quick_xml/writer.rs
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//! Contains high-level interface for an events-based XML emitter.
use std::borrow::Cow;
use std::io::{self, Write};
use crate::encoding::UTF8_BOM;
use crate::events::{attributes::Attribute, BytesCData, BytesPI, BytesStart, BytesText, Event};
#[cfg(feature = "async-tokio")]
mod async_tokio;
/// XML writer. Writes XML [`Event`]s to a [`std::io::Write`] or [`tokio::io::AsyncWrite`] implementor.
#[cfg(feature = "serialize")]
use {crate::se::SeError, serde::Serialize};
/// XML writer. Writes XML [`Event`]s to a [`std::io::Write`] implementor.
///
/// # Examples
///
/// ```
/// # use pretty_assertions::assert_eq;
/// use quick_xml::events::{Event, BytesEnd, BytesStart};
/// use quick_xml::reader::Reader;
/// use quick_xml::writer::Writer;
/// use std::io::Cursor;
///
/// let xml = r#"<this_tag k1="v1" k2="v2"><child>text</child></this_tag>"#;
/// let mut reader = Reader::from_str(xml);
/// let mut writer = Writer::new(Cursor::new(Vec::new()));
/// loop {
/// match reader.read_event() {
/// Ok(Event::Start(e)) if e.name().as_ref() == b"this_tag" => {
///
/// // crates a new element ... alternatively we could reuse `e` by calling
/// // `e.into_owned()`
/// let mut elem = BytesStart::new("my_elem");
///
/// // collect existing attributes
/// elem.extend_attributes(e.attributes().map(|attr| attr.unwrap()));
///
/// // copy existing attributes, adds a new my-key="some value" attribute
/// elem.push_attribute(("my-key", "some value"));
///
/// // writes the event to the writer
/// assert!(writer.write_event(Event::Start(elem)).is_ok());
/// },
/// Ok(Event::End(e)) if e.name().as_ref() == b"this_tag" => {
/// assert!(writer.write_event(Event::End(BytesEnd::new("my_elem"))).is_ok());
/// },
/// Ok(Event::Eof) => break,
/// // we can either move or borrow the event to write, depending on your use-case
/// Ok(e) => assert!(writer.write_event(e.borrow()).is_ok()),
/// Err(e) => panic!("Error at position {}: {:?}", reader.error_position(), e),
/// }
/// }
///
/// let result = writer.into_inner().into_inner();
/// let expected = r#"<my_elem k1="v1" k2="v2" my-key="some value"><child>text</child></my_elem>"#;
/// assert_eq!(result, expected.as_bytes());
/// ```
#[derive(Clone)]
pub struct Writer<W> {
/// underlying writer
writer: W,
indent: Option<Indentation>,
}
impl<W> Writer<W> {
/// Creates a `Writer` from a generic writer.
pub const fn new(inner: W) -> Writer<W> {
Writer {
writer: inner,
indent: None,
}
}
/// Creates a `Writer` with configured indents from a generic writer.
pub fn new_with_indent(inner: W, indent_char: u8, indent_size: usize) -> Writer<W> {
Writer {
writer: inner,
indent: Some(Indentation::new(indent_char, indent_size)),
}
}
/// Consumes this `Writer`, returning the underlying writer.
pub fn into_inner(self) -> W {
self.writer
}
/// Get a mutable reference to the underlying writer.
pub fn get_mut(&mut self) -> &mut W {
&mut self.writer
}
/// Get a reference to the underlying writer.
pub const fn get_ref(&self) -> &W {
&self.writer
}
/// Provides a simple, high-level API for writing XML elements.
///
/// Returns an [`ElementWriter`] that simplifies setting attributes and writing
/// content inside the element.
