From 9e5ef71c04a299088512e5686fb35608307c4658 Mon Sep 17 00:00:00 2001
From: Carl Jackson <carl@avtok.com>
Date: Sun, 23 Mar 2014 03:31:46 -0700
Subject: [PATCH] Automatic OPTIONS middleware

---
 default.go                |  1 +
 web/middleware/options.go | 63 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)
 create mode 100644 web/middleware/options.go

diff --git a/default.go b/default.go
index fca2a27..6ec68ed 100644
--- a/default.go
+++ b/default.go
@@ -14,6 +14,7 @@ func init() {
 	DefaultMux.Use("RequestId", middleware.RequestId)
 	DefaultMux.Use("Logger", middleware.Logger)
 	DefaultMux.Use("Recoverer", middleware.Recoverer)
+	DefaultMux.Use("AutomaticOptions", middleware.AutomaticOptions)
 }
 
 // Append the given middleware to the default Mux's middleware stack. See the
diff --git a/web/middleware/options.go b/web/middleware/options.go
new file mode 100644
index 0000000..ffa969b
--- /dev/null
+++ b/web/middleware/options.go
@@ -0,0 +1,63 @@
+package middleware
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+
+	"github.com/zenazn/goji/web"
+)
+
+// Automatically return an appropriate "Allow" header when the request method is
+// OPTIONS and the request would have otherwise been 404'd.
+func AutomaticOptions(c *web.C, h http.Handler) http.Handler {
+	fn := func(w http.ResponseWriter, r *http.Request) {
+		// This will probably slow down OPTIONS calls a bunch, but it
+		// probably won't happen too much, and it'll just be hitting the
+		// 404 route anyways.
+		var fw *httptest.ResponseRecorder
+		pw := w
+		if strings.ToUpper(r.Method) == "OPTIONS" {
+			fw = httptest.NewRecorder()
+			pw = fw
+		}
+
+		h.ServeHTTP(pw, r)
+
+		if fw == nil {
+			return
+		}
+
+		for k, v := range fw.Header() {
+			w.Header()[k] = v
+		}
+
+		methods := getValidMethods(*c)
+
+		if fw.Code == http.StatusNotFound && methods != nil {
+			w.Header().Set("Allow", strings.Join(methods, ", "))
+			w.WriteHeader(http.StatusOK)
+		} else {
+			w.WriteHeader(fw.Code)
+			io.Copy(w, fw.Body)
+		}
+	}
+
+	return http.HandlerFunc(fn)
+}
+
+func getValidMethods(c web.C) []string {
+	if c.Env == nil {
+		return nil
+	}
+	v, ok := c.Env["goji.web.validMethods"]
+	if !ok {
+		return nil
+	}
+	if methods, ok := v.([]string); ok {
+		return methods
+	} else {
+		return nil
+	}
+}