We will ignore malformed log lines in the JSON log file - so the rest of the logviewer continues to work

src/Umbraco.Core/Logging/Viewer/JsonLogViewer.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using Newtonsoft.Json;
 using Serilog.Events;
 using Serilog.Formatting.Compact.Reader;
 
@@ -10,13 +11,15 @@ namespace Umbraco.Core.Logging.Viewer
     internal class JsonLogViewer : LogViewerSourceBase
     {
         private readonly string _logsPath;
+        private readonly ILogger _logger;
 
-        public JsonLogViewer(string logsPath = "", string searchPath = "") : base(searchPath)
+        public JsonLogViewer(ILogger logger, string logsPath = "", string searchPath = "") : base(searchPath)
         {
             if (string.IsNullOrEmpty(logsPath))
                 logsPath = $@"{AppDomain.CurrentDomain.BaseDirectory}\App_Data\Logs\";
 
             _logsPath = logsPath;
+            _logger = logger;
         }
 
         private const int FileSizeCap = 100;
@@ -77,8 +80,14 @@ namespace Umbraco.Core.Logging.Viewer
                         using (var stream = new StreamReader(fs))
                         {
                             var reader = new LogEventReader(stream);
-                            while (reader.TryRead(out var evt))
+                            while (TryRead(reader, out var evt))
                             {
+                                //We may get a null if log line is malformed
+                                if (evt == null)
+                                {
+                                    continue;
+                                }
+
                                 if (count > skip + take)
                                 {
                                     break;
@@ -105,5 +114,21 @@ namespace Umbraco.Core.Logging.Viewer
             return logs;
         }
 
+        private bool TryRead(LogEventReader reader, out LogEvent evt)
+        {
+            try
+            {
+                return reader.TryRead(out evt);
+            }
+            catch (JsonReaderException ex)
+            {
+                // As we are reading/streaming one line at a time in the JSON file
+                // Thus we can not rpeort the line number, as it will always be 1
+                _logger.Error<JsonLogViewer>(ex, "Unable to parse a line in the JSON log file");
+
+                evt = null;
+                return true;
+            }
+        }
     }
 }

src/Umbraco.Core/Logging/Viewer/LogViewerComposer.cs

@@ -9,7 +9,7 @@ namespace Umbraco.Core.Logging.Viewer
     {
         public void Compose(Composition composition)
         {
-            composition.SetLogViewer(_ => new JsonLogViewer());
+            composition.SetLogViewer(_ => new JsonLogViewer(composition.Logger));
         }
     }
 }

src/Umbraco.Tests/Logging/LogviewerTests.cs

@@ -1,4 +1,5 @@
-using NUnit.Framework;
+using Moq;
+using NUnit.Framework;
 using System;
 using System.IO;
 using System.Linq;
@@ -47,7 +48,8 @@ namespace Umbraco.Tests.Logging
             File.Copy(exampleLogfilePath, _newLogfilePath, true);
             File.Copy(exampleSearchfilePath, _newSearchfilePath, true);
 
-            _logViewer = new JsonLogViewer(logsPath: _newLogfileDirPath, searchPath: _newSearchfilePath);
+            var logger = Mock.Of<Core.Logging.ILogger>();
+            _logViewer = new JsonLogViewer(logger, logsPath: _newLogfileDirPath, searchPath: _newSearchfilePath);
         }
 
         [OneTimeTearDown]