EncodingTests.cs

//
// Copyright (c) .NET Foundation and Contributors
// Portions Copyright (c) Microsoft Corporation.  All rights reserved.
// See LICENSE file in the project root for full license information.
//

using nanoFramework.TestFramework;
using System;
using System.Text;

namespace NFUnitTestStringBuilder
{
   [TestClass]
   public class EncodingTests
   {
     [TestMethod]
     public void Utf8EncodingTests_Test1()
     {
         string str = "this is a normal string that will be used to convert to bytes then back to a string";

         byte[] data = new byte[128];
         int len = str.Length;
         int idx = 0;

         Random rand = new Random();

         int cBytes = 0;

         while (len > 0)
         {
             int size = (len <= 2) ? len : rand.Next(len / 2) + 1;
             len -= size;

             int cnt = Encoding.UTF8.GetBytes(str, idx, size, data, cBytes);

             Assert.AreEqual(str.Substring(idx, size), new string(Encoding.UTF8.GetChars(data, cBytes, cnt)));

             cBytes += cnt;
             idx += size;
         }
         Assert.AreEqual(cBytes, str.Length);
         string strAfter = new string(Encoding.UTF8.GetChars(data, 0, cBytes));
         Assert.AreEqual(str, strAfter);
     }

     [TestMethod]
     public void Utf8EncodingTests_Test2()
     {
         string str = "this is a normal string that will be used to convert to bytes then back to a string";
         byte[] data = Encoding.UTF8.GetBytes(str);
         Assert.AreEqual(data.Length, str.Length);
         string strAfter = new string(Encoding.UTF8.GetChars(data));
         Assert.AreEqual(str, strAfter);
     }

     [TestMethod]
     public void Utf8EncodingTests_Test3()
     {
         // This tests involves a string with a special character
         string str = "AB\u010DAB";
         byte[] data = new byte[4];
         int count = Encoding.UTF8.GetBytes(str, 1, 3, data, 0);
         Assert.AreEqual(4, count);
         Assert.AreEqual("B\u010DA", new string(Encoding.UTF8.GetChars(data)));
         
     }

     private void RoundtripUtf8(byte[] input, byte[] expected, int expectedStringLength)
     {
         string decoded = Encoding.UTF8.GetString(input,0, input.Length);
         byte[] reencoded = Encoding.UTF8.GetBytes(decoded);
         Assert.AreEqual(expectedStringLength, decoded.Length);
         CollectionAssert.AreEqual(expected, reencoded, $"Failed on input: {BitConverter.ToString(input)}");
     }

     [TestMethod]
     public void Utf8EncodingTests_TestValid2ByteSequence()
     {
         byte[] input = new byte[] { 0xC2, 0xA9 }; // U+00A9 ©
         byte[] expected = new byte[] { 0xC2, 0xA9 };
         RoundtripUtf8(input, expected, 1);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestValid3ByteSequence()
     {
         byte[] input = new byte[] { 0xE2, 0x82, 0xAC }; // U+20AC €
         byte[] expected = new byte[] { 0xE2, 0x82, 0xAC };
         RoundtripUtf8(input, expected, 1);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestValid4ByteSequence()
     {
         byte[] input = new byte[] { 0xF0, 0x9F, 0x98, 0x80 }; // U+1F600 😀
         byte[] expected = new byte[] { 0xF0, 0x9F, 0x98, 0x80 };
         RoundtripUtf8(input, expected, 2);
     }

    
     [TestMethod]
     public void Utf8EncodingTests_TestOverlongEncoding1()
     {
         // Should produce � (U+FFFD) for each bad byte pair
         byte[] input = new byte[] { 0xC0, 0xAF }; // Overlong '/'
         byte[] expected = new byte[] { 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD };
         RoundtripUtf8(input, expected, 2);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestOverlongEncoding2()
     {
         byte[] input = new byte[] { 0xE0, 0x80, 0xAF }; // Overlong '/'
         byte[] expected = new byte[] { 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD };
         RoundtripUtf8(input, expected, 3);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestInvalid3ByteLastByteInvalid()
     {
         byte[] input = new byte[] { 0xE2, 0x82, 0xFE }; // UTF-8 3 bytes, 0xFE is the invalid character
         byte[] expected = new byte[] { 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD };
         RoundtripUtf8(input, expected, 2);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestInvalid3ByteMiddleByteInvalid()
     {
         byte[] input = new byte[] { 0xE2, 0xFE, 0xAC }; // UTF-8 3 bytes, 0xFE is the invalid character
         byte[] expected = new byte[] { 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD };
         RoundtripUtf8(input, expected, 3);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestInvalid4ByteLastByteInvalid()
     {
         byte[] input = new byte[] { 0xF0, 0x9F, 0x98, 0xFE }; // UTF-8 4 bytes, 0xFE is the invalid character
         byte[] expected = new byte[] { 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD };
         RoundtripUtf8(input, expected, 2);
     }

