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
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
//! # Serialization Flavors
//!
//! "Flavors" in `postcard` are used as modifiers to the serialization or deserialization
//! process. Flavors typically modify one or both of the following:
//!
//! 1. The output medium of the serialization, e.g. whether the data is serialized to a `[u8]` slice, or a `heapless::Vec`.
//! 2. The format of the serialization, such as encoding the serialized output in a COBS format, performing CRC32 checksumming while serializing, etc.
//!
//! Flavors are implemented using the [`Flavor`] trait, which acts as a "middleware" for receiving the bytes as serialized by `serde`.
//! Multiple flavors may be combined to obtain a desired combination of behavior and storage.
//! When flavors are combined, it is expected that the storage flavor (such as `Slice` or `HVec`) is the innermost flavor.
//!
//! Custom flavors may be defined by users of the `postcard` crate, however some commonly useful flavors have been provided in
//! this module. If you think your custom flavor would be useful to others, PRs adding flavors are very welcome!
//!
//! ## Usability
//!
//! Flavors may not always be convenient to use directly, as they may expose some implementation details of how the
//! inner workings of the flavor behaves. It is typical to provide a convenience method for using a flavor, to prevent
//! the user from having to specify generic parameters, setting correct initialization values, or handling the output of
//! the flavor correctly. See `postcard::to_vec()` for an example of this.
//!
//! It is recommended to use the [`serialize_with_flavor()`](../fn.serialize_with_flavor.html) method for serialization. See it's documentation for information
//! regarding usage and generic type parameters.
//!
//! ## When to use (multiple) flavors
//!
//! Combining flavors are nice for convenience, as they perform potentially multiple steps of
//! serialization at one time.
//!
//! This can often be more memory efficient, as intermediate buffers are not typically required.
//!
//! ## When NOT to use (multiple) flavors
//!
//! The downside of passing serialization through multiple steps is that it is typically slower than
//! performing each step serially. Said simply, "cobs encoding while serializing" is often slower
//! than "serialize then cobs encode", due to the ability to handle longer "runs" of data in each
//! stage. The downside is that if these stages can not be performed in-place on the buffer, you
//! will need additional buffers for each stage.
//!
//! ## Examples
//!
//! ### Using a single flavor
//!
//! In the first example, we use the `Slice` flavor, to store the serialized output into a mutable `[u8]` slice.
//! No other modification is made to the serialization process.
//!
//! ```rust
//! use postcard::{
//!     serialize_with_flavor,
//!     ser_flavors::Slice,
//! };
//!
//! let mut buf = [0u8; 32];
//!
//! let data: &[u8] = &[0x01, 0x00, 0x20, 0x30];
//! let buffer = &mut [0u8; 32];
//! let res = serialize_with_flavor::<[u8], Slice, &mut [u8]>(
//!     data,
//!     Slice::new(buffer)
//! ).unwrap();
//!
//! assert_eq!(res, &[0x04, 0x01, 0x00, 0x20, 0x30]);
//! ```
//!
//! ### Using combined flavors
//!
//! In the second example, we mix `Slice` with `Cobs`, to cobs encode the output while
//! the data is serialized. Notice how `Slice` (the storage flavor) is the innermost flavor used.
//!
//! ```rust
//! use postcard::{
//!     serialize_with_flavor,
//!     ser_flavors::{Cobs, Slice},
//! };
//!
//! let mut buf = [0u8; 32];
//!
//! let data: &[u8] = &[0x01, 0x00, 0x20, 0x30];
//! let buffer = &mut [0u8; 32];
//! let res = serialize_with_flavor::<[u8], Cobs<Slice>, &mut [u8]>(
//!     data,
//!     Cobs::try_new(Slice::new(buffer)).unwrap(),
//! ).unwrap();
//!
//! assert_eq!(res, &[0x03, 0x04, 0x01, 0x03, 0x20, 0x30, 0x00]);
//! ```

use crate::error::{Error, Result};
use cobs::{EncoderState, PushResult};
use core::marker::PhantomData;
use core::ops::Index;
use core::ops::IndexMut;

#[cfg(feature = "heapless")]
pub use heapless_vec::*;

#[cfg(feature = "use-std")]
pub use std_vec::*;

#[cfg(feature = "alloc")]
pub use alloc_vec::*;

#[cfg(feature = "alloc")]
extern crate alloc;

