Struct quick_xml::reader::NsReader

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pub struct NsReader<R> { /* private fields */ }
Expand description

A low level encoding-agnostic XML event reader that performs namespace resolution.

Consumes a BufRead and streams XML Events.

Implementations§

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impl<R> NsReader<R>

Builder methods

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pub fn from_reader(reader: R) -> Self

Creates a NsReader that reads from a reader.

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pub fn expand_empty_elements(&mut self, val: bool) -> &mut Self

Changes whether empty elements should be split into an Open and a Close event.

When set to true, all Empty events produced by a self-closing tag like <tag/> are expanded into a Start event followed by an End event. When set to false (the default), those tags are represented by an Empty event instead.

Note, that setting this to true will lead to additional allocates that needed to store tag name for an End event. However if check_end_names is also set, only one additional allocation will be performed that support both these options.

(false by default)

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pub fn trim_text(&mut self, val: bool) -> &mut Self

Changes whether whitespace before and after character data should be removed.

When set to true, all Text events are trimmed. If after that the event is empty it will not be pushed.

Changing this option automatically changes the trim_text_end option.

(false by default).

WARNING: With this option every text events will be trimmed which is incorrect behavior when text events delimited by comments, processing instructions or CDATA sections. To correctly trim data manually apply BytesText::inplace_trim_start and BytesText::inplace_trim_end only to necessary events.

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pub fn trim_text_end(&mut self, val: bool) -> &mut Self

Changes whether whitespace after character data should be removed.

When set to true, trailing whitespace is trimmed in Text events. If after that the event is empty it will not be pushed.

(false by default).

WARNING: With this option every text events will be trimmed which is incorrect behavior when text events delimited by comments, processing instructions or CDATA sections. To correctly trim data manually apply BytesText::inplace_trim_start and BytesText::inplace_trim_end only to necessary events.

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pub fn trim_markup_names_in_closing_tags(&mut self, val: bool) -> &mut Self

Changes whether trailing whitespaces after the markup name are trimmed in closing tags </a >.

If true the emitted End event is stripped of trailing whitespace after the markup name.

Note that if set to false and check_end_names is true the comparison of markup names is going to fail erroneously if a closing tag contains trailing whitespaces.

(true by default)

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pub fn check_end_names(&mut self, val: bool) -> &mut Self

Changes whether mismatched closing tag names should be detected.

Note, that start and end tags should match literally, they cannot have different prefixes even if both prefixes resolve to the same namespace. The XML

<outer xmlns="namespace" xmlns:p="namespace">
</p:outer>

is not valid, even though semantically the start tag is the same as the end tag. The reason is that namespaces are an extension of the original XML specification (without namespaces) and it should be backward-compatible.

When set to false, it won’t check if a closing tag matches the corresponding opening tag. For example, <mytag></different_tag> will be permitted.

If the XML is known to be sane (already processed, etc.) this saves extra time.

Note that the emitted End event will not be modified if this is disabled, ie. it will contain the data of the mismatched end tag.

Note, that setting this to true will lead to additional allocates that needed to store tag name for an End event. However if expand_empty_elements is also set, only one additional allocation will be performed that support both these options.

(true by default)

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pub fn check_comments(&mut self, val: bool) -> &mut Self

Changes whether comments should be validated.

When set to true, every Comment event will be checked for not containing --, which is not allowed in XML comments. Most of the time we don’t want comments at all so we don’t really care about comment correctness, thus the default value is false to improve performance.

(false by default)

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impl<R> NsReader<R>

Getters

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pub fn into_inner(self) -> R

Consumes NsReader returning the underlying reader

See the Reader::into_inner for examples

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pub fn get_mut(&mut self) -> &mut R

Gets a mutable reference to the underlying reader.

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pub fn resolve<'n>( &self, name: QName<'n>, attribute: bool ) -> (ResolveResult<'_>, LocalName<'n>)

Resolves a potentially qualified element name or attribute name into (namespace name, local name).

