compiler/rustc_serialize/src/opaque.rs

   1 use crate::leb128::{self, max_leb128_len};
   2 use crate::serialize::{self, Decoder as _, Encoder as _};
   3 use std::convert::TryInto;
   4 use std::fs::File;
   5 use std::io::{self, Write};
   6 use std::mem::MaybeUninit;
   7 use std::path::Path;
   8 use std::ptr;
   9
  10 // -----------------------------------------------------------------------------
  11 // Encoder
  12 // -----------------------------------------------------------------------------
  13
  14 pub type EncodeResult = Result<(), !>;
  15
  16 pub struct Encoder {
  17     pub data: Vec<u8>,
  18 }
  19
  20 impl Encoder {
  21     pub fn new(data: Vec<u8>) -> Encoder {
  22         Encoder { data }
  23     }
  24
  25     pub fn into_inner(self) -> Vec<u8> {
  26         self.data
  27     }
  28
  29     #[inline]
  30     pub fn position(&self) -> usize {
  31         self.data.len()
  32     }
  33 }
  34
  35 macro_rules! write_leb128 {
  36     ($enc:expr, $value:expr, $int_ty:ty, $fun:ident) => {{
  37         const MAX_ENCODED_LEN: usize = max_leb128_len!($int_ty);
  38         let old_len = $enc.data.len();
  39
  40         if MAX_ENCODED_LEN > $enc.data.capacity() - old_len {
  41             $enc.data.reserve(MAX_ENCODED_LEN);
  42         }
  43
  44         // SAFETY: The above check and `reserve` ensures that there is enough
  45         // room to write the encoded value to the vector's internal buffer.
  46         unsafe {
  47             let buf = &mut *($enc.data.as_mut_ptr().add(old_len)
  48                 as *mut [MaybeUninit<u8>; MAX_ENCODED_LEN]);
  49             let encoded = leb128::$fun(buf, $value);
  50             $enc.data.set_len(old_len + encoded.len());
  51         }
  52
  53         Ok(())
  54     }};
  55 }
  56
  57 /// A byte that [cannot occur in UTF8 sequences][utf8]. Used to mark the end of a string.
  58 /// This way we can skip validation and still be relatively sure that deserialization
  59 /// did not desynchronize.
  60 ///
  61 /// [utf8]: https://en.wikipedia.org/w/index.php?title=UTF-8&oldid=1058865525#Codepage_layout
  62 const STR_SENTINEL: u8 = 0xC1;
  63
  64 impl serialize::Encoder for Encoder {
  65     type Error = !;
  66
  67     #[inline]
  68     fn emit_unit(&mut self) -> EncodeResult {
  69         Ok(())
  70     }
  71
  72     #[inline]
  73     fn emit_usize(&mut self, v: usize) -> EncodeResult {
  74         write_leb128!(self, v, usize, write_usize_leb128)
  75     }
  76
  77     #[inline]
  78     fn emit_u128(&mut self, v: u128) -> EncodeResult {
  79         write_leb128!(self, v, u128, write_u128_leb128)
  80     }
  81
  82     #[inline]
  83     fn emit_u64(&mut self, v: u64) -> EncodeResult {
  84         write_leb128!(self, v, u64, write_u64_leb128)
  85     }
  86
  87     #[inline]
  88     fn emit_u32(&mut self, v: u32) -> EncodeResult {
  89         write_leb128!(self, v, u32, write_u32_leb128)
  90     }
  91
  92     #[inline]
  93     fn emit_u16(&mut self, v: u16) -> EncodeResult {
  94         self.data.extend_from_slice(&v.to_le_bytes());
  95         Ok(())
  96     }
  97
  98     #[inline]
  99     fn emit_u8(&mut self, v: u8) -> EncodeResult {
 100         self.data.push(v);
 101         Ok(())
 102     }
 103
 104     #[inline]
 105     fn emit_isize(&mut self, v: isize) -> EncodeResult {
