From a543c9faee47c33d1f081f9c9b41b9281f7540df Mon Sep 17 00:00:00 2001
From: NZSmartie <nzsmartie@gmail.com>
Date: Fri, 23 Mar 2018 09:59:40 +1300
Subject: [PATCH] Coorect the byte order in Block1/Block2 as it was backwards

Relevant tweet: https://twitter.com/NZSmartie/status/976926060938805249
---
 src/CoAPNet/Options/BlockWise.cs        | 37 ++++++-------------------
 tests/CoAPNet.Tests/CoapOptionsTests.cs | 19 +++++++------
 2 files changed, 18 insertions(+), 38 deletions(-)

diff --git a/src/CoAPNet/Options/BlockWise.cs b/src/CoAPNet/Options/BlockWise.cs
index 8589912..9ec6396 100644
--- a/src/CoAPNet/Options/BlockWise.cs
+++ b/src/CoAPNet/Options/BlockWise.cs
@@ -113,28 +113,18 @@ public override void FromBytes(byte[] data)
                 BlockNumber = 0;
                 last = 0;
             }
-            else if (data.Length == 1)
+            else if (data.Length <= 3)
             {
-                BlockNumber = (int)ValueUInt & 0x0F;
-                last = (ValueUInt & 0xF0) >> 4;
-            }
-            else if (data.Length == 2)
-            {
-                BlockNumber = (int)ValueUInt & 0x0FFF;
-                last = (ValueUInt & 0xF000) >> 12;
-            }
-            else if (data.Length == 3)
-            {
-                BlockNumber = (int)ValueUInt & 0x0FFFFF;
-                last = (ValueUInt & 0xF00000) >> 20;
+                BlockNumber = (int)(ValueUInt & 0xFFFFF0) >> 4;
+                last = ValueUInt & 0x0F;
             }
             else
             {
                 throw new CoapOptionException($"Invalid length ({data.Length}) of Block1/Block2 option");
             }
 
-            IsMoreFollowing = (last & 0x01) > 0;
-            var szx = (int)((last >> 1));
+            IsMoreFollowing = (last & 0x08) > 0;
+            var szx = (int)((last & 0x07));
             BlockSize = InternalSupportedBlockSizes.First(b => b.Item1 == szx).Item2;
         }
 
@@ -142,21 +132,10 @@ public override void FromBytes(byte[] data)
         public override byte[] GetBytes()
         {
             var szx = InternalSupportedBlockSizes.First(b => b.Item2 == BlockSize).Item1;
-            var last = (byte)((szx & 0x07) << 5) | (IsMoreFollowing ? 0x10 : 0x00);
-
-            if (BlockNumber <= 0x0F)
-            {
-                ValueUInt = (uint)(last | (BlockNumber & 0x0F));
-            }
-            else if (BlockNumber <= 0x0FFF)
-            {
-                ValueUInt = (uint)((last << 8) | (BlockNumber & 0x0FFF));
-            }
-            else if (BlockNumber <= 0x0FFFFF)
-            {
-                ValueUInt = (uint)((last << 16) | (BlockNumber & 0x0FFFFF));
-            }
+            var last = (byte)((szx & 0x07) | (IsMoreFollowing ? 0x08 : 0x00));
 
+            ValueUInt = (uint)(last | ((BlockNumber << 4) & 0xFFFFF0));
+            
             return base.GetBytes();
         }
 
diff --git a/tests/CoAPNet.Tests/CoapOptionsTests.cs b/tests/CoAPNet.Tests/CoapOptionsTests.cs
index 325e764..fdcd501 100644
--- a/tests/CoAPNet.Tests/CoapOptionsTests.cs
+++ b/tests/CoAPNet.Tests/CoapOptionsTests.cs
@@ -469,15 +469,16 @@ public void TestOptionInvalidCastException()
 
         [Category("[RFC7959] Section 2.2"), Category("Blocks")]
         [TestCase(0, 16, false, new byte[] { })]
-        [TestCase(1, 16, false, new byte[] { 0x01 })]
-        [TestCase(2, 32, false, new byte[] { 0x22 })]
-        [TestCase(3, 64, true, new byte[] { 0x53 })]
-        [TestCase(4095, 128, true, new byte[] { 0x7F, 0xFF })]
-        [TestCase(1048575, 256, true, new byte[] { 0x9F, 0xFF, 0xFF})]
-        [TestCase(15, 16, true, new byte[] { 0x1F })]
-        [TestCase(16, 16, true, new byte[] { 0x10, 0x10 })]
-        [TestCase(39, 16, false, new byte[] { 0, 39 })]
-        [TestCase(79, 16, false, new byte[] { 0, 79 })]
+        [TestCase(1, 16, false, new byte[] { 0x10 })]
+        [TestCase(2, 32, false, new byte[] { 0x21 })]
+        [TestCase(3, 64, true, new byte[] { 0x3A })]
+        [TestCase(4095, 128, true, new byte[] { 0xFF, 0xFB })]
+        [TestCase(1048575, 256, true, new byte[] { 0xFF, 0xFF, 0xFC})]
+        [TestCase(15, 16, true, new byte[] { 0xF8 })]
+        [TestCase(16, 16, true, new byte[] { 0x01, 0x08 })]
+        [TestCase(39, 16, false, new byte[] { 0x02, 0x70 })]
+        [TestCase(79, 16, false, new byte[] { 0x04, 0xF0 })]
+        [TestCase(0, 128, true, new byte[] { 0x0b })]
         public void TestBlockOption(int blockNumber, int blockSize, bool more, byte[] expected)
         {
             var optionToBytes = new Options.Block1(blockNumber, blockSize, more);