use crate::error::{Error, ErrorCode, Result};
use alloc::vec::Vec;
use core::cmp;
use core::mem;
use core::ops::Deref;
use core::str;
#[cfg(feature = "std")]
use crate::io;
#[cfg(feature = "std")]
use crate::iter::LineColIterator;
#[cfg(feature = "raw_value")]
use crate::raw::BorrowedRawDeserializer;
#[cfg(all(feature = "raw_value", feature = "std"))]
use crate::raw::OwnedRawDeserializer;
#[cfg(all(feature = "raw_value", feature = "std"))]
use alloc::string::String;
#[cfg(feature = "raw_value")]
use serde::de::Visitor;
/// Trait used by the deserializer for iterating over input. This is manually
/// "specialized" for iterating over `&[u8]`. Once feature(specialization) is
/// stable we can use actual specialization.
///
/// This trait is sealed and cannot be implemented for types outside of
/// `serde_json`.
pub trait Read<'de>: private::Sealed {
#[doc(hidden)]
fn next(&mut self) -> Result<Option<u8>>;
#[doc(hidden)]
fn peek(&mut self) -> Result<Option<u8>>;
/// Only valid after a call to peek(). Discards the peeked byte.
#[doc(hidden)]
fn discard(&mut self);
/// Position of the most recent call to next().
///
/// The most recent call was probably next() and not peek(), but this method
/// should try to return a sensible result if the most recent call was
/// actually peek() because we don't always know.
///
/// Only called in case of an error, so performance is not important.
#[doc(hidden)]
fn position(&self) -> Position;
/// Position of the most recent call to peek().
///
/// The most recent call was probably peek() and not next(), but this method
/// should try to return a sensible result if the most recent call was
/// actually next() because we don't always know.
///
/// Only called in case of an error, so performance is not important.
#[doc(hidden)]
fn peek_position(&self) -> Position;
/// Offset from the beginning of the input to the next byte that would be
/// returned by next() or peek().
#[doc(hidden)]
fn byte_offset(&self) -> usize;
/// Assumes the previous byte was a quotation mark. Parses a JSON-escaped
/// string until the next quotation mark using the given scratch space if
/// necessary. The scratch space is initially empty.
#[doc(hidden)]
fn parse_str<'s>(&'s mut self, scratch: &'s mut Vec<u8>) -> Result<Reference<'de, 's, str>>;
/// Assumes the previous byte was a quotation mark. Parses a JSON-escaped
/// string until the next quotation mark using the given scratch space if
/// necessary. The scratch space is initially empty.
///
/// This function returns the raw bytes in the string with escape sequences
/// expanded but without performing unicode validation.
#[doc(hidden)]
fn parse_str_raw<'s>(
&'s mut self,
scratch: &'s mut Vec<u8>,
) -> Result<Reference<'de, 's, [u8]>>;
/// Assumes the previous byte was a quotation mark. Parses a JSON-escaped
/// string until the next quotation mark but discards the data.
#[doc(hidden)]
fn ignore_str(&mut self) -> Result<()>;
/// Assumes the previous byte was a hex escape sequence ('\u') in a string.
/// Parses next hexadecimal sequence.
#[doc(hidden)]
fn decode_hex_escape(&mut self) -> Result<u16>;
/// Switch raw buffering mode on.
///
/// This is used when deserializing `RawValue`.
#[cfg(feature = "raw_value")]
#[doc(hidden)]
fn begin_raw_buffering(&mut self);
/// Switch raw buffering mode off and provides the raw buffered data to the
/// given visitor.
#[cfg(feature = "raw_value")]
#[doc(hidden)]
fn end_raw_buffering<V>(&mut self, visitor: V) -> Result<V::Value>
where
V: Visitor<'de>;
/// Whether StreamDeserializer::next needs to check the failed flag. True
/// for IoRead, false for StrRead and SliceRead which can track failure by
/// truncating their input slice to avoid the extra check on every next
/// call.
