frostfs-sdk-csharp/src/FrostFS.SDK.Client/Pool/ClientWrapper.cs

using System;
using System.Threading.Tasks;

using Grpc.Core;

namespace FrostFS.SDK.Client;

// clientWrapper is used by default, alternative implementations are intended for testing purposes only.
public class ClientWrapper : ClientStatusMonitor
{
    private readonly object _lock = new();
    private SessionCache sessionCache;

    internal ClientWrapper(WrapperPrm wrapperPrm, Pool pool) : base(wrapperPrm.Logger, wrapperPrm.Address)
    {
        WrapperPrm = wrapperPrm;
        ErrorThreshold = wrapperPrm.ErrorThreshold;

        sessionCache = pool.SessionCache;
        Client = new FrostFSClient(WrapperPrm, sessionCache);
    }

    internal FrostFSClient? Client { get; private set; }

    internal WrapperPrm WrapperPrm { get; }

    internal FrostFSClient? GetClient()
    {
        lock (_lock)
        {
            if (IsHealthy())
            {
                return Client;
            }

            return null;
        }
    }

    // dial establishes a connection to the server from the FrostFS network.
    // Returns an error describing failure reason. If failed, the client
    // SHOULD NOT be used.
    internal async Task Dial(CallContext ctx)
    {
        var client = GetClient() ?? throw new FrostFsInvalidObjectException("pool client unhealthy");

        await client.Dial(ctx).ConfigureAwait(false);
    }

    internal void HandleError(Exception ex)
    {
        if (ex is FrostFsResponseException responseException && responseException.Status != null)
        {
            switch (responseException.Status.Code)
            {
                case FrostFsStatusCode.Internal:
                case FrostFsStatusCode.WrongMagicNumber:
                case FrostFsStatusCode.SignatureVerificationFailure:
                case FrostFsStatusCode.NodeUnderMaintenance:
                    IncErrorRate();
                    return;
            }
        }

        IncErrorRate();
    }

    private async Task ScheduleGracefulClose()
    {
        if (Client == null)
            return;

        await Task.Delay((int)WrapperPrm.GracefulCloseOnSwitchTimeout).ConfigureAwait(false);

        Client.Close();
    }

    // restartIfUnhealthy checks healthy status of client and recreate it if status is unhealthy.
    // Indicating if status was changed by this function call and returns error that caused unhealthy status.
    internal async Task<bool> RestartIfUnhealthy(CallContext ctx)
    {
        bool wasHealthy;

        try
        {
            var response = await Client!.GetNodeInfoAsync(ctx).ConfigureAwait(false);
            return false;
        }
        catch (RpcException)
        {
            wasHealthy = true;
        }

        // if connection is dialed before, to avoid routine/connection leak,
        // pool has to close it and then initialize once again.
        if (IsDialed())
        {
            await ScheduleGracefulClose().ConfigureAwait(false);
        }

        FrostFSClient? client = null;

        try
        {
            client = new(WrapperPrm, sessionCache);

            var dialCtx = new CallContext(TimeSpan.FromTicks((long)WrapperPrm.DialTimeout), ctx.CancellationToken);

            var error = await client.Dial(ctx).ConfigureAwait(false);
            if (!string.IsNullOrEmpty(error))
            {
                SetUnhealthyOnDial();
                return wasHealthy;
            }

            lock (_lock)
            {
                Client = client;
            }

            client = null;
        }
        finally
        {
            client?.Dispose();
        }

        try
        {
            var res = await Client.GetNodeInfoAsync(ctx).ConfigureAwait(false);
        }
        catch (FrostFsException)
        {
            SetUnhealthy();
            
            return wasHealthy;
        }

        SetHealthy();
        return !wasHealthy;
    }

    internal void IncRequests(ulong elapsed, MethodIndex method)
    {
        var methodStat = Methods[(int)method];

        methodStat.IncRequests(elapsed);
    }
}