     //  0xF0, 0x9F, 0x98, 0x80
     [TestMethod]
     public void Utf8EncodingTests_TestInvalid4ByteThirdByteInvalid()
     {
         byte[] input = new byte[] { 0xF0, 0x9F, 0xFE, 0x80 };  // UTF-8 4 bytes, 0xFE is the invalid character
         byte[] expected = new byte[] { 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD };
         RoundtripUtf8(input, expected, 3);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestInvalid4ByteSecondByteInvalid()
     {
         byte[] input = new byte[] { 0xF0, 0xFE, 0x98, 0x80 }; // UTF-8 4 bytes, 0xFE is the invalid character
         byte[] expected = new byte[] { 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD };
         RoundtripUtf8(input, expected, 4);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestIsolatedContinuationByte()
     {
         byte[] input = new byte[] { 0x80 }; // Invalid lone continuation byte
         string decoded = Encoding.UTF8.GetString(input, 0, input.Length);
         byte[] reencoded = Encoding.UTF8.GetBytes(decoded);
         CollectionAssert.AreEqual(new byte[] { 0xEF, 0xBF, 0xBD }, reencoded);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestIllegalCodePositionSurrogate()
     {
         byte[] input = new byte[] { 0xED, 0xA0, 0x80 }; // U+D800 high surrogate
         string decoded = Encoding.UTF8.GetString(input, 0, input.Length);
         byte[] reencoded = Encoding.UTF8.GetBytes(decoded);
         CollectionAssert.AreEqual(new byte[] { 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD }, reencoded);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestMaximumValidCodepoint()
     {
         byte[] input = new byte[] { 0xF4, 0x8F, 0xBF, 0xBF }; // U+10FFFF
         byte[] expected = new byte[] { 0xF4, 0x8F, 0xBF, 0xBF };
         string decoded = Encoding.UTF8.GetString(input, 0, input.Length);
         RoundtripUtf8(input, expected, 2);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestCodepointBeyondUPlus10FFFF()
     {
         byte[] input = new byte[] { 0xF4, 0x90, 0x80, 0x80 }; // > U+10FFFF
         string decoded = Encoding.UTF8.GetString(input, 0, input.Length);
         byte[] reencoded = Encoding.UTF8.GetBytes(decoded);
         // All 4 bytes become one or two � depending on how it was handled
         CollectionAssert.AreEqual(
             new byte[] { 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD }, reencoded);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestUnexpectedContinuationSequence()
     {
         byte[] input = new byte[] { 0xC2, 0x41 }; // Valid 0xC2 (start of 2-byte), but 0x41 (A) not valid continuation
         string decoded = Encoding.UTF8.GetString(input, 0, input.Length);
         byte[] reencoded = Encoding.UTF8.GetBytes(decoded);
         // Expect: �A
         CollectionAssert.AreEqual(new byte[] { 0xEF, 0xBF, 0xBD, 0x41 }, reencoded);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestASCII()
     {
         byte[] input = new byte[] { 0x47, 0x6F, 0x6F, 0x64 }; // "Good"
         byte[] expected = new byte[] { 0x47, 0x6F, 0x6F, 0x64 };
         RoundtripUtf8(input, expected, 4);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestASCIIWithInvalidByte()
     {
         byte[] input = new byte[] { 0x42, 0x41, 0x44, 0xEF, 0xFF }; // BAD��
         byte[] expected = new byte[] { 0x42, 0x41, 0x44, 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD };
         RoundtripUtf8(input, expected, 5);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestASCIIWithInvalidByteInBetween()
     {
         byte[] input = new byte[] { 0x42, 0x41, 0x44, 0xEF, 0xFF, 0x42, 0x41, 0x44 }; // BAD��BAD
         byte[] expected = new byte[] { 0x42, 0x41, 0x44, 0xEF, 0xBF, 0xBD, 0xEF, 0xBF, 0xBD, 0x42, 0x41, 0x44 };
         RoundtripUtf8(input, expected, 8);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestASCIIWithNull()
     {
         // All characters will be dropped after the null character in nanoFramework
         byte[] input = new byte[] { 0x54, 0x65, 0x73, 0x74, 0x20, 0x6E, 0x75, 0x6C, 0x6C, 0x00, 
                                     0x61, 0x66, 0x74, 0x65, 0x72, 0x20, 0x6E, 0x75, 0x6C, 0x6C }; // Test null\0after null
         byte[] expected = new byte[] { 0x54, 0x65, 0x73, 0x74, 0x20, 0x6E, 0x75, 0x6C, 0x6C };
         RoundtripUtf8(input, expected, 9);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestStringWithEmoji()
     {
         string strInput = "nanoFramework is fantastic 🚀";
         var input = Encoding.UTF8.GetBytes(strInput);
         byte[] expected = new byte[] { 0x6E, 0x61, 0x6E, 0x6F, 0x46, 0x72, 0x61, 0x6D, 0x65, 0x77, 0x6F, 0x72, 0x6B, 0x20, 0x69,
                         0x73, 0x20, 0x66, 0x61, 0x6E, 0x74, 0x61, 0x73, 0x74, 0x69, 0x63, 0x20, 0xF0, 0x9F, 0x9A, 0x80 };
         RoundtripUtf8(input, expected, 29);
     }

     [TestMethod]
     public void Utf8EncodingTests_TestFullASCIIRange()
     {
         // Full ASCII Range except the null character
         byte[] input = new byte[]
         {
                 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
           0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F,
           0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
           0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F,
           0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27,
           0x28, 0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E, 0x2F,
           0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37,
           0x38, 0x39, 0x3A, 0x3B, 0x3C, 0x3D, 0x3E, 0x3F,
           0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47,
           0x48, 0x49, 0x4A, 0x4B, 0x4C, 0x4D, 0x4E, 0x4F,
           0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57,
           0x58, 0x59, 0x5A, 0x5B, 0x5C, 0x5D, 0x5E, 0x5F,
           0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,
           0x68, 0x69, 0x6A, 0x6B, 0x6C, 0x6D, 0x6E, 0x6F,
           0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77,
           0x78, 0x79, 0x7A, 0x7B, 0x7C, 0x7D, 0x7E, 0x7F
         };
         string decoded = Encoding.UTF8.GetString(input, 0, input.Length);
         byte[] reencoded = Encoding.UTF8.GetBytes(decoded);
         RoundtripUtf8(reencoded, input, 127);
     }
 }
}