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use crate::{
bytes::Bytes,
stream::Stream,
util::{
constants::{punctuators::*, *},
is_numeric_like, is_numeric_or_negative,
},
};
use std::collections::HashMap;
#[derive(Debug)]
/// An error returned by the parser
/// in the event that the input JSON is malformed.
pub enum ParseError {
/// The parser encountered a symbol (character) in a place it wasn't expecting.
UnexpectedSymbol(char),
/// The parser reached the end of the input prematurely.
UnexpectedEndOfInput,
/// An internal error that gets thrown if a number somehow fails to parse.
/// If this is returned, please open an issue.
NumberParseError
}
#[derive(Debug, PartialEq)]
/// A value as represented in parsed JSON.
pub enum Value<'a> {
/// A string, composed of bytes borrowed from the input.
String(Bytes<'a>),
/// A 64-bit precision floating point number.
Number(f64),
/// A boolean.
Boolean(bool),
/// An object, represented as a HashMap of a String to a Value.
Object(HashMap<Bytes<'a>, Value<'a>>),
/// An array, represented as a Vec of Values.
Array(Vec<Value<'a>>),
/// Null (No value).
Null,
/// The supplied JSON is completely empty.
Nothing,
}
/// The parser itself. Create a new parser with the `new` method,
/// and parse it using the `parse` method.
pub struct Parser<'a> {
stream: Stream<'a, u8>,
}
impl<'a> Parser<'a> {
/// Create a new parser from raw JSON encoded as a Vec of u8s
/// THIS IS SUBJECT TO CHANGE.
pub fn new(input: &'a [u8]) -> Parser {
Parser {
stream: Stream::new(input),
}
}
/// Parse a single Value.
/// This function DOES NOT consume self as it is called recursively.
/// However,this function is only designed to be called externally once.
/// This will be fixed in an upcoming release.
pub fn parse(&mut self) -> Result<Value<'a>, ParseError> {
self.skip_whitespace_no_eof()?;
let initial = self.stream.current_unchecked();
match initial {
FALSE_IDENT | TRUE_IDENT => self.parse_boolean(),
NULL_IDENT => self.parse_null(),
STRING_BOUNDARY => Ok(Value::String(self.parse_string()?)),
OBJECT_OPEN | ARRAY_OPEN => self.parse_from_punctuator(initial),
_ => {
if is_numeric_or_negative(initial) {
self.parse_number()
} else {
Err(ParseError::UnexpectedSymbol(initial as char))
}
}
}
}
fn parse_from_punctuator(&mut self, punctuator: u8) -> Result<Value<'a>, ParseError> {
match punctuator {
ARRAY_OPEN => self.parse_array(),
OBJECT_OPEN => self.parse_object(),
_ => Err(ParseError::UnexpectedSymbol(punctuator as char)),
}
}
fn parse_array(&mut self) -> Result<Value<'a>, ParseError> {
// at this point the stream is pointing at the opening punctuator for the array.
let mut inner: Vec<Value> = vec![];
let mut has_read_initial = false;
while !self.stream.is_eof() {
self.stream.skip();
self.skip_whitespace_no_eof()?;
let next = self.stream.current_unchecked();
match next {
ARRAY_DELIMITER => {
let parsed = self.parse_array_punctuator(next)?;
inner.push(parsed);
}
ARRAY_CLOSE => {
break;
}
_ => {
// this guard exists to allow the first element to not be delimited (a.k.a [1])
// but disallows subsequent elements from not being delimited (a.k.a [1 1])
if !has_read_initial {
inner.push(self.parse()?);
has_read_initial = true;
} else {
return Err(ParseError::UnexpectedSymbol(next as char));
}
}
}
}
Ok(Value::Array(inner))
}
fn parse_array_punctuator(&mut self, punctuator: u8) -> Result<Value<'a>, ParseError> {
match punctuator {
ARRAY_CLOSE => Ok(Value::Nothing),
ARRAY_DELIMITER => {
// we're on the delimiter, must skip past it to get to the expression to parse
self.stream.skip();
if self.stream.is_eof() {
return Err(ParseError::UnexpectedEndOfInput);
}
Ok(self.parse()?)
