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Deflate sample sniffing "deflate" vs "zlib" format #133

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Deflate sample sniffing "deflate" vs "zlib" format #133

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67 changes: 62 additions & 5 deletions eg/Program.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,10 +7,12 @@ namespace WebLinq.Samples
using System.Data;
using System.Globalization;
using System.IO;
using System.IO.Compression;
using System.Linq;
using System.Net;
using System.Reactive.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Text.RegularExpressions;
using System.Xml.Linq;
using Dsv;
Expand Down Expand Up @@ -362,11 +364,66 @@ from e in Http.Get(FormatUri($@"http://httpbin.org/redirect-to

static IObservable<object> Compression() =>

Http.Get(new Uri("https://httpbin.org/gzip"))
.Accept("application/json")
.AutomaticDecompression(DecompressionMethods.GZip)
.Text()
.Content();
from f in
Observable.Concat(
Http.Get(new Uri("https://httpbin.org/gzip"))
.Accept("application/json")
.AutomaticDecompression(DecompressionMethods.GZip)
.Text(),
Http.Get(new Uri("https://httpbin.org/deflate"))
.Accept("application/json")
.ReadContent(async f =>
{
string contentEncoding = f.ContentHeaders["Content-Encoding"];
if (string.IsNullOrEmpty(contentEncoding))
return await f.Content.ReadAsStringAsync().ConfigureAwait(false);

if (!"deflate".Equals(contentEncoding, StringComparison.OrdinalIgnoreCase))
throw new NotSupportedException($"Unsupported content encoding: {contentEncoding}");

var data = await f.Content.ReadAsByteArrayAsync().ConfigureAwait(false);
using (var input = new MemoryStream(data))
using (var output = new MemoryStream())
{
// DeflateStream chokes on the "zlib" format, which is
// what an encoding of "deflate" means; see section
// 4.2.2, "Delate Encoding" of the HTTP specification:
// https://tools.ietf.org/html/rfc7230#section-4.2.2
//
// So sniff whether the actual format is "deflate" or
// "zlib". Since "zlib" is generally a header plus
// "deflate" data, one can strip out the header and
// just feed the rest to DeflateStream.
//
// For more information:
// https://github.com/weblinq/WebLinq/issues/132

// A zlib stream starts with a 2 byte header: CMF + FLG
//
// where CMF is two nibbles:
//
// - bits 0 to 3 CM Compression method
// - bits 4 to 7 CINFO Compression info
//
// CM = 8 denotes the "deflate" compression method with
// a window size up to 32K.
//
// Source: https://tools.ietf.org/html/rfc1950

var cm = input.ReadByte() & 0x0f;
if (cm == 8) // 8 = deflate
input.ReadByte(); // skip second header byte (FLG)
else
input.Position = 0; // rewind; this is the naked "deflate" format

using (var ds = new DeflateStream(input, CompressionMode.Decompress))
ds.CopyTo(output);

var encoding = f.ContentCharSetEncoding ?? Encoding.UTF8;
return encoding.GetString(output.GetBuffer(), 0, (int) output.Length);
}
}))
select f.Content;

static IObservable<object> FormPost() =>

Expand Down