1 files changed, 30 insertions, 0 deletions
diff --git a/src/StardewModdingAPI.Web/Framework/RewriteSubdomainRule.cs b/src/StardewModdingAPI.Web/Framework/RewriteSubdomainRule.cs
new file mode 100644
index 00000000..9b89cb65
--- /dev/null
+++ b/src/StardewModdingAPI.Web/Framework/RewriteSubdomainRule.cs
@@ -0,0 +1,30 @@
+using System;
+using Microsoft.AspNetCore.Rewrite;
+
+namespace StardewModdingAPI.Web.Framework
+{
+    /// <summary>Rewrite requests to prepend the subdomain portion (if any) to the path.</summary>
+    /// <remarks>Derived from <a href="https://stackoverflow.com/a/44526747/262123" />.</remarks>
+    public class RewriteSubdomainRule : IRule
+    {
+        /// <summary>Applies the rule. Implementations of ApplyRule should set the value for <see cref="RewriteContext.Result" /> (defaults to RuleResult.ContinueRules).</summary>
+        /// <param name="context">The rewrite context.</param>
+        public void ApplyRule(RewriteContext context)
+        {
+            context.Result = RuleResult.ContinueRules;
+
+            // get host parts
+            string host = context.HttpContext.Request.Host.Host;
+            string[] parts = host.Split('.');
+
+            // validate
+            if (parts.Length < 2)
+                return;
+            if (parts.Length < 3 && !"localhost".Equals(parts[1], StringComparison.InvariantCultureIgnoreCase))
+                return;
+
+            // prepend to path
+            context.HttpContext.Request.Path = $"/{parts[0]}{context.HttpContext.Request.Path}";
+        }
+    }
+}