feat: echo request headers in response over REST transport (#1509)

util/genrest/goviewcreator.go

@@ -93,6 +93,8 @@ func NewView(model *gomodel.Model) (*goview.View, error) {
 			source.P(`  backend.StdLog.Printf("  urlPathParams (expect %d, have %%d): %%q", numUrlPathParams, urlPathParams)`, len(allURLVariables))
 			source.P(`  backend.StdLog.Printf("  urlRequestHeaders:\n%%s", resttools.PrettyPrintHeaders(r, "    "))`)
 			source.P("")
+			source.P("  resttools.IncludeRequestHeadersInResponse(w, r)")
+			source.P("")
 			source.P("  if numUrlPathParams!=%d {", len(allURLVariables))
 			source.P(`    backend.Error(w, http.StatusBadRequest, "found unexpected number of URL variables: expected %d, have %%d: %%#v", numUrlPathParams, urlPathParams)`, len(allURLVariables))
 			source.P("    return")

util/genrest/resttools/headers.go

@@ -98,3 +98,16 @@ func PrettyPrintHeaders(request *http.Request, indentation string) string {
 	}
 	return strings.Join(lines, "\n")
 }
+
+// IncludeRequestHeadersInResponse includes all headers in the request `r` and includes them in the response `w`,
+// prefixing each of these header keys with a constant to reflect they came from the request.
+func IncludeRequestHeadersInResponse(w http.ResponseWriter, r *http.Request) {
+	const prefix = "x-showcase-request-"
+
+	responseHeaders := w.Header()
+	for requestKey, valueList := range r.Header {
+		for _, value := range valueList {
+			responseHeaders.Add(prefix+requestKey, value)
+		}
+	}
+}