feat: configurable default http handler

options.go

@@ -2,6 +2,7 @@ package proxy
 
 import (
 	"context"
+	"net/http"
 	"net/http/httputil"
 	"net/url"
 )
@@ -11,6 +12,7 @@ type Options struct {
 	RequestTransformers  []RequestTransformer
 	ResponseTransformers []ResponseTransformer
 	ReverseProxyFactory  ReverseProxyFactory
+	DefaultHandler       http.Handler
 }
 
 func defaultOptions() *Options {
@@ -19,6 +21,7 @@ func defaultOptions() *Options {
 		RequestTransformers:  make([]RequestTransformer, 0),
 		ResponseTransformers: make([]ResponseTransformer, 0),
 		ReverseProxyFactory:  DefaultReverseProxyFactory,
+		DefaultHandler:       DefaultHandler,
 	}
 }
 
@@ -53,3 +56,13 @@ func WithReverseProxyFactory(fn ReverseProxyFactory) OptionFunc {
 func DefaultReverseProxyFactory(ctx context.Context, target *url.URL) *httputil.ReverseProxy {
 	return httputil.NewSingleHostReverseProxy(target)
 }
+
+func WithDefaultHandler(handler http.Handler) OptionFunc {
+	return func(o *Options) {
+		o.DefaultHandler = handler
+	}
+}
+
+var DefaultHandler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	http.Error(w, http.StatusText(http.StatusBadGateway), http.StatusBadGateway)
+})

proxy.go

@@ -17,6 +17,7 @@ type Proxy struct {
 	responseTransformers []ResponseTransformer
 	requestTransformers  []RequestTransformer
 	reverseProxyFactory  ReverseProxyFactory
+	defaultHandler       http.Handler
 }
 
 // ServeHTTP implements http.Handler
@@ -82,8 +83,7 @@ func (p *Proxy) proxyRequest(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if reverser == nil {
-		http.Error(w, http.StatusText(http.StatusBadGateway), http.StatusBadGateway)
-
+		p.defaultHandler.ServeHTTP(w, r)
 		return
 	}
 
@@ -103,6 +103,7 @@ func New(funcs ...OptionFunc) *Proxy {
 	proxy.requestTransformers = opts.RequestTransformers
 	proxy.responseTransformers = opts.ResponseTransformers
 	proxy.reverseProxyFactory = opts.ReverseProxyFactory
+	proxy.defaultHandler = opts.DefaultHandler
 
 	return proxy
 }