///
/// # Example
///
/// ```
/// # use quick_xml::Result;
/// # fn main() -> Result<()> {
/// use quick_xml::events::{BytesStart, BytesText, Event};
/// use quick_xml::writer::Writer;
/// use quick_xml::Error;
/// use std::io::Cursor;
///
/// let mut writer = Writer::new(Cursor::new(Vec::new()));
///
/// // writes <tag attr1="value1"/>
/// writer.create_element("tag")
/// .with_attribute(("attr1", "value1")) // chain `with_attribute()` calls to add many attributes
/// .write_empty()?;
///
/// // writes <tag attr1="value1" attr2="value2">with some text inside</tag>
/// writer.create_element("tag")
/// .with_attributes(vec![("attr1", "value1"), ("attr2", "value2")].into_iter()) // or add attributes from an iterator
/// .write_text_content(BytesText::new("with some text inside"))?;
///
/// // writes <tag><fruit quantity="0">apple</fruit><fruit quantity="1">orange</fruit></tag>
/// writer.create_element("tag")
/// // We need to provide error type, because it is not named somewhere explicitly
/// .write_inner_content(|writer| {
/// let fruits = ["apple", "orange"];
/// for (quant, item) in fruits.iter().enumerate() {
/// writer
/// .create_element("fruit")
/// .with_attribute(("quantity", quant.to_string().as_str()))
/// .write_text_content(BytesText::new(item))?;
/// }
/// Ok(())
/// })?;
/// # Ok(())
/// # }
/// ```
#[must_use]
pub fn create_element<'a, N>(&'a mut self, name: N) -> ElementWriter<'a, W>
where
N: Into<Cow<'a, str>>,
{
ElementWriter {
writer: self,
start_tag: BytesStart::new(name),
state: AttributeIndent::NoneAttributesWritten,
spaces: Vec::new(),
}
}
}
impl<W: Write> Writer<W> {
/// Write a [Byte-Order-Mark] character to the document.
///
/// # Example
///
/// ```rust
/// # use quick_xml::Result;
/// # fn main() -> Result<()> {
/// use quick_xml::events::{BytesStart, BytesText, Event};
/// use quick_xml::writer::Writer;
/// use quick_xml::Error;
/// use std::io::Cursor;
///
/// let mut buffer = Vec::new();
/// let mut writer = Writer::new_with_indent(&mut buffer, b' ', 4);
///
/// writer.write_bom()?;
/// writer
/// .create_element("empty")
/// .with_attribute(("attr1", "value1"))
/// .write_empty()
/// .expect("failure");
///
/// assert_eq!(
/// std::str::from_utf8(&buffer).unwrap(),
/// "\u{FEFF}<empty attr1=\"value1\"/>"
/// );
/// # Ok(())
/// # }
/// ```
/// [Byte-Order-Mark]: https://unicode.org/faq/utf_bom.html#BOM
pub fn write_bom(&mut self) -> io::Result<()> {
self.write(UTF8_BOM)
}
/// Writes the given event to the underlying writer.
pub fn write_event<'a, E: Into<Event<'a>>>(&mut self, event: E) -> io::Result<()> {
let mut next_should_line_break = true;
let result = match event.into() {
Event::Start(e) => {
let result = self.write_wrapped(b"<", &e, b">");
if let Some(i) = self.indent.as_mut() {
i.grow();
}
result
}
Event::End(e) => {
if let Some(i) = self.indent.as_mut() {
i.shrink();
}
self.write_wrapped(b"</", &e, b">")
}
Event::Empty(e) => self.write_wrapped(b"<", &e, b"/>"),
Event::Text(e) => {
next_should_line_break = false;
self.write(&e)
}
Event::Comment(e) => self.write_wrapped(b"<!--", &e, b"-->"),
Event::CData(e) => {
next_should_line_break = false;
self.write(b"<![CDATA[")?;
self.write(&e)?;
self.write(b"]]>")
}
Event::Decl(e) => self.write_wrapped(b"<?", &e, b"?>"),
Event::PI(e) => self.write_wrapped(b"<?", &e, b"?>"),
Event::DocType(e) => self.write_wrapped(b"<!DOCTYPE ", &e, b">"),
Event::Eof => Ok(()),
};
if let Some(i) = self.indent.as_mut() {
i.should_line_break = next_should_line_break;
}
result
}
/// Writes bytes
#[inline]
pub(crate) fn write(&mut self, value: &[u8]) -> io::Result<()> {
self.writer.write_all(value).map_err(Into::into)
}
#[inline]
fn write_wrapped(&mut self, before: &[u8], value: &[u8], after: &[u8]) -> io::Result<()> {
if let Some(ref i) = self.indent {
if i.should_line_break {
self.writer.write_all(b"\n")?;
self.writer.write_all(i.current())?;
}
}
self.write(before)?;
self.write(value)?;
self.write(after)?;
Ok(())
}
/// Manually write a newline and indentation at the proper level.
