ControlByte payloadSize determined for values smaller than 29. On to the next challenge.

Signed-off-by: Adam Rocska <adam.rocska@adams.solutions>

Sources/MaxMindDBReader/ControlByte.swift

@@ -3,6 +3,7 @@ import Foundation
 struct ControlByte {
 
   let type:        DataType
+  let payloadSize: UInt32
 
   init?(bytes: Data) {
     if bytes.count == 0 || bytes.count > 5 { return nil }
@@ -16,6 +17,15 @@ struct ControlByte {
       else {
       return nil
     }
+
+    let payloadSizeDefinition = firstByte & 0b0001_1111
+    switch payloadSizeDefinition {
+      case _ where payloadSizeDefinition < 29:
+        payloadSize = UInt32(payloadSizeDefinition)
+      default:
+        return nil
+    }
+
     self.type = type
   }
 

Tests/MaxMindDBReaderTests/ControlByteTest.swift

@@ -51,4 +51,25 @@ class ControlByteTest: XCTestCase {
     }
   }
 
+  func testInit_nilIfDataTypeNotRecognized() {
+    XCTAssertNil(ControlByte(bytes: Data([0b0000_1111, 0b0000_1111, 0b0000_0000])))
+  }
+
+  func testInit_payloadSizeDefinition_lessThan29() {
+    let testInput: [(expectedPayloadSize: UInt32, byte: UInt8)] = ControlByteTest
+      .nonExtendedRawValues
+      .reduce([]) { byteSequence, typeDefinition in
+      byteSequence + (0..<29).map({
+        (expectedPayloadSize: UInt32($0), byte: $0 | (typeDefinition << 5))
+      })
+    }
+
+    for (expectedPayloadSize, byte) in testInput {
+      XCTAssertEqual(
+        expectedPayloadSize,
+        ControlByte(bytes: Data([byte]))?.payloadSize
+      )
+    }
+
+  }
 }