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
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
use {codec, AsyncRead, AsyncWrite};

use bytes::{Buf, BufMut, BytesMut, IntoBuf, BigEndian, LittleEndian};
use bytes::buf::Chain;

use futures::{Async, AsyncSink, Stream, Sink, StartSend, Poll};

use std::{cmp, fmt};
use std::error::Error as StdError;
use std::io::{self, Cursor};

/// Configure length delimited `FramedRead`, `FramedWrite`, and `Framed` values.
///
/// `Builder` enables constructing configured length delimited framers. Note
/// that not all configuration settings apply to both encoding and decoding. See
/// the documentation for specific methods for more detail.
#[derive(Debug, Clone, Copy)]
pub struct Builder {
    // Maximum frame length
    max_frame_len: usize,

    // Number of bytes representing the field length
    length_field_len: usize,

    // Number of bytes in the header before the length field
    length_field_offset: usize,

    // Adjust the length specified in the header field by this amount
    length_adjustment: isize,

    // Total number of bytes to skip before reading the payload, if not set,
    // `length_field_len + length_field_offset`
    num_skip: Option<usize>,

    // Length field byte order (little or big endian)
    length_field_is_big_endian: bool,
}

/// Adapts a byte stream into a unified `Stream` and `Sink` that works over
/// entire frame values.
///
/// See [module level] documentation for more detail.
///
/// [module level]: index.html
pub struct Framed<T, B: IntoBuf = BytesMut> {
    inner: FramedRead<FramedWrite<T, B>>,
}

/// Adapts a byte stream to a `Stream` yielding entire frame values.
///
/// See [module level] documentation for more detail.
///
/// [module level]: index.html
#[derive(Debug)]
pub struct FramedRead<T> {
    inner: codec::FramedRead<T, Decoder>,
}

/// An error when the number of bytes read is more than max frame length.
pub struct FrameTooBig {
    _priv: (),
}

#[derive(Debug)]
struct Decoder {
    // Configuration values
    builder: Builder,

    // Read state
    state: DecodeState,
}

#[derive(Debug, Clone, Copy)]
enum DecodeState {
    Head,
    Data(usize),
}

/// Adapts a byte stream to a `Sink` accepting entire frame values.
///
/// See [module level] documentation for more detail.
///
/// [module level]: index.html
pub struct FramedWrite<T, B: IntoBuf = BytesMut> {
    // I/O type
    inner: T,

    // Configuration values
    builder: Builder,

    // Current frame being written
    frame: Option<Chain<Cursor<BytesMut>, B::Buf>>,
}

// ===== impl Framed =====

impl<T: AsyncRead + AsyncWrite, B: IntoBuf> Framed<T, B> {
    /// Creates a new `Framed` with default configuration values.
    pub fn new(inner: T) -> Framed<T, B> {
        Builder::new().new_framed(inner)
    }
}

impl<T, B: IntoBuf> Framed<T, B> {
    /// Returns a reference to the underlying I/O stream wrapped by `Framed`.
    ///
    /// Note that care should be taken to not tamper with the underlying stream
    /// of data coming in as it may corrupt the stream of frames otherwise
    /// being worked with.
    pub fn get_ref(&self) -> &T {
        self.inner.get_ref().get_ref()
    }

    /// Returns a mutable reference to the underlying I/O stream wrapped by
    /// `Framed`.
    ///
    /// Note that care should be taken to not tamper with the underlying stream
    /// of data coming in as it may corrupt the stream of frames otherwise being
    /// worked with.
    pub fn get_mut(&mut self) -> &mut T {
        self.inner.get_mut().get_mut()
    }