/// The serialization Flavor trait
///
/// This is used as the primary way to encode serialized data into some kind of buffer,
/// or modify that data in a middleware style pattern.
///
/// See the module level docs for an example of how flavors are used.
pub trait Flavor {
    /// The `Output` type is what this storage "resolves" to when the serialization is complete,
    /// such as a slice or a Vec of some sort.
    type Output;

    /// The try_extend() trait method can be implemented when there is a more efficient way of processing
    /// multiple bytes at once, such as copying a slice to the output, rather than iterating over one byte
    /// at a time.
    #[inline]
    fn try_extend(&mut self, data: &[u8]) -> Result<()> {
        data.iter().try_for_each(|d| self.try_push(*d))
    }

    /// The try_push() trait method can be used to push a single byte to be modified and/or stored
    fn try_push(&mut self, data: u8) -> Result<()>;

    /// Finalize the serialization process
    fn finalize(self) -> Result<Self::Output>;
}

////////////////////////////////////////
// Slice
////////////////////////////////////////

/// The `Slice` flavor is a storage flavor, storing the serialized (or otherwise modified) bytes into a plain
/// `[u8]` slice. The `Slice` flavor resolves into a sub-slice of the original slice buffer.
pub struct Slice<'a> {
    start: *mut u8,
    cursor: *mut u8,
    end: *mut u8,
    _pl: PhantomData<&'a [u8]>,
}

impl<'a> Slice<'a> {
    /// Create a new `Slice` flavor from a given backing buffer
    pub fn new(buf: &'a mut [u8]) -> Self {
        let ptr = buf.as_mut_ptr();
        Slice {
            start: ptr,
            cursor: ptr,
            end: unsafe { ptr.add(buf.len()) },
            _pl: PhantomData,
        }
    }
}

impl<'a> Flavor for Slice<'a> {
    type Output = &'a mut [u8];

    #[inline(always)]
    fn try_push(&mut self, b: u8) -> Result<()> {
        if self.cursor == self.end {
            Err(Error::SerializeBufferFull)
        } else {
            unsafe {
                self.cursor.write(b);
                self.cursor = self.cursor.add(1);
            }
            Ok(())
        }
    }

    #[inline(always)]
    fn try_extend(&mut self, b: &[u8]) -> Result<()> {
        let remain = (self.end as usize) - (self.cursor as usize);
        let blen = b.len();
        if blen > remain {
            Err(Error::SerializeBufferFull)
        } else {
            unsafe {
                core::ptr::copy_nonoverlapping(b.as_ptr(), self.cursor, blen);
                self.cursor = self.cursor.add(blen);
            }
            Ok(())
        }
    }

    fn finalize(self) -> Result<Self::Output> {
        let used = (self.cursor as usize) - (self.start as usize);
        let sli = unsafe { core::slice::from_raw_parts_mut(self.start, used) };
        Ok(sli)
    }
}

impl<'a> Index<usize> for Slice<'a> {
    type Output = u8;

    fn index(&self, idx: usize) -> &u8 {
        let len = (self.end as usize) - (self.start as usize);
        assert!(idx < len);
        unsafe { &*self.start.add(idx) }
    }
}

impl<'a> IndexMut<usize> for Slice<'a> {
    fn index_mut(&mut self, idx: usize) -> &mut u8 {
        let len = (self.end as usize) - (self.start as usize);
        assert!(idx < len);
        unsafe { &mut *self.start.add(idx) }
    }
}

/// Wrapper over a [`std::iter::Extend<u8>`] that implements the flavor trait
pub struct ExtendFlavor<T> {
    iter: T,
}

impl<T> ExtendFlavor<T>
where
    T: core::iter::Extend<u8>,
{
    /// Create a new [Self] flavor from a given [`std::iter::Extend<u8>`]
    pub fn new(iter: T) -> Self {
        Self { iter }
    }
}

impl<T> Flavor for ExtendFlavor<T>
where
    T: core::iter::Extend<u8>,
{
    type Output = T;

    #[inline(always)]
    fn try_push(&mut self, data: u8) -> Result<()> {
        self.iter.extend([data]);
        Ok(())
    }

    #[inline(always)]
    fn try_extend(&mut self, b: &[u8]) -> Result<()> {
        self.iter.extend(b.iter().cloned());
        Ok(())
    }

    fn finalize(self) -> Result<Self::Output> {
        Ok(self.iter)
    }
}

/// Support for the [`embedded-io`](crate::eio::embedded_io) traits
#[cfg(any(feature = "embedded-io-04", feature = "embedded-io-06"))]
pub mod eio {

    use super::Flavor;
    use crate::{Error, Result};

