pions / transport / 35

91%

master: 89%

Pull #7

travis-ci

Add packetio interface for network buffering

We're not able to use `bytes.Buffer` because it would combine multiple
Writes into a single Read. `packetio.Buffer` provides a similar but is
designed to work with packets, avoiding this situation.

There are similar buffers implemented separarely in webrtc/srtp/ice/mux.
These used channels and were too slow to keep up with the read loop. I
wrote a benchmark for comparison:

```
name                   old time/op    new time/op     delta
BenchmarkBuffer14-8       859ns ± 5%      129ns ± 4%   -84.93%
BenchmarkBuffer140-8      832ns ± 4%      154ns ± 4%   -81.43%
BenchmarkBuffer1400-8     825ns ± 8%      351ns ± 4%   -57.49%

name                   old speed      new speed       delta
BenchmarkBuffer14-8    16.3MB/s ± 5%  107.8MB/s ± 3%  +561.08%
BenchmarkBuffer140-8    168MB/s ± 4%    904MB/s ± 4%  +436.70%
BenchmarkBuffer1400-8  1.70GB/s ± 8%   3.99GB/s ± 4%  +134.74%
```

Note that the channel implementation has no buffer. packetio.Buffer has
a configurable buffer size with `SetLimitCount` and `SetLimitSize`.

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