[Firebird-net-provider] [FB-Tracker] Created: (DNET-509) Firebird .NET Data Provider reads Guids incorrectly on little-endian systems

[Herman S. (JIRA) <tr...@fi...>]

Firebird .NET Data Provider reads Guids incorrectly on little-endian systems
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                 Key: DNET-509
                 URL: http://tracker.firebirdsql.org/browse/DNET-509
             Project: .NET Data provider
          Issue Type: Bug
          Components: ADO.NET Provider
    Affects Versions: 3.0.2.0
            Reporter: Herman Schoenfeld
            Assignee: Jiri Cincura


On a little-endian systems Guids values are not being correctly hydrated by the Firebird ADO.NET provider.

For example, a user may insert a Guid via a query of the form 

  ..." INSERT INTO MyTable VALUES (UUID_TO_CHAR(" + guid.ToString() + " ))"

But when that user loads the Guid back via the provider (on a little endian system), the value is different than the correct value stored on the database value.

The problem is that Uuid & Guid vary in storage format but not it presentation format.The  The CHAR(16) octets contain the Uuid bytes in big endian layout. When hydrating these bytes into a Guid, the provider does not compensate for the Guid's storage of certain parts as the native endian. The correct way to parse the uuid into a guid is:

			var rfc4122bytes =  ... uuid byte array returned from firebird ..
			if (BitConverter.IsLittleEndian) {
				Array.Reverse(rfc4122bytes, 0, 4);
				Array.Reverse(rfc4122bytes, 4, 2);
				Array.Reverse(rfc4122bytes, 6, 2);
			}
			var guid = new Guid(rfc4122bytes);

Suspected location of bug is in class 'DbValue' method 'GetGuid'.

As a work-around, I've written a wrapper for the FbDataReader which will correct the invalid guid value.

	public class FirebirdCorrectingReader : IDataReader {
		private readonly IDataReader _decoratedReader;

		public FirebirdCorrectingReader(IDataReader decoratedReader) {
			_decoratedReader = decoratedReader;	
		}

		#region IDataReader Impl

		public void Dispose() {
			_decoratedReader.Dispose();
		}

		public string GetName(int i) {
			return _decoratedReader.GetName(i);
		}

		public string GetDataTypeName(int i) {
			return _decoratedReader.GetDataTypeName(i);
		}

		public Type GetFieldType(int i) {
			return _decoratedReader.GetFieldType(i);
		}

		public object GetValue(int i) {
			var result = _decoratedReader.GetValue(i);
			if (result is Guid) {
				result = CorrectGuid((Guid)result);
			}
			return result;
		}

		public int GetValues(object[] values) {
			return _decoratedReader.GetValues(values);
		}

		public int GetOrdinal(string name) {
			return _decoratedReader.GetOrdinal(name);
		}

		public bool GetBoolean(int i) {
			return _decoratedReader.GetBoolean(i);
		}

		public byte GetByte(int i) {
			return _decoratedReader.GetByte(i);
		}

		public long GetBytes(int i, long fieldOffset, byte[] buffer, int bufferoffset, int length) {
			return _decoratedReader.GetBytes(i, fieldOffset, buffer, bufferoffset, length);
		}

		public char GetChar(int i) {
			return _decoratedReader.GetChar(i);
		}

		public long GetChars(int i, long fieldoffset, char[] buffer, int bufferoffset, int length) {
			return _decoratedReader.GetChars(i, fieldoffset, buffer, bufferoffset, length);
		}

		public Guid GetGuid(int i) {
			return CorrectGuid(_decoratedReader.GetGuid(i));
		}

		public short GetInt16(int i) {
			return _decoratedReader.GetInt16(i);
		}

		public int GetInt32(int i) {
			return _decoratedReader.GetInt32(i);
		}

		public long GetInt64(int i) {
			return _decoratedReader.GetInt64(i);
		}

		public float GetFloat(int i) {
			return _decoratedReader.GetFloat(i);
		}

		public double GetDouble(int i) {
			return _decoratedReader.GetDouble(i);
		}

		public string GetString(int i) {
			return _decoratedReader.GetString(i);
		}

		public decimal GetDecimal(int i) {
			return _decoratedReader.GetDecimal(i);
		}

		public DateTime GetDateTime(int i) {
			return _decoratedReader.GetDateTime(i);
		}

		public IDataReader GetData(int i) {
			return _decoratedReader.GetData(i);
		}

		public bool IsDBNull(int i) {
			return _decoratedReader.IsDBNull(i);
		}

		public int FieldCount { get { return _decoratedReader.FieldCount; } }

		object IDataRecord.this[int i] {
			get { return _decoratedReader[i]; }
		}

		object IDataRecord.this[string name] {
			get {return _decoratedReader[name]; }
		}

		public void Close() {
			_decoratedReader.Close();
		}

		public DataTable GetSchemaTable() {
			return _decoratedReader.GetSchemaTable();
		}

		public bool NextResult() {
			return _decoratedReader.NextResult();
		}

		public bool Read() {
			return _decoratedReader.Read();
		}

		public int Depth { get { return _decoratedReader.Depth; } }
		public bool IsClosed { get { return _decoratedReader.IsClosed; } }
		public int RecordsAffected { get { return _decoratedReader.RecordsAffected; } }

		#endregion

		public static Guid CorrectGuid(Guid badlyParsedGuid) {
			var rfc4122bytes = badlyParsedGuid.ToByteArray();
			if (BitConverter.IsLittleEndian) {
				Array.Reverse(rfc4122bytes, 0, 4);
				Array.Reverse(rfc4122bytes, 4, 2);
				Array.Reverse(rfc4122bytes, 6, 2);
			}
			return new Guid(rfc4122bytes);
		}
	}


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