    /// Consumes the `Framed`, returning its underlying I/O stream.
    ///
    /// Note that care should be taken to not tamper with the underlying stream
    /// of data coming in as it may corrupt the stream of frames otherwise being
    /// worked with.
    pub fn into_inner(self) -> T {
        self.inner.into_inner().into_inner()
    }
}

impl<T: AsyncRead, B: IntoBuf> Stream for Framed<T, B> {
    type Item = BytesMut;
    type Error = io::Error;

    fn poll(&mut self) -> Poll<Option<BytesMut>, io::Error> {
        self.inner.poll()
    }
}

impl<T: AsyncWrite, B: IntoBuf> Sink for Framed<T, B> {
    type SinkItem = B;
    type SinkError = io::Error;

    fn start_send(&mut self, item: B) -> StartSend<B, io::Error> {
        self.inner.start_send(item)
    }

    fn poll_complete(&mut self) -> Poll<(), io::Error> {
        self.inner.poll_complete()
    }

    fn close(&mut self) -> Poll<(), io::Error> {
        self.inner.close()
    }
}

impl<T, B: IntoBuf> fmt::Debug for Framed<T, B>
    where T: fmt::Debug,
          B::Buf: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("Framed")
            .field("inner", &self.inner)
            .finish()
    }
}

// ===== impl FramedRead =====

impl<T: AsyncRead> FramedRead<T> {
    /// Creates a new `FramedRead` with default configuration values.
    pub fn new(inner: T) -> FramedRead<T> {
        Builder::new().new_read(inner)
    }
}

impl<T> FramedRead<T> {
    /// Returns the current max frame setting
    ///
    /// This is the largest size this codec will accept from the wire. Larger
    /// frames will be rejected.
    pub fn max_frame_length(&self) -> usize {
        self.inner.decoder().builder.max_frame_len
    }

    /// Updates the max frame setting.
    ///
    /// The change takes effect the next time a frame is decoded. In other
    /// words, if a frame is currently in process of being decoded with a frame
    /// size greater than `val` but less than the max frame length in effect
    /// before calling this function, then the frame will be allowed.
    pub fn set_max_frame_length(&mut self, val: usize) {
        self.inner.decoder_mut().builder.max_frame_length(val);
    }

    /// Returns a reference to the underlying I/O stream wrapped by `FramedRead`.
    ///
    /// Note that care should be taken to not tamper with the underlying stream
    /// of data coming in as it may corrupt the stream of frames otherwise
    /// being worked with.
    pub fn get_ref(&self) -> &T {
        self.inner.get_ref()
    }

    /// Returns a mutable reference to the underlying I/O stream wrapped by
    /// `FramedRead`.
    ///
    /// Note that care should be taken to not tamper with the underlying stream
    /// of data coming in as it may corrupt the stream of frames otherwise being
    /// worked with.
    pub fn get_mut(&mut self) -> &mut T {
        self.inner.get_mut()
    }

    /// Consumes the `FramedRead`, returning its underlying I/O stream.
    ///
    /// Note that care should be taken to not tamper with the underlying stream
    /// of data coming in as it may corrupt the stream of frames otherwise being
    /// worked with.
    pub fn into_inner(self) -> T {
        self.inner.into_inner()
    }
}

impl<T: AsyncRead> Stream for FramedRead<T> {
    type Item = BytesMut;
    type Error = io::Error;

    fn poll(&mut self) -> Poll<Option<BytesMut>, io::Error> {
        self.inner.poll()
    }
}

impl<T: Sink> Sink for FramedRead<T> {
    type SinkItem = T::SinkItem;
    type SinkError = T::SinkError;

    fn start_send(&mut self, item: T::SinkItem) -> StartSend<T::SinkItem, T::SinkError> {
        self.inner.start_send(item)
    }

    fn poll_complete(&mut self) -> Poll<(), T::SinkError> {
        self.inner.poll_complete()
    }

    fn close(&mut self) -> Poll<(), T::SinkError> {
        self.inner.close()
    }
}

impl<T: io::Write> io::Write for FramedRead<T> {
    fn write(&mut self, src: &[u8]) -> io::Result<usize> {
        self.inner.get_mut().write(src)
    }

    fn flush(&mut self) -> io::Result<()> {
        self.inner.get_mut().flush()
    }
}

impl<T: AsyncWrite> AsyncWrite for FramedRead<T> {
    fn shutdown(&mut self) -> Poll<(), io::Error> {
        self.inner.get_mut().shutdown()
    }

    fn write_buf<B: Buf>(&mut self, buf: &mut B) -> Poll<usize, io::Error> {
        self.inner.get_mut().write_buf(buf)
    }
}

