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use std::collections::HashMap;
use std::str::FromStr;
use crate::error::ParseError;
use crate::values::Values;
use crate::{FALSE, NULL, TRUE};
#[macro_use]
pub(crate) mod macros {
macro_rules! expect_byte {
($parser:ident) => {{
if $parser.is_eof() {
return Err(ParseError::new());
}
let ch = $parser.read_byte();
$parser.bump();
ch
}};
}
// Expect a sequence of specific bytes in specific order, error otherwise.
// This is useful for reading the 3 JSON identifiers:
//
// - "t" has to be followed by "rue"
// - "f" has to be followed by "alse"
// - "n" has to be followed by "ull"
//
// Anything else is an error.
macro_rules! expect_sequence {
($parser:ident, $( $ch:pat ),*) => {
$(
match expect_byte!($parser) {
$ch => {}
_ => return $parser.unexpected_character(),
}
)*
}
}
// A drop in macro for when we expect to read a byte, but we don't care
// about any whitespace characters that might occur before it.
macro_rules! expect_byte_ignore_whitespace {
($parser:ident) => {{
let mut ch = expect_byte!($parser);
// Don't go straight for the loop, assume we are in the clear first.
match ch {
// whitespace
9..=13 | 32 => loop {
match expect_byte!($parser) {
9..=13 | 32 => {}
next => {
ch = next;
break;
}
}
},
_ => {}
}
ch
}};
}
// Expect to find EOF or just whitespaces leading to EOF after a JSON value
macro_rules! expect_eof {
($parser:ident) => {{
while !$parser.is_eof() {
match $parser.read_byte() {
9..=13 | 32 => $parser.bump(),
_ => {
$parser.bump();
return $parser.unexpected_character();
}
}
}
}};
}
// Expect a particular byte to be next. Also available with a variant
// creates a `match` expression just to ease some pain.
macro_rules! expect {
($parser:ident, $byte:expr) => ({
let ch = expect_byte_ignore_whitespace!($parser);
if ch != $byte {
return $parser.unexpected_character();
}
});
{$parser:ident $(, $byte:pat => $then:expr )*} => ({
let ch = expect_byte_ignore_whitespace!($parser);
match ch {
$(
$byte => $then,
)*
_ => return $parser.unexpected_character()
}
})
}
}
pub struct Parser {
byte_ptr: *const u8,
index: usize,
length: usize,
}
struct StackBlock(Values, String);
impl<'a> Parser {
pub fn parse(&mut self) -> Result<Values, ParseError> {
let mut stack = Vec::with_capacity(3);
let mut ch = expect_byte_ignore_whitespace!(self);
'parsing: loop {
let mut value = match ch {
b'[' => {
ch = expect_byte_ignore_whitespace!(self);
if ch != b']' {
stack.push(StackBlock(
Values::Array(Vec::with_capacity(2)),
"UNIMPORTANT".into(),
));
continue 'parsing;
}
Values::Array(Vec::new())
}
b'{' => {
ch = expect_byte_ignore_whitespace!(self);
if ch != b'}' {
let mut map = HashMap::with_capacity(3);
if ch != b'"' {
return self.unexpected_character();
}
let index = self.expect_string()?;
map.insert(index.clone(), NULL);
expect!(self, b':');
stack.push(StackBlock(Values::Struct(map), index));
ch = expect_byte_ignore_whitespace!(self);
continue 'parsing;
}
Values::Struct(HashMap::new())
}
b'"' => Values::String(self.expect_string()?),
b'0'..=b'9' => Values::Number(self.expect_number(ch)?),
b'-' => {
let ch = expect_byte!(self);
Values::Number(-match ch {
b'0'..=b'9' => self.expect_number(ch)?,
_ => return self.unexpected_character(),
})
}
b't' => {
expect_sequence!(self, b'r', b'u', b'e');
TRUE
}
b'f' => {
expect_sequence!(self, b'a', b'l', b's', b'e');
FALSE
}
b'n' => {
expect_sequence!(self, b'u', b'l', b'l');
NULL
}
_ => return self.unexpected_character(),
};
'popping: loop {
match stack.last_mut() {
None => {
expect_eof!(self);
return Ok(value);
}
Some(&mut StackBlock(Values::Array(ref mut array), _)) => {
array.insert(0, value);
ch = expect_byte_ignore_whitespace!(self);
match ch {
b',' => {
ch = expect_byte_ignore_whitespace!(self);
continue 'parsing;
}
b']' => {}
_ => return self.unexpected_character(),
}
}
Some(&mut StackBlock(Values::Struct(ref mut object), ref mut index)) => {
object.insert(index.to_string(), value);
ch = expect_byte_ignore_whitespace!(self);
match ch {
b',' => {
expect!(self, b'"');
let string = self.expect_string()?;
object.insert(string.clone(), Values::Null);
*index = string;
expect!(self, b':');
ch = expect_byte_ignore_whitespace!(self);
continue 'parsing;
}
b'}' => {}
_ => return self.unexpected_character(),
}
}
_ => unreachable!(),
}
value = match stack.pop() {
Some(StackBlock(value, _)) => value,
None => break 'popping,
}
}
}
}
pub fn new(source: &'a str) -> Self {
Parser {
byte_ptr: source.as_ptr(),
index: 0,
length: source.len(),
}
}
fn expect_string(&mut self) -> Result<String, ParseError> {
let mut string = String::new();
loop {
let char = self.read_byte();
if char == b'"' {
self.bump();
return Ok(string);
}
if char == b'\\' {
self.bump();
let escaped = expect_byte!(self);
let escaped = match escaped {
b'u' => {
// Unicode Characters are not supported
continue;
}
b'"' => b'\"',
b'\\' | b'/' => escaped,
b'b' => 0x8,
b'f' => 0xC,
b't' => b'\t',
b'r' => b'\r',
b'n' => b'\n',
_ => return self.unexpected_character(),
};
string.push(char::from(escaped));
} else {
string.push(char::from(char));
self.bump();
}
}
}
fn expect_number(&mut self, mut num: u8) -> Result<f64, ()> {
let mut string = String::from(char::from(num));
loop {
if !self.is_eof() {
num = self.read_byte();
} else {
return f64::from_str(string.as_str()).map_err(|_err| ());
}
match num {
b'\\' | b' ' | b',' | b']' | b'}' | b'\n' | b'\r' => break,
_ => {
string.push(char::from(num));
self.bump();
}
}
}
f64::from_str(string.as_str()).map_err(|_err| ())
}
fn is_eof(&self) -> bool {
self.index >= self.length
}
fn read_byte(&self) -> u8 {
debug_assert!(self.index < self.length, "Reading out of bounds");
unsafe { *self.byte_ptr.add(self.index) }
}
fn bump(&mut self) {
self.index = self.index.wrapping_add(1);
}
fn unexpected_character<T: Sized>(&mut self) -> Result<T, ParseError> {
Err(ParseError::new())
}
}