///
/// This can be used when the heuristic to line break and indent after any
/// [`Event`] apart from [`Text`] fails such as when a [`Start`] occurs directly
/// after [`Text`].
///
/// This method will do nothing if `Writer` was not constructed with [`new_with_indent`].
///
/// [`Text`]: Event::Text
/// [`Start`]: Event::Start
/// [`new_with_indent`]: Self::new_with_indent
pub fn write_indent(&mut self) -> io::Result<()> {
if let Some(ref i) = self.indent {
self.writer.write_all(b"\n")?;
self.writer.write_all(i.current())?;
}
Ok(())
}
/// Write an arbitrary serializable type
///
/// Note: If you are attempting to write XML in a non-UTF-8 encoding, this may not
/// be safe to use. Rust basic types assume UTF-8 encodings.
///
/// ```rust
/// # use pretty_assertions::assert_eq;
/// # use serde::Serialize;
/// # use quick_xml::events::{BytesStart, Event};
/// # use quick_xml::writer::Writer;
/// # use quick_xml::se::SeError;
/// # fn main() -> Result<(), SeError> {
/// #[derive(Debug, PartialEq, Serialize)]
/// struct MyData {
/// question: String,
/// answer: u32,
/// }
///
/// let data = MyData {
/// question: "The Ultimate Question of Life, the Universe, and Everything".into(),
/// answer: 42,
/// };
///
/// let mut buffer = Vec::new();
/// let mut writer = Writer::new_with_indent(&mut buffer, b' ', 4);
///
/// let start = BytesStart::new("root");
/// let end = start.to_end();
///
/// writer.write_event(Event::Start(start.clone()))?;
/// writer.write_serializable("my_data", &data)?;
/// writer.write_event(Event::End(end))?;
///
/// assert_eq!(
/// std::str::from_utf8(&buffer)?,
/// r#"<root>
/// <my_data>
/// <question>The Ultimate Question of Life, the Universe, and Everything</question>
/// <answer>42</answer>
/// </my_data>
/// </root>"#
/// );
/// # Ok(())
/// # }
/// ```
#[cfg(feature = "serialize")]
pub fn write_serializable<T: Serialize>(
&mut self,
tag_name: &str,
content: &T,
) -> Result<(), SeError> {
use crate::se::{Indent, Serializer};
self.write_indent()?;
let mut fmt = ToFmtWrite(&mut self.writer);
let mut serializer = Serializer::with_root(&mut fmt, Some(tag_name))?;
if let Some(indent) = &mut self.indent {
serializer.set_indent(Indent::Borrow(indent));
}
content.serialize(serializer)?;
Ok(())
}
}
/// Track indent inside elements state
///
/// ```mermaid
/// stateDiagram-v2
/// [*] --> NoneAttributesWritten
/// NoneAttributesWritten --> Spaces : .with_attribute()
/// NoneAttributesWritten --> WriteConfigured : .new_line()
///
/// Spaces --> Spaces : .with_attribute()
/// Spaces --> WriteSpaces : .new_line()
///
/// WriteSpaces --> Spaces : .with_attribute()
/// WriteSpaces --> WriteSpaces : .new_line()
///
/// Configured --> Configured : .with_attribute()
/// Configured --> WriteConfigured : .new_line()
///
/// WriteConfigured --> Configured : .with_attribute()
/// WriteConfigured --> WriteConfigured : .new_line()
/// ```
#[derive(Debug)]
enum AttributeIndent {
/// Initial state. `ElementWriter` was just created and no attributes written yet
NoneAttributesWritten,
/// Write specified count of spaces to indent before writing attribute in `with_attribute()`
WriteSpaces(usize),
/// Keep space indent that should be used if `new_line()` would be called
Spaces(usize),
/// Write specified count of indent characters before writing attribute in `with_attribute()`
WriteConfigured(usize),
/// Keep indent that should be used if `new_line()` would be called
Configured(usize),
}
/// A struct to write an element. Contains methods to add attributes and inner
/// elements to the element
pub struct ElementWriter<'a, W> {
writer: &'a mut Writer<W>,
start_tag: BytesStart<'a>,
state: AttributeIndent,
/// Contains spaces used to write space indents of attributes
spaces: Vec<u8>,
}
impl<'a, W> ElementWriter<'a, W> {
/// Adds an attribute to this element.
pub fn with_attribute<'b, I>(mut self, attr: I) -> Self
where
I: Into<Attribute<'b>>,
{
self.write_attr(attr.into());
self
}
/// Add additional attributes to this element using an iterator.
