From 69eddfab1ffa7ec3a3e635a99703c779928c4922 Mon Sep 17 00:00:00 2001
From: Edwin Engelen <edwin@engelen.name>
Date: Tue, 24 Mar 2020 12:45:59 +0100
Subject: [PATCH] Send fractions of a second to Fluentd

Previously the timestamp did have a a precision of one second. The fraction got lost.

The timestamp is now of the EventTime time according to specification:
https://github.com/fluent/fluentd/wiki/Forward-Protocol-Specification-v1#eventtime-ext-format

EventTime has nanosecond precision, but .NET only supports 100 nanoseconds (ticks).

Fixes #12

Signed-off-by: Edwin Engelen <edwin@engelen.name>
---
 src/NLog.Targets.Fluentd/Fluentd.cs          | 14 +++---
 src/NLog.Targets.Fluentd/PackerExtensions.cs | 47 ++++++++++++++++++++
 2 files changed, 54 insertions(+), 7 deletions(-)
 create mode 100644 src/NLog.Targets.Fluentd/PackerExtensions.cs

diff --git a/src/NLog.Targets.Fluentd/Fluentd.cs b/src/NLog.Targets.Fluentd/Fluentd.cs
index bdb56fc..e4cd12c 100644
--- a/src/NLog.Targets.Fluentd/Fluentd.cs
+++ b/src/NLog.Targets.Fluentd/Fluentd.cs
@@ -16,11 +16,11 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.IO;
-using System.Text;
 using System.Net.Sockets;
-using System.Diagnostics;
 using System.Reflection;
+using System.Text;
 using MsgPack;
 using MsgPack.Serialization;
 
@@ -154,17 +154,15 @@ public void UnpackTo(Unpacker unpacker, object collection)
 
     internal class FluentdEmitter
     {
-        private static DateTime unixEpoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
         private readonly Packer packer;
         private readonly SerializationContext serializationContext;
         private readonly Stream destination;
 
         public void Emit(DateTime timestamp, string tag, IDictionary<string, object> data)
         {
-            long unixTimestamp = timestamp.ToUniversalTime().Subtract(unixEpoch).Ticks / 10000000;
             this.packer.PackArrayHeader(3);
             this.packer.PackString(tag, Encoding.UTF8);
-            this.packer.Pack((ulong)unixTimestamp);
+            this.packer.PackEventTime(timestamp);
             this.packer.Pack(data, serializationContext);
             this.destination.Flush();    // Change to packer.Flush() when packer is upgraded
         }
@@ -172,8 +170,10 @@ public void Emit(DateTime timestamp, string tag, IDictionary<string, object> dat
         public FluentdEmitter(Stream stream)
         {
             this.destination = stream;
-            this.packer = Packer.Create(destination);
-            var embeddedContext  = new SerializationContext(this.packer.CompatibilityOptions);
+
+            // PackerCompatibilityOptions.ProhibitExtendedTypeObjects must be turned off in order to use the PackExtendedTypeValue method
+            this.packer = Packer.Create(destination, Packer.DefaultCompatibilityOptions & ~PackerCompatibilityOptions.ProhibitExtendedTypeObjects);
+            var embeddedContext = new SerializationContext(this.packer.CompatibilityOptions);
             embeddedContext.Serializers.Register(new OrdinaryDictionarySerializer(embeddedContext, null));
             this.serializationContext = new SerializationContext(PackerCompatibilityOptions.PackBinaryAsRaw);
             this.serializationContext.Serializers.Register(new OrdinaryDictionarySerializer(this.serializationContext, embeddedContext));
diff --git a/src/NLog.Targets.Fluentd/PackerExtensions.cs b/src/NLog.Targets.Fluentd/PackerExtensions.cs
new file mode 100644
index 0000000..0b774f8
--- /dev/null
+++ b/src/NLog.Targets.Fluentd/PackerExtensions.cs
@@ -0,0 +1,47 @@
+using System;
+
+namespace NLog.Targets
+{
+    using MsgPack;
+
+    internal static class PackerExtensions
+    {
+        private const int nanoSecondsPerSecond = 1 * 1000 * 1000 * 1000;
+        private const double ticksToNanoSecondsFactor = (double)nanoSecondsPerSecond / TimeSpan.TicksPerSecond;
+        private static readonly long unixEpochTicks = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc).Ticks;
+
+        /// <summary>
+        /// Write according to Fluend EventTime specification.
+        /// </summary>
+        /// <remarks>
+        /// Specification: https://github.com/fluent/fluentd/wiki/Forward-Protocol-Specification-v1#eventtime-ext-format"
+        /// </remarks>
+        public static Packer PackEventTime(this Packer that, DateTime value)
+        {
+            DateTimeToEpoch(value, out var secondsFromEpoch, out var nanoSeconds);
+
+            that.PackExtendedTypeValue(
+                0x0,
+                new[]
+                {
+                    (byte) ((ulong) (secondsFromEpoch >> 24) & (ulong) byte.MaxValue),
+                    (byte) ((ulong) (secondsFromEpoch >> 16) & (ulong) byte.MaxValue),
+                    (byte) ((ulong) (secondsFromEpoch >> 8) & (ulong) byte.MaxValue),
+                    (byte) ((ulong) secondsFromEpoch & (ulong) byte.MaxValue),
+                    (byte) ((ulong) (nanoSeconds >> 24) & (ulong) byte.MaxValue),
+                    (byte) ((ulong) (nanoSeconds >> 16) & (ulong) byte.MaxValue),
+                    (byte) ((ulong) (nanoSeconds >> 8) & (ulong) byte.MaxValue),
+                    (byte) ((ulong) nanoSeconds & (ulong) byte.MaxValue),
+                });
+
+            return that;
+        }
+
+        private static void DateTimeToEpoch(DateTime value, out uint secondsFromEpoch, out uint nanoSeconds)
+        {
+            var fromEpochTicks = value.ToUniversalTime().Ticks - unixEpochTicks;
+            secondsFromEpoch = (uint)(fromEpochTicks / TimeSpan.TicksPerSecond);
+            nanoSeconds = (uint)((fromEpochTicks - secondsFromEpoch * TimeSpan.TicksPerSecond) * ticksToNanoSecondsFactor);
+        }
+    }
+}