From Byte[] to unixTimestamp in miliseconds

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I have a simple buffer like this one:

Byte[] buffer = new byte[] { 0x01, 0x72, 0x60, 0x77, 0x59, 0x80};

And I need to obtain the Date from this value (it's in Unix timeStamp miliseconds)

So I tried to converting to long and then passing to a function I found to convert from long to dateTime like so:

public static DateTime unixTimeStampToDateTime(long unixTimeStamp)
{
    // Unix timestamp is seconds past epoch
    DateTime  dtDateTime = new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc);
    dtDateTime = dtDateTime.AddSeconds(unixTimeStamp).ToLocalTime();
    return dtDateTime;
}

I try to get the long value from the array like this:

    long timestamp = BitConverter.ToInt64(buffer,0);

But I get this error:

System.ArgumentException: 'Destination array is not long enough to copy all the items in the collection. Check array index and length. '

What am I missing here? Thanks in advance.

EDIT the expected value out of the convertion is: 05/29/2020 14:45

asp.net-core-3.1 datetime-format datetime c#
1 Answers

You can try to Aggregate array's items with a help of Linq in order to have Int64 value:

  using System.Linq;

  ... 

  byte[] buffer = new byte[] { 0x01, 0x72, 0x60, 0x77, 0x59, 0x80 };

  ...

  long shift = buffer.Aggregate(0L, (s, a) => s * 256 + a);

  DateTime result = new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc)
    .AddMilliseconds(shift);

  Console.WriteLine($"{result:d MMMM yyyy HH:mm:ss}");

Outcome:

  29 May 2020 12:45:33

As you can see, the time is 12:45, not 14:45, so you, probably, want to deal with DateTimeKind.Utc fragment. If buffer represents local time, not UTC:

  DateTime result = new DateTime(1970, 1, 1, 0, 0, 0, 0).AddMilliseconds(shift);

if buffer represents UTC, but you want to have local time:

  DateTime result = new DateTime(1970, 1, 1, 0, 0, 0, 0, DateTimeKind.Utc)
    .AddMilliseconds(shift);

  result = result.ToLocalTime();
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