Qualified names have the form prefix:local-name where the prefix is defined on any containing XML element via xmlns:prefix="the:namespace:uri". The namespace prefix can be defined on the same element as the name in question.

The method returns following results depending on the name shape, attribute flag and the presence of the default namespace:

attributexmlns="..."QNameResolveResultLocalName
trueNot definedlocal-nameUnboundlocal-name
trueDefinedlocal-nameUnboundlocal-name
trueanyprefix:local-nameBound / Unknownlocal-name
falseNot definedlocal-nameUnboundlocal-name
falseDefinedlocal-nameBound (default)local-name
falseanyprefix:local-nameBound / Unknownlocal-name

If you want to clearly indicate that name that you resolve is an element or an attribute name, you could use resolve_attribute() or resolve_element() methods.

§Lifetimes
  • 'n: lifetime of a name. Returned local name will be bound to the same lifetime as the name in question.
  • returned namespace name will be bound to the reader itself
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pub fn resolve_element<'n>( &self, name: QName<'n> ) -> (ResolveResult<'_>, LocalName<'n>)

Resolves a potentially qualified element name into (namespace name, local name).

Qualified element names have the form prefix:local-name where the prefix is defined on any containing XML element via xmlns:prefix="the:namespace:uri". The namespace prefix can be defined on the same element as the element in question.

Unqualified elements inherits the current default namespace.

The method returns following results depending on the name shape and the presence of the default namespace:

xmlns="..."QNameResolveResultLocalName
Not definedlocal-nameUnboundlocal-name
Definedlocal-nameBound (default)local-name
anyprefix:local-nameBound / Unknownlocal-name
§Lifetimes
  • 'n: lifetime of an element name. Returned local name will be bound to the same lifetime as the name in question.
  • returned namespace name will be bound to the reader itself
§Examples

This example shows how you can resolve qualified name into a namespace. Note, that in the code like this you do not need to do that manually, because the namespace resolution result returned by the read_resolved_event().

use quick_xml::events::Event;
use quick_xml::name::{Namespace, QName, ResolveResult::*};
use quick_xml::reader::NsReader;

let mut reader = NsReader::from_str("<tag xmlns='root namespace'/>");

match reader.read_event().unwrap() {
    Event::Empty(e) => assert_eq!(
        reader.resolve_element(e.name()),
        (Bound(Namespace(b"root namespace")), QName(b"tag").into())
    ),
    _ => unreachable!(),
}
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pub fn resolve_attribute<'n>( &self, name: QName<'n> ) -> (ResolveResult<'_>, LocalName<'n>)

Resolves a potentially qualified attribute name into (namespace name, local name).

Qualified attribute names have the form prefix:local-name where the prefix is defined on any containing XML element via xmlns:prefix="the:namespace:uri". The namespace prefix can be defined on the same element as the attribute in question.

Unqualified attribute names do not inherit the current default namespace.

The method returns following results depending on the name shape and the presence of the default namespace:

xmlns="..."QNameResolveResultLocalName
Not definedlocal-nameUnboundlocal-name
Definedlocal-nameUnboundlocal-name
anyprefix:local-nameBound / Unknownlocal-name
§Lifetimes
  • 'n: lifetime of an attribute name. Returned local name will be bound to the same lifetime as the name in question.
  • returned namespace name will be bound to the reader itself
§Examples
use quick_xml::events::Event;
use quick_xml::events::attributes::Attribute;
use quick_xml::name::{Namespace, QName, ResolveResult::*};
use quick_xml::reader::NsReader;

let mut reader = NsReader::from_str("
    <tag one='1'
         p:two='2'
         xmlns='root namespace'
         xmlns:p='other namespace'/>
");
reader.trim_text(true);

match reader.read_event().unwrap() {
    Event::Empty(e) => {
        let mut iter = e.attributes();

        // Unlike elements, attributes without explicit namespace
        // not bound to any namespace
        let one = iter.next().unwrap().unwrap();
        assert_eq!(
            reader.resolve_attribute(one.key),
            (Unbound, QName(b"one").into())
        );

        let two = iter.next().unwrap().unwrap();
        assert_eq!(
            reader.resolve_attribute(two.key),
            (Bound(Namespace(b"other namespace")), QName(b"two").into())
        );
    }
    _ => unreachable!(),
}
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impl<R: BufRead> NsReader<R>

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pub fn read_event_into<'b>(&mut self, buf: &'b mut Vec<u8>) -> Result<Event<'b>>

Reads the next event into given buffer.