#[doc(hidden)]
const should_early_return_if_failed: bool;
/// Mark a persistent failure of StreamDeserializer, either by setting the
/// flag or by truncating the input data.
#[doc(hidden)]
fn set_failed(&mut self, failed: &mut bool);
}
pub struct Position {
pub line: usize,
pub column: usize,
}
pub enum Reference<'b, 'c, T>
where
T: ?Sized + 'static,
{
Borrowed(&'b T),
Copied(&'c T),
}
impl<'b, 'c, T> Deref for Reference<'b, 'c, T>
where
T: ?Sized + 'static,
{
type Target = T;
fn deref(&self) -> &Self::Target {
match *self {
Reference::Borrowed(b) => b,
Reference::Copied(c) => c,
}
}
}
/// JSON input source that reads from a std::io input stream.
#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
pub struct IoRead<R>
where
R: io::Read,
{
iter: LineColIterator<io::Bytes<R>>,
/// Temporary storage of peeked byte.
ch: Option<u8>,
#[cfg(feature = "raw_value")]
raw_buffer: Option<Vec<u8>>,
}
/// JSON input source that reads from a slice of bytes.
//
// This is more efficient than other iterators because peek() can be read-only
// and we can compute line/col position only if an error happens.
pub struct SliceRead<'a> {
slice: &'a [u8],
/// Index of the *next* byte that will be returned by next() or peek().
index: usize,
#[cfg(feature = "raw_value")]
raw_buffering_start_index: usize,
}
/// JSON input source that reads from a UTF-8 string.
//
// Able to elide UTF-8 checks by assuming that the input is valid UTF-8.
pub struct StrRead<'a> {
delegate: SliceRead<'a>,
#[cfg(feature = "raw_value")]
data: &'a str,
}
// Prevent users from implementing the Read trait.
mod private {
pub trait Sealed {}
}
//////////////////////////////////////////////////////////////////////////////
#[cfg(feature = "std")]
impl<R> IoRead<R>
where
R: io::Read,
{
/// Create a JSON input source to read from a std::io input stream.
pub fn new(reader: R) -> Self {
IoRead {
iter: LineColIterator::new(reader.bytes()),
ch: None,
#[cfg(feature = "raw_value")]
raw_buffer: None,
}
}
}
#[cfg(feature = "std")]
impl<R> private::Sealed for IoRead<R> where R: io::Read {}
#[cfg(feature = "std")]
impl<R> IoRead<R>
where
R: io::Read,
{
fn parse_str_bytes<'s, T, F>(
&'s mut self,
scratch: &'s mut Vec<u8>,
validate: bool,
result: F,
) -> Result<T>
where
T: 's,
F: FnOnce(&'s Self, &'s [u8]) -> Result<T>,
{
loop {
let ch = tri!(next_or_eof(self));
if !is_escape(ch, true) {
scratch.push(ch);
continue;
}
match ch {
b'"' => {
return result(self, scratch);
}
b'\\' => {
tri!(parse_escape(self, validate, scratch));
}
_ => {
if validate {
return error(self, ErrorCode::ControlCharacterWhileParsingString);
}
scratch.push(ch);
}
}
}
}
}
#[cfg(feature = "std")]
impl<'de, R> Read<'de> for IoRead<R>
where
R: io::Read,
{
#[inline]
fn next(&mut self) -> Result<Option<u8>> {
match self.ch.take() {
Some(ch) => {
#[cfg(feature = "raw_value")]
{
if let Some(buf) = &mut self.raw_buffer {
buf.push(ch);
}
}
Ok(Some(ch))
}
None => match self.iter.next() {
Some(Err(err)) => Err(Error::io(err)),
Some(Ok(ch)) => {
#[cfg(feature = "raw_value")]
{
if let Some(buf) = &mut self.raw_buffer {
buf.push(ch);
}
}
Ok(Some(ch))
}
None => Ok(None),
},
}
}
#[inline]
fn peek(&mut self) -> Result<Option<u8>> {
match self.ch {
Some(ch) => Ok(Some(ch)),
None => match self.iter.next() {
Some(Err(err)) => Err(Error::io(err)),
Some(Ok(ch)) => {
self.ch = Some(ch);
Ok(self.ch)
}
None => Ok(None),
},
}
}
#[cfg(not(feature = "raw_value"))]
#[inline]
fn discard(&mut self) {
self.ch = None;
}
#[cfg(feature = "raw_value")]
fn discard(&mut self) {
if let Some(ch) = self.ch.take() {
if let Some(buf) = &mut self.raw_buffer {
buf.push(ch);
}
}
}
fn position(&self) -> Position {
Position {
line: self.iter.line(),
column: self.iter.col(),
}
}
fn peek_position(&self) -> Position {
// The LineColIterator updates its position during peek() so it has the
// right one here.
