Add `ResourceType` and `Resource` for defining resources

[aaronpowell]

Is your feature request related to a problem? Please describe.
Similar to #70.

The API for McpToolType and McpTool (combined with the WithTools method) makes it really easy to define tools. It'd be great to have a comparable API for Resources.

Describe the solution you'd like
I'd like to be able to have code like this:

[ResourceType]
public static class SampleResource {
  [Resource("text/plain"), Description("This is a sample resource")]
  public static string Sample() => "test://static/resource/sample.txt";
}

// in program.cs
builder.Services
    .AddMcpServer()
    .WithStdioServerTransport()
    .WithTools()
    .WithResources();

Describe alternatives you've considered
Currently, the only solution would be to implement this via WithListResourcesHandler and WithReadResourceHandler.

[Redth]

I opened #74 to track Resource Templates separately, but I think ideally they are related to the implementation which would happen for static Resources.

[aaronpowell]

Yep, looks like they are similar in theme.

[PederHP]

How do you provide the actual resource contents with this approach?

[aaronpowell]

How do you provide the actual resource contents with this approach?

This is how I imagine it to be:

[McpServerResourceType]
public class MyResources {
    [McpServerResource("file://myresource/foo.txt"), Description("This is a foo text file")]
    public static string Foo(
        Uri uri // this would be injected by the MCP server and map to `file://myresource/foo.txt` in this case
    )
    {
        return """
        This is a foo text file.

        It could be multiple lines long.
        """;
    }

    [McpServerResource("file://myresource/bar.png", MimeType = "image/png"), Description("This is a bar image")]
    public static byte[] Bar(
        Uri uri // this would be injected by the MCP server and map to `file://myresource/bar.png` in this case
    )
    {
        return ... // PNG file content
    }

    [McpServerResource("file://myresource/baz.csv"), Description("This is a baz text file")]
    public static DataContent Baz(
        Uri uri // this would be injected by the MCP server and map to `file://myresource/baz.csv` in this case
    )
    {
        return new DataContent {
            MimeType = "text/csv",
            Blob = ... // CSV file content
        }
    }
}

These are obviously static resources routes, but the same approach could be applied to dynamic ones like file://foo/{id}, and maybe in that cause you could map a route parameter of id onto the URI segment, like in minimal API.

[Tyler-R-Kendrick]

How would you handle providing content from something like Azure Storage as a file provider (or any other valid URIs on alternative file systems?)

Since we're already including the file provider apis in this project, why not do:

builder.WithResources([fileInfo1, fileInfo2, ...otherFileInfos]);

and just load the resources using the built-in apis for that?

[Tyler-R-Kendrick]

I added a PR that addresses my feedback around existing packages.
I like the idea of a consistent way to provide registered types, and the addition of attributes in the design of McpServerResourceAttribute for loading types would be useful. However, I think my implementation implements the initial request at minimum and can be extended to support attribute registration.

@aaronpowell @Redth What do you all think?

For reading resources, a default or custom handler could be registered using file provider APIs that require a file provider instance to be configured in the McpServer.ServiceProvider if a custom handler isn't registered.

[Meir017]

I think WithResources should be WithResourcesFromAssembly