src/stream/xml_writer.rs

use base64;
use line_wrap;
use std::borrow::Cow;
use std::io::Write;
use xml_rs::name::Name;
use xml_rs::namespace::Namespace;
use xml_rs::writer::{EmitterConfig, Error as XmlWriterError, EventWriter, XmlEvent};

use stream::{Event, Writer};
use Error;

static XML_PROLOGUE: &str = r#"<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
"#;

impl From<XmlWriterError> for Error {
    fn from(err: XmlWriterError) -> Error {
        match err {
            XmlWriterError::Io(err) => Error::Io(err),
            _ => Error::InvalidData,
        }
    }
}

#[derive(PartialEq)]
enum Element {
    Dictionary,
    Array,
}

pub struct XmlWriter<W: Write> {
    xml_writer: EventWriter<W>,
    stack: Vec<Element>,
    expecting_key: bool,
    written_prologue: bool,
    // Not very nice
    empty_namespace: Namespace,
}

impl<W: Write> XmlWriter<W> {
    pub fn new(writer: W) -> XmlWriter<W> {
        let config = EmitterConfig::new()
            .line_separator("\n")
            .indent_string("\t")
            .perform_indent(true)
            .write_document_declaration(false)
            .normalize_empty_elements(true)
            .cdata_to_characters(true)
            .keep_element_names_stack(false)
            .autopad_comments(true);

        XmlWriter {
            xml_writer: EventWriter::new_with_config(writer, config),
            stack: Vec::new(),
            expecting_key: false,
            written_prologue: false,
            empty_namespace: Namespace::empty(),
        }
    }

    fn write_element_and_value(&mut self, name: &str, value: &str) -> Result<(), Error> {
        self.start_element(name)?;
        self.write_value(value)?;
        self.end_element(name)?;
        Ok(())
    }

    fn start_element(&mut self, name: &str) -> Result<(), Error> {
        self.xml_writer.write(XmlEvent::StartElement {
            name: Name::local(name),
            attributes: Cow::Borrowed(&[]),
            namespace: Cow::Borrowed(&self.empty_namespace),
        })?;
        Ok(())
    }

    fn end_element(&mut self, name: &str) -> Result<(), Error> {
        self.xml_writer.write(XmlEvent::EndElement {
            name: Some(Name::local(name)),
        })?;
        Ok(())
    }

    fn write_value(&mut self, value: &str) -> Result<(), Error> {
        self.xml_writer.write(XmlEvent::Characters(value))?;
        Ok(())
    }

    pub fn write(&mut self, event: &Event) -> Result<(), Error> {
        <Self as Writer>::write(self, event)
    }

    pub fn into_inner(self) -> W {
        self.xml_writer.into_inner()
    }
}

impl<W: Write> Writer for XmlWriter<W> {
    fn write(&mut self, event: &Event) -> Result<(), Error> {
        if !self.written_prologue {
            self.xml_writer
                .inner_mut()
                .write_all(XML_PROLOGUE.as_bytes())?;

            self.written_prologue = true;
        }

        if self.expecting_key {
            match *event {
                Event::EndDictionary => match self.stack.pop() {
                    Some(Element::Dictionary) => {
                        self.end_element("dict")?;
                        self.expecting_key = self.stack.last() == Some(&Element::Dictionary);
                    }
                    _ => return Err(Error::InvalidData),
                },
                Event::StringValue(ref value) => {
                    self.write_element_and_value("key", &*value)?;
                    self.expecting_key = false;
                }
                _ => return Err(Error::InvalidData),
            }
        } else {
            match *event {
                Event::StartArray(_) => {
                    self.start_element("array")?;
                    self.stack.push(Element::Array);
                }
                Event::EndArray => match self.stack.pop() {
                    Some(Element::Array) => self.end_element("array")?,
                    _ => return Err(Error::InvalidData),
                },

                Event::StartDictionary(_) => {
                    self.start_element("dict")?;
                    self.stack.push(Element::Dictionary);
                }
                Event::EndDictionary => return Err(Error::InvalidData),

                Event::BooleanValue(true) => {
                    self.start_element("true")?;
                    self.end_element("true")?;
                }
                Event::BooleanValue(false) => {
                    self.start_element("false")?;
                    self.end_element("false")?;
                }
                Event::DataValue(ref value) => {
                    let base64_data = base64_encode_plist(&value, self.stack.len());
                    self.write_element_and_value("data", &base64_data)?;
                }
                Event::DateValue(ref value) => {
                    self.write_element_and_value("date", &value.to_rfc3339())?
                }
                Event::IntegerValue(ref value) => {
                    self.write_element_and_value("integer", &value.to_string())?
                }
                Event::RealValue(ref value) => {
                    self.write_element_and_value("real", &value.to_string())?
                }
                Event::StringValue(ref value) => self.write_element_and_value("string", &*value)?,
            };

            self.expecting_key = self.stack.last() == Some(&Element::Dictionary);
        }

        // If there are no more open tags then write the </plist> element
        if self.stack.len() == 0 {
            // We didn't tell the xml_writer about the <plist> tag so we'll skip telling it
            // about the </plist> tag as well.
            self.xml_writer.inner_mut().write_all(b"\n</plist>")?;
        }

