quick_xml::reader

Struct Reader

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

A low level encoding-agnostic XML event reader.

Consumes bytes and streams XML Events.

This reader does not manage namespace declarations and not able to resolve prefixes. If you want these features, use the NsReader.

§Examples

use quick_xml::events::Event;
use quick_xml::reader::Reader;

let xml = r#"<tag1 att1 = "test">
                <tag2><!--Test comment-->Test</tag2>
                <tag2>Test 2</tag2>
             </tag1>"#;
let mut reader = Reader::from_str(xml);
reader.config_mut().trim_text(true);

let mut count = 0;
let mut txt = Vec::new();
let mut buf = Vec::new();

// The `Reader` does not implement `Iterator` because it outputs borrowed data (`Cow`s)
loop {
    // NOTE: this is the generic case when we don't know about the input BufRead.
    // when the input is a &str or a &[u8], we don't actually need to use another
    // buffer, we could directly call `reader.read_event()`
    match reader.read_event_into(&mut buf) {
        Err(e) => panic!("Error at position {}: {:?}", reader.error_position(), e),
        // exits the loop when reaching end of file
        Ok(Event::Eof) => break,

        Ok(Event::Start(e)) => {
            match e.name().as_ref() {
                b"tag1" => println!("attributes values: {:?}",
                                    e.attributes().map(|a| a.unwrap().value)
                                    .collect::<Vec<_>>()),
                b"tag2" => count += 1,
                _ => (),
            }
        }
        Ok(Event::Text(e)) => txt.push(e.unescape().unwrap().into_owned()),

        // There are several other `Event`s we do not consider here
        _ => (),
    }
    // if we don't keep a borrow elsewhere, we can clear the buffer to keep memory usage low
    buf.clear();
}

Implementations§

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impl<R: AsyncBufRead + Unpin> Reader<R>

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

Available on crate feature async-tokio only.

An asynchronous version of read_event_into(). Reads the next event into given buffer.

This is the main entry point for reading XML Events when using an async reader.

See the documentation of read_event_into() for more information.

§Examples
use quick_xml::events::Event;
use quick_xml::reader::Reader;

// This explicitly uses `from_reader("...".as_bytes())` to use a buffered
// reader instead of relying on the zero-copy optimizations for reading
// from byte slices, which is provides the sync interface anyway.
let mut reader = Reader::from_reader(r#"
    <tag1 att1 = "test">
       <tag2><!--Test comment-->Test</tag2>
       <tag2>Test 2</tag2>
    </tag1>
"#.as_bytes());
reader.config_mut().trim_text(true);

let mut count = 0;
let mut buf = Vec::new();
let mut txt = Vec::new();
loop {
    match reader.read_event_into_async(&mut buf).await {
        Ok(Event::Start(_)) => count += 1,
        Ok(Event::Text(e)) => txt.push(e.unescape().unwrap().into_owned()),
        Err(e) => panic!("Error at position {}: {:?}", reader.error_position(), e),
        Ok(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 async fn read_to_end_into_async<'n>( &mut self, end: QName<'n>, buf: &mut Vec<u8>, ) -> Result<Span>

Available on crate feature async-tokio only.

An asynchronous version of read_to_end_into(). Reads asynchronously 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.

See the documentation of read_to_end_into() for more information.

§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::reader::Reader;

let mut reader = Reader::from_reader(r#"
    <outer>
        <inner>
            <inner></inner>
            <inner/>
            <outer></outer>
            <outer/>
        </inner>
    </outer>
"#.as_bytes());
reader.config_mut().trim_text(true);
let mut buf = Vec::new();

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

// First, we read a start event...
assert_eq!(reader.read_event_into_async(&mut buf).await.unwrap(), 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_async(end.name(), &mut buf).await.unwrap();

// At the end we should get an Eof event, because we ate the whole XML
assert_eq!(reader.read_event_into_async(&mut buf).await.unwrap(), Event::Eof);
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impl<R: BufRead> Reader<R>

This is an implementation for reading from a BufRead as underlying byte stream.

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

Reads the next Event.

This is the main entry point for reading XML Events.

Events borrow buf and can be converted to own their data if needed (uses Cow internally).