}
_ => self.parse_from_punctuator(punctuator),
}
}
fn parse_boolean(&mut self) -> Result<Value<'a>, ParseError> {
let next_4 = self.stream.slice_len(self.stream.position(), 4);
if next_4.eq(TRUE) {
self.stream.skip_n(3);
Ok(Value::Boolean(true))
} else if self.stream.slice_len(self.stream.position(), 5).eq(FALSE) {
self.stream.skip_n(4);
Ok(Value::Boolean(false))
} else {
Err(ParseError::UnexpectedSymbol(
self.stream.current_unchecked() as char,
))
}
}
fn parse_null(&mut self) -> Result<Value<'a>, ParseError> {
let next_4 = self.stream.slice_len(self.stream.position(), 4);
if next_4.eq(NULL) {
self.stream.skip_n(3);
Ok(Value::Null)
} else {
Err(ParseError::UnexpectedSymbol(
self.stream.current_unchecked() as char,
))
}
}
fn parse_number(&mut self) -> Result<Value<'a>, ParseError> {
let start = self.stream.position();
let mut is_first_iteration = true;
self.skip_whitespace_no_eof()?;
while !self.stream.is_eof() {
let next_char = self.stream.current_unchecked();
if next_char == NEGATIVE && is_first_iteration {
self.stream.skip();
continue;
}
if !is_numeric_like(next_char) || self.stream.peek().is_none() {
let res = Ok(Value::Number(
std::str::from_utf8(self.stream.slice_unchecked(start, self.stream.position()))
.ok()
.unwrap()
.parse::<f64>()
.ok()
.unwrap(),
));
self.stream.unskip();
return res;
}
self.stream.skip();
is_first_iteration = false;
}
Err(ParseError::NumberParseError)
}
fn parse_object(&mut self) -> Result<Value<'a>, ParseError> {
let mut inner: HashMap<Bytes<'a>, Value<'a>> = HashMap::new();
let mut is_first_entry = true;
while !self.stream.is_eof() {
self.stream.skip();
self.skip_whitespace_no_eof()?;
// the value read here should always be a string boundary
let mut next = self.stream.current_unchecked();
let key: Bytes<'a>;
// checking that the key is a string or if this is an empty object
match next {
STRING_BOUNDARY => key = self.parse_string()?,
OBJECT_CLOSE => {
// this check disallows { "key": "value", }, but permits {}
// by checking if any entries have been parsed yet
// we should never get to this point if the json is
// { "key": "value" } because another check for } is made
// later in this loop.
if !is_first_entry {
return Err(ParseError::UnexpectedSymbol(next as char));
} else {
return Ok(Value::Object(inner));
}
}
_ => return Err(ParseError::UnexpectedSymbol(next as char)),
}
// still on string closing boundary
self.stream.skip();
self.skip_whitespace_no_eof()?;
next = self.stream.current_unchecked();
if next != OBJECT_KV_DELIMITER {
return Err(ParseError::UnexpectedSymbol(next as char));
};
// next entry in the data should be the value itself, but this can be any type so we will just parse it
// we are still on the divider at this stage so we will skip to the start of the value
self.stream.skip();
self.skip_whitespace_no_eof()?;
let value = self.parse()?;
inner.insert(key, value);
self.stream.skip();
self.skip_whitespace_no_eof()?;
// next thing in the object could either be a delimiter between entries or a closing character
// delimiter is not valid if there are no more items, so we need to check for this
next = self.stream.current_unchecked();
match next {
OBJECT_ENTRY_DELIMITER => {
is_first_entry = false;
continue;
}
OBJECT_CLOSE => {
break;
}
_ => return Err(ParseError::UnexpectedSymbol(next as char)),
}
}
Ok(Value::Object(inner))
}
fn parse_string(&mut self) -> Result<Bytes<'a>, ParseError> {
let start = self.stream.position() + 1;
while !self.stream.is_eof() {
let next_char = *self.stream.next_unchecked();
if next_char == ESCAPE {
self.stream.skip();
} else if next_char == STRING_BOUNDARY {
return Ok(Bytes::from(
self.stream.slice_unchecked(start, self.stream.position()),
));
}
}
Err(ParseError::UnexpectedEndOfInput)
}
/// Skips whitespace and checks if there is anything left.
fn skip_whitespace_no_eof(&mut self) -> Result<(), ParseError> {
while !self.stream.is_eof() {
let character = self.stream.current_unchecked();
if !WHITESPACE.contains(&character) {
break;
}
self.stream.skip();
}
if self.stream.is_eof() {
Err(ParseError::UnexpectedEndOfInput)
} else {
Ok(())
}
}
}