Moved headers middleware into its own package

Further trying out spreading out the code outside of the nested functions

middleware/headers/headers.go

+package headers
+
+import (
+	"net/http"
+
+	"github.com/mholt/caddy/middleware/util"
+)
+
+// Headers is middleware that adds headers to the responses
+// for requests matching a certain path.
+type Headers struct {
+	next  http.HandlerFunc
+	rules []headers
+}
+
+// ServeHTTP implements the http.Handler interface and serves the requests,
+// adding headers to the response according to the configured rules.
+func (h *Headers) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	for _, rule := range h.rules {
+		if util.Path(r.URL.Path).Matches(rule.Url) {
+			for _, header := range rule.Headers {
+				w.Header().Set(header.Name, header.Value)
+			}
+		}
+	}
+	h.next(w, r)
+}
+
+type (
+	// Headers groups a slice of HTTP headers by a URL pattern.
+	// TODO: use http.Header type instead??
+	headers struct {
+		Url     string
+		Headers []header
+	}
+
+	// Header represents a single HTTP header, simply a name and value.
+	header struct {
+		Name  string
+		Value string
+	}
+)

middleware/headers/new.go

+package headers
+
+import (
+	"net/http"
+
+	"github.com/mholt/caddy/middleware"
+)
+
+// New constructs and configures a new headers middleware instance.
+func New(c middleware.Controller) (middleware.Middleware, error) {
+
+	rules, err := parse(c)
+	if err != nil {
+		return nil, err
+	}
+
+	return func(next http.HandlerFunc) http.HandlerFunc {
+		head := Headers{
+			next:  next,
+			rules: rules,
+		}
+		return head.ServeHTTP
+	}, nil
+}

middleware/headers.go → middleware/headers/parse.go

-package middleware
+package headers
 
-import "net/http"
+import "github.com/mholt/caddy/middleware"
 
-// Headers is middleware that adds headers to the responses
-// for requests matching a certain path.
-func Headers(p parser) Middleware {
-	type (
-		// Header represents a single HTTP header, simply a name and value.
-		header struct {
-			Name  string
-			Value string
-		}
-
-		// Headers groups a slice of HTTP headers by a URL pattern.
-		headers struct {
-			Url     string
-			Headers []header
-		}
-	)
+func parse(c middleware.Controller) ([]headers, error) {
 	var rules []headers
 
-	for p.NextLine() {
+	for c.NextLine() {
 		var head headers
 		var isNewPattern bool
 
-		if !p.NextArg() {
-			return p.ArgErr()
+		if !c.NextArg() {
+			return rules, c.ArgErr()
 		}
-		pattern := p.Val()
+		pattern := c.Val()
 
 		// See if we already have a definition for this URL pattern...
 		for _, h := range rules {
@@ -43,22 +28,22 @@ func Headers(p parser) Middleware {
 			isNewPattern = true
 		}
 
-		for p.NextBlock() {
-			h := header{Name: p.Val()}
+		for c.NextBlock() {
+			h := header{Name: c.Val()}
 
-			if p.NextArg() {
-				h.Value = p.Val()
+			if c.NextArg() {
+				h.Value = c.Val()
 			}
 
 			head.Headers = append(head.Headers, h)
 		}
-		if p.NextArg() {
-			h := header{Name: p.Val()}
+		if c.NextArg() {
+			h := header{Name: c.Val()}
 
-			h.Value = p.Val()
+			h.Value = c.Val()
 
-			if p.NextArg() {
-				h.Value = p.Val()
+			if c.NextArg() {
+				h.Value = c.Val()
 			}
 
 			head.Headers = append(head.Headers, h)
@@ -76,16 +61,5 @@ func Headers(p parser) Middleware {
 		}
 	}
 
-	return func(next http.HandlerFunc) http.HandlerFunc {
-		return func(w http.ResponseWriter, r *http.Request) {
-			for _, rule := range rules {
-				if Path(r.URL.Path).Matches(rule.Url) {
-					for _, header := range rule.Headers {
-						w.Header().Set(header.Name, header.Value)
-					}
-				}
-			}
-			next(w, r)
-		}
-	}
+	return rules, nil
 }