 106         write_leb128!(self, v, isize, write_isize_leb128)
 107     }
 108
 109     #[inline]
 110     fn emit_i128(&mut self, v: i128) -> EncodeResult {
 111         write_leb128!(self, v, i128, write_i128_leb128)
 112     }
 113
 114     #[inline]
 115     fn emit_i64(&mut self, v: i64) -> EncodeResult {
 116         write_leb128!(self, v, i64, write_i64_leb128)
 117     }
 118
 119     #[inline]
 120     fn emit_i32(&mut self, v: i32) -> EncodeResult {
 121         write_leb128!(self, v, i32, write_i32_leb128)
 122     }
 123
 124     #[inline]
 125     fn emit_i16(&mut self, v: i16) -> EncodeResult {
 126         self.data.extend_from_slice(&v.to_le_bytes());
 127         Ok(())
 128     }
 129
 130     #[inline]
 131     fn emit_i8(&mut self, v: i8) -> EncodeResult {
 132         self.emit_u8(v as u8)
 133     }
 134
 135     #[inline]
 136     fn emit_bool(&mut self, v: bool) -> EncodeResult {
 137         self.emit_u8(if v { 1 } else { 0 })
 138     }
 139
 140     #[inline]
 141     fn emit_f64(&mut self, v: f64) -> EncodeResult {
 142         let as_u64: u64 = v.to_bits();
 143         self.emit_u64(as_u64)
 144     }
 145
 146     #[inline]
 147     fn emit_f32(&mut self, v: f32) -> EncodeResult {
 148         let as_u32: u32 = v.to_bits();
 149         self.emit_u32(as_u32)
 150     }
 151
 152     #[inline]
 153     fn emit_char(&mut self, v: char) -> EncodeResult {
 154         self.emit_u32(v as u32)
 155     }
 156
 157     #[inline]
 158     fn emit_str(&mut self, v: &str) -> EncodeResult {
 159         self.emit_usize(v.len())?;
 160         self.emit_raw_bytes(v.as_bytes())?;
 161         self.emit_u8(STR_SENTINEL)
 162     }
 163
 164     #[inline]
 165     fn emit_raw_bytes(&mut self, s: &[u8]) -> EncodeResult {
 166         self.data.extend_from_slice(s);
 167         Ok(())
 168     }
 169 }
 170
 171 pub type FileEncodeResult = Result<(), io::Error>;
 172
 173 // `FileEncoder` encodes data to file via fixed-size buffer.
 174 //
 175 // When encoding large amounts of data to a file, using `FileEncoder` may be
 176 // preferred over using `Encoder` to encode to a `Vec`, and then writing the
 177 // `Vec` to file, as the latter uses as much memory as there is encoded data,
 178 // while the former uses the fixed amount of memory allocated to the buffer.
 179 // `FileEncoder` also has the advantage of not needing to reallocate as data
 180 // is appended to it, but the disadvantage of requiring more error handling,
 181 // which has some runtime overhead.
 182 pub struct FileEncoder {
 183     // The input buffer. For adequate performance, we need more control over
 184     // buffering than `BufWriter` offers. If `BufWriter` ever offers a raw
 185     // buffer access API, we can use it, and remove `buf` and `buffered`.
 186     buf: Box<[MaybeUninit<u8>]>,
 187     buffered: usize,
 188     flushed: usize,
 189     file: File,
 190 }
 191
 192 impl FileEncoder {
 193     pub fn new<P: AsRef<Path>>(path: P) -> io::Result<Self> {
 194         const DEFAULT_BUF_SIZE: usize = 8192;
 195         FileEncoder::with_capacity(path, DEFAULT_BUF_SIZE)
 196     }
 197
 198     pub fn with_capacity<P: AsRef<Path>>(path: P, capacity: usize) -> io::Result<Self> {
 199         // Require capacity at least as large as the largest LEB128 encoding
 200         // here, so that we don't have to check or handle this on every write.
