avoid some string and array alloc in ParseVersion (#7349)

* avoid some string alloc in ParseVersion

* Simplify

* Change parameter type and improve naming

* Remove string split from ctor

---------

Co-authored-by: Brandon Ording <[email protected]>

Author: SimonCropp

src/NServiceBus.Core/Routing/MessageDrivenSubscriptions/MessageType.cs

@@ -1,7 +1,6 @@
 namespace NServiceBus.Unicast.Subscriptions;
 
 using System;
-using System.Linq;
 
 /// <summary>
 /// Representation of a message type that clients can be subscribed to.
@@ -24,9 +23,18 @@ public MessageType(Type type)
     public MessageType(string messageTypeString)
     {
         ArgumentException.ThrowIfNullOrWhiteSpace(messageTypeString);
-        var parts = messageTypeString.Split(',');
+
         Version = ParseVersion(messageTypeString);
-        TypeName = parts.First();
+
+        var messageTypeSpan = messageTypeString.AsSpan();
+        var index = messageTypeSpan.IndexOf(',');
+
+        if (index >= 0)
+        {
+            messageTypeSpan = messageTypeSpan[..index];
+        }
+
+        TypeName = messageTypeSpan.ToString();
     }
 
     /// <summary>
@@ -62,17 +70,19 @@ public MessageType(string typeName, Version version)
     /// </summary>
     public Version Version { get; }
 
-    static Version ParseVersion(string versionString)
+    static Version ParseVersion(ReadOnlySpan<char> input)
     {
-        const string version = "Version=";
-        var index = versionString.IndexOf(version);
+        const string versionPrefix = "Version=";
+        var versionPrefixIndex = input.IndexOf(versionPrefix);
 
-        if (index >= 0)
+        if (versionPrefixIndex >= 0)
         {
-            versionString = versionString.Substring(index + version.Length)
-                .Split(',').First();
+            input = input[(versionPrefixIndex + versionPrefix.Length)..];
+            var firstComma = input.IndexOf(',');
+            input = input[..firstComma];
         }
-        return Version.Parse(versionString);
+
+        return Version.Parse(input);
     }
 
     /// <summary>