Fix IPTC tags written on jpg files that contains non-English characters can't be correctly displayed on external apps #2212

[lmerino-ep]

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Description

This fixes the issue of incorrect characters showed on IPTC tags that contains non-English characters.

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[brianpopow]

@lmerino-ep thanks for the contribution. I have added a test for making sure the envelope data is written when UTF-8 data is present. I think this is good to go into main now.

[lmerino-ep]

Thank you, @brianpopow it looks beautiful now. El mié, 24 ago 2022 a las 7:07, Brian Popow ***@***.***>) escribió:

…

***@***.**** approved this pull request. @lmerino-ep <https://github.com/lmerino-ep> thanks for the contribution. I have added a test for making sure the envelope data is written when UTF-8 data is present. I think this is good to go into main now. — Reply to this email directly, view it on GitHub <#2213 (review)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/A2UPGMW3KF7MBZRAJKAUVHDV2WU2TANCNFSM57KPW5CA> . You are receiving this because you were mentioned.Message ID: ***@***.***>

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[gfoidl]

Suggested change

	private static readonly byte[] CodedCharacterSetUtf8Value = { 0x1B, 0x25, 0x47 };
	// Uses C#'s optimization to refer to the data segment in the assembly direclty, no allocation occurs.
	private static ReadOnlySpan<byte> CodedCharacterSetUtf8Value => new byte[]{ 0x1B, 0x25, 0x47 };

And update WriteRecord (L294) to take a ROS.

[gfoidl]

The cool thing is that with the above suggestion the JIT will treat CodedCharacterSetUtf8Value.Length as constant (3) here.

[gfoidl]

Here the JIT needs to introduce a bound check for each access to Data. These can be avoided by

Span<byte> data = this.Data.AsSpan(offset, 5);
data[0] = IptcTagMarkerByte;
data[1] = recordNumber;
data[2] = recordBinaryRepresentation;
data[3] = (byte)(recordData.Length >> 8);
data[4] = (byte)recordData.Length;
offset += 5;

So if the AsSpan succeeds the JIT knows that all index accesses are within bounds, so no bounds check needs to be emitted (tested with .NET 6).

[gfoidl]

This will become

Suggested change

	Buffer.BlockCopy(recordData, 0, this.Data, offset, recordData.Length);
	recordData.CopyTo(this.Data.AsSpan(offset));

[brianpopow]

thanks @gfoidl, I have added your suggestions.