 201         assert!(capacity >= max_leb128_len());
 202
 203         // Require capacity small enough such that some capacity checks can be
 204         // done using guaranteed non-overflowing add rather than sub, which
 205         // shaves an instruction off those code paths (on x86 at least).
 206         assert!(capacity <= usize::MAX - max_leb128_len());
 207
 208         let file = File::create(path)?;
 209
 210         Ok(FileEncoder { buf: Box::new_uninit_slice(capacity), buffered: 0, flushed: 0, file })
 211     }
 212
 213     #[inline]
 214     pub fn position(&self) -> usize {
 215         // Tracking position this way instead of having a `self.position` field
 216         // means that we don't have to update the position on every write call.
 217         self.flushed + self.buffered
 218     }
 219
 220     pub fn flush(&mut self) -> FileEncodeResult {
 221         // This is basically a copy of `BufWriter::flush`. If `BufWriter` ever
 222         // offers a raw buffer access API, we can use it, and remove this.
 223
 224         /// Helper struct to ensure the buffer is updated after all the writes
 225         /// are complete. It tracks the number of written bytes and drains them
 226         /// all from the front of the buffer when dropped.
 227         struct BufGuard<'a> {
 228             buffer: &'a mut [u8],
 229             encoder_buffered: &'a mut usize,
 230             encoder_flushed: &'a mut usize,
 231             flushed: usize,
 232         }
 233
 234         impl<'a> BufGuard<'a> {
 235             fn new(
 236                 buffer: &'a mut [u8],
 237                 encoder_buffered: &'a mut usize,
 238                 encoder_flushed: &'a mut usize,
 239             ) -> Self {
 240                 assert_eq!(buffer.len(), *encoder_buffered);
 241                 Self { buffer, encoder_buffered, encoder_flushed, flushed: 0 }
 242             }
 243
 244             /// The unwritten part of the buffer
 245             fn remaining(&self) -> &[u8] {
 246                 &self.buffer[self.flushed..]
 247             }
 248
 249             /// Flag some bytes as removed from the front of the buffer
 250             fn consume(&mut self, amt: usize) {
 251                 self.flushed += amt;
 252             }
 253
 254             /// true if all of the bytes have been written
 255             fn done(&self) -> bool {
 256                 self.flushed >= *self.encoder_buffered
 257             }
 258         }
 259
 260         impl Drop for BufGuard<'_> {
 261             fn drop(&mut self) {
 262                 if self.flushed > 0 {
 263                     if self.done() {
 264                         *self.encoder_flushed += *self.encoder_buffered;
 265                         *self.encoder_buffered = 0;
 266                     } else {
 267                         self.buffer.copy_within(self.flushed.., 0);
 268                         *self.encoder_flushed += self.flushed;
 269                         *self.encoder_buffered -= self.flushed;
 270                     }
 271                 }
 272             }
 273         }
 274
 275         let mut guard = BufGuard::new(
 276             unsafe { MaybeUninit::slice_assume_init_mut(&mut self.buf[..self.buffered]) },
 277             &mut self.buffered,
 278             &mut self.flushed,
 279         );
 280
 281         while !guard.done() {
 282             match self.file.write(guard.remaining()) {
 283                 Ok(0) => {
 284                     return Err(io::Error::new(
 285                         io::ErrorKind::WriteZero,
 286                         "failed to write the buffered data",
 287                     ));
 288                 }
 289                 Ok(n) => guard.consume(n),
 290                 Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
 291                 Err(e) => return Err(e),
 292             }
 293         }
 294
 295         Ok(())
 296     }
 297
 298     #[inline]
 299     fn capacity(&self) -> usize {
 300         self.buf.len()
 301     }
 302
 303     #[inline]
 304     fn write_one(&mut self, value: u8) -> FileEncodeResult {
 305         // We ensure this during `FileEncoder` construction.
 306         debug_assert!(self.capacity() >= 1);
 307
 308         let mut buffered = self.buffered;
 309
 310         if std::intrinsics::unlikely(buffered >= self.capacity()) {
 311             self.flush()?;
 312             buffered = 0;
 313         }
 314
 315         // SAFETY: The above check and `flush` ensures that there is enough
 316         // room to write the input to the buffer.
