jellyfin-server/Jellyfin.Api/Controllers/TimeSyncController.cs

using System;
using MediaBrowser.Model.SyncPlay;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;

namespace Jellyfin.Api.Controllers;

/// <summary>
/// The time sync controller.
/// </summary>
[Route("")]
public class TimeSyncController : BaseJellyfinApiController
{
    /// <summary>
    /// Gets the current UTC time.
    /// </summary>
    /// <response code="200">Time returned.</response>
    /// <returns>An <see cref="UtcTimeResponse"/> to sync the client and server time.</returns>
    [HttpGet("GetUtcTime")]
    [ProducesResponseType(statusCode: StatusCodes.Status200OK)]
    public ActionResult<UtcTimeResponse> GetUtcTime()
    {
        // Important to keep the following line at the beginning
        var requestReceptionTime = DateTime.UtcNow;

        // Important to keep the following line at the end
        var responseTransmissionTime = DateTime.UtcNow;

        // Implementing NTP on such a high level results in this useless
        // information being sent. On the other hand it enables future additions.
        return new UtcTimeResponse(requestReceptionTime, responseTransmissionTime);
    }
}