This method manages namespaces but doesn’t resolve them automatically. You should call resolve_element() if you want to get a namespace.

You also can use read_resolved_event_into() instead if you want to resolve namespace as soon as you get an event.

§Examples
use quick_xml::events::Event;
use quick_xml::name::{Namespace, ResolveResult::*};
use quick_xml::reader::NsReader;

let mut reader = NsReader::from_str(r#"
    <x:tag1 xmlns:x="www.xxxx" xmlns:y="www.yyyy" att1 = "test">
       <y:tag2><!--Test comment-->Test</y:tag2>
       <y:tag2>Test 2</y:tag2>
    </x:tag1>
"#);
reader.trim_text(true);

let mut count = 0;
let mut buf = Vec::new();
let mut txt = Vec::new();
loop {
    match reader.read_event_into(&mut buf).unwrap() {
        Event::Start(e) => {
            count += 1;
            let (ns, local) = reader.resolve_element(e.name());
            match local.as_ref() {
                b"tag1" => assert_eq!(ns, Bound(Namespace(b"www.xxxx"))),
                b"tag2" => assert_eq!(ns, Bound(Namespace(b"www.yyyy"))),
                _ => unreachable!(),
            }
        }
        Event::Text(e) => {
            txt.push(e.unescape().unwrap().into_owned())
        }
        Event::Eof => break,
        _ => (),
    }
    buf.clear();
}
assert_eq!(count, 3);
assert_eq!(txt, vec!["Test".to_string(), "Test 2".to_string()]);
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pub fn read_resolved_event_into<'b>( &mut self, buf: &'b mut Vec<u8> ) -> Result<(ResolveResult<'_>, Event<'b>)>

Reads the next event into given buffer and resolves its namespace (if applicable).

Namespace is resolved only for Start, Empty and End events. For all other events the concept of namespace is not defined, so a ResolveResult::Unbound is returned.

If you are not interested in namespaces, you can use read_event_into() which will not automatically resolve namespaces for you.

§Examples
use quick_xml::events::Event;
use quick_xml::name::{Namespace, QName, ResolveResult::*};
use quick_xml::reader::NsReader;

let mut reader = NsReader::from_str(r#"
    <x:tag1 xmlns:x="www.xxxx" xmlns:y="www.yyyy" att1 = "test">
       <y:tag2><!--Test comment-->Test</y:tag2>
       <y:tag2>Test 2</y:tag2>
    </x:tag1>
"#);
reader.trim_text(true);

let mut count = 0;
let mut buf = Vec::new();
let mut txt = Vec::new();
loop {
    match reader.read_resolved_event_into(&mut buf).unwrap() {
        (Bound(Namespace(b"www.xxxx")), Event::Start(e)) => {
            count += 1;
            assert_eq!(e.local_name(), QName(b"tag1").into());
        }
        (Bound(Namespace(b"www.yyyy")), Event::Start(e)) => {
            count += 1;
            assert_eq!(e.local_name(), QName(b"tag2").into());
        }
        (_, Event::Start(_)) => unreachable!(),

        (_, Event::Text(e)) => {
            txt.push(e.unescape().unwrap().into_owned())
        }
        (_, Event::Eof) => break,
        _ => (),
    }
    buf.clear();
}
assert_eq!(count, 3);
assert_eq!(txt, vec!["Test".to_string(), "Test 2".to_string()]);
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pub fn read_to_end_into( &mut self, end: QName<'_>, buf: &mut Vec<u8> ) -> Result<Span>

Reads until end element is found using provided buffer as intermediate storage for events content. This function is supposed to be called after you already read a Start event.