// ===== impl Decoder ======

impl Decoder {
    fn decode_head(&mut self, src: &mut BytesMut) -> io::Result<Option<usize>> {
        let head_len = self.builder.num_head_bytes();
        let field_len = self.builder.length_field_len;

        if src.len() < head_len {
            // Not enough data
            return Ok(None);
        }

        let n = {
            let mut src = Cursor::new(&mut *src);

            // Skip the required bytes
            src.advance(self.builder.length_field_offset);

            // match endianess
            let n = if self.builder.length_field_is_big_endian {
                src.get_uint::<BigEndian>(field_len)
            } else {
                src.get_uint::<LittleEndian>(field_len)
            };

            if n > self.builder.max_frame_len as u64 {
                return Err(io::Error::new(io::ErrorKind::InvalidData, FrameTooBig {
                    _priv: (),
                }));
            }

            // The check above ensures there is no overflow
            let n = n as usize;

            // Adjust `n` with bounds checking
            let n = if self.builder.length_adjustment < 0 {
                n.checked_sub(-self.builder.length_adjustment as usize)
            } else {
                n.checked_add(self.builder.length_adjustment as usize)
            };

            // Error handling
            match n {
                Some(n) => n,
                None => return Err(io::Error::new(io::ErrorKind::InvalidInput, "provided length would overflow after adjustment")),
            }
        };

        let num_skip = self.builder.get_num_skip();

        if num_skip > 0 {
            let _ = src.split_to(num_skip);
        }

        // Ensure that the buffer has enough space to read the incoming
        // payload
        src.reserve(n);

        return Ok(Some(n));
    }

    fn decode_data(&self, n: usize, src: &mut BytesMut) -> io::Result<Option<BytesMut>> {
        // At this point, the buffer has already had the required capacity
        // reserved. All there is to do is read.
        if src.len() < n {
            return Ok(None);
        }

        Ok(Some(src.split_to(n)))
    }
}

impl codec::Decoder for Decoder {
    type Item = BytesMut;
    type Error = io::Error;

    fn decode(&mut self, src: &mut BytesMut) -> io::Result<Option<BytesMut>> {
        let n = match self.state {
            DecodeState::Head => {
                match try!(self.decode_head(src)) {
                    Some(n) => {
                        self.state = DecodeState::Data(n);
                        n
                    }
                    None => return Ok(None),
                }
            }
            DecodeState::Data(n) => n,
        };

        match try!(self.decode_data(n, src)) {
            Some(data) => {
                // Update the decode state
                self.state = DecodeState::Head;

                // Make sure the buffer has enough space to read the next head
                src.reserve(self.builder.num_head_bytes());

                Ok(Some(data))
            }
            None => Ok(None),
        }
    }
}

// ===== impl FramedWrite =====

impl<T: AsyncWrite, B: IntoBuf> FramedWrite<T, B> {
    /// Creates a new `FramedWrite` with default configuration values.
    pub fn new(inner: T) -> FramedWrite<T, B> {
        Builder::new().new_write(inner)
    }
}

impl<T, B: IntoBuf> FramedWrite<T, B> {
    /// Returns a reference to the underlying I/O stream wrapped by
    /// `FramedWrite`.
    ///
    /// Note that care should be taken to not tamper with the underlying stream
    /// of data coming in as it may corrupt the stream of frames otherwise
    /// being worked with.
    pub fn get_ref(&self) -> &T {
        &self.inner
    }

    /// Returns a mutable reference to the underlying I/O stream wrapped by
    /// `FramedWrite`.
    ///
    /// Note that care should be taken to not tamper with the underlying stream
    /// of data coming in as it may corrupt the stream of frames otherwise being
    /// worked with.
    pub fn get_mut(&mut self) -> &mut T {
        &mut self.inner
    }

