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//! The YAML data format.
use std::io::{self, BufRead, BufReader, Write};
use std::str;
use serde::{de, ser};
use crate::input::{self, Input, Ref};
use crate::transcode;
mod chunker;
mod encoding;
use self::chunker::Chunker;
use self::encoding::{Encoder, Encoding};
pub(crate) fn input_matches(mut input: Ref) -> io::Result<bool> {
// YAML can be surprisingly liberal in what it accepts. Many non-YAML text documents can be
// parsed as a YAML scalar (i.e. a giant string), including TOML documents that start with
// plain key-value assignments rather than a table header. To prevent these kinds of weird
// matches, we only detect input as YAML when the first document in the stream encodes a
// collection (map or sequence).
let encoding = Encoding::detect(input.prefix(Encoding::DETECT_LEN)?);
let chunk = match &mut input {
Ref::Slice(b) => Chunker::new(Encoder::new(b, encoding)).next(),
Ref::Reader(r) => Chunker::new(Encoder::new(BufReader::new(r), encoding)).next(),
};
match chunk {
Some(Ok(doc)) => Ok(doc.is_collection()),
Some(Err(err)) if err.kind() == io::ErrorKind::InvalidData => Ok(false),
Some(Err(err)) => Err(err),
None => Ok(false),
}
}
pub(crate) fn transcode<O>(input: input::Handle, mut output: O) -> crate::Result<()>
where
O: crate::Output,
{
match input.into() {
Input::Reader(r) => transcode_reader(BufReader::new(r), output),
Input::Slice(b) => match str::from_utf8(&b) {
Ok(s) => {
for de in serde_yaml::Deserializer::from_str(s) {
output.transcode_from(de)?;
}
Ok(())
}
Err(_) => {
// The reader path re-encodes UTF-16 and UTF-32. See transcode_reader for details.
transcode_reader(&*b, output)
}
},
}
}
fn transcode_reader<R, O>(input: R, mut output: O) -> crate::Result<()>
where
R: BufRead,
O: crate::Output,
{
// serde_yaml imposes a couple of interesting limitations on us, which aren't clear from its
// documentation but are reflected in this usage.
//
// First, while serde_yaml supports creating a Deserializer from a reader, this actually slurps
// the entire input into a buffer for parsing. We support streaming parsing by implementing our
// own "chunker" that splits an unbounded YAML stream into a sequence of buffered documents.
// This is a terrible hack, and I'd love to have the time and energy someday to implement
// something more proper.
//
// Second, serde_yaml doesn't support UTF-16 or UTF-32, even though YAML 1.2 requires both.
// In addition to our chunker, we implement a streaming encoder that can detect the encoding of
// any valid YAML stream and convert it to UTF-8. The encoder also strips any byte order mark
// from the beginning of the stream, as serde_yaml will choke on it. This still doesn't cover
// the full YAML spec, which allows BOMs in UTF-8 streams and at the starts of individual
// documents in the stream. Hopefully these cases are rarer than that of a single BOM at the
// start of a UTF-16 or UTF-32 stream.
for doc in Chunker::new(Encoder::from_reader(input)?) {
let doc = doc?;
let de = serde_yaml::Deserializer::from_str(doc.content());
output.transcode_from(de)?;
}
Ok(())
}
pub(crate) struct Output<W: Write>(W);
impl<W: Write> Output<W> {
pub(crate) fn new(w: W) -> Output<W> {
Output(w)
}
}
impl<W: Write> crate::Output for Output<W> {
fn transcode_from<'de, D, E>(&mut self, de: D) -> crate::Result<()>
where
D: de::Deserializer<'de, Error = E>,
E: de::Error + Send + Sync + 'static,
{
writeln!(&mut self.0, "---")?;
let mut ser = serde_yaml::Serializer::new(&mut self.0);
transcode::transcode(&mut ser, de)?;
Ok(())
}
fn transcode_value<S>(&mut self, value: S) -> crate::Result<()>
where
S: ser::Serialize,
{
writeln!(&mut self.0, "---")?;
serde_yaml::to_writer(&mut self.0, &value)?;
Ok(())
}
fn flush(&mut self) -> io::Result<()> {
self.0.flush()
}
}