 317         unsafe {
 318             *MaybeUninit::slice_as_mut_ptr(&mut self.buf).add(buffered) = value;
 319         }
 320
 321         self.buffered = buffered + 1;
 322
 323         Ok(())
 324     }
 325
 326     #[inline]
 327     fn write_all(&mut self, buf: &[u8]) -> FileEncodeResult {
 328         let capacity = self.capacity();
 329         let buf_len = buf.len();
 330
 331         if std::intrinsics::likely(buf_len <= capacity) {
 332             let mut buffered = self.buffered;
 333
 334             if std::intrinsics::unlikely(buf_len > capacity - buffered) {
 335                 self.flush()?;
 336                 buffered = 0;
 337             }
 338
 339             // SAFETY: The above check and `flush` ensures that there is enough
 340             // room to write the input to the buffer.
 341             unsafe {
 342                 let src = buf.as_ptr();
 343                 let dst = MaybeUninit::slice_as_mut_ptr(&mut self.buf).add(buffered);
 344                 ptr::copy_nonoverlapping(src, dst, buf_len);
 345             }
 346
 347             self.buffered = buffered + buf_len;
 348
 349             Ok(())
 350         } else {
 351             self.write_all_unbuffered(buf)
 352         }
 353     }
 354
 355     fn write_all_unbuffered(&mut self, mut buf: &[u8]) -> FileEncodeResult {
 356         if self.buffered > 0 {
 357             self.flush()?;
 358         }
 359
 360         // This is basically a copy of `Write::write_all` but also updates our
 361         // `self.flushed`. It's necessary because `Write::write_all` does not
 362         // return the number of bytes written when an error is encountered, and
 363         // without that, we cannot accurately update `self.flushed` on error.
 364         while !buf.is_empty() {
 365             match self.file.write(buf) {
 366                 Ok(0) => {
 367                     return Err(io::Error::new(
 368                         io::ErrorKind::WriteZero,
 369                         "failed to write whole buffer",
 370                     ));
 371                 }
 372                 Ok(n) => {
 373                     buf = &buf[n..];
 374                     self.flushed += n;
 375                 }
 376                 Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
 377                 Err(e) => return Err(e),
 378             }
 379         }
 380
 381         Ok(())
 382     }
 383 }
 384
 385 impl Drop for FileEncoder {
 386     fn drop(&mut self) {
 387         let _result = self.flush();
 388     }
 389 }
 390
 391 macro_rules! file_encoder_write_leb128 {
 392     ($enc:expr, $value:expr, $int_ty:ty, $fun:ident) => {{
 393         const MAX_ENCODED_LEN: usize = max_leb128_len!($int_ty);
 394
 395         // We ensure this during `FileEncoder` construction.
 396         debug_assert!($enc.capacity() >= MAX_ENCODED_LEN);
 397
 398         let mut buffered = $enc.buffered;
 399
 400         // This can't overflow. See assertion in `FileEncoder::with_capacity`.
 401         if std::intrinsics::unlikely(buffered + MAX_ENCODED_LEN > $enc.capacity()) {
 402             $enc.flush()?;
 403             buffered = 0;
 404         }
 405
 406         // SAFETY: The above check and flush ensures that there is enough
 407         // room to write the encoded value to the buffer.