Returns a span that cover content between > of an opening tag and < of a closing tag or an empty slice, if expand_empty_elements is set and this method was called after reading expanded Start event.

Manages nested cases where parent and child elements have the literally same name.

If corresponding End event will not be found, the UnexpectedEof will be returned. In particularly, that error will be returned if you call this method without consuming the corresponding Start event first.

If your reader created from a string slice or byte array slice, it is better to use read_to_end() method, because it will not copy bytes into intermediate buffer.

The provided buf buffer will be filled only by one event content at time. Before reading of each event the buffer will be cleared. If you know an appropriate size of each event, you can preallocate the buffer to reduce number of reallocations.

The end parameter should contain name of the end element in the reader encoding. It is good practice to always get that parameter using BytesStart::to_end() method.

§Namespaces

While the NsReader does namespace resolution, namespaces does not change the algorithm for comparing names. Although the names a:name and b:name where both prefixes a and b resolves to the same namespace, are semantically equivalent, </b:name> cannot close <a:name>, because according to the specification

The end of every element that begins with a start-tag MUST be marked by an end-tag containing a name that echoes the element’s type as given in the start-tag

§Examples

This example shows, how you can skip XML content after you read the start event.

use quick_xml::events::{BytesStart, Event};
use quick_xml::name::{Namespace, ResolveResult};
use quick_xml::reader::NsReader;

let mut reader = NsReader::from_str(r#"
    <outer xmlns="namespace 1">
        <inner xmlns="namespace 2">
            <outer></outer>
        </inner>
        <inner>
            <inner></inner>
            <inner/>
            <outer></outer>
            <p:outer xmlns:p="ns"></p:outer>
            <outer/>
        </inner>
    </outer>
"#);
reader.trim_text(true);
let mut buf = Vec::new();

let ns = Namespace(b"namespace 1");
let start = BytesStart::from_content(r#"outer xmlns="namespace 1""#, 5);
let end   = start.to_end().into_owned();

// First, we read a start event...
assert_eq!(
    reader.read_resolved_event_into(&mut buf).unwrap(),
    (ResolveResult::Bound(ns), Event::Start(start))
);

// ...then, we could skip all events to the corresponding end event.
// This call will correctly handle nested <outer> elements.
// Note, however, that this method does not handle namespaces.
reader.read_to_end_into(end.name(), &mut buf).unwrap();

// At the end we should get an Eof event, because we ate the whole XML
assert_eq!(
    reader.read_resolved_event_into(&mut buf).unwrap(),
    (ResolveResult::Unbound, Event::Eof)
);
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impl NsReader<BufReader<File>>

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pub fn from_file<P: AsRef<Path>>(path: P) -> Result<Self>

Creates an XML reader from a file path.

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impl<'i> NsReader<&'i [u8]>

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pub fn from_str(s: &'i str) -> Self

Creates an XML reader from a string slice.

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pub fn read_event(&mut self) -> Result<Event<'i>>

Reads the next event, borrow its content from the input buffer.

This method manages namespaces but doesn’t resolve them automatically. You should call resolve_element() if you want to get a namespace.

You also can use read_resolved_event() instead if you want to resolve namespace as soon as you get an event.

There is no asynchronous read_event_async() version of this function, because it is not necessary – the contents are already in memory and no IO is needed, therefore there is no potential for blocking.

§Examples
use quick_xml::events::Event;
use quick_xml::name::{Namespace, ResolveResult::*};
use quick_xml::reader::NsReader;

let mut reader = NsReader::from_str(r#"
    <x:tag1 xmlns:x="www.xxxx" xmlns:y="www.yyyy" att1 = "test">
       <y:tag2><!--Test comment-->Test</y:tag2>
       <y:tag2>Test 2</y:tag2>
    </x:tag1>
"#);
reader.trim_text(true);

