optimize log parser for very long multi-line messages

2 files changed, 122 insertions, 30 deletions

diff --git a/src/SMAPI.Web/Framework/LogParsing/LogMessageBuilder.cs b/src/SMAPI.Web/Framework/LogParsing/LogMessageBuilder.cs
new file mode 100644
index 00000000..371acfd3
--- /dev/null
+++ b/src/SMAPI.Web/Framework/LogParsing/LogMessageBuilder.cs
@@ -0,0 +1,88 @@
+using System;
+using System.Text;
+using StardewModdingAPI.Web.Framework.LogParsing.Models;
+
+namespace StardewModdingAPI.Web.Framework.LogParsing
+{
+    /// <summary>Handles constructing log message instances with minimal memory allocation.</summary>
+    internal class LogMessageBuilder
+    {
+        /*********
+        ** Fields
+        *********/
+        /// <summary>The local time when the next log was posted.</summary>
+        public string Time { get; set; }
+
+        /// <summary>The log level for the next log message.</summary>
+        public LogLevel Level { get; set; }
+
+        /// <summary>The mod name for the next log message.</summary>
+        public string Mod { get; set; }
+
+        /// <summary>The text for the next log message.</summary>
+        private readonly StringBuilder Text = new StringBuilder();
+
+
+        /*********
+        ** Accessors
+        *********/
+        /// <summary>Whether the next log message has been started.</summary>
+        public bool Started { get; private set; }
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Start accumulating values for a new log message.</summary>
+        /// <param name="time">The local time when the log was posted.</param>
+        /// <param name="level">The log level.</param>
+        /// <param name="mod">The mod name.</param>
+        /// <param name="text">The initial log text.</param>
+        /// <exception cref="InvalidOperationException">A log message is already started; call <see cref="Clear"/> before starting a new message.</exception>
+        public void Start(string time, LogLevel level, string mod, string text)
+        {
+            if (this.Started)
+                throw new InvalidOperationException("Can't start new message, previous log message isn't done yet.");
+
+            this.Started = true;
+
+            this.Time = time;
+            this.Level = level;
+            this.Mod = mod;
+            this.Text.AppendLine(text);
+        }
+
+        /// <summary>Add a new line to the next log message being built.</summary>
+        /// <param name="text">The line to add.</param>
+        /// <exception cref="InvalidOperationException">A log message hasn't been started yet.</exception>
+        public void AddLine(string text)
+        {
+            if (!this.Started)
+                throw new InvalidOperationException("Can't add text, no log message started yet.");
+
+            this.Text.AppendLine(text);
+        }
+
+        /// <summary>Get a log message for the accumulated values.</summary>
+        public LogMessage Build()
+        {
+            if (!this.Started)
+                return null;
+
+            return new LogMessage
+            {
+                Time = this.Time,
+                Level = this.Level,
+                Mod = this.Mod,
+                Text = this.Text.ToString()
+            };
+        }
+
+        /// <summary>Reset to start a new log message.</summary>
+        public void Clear()
+        {
+            this.Started = false;
+            this.Text.Clear();
+        }
+    }
+}
diff --git a/src/SMAPI.Web/Framework/LogParsing/LogParser.cs b/src/SMAPI.Web/Framework/LogParsing/LogParser.cs
index cc91ec51..9ef1c53f 100644
--- a/src/SMAPI.Web/Framework/LogParsing/LogParser.cs
+++ b/src/SMAPI.Web/Framework/LogParsing/LogParser.cs
@@ -282,43 +282,47 @@ namespace StardewModdingAPI.Web.Framework.LogParsing
         /// <exception cref="LogParseException">The log text can't be parsed successfully.</exception>
         private IEnumerable<LogMessage> GetMessages(string logText)
         {
-            LogMessage message = new LogMessage();
-            using (StringReader reader = new StringReader(logText))
+            LogMessageBuilder builder = new LogMessageBuilder();
+            using StringReader reader = new StringReader(logText);
+            while (true)
             {
-                while (true)
-                {
-                    // read data
-                    string line = reader.ReadLine();
-                    if (line == null)
-                        break;
-                    Match header = this.MessageHeaderPattern.Match(line);
-
-                    // validate
-                    if (message.Text == null && !header.Success)
-                        throw new LogParseException("Found a log message with no SMAPI metadata. Is this a SMAPI log file?");
+                // read line
+                string line = reader.ReadLine();
+                if (line == null)
+                    break;
 
-                    // start or continue message
-                    if (header.Success)
-                    {
-                        if (message.Text != null)
-                            yield return message;
+                // match header
+                Match header = this.MessageHeaderPattern.Match(line);
+                bool isNewMessage = header.Success;
 
-                        message = new LogMessage
-                        {
-                            Time = header.Groups["time"].Value,
-                            Level = Enum.Parse<LogLevel>(header.Groups["level"].Value, ignoreCase: true),
-                            Mod = header.Groups["modName"].Value,
-                            Text = line.Substring(header.Length)
-                        };
+                // start/continue message
+                if (isNewMessage)
+                {
+                    if (builder.Started)
+                    {
+                        yield return builder.Build();
+                        builder.Clear();
                     }
-                    else
-                        message.Text += "\n" + line;
+
+                    builder.Start(
+                        time: header.Groups["time"].Value,
+                        level: Enum.Parse<LogLevel>(header.Groups["level"].Value, ignoreCase: true),
+                        mod: header.Groups["modName"].Value,
+                        text: line.Substring(header.Length)
+                    );
                 }
+                else
+                {
+                    if (!builder.Started)
+                        throw new LogParseException("Found a log message with no SMAPI metadata. Is this a SMAPI log file?");
 
-                // end last message
-                if (message.Text != null)
-                    yield return message;
+                    builder.AddLine(line);
+                }
             }
+
+            // end last message
+            if (builder.Started)
+                yield return builder.Build();
         }
     }
 }