Decode data and release resources at explicit boundaries

First, build a mental model

A file handle is a resource with a lifetime. JSON is external data with a shape and meaning that may differ from your current model. Release the resource and validate the data as two separate responsibilities.

1. using disposes an IDisposable resource when its scope ends, including when an exception leaves the scope.
2. Use await using for an IAsyncDisposable resource when asynchronous disposal is appropriate; it is not a replacement for every using.
3. DeserializeAsync<T> can fail or produce null; matching C# types does not prove domain validity.
4. Validate required fields and allowed ranges before turning a transport DTO into trusted application state. Avoid accepting arbitrary file paths from untrusted input.

using System.Text.Json;

using var stream = File.OpenRead("player.json");
PlayerDto? dto = await JsonSerializer.DeserializeAsync<PlayerDto>(stream);
if (dto is null || string.IsNullOrWhiteSpace(dto.Name) || dto.Score < 0)
    throw new InvalidDataException("Invalid player file");
Console.WriteLine(dto.Name);

record PlayerDto(string Name, int Score);
// Example file: {"Name":"Ada","Score":12}

1. Acquire

   OpenRead returns a stream owned by this scope.

2. Decode and validate

   The code checks both an actual DTO and the name/score rules.

3. Release

   The using declaration disposes the stream when the scope ends, even on rejection.