self.position()
}
fn byte_offset(&self) -> usize {
match self.ch {
Some(_) => self.iter.byte_offset() - 1,
None => self.iter.byte_offset(),
}
}
fn parse_str<'s>(&'s mut self, scratch: &'s mut Vec<u8>) -> Result<Reference<'de, 's, str>> {
self.parse_str_bytes(scratch, true, as_str)
.map(Reference::Copied)
}
fn parse_str_raw<'s>(
&'s mut self,
scratch: &'s mut Vec<u8>,
) -> Result<Reference<'de, 's, [u8]>> {
self.parse_str_bytes(scratch, false, |_, bytes| Ok(bytes))
.map(Reference::Copied)
}
fn ignore_str(&mut self) -> Result<()> {
loop {
let ch = tri!(next_or_eof(self));
if !is_escape(ch, true) {
continue;
}
match ch {
b'"' => {
return Ok(());
}
b'\\' => {
tri!(ignore_escape(self));
}
_ => {
return error(self, ErrorCode::ControlCharacterWhileParsingString);
}
}
}
}
fn decode_hex_escape(&mut self) -> Result<u16> {
let a = tri!(next_or_eof(self));
let b = tri!(next_or_eof(self));
let c = tri!(next_or_eof(self));
let d = tri!(next_or_eof(self));
match decode_four_hex_digits(a, b, c, d) {
Some(val) => Ok(val),
None => error(self, ErrorCode::InvalidEscape),
}
}
#[cfg(feature = "raw_value")]
fn begin_raw_buffering(&mut self) {
self.raw_buffer = Some(Vec::new());
}
#[cfg(feature = "raw_value")]
fn end_raw_buffering<V>(&mut self, visitor: V) -> Result<V::Value>
where
V: Visitor<'de>,
{
let raw = self.raw_buffer.take().unwrap();
let raw = match String::from_utf8(raw) {
Ok(raw) => raw,
Err(_) => return error(self, ErrorCode::InvalidUnicodeCodePoint),
};
visitor.visit_map(OwnedRawDeserializer {
raw_value: Some(raw),
})
}
const should_early_return_if_failed: bool = true;
#[inline]
#[cold]
fn set_failed(&mut self, failed: &mut bool) {
*failed = true;
}
}
//////////////////////////////////////////////////////////////////////////////
impl<'a> SliceRead<'a> {
/// Create a JSON input source to read from a slice of bytes.
pub fn new(slice: &'a [u8]) -> Self {
SliceRead {
slice,
index: 0,
#[cfg(feature = "raw_value")]
raw_buffering_start_index: 0,
}
}
fn position_of_index(&self, i: usize) -> Position {
let start_of_line = match memchr::memrchr(b'\n', &self.slice[..i]) {
Some(position) => position + 1,
None => 0,
};
Position {
line: 1 + memchr::memchr_iter(b'\n', &self.slice[..start_of_line]).count(),
column: i - start_of_line,
}
}
fn skip_to_escape(&mut self, forbid_control_characters: bool) {
// Immediately bail-out on empty strings and consecutive escapes (e.g. \u041b\u0435)
if self.index == self.slice.len()
|| is_escape(self.slice[self.index], forbid_control_characters)
{
return;
}
self.index += 1;
let rest = &self.slice[self.index..];
if !forbid_control_characters {
self.index += memchr::memchr2(b'"', b'\\', rest).unwrap_or(rest.len());
return;
}
// We wish to find the first byte in range 0x00..=0x1F or " or \. Ideally, we'd use
// something akin to memchr3, but the memchr crate does not support this at the moment.
