I'm trying to build a custom JSON Converter using the System.Text.Json library. A specific enhancement of the given converter needs to call an async method inside the public override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) method (link to microsoft help page: https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-converters-how-to?pivots=dotnet-5-0).
The easiest path would be to have the Read method marked as async, but I cannot due to the ref Utf8JsonReader parameter being ref (cannot have ref parameter in async method).
I've also looked for some other possibilities, like blocking the async call:
- async/await deadlocking when using a SynchronizationContext
- How to call asynchronous method from synchronous method in C#?
- C# Async Task Method Without Await or Return
- Using async without await?
Like, I've read dozens of topic, and tried dozens of possible solution, but I had no luck with any of them. Therefore, I'm back to trying to see if it's possible to have the Read method marked as async is some way.. But I haven't found any solution so far.
Just to add one thing: I cannot rework my method to be NOT async.
Frankly, I'm not even sure this is possible, because even if marked async, I should be sure that the method that calls the converter awaits, which is an assumption I don't think I can make.
Therefore, I'm also open to some other suggestions or workaround for this.
EDIT: Due to the comment, I'm posting a sample code, but the complete example would be like my whole program. Therefore, I'm posting a simpler example:
public class TestJsonConverter : JsonConverter<string>
{
private async Task<string> GetString()
{
await Task.Delay(500);
return "Test";
}
public override string Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
{
if (reader.TokenType == JsonTokenType.String)
{
string value = reader.GetString();
// The following line is an error: cannot use `await` here.
// Should mark the method as `async`, but cannot (can't even try because of the `ref` parameter.
string valueEnhancned = value + await GetString();
return valueEnhancned;
}
throw new Exception("invalid");
}
public override void Write(Utf8JsonWriter writer, string value, JsonSerializerOptions options)
{
throw new NotImplementedException();
}
}
As you can see, what I'd like to achieve is the call of GetString() inside the Read method. But, I cannot mark async that method.
EDIT2: Adding image to response a comment.
As you can see, if the method is marked as async, it needs to return Task:
