[API Proposal]: Convert.TryFromHexString

[Socolin]

Background and motivation

Convert.FromHexString("not-hex"); is throwing a System.FormatException when input string is not a valid hex.

Like Convert.TryFromBase64Chars() Convert.TryFromBase64String() it would be nice to have Convert.TryFromHexString(); when validating user input it's not great to be force to put a whole try/catch block arround for readability

byte[] myBytes;
try
{
	myBytes = Convert.FromHexString(inputString);
}
catch (FormatException ex)
{
	throw new InvalidXxx(ex);
}

I think It would be much nicer to do

if (!Convert.TryFromHexString(inputString, out var myBytes))
	throw new InvalidXxx(ex);

API Proposal

namespace System;

public class Convert
{
    public static bool TryFromHexString(string s, Span<byte> bytes, out int bytesWritten)
}

API Usage

if (!Convert.TryFromHexString(inputString, out var myBytes))
	throw new InvalidXxx(ex);

Alternative Designs

TryFromBase64String returns a Span bytes instead with the number bytesWritten, so maybe it should be the same, but since the number of bytes are easy to guest with hex string (just divide string length by 2) I'm not sure it's useful

public static bool TryFromHexString(string s, Span<byte> bytes, out int bytesWritten)

Risks

I don't see any

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Issue Details

---

Background and motivation

Convert.FromHexString("not-hex"); is throwing a System.FormatException when input string is not a valid hex.

Like Convert.TryFromBase64Chars() Convert.TryFromBase64String() it would be nice to have Convert.TryFromHexString(); when validating user input it's not great to be force to put a whole try/catch block arround for readability

byte[] myBytes;
try
{
	myBytes = Convert.FromHexString(inputString);
}
catch (FormatException ex)
{
	throw new InvalidXxx(ex);
}

I think It would be much nicer to do

if (!Convert.TryFromHexString(inputString, out var myBytes))
	throw new InvalidXxx(ex);

API Proposal

namespace System;

public class Convert
{
    public static bool TryFromHexString(string s, out byte[] bytes);
}

API Usage

if (!Convert.TryFromHexString(inputString, out var myBytes))
	throw new InvalidXxx(ex);

Alternative Designs

TryFromBase64String returns a Span bytes instead with the number bytesWritten, so maybe it should be the same, but since the number of bytes are easy to guest with hex string (just divide string length by 2) I'm not sure it's useful

public static bool TryFromHexString(string s, Span<byte> bytes, out int bytesWritten)

Risks

I don't see any

Author:	Socolin
Assignees:	-
Labels:	api-suggestion, area-System.Runtime, untriaged
Milestone:	-

[dakersnar]

This is a reasonable proposal. We would want to match existing patterns (the version called out in your Alternative Designs section), mostly because Span<Byte> doesn't need to be allocated. Can you update your proposal?

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[Socolin]

This is a reasonable proposal. We would want to match existing patterns (the version called out in your Alternative Designs section), mostly because Span<Byte> doesn't need to be allocated. Can you update your proposal?

I've updated my proposal