// Therefore, we use a variation on Mycroft's algorithm [1] to provide performance better
// than a naive loop. It runs faster than equivalent two-pass memchr2+SWAR code on
// benchmarks and it's cross-platform, so probably the right fit.
// [1]: https://groups.google.com/forum/#!original/comp.lang.c/2HtQXvg7iKc/xOJeipH6KLMJ
#[cfg(fast_arithmetic = "64")]
type Chunk = u64;
#[cfg(fast_arithmetic = "32")]
type Chunk = u32;
const STEP: usize = mem::size_of::<Chunk>();
const ONE_BYTES: Chunk = Chunk::MAX / 255; // 0x0101...01
for chunk in rest.chunks_exact(STEP) {
let chars = Chunk::from_le_bytes(chunk.try_into().unwrap());
let contains_ctrl = chars.wrapping_sub(ONE_BYTES * 0x20) & !chars;
let chars_quote = chars ^ (ONE_BYTES * Chunk::from(b'"'));
let contains_quote = chars_quote.wrapping_sub(ONE_BYTES) & !chars_quote;
let chars_backslash = chars ^ (ONE_BYTES * Chunk::from(b'\\'));
let contains_backslash = chars_backslash.wrapping_sub(ONE_BYTES) & !chars_backslash;
let masked = (contains_ctrl | contains_quote | contains_backslash) & (ONE_BYTES << 7);
if masked != 0 {
// SAFETY: chunk is in-bounds for slice
self.index = unsafe { chunk.as_ptr().offset_from(self.slice.as_ptr()) } as usize
+ masked.trailing_zeros() as usize / 8;
return;
}
}
self.index += rest.len() / STEP * STEP;
self.skip_to_escape_slow();
}
#[cold]
#[inline(never)]
fn skip_to_escape_slow(&mut self) {
while self.index < self.slice.len() && !is_escape(self.slice[self.index], true) {
self.index += 1;
}
}
/// The big optimization here over IoRead is that if the string contains no
/// backslash escape sequences, the returned &str is a slice of the raw JSON
/// data so we avoid copying into the scratch space.
fn parse_str_bytes<'s, T, F>(
&'s mut self,
scratch: &'s mut Vec<u8>,
validate: bool,
result: F,
) -> Result<Reference<'a, 's, T>>
where
T: ?Sized + 's,
F: for<'f> FnOnce(&'s Self, &'f [u8]) -> Result<&'f T>,
{
// Index of the first byte not yet copied into the scratch space.
let mut start = self.index;
loop {
self.skip_to_escape(validate);
if self.index == self.slice.len() {
return error(self, ErrorCode::EofWhileParsingString);
}
match self.slice[self.index] {
b'"' => {
if scratch.is_empty() {
// Fast path: return a slice of the raw JSON without any
// copying.
let borrowed = &self.slice[start..self.index];
self.index += 1;
return result(self, borrowed).map(Reference::Borrowed);
} else {
scratch.extend_from_slice(&self.slice[start..self.index]);
self.index += 1;
return result(self, scratch).map(Reference::Copied);
}
}
b'\\' => {
scratch.extend_from_slice(&self.slice[start..self.index]);
self.index += 1;
tri!(parse_escape(self, validate, scratch));
start = self.index;
}
_ => {
self.index += 1;
return error(self, ErrorCode::ControlCharacterWhileParsingString);
}
}
}
}
}
impl<'a> private::Sealed for SliceRead<'a> {}
impl<'a> Read<'a> for SliceRead<'a> {
#[inline]
fn next(&mut self) -> Result<Option<u8>> {
// `Ok(self.slice.get(self.index).map(|ch| { self.index += 1; *ch }))`
// is about 10% slower.
