fix: merged headers

builder.go

@@ -265,7 +265,11 @@ func (builder Builder) Merge(other Builder) Builder {
 	}
 
 	if other.headers != nil {
-		builder.headers = other.headers
+		for key, values := range other.headers {
+			for _, value := range values {
+				builder.headers.Add(key, value)
+			}
+		}
 	}
 
 	if other.body != nil {

handler.go

@@ -2,6 +2,7 @@ package akumu
 
 import (
 	"context"
+	"fmt"
 	"net/http"
 )
 
@@ -22,7 +23,9 @@ func handleError(writer http.ResponseWriter, request *http.Request, err error, p
 
 	if builder, ok := err.(Builder); ok {
 		if parent != nil {
-			parent.Merge(builder).Handle(writer, request)
+			parent.
+				Merge(builder).
+				Handle(writer, request)
 
 			return
 		}
@@ -33,6 +36,8 @@ func handleError(writer http.ResponseWriter, request *http.Request, err error, p
 	}
 
 	if responder, ok := err.(Responder); ok {
+		fmt.Printf("Responder: %T\n %#v", responder, parent)
+
 		if parent != nil {
 			parent.
 				Merge(responder.Respond(request)).

problem_test.go

@@ -23,6 +23,12 @@ func customProblemHandler(request *http.Request) error {
 	)
 }
 
+func customProblemHandler2(request *http.Request) error {
+	return akumu.
+		Failed(ErrNotAuthenticated).
+		Header("X-Foo", "Bar")
+}
+
 func problemHandler(request *http.Request) error {
 	return akumu.Failed(akumu.Problem{
 		Type:     "http://example.com/problems/not-found",
@@ -33,6 +39,25 @@ func problemHandler(request *http.Request) error {
 	})
 }
 
+func TestItHandlesErrorsWithHeaders(t *testing.T) {
+	request, err := http.NewRequest("GET", "/", nil)
+	request.Header.Add("Accept", "application/problem+json")
+
+	if err != nil {
+		t.Fatalf("unable to create request: %s", err)
+	}
+
+	response := akumu.Record(customProblemHandler2, request)
+
+	if response.Code != ErrNotAuthenticated.Status {
+		t.Fatalf("unexpected status code: %d, expected %d", response.Code, ErrNotAuthenticated.Status)
+	}
+
+	if value := response.Header().Get("X-Foo"); value != "Bar" {
+		t.Fatalf("unexpected header value: %s, expected %s", value, "Bar")
+	}
+}
+
 func TestProblemHandler(t *testing.T) {
 	request, err := http.NewRequest("GET", "/", nil)