    /// Wrapper over a [`embedded_io Write`](crate::eio::Write) that implements the flavor trait
    pub struct WriteFlavor<T> {
        writer: T,
    }

    impl<T> WriteFlavor<T>
    where
        T: crate::eio::Write,
    {
        /// Create a new [Self] flavor from a given [`embedded_io Write`](crate::eio::Write)
        pub fn new(writer: T) -> Self {
            Self { writer }
        }
    }

    impl<T> Flavor for WriteFlavor<T>
    where
        T: crate::eio::Write,
    {
        type Output = T;

        #[inline(always)]
        fn try_push(&mut self, data: u8) -> Result<()> {
            self.writer
                .write_all(&[data])
                .map_err(|_| Error::SerializeBufferFull)?;
            Ok(())
        }

        #[inline(always)]
        fn try_extend(&mut self, b: &[u8]) -> Result<()> {
            self.writer
                .write_all(b)
                .map_err(|_| Error::SerializeBufferFull)?;
            Ok(())
        }

        fn finalize(mut self) -> Result<Self::Output> {
            self.writer
                .flush()
                .map_err(|_| Error::SerializeBufferFull)?;
            Ok(self.writer)
        }
    }
}

/// Support for the [std::io] traits
#[cfg(feature = "use-std")]
pub mod io {

    use super::Flavor;
    use crate::{Error, Result};

    /// Wrapper over a [std::io::Write] that implements the flavor trait
    pub struct WriteFlavor<T> {
        writer: T,
    }

    impl<T> WriteFlavor<T>
    where
        T: std::io::Write,
    {
        /// Create a new [Self] flavor from a given [std::io::Write]
        pub fn new(writer: T) -> Self {
            Self { writer }
        }
    }

    impl<T> Flavor for WriteFlavor<T>
    where
        T: std::io::Write,
    {
        type Output = T;

        #[inline(always)]
        fn try_push(&mut self, data: u8) -> Result<()> {
            self.writer
                .write_all(&[data])
                .map_err(|_| Error::SerializeBufferFull)?;
            Ok(())
        }

        #[inline(always)]
        fn try_extend(&mut self, b: &[u8]) -> Result<()> {
            self.writer
                .write_all(b)
                .map_err(|_| Error::SerializeBufferFull)?;
            Ok(())
        }

        fn finalize(mut self) -> Result<Self::Output> {
            self.writer
                .flush()
                .map_err(|_| Error::SerializeBufferFull)?;
            Ok(self.writer)
        }
    }
}

#[cfg(feature = "heapless")]
mod heapless_vec {
    use super::Flavor;
    use super::Index;
    use super::IndexMut;
    use crate::{Error, Result};
    use heapless::Vec;

    ////////////////////////////////////////
    // HVec
    ////////////////////////////////////////

    /// The `HVec` flavor is a wrapper type around a `heapless::Vec`. This is a stack
    /// allocated data structure, with a fixed maximum size and variable amount of contents.
    #[derive(Default)]
    pub struct HVec<const B: usize> {
        /// the contained data buffer
        vec: Vec<u8, B>,
    }

    impl<const B: usize> HVec<B> {
        /// Create a new, currently empty, [heapless::Vec] to be used for storing serialized
        /// output data.
        pub fn new() -> Self {
            Self::default()
        }
    }

    impl<const B: usize> Flavor for HVec<B> {
        type Output = Vec<u8, B>;

        #[inline(always)]
        fn try_extend(&mut self, data: &[u8]) -> Result<()> {
            self.vec
                .extend_from_slice(data)
                .map_err(|_| Error::SerializeBufferFull)
        }

        #[inline(always)]
        fn try_push(&mut self, data: u8) -> Result<()> {
            self.vec.push(data).map_err(|_| Error::SerializeBufferFull)
        }

        fn finalize(self) -> Result<Vec<u8, B>> {
            Ok(self.vec)
        }
    }

    impl<const B: usize> Index<usize> for HVec<B> {
        type Output = u8;

        fn index(&self, idx: usize) -> &u8 {
            &self.vec[idx]
        }
    }

    impl<const B: usize> IndexMut<usize> for HVec<B> {
        fn index_mut(&mut self, idx: usize) -> &mut u8 {
            &mut self.vec[idx]
        }
    }
}

#[cfg(feature = "use-std")]
mod std_vec {
    /// The `StdVec` flavor is a wrapper type around a `std::vec::Vec`.
    ///
    /// This type is only available when the (non-default) `use-std` feature is active
    pub type StdVec = super::alloc_vec::AllocVec;
}

