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use std::num::FpCategory;
#[derive(Debug, Clone)]
pub struct JsonWriter {
buffer: Vec<u8>,
needs_separator: bool,
}
#[derive(thiserror::Error, Debug)]
pub enum JsonWriterError {
#[error("JsonWriter produced invalid UTF8 string")]
InvalidUtf8Conversion(#[from] std::string::FromUtf8Error),
#[error("IoError")]
FromIo(#[from] std::io::Error),
#[error("Serde Json error")]
FromSerdeJson(#[from] serde_json::Error),
#[error("Invalid f64 value {value:?}")]
InvalidF64Value { value: f64 },
}
#[cfg(test)]
impl Default for JsonWriter {
fn default() -> Self {
Self {
buffer: Vec::new(),
needs_separator: false,
}
}
}
impl JsonWriter {
pub fn with_capacity(capacity: usize) -> Self {
Self {
buffer: Vec::with_capacity(capacity),
needs_separator: false,
}
}
pub fn write_key(&mut self, key: &str) -> Result<(), JsonWriterError> {
self.maybe_separate();
let () = serde_json::to_writer(&mut self.buffer, key)?;
self.buffer.push(b':');
self.needs_separator = false;
Ok(())
}
pub fn write_str(&mut self, s: &str) -> Result<(), JsonWriterError> {
self.maybe_separate();
let () = serde_json::to_writer(&mut self.buffer, s)?;
self.needs_separator = true;
Ok(())
}
pub fn write_f64(&mut self, value: f64) -> Result<(), JsonWriterError> {
self.maybe_separate();
match value.classify() {
FpCategory::Normal | FpCategory::Zero | FpCategory::Subnormal => {
let () = serde_json::to_writer(&mut self.buffer, &value)?;
self.needs_separator = true;
Ok(())
}
FpCategory::Infinite | FpCategory::Nan => {
Err(JsonWriterError::InvalidF64Value { value })
}
}
}
pub fn write_open_obj(&mut self) {
self.maybe_separate();
self.buffer.push(b'{');
}
pub fn write_close_obj(&mut self) {
self.buffer.push(b'}');
self.needs_separator = true;
}
pub fn into_string(self) -> Result<String, JsonWriterError> {
Ok(String::from_utf8(self.buffer)?)
}
fn maybe_separate(&mut self) {
if self.needs_separator {
self.buffer.push(b',');
self.needs_separator = false;
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn write_empty_message() -> anyhow::Result<()> {
let mut jw = JsonWriter::default();
jw.write_open_obj();
jw.write_close_obj();
assert_eq!(jw.into_string()?, "{}");
Ok(())
}
#[test]
fn write_invalid_f64_message() -> anyhow::Result<()> {
let mut jw = JsonWriter::default();
let value = 1.0 / 0.0;
let error = jw.write_f64(value).unwrap_err();
assert_eq!(error.to_string(), "Invalid f64 value inf");
Ok(())
}
#[test]
fn write_key_with_quote() -> anyhow::Result<()> {
let mut jw = JsonWriter::with_capacity(128);
jw.write_key("va\"lue")?;
assert_eq!(jw.into_string()?, "\"va\\\"lue\":");
Ok(())
}
#[test]
fn write_timestamp_message() -> anyhow::Result<()> {
let mut jw = JsonWriter::with_capacity(128);
jw.write_open_obj();
jw.write_key("time")?;
jw.write_str("2013-06-22T17:03:14.123+02:00")?;
jw.write_close_obj();
assert_eq!(
jw.into_string()?,
r#"{"time":"2013-06-22T17:03:14.123+02:00"}"#
);
Ok(())
}
#[test]
fn write_single_value_message() -> anyhow::Result<()> {
let mut jw = JsonWriter::with_capacity(128);
jw.write_open_obj();
jw.write_key("time")?;
jw.write_str("2013-06-22T17:03:14.123+02:00")?;
jw.write_key("temperature")?;
jw.write_f64(128.0)?;
jw.write_close_obj();
assert_eq!(
jw.into_string()?,
r#"{"time":"2013-06-22T17:03:14.123+02:00","temperature":128.0}"#
);
Ok(())
}
#[test]
fn write_multivalue_message() -> anyhow::Result<()> {
let mut jw = JsonWriter::with_capacity(128);
jw.write_open_obj();
jw.write_key("time")?;
jw.write_str("2013-06-22T17:03:14.123+02:00")?;
jw.write_key("temperature")?;
jw.write_f64(128.0)?;
jw.write_key("location")?;
jw.write_open_obj();
jw.write_key("altitude")?;
jw.write_f64(1028.0)?;
jw.write_key("longitude")?;
jw.write_f64(1288.0)?;
jw.write_key("longitude")?;
jw.write_f64(1280.0)?;
jw.write_close_obj();
jw.write_close_obj();
assert_eq!(
jw.into_string()?,
r#"{"time":"2013-06-22T17:03:14.123+02:00","temperature":128.0,"location":{"altitude":1028.0,"longitude":1288.0,"longitude":1280.0}}"#
);
Ok(())
}
}
|
