Connection Improvements¶

As described in the DNS topic, DNS queries can be prefetched and cached on startup, long before the first user interaction, so the first request does not have to wait for name resolution.

There is also a new TCP connection step after the DNS query. The old logic walked the IP addresses from the DNS result one by one. If the first address was slow and used up the request's connect time, the whole request timed out, even though another address could have connected quickly.

To resolve this issue, and even improve on the connection speed in v3, if there are multiple addresses it will try to connect to a maximum of 4 (by default, it's configurable) at once and pick the fastest connecting one! Those addresses that fail to connect are marked as such, and if there's a need for a new connection, those IP addresses will be tried last.

Another new feature is that custom IP address shuffling algorithms can be added and implemented.

High-Level Flow¶

Here's a high-level view about the algorithm:

graph TD
    Start(Start)
    Start --> A

    subgraph _start [DNS & TCP Connection]

        subgraph DNS [DNSCache]
            A(Query/Prefetch) --> B(Check DNS Cache)
            B -->|Cache Hit| L[Return Cached Entry]
            B -->|Cache Miss| C(DNS Query)
            C --> D[Cache DNS Result]
            D --> L[Return Cached Entry]
        end

        subgraph Connect [TCP Connection Logic]
            F{Are there multiple IP addresses?} -->|Yes| M
            M[Shuffle Addresses] --> G
            F -->|No| H[Single Connection Attempt]
            G[Parallel Connection Attempts] --> Q
            G[Parallel Connection Attempts] --> Q
            G[Parallel Connection Attempts] --> Q
            G[Parallel Connection Attempts] --> Q
            Q{"Connection Success?"} -->|Yes| J
            Q -->|No| K
            N{Has More Address?} -->|Yes| I
            H --> Q
            J["Select First (Fastest) Connection"]
            K[Mark IP Failure] --> N
            I[Try Next IP Address] --> Q
        end

    end

    L --> F
    J --> NEG
    N -->|No| NEG

    subgraph NEG ["Further Connection/Negotiation Process"]
        Failure
        Success
    end

Sockets that lose the race¶

The first socket that connects is the one the request uses. The other attempts are not discarded when they connect later.

A socket that finishes connecting after a winner has already been chosen is kept in a shared cache, keyed by host name and port. The next connection to that same host and port takes the cached socket and skips a new race, as long as the socket is still connected. Sockets that fail to connect are still reported as non-working and are not cached. A cached socket that has already closed is dropped, and the lookup continues with the next entry.

Cached sockets expire. The defaults are 20 seconds (UnusedSocketCacheDuration) and 256 sockets (MaxCachedSockets). Either limit turns the cache off when it is set to zero or a negative value. A full cache, or the application quitting, closes the late socket instead of storing it.

Both values come from the host's TCPRingmasterSettings at the moment the race starts:

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Best.HTTP.Shared.HTTPManager.PerHostSettings.Get("example.com")
    .TCPRingmasterSettings.UnusedSocketCacheDuration = TimeSpan.FromMinutes(1);

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var settings = Best.HTTP.Shared.HTTPManager.PerHostSettings.Get("*");
settings.TCPRingmasterSettings.UnusedSocketCacheDuration = TimeSpan.Zero;

UnusedSocketCacheDuration = TimeSpan.Zero and MaxCachedSockets = 0 both disable the cache.

Code Examples¶

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Best.HTTP.Shared.HTTPManager.PerHostSettings.Get("example.com")
                .TCPRingmasterSettings.ShuffleAddresses = false;

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Best.HTTP.Shared.HTTPManager.PerHostSettings.Get("*")
                .TCPRingmasterSettings.ShuffleAddresses = false;

More about how to use PerHostSettings can be found under the Per-Host Settings topic.

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Best.HTTP.Shared.HTTPManager.PerHostSettings.Get("example.com")
                .TCPRingmasterSettings.CustomAddressShuffleAlgorithm 
                    = (@params) =>
                    {
                        var rand = new System.Random();
                        int n = @params.Addresses.Length;
                        while (n > 1)
                        {
                            int k = rand.Next(n--);
                            (@params.Addresses[n], @params.Addresses[k]) = (@params.Addresses[k], @params.Addresses[n]);
                        }
                    };

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var settings = Best.HTTP.Shared.HTTPManager.PerHostSettings.Get("example.com");
            settings.TCPRingmasterSettings.MaxSimultaneousRacers = 1;
            settings.TCPRingmasterSettings.ShuffleAddresses = false;

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