Add changes to enable searching for .msg files in sub-directories

rosbag2_storage_mcap/src/message_definition_cache.cpp

@@ -44,6 +44,12 @@ static const std::unordered_set<std::string> PRIMITIVE_TYPES{
   "bool",  "byte",   "char",  "float32", "float64", "int8",   "uint8",
   "int16", "uint16", "int32", "uint32",  "int64",   "uint64", "string"};
 
+#ifdef _WIN32
+static const char SEPARATOR[] = "\\";
+#else
+static const char SEPARATOR[] = "/";
+#endif
+
 static std::set<std::string> parse_msg_dependencies(const std::string & text,
                                                     const std::string & package_context)
 {
@@ -119,6 +125,24 @@ static std::string delimiter(const DefinitionIdentifier & definition_identifier)
   return result;
 }
 
+static std::vector<std::string> split_string(const std::string & str,
+                                             const std::string & delimiter = "\n")
+{
+  std::vector<std::string> strings;
+  std::string::size_type pos = 0;
+  std::string::size_type prev = 0;
+
+  while ((pos = str.find(delimiter, prev)) != std::string::npos) {
+    strings.push_back(str.substr(prev, pos - prev));
+    prev = pos + delimiter.size();
+  }
+
+  // Get the last substring (or only, if delimiter is not found)
+  strings.push_back(str.substr(prev));
+
+  return strings;
+}
+
 MessageSpec::MessageSpec(Format format, std::string text, const std::string & package_context)
     : dependencies(parse_dependencies(format, text, package_context))
     , text(std::move(text))
@@ -139,15 +163,34 @@ const MessageSpec & MessageDefinitionCache::load_message_spec(
     throw std::invalid_argument("Invalid package resource name: " +
                                 definition_identifier.package_resource_name);
   }
-  std::string package = match[1];
-  std::string share_dir = ament_index_cpp::get_package_share_directory(package);
-  std::ifstream file{share_dir + "/msg/" + match[2].str() +
-                     extension_for_format(definition_identifier.format)};
-  if (!file.good()) {
+  const std::string package = match[1].str();
+  const std::string filename = match[2].str() + extension_for_format(definition_identifier.format);
+
+  // Get the package share directory, or throw a PackageNotFoundError
+  const std::string share_dir = ament_index_cpp::get_package_share_directory(package);
+
+  // Get the rosidl_interfaces index contents for this package
+  std::string index_contents;
+  if (!ament_index_cpp::get_resource("rosidl_interfaces", package, index_contents)) {
     throw DefinitionNotFoundError(definition_identifier.package_resource_name);
   }
 
-  std::string contents{std::istreambuf_iterator(file), {}};
+  // Find the first line that ends with the filename we're looking for
+  const auto lines = split_string(index_contents);
+  const auto it = std::find_if(lines.begin(), lines.end(), [&filename](const std::string & line) {
+    return line.size() >= filename.size() &&
+           line.compare(line.size() - filename.size(), filename.size(), filename) == 0;
+  });
+  if (it == lines.end()) {
+    throw DefinitionNotFoundError(definition_identifier.package_resource_name);
+  }
+
+  // Read the file
+  const std::string full_path = share_dir + SEPARATOR + *it;
+  std::ifstream file{full_path};
+
+  const std::string contents{std::istreambuf_iterator(file), {}};
+
   const MessageSpec & spec =
     msg_specs_by_definition_identifier_
       .emplace(definition_identifier,