 408         let buf = unsafe {
 409             &mut *($enc.buf.as_mut_ptr().add(buffered) as *mut [MaybeUninit<u8>; MAX_ENCODED_LEN])
 410         };
 411
 412         let encoded = leb128::$fun(buf, $value);
 413         $enc.buffered = buffered + encoded.len();
 414
 415         Ok(())
 416     }};
 417 }
 418
 419 impl serialize::Encoder for FileEncoder {
 420     type Error = io::Error;
 421
 422     #[inline]
 423     fn emit_unit(&mut self) -> FileEncodeResult {
 424         Ok(())
 425     }
 426
 427     #[inline]
 428     fn emit_usize(&mut self, v: usize) -> FileEncodeResult {
 429         file_encoder_write_leb128!(self, v, usize, write_usize_leb128)
 430     }
 431
 432     #[inline]
 433     fn emit_u128(&mut self, v: u128) -> FileEncodeResult {
 434         file_encoder_write_leb128!(self, v, u128, write_u128_leb128)
 435     }
 436
 437     #[inline]
 438     fn emit_u64(&mut self, v: u64) -> FileEncodeResult {
 439         file_encoder_write_leb128!(self, v, u64, write_u64_leb128)
 440     }
 441
 442     #[inline]
 443     fn emit_u32(&mut self, v: u32) -> FileEncodeResult {
 444         file_encoder_write_leb128!(self, v, u32, write_u32_leb128)
 445     }
 446
 447     #[inline]
 448     fn emit_u16(&mut self, v: u16) -> FileEncodeResult {
 449         self.write_all(&v.to_le_bytes())
 450     }
 451
 452     #[inline]
 453     fn emit_u8(&mut self, v: u8) -> FileEncodeResult {
 454         self.write_one(v)
 455     }
 456
 457     #[inline]
 458     fn emit_isize(&mut self, v: isize) -> FileEncodeResult {
 459         file_encoder_write_leb128!(self, v, isize, write_isize_leb128)
 460     }
 461
 462     #[inline]
 463     fn emit_i128(&mut self, v: i128) -> FileEncodeResult {
 464         file_encoder_write_leb128!(self, v, i128, write_i128_leb128)
 465     }
 466
 467     #[inline]
 468     fn emit_i64(&mut self, v: i64) -> FileEncodeResult {
 469         file_encoder_write_leb128!(self, v, i64, write_i64_leb128)
 470     }
 471
 472     #[inline]
 473     fn emit_i32(&mut self, v: i32) -> FileEncodeResult {
 474         file_encoder_write_leb128!(self, v, i32, write_i32_leb128)
 475     }
 476
 477     #[inline]
 478     fn emit_i16(&mut self, v: i16) -> FileEncodeResult {
 479         self.write_all(&v.to_le_bytes())
 480     }
 481
 482     #[inline]
 483     fn emit_i8(&mut self, v: i8) -> FileEncodeResult {
 484         self.emit_u8(v as u8)
 485     }
 486
 487     #[inline]
 488     fn emit_bool(&mut self, v: bool) -> FileEncodeResult {
 489         self.emit_u8(if v { 1 } else { 0 })
 490     }
 491
 492     #[inline]
 493     fn emit_f64(&mut self, v: f64) -> FileEncodeResult {
 494         let as_u64: u64 = v.to_bits();
 495         self.emit_u64(as_u64)
 496     }
 497
 498     #[inline]
 499     fn emit_f32(&mut self, v: f32) -> FileEncodeResult {
 500         let as_u32: u32 = v.to_bits();
 501         self.emit_u32(as_u32)
 502     }
 503
 504     #[inline]
 505     fn emit_char(&mut self, v: char) -> FileEncodeResult {
 506         self.emit_u32(v as u32)
 507     }
 508
 509     #[inline]
 510     fn emit_str(&mut self, v: &str) -> FileEncodeResult {
 511         self.emit_usize(v.len())?;
 512         self.emit_raw_bytes(v.as_bytes())?;
 513         self.emit_u8(STR_SENTINEL)
 514     }
 515
 516     #[inline]
 517     fn emit_raw_bytes(&mut self, s: &[u8]) -> FileEncodeResult {
 518         self.write_all(s)
 519     }
 520 }
 521
 522 // -----------------------------------------------------------------------------
 523 // Decoder
 524 // -----------------------------------------------------------------------------
 525
 526 pub struct Decoder<'a> {
 527     pub data: &'a [u8],
 528     position: usize,
 529 }
 530
 531 impl<'a> Decoder<'a> {
 532     #[inline]
 533     pub fn new(data: &'a [u8], position: usize) -> Decoder<'a> {
 534         Decoder { data, position }
 535     }
 536
 537     #[inline]
 538     pub fn position(&self) -> usize {