Ok(if self.index < self.slice.len() {
let ch = self.slice[self.index];
self.index += 1;
Some(ch)
} else {
None
})
}
#[inline]
fn peek(&mut self) -> Result<Option<u8>> {
// `Ok(self.slice.get(self.index).map(|ch| *ch))` is about 10% slower
// for some reason.
Ok(if self.index < self.slice.len() {
Some(self.slice[self.index])
} else {
None
})
}
#[inline]
fn discard(&mut self) {
self.index += 1;
}
fn position(&self) -> Position {
self.position_of_index(self.index)
}
fn peek_position(&self) -> Position {
// Cap it at slice.len() just in case the most recent call was next()
// and it returned the last byte.
self.position_of_index(cmp::min(self.slice.len(), self.index + 1))
}
fn byte_offset(&self) -> usize {
self.index
}
fn parse_str<'s>(&'s mut self, scratch: &'s mut Vec<u8>) -> Result<Reference<'a, 's, str>> {
self.parse_str_bytes(scratch, true, as_str)
}
fn parse_str_raw<'s>(
&'s mut self,
scratch: &'s mut Vec<u8>,
) -> Result<Reference<'a, 's, [u8]>> {
self.parse_str_bytes(scratch, false, |_, bytes| Ok(bytes))
}
fn ignore_str(&mut self) -> Result<()> {
loop {
self.skip_to_escape(true);
if self.index == self.slice.len() {
return error(self, ErrorCode::EofWhileParsingString);
}
match self.slice[self.index] {
b'"' => {
self.index += 1;
return Ok(());
}
b'\\' => {
self.index += 1;
tri!(ignore_escape(self));
}
_ => {
return error(self, ErrorCode::ControlCharacterWhileParsingString);
}
}
}
}
#[inline]
fn decode_hex_escape(&mut self) -> Result<u16> {
match self.slice[self.index..] {
[a, b, c, d, ..] => {
self.index += 4;
match decode_four_hex_digits(a, b, c, d) {
Some(val) => Ok(val),
None => error(self, ErrorCode::InvalidEscape),
}
}
_ => {
self.index = self.slice.len();
error(self, ErrorCode::EofWhileParsingString)
}
}
}
#[cfg(feature = "raw_value")]
fn begin_raw_buffering(&mut self) {
self.raw_buffering_start_index = self.index;
}
#[cfg(feature = "raw_value")]
fn end_raw_buffering<V>(&mut self, visitor: V) -> Result<V::Value>
where
V: Visitor<'a>,
{
let raw = &self.slice[self.raw_buffering_start_index..self.index];
let raw = match str::from_utf8(raw) {
Ok(raw) => raw,
Err(_) => return error(self, ErrorCode::InvalidUnicodeCodePoint),
};
visitor.visit_map(BorrowedRawDeserializer {
raw_value: Some(raw),
})
}
const should_early_return_if_failed: bool = false;
#[inline]
#[cold]
fn set_failed(&mut self, _failed: &mut bool) {
self.slice = &self.slice[..self.index];
}
}
//////////////////////////////////////////////////////////////////////////////
impl<'a> StrRead<'a> {
/// Create a JSON input source to read from a UTF-8 string.
