1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
// Copyright 2017 Serde Developers
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use std::ops::Deref;
use std::{char, cmp, io, str};

use iter::LineColIterator;

use super::error::{Error, ErrorCode, Result};

/// 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) -> io::Result<Option<u8>>;
    #[doc(hidden)]
    fn peek(&mut self) -> io::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<()>;
}

pub struct Position {
    pub line: usize,
    pub column: usize,
}

pub enum Reference<'b, 'c, T: ?Sized + 'static> {
    Borrowed(&'b T),
    Copied(&'c T),
}

impl<'b, 'c, T: ?Sized + 'static> Deref for Reference<'b, 'c, T> {
    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.
pub struct IoRead<R>
where
    R: io::Read,
{
    iter: LineColIterator<io::Bytes<R>>,
    /// Temporary storage of peeked byte.
    ch: Option<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,
}

/// 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>,
}

// Prevent users from implementing the Read trait.
mod private {
    pub trait Sealed {}
}

//////////////////////////////////////////////////////////////////////////////

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,
        }
    }
}

impl<R> private::Sealed for IoRead<R> where R: io::Read {}

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 = try!(next_or_eof(self));
            if !ESCAPE[ch as usize] {
                scratch.push(ch);
                continue;
            }
            match ch {
                b'"' => {
                    return result(self, scratch);
                }
                b'\\' => {
                    try!(parse_escape(self, scratch));
                }
                _ => {
                    if validate {
                        return error(self, ErrorCode::ControlCharacterWhileParsingString);
                    }
                    scratch.push(ch);
                }
            }
        }
    }
}

impl<'de, R> Read<'de> for IoRead<R>
where
    R: io::Read,
{
    #[inline]
    fn next(&mut self) -> io::Result<Option<u8>> {
        match self.ch.take() {
            Some(ch) => Ok(Some(ch)),
            None => match self.iter.next() {
                Some(Err(err)) => Err(err),
                Some(Ok(ch)) => Ok(Some(ch)),
                None => Ok(None),
            },
        }
    }

    #[inline]
    fn peek(&mut self) -> io::Result<Option<u8>> {
        match self.ch {
            Some(ch) => Ok(Some(ch)),
            None => match self.iter.next() {
                Some(Err(err)) => Err(err),
                Some(Ok(ch)) => {
                    self.ch = Some(ch);
                    Ok(self.ch)
                }
                None => Ok(None),
            },
        }
    }

    #[inline]
    fn discard(&mut self) {
        self.ch = None;
    }

    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 = try!(next_or_eof(self));
            if !ESCAPE[ch as usize] {
                continue;
            }
            match ch {
                b'"' => {
                    return Ok(());
                }
                b'\\' => {
                    try!(ignore_escape(self));
                }
                _ => {
                    return error(self, ErrorCode::ControlCharacterWhileParsingString);
                }
            }
        }
    }
}

//////////////////////////////////////////////////////////////////////////////

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: slice,
            index: 0,
        }
    }

    fn position_of_index(&self, i: usize) -> Position {
        let mut position = Position { line: 1, column: 0 };
        for ch in &self.slice[..i] {
            match *ch {
                b'\n' => {
                    position.line += 1;
                    position.column = 0;
                }
                _ => {
                    position.column += 1;
                }
            }
        }
        position
    }

    /// 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: ?Sized, F>(
        &'s mut self,
        scratch: &'s mut Vec<u8>,
        validate: bool,
        result: F,
    ) -> Result<Reference<'a, 's, T>>
    where
        T: '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 {
            while self.index < self.slice.len() && !ESCAPE[self.slice[self.index] as usize] {
                self.index += 1;
            }
            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;
                    try!(parse_escape(self, scratch));
                    start = self.index;
                }
                _ => {
                    if validate {
                        return error(self, ErrorCode::ControlCharacterWhileParsingString);
                    }
                    self.index += 1;
                }
            }
        }
    }
}

impl<'a> private::Sealed for SliceRead<'a> {}

impl<'a> Read<'a> for SliceRead<'a> {
    #[inline]
    fn next(&mut self) -> io::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) -> io::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 {
            while self.index < self.slice.len() && !ESCAPE[self.slice[self.index] as usize] {
                self.index += 1;
            }
            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;
                    try!(ignore_escape(self));
                }
                _ => {
                    return error(self, ErrorCode::ControlCharacterWhileParsingString);
                }
            }
        }
    }
}

//////////////////////////////////////////////////////////////////////////////

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()),
        }
    }
}

impl<'a> private::Sealed for StrRead<'a> {}

impl<'a> Read<'a> for StrRead<'a> {
    #[inline]
    fn next(&mut self) -> io::Result<Option<u8>> {
        self.delegate.next()
    }

    #[inline]
    fn peek(&mut self) -> io::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 input is assumed to be valid UTF-8 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()
    }
}

//////////////////////////////////////////////////////////////////////////////

const CT: bool = true; // control character \x00...\x1F
const QU: bool = true; // quote \x22
const BS: bool = true; // backslash \x5C
const O: bool = false; // allow unescaped

