quick-xml 0.42.0

v0.42.0 - String Ergonomics

on Rust Cargo

What's Changed

0.42.0 -- 2026-08-22

This is a large release. The primary change is an ergonomic improvement across the entire API -
quick_xml now makes use of &str and String types where possible instead of
&[u8] and Vec<u8>. This requires significant refactoring of downstream code,
but should result in a net simplification as well as potential performance improvements,
and opens up additional opportunities in future releases.

The MSRV has been raised to 1.86. We now use Rust 2024 Edition.

Breaking Changes

• #963: Reader now validates that input is valid UTF-8 when constructing events.
  Non-UTF-8 input passed to Reader::from_reader() without DecodingReader will now
  produce Error::Encoding instead of silently passing through invalid bytes.
  Use DecodingReader to transcode non-UTF-8 sources.
• #963: Name types (QName, LocalName, Prefix, Namespace, PrefixDeclaration)
  now wrap &str instead of &[u8]. into_inner() returns &str, and AsRef<str>
  is implemented (AsRef<[u8]> has been removed). ResolveResult::Unknown now contains String
  instead of Vec<u8>, and NamespaceError variants contain String instead of Vec<u8>.
• #963: Removed the decoder: Decoder field from event types (BytesStart, BytesText,
  BytesCData, BytesRef) and Attributes. The decoder() method is no longer available
  on these types. Decode methods on events now always assume UTF-8 input.
  Error::missed_end() no longer takes a Decoder parameter.
• #963: Event types (BytesStart, BytesEnd, BytesText, BytesCData, BytesPI,
  BytesRef) now store Cow<str> internally instead of Cow<[u8]>. into_inner() on
  BytesText, BytesCData, BytesPI, and BytesRef now returns Cow<str>.
  BytesStart::set_name() now takes &str instead of &[u8].
• #963: All event types and the Event enum now implement Deref<Target = str>
  instead of Deref<Target = [u8]>. Explicit AsRef<str> impls are provided to
  avoid ambiguity.
• #963: Removed decode() methods from BytesText, BytesCData, and BytesRef.
  Content is already available as &str via Deref. The xml10_content(),
  xml11_content(), xml_content(), and html_content() methods now return
  Cow<str> directly instead of Result<Cow<str>, EncodingError>.
• #963: Attribute::value is now Cow<'a, str> instead of Cow<'a, [u8]>.
  The From<(&[u8], &[u8])> impl has been removed.
• #963: BytesDecl::version(), encoding(), and standalone() now return
  Cow<'_, str> instead of Cow<'_, [u8]>.
• #963: Removed Reader::decoder() method. Use Reader::encoding() instead
  (available with the encoding feature). Removed decoder() from the XmlRead
  serde trait. Removed all methods from Decoder (the struct is kept only for
  backward compatibility with deprecated Attribute methods).
• #980: NamespaceError::TooManyDeclarations has been renamed to TooManyBindings,
  and NamespaceResolver::set_max_declarations_per_element has been renamed to
  NamespaceResolver::set_max_namespace_bindings, and the semantic behavior has
  changed slightly. The default maximum has also been reduced from 256 to 128.
• #1000: DeError::UnexpectedStart renamed to DeError::MixedContent. That error
  is emitted when you try to deserialize boolean, number or string field from
  something like <field>text <tag/> another text</field>.

Bug Fixes

• #670: Serde serializer now escapes \r, \n, and \t in attribute values
  as 
, 
, and 	 respectively, preventing silent data loss from
  XML attribute-value normalization on round-trip. Likewise Attribute::from
  performs the same transformation.
• #953: The serde Deserializer now correctly handles namespaces. Previously
  the namespace bindings might be applied or removed before the event actually
  was consumed which lead to a couple of bugs.
• #989: Attributes::new and Attributes::html now return empty iterators when
  their starting position is past the end of the input instead of panicking.
• #977: NamespaceResolver::push (and hence every NsReader Start/Empty
  event) now returns the new NamespaceError::TooDeeplyNested when a document
  nests elements deeper than u16::MAX, instead of overflowing the internal
  u16 depth counter. Previously the unguarded nesting_level += 1 panicked
  under overflow-checks builds and silently wrapped in release, corrupting
  namespace-scope bookkeeping on deeply nested untrusted input.
• #980: NamespaceResolver now caps the total number of in-scope namespace
  bindings (default 128, configurable via set_max_namespace_bindings),
  replacing the previous per-element max_declarations_per_element limit.
• #978: The serde Deserializer now enforces a configurable recursion-depth
  limit (default 128, matching serde_json). Deeply nested XML returns
  DeError::TooDeeplyNested instead of overflowing the native call stack.
  Use Deserializer::recursion_limit() to adjust.
• #990: \r in text content is now escaped as 
 by the serde serializer,
  BytesText::new(), escape(), partial_escape(), and minimal_escape(),
  preventing silent conversion to \n from XML end-of-line normalization on
  round-trip. Note that \r cannot be preserved through CDATA serialization
  because character references are not permitted inside CDATA sections.

Misc Changes

• #269: Added getting-started examples (getting_started, writer,
  serde_roundtrip, reader_patterns, visitor) and an examples/README.md
  guide on choosing between the serde and pull-reader/writer APIs.
• #331: Documentation about lifetimes of the events and attributes has been clarified.
• #859: Added an example showing how to pretty-print serialized XML.
• #983: Adopted an AI use and contribution policy for new upstream contributions.
• #963: MSRV bumped to 1.86 (April 2025)
• #963: Deprecated Attribute methods that take a Decoder parameter, since
  attribute values are now always valid UTF-8: decoded_and_normalized_value(),
  decoded_and_normalized_value_with(), decode_and_unescape_value(), and
  decode_and_unescape_value_with(). Use normalized_value() and
  normalized_value_with() instead.
• #1002: Added NamespaceResolver::with that allows temporary applying namespace
  bindings from the start tag for the scope of a provided closure F, without making any
  persistent change to the resolver. It is useful to check a peeked event which is
  not yet consumed in custom implementations of peekable reader.
• #1002: Added Deserializer::resolver and Deserializer::resolver_mut methods
  to get a namespace resolver used by this deserializer, because it no longer uses
  an NsReader internally.
• #1005: Implement Hash, PartialOrd, and Ord for BytesText and BytesCData types.

New Contributors

• @maxtaran2010 made their first contribution in #976
• @scadastrangelove made their first contribution in #979
• @lntutor made their first contribution in #992

Full Changelog: v0.41.0...v0.42.0