    /// Consumes the `FramedWrite`, returning its underlying I/O stream.
    ///
    /// Note that care should be taken to not tamper with the underlying stream
    /// of data coming in as it may corrupt the stream of frames otherwise being
    /// worked with.
    pub fn into_inner(self) -> T {
        self.inner
    }
}

impl<T: AsyncWrite, B: IntoBuf> FramedWrite<T, B> {
    // If there is a buffered frame, try to write it to `T`
    fn do_write(&mut self) -> Poll<(), io::Error> {
        if self.frame.is_none() {
            return Ok(Async::Ready(()));
        }

        loop {
            let frame = self.frame.as_mut().unwrap();
            try_ready!(self.inner.write_buf(frame));

            if !frame.has_remaining() {
                break;
            }
        }

        self.frame = None;

        Ok(Async::Ready(()))
    }

    fn set_frame(&mut self, buf: B::Buf) -> io::Result<()> {
        let mut head = BytesMut::with_capacity(8);
        let n = buf.remaining();

        if n > self.builder.max_frame_len {
            return Err(io::Error::new(io::ErrorKind::InvalidInput, FrameTooBig {
                _priv: (),
            }));
        }

        // Adjust `n` with bounds checking
        let n = if self.builder.length_adjustment < 0 {
            n.checked_add(-self.builder.length_adjustment as usize)
        } else {
            n.checked_sub(self.builder.length_adjustment as usize)
        };

        // Error handling
        let n = match n {
            Some(n) => n,
            None => return Err(io::Error::new(io::ErrorKind::InvalidInput, "provided length would overflow after adjustment")),
        };

        if self.builder.length_field_is_big_endian {
            head.put_uint::<BigEndian>(n as u64, self.builder.length_field_len);
        } else {
            head.put_uint::<LittleEndian>(n as u64, self.builder.length_field_len);
        }

        debug_assert!(self.frame.is_none());

        self.frame = Some(head.into_buf().chain(buf));

        Ok(())
    }
}

impl<T: AsyncWrite, B: IntoBuf> Sink for FramedWrite<T, B> {
    type SinkItem = B;
    type SinkError = io::Error;

    fn start_send(&mut self, item: B) -> StartSend<B, io::Error> {
        if !try!(self.do_write()).is_ready() {
            return Ok(AsyncSink::NotReady(item));
        }

        try!(self.set_frame(item.into_buf()));

        Ok(AsyncSink::Ready)
    }

    fn poll_complete(&mut self) -> Poll<(), io::Error> {
        // Write any buffered frame to T
        try_ready!(self.do_write());

        // Try flushing the underlying IO
        try_nb!(self.inner.flush());

        return Ok(Async::Ready(()));
    }

    fn close(&mut self) -> Poll<(), io::Error> {
        try_ready!(self.poll_complete());
        self.inner.shutdown()
    }
}

impl<T: Stream, B: IntoBuf> Stream for FramedWrite<T, B> {
    type Item = T::Item;
    type Error = T::Error;

    fn poll(&mut self) -> Poll<Option<T::Item>, T::Error> {
        self.inner.poll()
    }
}

impl<T: io::Read, B: IntoBuf> io::Read for FramedWrite<T, B> {
    fn read(&mut self, dst: &mut [u8]) -> io::Result<usize> {
        self.get_mut().read(dst)
    }
}

impl<T: AsyncRead, U: IntoBuf> AsyncRead for FramedWrite<T, U> {
    fn read_buf<B: BufMut>(&mut self, buf: &mut B) -> Poll<usize, io::Error> {
        self.get_mut().read_buf(buf)
    }

    unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool {
        self.get_ref().prepare_uninitialized_buffer(buf)
    }
}

impl<T, B: IntoBuf> fmt::Debug for FramedWrite<T, B>
    where T: fmt::Debug,
          B::Buf: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("FramedWrite")
            .field("inner", &self.inner)
            .field("builder", &self.builder)
            .field("frame", &self.frame)
            .finish()
    }
}

// ===== impl Builder =====

impl Builder {
    /// Creates a new length delimited framer builder with default configuration
    /// values.
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio_io::AsyncRead;
    /// use tokio_io::codec::length_delimited::Builder;
    ///
    /// # fn bind_read<T: AsyncRead>(io: T) {
    /// Builder::new()
    ///     .length_field_offset(0)
    ///     .length_field_length(2)
    ///     .length_adjustment(0)
    ///     .num_skip(0)
    ///     .new_read(io);
    /// # }
    /// ```
    pub fn new() -> Builder {
        Builder {
            // Default max frame length of 8MB
            max_frame_len: 8 * 1_024 * 1_024,

