Fix StaticCache::getData() returning true on empty cache

StaticCache::getData() unconditionally returned true even when no data
had been inserted, causing callers to read uninitialized storage.

Add a populated_ flag that tracks whether insertData() has been called.
getData() now returns false with an appropriate error when the cache is
empty. Also fix clearList() to reset the flag and getListLength() to
return 0 when empty.

Fixes #769

Signed-off-by: Pavel Guzenfeld <me@pavelguzenfeld.com>

Author: PavelGuzenfeld

tf2/include/tf2/time_cache.hpp

@@ -191,6 +191,7 @@ class StaticCache : public TimeCacheInterface
 
 private:
   TransformStorage storage_;
+  bool populated_{false};
 };
 }  // namespace tf2
 #endif  // TF2__TIME_CACHE_HPP_

tf2/src/static_cache.cpp

@@ -40,8 +40,16 @@ bool tf2::StaticCache::getData(
   tf2::TimePoint time,
   tf2::TransformStorage & data_out, std::string * error_str, TF2Error * error_code)
 {
-  (void)error_code;
-  (void)error_str;
+  (void)time;
+  if (!populated_) {
+    if (error_str) {
+      *error_str = "Static cache is empty";
+    }
+    if (error_code) {
+      *error_code = TF2Error::TF2_LOOKUP_ERROR;
+    }
+    return false;
+  }
   data_out = storage_;
   data_out.stamp_ = time;
   return true;
@@ -50,12 +58,13 @@ bool tf2::StaticCache::getData(
 bool tf2::StaticCache::insertData(const tf2::TransformStorage & new_data)
 {
   storage_ = new_data;
+  populated_ = true;
   return true;
 }
 
-void tf2::StaticCache::clearList() {}
+void tf2::StaticCache::clearList() {populated_ = false;}
 
-unsigned tf2::StaticCache::getListLength() {return 1;}
+unsigned tf2::StaticCache::getListLength() {return populated_ ? 1 : 0;}
 
 tf2::CompactFrameID tf2::StaticCache::getParent(
   tf2::TimePoint time, std::string * error_str,
@@ -64,7 +73,7 @@ tf2::CompactFrameID tf2::StaticCache::getParent(
   (void)time;
   (void)error_code;
   (void)error_str;
-  return storage_.frame_id_;
+  return populated_ ? storage_.frame_id_ : 0;
 }
 
 tf2::P_TimeAndFrameID tf2::StaticCache::getLatestTimeAndParent()