#[cfg(feature = "alloc")]
mod alloc_vec {
    extern crate alloc;
    use super::Flavor;
    use super::Index;
    use super::IndexMut;
    use crate::Result;
    use alloc::vec::Vec;

    /// The `AllocVec` flavor is a wrapper type around an [alloc::vec::Vec].
    ///
    /// This type is only available when the (non-default) `alloc` feature is active
    #[derive(Default)]
    pub struct AllocVec {
        /// The vec to be used for serialization
        vec: Vec<u8>,
    }

    impl AllocVec {
        /// Create a new, currently empty, [alloc::vec::Vec] to be used for storing serialized
        /// output data.
        pub fn new() -> Self {
            Self::default()
        }
    }

    impl Flavor for AllocVec {
        type Output = Vec<u8>;

        #[inline(always)]
        fn try_extend(&mut self, data: &[u8]) -> Result<()> {
            self.vec.extend_from_slice(data);
            Ok(())
        }

        #[inline(always)]
        fn try_push(&mut self, data: u8) -> Result<()> {
            self.vec.push(data);
            Ok(())
        }

        fn finalize(self) -> Result<Self::Output> {
            Ok(self.vec)
        }
    }

    impl Index<usize> for AllocVec {
        type Output = u8;

        #[inline]
        fn index(&self, idx: usize) -> &u8 {
            &self.vec[idx]
        }
    }

    impl IndexMut<usize> for AllocVec {
        #[inline]
        fn index_mut(&mut self, idx: usize) -> &mut u8 {
            &mut self.vec[idx]
        }
    }
}

////////////////////////////////////////////////////////////////////////////////
// Modification Flavors
////////////////////////////////////////////////////////////////////////////////

////////////////////////////////////////
// COBS
////////////////////////////////////////

/// The `Cobs` flavor implements [Consistent Overhead Byte Stuffing] on
/// the serialized data. The output of this flavor includes the termination/sentinel
/// byte of `0x00`.
///
/// This protocol is useful when sending data over a serial interface without framing such as a UART
///
/// [Consistent Overhead Byte Stuffing]: https://en.wikipedia.org/wiki/Consistent_Overhead_Byte_Stuffing
pub struct Cobs<B>
where
    B: Flavor + IndexMut<usize, Output = u8>,
{
    flav: B,
    cobs: EncoderState,
}

impl<B> Cobs<B>
where
    B: Flavor + IndexMut<usize, Output = u8>,
{
    /// Create a new Cobs modifier Flavor. If there is insufficient space
    /// to push the leading header byte, the method will return an Error
    pub fn try_new(mut bee: B) -> Result<Self> {
        bee.try_push(0).map_err(|_| Error::SerializeBufferFull)?;
        Ok(Self {
            flav: bee,
            cobs: EncoderState::default(),
        })
    }
}

impl<B> Flavor for Cobs<B>
where
    B: Flavor + IndexMut<usize, Output = u8>,
{
    type Output = <B as Flavor>::Output;

    #[inline(always)]
    fn try_push(&mut self, data: u8) -> Result<()> {
        use PushResult::*;
        match self.cobs.push(data) {
            AddSingle(n) => self.flav.try_push(n),
            ModifyFromStartAndSkip((idx, mval)) => {
                self.flav[idx] = mval;
                self.flav.try_push(0)
            }
            ModifyFromStartAndPushAndSkip((idx, mval, nval)) => {
                self.flav[idx] = mval;
                self.flav.try_push(nval)?;
                self.flav.try_push(0)
            }
        }
    }

    fn finalize(mut self) -> Result<Self::Output> {
        let (idx, mval) = self.cobs.finalize();
        self.flav[idx] = mval;
        self.flav.try_push(0)?;
        self.flav.finalize()
    }
}

////////////////////////////////////////
// CRC
////////////////////////////////////////

/// This Cyclic Redundancy Check flavor applies [the CRC crate's `Algorithm`](https://docs.rs/crc/latest/crc/struct.Algorithm.html) struct on
/// the serialized data. The output of this flavor receives the CRC appended to the bytes.
///
/// CRCs are used for error detection when reading data back.
///
/// The `crc` feature requires enabling to use this module.
///
/// More on CRCs: <https://en.wikipedia.org/wiki/Cyclic_redundancy_check>.
#[cfg(feature = "use-crc")]
#[cfg_attr(docsrs, doc(cfg(feature = "use-crc")))]
pub mod crc {
    use crc::Digest;
    use crc::Width;
    use serde::Serialize;

