bugfix: handle empty stacks correctly

matthiasrichter · matthiasrichter · commit 7069eded34d5 · 2018-05-29T09:44:26.000+02:00
diff --git a/DataFormats/Headers/include/Headers/DataHeader.h b/DataFormats/Headers/include/Headers/DataHeader.h
@@ -524,13 +524,34 @@ struct Stack {
   static byte* inject(byte* here, const T& h, const Args... args) noexcept {
     auto alsohere = inject(here, h);
     // the type might be a stack itself, loop through headers and set the flag in the last one
-    BaseHeader* next = BaseHeader::get(here);
-    while (next->flagsNextHeader) {
-      next = next->next();
+    if (h.size() > 0) {
+      BaseHeader* next = BaseHeader::get(here);
+      while (next->flagsNextHeader) {
+        next = next->next();
+      }
+      next->flagsNextHeader = hasNonEmptyArg(args...);
     }
-    next->flagsNextHeader = true;
     return inject(alsohere, args...);
   }
+
+  // helper function to check if there is at least one non-empty header/stack in the argument pack
+  template <typename T, typename... Args>
+  static bool hasNonEmptyArg(const T& h, const Args&... args) noexcept
+  {
+    if (h.size() > 0) {
+      return true;
+    }
+    return hasNonEmptyArg(args...);
+  }
+
+  template <typename T>
+  static bool hasNonEmptyArg(const T& h) noexcept
+  {
+    if (h.size() > 0) {
+      return true;
+    }
+    return false;
+  }
 };
 
 //__________________________________________________________________________________________________
diff --git a/DataFormats/Headers/test/testDataHeader.cxx b/DataFormats/Headers/test/testDataHeader.cxx
@@ -200,16 +200,35 @@ namespace o2 {
       BOOST_CHECK(h2->size() == sizeof(NameHeader<9>));
       BOOST_CHECK(h2->getNameLength() == 9);
 
+      // create new stack from stack and additional header
       auto meta = test::MetaHeader{ 42 };
       Stack s2{ s1, meta };
       BOOST_CHECK(s2.size() == s1.size() + sizeof(decltype(meta)));
 
       auto* h3 = get<test::MetaHeader*>(s1.data());
       BOOST_CHECK(h3 == nullptr);
       h3 = get<test::MetaHeader*>(s2.data());
-      BOOST_CHECK(h3 != nullptr);
+      BOOST_REQUIRE(h3 != nullptr);
+      BOOST_CHECK(h3->flagsNextHeader == false);
       h1 = get<DataHeader*>(s2.data());
-      BOOST_CHECK(h1 != nullptr);
+      BOOST_REQUIRE(h1 != nullptr);
+      BOOST_CHECK(h1->flagsNextHeader == true);
+
+      // create stack from header and empty stack
+      Stack s3{ meta, Stack{} };
+      BOOST_CHECK(s3.size() == sizeof(meta));
+      h3 = get<test::MetaHeader*>(s3.data());
+      BOOST_REQUIRE(h3 != nullptr);
+      // no next header to be flagged as the stack was empty
+      BOOST_CHECK(h3->flagsNextHeader == false);
+
+      // create new stack from stack, empty stack, and header
+      Stack s4{ s1, Stack{}, meta };
+      BOOST_CHECK(s4.size() == s1.size() + sizeof(meta));
+      // check if we can find the header even though there was an empty stack in the middle
+      h3 = get<test::MetaHeader*>(s4.data());
+      BOOST_REQUIRE(h3 != nullptr);
+      BOOST_CHECK(h3->secret == 42);
     }
 
     BOOST_AUTO_TEST_CASE(Descriptor_benchmark)