 539         self.position
 540     }
 541
 542     #[inline]
 543     pub fn set_position(&mut self, pos: usize) {
 544         self.position = pos
 545     }
 546
 547     #[inline]
 548     pub fn advance(&mut self, bytes: usize) {
 549         self.position += bytes;
 550     }
 551 }
 552
 553 macro_rules! read_leb128 {
 554     ($dec:expr, $fun:ident) => {{ leb128::$fun($dec.data, &mut $dec.position) }};
 555 }
 556
 557 impl<'a> serialize::Decoder for Decoder<'a> {
 558     #[inline]
 559     fn read_u128(&mut self) -> u128 {
 560         read_leb128!(self, read_u128_leb128)
 561     }
 562
 563     #[inline]
 564     fn read_u64(&mut self) -> u64 {
 565         read_leb128!(self, read_u64_leb128)
 566     }
 567
 568     #[inline]
 569     fn read_u32(&mut self) -> u32 {
 570         read_leb128!(self, read_u32_leb128)
 571     }
 572
 573     #[inline]
 574     fn read_u16(&mut self) -> u16 {
 575         let bytes = [self.data[self.position], self.data[self.position + 1]];
 576         let value = u16::from_le_bytes(bytes);
 577         self.position += 2;
 578         value
 579     }
 580
 581     #[inline]
 582     fn read_u8(&mut self) -> u8 {
 583         let value = self.data[self.position];
 584         self.position += 1;
 585         value
 586     }
 587
 588     #[inline]
 589     fn read_usize(&mut self) -> usize {
 590         read_leb128!(self, read_usize_leb128)
 591     }
 592
 593     #[inline]
 594     fn read_i128(&mut self) -> i128 {
 595         read_leb128!(self, read_i128_leb128)
 596     }
 597
 598     #[inline]
 599     fn read_i64(&mut self) -> i64 {
 600         read_leb128!(self, read_i64_leb128)
 601     }
 602
 603     #[inline]
 604     fn read_i32(&mut self) -> i32 {
 605         read_leb128!(self, read_i32_leb128)
 606     }
 607
 608     #[inline]
 609     fn read_i16(&mut self) -> i16 {
 610         let bytes = [self.data[self.position], self.data[self.position + 1]];
 611         let value = i16::from_le_bytes(bytes);
 612         self.position += 2;
 613         value
 614     }
 615
 616     #[inline]
 617     fn read_i8(&mut self) -> i8 {
 618         let value = self.data[self.position];
 619         self.position += 1;
 620         value as i8
 621     }
 622
 623     #[inline]
 624     fn read_isize(&mut self) -> isize {
 625         read_leb128!(self, read_isize_leb128)
 626     }
 627
 628     #[inline]
 629     fn read_bool(&mut self) -> bool {
 630         let value = self.read_u8();
 631         value != 0
 632     }
 633
 634     #[inline]
 635     fn read_f64(&mut self) -> f64 {
 636         let bits = self.read_u64();
 637         f64::from_bits(bits)
 638     }
 639
 640     #[inline]
 641     fn read_f32(&mut self) -> f32 {
 642         let bits = self.read_u32();
 643         f32::from_bits(bits)
 644     }
 645
 646     #[inline]
 647     fn read_char(&mut self) -> char {
 648         let bits = self.read_u32();
 649         std::char::from_u32(bits).unwrap()
 650     }
 651
 652     #[inline]
 653     fn read_str(&mut self) -> &'a str {
 654         let len = self.read_usize();
 655         let sentinel = self.data[self.position + len];
 656         assert!(sentinel == STR_SENTINEL);
 657         let s = unsafe {
 658             std::str::from_utf8_unchecked(&self.data[self.position..self.position + len])
 659         };
 660         self.position += len + 1;
 661         s
 662     }
 663
 664     #[inline]
 665     fn read_raw_bytes(&mut self, bytes: usize) -> &'a [u8] {
 666         let start = self.position;
 667         self.position += bytes;
 668         &self.data[start..self.position]
 669     }
 670 }
 671
 672 // Specializations for contiguous byte sequences follow. The default implementations for slices
 673 // encode and decode each element individually. This isn't necessary for `u8` slices when using
 674 // opaque encoders and decoders, because each `u8` is unchanged by encoding and decoding.