///
/// The yielded items must be convertible to [`Attribute`] using `Into`.
pub fn with_attributes<'b, I>(mut self, attributes: I) -> Self
where
I: IntoIterator,
I::Item: Into<Attribute<'b>>,
{
let mut iter = attributes.into_iter();
if let Some(attr) = iter.next() {
self.write_attr(attr.into());
self.start_tag.extend_attributes(iter);
}
self
}
/// Push a new line inside an element between attributes. Note, that this
/// method does nothing if [`Writer`] was created without indentation support.
///
/// # Examples
///
/// The following code
///
/// ```
/// # use quick_xml::writer::Writer;
/// let mut buffer = Vec::new();
/// let mut writer = Writer::new_with_indent(&mut buffer, b' ', 2);
/// writer
/// .create_element("element")
/// //.new_line() (1)
/// .with_attribute(("first", "1"))
/// .with_attribute(("second", "2"))
/// .new_line()
/// .with_attributes([
/// ("third", "3"),
/// ("fourth", "4"),
/// ])
/// //.new_line() (2)
/// .write_empty();
/// ```
/// will produce the following XMLs:
/// ```xml
/// <!-- result of the code above. Spaces always is used -->
/// <element first="1" second="2"
/// third="3" fourth="4"/>
///
/// <!-- if uncomment only (1) - indent depends on indentation
/// settings - 2 spaces here -->
/// <element
/// first="1" second="2"
/// third="3" fourth="4"/>
///
/// <!-- if uncomment only (2). Spaces always is used -->
/// <element first="1" second="2"
/// third="3" fourth="4"
/// />
/// ```
pub fn new_line(mut self) -> Self {
if let Some(i) = self.writer.indent.as_mut() {
match self.state {
// .new_line() called just after .create_element().
// Use element indent to additionally indent attributes
AttributeIndent::NoneAttributesWritten => {
self.state = AttributeIndent::WriteConfigured(i.indent_size)
}
AttributeIndent::WriteSpaces(_) => {}
// .new_line() called when .with_attribute() was called at least once.
// The spaces should be used to indent
// Plan saved indent
AttributeIndent::Spaces(indent) => {
self.state = AttributeIndent::WriteSpaces(indent)
}
AttributeIndent::WriteConfigured(_) => {}
// .new_line() called when .with_attribute() was called at least once.
// The configured indent characters should be used to indent
// Plan saved indent
AttributeIndent::Configured(indent) => {
self.state = AttributeIndent::WriteConfigured(indent)
}
}
self.start_tag.push_newline();
};
self
}
/// Writes attribute and maintain indentation state
fn write_attr<'b>(&mut self, attr: Attribute<'b>) {
if let Some(i) = self.writer.indent.as_mut() {
// Save the indent that we should use next time when .new_line() be called
self.state = match self.state {
// Neither .new_line() or .with_attribute() yet called
// If newline inside attributes will be requested, we should indent them
// by the length of tag name and +1 for `<` and +1 for one space
AttributeIndent::NoneAttributesWritten => {
self.start_tag.push_attribute(attr);
AttributeIndent::Spaces(self.start_tag.name().as_ref().len() + 2)
}
// Indent was requested by previous call to .new_line(), write it
// New line was already written
AttributeIndent::WriteSpaces(indent) => {
if self.spaces.len() < indent {
self.spaces.resize(indent, b' ');
}
self.start_tag.push_indent(&self.spaces[..indent]);
self.start_tag.push_attr(attr.into());
AttributeIndent::Spaces(indent)
}
// .new_line() was not called, but .with_attribute() was.
// use the previously calculated indent
AttributeIndent::Spaces(indent) => {
self.start_tag.push_attribute(attr);
AttributeIndent::Spaces(indent)
}
// Indent was requested by previous call to .new_line(), write it
// New line was already written
AttributeIndent::WriteConfigured(indent) => {
self.start_tag.push_indent(i.additional(indent));
self.start_tag.push_attr(attr.into());
AttributeIndent::Configured(indent)
}
// .new_line() was not called, but .with_attribute() was.