pub fn new(s: &'a str) -> Self {
StrRead {
delegate: SliceRead::new(s.as_bytes()),
#[cfg(feature = "raw_value")]
data: s,
}
}
}
impl<'a> private::Sealed for StrRead<'a> {}
impl<'a> Read<'a> for StrRead<'a> {
#[inline]
fn next(&mut self) -> Result<Option<u8>> {
self.delegate.next()
}
#[inline]
fn peek(&mut self) -> Result<Option<u8>> {
self.delegate.peek()
}
#[inline]
fn discard(&mut self) {
self.delegate.discard();
}
fn position(&self) -> Position {
self.delegate.position()
}
fn peek_position(&self) -> Position {
self.delegate.peek_position()
}
fn byte_offset(&self) -> usize {
self.delegate.byte_offset()
}
fn parse_str<'s>(&'s mut self, scratch: &'s mut Vec<u8>) -> Result<Reference<'a, 's, str>> {
self.delegate.parse_str_bytes(scratch, true, |_, bytes| {
// The deserialization input came in as &str with a UTF-8 guarantee,
// and the \u-escapes are checked along the way, so don't need to
// check here.
Ok(unsafe { str::from_utf8_unchecked(bytes) })
})
}
fn parse_str_raw<'s>(
&'s mut self,
scratch: &'s mut Vec<u8>,
) -> Result<Reference<'a, 's, [u8]>> {
self.delegate.parse_str_raw(scratch)
}
fn ignore_str(&mut self) -> Result<()> {
self.delegate.ignore_str()
}
fn decode_hex_escape(&mut self) -> Result<u16> {
self.delegate.decode_hex_escape()
}
#[cfg(feature = "raw_value")]
fn begin_raw_buffering(&mut self) {
self.delegate.begin_raw_buffering();
}
#[cfg(feature = "raw_value")]
fn end_raw_buffering<V>(&mut self, visitor: V) -> Result<V::Value>
where
V: Visitor<'a>,
{
let raw = &self.data[self.delegate.raw_buffering_start_index..self.delegate.index];
visitor.visit_map(BorrowedRawDeserializer {
raw_value: Some(raw),
})
}
const should_early_return_if_failed: bool = false;
#[inline]
#[cold]
fn set_failed(&mut self, failed: &mut bool) {
self.delegate.set_failed(failed);
}
}
//////////////////////////////////////////////////////////////////////////////
impl<'a, 'de, R> private::Sealed for &'a mut R where R: Read<'de> {}
impl<'a, 'de, R> Read<'de> for &'a mut R
where
R: Read<'de>,
{
fn next(&mut self) -> Result<Option<u8>> {
R::next(self)
}
fn peek(&mut self) -> Result<Option<u8>> {
R::peek(self)
}
fn discard(&mut self) {
R::discard(self);
}
fn position(&self) -> Position {
R::position(self)
}
fn peek_position(&self) -> Position {
R::peek_position(self)
}
fn byte_offset(&self) -> usize {
R::byte_offset(self)
}
fn parse_str<'s>(&'s mut self, scratch: &'s mut Vec<u8>) -> Result<Reference<'de, 's, str>> {
R::parse_str(self, scratch)
}
fn parse_str_raw<'s>(
&'s mut self,
scratch: &'s mut Vec<u8>,
) -> Result<Reference<'de, 's, [u8]>> {
R::parse_str_raw(self, scratch)
}
fn ignore_str(&mut self) -> Result<()> {
R::ignore_str(self)
}
fn decode_hex_escape(&mut self) -> Result<u16> {
R::decode_hex_escape(self)
}
#[cfg(feature = "raw_value")]
fn begin_raw_buffering(&mut self) {
R::begin_raw_buffering(self);
}
#[cfg(feature = "raw_value")]
fn end_raw_buffering<V>(&mut self, visitor: V) -> Result<V::Value>
where
V: Visitor<'de>,
{
R::end_raw_buffering(self, visitor)
}
const should_early_return_if_failed: bool = R::should_early_return_if_failed;
fn set_failed(&mut self, failed: &mut bool) {
R::set_failed(self, failed);
}
}
//////////////////////////////////////////////////////////////////////////////
/// Marker for whether StreamDeserializer can implement FusedIterator.
