json_event_parser/write.rs
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use crate::JsonEvent;
use std::io::{Error, ErrorKind, Result, Write};
#[cfg(feature = "async-tokio")]
use tokio::io::{AsyncWrite, AsyncWriteExt};
/// A JSON streaming writer writing to a [`Write`] implementation.
///
/// ```
/// use json_event_parser::{ToWriteJsonWriter, JsonEvent};
///
/// let mut writer = ToWriteJsonWriter::new(Vec::new());
/// writer.write_event(JsonEvent::StartObject)?;
/// writer.write_event(JsonEvent::ObjectKey("foo".into()))?;
/// writer.write_event(JsonEvent::Number("1".into()))?;
/// writer.write_event(JsonEvent::EndObject)?;
///
/// assert_eq!(writer.finish()?.as_slice(), b"{\"foo\":1}");
/// # std::io::Result::Ok(())
/// ```
pub struct ToWriteJsonWriter<W: Write> {
write: W,
writer: LowLevelJsonWriter,
}
impl<W: Write> ToWriteJsonWriter<W> {
pub const fn new(write: W) -> Self {
Self {
write,
writer: LowLevelJsonWriter::new(),
}
}
pub fn write_event(&mut self, event: JsonEvent<'_>) -> Result<()> {
self.writer.write_event(event, &mut self.write)
}
pub fn finish(self) -> Result<W> {
self.writer.validate_eof()?;
Ok(self.write)
}
}
/// A JSON streaming writer writing to an [`AsyncWrite`] implementation.
///
/// ```
/// use json_event_parser::{ToTokioAsyncWriteJsonWriter, JsonEvent};
///
/// # #[tokio::main(flavor = "current_thread")]
/// # async fn main() -> ::std::io::Result<()> {
/// let mut writer = ToTokioAsyncWriteJsonWriter::new(Vec::new());
/// writer.write_event(JsonEvent::StartObject).await?;
/// writer.write_event(JsonEvent::ObjectKey("foo".into())).await?;
/// writer.write_event(JsonEvent::Number("1".into())).await?;
/// writer.write_event(JsonEvent::EndObject).await?;
/// assert_eq!(writer.finish()?.as_slice(), b"{\"foo\":1}");
/// # Ok(())
/// # }
/// ```
#[cfg(feature = "async-tokio")]
pub struct ToTokioAsyncWriteJsonWriter<W: AsyncWrite + Unpin> {
write: W,
writer: LowLevelJsonWriter,
buffer: Vec<u8>,
}
#[cfg(feature = "async-tokio")]
impl<W: AsyncWrite + Unpin> ToTokioAsyncWriteJsonWriter<W> {
pub const fn new(write: W) -> Self {
Self {
write,
writer: LowLevelJsonWriter::new(),
buffer: Vec::new(),
}
}
pub async fn write_event(&mut self, event: JsonEvent<'_>) -> Result<()> {
self.writer.write_event(event, &mut self.buffer)?;
self.write.write_all(&self.buffer).await?;
self.buffer.clear();
Ok(())
}
pub fn finish(self) -> Result<W> {
self.writer.validate_eof()?;
Ok(self.write)
}
}
/// A low-level JSON streaming writer writing to a [`Write`] implementation.
///
/// YOu probably want to use [`ToWriteJsonWriter`] instead.
