messages: throw AccessException when trying to access invalid field/i…

…ndex

And check for it in the ulog_data example

examples/ulog_data.cpp

@@ -49,6 +49,7 @@ int main(int argc, char** argv)
   for (const auto& sub : subscription_names) {
     std::cout << sub << "\n";
   }
+  std::cout << "\n";
 
   // Get a particular subscription
   if (subscription_names.find("vehicle_status") != subscription_names.end()) {
@@ -62,30 +63,34 @@ int main(int argc, char** argv)
     std::cout << "Field names: "
               << "\n";
     for (const std::string& field : subscription->fieldNames()) {
-      std::cout << field << "\n";
+      std::cout << "  " << field << "\n";
     }
 
     // Get particular field
-    auto nav_state_field = subscription->field("nav_state");
+    try {
+      auto nav_state_field = subscription->field("nav_state");
 
-    // Iterate over all samples
-    std::cout << "nav_state values: \n";
-    for (const auto& sample : *subscription) {
-      // always correctly extracts the type as defined in the message definition,
-      // gets cast to the value you put in int.
-      // This also works for arrays and strings.
-      auto nav_state = sample[nav_state_field].as<int>();
-      std::cout << nav_state << ", ";
-    }
-    std::cout << "\n";
+      // Iterate over all samples
+      std::cout << "nav_state values: \n  ";
+      for (const auto& sample : *subscription) {
+        // always correctly extracts the type as defined in the message definition,
+        // gets cast to the value you put in int.
+        // This also works for arrays and strings.
+        auto nav_state = sample[nav_state_field].as<int>();
+        std::cout << nav_state << ", ";
+      }
+      std::cout << "\n";
 
-    // get a specific sample
-    auto sample_12 = subscription->at(12);
+      // get a specific sample
+      auto sample_12 = subscription->at(12);
 
-    // access values by name
-    auto timestamp = sample_12["timestamp"].as<uint64_t>();
+      // access values by name
+      auto timestamp = sample_12["timestamp"].as<uint64_t>();
 
-    std::cout << timestamp << "\n";
+      std::cout << "timestamp at sample 12: " << timestamp << "\n";
+    } catch (const ulog_cpp::AccessException& exception) {
+      std::cout << "AccessException: " << exception.what() << "\n";
+    }
   } else {
     std::cout << "No vehicle_status subscription found\n";
   }
@@ -95,16 +100,20 @@ int main(int argc, char** argv)
     const auto& message_format = data_container->messageFormats().at("esc_status");
     std::cout << "Message format: " << message_format->name() << "\n";
     for (const auto& field_name : message_format->fieldNames()) {
-      std::cout << field_name << "\n";
+      std::cout << "  " << field_name << "\n";
     }
   } else {
     std::cout << "No esc_status message format found\n";
   }
 
   if (subscription_names.find("esc_status") != subscription_names.end()) {
-    auto esc_status = data_container->subscription("esc_status");
-    for (const auto& sample : *esc_status) {
-      std::cout << "esc_power: " << sample["esc"][7]["esc_power"].as<int>() << "\n";
+    try {
+      auto esc_status = data_container->subscription("esc_status");
+      for (const auto& sample : *esc_status) {
+        std::cout << "esc_power: " << sample["esc"][7]["esc_power"].as<int>() << "\n";
+      }
+    } catch (const ulog_cpp::AccessException& exception) {
+      std::cout << "AccessException: " << exception.what() << "\n";
     }
   } else {
     std::cout << "No esc_status subscription found\n";

test/read_api_test.cpp

@@ -259,6 +259,12 @@ TEST_CASE("Write complicated, nested data format, then read it")
       sample[f_child_1][f_c1_c1_2][2][f_c1_c1_2_byte_b].asNativeTypeVariant()));
   CHECK(std::holds_alternative<std::vector<uint64_t>>(
       sample[f_child_1][f_c1_unsigned_long].asNativeTypeVariant()));
+
+  // Check exceptions
+  CHECK_THROWS_AS(sample["non_existent"], ulog_cpp::AccessException);
+  CHECK_THROWS_AS(sample[f_child_1][f_c1_unsigned_long][100], ulog_cpp::AccessException);
+  CHECK_THROWS_AS(data_container->subscription("non_existent_subscription"),
+                  ulog_cpp::AccessException);
 }
 
 TEST_SUITE_END();

ulog_cpp/data_container.hpp

@@ -105,14 +105,13 @@ class DataContainer : public DataHandlerInterface {
     return names;
   }
 
-  std::shared_ptr<Subscription> subscription(const std::string& name, int multi_id) const
+  std::shared_ptr<Subscription> subscription(const std::string& name, int multi_id = 0) const
   {
-    return _subscriptions_by_name_and_multi_id.at({name, multi_id});
-  }
-
-  std::shared_ptr<Subscription> subscription(const std::string& name) const
-  {
-    return _subscriptions_by_name_and_multi_id.at({name, 0});
+    const auto it = _subscriptions_by_name_and_multi_id.find({name, multi_id});
+    if (it == _subscriptions_by_name_and_multi_id.end()) {
+      throw AccessException("Subscription not found: " + name);
+    }
+    return it->second;
   }
 
  protected:

ulog_cpp/messages.hpp

@@ -605,7 +605,14 @@ class MessageFormat {
    * @param name the name of the field
    * @return the requested field
    */
-  std::shared_ptr<Field> field(const std::string& name) const { return _fields.at(name); }
+  std::shared_ptr<Field> field(const std::string& name) const
+  {
+    const auto it = _fields.find(name);
+    if (it == _fields.end()) {
+      throw AccessException("Field not found: " + name);
+    }
+    return it->second;
+  }
 
  private:
   std::string _name;

ulog_cpp/subscription.hpp

@@ -260,7 +260,13 @@ class Subscription {
                                                                    _message_format);
   }
 
-  TypedDataView at(std::size_t n) const { return begin()[n]; }
+  TypedDataView at(std::size_t n) const
+  {
+    if (n >= size()) {
+      throw AccessException("Index out of range: " + std::to_string(n));
+    }
+    return begin()[n];
+  }
 
   TypedDataView operator[](std::size_t n) { return at(n); }