            // Default byte length of 4
            length_field_len: 4,

            // Default to the header field being at the start of the header.
            length_field_offset: 0,

            length_adjustment: 0,

            // Total number of bytes to skip before reading the payload, if not set,
            // `length_field_len + length_field_offset`
            num_skip: None,

            // Default to reading the length field in network (big) endian.
            length_field_is_big_endian: true,
        }
    }

    /// Read the length field as a big endian integer
    ///
    /// This is the default setting.
    ///
    /// This configuration option applies to both encoding and decoding.
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio_io::AsyncRead;
    /// use tokio_io::codec::length_delimited::Builder;
    ///
    /// # fn bind_read<T: AsyncRead>(io: T) {
    /// Builder::new()
    ///     .big_endian()
    ///     .new_read(io);
    /// # }
    /// ```
    pub fn big_endian(&mut self) -> &mut Self {
        self.length_field_is_big_endian = true;
        self
    }

    /// Read the length field as a little endian integer
    ///
    /// The default setting is big endian.
    ///
    /// This configuration option applies to both encoding and decoding.
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio_io::AsyncRead;
    /// use tokio_io::codec::length_delimited::Builder;
    ///
    /// # fn bind_read<T: AsyncRead>(io: T) {
    /// Builder::new()
    ///     .little_endian()
    ///     .new_read(io);
    /// # }
    /// ```
    pub fn little_endian(&mut self) -> &mut Self {
        self.length_field_is_big_endian = false;
        self
    }

    /// Sets the max frame length
    ///
    /// This configuration option applies to both encoding and decoding. The
    /// default value is 8MB.
    ///
    /// When decoding, the length field read from the byte stream is checked
    /// against this setting **before** any adjustments are applied. When
    /// encoding, the length of the submitted payload is checked against this
    /// setting.
    ///
    /// When frames exceed the max length, an `io::Error` with the custom value
    /// of the `FrameTooBig` type will be returned.
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio_io::AsyncRead;
    /// use tokio_io::codec::length_delimited::Builder;
    ///
    /// # fn bind_read<T: AsyncRead>(io: T) {
    /// Builder::new()
    ///     .max_frame_length(8 * 1024)
    ///     .new_read(io);
    /// # }
    /// ```
    pub fn max_frame_length(&mut self, val: usize) -> &mut Self {
        self.max_frame_len = val;
        self
    }

    /// Sets the number of bytes used to represent the length field
    ///
    /// The default value is `4`. The max value is `8`.
    ///
    /// This configuration option applies to both encoding and decoding.
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio_io::AsyncRead;
    /// use tokio_io::codec::length_delimited::Builder;
    ///
    /// # fn bind_read<T: AsyncRead>(io: T) {
    /// Builder::new()
    ///     .length_field_length(4)
    ///     .new_read(io);
    /// # }
    /// ```
    pub fn length_field_length(&mut self, val: usize) -> &mut Self {
        assert!(val > 0 && val <= 8, "invalid length field length");
        self.length_field_len = val;
        self
    }

    /// Sets the number of bytes in the header before the length field
    ///
    /// This configuration option only applies to decoding.
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio_io::AsyncRead;
    /// use tokio_io::codec::length_delimited::Builder;
    ///
    /// # fn bind_read<T: AsyncRead>(io: T) {
    /// Builder::new()
    ///     .length_field_offset(1)
    ///     .new_read(io);
    /// # }
    /// ```
    pub fn length_field_offset(&mut self, val: usize) -> &mut Self {
        self.length_field_offset = val;
        self
    }

    /// Delta between the payload length specified in the header and the real
    /// payload length
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio_io::AsyncRead;
    /// use tokio_io::codec::length_delimited::Builder;
    ///
    /// # fn bind_read<T: AsyncRead>(io: T) {
    /// Builder::new()
    ///     .length_adjustment(-2)
    ///     .new_read(io);
    /// # }
    /// ```
    pub fn length_adjustment(&mut self, val: isize) -> &mut Self {
        self.length_adjustment = val;
        self
    }