 675 // Therefore, we can use more efficient implementations that process the entire sequence at once.
 676
 677 // Specialize encoding byte slices. This specialization also applies to encoding `Vec<u8>`s, etc.,
 678 // since the default implementations call `encode` on their slices internally.
 679 impl serialize::Encodable<Encoder> for [u8] {
 680     fn encode(&self, e: &mut Encoder) -> EncodeResult {
 681         serialize::Encoder::emit_usize(e, self.len())?;
 682         e.emit_raw_bytes(self)
 683     }
 684 }
 685
 686 impl serialize::Encodable<FileEncoder> for [u8] {
 687     fn encode(&self, e: &mut FileEncoder) -> FileEncodeResult {
 688         serialize::Encoder::emit_usize(e, self.len())?;
 689         e.emit_raw_bytes(self)
 690     }
 691 }
 692
 693 // Specialize decoding `Vec<u8>`. This specialization also applies to decoding `Box<[u8]>`s, etc.,
 694 // since the default implementations call `decode` to produce a `Vec<u8>` internally.
 695 impl<'a> serialize::Decodable<Decoder<'a>> for Vec<u8> {
 696     fn decode(d: &mut Decoder<'a>) -> Self {
 697         let len = serialize::Decoder::read_usize(d);
 698         d.read_raw_bytes(len).to_owned()
 699     }
 700 }
 701
 702 // An integer that will always encode to 8 bytes.
 703 pub struct IntEncodedWithFixedSize(pub u64);
 704
 705 impl IntEncodedWithFixedSize {
 706     pub const ENCODED_SIZE: usize = 8;
 707 }
 708
 709 impl serialize::Encodable<Encoder> for IntEncodedWithFixedSize {
 710     #[inline]
 711     fn encode(&self, e: &mut Encoder) -> EncodeResult {
 712         let _start_pos = e.position();
 713         e.emit_raw_bytes(&self.0.to_le_bytes())?;
 714         let _end_pos = e.position();
 715         debug_assert_eq!((_end_pos - _start_pos), IntEncodedWithFixedSize::ENCODED_SIZE);
 716         Ok(())
 717     }
 718 }
 719
 720 impl serialize::Encodable<FileEncoder> for IntEncodedWithFixedSize {
 721     #[inline]
 722     fn encode(&self, e: &mut FileEncoder) -> FileEncodeResult {
 723         let _start_pos = e.position();
 724         e.emit_raw_bytes(&self.0.to_le_bytes())?;
 725         let _end_pos = e.position();
 726         debug_assert_eq!((_end_pos - _start_pos), IntEncodedWithFixedSize::ENCODED_SIZE);
 727         Ok(())
 728     }
 729 }
 730
 731 impl<'a> serialize::Decodable<Decoder<'a>> for IntEncodedWithFixedSize {
 732     #[inline]
 733     fn decode(decoder: &mut Decoder<'a>) -> IntEncodedWithFixedSize {
 734         let _start_pos = decoder.position();
 735         let bytes = decoder.read_raw_bytes(IntEncodedWithFixedSize::ENCODED_SIZE);
 736         let value = u64::from_le_bytes(bytes.try_into().unwrap());
 737         let _end_pos = decoder.position();
 738         debug_assert_eq!((_end_pos - _start_pos), IntEncodedWithFixedSize::ENCODED_SIZE);
 739
 740         IntEncodedWithFixedSize(value)
 741     }
 742 }