    #[cfg(feature = "alloc")]
    use super::alloc;
    use super::Flavor;
    use super::Slice;

    use crate::serialize_with_flavor;
    use crate::Result;
    use paste::paste;

    /// Manages CRC modifications as a flavor.
    pub struct CrcModifier<'a, B, W>
    where
        B: Flavor,
        W: Width,
    {
        flav: B,
        digest: Digest<'a, W>,
    }

    impl<'a, B, W> CrcModifier<'a, B, W>
    where
        B: Flavor,
        W: Width,
    {
        /// Create a new CRC modifier Flavor.
        pub fn new(bee: B, digest: Digest<'a, W>) -> Self {
            Self { flav: bee, digest }
        }
    }

    macro_rules! impl_flavor {
        ($( $int:ty ),*) => {
            $(
                paste! {
                    impl<'a, B> Flavor for CrcModifier<'a, B, $int>
                    where
                        B: Flavor,
                    {
                        type Output = <B as Flavor>::Output;

                        #[inline(always)]
                        fn try_push(&mut self, data: u8) -> Result<()> {
                            self.digest.update(&[data]);
                            self.flav.try_push(data)
                        }

                        fn finalize(mut self) -> Result<Self::Output> {
                            let crc = self.digest.finalize();
                            for byte in crc.to_le_bytes() {
                                self.flav.try_push(byte)?;
                            }
                            self.flav.finalize()
                        }
                    }

                    /// Serialize a `T` to the given slice, with the resulting slice containing
                    /// data followed by a CRC. The CRC bytes are included in the output buffer.
                    ///
                    /// When successful, this function returns the slice containing the
                    /// serialized and encoded message.
                    pub fn [<to_slice_ $int>]<'a, T>(
                        value: &T,
                        buf: &'a mut [u8],
                        digest: Digest<'_, $int>,
                    ) -> Result<&'a mut [u8]>
                    where
                        T: Serialize + ?Sized,
                    {
                        serialize_with_flavor(value, CrcModifier::new(Slice::new(buf), digest))
                    }

                    /// Serialize a `T` to a `heapless::Vec<u8>`, with the `Vec` containing
                    /// data followed by a CRC. The CRC bytes are included in the output `Vec`.
                    #[cfg(feature = "heapless")]
                    #[cfg_attr(docsrs, doc(cfg(feature = "heapless")))]
                    pub fn [<to_vec_ $int>]<T, const B: usize>(
                        value: &T,
                        digest: Digest<'_, $int>,
                    ) -> Result<heapless::Vec<u8, B>>
                    where
                        T: Serialize + ?Sized,
                    {
                        use super::HVec;

                        serialize_with_flavor(value, CrcModifier::new(HVec::default(), digest))
                    }

                    /// Serialize a `T` to a `heapless::Vec<u8>`, with the `Vec` containing
                    /// data followed by a CRC. The CRC bytes are included in the output `Vec`.
                    #[cfg(feature = "alloc")]
                    #[cfg_attr(docsrs, doc(cfg(feature = "alloc")))]
                    pub fn [<to_allocvec_ $int>]<T>(value: &T, digest: Digest<'_, $int>) -> Result<alloc::vec::Vec<u8>>
                    where
                        T: Serialize + ?Sized,
                    {
                        use super::AllocVec;

                        serialize_with_flavor(value, CrcModifier::new(AllocVec::new(), digest))
                    }
                }
            )*
        };
    }

    impl_flavor![u8, u16, u32, u64, u128];
}

/// The `Size` flavor is a measurement flavor, which accumulates the number of bytes needed to
/// serialize the data.
///
/// ```
/// use postcard::{serialize_with_flavor, ser_flavors};
///
/// let value = false;
/// let size = serialize_with_flavor(&value, ser_flavors::Size::default()).unwrap();
///
/// assert_eq!(size, 1);
/// ```
#[derive(Default)]
pub struct Size {
    size: usize,
}

impl Flavor for Size {
    type Output = usize;

    #[inline(always)]
    fn try_push(&mut self, _b: u8) -> Result<()> {
        self.size += 1;
        Ok(())
    }

    #[inline(always)]
    fn try_extend(&mut self, b: &[u8]) -> Result<()> {
        self.size += b.len();
        Ok(())
    }

    fn finalize(self) -> Result<Self::Output> {
        Ok(self.size)
    }
}