/// <summary>
/// Checks whether a byte array starts with a known header, containing the app name and an
/// optional revision number.
/// </summary>
/// <param name="packedCipher">Byte array to examine.</param>
/// <param name="expectedAppName">The header must start with this app name.</param>
/// <param name="revision">reveives the revision number.</param>
/// <returns>Returns true if the array starts with a valid header, otherwise false.</returns>
public static bool HasMatchingHeader(byte[] packedCipher, string expectedAppName, out int revision)
{
if (packedCipher != null)
{
// test for app name
if (ByteArrayExtensions.ContainsAt(packedCipher, CryptoUtils.StringToBytes(expectedAppName), 0))
{
int position = expectedAppName.Length;
// Followed by separator?
if (ByteArrayExtensions.ContainsAt(packedCipher, (byte)Separator, position))
{
revision = 1;
return(true);
}
if (ByteArrayExtensions.ContainsAt(packedCipher, CryptoUtils.StringToBytes(RevisionSeparator), position))
{
int digitsStart = position + RevisionSeparator.Length;
int digitsEnd = digitsStart;
// Skip digits
while (ByteArrayExtensions.ContainsDigitCharAt(packedCipher, digitsEnd))
{
digitsEnd++;
}
// Followed by separator?
if ((digitsEnd > digitsStart) &&
(ByteArrayExtensions.ContainsAt(packedCipher, (byte)Separator, digitsEnd)))
{
byte[] digitsPart = new byte[digitsEnd - digitsStart];
Array.Copy(packedCipher, digitsStart, digitsPart, 0, digitsPart.Length);
revision = int.Parse(CryptoUtils.BytesToString(digitsPart));
return(true);
}
}
}
}
revision = 0;
return(false);
}
public void ByteArrayStartsWithHandlesNullAndEmpty()
{
byte[] haystack = null;
byte[] needle = null;
Assert.Throws <ArgumentNullException>(delegate { ByteArrayExtensions.ContainsAt(haystack, needle, 0); });
// Works the same way as string.StartsWith
bool expectedResult = string.Empty.StartsWith(string.Empty);
haystack = new byte[0];
needle = new byte[0];
Assert.AreEqual(expectedResult, haystack.ContainsAt(needle, 0));
Assert.IsTrue(expectedResult);
expectedResult = "test".StartsWith(string.Empty);
haystack = new byte[] { 1, 2, 3 };
needle = new byte[0];
Assert.AreEqual(expectedResult, haystack.ContainsAt(needle, 0));
Assert.IsTrue(expectedResult);
}
