Remote configuration tests and performance improvements

tracer/src/Datadog.Trace/RemoteConfigurationManagement/RemoteConfigurationPath.cs

@@ -3,14 +3,15 @@
 // This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2017 Datadog, Inc.
 // </copyright>
 
-using System.Text.RegularExpressions;
+using System;
 using Datadog.Trace.Util;
 
 namespace Datadog.Trace.RemoteConfigurationManagement
 {
     internal sealed record RemoteConfigurationPath
     {
-        private static readonly Regex PathRegex = new Regex("^(datadog/\\d+|employee)/([^/]+)/([^/]+)/[^/]+$", RegexOptions.Compiled);
+        private const string DatadogPrefix = "datadog/";
+        private const string EmployeePrefix = "employee/";
 
         private RemoteConfigurationPath(string path, string product, string id)
         {
@@ -27,14 +28,72 @@ private RemoteConfigurationPath(string path, string product, string id)
 
         public static RemoteConfigurationPath FromPath(string path)
         {
-            var matcher = PathRegex.Match(path);
-            if (!matcher.Success)
+            // Previous regex: ^(datadog/\d+|employee)/([^/]+)/([^/]+)/[^/]+$
+            // Determine prefix and find the start of the product segment.
+            // "datadog/{digits}/{product}/{id}/{filename}"
+            // "employee/{product}/{id}/{filename}"
+            int productStart;
+
+            if (path is null)
+            {
+                ThrowHelper.ThrowException("Error parsing path: path is null");
+                return default; // unreachable, satisfies compiler
+            }
+            else if (path.StartsWith(DatadogPrefix, StringComparison.Ordinal))
+            {
+                // Find the slash after the digits: "datadog/{digits}/"
+                var digitStart = DatadogPrefix.Length;
+                var secondSlash = path.IndexOf('/', digitStart);
+                if (secondSlash < 0 || secondSlash == digitStart)
+                {
+                    ThrowHelper.ThrowException($"Error parsing path: {path}");
+                }
+
+                // Verify all characters between are digits
+                for (var i = digitStart; i < secondSlash; i++)
+                {
+                    if (path[i] is < '0' or > '9')
+                    {
+                        ThrowHelper.ThrowException($"Error parsing path: {path}");
+                    }
+                }
+
+                productStart = secondSlash + 1;
+            }
+            else if (path.StartsWith(EmployeePrefix, StringComparison.Ordinal))
+            {
+                productStart = EmployeePrefix.Length;
+            }
+            else
+            {
+                ThrowHelper.ThrowException($"Error parsing path: {path}");
+                return default; // unreachable, satisfies compiler
+            }
+
+            // From productStart we need exactly: {product}/{id}/{filename}
+            // i.e. two more slashes, no empty segments, no trailing content after filename.
+            var thirdSlash = path.IndexOf('/', productStart);
+            if (thirdSlash < 0 || thirdSlash == productStart)
+            {
+                ThrowHelper.ThrowException($"Error parsing path: {path}");
+            }
+
+            var idStart = thirdSlash + 1;
+            var fourthSlash = path.IndexOf('/', idStart);
+            if (fourthSlash < 0 || fourthSlash == idStart)
+            {
+                ThrowHelper.ThrowException($"Error parsing path: {path}");
+            }
+
+            // Filename must be non-empty and there must be no more slashes
+            var filenameStart = fourthSlash + 1;
+            if (filenameStart >= path.Length || path.IndexOf('/', filenameStart) >= 0)
             {
                 ThrowHelper.ThrowException($"Error parsing path: {path}");
             }
 
-            var product = matcher.Groups[2].Value;
-            var id = matcher.Groups[3].Value;
+            var product = path.Substring(productStart, thirdSlash - productStart);
+            var id = path.Substring(idStart, fourthSlash - idStart);
 
             return new RemoteConfigurationPath(path, product, id);
         }