///
/// ```
/// use json_event_parser::{JsonEvent, LowLevelJsonWriter};
///
/// let mut writer = LowLevelJsonWriter::new();
/// let mut output = Vec::new();
/// writer.write_event(JsonEvent::StartObject, &mut output)?;
/// writer.write_event(JsonEvent::ObjectKey("foo".into()), &mut output)?;
/// writer.write_event(JsonEvent::Number("1".into()), &mut output)?;
/// writer.write_event(JsonEvent::EndObject, &mut output)?;
///
/// assert_eq!(output.as_slice(), b"{\"foo\":1}");
/// # std::io::Result::Ok(())
/// ```
#[derive(Default)]
pub struct LowLevelJsonWriter {
state_stack: Vec<JsonState>,
element_written: bool,
}
impl LowLevelJsonWriter {
pub const fn new() -> Self {
Self {
state_stack: Vec::new(),
element_written: false,
}
}
pub fn write_event(&mut self, event: JsonEvent<'_>, mut write: impl Write) -> Result<()> {
match event {
JsonEvent::String(s) => {
self.before_value(&mut write)?;
write_escaped_json_string(&s, write)
}
JsonEvent::Number(number) => {
self.before_value(&mut write)?;
write.write_all(number.as_bytes())
}
JsonEvent::Boolean(b) => {
self.before_value(&mut write)?;
write.write_all(if b { b"true" } else { b"false" })
}
JsonEvent::Null => {
self.before_value(&mut write)?;
write.write_all(b"null")
}
JsonEvent::StartArray => {
self.before_value(&mut write)?;
self.state_stack.push(JsonState::OpenArray);
write.write_all(b"[")
}
JsonEvent::EndArray => match self.state_stack.pop() {
Some(JsonState::OpenArray) | Some(JsonState::ContinuationArray) => {
write.write_all(b"]")
}
Some(s) => {
self.state_stack.push(s);
Err(Error::new(
ErrorKind::InvalidInput,
"Closing a not opened array",
))
}
None => Err(Error::new(
ErrorKind::InvalidInput,
"Closing a not opened array",
)),
},
JsonEvent::StartObject => {
self.before_value(&mut write)?;
self.state_stack.push(JsonState::OpenObject);
write.write_all(b"{")
}
JsonEvent::EndObject => match self.state_stack.pop() {
Some(JsonState::OpenObject) | Some(JsonState::ContinuationObject) => {
write.write_all(b"}")
}
Some(s) => {
self.state_stack.push(s);
Err(Error::new(
ErrorKind::InvalidInput,
"Closing a not opened object",
))
}
None => Err(Error::new(
ErrorKind::InvalidInput,
"Closing a not opened object",
)),
},
JsonEvent::ObjectKey(key) => {
match self.state_stack.pop() {
Some(JsonState::OpenObject) => (),
Some(JsonState::ContinuationObject) => write.write_all(b",")?,
_ => {
return Err(Error::new(
ErrorKind::InvalidInput,
"Trying to write an object key in an not object",
))
}
}
self.state_stack.push(JsonState::ContinuationObject);
self.state_stack.push(JsonState::ObjectValue);
write_escaped_json_string(&key, &mut write)?;
write.write_all(b":")
}
JsonEvent::Eof => Err(Error::new(
ErrorKind::InvalidInput,
"EOF is not allowed in JSON writer",
)),
}
}
fn before_value(&mut self, mut write: impl Write) -> Result<()> {
match self.state_stack.pop() {
Some(JsonState::OpenArray) => {
self.state_stack.push(JsonState::ContinuationArray);
Ok(())
}
Some(JsonState::ContinuationArray) => {
self.state_stack.push(JsonState::ContinuationArray);
write.write_all(b",")?;
Ok(())
}
Some(last_state @ JsonState::OpenObject)
| Some(last_state @ JsonState::ContinuationObject) => {
self.state_stack.push(last_state);
Err(Error::new(
ErrorKind::InvalidInput,
"Object key expected, string found",
))
}
Some(JsonState::ObjectValue) => Ok(()),
None => {
if self.element_written {
Err(Error::new(
ErrorKind::InvalidInput,
"A root JSON value has already been written",
))
} else {
self.element_written = true;
Ok(())
}
}
}
}
fn validate_eof(&self) -> Result<()> {
if !self.state_stack.is_empty() {
return Err(Error::new(
ErrorKind::InvalidInput,
"The written JSON is not balanced: an object or an array has not been closed",
));
}
if !self.element_written {
return Err(Error::new(
ErrorKind::InvalidInput,
"A JSON file can't be empty",
));
}
Ok(())
}
}
enum JsonState {
OpenArray,
ContinuationArray,
OpenObject,
ContinuationObject,
ObjectValue,
}
fn write_escaped_json_string(s: &str, mut write: impl Write) -> Result<()> {
write.write_all(b"\"")?;
let mut buffer = [b'\\', b'u', 0, 0, 0, 0];
for c in s.chars() {
match c {
'\\' => write.write_all(b"\\\\"),
'"' => write.write_all(b"\\\""),
c => {
if c < char::from(32) {
match c {
'\u{08}' => write.write_all(b"\\b"),
'\u{0C}' => write.write_all(b"\\f"),
'\n' => write.write_all(b"\\n"),
'\r' => write.write_all(b"\\r"),
'\t' => write.write_all(b"\\t"),
c => {
let mut c = c as u8;
for i in (2..6).rev() {
let ch = c % 16;
buffer[i] = if ch < 10 { b'0' + ch } else { b'A' + ch - 10 };
c /= 16;
}
write.write_all(&buffer)
}
}
} else {
write.write_all(c.encode_utf8(&mut buffer[2..]).as_bytes())
}
}
}?;
}
write.write_all(b"\"")?;
Ok(())
}