Having the possibility to control the internal buffers gives you some additional benefits such as:

  • Reduce the number of allocations by reusing the same buffer. For constrained systems, you can call buf.clear() once you are done with processing the event (typically at the end of your loop).
  • Reserve the buffer length if you know the file size (using Vec::with_capacity).
§Examples
use quick_xml::events::Event;
use quick_xml::reader::Reader;

let xml = r#"<tag1 att1 = "test">
                <tag2><!--Test comment-->Test</tag2>
                <tag2>Test 2</tag2>
             </tag1>"#;
let mut reader = Reader::from_str(xml);
reader.config_mut().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) {
        Ok(Event::Start(_)) => count += 1,
        Ok(Event::Text(e)) => txt.push(e.unescape().unwrap().into_owned()),
        Err(e) => panic!("Error at position {}: {:?}", reader.error_position(), e),
        Ok(Event::Eof) => break,
        _ => (),
    }
    buf.clear();
}
assert_eq!(count, 3);
assert_eq!(txt, vec!["Test".to_string(), "Test 2".to_string()]);
Source

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 a corresponding End event is not found, an error of type Error::IllFormed 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.

The correctness of the skipped events does not checked, if you disabled the check_end_names option.

§Namespaces

While the Reader does not support 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::reader::Reader;

let mut reader = Reader::from_str(r#"
    <outer>
        <inner>
            <inner></inner>
            <inner/>
            <outer></outer>
            <outer/>
        </inner>
    </outer>
"#);
reader.config_mut().trim_text(true);
let mut buf = Vec::new();

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

// First, we read a start event...
assert_eq!(reader.read_event_into(&mut buf).unwrap(), 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_event_into(&mut buf).unwrap(), Event::Eof);
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impl Reader<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<'a> Reader<&'a [u8]>

This is an implementation for reading from a &[u8] as underlying byte stream. This implementation supports not using an intermediate buffer as the byte slice itself can be used to borrow from.

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

Creates an XML reader from a string slice.

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

Read an event that borrows from the input rather than a buffer.

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::reader::Reader;

let mut reader = Reader::from_str(r#"
    <tag1 att1 = "test">
       <tag2><!--Test comment-->Test</tag2>
       <tag2>Test 2</tag2>
    </tag1>
"#);
reader.config_mut().trim_text(true);

let mut count = 0;
let mut txt = Vec::new();
loop {
    match reader.read_event().unwrap() {
        Event::Start(e) => count += 1,
        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()]);
Source

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 a corresponding End event is not found, an error of type Error::IllFormed 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.

The correctness of the skipped events does not checked, if you disabled the check_end_names option.

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 Reader does not support 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::reader::Reader;

let mut reader = Reader::from_str(r#"
    <outer>
        <inner>
            <inner></inner>
            <inner/>
            <outer></outer>
            <outer/>
        </inner>
    </outer>
"#);
reader.config_mut().trim_text(true);

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

// First, we read a start event...
assert_eq!(reader.read_event().unwrap(), 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_event().unwrap(), Event::Eof);
Source

pub fn read_text(&mut self, end: QName<'_>) -> Result<Cow<'a, 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::Reader;

let mut reader = Reader::from_str("
    <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.config_mut().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.config_mut().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;
    "#));
assert!(matches!(text, Cow::Borrowed(_)));

// Now we can enable checks again
reader.config_mut().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);
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impl<R> Reader<R>

Builder methods

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pub fn from_reader(reader: R) -> Self

Creates a Reader that reads from a given reader.

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pub const fn config(&self) -> &Config

Returns reference to the parser configuration

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pub fn config_mut(&mut self) -> &mut Config

Returns mutable reference to the parser configuration

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impl<R> Reader<R>

Getters

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pub fn into_inner(self) -> R