        Ok(())
    }
}

fn base64_encode_plist(data: &[u8], indent: usize) -> String {
    // XML plist data elements are always formatted by apple tools as
    // <data>
    // AAAA..AA (68 characters per line)
    // </data>
    // Allocate space for base 64 string and line endings up front
    const LINE_LEN: usize = 68;
    let mut line_ending = Vec::with_capacity(1 + indent);
    line_ending.push(b'\n');
    (0..indent).for_each(|_| line_ending.push(b'\t'));

    // Find the max length of `data` encoded as a base 64 string with padding
    let base64_max_string_len = data.len() * 4 / 3 + 4;

    // Find the max length of the formatted base 64 string as: max length of the base 64 string
    // + line endings and indents at the start of the string and after every line
    let base64_max_string_len_with_formatting =
        base64_max_string_len + (2 + base64_max_string_len / LINE_LEN) * line_ending.len();

    let mut output = vec![0; base64_max_string_len_with_formatting];

    // Start output with a line ending and indent
    &mut output[..line_ending.len()].copy_from_slice(&line_ending);

    // Encode `data` as a base 64 string
    let base64_string_len =
        base64::encode_config_slice(data, base64::STANDARD, &mut output[line_ending.len()..]);

    // Line wrap the base 64 encoded string
    let line_wrap_len = line_wrap::line_wrap(
        &mut output[line_ending.len()..],
        base64_string_len,
        LINE_LEN,
        &line_wrap::SliceLineEnding::new(&line_ending),
    );

    // Add the final line ending and indent
    &mut output[line_ending.len() + base64_string_len + line_wrap_len..][..line_ending.len()]
        .copy_from_slice(&line_ending);

    // Ensure output is the correct length
    output.truncate(base64_string_len + line_wrap_len + 2 * line_ending.len());
    String::from_utf8(output).expect("base 64 string must be valid utf8")
}

#[cfg(test)]
mod tests {
    use humantime::parse_rfc3339_weak;
    use std::io::Cursor;

    use super::*;
    use stream::Event::*;

    #[test]
    fn streaming_parser() {
        let plist = &[
            StartDictionary(None),
            StringValue("Author".to_owned()),
            StringValue("William Shakespeare".to_owned()),
            StringValue("Lines".to_owned()),
            StartArray(None),
            StringValue("It is a tale told by an idiot,".to_owned()),
            StringValue("Full of sound and fury, signifying nothing.".to_owned()),
            DataValue((0..128).collect::<Vec<_>>()),
            EndArray,
            StringValue("Death".to_owned()),
            IntegerValue(1564),
            StringValue("Height".to_owned()),
            RealValue(1.60),
            StringValue("Data".to_owned()),
            DataValue(vec![0, 0, 0, 190, 0, 0, 0, 3, 0, 0, 0, 30, 0, 0, 0]),
            StringValue("Birthdate".to_owned()),
            DateValue(parse_rfc3339_weak("1981-05-16 11:32:06").unwrap().into()),
            StringValue("Comment".to_owned()),
            StringValue("2 < 3".to_owned()), // make sure characters are escaped
            EndDictionary,
        ];

        let mut cursor = Cursor::new(Vec::new());

        {
            let mut plist_w = XmlWriter::new(&mut cursor);

            for item in plist {
                plist_w.write(item).unwrap();
            }
        }

        let comparison = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<!DOCTYPE plist PUBLIC \"-//Apple//DTD PLIST 1.0//EN\" \"http://www.apple.com/DTDs/PropertyList-1.0.dtd\">
<plist version=\"1.0\">
<dict>
\t<key>Author</key>
\t<string>William Shakespeare</string>
\t<key>Lines</key>
\t<array>
\t\t<string>It is a tale told by an idiot,</string>
\t\t<string>Full of sound and fury, signifying nothing.</string>
\t\t<data>
\t\tAAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8gISIjJCUmJygpKissLS4vMDEy
\t\tMzQ1Njc4OTo7PD0+P0BBQkNERUZHSElKS0xNTk9QUVJTVFVWV1hZWltcXV5fYGFiY2Rl
\t\tZmdoaWprbG1ub3BxcnN0dXZ3eHl6e3x9fn8=
\t\t</data>
\t</array>
\t<key>Death</key>
\t<integer>1564</integer>
\t<key>Height</key>
\t<real>1.6</real>
\t<key>Data</key>
\t<data>
\tAAAAvgAAAAMAAAAeAAAA
\t</data>
\t<key>Birthdate</key>
\t<date>1981-05-16T11:32:06Z</date>
\t<key>Comment</key>
\t<string>2 &lt; 3</string>
</dict>
</plist>";

        let s = String::from_utf8(cursor.into_inner()).unwrap();

        assert_eq!(s, comparison);
    }
}