System.UriBuilder cannot build a correct mailto URI

[jrdodds]

Description

The System.UriBuilder class cannot be used to build a mailto URI.

Reproduction Steps

The following code

var builder = new UriBuilder
{
    Scheme = Uri.UriSchemeMailto,
    UserName = "someone",
    Host = "example.com",
    Query = "subject=Testing",
    Path = string.Empty,
};
Console.WriteLine(builder.ToString());

produces a URI value of

mailto:someone@example.com/?subject=Testing

which is not a valid mailto URI.

Expected behavior

A valid URI would be

mailto:someone@example.com?subject=Testing

There should not be a '/' character.

Actual behavior

The Path setter sets the value to '/' when the value is the empty string.

    [AllowNull]
    public string Path
    {
        get => _path;
        set
        {
            _path = string.IsNullOrEmpty(value)
                ? "/"
                : Uri.InternalEscapeString(value.Replace('\\', '/'));
            _changed = true;
        }
    }

This makes sense for HTTP/S but makes the class unusable for mailto.

Regression?

No response

Known Workarounds

No response

Configuration

.Net 7.0.203
Windows 11 x64

Other information

No response

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Issue Details

---

Description

The UriBuilder cannot be used to build a mailto URI.

Reproduction Steps

The following code

var builder = new UriBuilder
{
    Scheme = Uri.UriSchemeMailto,
    UserName = "someone",
    Host = "example.com",
    Query = "subject=Testing",
    Path = string.Empty,
};
Console.WriteLine(builder.ToString());

produces a URI value of

mailto:someone@example.com/?subject=Testing

which is not a valid mailto URI.

Expected behavior

A valid URI would be

mailto:someone@example.com?subject=Testing

There should not be a '/' character.

Actual behavior

The Path setter sets the value to '/' when the value is the empty string.

    [AllowNull]
    public string Path
    {
        get => _path;
        set
        {
            _path = string.IsNullOrEmpty(value)
                ? "/"
                : Uri.InternalEscapeString(value.Replace('\\', '/'));
            _changed = true;
        }
    }

This makes sense for HTTP/S but makes the class unusable for mailto.

Regression?

No response

Known Workarounds

No response

Configuration

.Net 7.0.203
Windows 11 x64

Other information

No response

Author:	jrdodds
Assignees:	-
Labels:	area-System.Net
Milestone:	-

[MihaZupan]

How did you run into this issue?
In an isolated example, the answer would be to just not set Path to empty, but you probably ran into it in more complex logic?

If this is causing issues, we probably could special-case this and avoid appending the slash, though I would also assume that this issue would be quickly spotted if someone did run into it.

[jrdodds]

... the answer would be to just not set Path to empty ...

Setting Path is something non-empty will also mangle the mailto URI.

e.g. setting a space:

mailto:someone@example.com ?subject=Testing

Path doesn't have a meaning for the mailto scheme, so a possible fix may be to change the ToString() method to append the Path if the scheme is not mailto.

[MihaZupan]

Right, what I was getting at is that if you're constructing a mailto Uri like in your example, you can just skip setting Path - it will default to "actually empty" already. -- disregard, see comment below

[jrdodds]

Right, what I was getting at is that if you're constructing a mailto Uri like in your example, you can just skip setting Path - it will default to "actually empty" already.

It doesn't behave that way.

"actually empty" doesn't exist. The initial value of Path is '/'.

[mrudat]

Given that the mailto URI scheme has different functionality for formatting the URI, wouldn't the Right Way be to create a shiny new MailtoUri class that correctly formats a mailto URI and hooks into the existing UriBuilder and Uri?