// use the previously calculated indent
AttributeIndent::Configured(indent) => {
self.start_tag.push_attribute(attr);
AttributeIndent::Configured(indent)
}
};
} else {
self.start_tag.push_attribute(attr);
}
}
}
impl<'a, W: Write> ElementWriter<'a, W> {
/// Write some text inside the current element.
pub fn write_text_content(self, text: BytesText) -> io::Result<&'a mut Writer<W>> {
self.writer
.write_event(Event::Start(self.start_tag.borrow()))?;
self.writer.write_event(Event::Text(text))?;
self.writer
.write_event(Event::End(self.start_tag.to_end()))?;
Ok(self.writer)
}
/// Write a CData event `<![CDATA[...]]>` inside the current element.
pub fn write_cdata_content(self, text: BytesCData) -> io::Result<&'a mut Writer<W>> {
self.writer
.write_event(Event::Start(self.start_tag.borrow()))?;
self.writer.write_event(Event::CData(text))?;
self.writer
.write_event(Event::End(self.start_tag.to_end()))?;
Ok(self.writer)
}
/// Write a processing instruction `<?...?>` inside the current element.
pub fn write_pi_content(self, pi: BytesPI) -> io::Result<&'a mut Writer<W>> {
self.writer
.write_event(Event::Start(self.start_tag.borrow()))?;
self.writer.write_event(Event::PI(pi))?;
self.writer
.write_event(Event::End(self.start_tag.to_end()))?;
Ok(self.writer)
}
/// Write an empty (self-closing) tag.
pub fn write_empty(self) -> io::Result<&'a mut Writer<W>> {
self.writer.write_event(Event::Empty(self.start_tag))?;
Ok(self.writer)
}
/// Create a new scope for writing XML inside the current element.
pub fn write_inner_content<F>(self, closure: F) -> io::Result<&'a mut Writer<W>>
where
F: FnOnce(&mut Writer<W>) -> io::Result<()>,
{
self.writer
.write_event(Event::Start(self.start_tag.borrow()))?;
closure(self.writer)?;
self.writer
.write_event(Event::End(self.start_tag.to_end()))?;
Ok(self.writer)
}
}
#[cfg(feature = "serialize")]
struct ToFmtWrite<T>(pub T);
#[cfg(feature = "serialize")]
impl<T> std::fmt::Write for ToFmtWrite<T>
where
T: std::io::Write,
{
fn write_str(&mut self, s: &str) -> std::fmt::Result {
self.0.write_all(s.as_bytes()).map_err(|_| std::fmt::Error)
}
}
#[derive(Clone)]
pub(crate) struct Indentation {
/// todo: this is an awkward fit as it has no impact on indentation logic, but it is
/// only applicable when an indentation exists. Potentially refactor later
should_line_break: bool,
/// The character code to be used for indentations (e.g. ` ` or `\t`)
indent_char: u8,
/// How many instances of the indent character ought to be used for each level of indentation
indent_size: usize,
/// Used as a cache for the bytes used for indentation
indents: Vec<u8>,
/// The current amount of indentation
current_indent_len: usize,
}
impl Indentation {
pub fn new(indent_char: u8, indent_size: usize) -> Self {
Self {
should_line_break: false,
indent_char,
indent_size,
indents: vec![indent_char; 128],
current_indent_len: 0, // invariant - needs to remain less than indents.len()
}
}
/// Increase indentation by one level
pub fn grow(&mut self) {
self.current_indent_len += self.indent_size;
self.ensure(self.current_indent_len);
}
/// Decrease indentation by one level. Do nothing, if level already zero
pub fn shrink(&mut self) {
self.current_indent_len = self.current_indent_len.saturating_sub(self.indent_size);
}
/// Returns indent string for current level
pub fn current(&self) -> &[u8] {
&self.indents[..self.current_indent_len]
}
/// Returns indent with current indent plus additional indent
pub fn additional(&mut self, additional_indent: usize) -> &[u8] {
let new_len = self.current_indent_len + additional_indent;
self.ensure(new_len);
&self.indents[..new_len]
}
fn ensure(&mut self, new_len: usize) {
if self.indents.len() < new_len {
self.indents.resize(new_len, self.indent_char);
}
}
}