[API Proposal]: System.Security.Cryptography.Oid should have a ToString() implementation

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Background and motivation

The ToString() method of the Oid class currently always prints System.Security.Cryptography.Oid which is pretty much useless.

A nicer implementation would display the oid value and the friendly name if available.

API Proposal

namespace System.Security.Cryptography;

public sealed class Oid
{
    public override string ToString()
    {
        return Value?.Length > 0 && FriendlyName?.Length > 0 ? $"{Value} ({FriendlyName})" : Value ?? "";
    }
}

API Usage

var dsaOid = new Oid("1.3.14.3.2.12");
Console.WriteLine(dsaOid.ToString()); // prints "1.3.14.3.2.12 (DSA)"

var dummyOid = new Oid("1.2.3");
Console.WriteLine(dummyOid.ToString()); // prints "1.2.3"

var emptyOid = new Oid();
Console.WriteLine(emptyOid.ToString()); // prints "" (empty string)

Alternative Designs

Not applicable.

Risks

Probably very low.

[dotnet-policy-service[bot]]

Tagging subscribers to this area: @dotnet/area-system-security, @bartonjs, @vcsjones See info in area-owners.md if you want to be subscribed.

[vcsjones]

There are some edge cases here that probably need to be considered.

First, it is possible to have an Oid that has a friendly name, but not a value. For example:

using System;
using System.Security.Cryptography;

#pragma warning disable CA1416 // Validate platform compatibility

using ECDiffieHellmanCng ecdh = new(ECCurve.CreateFromFriendlyName("Curve25519"));
ECParameters p = ecdh.ExportParameters(false);
Console.WriteLine(p.Curve.Oid.FriendlyName);
Console.WriteLine(p.Curve.Oid.Value);

On Windows, Curve25519 is a named-only curve and has no Value. Or more simply, just doing Oid oid = new(null, "Potato");. But the Curve25519 highlights that there is an actual real-world case for this happening.

We could do something like this:

public override string ToString()
{
    return (Value, FriendlyName) switch
    {
        (string v, string f) => $"{v} ({f})",
        (string v, null) => v,
        (null, string f) => f,
        (null, null) => string.Empty
    };
}

But it has a certain amount of ambiguity to the output that I don't love.

Second, and this might be fixed now, is that touching FriendlyName on Windows can have surprisingly bad perf characteristics on first-use, which would apply to ToString.

[bartonjs]

Given that there are 4 possible output formats (as demonstrated by @vcsjones)... what are you hoping to do with this information?

Basically, any runtime ToString() of this type is going to be problematic. A calling application/library should be looking at the constituent parts and handling null in a way that makes sense to their context. If you just want it for the debugger, then it might be a reasonable Debugger-Display value (while .ToString() is the default, the debugger-display value can be different)

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