`EnumStringConverter` fails on Enum serialization when multiple members have same value

[nazar-kuzo]

Nuget Package

Json.More.Net

Package Version

2.1.0

Operating System

Windows

.Net Target (if relevant, please specify the version in the description)

.Net (5 or after)

A clear and concise description of the bug.

EnumStringConverter fails on Enum serialization when multiple members have same value.

This could be reproduced by Serializing System.Net.HttpStatusCode which has both members (Ambiguous, MultipleChoices) assigned to same value (300).

What did you expect?

While this is really edge case scenario, I would say that since C# supports such enum declaration, EnumStringConverter should conform to it.

When serializing, I would expect that it should rely on member name or member DescriptionAttribute without value.
When deserializing, I assume library doesnt support parsing number values, therefore no changes required.

Please add test code or steps to reproduce the behavior.

JsonSerializer.Serialize(HttpStatusCode.BadRequest, new JsonSerializerOptions { Converters = { new EnumStringConverter<HttpStatusCode>() } });

Is there any other information you'd like to share regarding this bug?

Converter fails in EnsureMap() method since it tries to create write cache dictionary based on enum values, which does not support duplicates.

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[gregsdennis]

Thanks for the report. I really didn't expect that an enum would have duplicate names for the same underlying value.

Regarding why it saves the numeric value, it's also tolerant to being able to deserialize numbers. In this case, it should just pick whichever name appears first in the enum declaration, but I can't be sure. There's probably a good test case in here.

I'm sure there's an easy fix here. If you'd like to tackle it, I'd be happy to review a PR.

[nazar-kuzo]

Thanks for the quick reply.

I can confirm that Enum.Parse will pick the first matching member for a value, so converter can accommodate the same behavior

[nazar-kuzo]

@gregsdennis keep in mind that this PR does not provide round trip to exact enum member since EnsureMap() uses Enum.Parse to instantiate enum member, therefore all member names in cache will have the same enum member value instance.

Example:

// produces "\"MultipleChoices\"";
var json = JsonSerializer.Serialize(HttpStatusCode.MultipleChoices) 

// instantiates HttpStatusCode.Ambiguous since it was listed first
var value = JsonSerializer.Deserialize<HttpStatusCode>(json);

While the values are equal, they are not the same.