pub trait Fused: private::Sealed {}
impl<'a> Fused for SliceRead<'a> {}
impl<'a> Fused for StrRead<'a> {}
fn is_escape(ch: u8, including_control_characters: bool) -> bool {
ch == b'"' || ch == b'\\' || (including_control_characters && ch < 0x20)
}
fn next_or_eof<'de, R>(read: &mut R) -> Result<u8>
where
R: ?Sized + Read<'de>,
{
match tri!(read.next()) {
Some(b) => Ok(b),
None => error(read, ErrorCode::EofWhileParsingString),
}
}
fn peek_or_eof<'de, R>(read: &mut R) -> Result<u8>
where
R: ?Sized + Read<'de>,
{
match tri!(read.peek()) {
Some(b) => Ok(b),
None => error(read, ErrorCode::EofWhileParsingString),
}
}
fn error<'de, R, T>(read: &R, reason: ErrorCode) -> Result<T>
where
R: ?Sized + Read<'de>,
{
let position = read.position();
Err(Error::syntax(reason, position.line, position.column))
}
fn as_str<'de, 's, R: Read<'de>>(read: &R, slice: &'s [u8]) -> Result<&'s str> {
str::from_utf8(slice).or_else(|_| error(read, ErrorCode::InvalidUnicodeCodePoint))
}
/// Parses a JSON escape sequence and appends it into the scratch space. Assumes
/// the previous byte read was a backslash.
fn parse_escape<'de, R: Read<'de>>(
read: &mut R,
validate: bool,
scratch: &mut Vec<u8>,
) -> Result<()> {
let ch = tri!(next_or_eof(read));
match ch {
b'"' => scratch.push(b'"'),
b'\\' => scratch.push(b'\\'),
b'/' => scratch.push(b'/'),
b'b' => scratch.push(b'\x08'),
b'f' => scratch.push(b'\x0c'),
b'n' => scratch.push(b'\n'),
b'r' => scratch.push(b'\r'),
b't' => scratch.push(b'\t'),
b'u' => return parse_unicode_escape(read, validate, scratch),
_ => return error(read, ErrorCode::InvalidEscape),
}
Ok(())
}
/// Parses a JSON \u escape and appends it into the scratch space. Assumes `\u`
/// has just been read.
#[cold]
fn parse_unicode_escape<'de, R: Read<'de>>(
read: &mut R,
validate: bool,
scratch: &mut Vec<u8>,
) -> Result<()> {
let mut n = tri!(read.decode_hex_escape());
// Non-BMP characters are encoded as a sequence of two hex escapes,
// representing UTF-16 surrogates. If deserializing a utf-8 string the
// surrogates are required to be paired, whereas deserializing a byte string
// accepts lone surrogates.
if validate && n >= 0xDC00 && n <= 0xDFFF {
// XXX: This is actually a trailing surrogate.
return error(read, ErrorCode::LoneLeadingSurrogateInHexEscape);
}
loop {
if n < 0xD800 || n > 0xDBFF {
// Every u16 outside of the surrogate ranges is guaranteed to be a
// legal char.
push_wtf8_codepoint(n as u32, scratch);
return Ok(());
}
// n is a leading surrogate, we now expect a trailing surrogate.
let n1 = n;
if tri!(peek_or_eof(read)) == b'\\' {
read.discard();
} else {
return if validate {
read.discard();
error(read, ErrorCode::UnexpectedEndOfHexEscape)
} else {
push_wtf8_codepoint(n1 as u32, scratch);
Ok(())
};
}
if tri!(peek_or_eof(read)) == b'u' {
read.discard();
} else {
return if validate {
read.discard();
error(read, ErrorCode::UnexpectedEndOfHexEscape)
} else {
push_wtf8_codepoint(n1 as u32, scratch);
// The \ prior to this byte started an escape sequence, so we
// need to parse that now. This recursive call does not blow the
// stack on malicious input because the escape is not \u, so it
// will be handled by one of the easy nonrecursive cases.
