HappyTime

HappyTime is a small .NET implementation of the classic RFC 868 Time Protocol.

It listens for Time Protocol requests over TCP and UDP and returns the current time as a 32-bit unsigned integer representing the number of seconds since 1900-01-01 00:00:00 UTC, encoded in network byte order (big-endian).

Protocol

RFC 868 uses port 37.

TCP

A client connects to TCP port 37.

The server immediately sends exactly four bytes containing the current Time Protocol timestamp, then closes the connection.

UDP

A client sends a datagram to UDP port 37.

The server replies with a four-byte Time Protocol timestamp.

The contents of the request datagram are not significant.

Timestamp Format

The wire value is:

uint32 seconds since 1900-01-01 00:00:00 UTC

The value is transmitted in big-endian byte order.

Example:

EE 77 AC 73

decodes to:

4000820339 seconds since 1900-01-01
2026-10-12 18:58:59 UTC

Because RFC 868 uses an unsigned 32-bit counter, the timestamp wraps in February 2036.

Requirements

• .NET 10 SDK
• Windows or Linux
• Permission to bind the configured TCP and UDP ports

HappyTime uses JoyfulReaperLib for its shared TCP server infrastructure.

Build

dotnet build

Run

dotnet run

By default, HappyTime is intended to use TCP and UDP port 37. If you are developing without elevated privileges, configure a higher port such as 1037.

Configuration

HappyTime uses the standard .NET configuration system.

Typical options include:

{
  "HappyTime": {
    "ListenAddress": "0.0.0.0",
    "Port": 37,
    "MaxConcurrentConnections": 100,
    "RequestTimeoutSeconds": 5,
    "UdpEnabled": true,
    "UdpPort": 37
  }
}

Exact option names should match HappyTimeOptions.

Testing from PowerShell

TCP

$client = [System.Net.Sockets.TcpClient]::new("127.0.0.1", 37)

try {
    $stream = $client.GetStream()
    $buffer = [byte[]]::new(4)
    $read = 0

    while ($read -lt 4) {
        $n = $stream.Read($buffer, $read, 4 - $read)
        if ($n -eq 0) { break }
        $read += $n
    }

    if ($read -ne 4) {
        throw "Expected 4 bytes, received $read"
    }

    $seconds = [System.Buffers.Binary.BinaryPrimitives]::ReadUInt32BigEndian($buffer)
    $epoch = [DateTimeOffset]::new(1900, 1, 1, 0, 0, 0, [TimeSpan]::Zero)

    "Raw bytes: $([Convert]::ToHexString($buffer))"
    "Seconds since 1900: $seconds"
    "Server time (UTC): $($epoch.AddSeconds($seconds).ToString('u'))"
}
finally {
    if ($null -ne $client) {
        $client.Dispose()
    }
}

UDP

$udp = [System.Net.Sockets.UdpClient]::new()
$udp.Client.ReceiveTimeout = 3000

try {
    $udp.Connect("127.0.0.1", 37)

    [void]$udp.Send([byte[]]@(0), 1)

    $remote = [System.Net.IPEndPoint]::new(
        [System.Net.IPAddress]::Any, 0)

    $buffer = $udp.Receive([ref]$remote)

    if ($buffer.Length -ne 4) {
        throw "Expected 4 bytes, received $($buffer.Length)"
    }

    $seconds = [System.Buffers.Binary.BinaryPrimitives]::ReadUInt32BigEndian($buffer)
    $epoch = [DateTimeOffset]::new(1900, 1, 1, 0, 0, 0, [TimeSpan]::Zero)

    "Raw bytes: $([Convert]::ToHexString($buffer))"
    "Seconds since 1900: $seconds"
    "Server time (UTC): $($epoch.AddSeconds($seconds).ToString('u'))"
}
finally {
    $udp.Dispose()
}

If HappyTime is configured on a development port such as 1037, replace 37 in the examples above.

Status

The core RFC 868 implementation has been verified locally over both:

• TCP
• UDP

Planned follow-up work includes:

• Mission Control telemetry
• Production deployment
• Remote TCP and UDP verification

License

Copyright (c) 2026 Kyle Givler

Licensed under the MIT License.

References

• RFC 868 — Time Protocol