From ec0e0ec0797e7c772c03e21ff02d561777c3d915 Mon Sep 17 00:00:00 2001
From: CheddarCrisp <cheddar@crispbyte.com>
Date: Tue, 9 Jan 2024 21:04:25 -0500
Subject: [PATCH] Decoder implementation

---
 SDBD.Codec/Codec.cs          | 47 ++++++++++++++++++++++++++++++------
 SDBD.Codec/HeaderListener.cs | 16 ++++++++++++
 2 files changed, 56 insertions(+), 7 deletions(-)
 create mode 100644 SDBD.Codec/HeaderListener.cs

diff --git a/SDBD.Codec/Codec.cs b/SDBD.Codec/Codec.cs
index a9593c7..1f72257 100644
--- a/SDBD.Codec/Codec.cs
+++ b/SDBD.Codec/Codec.cs
@@ -2,12 +2,14 @@
 
 public class Codec : ICodec {
   public Document Decode(byte[] data) {
-    return new(
-      new () {
-        { "content-name", "text.txt" }
-      },
-      data
-    );
+    using var input = new MemoryStream(data);
+
+    var version = input.ReadByte();
+
+    return version switch {
+      0x01 => DecodeV1(input),
+      _ => throw new Exception("Unsupported version")
+    };
   }
 
   public byte[] Encode(Document document) {
@@ -29,9 +31,40 @@ public class Codec : ICodec {
     return output.ToArray();
   }
 
+  private Document DecodeV1(Stream stream) {
+    var headerLengthBytes = new byte[2];
+    stream.ReadExactly(headerLengthBytes);
+
+    var headerLength = BitConverter.ToUInt16(headerLengthBytes);
+
+    var headerBytes = new byte[headerLength];
+    stream.ReadExactly(headerBytes);
+
+    var headers = unpackHeaders(headerBytes);
+    string contentLengthString;
+    headers.Remove("content-length", out contentLengthString);
+    var contentLength = int.Parse(contentLengthString);
+
+    var data = new byte[contentLength];
+    stream.ReadExactly(data);
+
+    return new Document(headers, data);
+  }
+
+  private Dictionary<string, string> unpackHeaders(byte[] packedHeaders) {
+    var decoder = new hpack.Decoder(8192, 4096);
+    var listener = new HeaderListener();
+
+    using var reader = new BinaryReader(new MemoryStream(packedHeaders));
+    decoder.Decode(reader, listener);
+    decoder.EndHeaderBlock();
+
+    return listener.Headers;
+  }
+
   private byte[] packHeaders(IEnumerable<KeyValuePair<string, string>> headers) {
     var encoder = new hpack.Encoder(0); //0 will disable dynamic table that we don't need anyways
-    
+
     using var output = new MemoryStream();
     using var writer = new BinaryWriter(output);
 
diff --git a/SDBD.Codec/HeaderListener.cs b/SDBD.Codec/HeaderListener.cs
new file mode 100644
index 0000000..0abaaf3
--- /dev/null
+++ b/SDBD.Codec/HeaderListener.cs
@@ -0,0 +1,16 @@
+using System.Text;
+
+internal class HeaderListener : hpack.IHeaderListener {
+  public Dictionary<string, string> Headers { get; private set; }
+
+  public HeaderListener() {
+    Headers = new Dictionary<string, string>();
+  }
+
+  public void AddHeader(byte[] nameBytes, byte[] valueBytes, bool sensitive) {
+    var name = Encoding.UTF8.GetString(nameBytes);
+    var value = Encoding.UTF8.GetString(valueBytes);
+
+    Headers.Add(name, value);
+  }
+}