://github.com/tafia/quick-xml/pull/437
 
 ## 0.23.0 -- 2022-05-08
 

benches/microbenches.rs

@@ -3,7 +3,7 @@ use pretty_assertions::assert_eq;
 use quick_xml::escape::{escape, unescape};
 use quick_xml::events::Event;
 use quick_xml::name::QName;
-use quick_xml::Reader;
+use quick_xml::{NsReader, Reader};
 
 static SAMPLE: &[u8] = include_bytes!("../tests/documents/sample_rss.xml");
 static PLAYERS: &[u8] = include_bytes!("../tests/documents/players.xml");
@@ -73,19 +73,18 @@ fn read_event(c: &mut Criterion) {
     group.finish();
 }
 
-/// Benchmarks the `Reader::read_namespaced_event` function with all XML well-formless
+/// Benchmarks the `NsReader::read_resolved_event_into` function with all XML well-formless
 /// checks disabled (with and without trimming content of #text nodes)
-fn read_namespaced_event(c: &mut Criterion) {
-    let mut group = c.benchmark_group("read_namespaced_event");
+fn read_resolved_event_into(c: &mut Criterion) {
+    let mut group = c.benchmark_group("NsReader::read_resolved_event_into");
     group.bench_function("trim_text = false", |b| {
         b.iter(|| {
-            let mut r = Reader::from_reader(SAMPLE);
+            let mut r = NsReader::from_bytes(SAMPLE);
             r.check_end_names(false).check_comments(false);
             let mut count = criterion::black_box(0);
             let mut buf = Vec::new();
-            let mut ns_buf = Vec::new();
             loop {
-                match r.read_namespaced_event(&mut buf, &mut ns_buf) {
+                match r.read_resolved_event_into(&mut buf) {
                     Ok((_, Event::Start(_))) | Ok((_, Event::Empty(_))) => count += 1,
                     Ok((_, Event::Eof)) => break,
                     _ => (),
@@ -101,15 +100,14 @@ fn read_namespaced_event(c: &mut Criterion) {
 
     group.bench_function("trim_text = true", |b| {
         b.iter(|| {
-            let mut r = Reader::from_reader(SAMPLE);
+            let mut r = NsReader::from_bytes(SAMPLE);
             r.check_end_names(false)
                 .check_comments(false)
                 .trim_text(true);
             let mut count = criterion::black_box(0);
             let mut buf = Vec::new();
-            let mut ns_buf = Vec::new();
             loop {
-                match r.read_namespaced_event(&mut buf, &mut ns_buf) {
+                match r.read_resolved_event_into(&mut buf) {
                     Ok((_, Event::Start(_))) | Ok((_, Event::Empty(_))) => count += 1,
                     Ok((_, Event::Eof)) => break,
                     _ => (),
@@ -393,7 +391,7 @@ purus. Consequat id porta nibh venenatis cras sed felis.";
 criterion_group!(
     benches,
     read_event,
-    read_namespaced_event,
+    read_resolved_event_into,
     one_event,
     attributes,
     escaping,

src/lib.rs

@@ -65,5 +65,5 @@ mod writer;
 #[cfg(feature = "serialize")]
 pub use crate::errors::serialize::DeError;
 pub use crate::errors::{Error, Result};
-pub use crate::reader::{Decoder, Reader};
+pub use crate::reader::{Decoder, NsReader, Reader};
 pub use crate::writer::{ElementWriter, Writer};

src/name.rs

@@ -274,13 +274,15 @@ impl<'a> AsRef<[u8]> for Namespace<'a> {
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////
 
-/// Result of [prefix] resolution which creates by [`Reader::attribute_namespace`],
-/// [`Reader::event_namespace`] and [`Reader::read_namespaced_event`] methods.
+/// Result of [prefix] resolution which creates by [`NsReader::resolve_attribute`],
+/// [`NsReader::resolve_element`], [`NsReader::read_resolved_event`] and
+/// [`NsReader::read_resolved_event_into`] methods.
 ///
 /// [prefix]: Prefix
-/// [`Reader::attribute_namespace`]: crate::reader::Reader::attribute_namespace
-/// [`Reader::event_namespace`]: crate::reader::Reader::event_namespace
-/// [`Reader::read_namespaced_event`]: crate::reader::Reader::read_namespaced_event
+/// [`NsReader::resolve_attribute`]: crate::reader::NsReader::resolve_attribute
+/// [`NsReader::resolve_element`]: crate::reader::NsReader::resolve_element
+/// [`NsReader::read_resolved_event`]: crate::reader::NsReader::read_resolved_event
+/// [`NsReader::read_resolved_event_into`]: crate::reader::NsReader::read_resolved_event_into
 #[derive(Clone, PartialEq, Eq, Hash)]
 pub enum ResolveResult<'ns> {
     /// Qualified name does not contain prefix, and resolver does not define