BrotliSharpLib

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Full C# port of Brotli compression algorithm

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# BrotliSharpLib

BrotliSharpLib is a full C# port of the brotli library/compression code [by Google](https://github.com/google/brotli). It is intended to be a mostly 1:1 conversion of the original C code. All code is correct as of v0.6.0 of the reference implementation.

The projects uses a minimal set of APIs to ensure compatibility with a wide range of frameworks including .NET Standard and .NET Core. It also supports little-endian and big-endian architectures and is optimised for x86, x64 and ARM processors.

BrotliSharpLib is licensed under [MIT](https://github.com/master131/BrotliSharpLib/blob/master/LICENSE).

## Installation
BrotliSharpLib can be installed via the NuGet package [here](https://www.nuget.org/packages/BrotliSharpLib/).
```
Install-Package BrotliSharpLib
```

## Usage
**Generic/basic usage:**
```c#
/** Decompression **/
byte[] brotliCompressedData = ...; // arbritary data source
byte[] uncompressedData = Brotli.DecompressBuffer(brotliCompressedData, 0, brotliCompressedData.Length /**, customDictionary **/);

/** Compression **/
byte[] uncompressedData = ...; // arbritary data source

// By default, brotli uses a quality value of 11 and window size of 22 if the parameters are omitted.
byte[] compressedData = Brotli.CompressBuffer(uncompressedData, 0, uncompressedData.Length /**, quality, windowSize, customDictionary **/);
```

**Stream usage:**
```c#
/** Decompression **/
using (var ms = new MemoryStream())
using (var bs = new BrotliStream(compressedStream, CompressionMode.Decompress))
{
    bs.CopyTo(ms);
}

/** Compression **/
using (var fs = File.OpenRead(filePath))
using (var ms = new MemoryStream())
{
    using (var bs = new BrotliStream(ms, CompressionMode.Compress))
    {
        // By default, BrotliSharpLib uses a quality value of 1 and window size of 22 if the methods are not called.
        /** bs.SetQuality(quality); **/
        /** bs.SetWindow(windowSize); **/
        /** bs.SetCustomDictionary(customDict); **/
        fs.CopyTo(bs);
    }

byte[] compressed = ms.ToArray();
}
```

**Real-life example:**
The following allows for acceptance and decompression of brotli encoded web content via a [HttpClient](https://msdn.microsoft.com/en-us/library/system.net.http.httpclient(v=vs.118).aspx) and falls back to gzip or deflate when required.
```c#
static class HttpClientEx
{
    private class BrotliCompressionHandler : DelegatingHandler
    {
        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            request.Headers.AcceptEncoding.Add(new StringWithQualityHeaderValue("br"));
            var response = await base.SendAsync(request, cancellationToken);
            IEnumerable<string> ce;
            if (response.Content.Headers.TryGetValues("Content-Encoding", out ce) && ce.First() == "br")
            {
                var buffer = await response.Content.ReadAsByteArrayAsync();
                response.Content = new ByteArrayContent(Brotli.DecompressBuffer(buffer, 0, buffer.Length));
            }
            return response;
        }
    }

public static HttpClient Create()
    {
        var handler = new HttpClientHandler();
        if (handler.SupportsAutomaticDecompression)
            handler.AutomaticDecompression = System.Net.DecompressionMethods.Deflate | System.Net.DecompressionMethods.GZip;
        return HttpClientFactory.Create(handler, new BrotliCompressionHandler());
    }
}
```

## Performance
### Considerations for Build
For optimal performance, ensure to build BrotliSharpLib in **Release** mode to enable all possible JIT optimisations.

Performance can also be further improved by building BrotliSharpLib using .NET Framework 4.5 or above (or any framework that supports AggressiveInlining). Selecting a specific target platform (instead of AnyCPU) where possible can also further improve performance. All of this however, is completely optional as BrotliSharpLib is designed to run in a wide range of contexts and configurations regardless.

### Benchmark

The following are benchmark results using [DotNetBenchmark](https://github.com/dotnet/BenchmarkDotNet) with BrotliSharpLib (v0.2.1) and [Google's C# implementation](https://github.com/google/brotli/tree/master/csharp/org/brotli/dec) built against .NET Framework 4.6.1. The original C version was compiled in Release mode using Visual Studio 2017 (v141) as a 64-bit Windows executable.

``` ini
BenchmarkDotNet=v0.10.6, OS=Windows 10 Redstone 2 (10.0.15063)
Processor=Intel Core i5-6600K CPU 3.50GHz (Skylake), ProcessorCount=4
Frequency=3421875 Hz, Resolution=292.2374 ns, Timer=TSC
  [Host]       : Clr 4.0.30319.42000, 64bit RyuJIT-v4.7.2046.0
  RyuJitX64    : Clr 4.0.30319.42000, 64bit RyuJIT-v4.7.2046.0
Runtime=Clr  
```
#### Decompression
File: UPX v3.91 (Windows Executable)

|         Method |     Mean |
 |--------------- |---------:|
 |     GoogleImpl | 12.75 ms |
 | BrotliSharpLib | 11.63 ms | 
 |     Original C | 11.17 ms |
 
 As seen above, BrotliSharpLib performs close to the original C version in terms of decompression.

#### Compression
 File: plrabn12.txt
 
 |         Method |  Quality |         Mean |
 |--------------- |--------- |-------------:|
 | BrotliSharpLib |        1 |     9.132 ms |
 |     Original C |        1 |     9.570 ms |
 | BrotliSharpLib |        6 |    58.720 ms |
 |     Original C |        6 |    36.540 ms |
 | BrotliSharpLib |        9 |   116.318 ms |
 |     Original C |        9 |    73.080 ms |
 | BrotliSharpLib |       11 |  1822.702 ms |
 |     Original C |       11 |    877.58 ms |
 
 While BrotliSharpLib performs comparatively at lower quality levels, it performs up to three times worse at level 11. Future versions of the port will hopefully bring this down.

BrotliSharpLib

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