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CSHARP-5611: Eliminate the temporary byte array allocation in ObjectId.ToString #1706

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CSHARP-5611: Eliminate the temporary byte array allocation in ObjectId.ToString #1706

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CSHARP-5611: Eliminate the temporary byte array allocation in ObjectI…
ugurpelister Jun 7, 2025
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CSHARP-5611: Eliminate the temporary byte array allocation in ObjectI…
ugurpelister Jun 7, 2025
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75 changes: 75 additions & 0 deletions src/MongoDB.Bson/ObjectModel/ObjectId.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -449,12 +449,86 @@ public void ToByteArray(byte[] destination, int offset)
destination[offset + 11] = (byte)(_c);
}

#if NET6_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER
/// <summary>
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@BorisDog BorisDog Feb 24, 2026

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There is no need for #if, we include the System.Memory package.

/// Converts the ObjectId to a byte buffer provided by the input span.
/// </summary>
/// <param name="destination">The destination byte span.</param>
/// <exception cref="ArgumentException">Not enough room in destination span.</exception>
public void ToByteSpan(Span<byte> destination)
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@BorisDog BorisDog Feb 24, 2026

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For completeness, please add internal ObjectId(ReadOnlySpan<byte> span) contstructor
And appropriate tests.

{
if (destination.Length < 12)
{
throw new ArgumentException("Not enough room in destination span.", "destination");
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@BorisDog BorisDog Feb 24, 2026

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I know that this is against the existing convention in the file, but for new methods we use should use nameof(...).

}

destination[0] = (byte)(_a >> 24);
destination[1] = (byte)(_a >> 16);
destination[2] = (byte)(_a >> 8);
destination[3] = (byte)(_a);
destination[4] = (byte)(_b >> 24);
destination[5] = (byte)(_b >> 16);
destination[6] = (byte)(_b >> 8);
destination[7] = (byte)(_b);
destination[8] = (byte)(_c >> 24);
destination[9] = (byte)(_c >> 16);
destination[10] = (byte)(_c >> 8);
destination[11] = (byte)(_c);
}

/// <summary>
/// Fills a character span with the characters corresponding to the string representation of the value.
/// </summary>
/// <param name="destination">The span to fill the characters in.</param>
/// <exception cref="ArgumentException">Not enough room in destination span.</exception>
public void ToCharSpan(Span<char> destination)
{
if (destination.Length < 24)
{
throw new ArgumentException("Not enough room in destination span.", "destination");
}

Span<byte> span = stackalloc byte[12];
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@BorisDog BorisDog Feb 24, 2026

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I think we should reuse the existing ToString implementation, to avoid the Span allocation (even thought it's on stack) and for easier review.

While ToString() should just fallback to ToCharSpan, as it does already, but for all TFMs.

ToByteSpan(span);
destination[0] = BsonUtils.ToHexChar(span[0] >> 4);
destination[1] = BsonUtils.ToHexChar(span[0] & 0xF);
destination[2] = BsonUtils.ToHexChar(span[1] >> 4);
destination[3] = BsonUtils.ToHexChar(span[1] & 0xF);
destination[4] = BsonUtils.ToHexChar(span[2] >> 4);
destination[5] = BsonUtils.ToHexChar(span[2] & 0xF);
destination[6] = BsonUtils.ToHexChar(span[3] >> 4);
destination[7] = BsonUtils.ToHexChar(span[3] & 0xF);
destination[8] = BsonUtils.ToHexChar(span[4] >> 4);
destination[9] = BsonUtils.ToHexChar(span[4] & 0xF);
destination[10] = BsonUtils.ToHexChar(span[5] >> 4);
destination[11] = BsonUtils.ToHexChar(span[5] & 0xF);
destination[12] = BsonUtils.ToHexChar(span[6] >> 4);
destination[13] = BsonUtils.ToHexChar(span[6] & 0xF);
destination[14] = BsonUtils.ToHexChar(span[7] >> 4);
destination[15] = BsonUtils.ToHexChar(span[7] & 0xF);
destination[16] = BsonUtils.ToHexChar(span[8] >> 4);
destination[17] = BsonUtils.ToHexChar(span[8] & 0xF);
destination[18] = BsonUtils.ToHexChar(span[9] >> 4);
destination[19] = BsonUtils.ToHexChar(span[9] & 0xF);
destination[20] = BsonUtils.ToHexChar(span[10] >> 4);
destination[21] = BsonUtils.ToHexChar(span[10] & 0xF);
destination[22] = BsonUtils.ToHexChar(span[11] >> 4);
destination[23] = BsonUtils.ToHexChar(span[11] & 0xF);
}
#endif

/// <summary>
/// Returns a string representation of the value.
/// </summary>
/// <returns>A string representation of the value.</returns>
public override string ToString()
{
#if NET6_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER
return string.Create(24, this, static (span, input) =>
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@BorisDog BorisDog Feb 24, 2026

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nit: expression-bodied method

{
input.ToCharSpan(span);
});
#else
var c = new char[24];
c[0] = BsonUtils.ToHexChar((_a >> 28) & 0x0f);
c[1] = BsonUtils.ToHexChar((_a >> 24) & 0x0f);
Expand All @@ -481,6 +555,7 @@ public override string ToString()
c[22] = BsonUtils.ToHexChar((_c >> 4) & 0x0f);
c[23] = BsonUtils.ToHexChar(_c & 0x0f);
return new string(c);
#endif
}

// explicit IConvertible implementation
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10 changes: 10 additions & 0 deletions tests/MongoDB.Bson.Tests/ObjectModel/ObjectIdTests.cs
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Expand Up @@ -87,6 +87,11 @@ public void TestByteArrayConstructor()
Assert.Equal(BsonConstants.UnixEpoch.AddSeconds(0x01020304), objectId.CreationTime);
Assert.Equal("0102030405060708090a0b0c", objectId.ToString());
Assert.True(bytes.SequenceEqual(objectId.ToByteArray()));
#if NET6_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER
Span<byte> span = new byte[12];
objectId.ToByteSpan(span);
Assert.True(span.SequenceEqual(bytes));
#endif
}

[Fact]
Expand All @@ -101,6 +106,11 @@ public void TestStringConstructor()
Assert.Equal(BsonConstants.UnixEpoch.AddSeconds(0x01020304), objectId.CreationTime);
Assert.Equal("0102030405060708090a0b0c", objectId.ToString());
Assert.True(bytes.SequenceEqual(objectId.ToByteArray()));
#if NET6_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER
Span<char> span = new char[24];
objectId.ToCharSpan(span);
Assert.True(span.SequenceEqual("0102030405060708090a0b0c"));
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@BorisDog BorisDog Feb 24, 2026

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Please add separate tests for the new methods, testing different cases:
ToByteSpan_should_return_expcted_results(byte[] data, byte[] expectedBytes)
ToCharSpan_should_return_expected_results(byte[] data, string expectedChars) (this one can also test Tostring)

#endif
}

[Fact]
Expand Down