add req/resp header forwarding modifiers

proxychain/responsemodifers/forward_response_headers.go

@@ -0,0 +1,51 @@
+package responsemodifers
+
+import (
+	"fmt"
+	"ladder/proxychain"
+	"net/url"
+	"strings"
+)
+
+var forwardBlacklist map[string]bool
+
+func init() {
+	forwardBlacklist = map[string]bool{
+		"content-length":            true,
+		"content-encoding":          true,
+		"transfer-encoding":         true,
+		"strict-transport-security": true,
+		"connection":                true,
+		"keep-alive":                true,
+	}
+}
+
+// ForwardResponseHeaders forwards the response headers from the upstream server to the client
+func ForwardResponseHeaders() proxychain.ResponseModification {
+	return func(chain *proxychain.ProxyChain) error {
+
+		for uname, headers := range chain.Response.Header {
+			name := strings.ToLower(uname)
+			if forwardBlacklist[name] {
+				continue
+			}
+
+			// patch location header to forward to proxy instead
+			if name == "location" {
+				u, err := url.Parse(chain.Context.BaseURL())
+				if err != nil {
+					return err
+				}
+				newLocation := fmt.Sprintf("%s://%s/%s", u.Scheme, u.Host, headers[0])
+				chain.Context.Set("location", newLocation)
+			}
+
+			// forward headers
+			for _, value := range headers {
+				chain.Context.Set(name, value)
+			}
+		}
+
+		return nil
+	}
+}