let mut count = 0;
let mut txt = Vec::new();
loop {
    match reader.read_event().unwrap() {
        Event::Start(e) => {
            count += 1;
            let (ns, local) = reader.resolve_element(e.name());
            match local.as_ref() {
                b"tag1" => assert_eq!(ns, Bound(Namespace(b"www.xxxx"))),
                b"tag2" => assert_eq!(ns, Bound(Namespace(b"www.yyyy"))),
                _ => unreachable!(),
            }
        }
        Event::Text(e) => {
            txt.push(e.unescape().unwrap().into_owned())
        }
        Event::Eof => break,
        _ => (),
    }
}
assert_eq!(count, 3);
assert_eq!(txt, vec!["Test".to_string(), "Test 2".to_string()]);
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pub fn read_resolved_event(&mut self) -> Result<(ResolveResult<'_>, Event<'i>)>

Reads the next event, borrow its content from the input buffer, and resolves its namespace (if applicable).

Namespace is resolved only for Start, Empty and End events. For all other events the concept of namespace is not defined, so a ResolveResult::Unbound is returned.

If you are not interested in namespaces, you can use read_event() which will not automatically resolve namespaces for you.

There is no asynchronous read_resolved_event_async() version of this function, because it is not necessary – the contents are already in memory and no IO is needed, therefore there is no potential for blocking.

§Examples
use quick_xml::events::Event;
use quick_xml::name::{Namespace, QName, ResolveResult::*};
use quick_xml::reader::NsReader;

let mut reader = NsReader::from_str(r#"
    <x:tag1 xmlns:x="www.xxxx" xmlns:y="www.yyyy" att1 = "test">
       <y:tag2><!--Test comment-->Test</y:tag2>
       <y:tag2>Test 2</y:tag2>
    </x:tag1>
"#);
reader.trim_text(true);

let mut count = 0;
let mut txt = Vec::new();
loop {
    match reader.read_resolved_event().unwrap() {
        (Bound(Namespace(b"www.xxxx")), Event::Start(e)) => {
            count += 1;
            assert_eq!(e.local_name(), QName(b"tag1").into());
        }
        (Bound(Namespace(b"www.yyyy")), Event::Start(e)) => {
            count += 1;
            assert_eq!(e.local_name(), QName(b"tag2").into());
        }
        (_, Event::Start(_)) => unreachable!(),

        (_, Event::Text(e)) => {
            txt.push(e.unescape().unwrap().into_owned())
        }
        (_, Event::Eof) => break,
        _ => (),
    }
}
assert_eq!(count, 3);
assert_eq!(txt, vec!["Test".to_string(), "Test 2".to_string()]);
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pub fn read_to_end(&mut self, end: QName<'_>) -> Result<Span>

Reads until end element is found. This function is supposed to be called after you already read a Start event.

Returns a span that cover content between > of an opening tag and < of a closing tag or an empty slice, if expand_empty_elements is set and this method was called after reading expanded Start event.

Manages nested cases where parent and child elements have the literally same name.

If corresponding End event will not be found, the UnexpectedEof will be returned. In particularly, that error will be returned if you call this method without consuming the corresponding Start event first.

The end parameter should contain name of the end element in the reader encoding. It is good practice to always get that parameter using BytesStart::to_end() method.

There is no asynchronous read_to_end_async() version of this function, because it is not necessary – the contents are already in memory and no IO is needed, therefore there is no potential for blocking.

§Namespaces

While the NsReader does namespace resolution, namespaces does not change the algorithm for comparing names. Although the names a:name and b:name where both prefixes a and b resolves to the same namespace, are semantically equivalent, </b:name> cannot close <a:name>, because according to the specification

The end of every element that begins with a start-tag MUST be marked by an end-tag containing a name that echoes the element’s type as given in the start-tag

§Examples

This example shows, how you can skip XML content after you read the start event.

use quick_xml::events::{BytesStart, Event};
use quick_xml::name::{Namespace, ResolveResult};
use quick_xml::reader::NsReader;

let mut reader = NsReader::from_str(r#"
    <outer xmlns="namespace 1">
        <inner xmlns="namespace 2">
            <outer></outer>
        </inner>
        <inner>
            <inner></inner>
            <inner/>
            <outer></outer>
            <p:outer xmlns:p="ns"></p:outer>
            <outer/>
        </inner>
    </outer>
"#);
reader.trim_text(true);

let ns = Namespace(b"namespace 1");
let start = BytesStart::from_content(r#"outer xmlns="namespace 1""#, 5);
let end   = start.to_end().into_owned();