    /// Sets the number of bytes to skip before reading the payload
    ///
    /// Default value is `length_field_len + length_field_offset`
    ///
    /// This configuration option only applies to decoding
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio_io::AsyncRead;
    /// use tokio_io::codec::length_delimited::Builder;
    ///
    /// # fn bind_read<T: AsyncRead>(io: T) {
    /// Builder::new()
    ///     .num_skip(4)
    ///     .new_read(io);
    /// # }
    /// ```
    pub fn num_skip(&mut self, val: usize) -> &mut Self {
        self.num_skip = Some(val);
        self
    }

    /// Create a configured length delimited `FramedRead`
    ///
    /// # Examples
    ///
    /// ```
    /// # use tokio_io::AsyncRead;
    /// use tokio_io::codec::length_delimited::Builder;
    ///
    /// # fn bind_read<T: AsyncRead>(io: T) {
    /// Builder::new()
    ///     .length_field_offset(0)
    ///     .length_field_length(2)
    ///     .length_adjustment(0)
    ///     .num_skip(0)
    ///     .new_read(io);
    /// # }
    /// ```
    pub fn new_read<T>(&self, upstream: T) -> FramedRead<T>
        where T: AsyncRead,
    {
        FramedRead {
            inner: codec::FramedRead::new(upstream, Decoder {
                builder: *self,
                state: DecodeState::Head,
            }),
        }
    }

    /// Create a configured length delimited `FramedWrite`
    ///
    /// # Examples
    ///
    /// ```
    /// # extern crate tokio_io;
    /// # extern crate bytes;
    /// # use tokio_io::AsyncWrite;
    /// # use tokio_io::codec::length_delimited;
    /// # use bytes::BytesMut;
    /// # fn write_frame<T: AsyncWrite>(io: T) {
    /// # let _: length_delimited::FramedWrite<T, BytesMut> =
    /// length_delimited::Builder::new()
    ///     .length_field_length(2)
    ///     .new_write(io);
    /// # }
    /// # pub fn main() {}
    /// ```
    pub fn new_write<T, B>(&self, inner: T) -> FramedWrite<T, B>
        where T: AsyncWrite,
              B: IntoBuf,
    {
        FramedWrite {
            inner: inner,
            builder: *self,
            frame: None,
        }
    }

    /// Create a configured length delimited `Framed`
    ///
    /// # Examples
    ///
    /// ```
    /// # extern crate tokio_io;
    /// # extern crate bytes;
    /// # use tokio_io::{AsyncRead, AsyncWrite};
    /// # use tokio_io::codec::length_delimited;
    /// # use bytes::BytesMut;
    /// # fn write_frame<T: AsyncRead + AsyncWrite>(io: T) {
    /// # let _: length_delimited::Framed<T, BytesMut> =
    /// length_delimited::Builder::new()
    ///     .length_field_length(2)
    ///     .new_framed(io);
    /// # }
    /// # pub fn main() {}
    /// ```
    pub fn new_framed<T, B>(&self, inner: T) -> Framed<T, B>
        where T: AsyncRead + AsyncWrite,
              B: IntoBuf
    {
        let inner = self.new_read(self.new_write(inner));
        Framed { inner: inner }
    }

    fn num_head_bytes(&self) -> usize {
        let num = self.length_field_offset + self.length_field_len;
        cmp::max(num, self.num_skip.unwrap_or(0))
    }

    fn get_num_skip(&self) -> usize {
        self.num_skip.unwrap_or(self.length_field_offset + self.length_field_len)
    }
}


// ===== impl FrameTooBig =====

impl fmt::Debug for FrameTooBig {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_struct("FrameTooBig")
            .finish()
    }
}

impl fmt::Display for FrameTooBig {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.write_str(self.description())
    }
}

impl StdError for FrameTooBig {
    fn description(&self) -> &str {
        "frame size too big"
    }
}