parse_escape(read, validate, scratch)
};
}
let n2 = tri!(read.decode_hex_escape());
if n2 < 0xDC00 || n2 > 0xDFFF {
if validate {
return error(read, ErrorCode::LoneLeadingSurrogateInHexEscape);
}
push_wtf8_codepoint(n1 as u32, scratch);
// If n2 is a leading surrogate, we need to restart.
n = n2;
continue;
}
// This value is in range U+10000..=U+10FFFF, which is always a valid
// codepoint.
let n = (((n1 - 0xD800) as u32) << 10 | (n2 - 0xDC00) as u32) + 0x1_0000;
push_wtf8_codepoint(n, scratch);
return Ok(());
}
}
/// Adds a WTF-8 codepoint to the end of the buffer. This is a more efficient
/// implementation of String::push. The codepoint may be a surrogate.
#[inline]
fn push_wtf8_codepoint(n: u32, scratch: &mut Vec<u8>) {
if n < 0x80 {
scratch.push(n as u8);
return;
}
scratch.reserve(4);
unsafe {
let ptr = scratch.as_mut_ptr().add(scratch.len());
let encoded_len = match n {
0..=0x7F => unreachable!(),
0x80..=0x7FF => {
ptr.write((n >> 6 & 0b0001_1111) as u8 | 0b1100_0000);
2
}
0x800..=0xFFFF => {
ptr.write((n >> 12 & 0b0000_1111) as u8 | 0b1110_0000);
ptr.add(1).write((n >> 6 & 0b0011_1111) as u8 | 0b1000_0000);
3
}
0x1_0000..=0x10_FFFF => {
ptr.write((n >> 18 & 0b0000_0111) as u8 | 0b1111_0000);
ptr.add(1)
.write((n >> 12 & 0b0011_1111) as u8 | 0b1000_0000);
ptr.add(2).write((n >> 6 & 0b0011_1111) as u8 | 0b1000_0000);
4
}
0x11_0000.. => unreachable!(),
};
ptr.add(encoded_len - 1)
.write((n & 0b0011_1111) as u8 | 0b1000_0000);
scratch.set_len(scratch.len() + encoded_len);
}
}
/// Parses a JSON escape sequence and discards the value. Assumes the previous
/// byte read was a backslash.
fn ignore_escape<'de, R>(read: &mut R) -> Result<()>
where
R: ?Sized + Read<'de>,
{
let ch = tri!(next_or_eof(read));
match ch {
b'"' | b'\\' | b'/' | b'b' | b'f' | b'n' | b'r' | b't' => {}
b'u' => {
// At this point we don't care if the codepoint is valid. We just
// want to consume it. We don't actually know what is valid or not
// at this point, because that depends on if this string will
// ultimately be parsed into a string or a byte buffer in the "real"
// parse.
tri!(read.decode_hex_escape());
}
_ => {
return error(read, ErrorCode::InvalidEscape);
}
}
Ok(())
}
const fn decode_hex_val_slow(val: u8) -> Option<u8> {
match val {
b'0'..=b'9' => Some(val - b'0'),
b'A'..=b'F' => Some(val - b'A' + 10),
b'a'..=b'f' => Some(val - b'a' + 10),
_ => None,
}
}
const fn build_hex_table(shift: usize) -> [i16; 256] {
let mut table = [0; 256];
let mut ch = 0;
while ch < 256 {
table[ch] = match decode_hex_val_slow(ch as u8) {
Some(val) => (val as i16) << shift,
None => -1,
};
ch += 1;
}
table
}
static HEX0: [i16; 256] = build_hex_table(0);
static HEX1: [i16; 256] = build_hex_table(4);
fn decode_four_hex_digits(a: u8, b: u8, c: u8, d: u8) -> Option<u16> {
let a = HEX1[a as usize] as i32;
let b = HEX0[b as usize] as i32;
let c = HEX1[c as usize] as i32;
let d = HEX0[d as usize] as i32;
let codepoint = ((a | b) << 8) | c | d;
// A single sign bit check.
if codepoint >= 0 {
Some(codepoint as u16)
} else {
None
}
}
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