Adds in a new API endpoint to get the size of logs - which will determine to display a warning message if the filesize is too big to read (to help prevent the CPU & memory being eaten up & killing the site)

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

@@ -44,6 +44,8 @@ namespace Umbraco.Core.Logging.Viewer
         /// </summary>
         IEnumerable<LogTemplate> GetMessageTemplates(DateTimeOffset startDate, DateTimeOffset endDate);
 
+        long GetLogSize(DateTimeOffset startDate, DateTimeOffset endDate);
+
         /// <summary>
         /// Returns the collection of logs
         /// </summary>

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

@@ -67,6 +67,45 @@ namespace Umbraco.Core.Logging.Viewer
             }
 
             return logs;
-        }        
+        }
+
+        /// <summary>
+        /// This default JSON disk implementation here - returns the total filesize & NOT the count of entries
+        /// Other implementations we would expect to return the count of entries
+        /// We use this number to help prevent the logviewer killing the site with CPU/Memory if the number of items too big to handle
+        /// </summary>
+        public override long GetLogSize(DateTimeOffset startDate, DateTimeOffset endDate)
+        {
+            //Open the JSON log file for the range of dates (and exclude machinename) Could be several for LB
+            var dateRange = endDate - startDate;
+
+            //Log Directory
+            var logDirectory = $@"{AppDomain.CurrentDomain.BaseDirectory}\App_Data\Logs\";
+
+            //Number of entries
+            long count = 0;
+
+            //foreach full day in the range - see if we can find one or more filenames that end with
+            //yyyyMMdd.json - Ends with due to MachineName in filenames - could be 1 or more due to load balancing
+            for (var day = startDate.Date; day.Date <= endDate.Date; day = day.AddDays(1))
+            {
+                //Filename ending to search for (As could be multiple)
+                var filesToFind = $"*{day.ToString("yyyyMMdd")}.json";
+
+                var filesForCurrentDay = Directory.GetFiles(logDirectory, filesToFind);
+
+                //Foreach file we find - open it
+                foreach (var filePath in filesForCurrentDay)
+                {
+                    //Get the current filesize in bytes !
+                    var byteFileSize = new FileInfo(filePath).Length;
+
+                    count += byteFileSize;
+                }
+            }
+
+            //Count contains a combination of file sizes in bytes
+            return count;
+        }
     }
 }

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

@@ -3,7 +3,6 @@ using System.Collections.Generic;
 using System.Linq;
 using Newtonsoft.Json;
 using Serilog.Events;
-using Serilog.Filters.Expressions;
 using Umbraco.Core.IO;
 using Umbraco.Core.Models;
 using Umbraco.Core.Persistence.DatabaseModelDefinitions;
@@ -17,6 +16,8 @@ namespace Umbraco.Core.Logging.Viewer
 
         public abstract IEnumerable<LogEvent> GetLogs(DateTimeOffset startDate, DateTimeOffset endDate, ILogFilter filter, int skip, int take);
 
+        public abstract long GetLogSize(DateTimeOffset startDate, DateTimeOffset endDate);
+
         public virtual IEnumerable<SavedLogSearch> GetSavedSearches()
         {
             //Our default implementation
@@ -137,6 +138,6 @@ namespace Umbraco.Core.Logging.Viewer
             {
                 Items = logMessages
             };
-        }        
+        }
     }
 }

src/Umbraco.Web/Editors/LogViewerController.cs

@@ -21,6 +21,35 @@ namespace Umbraco.Web.Editors
             _logViewer = logViewer;
         }
 
+        [HttpGet]
+        public IHttpActionResult GetLogSize()
+        {
+            //Returns 200 OK if the logs can be viewed
+
+            //Check if the ILogViewer is our JSON file 
+            var isJsonLogViewer = _logViewer is JsonLogViewer;
+
+            //Don't WARN or check if it's not our JSON disk file approach
+            if (isJsonLogViewer == false)
+            {                
+                return Ok();
+            }
+
+            //Go & fetch the number of log entries OR 
+            var logSize = _logViewer.GetLogSize(startDate: DateTime.Now.AddDays(-1), endDate: DateTime.Now);
+
+            //If the number of items is less than 
+            if (logSize >= 10)
+            {
+                return Ok(logSize);
+            }
+
+            //TODO: It may need to be an Umbraco request with errow/warning notification?!
+            //Depends how best to bubble up to UI - with some custom JS promise error that is caught
+            return BadRequest();
+
+        }
+
         [HttpGet]
         public int GetNumberOfErrors()
         {