// First, we read a start event...
assert_eq!(
    reader.read_resolved_event().unwrap(),
    (ResolveResult::Bound(ns), Event::Start(start))
);

// ...then, we could skip all events to the corresponding end event.
// This call will correctly handle nested <outer> elements.
// Note, however, that this method does not handle namespaces.
reader.read_to_end(end.name()).unwrap();

// At the end we should get an Eof event, because we ate the whole XML
assert_eq!(
    reader.read_resolved_event().unwrap(),
    (ResolveResult::Unbound, Event::Eof)
);
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pub fn read_text(&mut self, end: QName<'_>) -> Result<Cow<'i, str>>

Reads content between start and end tags, including any markup. This function is supposed to be called after you already read a Start event.

Manages nested cases where parent and child elements have the literally same name.

This method does not unescape read data, instead it returns content “as is” of the XML document. This is because it has no idea what text it reads, and if, for example, it contains CDATA section, attempt to unescape it content will spoil data.

Any text will be decoded using the XML current decoder().

Actually, this method perform the following code:

ⓘ
let span = reader.read_to_end(end)?;
let text = reader.decoder().decode(&reader.inner_slice[span]);
§Examples

This example shows, how you can read a HTML content from your XML document.

use quick_xml::events::{BytesStart, Event};
use quick_xml::reader::NsReader;

let mut reader = NsReader::from_str(r#"
    <html>
        <title>This is a HTML text</title>
        <p>Usual XML rules does not apply inside it
        <p>For example, elements not needed to be &quot;closed&quot;
    </html>
"#);
reader.trim_text(true);

let start = BytesStart::new("html");
let end   = start.to_end().into_owned();

// First, we read a start event...
assert_eq!(reader.read_event().unwrap(), Event::Start(start));
// ...and disable checking of end names because we expect HTML further...
reader.check_end_names(false);

// ...then, we could read text content until close tag.
// This call will correctly handle nested <html> elements.
let text = reader.read_text(end.name()).unwrap();
assert_eq!(text, Cow::Borrowed(r#"
        <title>This is a HTML text</title>
        <p>Usual XML rules does not apply inside it
        <p>For example, elements not needed to be &quot;closed&quot;
    "#));

// Now we can enable checks again
reader.check_end_names(true);

// At the end we should get an Eof event, because we ate the whole XML
assert_eq!(reader.read_event().unwrap(), Event::Eof);

Methods from Deref<Target = Reader<R>>§

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pub fn get_ref(&self) -> &R

Gets a reference to the underlying reader.

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pub fn buffer_position(&self) -> usize

Gets the current byte position in the input data.

Useful when debugging errors.

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pub fn decoder(&self) -> Decoder

Get the decoder, used to decode bytes, read by this reader, to the strings.

If encoding feature is enabled, the used encoding may change after parsing the XML declaration, otherwise encoding is fixed to UTF-8.

If encoding feature is enabled and no encoding is specified in declaration, defaults to UTF-8.

Trait Implementations§

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impl<R> Deref for NsReader<R>

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type Target = Reader<R>

The resulting type after dereferencing.
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fn deref(&self) -> &Self::Target

Dereferences the value.

Auto Trait Implementations§

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impl<R> Freeze for NsReader<R>
where R: Freeze,

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impl<R> RefUnwindSafe for NsReader<R>
where R: RefUnwindSafe,

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impl<R> Send for NsReader<R>
where R: Send,

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impl<R> Sync for NsReader<R>
where R: Sync,

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impl<R> Unpin for NsReader<R>
where R: Unpin,

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impl<R> UnwindSafe for NsReader<R>
where R: UnwindSafe,

Blanket Implementations§

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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, 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, U> TryFrom<U> for T
where U: Into<T>,

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type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.