download: Surface bundle download errors via debug logging

This change logs the error response body at debug level.
Since the errors could contain senstive info we don't
include them in the status message. So this approach helps to
get more information about the error at debug log level which
is mostly used in a non-prod setup.

Fixes: #6609

Signed-off-by: Ashutosh Narkar <anarkar4387@gmail.com>

download/download.go

@@ -405,6 +405,13 @@ func (d *Downloader) download(ctx context.Context, m metrics.Metrics) (*download
 			longPoll: d.longPollingEnabled,
 		}, nil
 	default:
+		if d.logger.GetLevel() == logging.Debug && resp.Body != nil {
+			body, err := io.ReadAll(resp.Body)
+			if err == nil {
+				d.logger.Debug("bundle download error response with response body: %s", body)
+			}
+		}
+
 		return nil, HTTPError{StatusCode: resp.StatusCode}
 	}
 }

download/download_test.go

@@ -641,6 +641,51 @@ func TestFailureUnexpected(t *testing.T) {
 	}
 }
 
+func TestFailureUnexpectedWithResponseBody(t *testing.T) {
+
+	ctx := context.Background()
+
+	expResp := "this is a bad http response"
+
+	fixture := newTestFixture(t)
+	fixture.server.expCode = 500
+	fixture.server.expResp = expResp
+
+	defer fixture.server.stop()
+
+	d := New(Config{}, fixture.client, "/bundles/test/bundle1")
+
+	logger := test.New()
+	logger.SetLevel(logging.Debug)
+	d.logger = logger
+
+	err := d.oneShot(ctx)
+	if err == nil {
+		t.Fatal("expected error")
+	}
+	var hErr HTTPError
+	if !errors.As(err, &hErr) {
+		t.Fatal("expected HTTPError")
+	}
+	if hErr.StatusCode != 500 {
+		t.Fatal("expected status code 500")
+	}
+
+	expectLogged := fmt.Sprintf("bundle download error response with response body: %s", expResp)
+
+	var found bool
+	for _, entry := range logger.Entries() {
+		if entry.Message == expectLogged {
+			found = true
+			break
+		}
+	}
+
+	if !found {
+		t.Errorf("Expected log entry: %s", expectLogged)
+	}
+}
+
 func TestEtagInResponse(t *testing.T) {
 	ctx := context.Background()
 	fixture := newTestFixture(t)

download/testharness.go

@@ -257,6 +257,7 @@ type testServer struct {
 	t              *testing.T
 	customAuth     func(http.ResponseWriter, *http.Request) error
 	expCode        int
+	expResp        string
 	expEtag        string
 	expAuth        string
 	bundles        map[string]bundle.Bundle
@@ -374,6 +375,11 @@ func (t *testServer) handle(w http.ResponseWriter, r *http.Request) {
 
 	if t.expCode != 0 {
 		w.WriteHeader(t.expCode)
+
+		if t.expResp != "" {
+			w.Write([]byte(t.expResp))
+		}
+
 		return
 	}