Creates incorrect MD5 hash for some files (#103)

* [core] Add test file that we create incorrect hash for

By 'incorrect' we mean "not what AWS S3 think is correct" for this
file.

* [domain] HexEncoder rewritten to correctly decode hex

* [domain] HexEncoder encode to uppercase

domain/src/main/scala/net/kemitix/thorp/domain/HexEncoder.scala

@@ -4,19 +4,17 @@ import java.math.BigInteger
 
 trait HexEncoder {
 
-  def encode(bytes: Array[Byte]): String = {
-    val bigInteger = new BigInteger(1, bytes)
-    String.format("%0" + (bytes.length << 1) + "x", bigInteger)
-  }
+  def encode(bytes: Array[Byte]): String =
+    String
+      .format("%0" + (bytes.length << 1) + "x", new BigInteger(1, bytes))
+      .toUpperCase
 
-  def decode(hexString: String): Array[Byte] = {
-    val byteArray = new BigInteger(hexString, 16).toByteArray
-    if (byteArray(0) == 0) {
-      val output = new Array[Byte](byteArray.length - 1)
-      System.arraycopy(byteArray, 1, output, 0, output.length)
-      output
-    } else byteArray
-  }
+  def decode(hexString: String): Array[Byte] =
+    hexString
+      .replaceAll("[^0-9A-Fa-f]", "")
+      .sliding(2, 2)
+      .toArray
+      .map(Integer.parseInt(_, 16).toByte)
 
 }
 

domain/src/test/scala/net/kemitix/thorp/domain/HexEncoderTest.scala

@@ -0,0 +1,23 @@
+package net.kemitix.thorp.domain
+
+import java.nio.charset.StandardCharsets
+
+import org.scalatest.FreeSpec
+
+class HexEncoderTest extends FreeSpec {
+
+  val text = "test text to encode to hex"
+  val hex  = "74657374207465787420746F20656E636F646520746F20686578"
+
+  "can round trip a hash decode then encode" in {
+    val input  = hex
+    val result = HexEncoder.encode(HexEncoder.decode(input))
+    assertResult(input)(result)
+  }
+  "can round trip a hash encode then decode" in {
+    val input  = hex.getBytes(StandardCharsets.UTF_8)
+    val result = HexEncoder.decode(HexEncoder.encode(input))
+    assertResult(input)(result)
+  }
+
+}