Add TryQueryOffset API

[Gsantomaggio]

Closes: #370

[Gsantomaggio]

@bangjiehan Better late than never :) WDYT?

[bangjiehan]

Thank you for trying to improve this API.

TryQueryOffset could be implemented without throwing any Exception at all. Maybe put actual implementation in TryQueryOffset(exception-free, of course) and reimplement QueryOffset by wrapping TryQueryOffset(if returned value is null, thrown exception to maintain old behavior).
Throwing exception is a somehow expensive operation in C#. It create exception object, capture calling stack, search exception handlers etc. So, in normal flow, we won't throw and capture an exception to process a value we could expect.

I found StreamStats.FirstOffset() and StreamStats.CommittedChunkId() have similar issue.

[Gsantomaggio]

Thank you @bangjiehan
I can't touch QueryOffset due to compatibility.

So you would do:

  try
            {
                var qOffset = await QueryOffset(reference, stream).ConfigureAwait(false);
                return qOffset;
            }
            catch (Exception)
            {
                return null;
            }

Isn't that misleading? I mean, any Exception?

About QueryOffset and TryQueryOffset I have to leave both the API for at least a reasonable time

[Gsantomaggio]

I found StreamStats.FirstOffset() and StreamStats.CommittedChunkId() have similar issue.

I can't remove these API I can Add other API(s) with TryFirstOffset and TryCommittedChunkId

thank you for let me know

[Gsantomaggio]

@bangjiehan ok now TryQueryOffset is excpetion Free.

@lukebakken WDYT?

[bangjiehan]

@Gsantomaggio
Sorry, my last comment was misleading and wrong. I did not notice there are other Exceptions could be thrown by different ResponseCode. I was thinking only about OffsetNotFoundException.

My original intention is below:

public async Task<ulong> QueryOffset(string reference, string stream)
{
    ulong? offset = await TryQueryOffset(reference, stream).ConfigureAwait(false);
    return offset ?? throw new OffsetNotFoundException($"QueryOffset stream: {stream}, reference: {reference}"));
}

// Mostly copied from original QueryOffset.
public async Task<ulong?> TryQueryOffset(string reference, string stream)
{
    MaybeThrowQueryException(reference, stream);

    var response = await _client.QueryOffset(reference, stream).ConfigureAwait(false);

    // Offset do not exist so just return null. There is no need to throw an OffsetNotFoundException and capture it.
    if (response.ResponseCode = ResponseCode.OffsetNotFound)
    {
        return null;
    }

    ClientExceptions.MaybeThrowException(response.ResponseCode, $"QueryOffset stream: {stream}, reference: {reference}");
    return response.Offset;
}

These codes just to convey my intention and it still just a workaround I think.

Maybe, QueryOffsetResponse should treat 'offset not exist' as one of its results in the end.

[Gsantomaggio]

@bangjiehan makes more sense now! I will merge thank you