propagation context from request to store

context/context.go

@@ -2,6 +2,7 @@ package context
 
 import (
 	"context"
+	"fmt"
 	"net/http"
 )
 
@@ -11,5 +12,10 @@ type Store interface {
 
 func Server(store Store) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
+		data, err := store.Fetch(r.Context())
+		if err != nil {
+			return
+		}
+		fmt.Fprint(w, data)
 	}
 }

context/context_test.go

@@ -2,6 +2,7 @@ package context
 
 import (
 	"context"
+	"errors"
 	"log"
 	"net/http"
 	"net/http/httptest"
@@ -40,6 +41,24 @@ func (s *SpyStore) Fetch(ctx context.Context) (string, error) {
 	}
 }
 
+type SpyResponseWriter struct {
+	written bool
+}
+
+func (s *SpyResponseWriter) Header() http.Header {
+	s.written = true
+	return nil
+}
+
+func (s *SpyResponseWriter) Write([]byte) (int, error) {
+	s.written = true
+	return 0, errors.New("not implemented")
+}
+
+func (s *SpyResponseWriter) WriteHeader(statusCode int) {
+	s.written = true
+}
+
 func TestServer(t *testing.T) {
 	t.Run("returns data from store", func(t *testing.T) {
 		data := "hello, world"
@@ -67,8 +86,12 @@ func TestServer(t *testing.T) {
 		time.AfterFunc(5*time.Millisecond, cancel)
 		request = request.WithContext(cancellingCtx)
 
-		response := httptest.NewRecorder()
+		response := &SpyResponseWriter{}
 
 		svr.ServeHTTP(response, request)
+
+		if response.written {
+			t.Error("a response should not have been written")
+		}
 	})
 }