From 6bf2d98114399ca05bc09b67b15701edb63a02d3 Mon Sep 17 00:00:00 2001
From: Atif Aziz <code@raboof.com>
Date: Fri, 17 Apr 2020 14:19:45 +0200
Subject: [PATCH] Add deflate sample sniffing deflate vs zlib format
---
eg/Program.cs | 67 +++++++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 62 insertions(+), 5 deletions(-)
diff --git a/eg/Program.cs b/eg/Program.cs
index f84b9cf..3e4739b 100644
--- a/eg/Program.cs
+++ b/eg/Program.cs
@@ -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;
@@ -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() =>