server: Wrap decision log error messages

Previously the server didn't wrap the error messages which made it
hard to determine the source of internal errors coming back from OPA
when deployed with a custom decision logger.

Fixes #1367

Signed-off-by: Torin Sandall <torinsandall@gmail.com>

server/server.go

@@ -2400,7 +2400,7 @@ func (l decisionLogger) Log(ctx context.Context, txn storage.Transaction, decisi
 
 	if l.logger != nil {
 		if err := l.logger(ctx, info); err != nil {
-			return err
+			return errors.Wrap(err, "decision_logs")
 		}
 	}
 

server/server_test.go

@@ -2780,6 +2780,22 @@ func TestDecisionLogging(t *testing.T) {
 
 }
 
+func TestDecisionLogErrorMessage(t *testing.T) {
+
+	f := newFixture(t)
+
+	f.server.WithDecisionLoggerWithErr(func(context.Context, *Info) error {
+		return fmt.Errorf("xxx")
+	})
+
+	if err := f.v1(http.MethodPost, "/data", "", 500, `{
+		"code": "internal_error",
+		"message": "decision_logs: xxx"
+	}`); err != nil {
+		t.Fatal(err)
+	}
+}
+
 func TestWatchParams(t *testing.T) {
 	f := newFixture(t)
 	r1 := newMockConn()