Consumes Reader returning the underlying reader

Can be used to compute line and column of a parsing error position

§Examples
use std::{str, io::Cursor};
use quick_xml::events::Event;
use quick_xml::reader::Reader;

let xml = r#"<tag1 att1 = "test">
                <tag2><!--Test comment-->Test</tag2>
                <tag3>Test 2</tag3>
             </tag1>"#;
let mut reader = Reader::from_reader(Cursor::new(xml.as_bytes()));
let mut buf = Vec::new();

fn into_line_and_column(reader: Reader<Cursor<&[u8]>>) -> (usize, usize) {
    // We known that size cannot exceed usize::MAX because we created parser from single &[u8]
    let end_pos = reader.buffer_position() as usize;
    let mut cursor = reader.into_inner();
    let s = String::from_utf8(cursor.into_inner()[0..end_pos].to_owned())
        .expect("can't make a string");
    let mut line = 1;
    let mut column = 0;
    for c in s.chars() {
        if c == '\n' {
            line += 1;
            column = 0;
        } else {
            column += 1;
        }
    }
    (line, column)
}

loop {
    match reader.read_event_into(&mut buf) {
        Ok(Event::Start(ref e)) => match e.name().as_ref() {
            b"tag1" | b"tag2" => (),
            tag => {
                assert_eq!(b"tag3", tag);
                assert_eq!((3, 22), into_line_and_column(reader));
                break;
            }
        },
        Ok(Event::Eof) => unreachable!(),
        _ => (),
    }
    buf.clear();
}
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pub const fn get_ref(&self) -> &R

Gets a reference to the underlying reader.

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

Gets a mutable reference to the underlying reader.

Avoid read from this reader because this will not update reader’s position and will lead to incorrect positions of errors. If you want to read, use stream() instead.

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pub const fn buffer_position(&self) -> u64

Gets the current byte position in the input data.

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pub const fn error_position(&self) -> u64

Gets the last error byte position in the input data. If there is no errors yet, returns 0.

Unlike buffer_position it will point to the place where it is rational to report error to the end user. For example, all SyntaxErrors are reported when the parser sees EOF inside of some kind of markup. The buffer_position() will point to the last byte of input which is not very useful. error_position() will point to the start of corresponding markup element (i. e. to the < character).

This position is always <= buffer_position().

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pub const 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.

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pub fn stream(&mut self) -> BinaryStream<'_, R> ⓘ

Get the direct access to the underlying reader, but tracks the amount of read data and update Reader::buffer_position() accordingly.

Note, that this method gives you access to the internal reader and read data will not be returned in any subsequent events read by read_event family of methods.

§Example

This example demonstrates how to read stream raw bytes from an XML document. This could be used to implement streaming read of text, or to read raw binary bytes embedded in an XML document. (Documents with embedded raw bytes are not valid XML, but XML-derived file formats exist where such documents are valid).

use std::io::{BufRead, Read};
use quick_xml::events::{BytesEnd, BytesStart, Event};
use quick_xml::reader::Reader;

let mut reader = Reader::from_str("<tag>binary << data&></tag>");
//                                 ^    ^               ^     ^
//                                 0    5              21    27

assert_eq!(
    (reader.read_event().unwrap(), reader.buffer_position()),
    // 5 - end of the `<tag>`
    (Event::Start(BytesStart::new("tag")), 5)
);

// Reading directly from underlying reader will not update position
// let mut inner = reader.get_mut();

// Reading from the stream() advances position
let mut inner = reader.stream();

// Read binary data. We must know its size
let mut binary = [0u8; 16];
inner.read_exact(&mut binary).unwrap();
assert_eq!(&binary, b"binary << data&>");
// 21 - end of the `binary << data&>`
assert_eq!(inner.offset(), 21);
assert_eq!(reader.buffer_position(), 21);

assert_eq!(
    (reader.read_event().unwrap(), reader.buffer_position()),
    // 27 - end of the `</tag>`
    (Event::End(BytesEnd::new("tag")), 27)
);

assert_eq!(reader.read_event().unwrap(), Event::Eof);

Trait Implementations§

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impl<R: Clone> Clone for Reader<R>

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fn clone(&self) -> Reader<R>

Returns a copy of the value. Read more
1.0.0 · Source§

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source. Read more

Auto Trait Implementations§

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

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

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

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

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

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impl<R> UnwindSafe for Reader<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> CloneToUninit for T
where T: Clone,

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unsafe fn clone_to_uninit(&self, dst: *mut T)

🔬This is a nightly-only experimental API. (clone_to_uninit)
Performs copy-assignment from self to dst. 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> ToOwned for T
where T: Clone,

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type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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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.