internal requests respond with defaultURL

links/links.go

@@ -39,11 +39,14 @@ func FromHeadersOrDefault(h *http.Header, r *http.Request, defaultURL *url.URL)
 		}
 	}
 	if !strings.HasPrefix(host, "api") {
-		log.Info(r.Context(), "X-Forwarded-Host is not an external host, using incoming request host", log.Data{
+		log.Info(r.Context(), "X-Forwarded-Host is not an external host, returning defaultURL", log.Data{
 			"r.Host":       r.Host,
 			"r.remoteAddr": r.RemoteAddr,
 		})
-		host = r.Host
+		defaultURL = defaultURL.JoinPath(path)
+		return &Builder{
+			URL: defaultURL,
+		}
 	}
 
 	scheme := h.Get("X-Forwarded-Proto")

links/links_test.go

@@ -297,3 +297,29 @@ func TestBuilder_BuildLink(t *testing.T) {
 	})
 
 }
+
+func Test_FromHeadersOrDefault_NonApiHost(t *testing.T) {
+	Convey("Given a non-api forwarded host", t, func() {
+		defaultURL, err := url.Parse("http://localhost:8080/")
+		So(err, ShouldBeNil)
+
+		h := &http.Header{}
+		h.Add("X-Forwarded-Host", "internalhost")
+		h.Add("X-Forwarded-Path-Prefix", "/prefix")
+
+		r := &http.Request{
+			URL:  &url.URL{},
+			Host: "differenthost:8080",
+		}
+
+		Convey("When the builder is created", func() {
+			builder := FromHeadersOrDefault(h, r, defaultURL)
+
+			Convey("Then the builder URL should be the default URL with the path prefix", func() {
+				So(builder, ShouldNotBeNil)
+				So(builder.URL, ShouldNotBeNil)
+				So(builder.URL.String(), ShouldEqual, "http://localhost:8080/prefix")
+			})
+		})
+	})
+}