// Lookup table of bytes that must be escaped. A value of true at index i means
// that byte i requires an escape sequence in the input.
#[cfg_attr(rustfmt, rustfmt_skip)]
static ESCAPE: [bool; 256] = [
    //   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
    CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, // 0
    CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, // 1
     O,  O, QU,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O, // 2
     O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O, // 3
     O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O, // 4
     O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O, BS,  O,  O,  O, // 5
     O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O, // 6
     O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O, // 7
     O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O, // 8
     O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O, // 9
     O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O, // A
     O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O, // B
     O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O, // C
     O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O, // D
     O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O, // E
     O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O,  O, // F
];

fn next_or_eof<'de, R: ?Sized + Read<'de>>(read: &mut R) -> Result<u8> {
    match try!(read.next().map_err(Error::io)) {
        Some(b) => Ok(b),
        None => error(read, ErrorCode::EofWhileParsingString),
    }
}

fn error<'de, R: ?Sized + Read<'de>, T>(read: &R, reason: ErrorCode) -> Result<T> {
    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, scratch: &mut Vec<u8>) -> Result<()> {
    let ch = try!(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' => {
            let c = match try!(decode_hex_escape(read)) {
                0xDC00...0xDFFF => {
                    return error(read, ErrorCode::LoneLeadingSurrogateInHexEscape);
                }

                // Non-BMP characters are encoded as a sequence of
                // two hex escapes, representing UTF-16 surrogates.
                n1 @ 0xD800...0xDBFF => {
                    if try!(next_or_eof(read)) != b'\\' {
                        return error(read, ErrorCode::UnexpectedEndOfHexEscape);
                    }
                    if try!(next_or_eof(read)) != b'u' {
                        return error(read, ErrorCode::UnexpectedEndOfHexEscape);
                    }

                    let n2 = try!(decode_hex_escape(read));

                    if n2 < 0xDC00 || n2 > 0xDFFF {
                        return error(read, ErrorCode::LoneLeadingSurrogateInHexEscape);
                    }

                    let n = (((n1 - 0xD800) as u32) << 10 | (n2 - 0xDC00) as u32) + 0x1_0000;

                    match char::from_u32(n) {
                        Some(c) => c,
                        None => {
                            return error(read, ErrorCode::InvalidUnicodeCodePoint);
                        }
                    }
                }

                n => match char::from_u32(n as u32) {
                    Some(c) => c,
                    None => {
                        return error(read, ErrorCode::InvalidUnicodeCodePoint);
                    }
                },
            };

            scratch.extend_from_slice(c.encode_utf8(&mut [0_u8; 4]).as_bytes());
        }
        _ => {
            return error(read, ErrorCode::InvalidEscape);
        }
    }

    Ok(())
}

/// Parses a JSON escape sequence and discards the value. Assumes the previous
/// byte read was a backslash.
fn ignore_escape<'de, R: ?Sized + Read<'de>>(read: &mut R) -> Result<()> {
    let ch = try!(next_or_eof(read));

    match ch {
        b'"' | b'\\' | b'/' | b'b' | b'f' | b'n' | b'r' | b't' => {}
        b'u' => {
            let n = match try!(decode_hex_escape(read)) {
                0xDC00...0xDFFF => {
                    return error(read, ErrorCode::LoneLeadingSurrogateInHexEscape);
                }

                // Non-BMP characters are encoded as a sequence of
                // two hex escapes, representing UTF-16 surrogates.
                n1 @ 0xD800...0xDBFF => {
                    if try!(next_or_eof(read)) != b'\\' {
                        return error(read, ErrorCode::UnexpectedEndOfHexEscape);
                    }
                    if try!(next_or_eof(read)) != b'u' {
                        return error(read, ErrorCode::UnexpectedEndOfHexEscape);
                    }

                    let n2 = try!(decode_hex_escape(read));

                    if n2 < 0xDC00 || n2 > 0xDFFF {
                        return error(read, ErrorCode::LoneLeadingSurrogateInHexEscape);
                    }

                    (((n1 - 0xD800) as u32) << 10 | (n2 - 0xDC00) as u32) + 0x1_0000
                }

                n => n as u32,
            };

            if char::from_u32(n).is_none() {
                return error(read, ErrorCode::InvalidUnicodeCodePoint);
            }
        }
        _ => {
            return error(read, ErrorCode::InvalidEscape);
        }
    }

    Ok(())
}

fn decode_hex_escape<'de, R: ?Sized + Read<'de>>(read: &mut R) -> Result<u16> {
    let mut n = 0;
    for _ in 0..4 {
        n = match try!(next_or_eof(read)) {
            c @ b'0'...b'9' => n * 16_u16 + ((c as u16) - (b'0' as u16)),
            b'a' | b'A' => n * 16_u16 + 10_u16,
            b'b' | b'B' => n * 16_u16 + 11_u16,
            b'c' | b'C' => n * 16_u16 + 12_u16,
            b'd' | b'D' => n * 16_u16 + 13_u16,
            b'e' | b'E' => n * 16_u16 + 14_u16,
            b'f' | b'F' => n * 16_u16 + 15_u16,
            _ => {
                return error(read, ErrorCode::InvalidEscape);
            }
        };
    }
    Ok(n)
}