add getField(), getDataType()

src/lib/ebus/data.cpp

@@ -997,6 +997,29 @@ string DataFieldSet::getName(ssize_t fieldIndex) const {
   return ostream.str();
 }
 
+const SingleDataField* DataFieldSet::getField(ssize_t fieldIndex) const {
+  if (fieldIndex < (ssize_t)m_ignoredCount) {
+    return nullptr;
+  }
+  if ((size_t)fieldIndex + m_ignoredCount >= m_fields.size()) {
+    return nullptr;
+  }
+  if (m_ignoredCount == 0) {
+    return m_fields[fieldIndex];
+  }
+  ssize_t remain = fieldIndex;
+  for (const auto field : m_fields) {
+    if (field->isIgnored()) {
+      continue;
+    }
+    remain--;
+    if (remain == 0) {
+      return field;
+    }
+  }
+  return nullptr;
+}
+
 result_t DataFieldSet::derive(const string& name, PartType partType, int divisor,
     const map<unsigned int, string>& values, map<string, string>* attributes,
     vector<const SingleDataField*>* fields) const {

src/lib/ebus/data.h

@@ -270,6 +270,13 @@ class DataField : public AttributedItem {
    */
   virtual string getName(ssize_t fieldIndex) const = 0;
 
+  /**
+   * Get the specified field.
+   * @param fieldIndex the index of the field (excluding ignored fields).
+   * @return the field, or @a nullptr if not available.
+   */
+  virtual const SingleDataField* getField(ssize_t fieldIndex) const = 0;
+
   /**
    * Dump the field settings to the output.
    * @param prependFieldSeparator whether to start with a @a FIELD_SEPARATOR.
@@ -417,6 +424,20 @@ class SingleDataField : public DataField {
     return isIgnored() || fieldIndex > 0 ? "" : m_name;
   }
 
+  // @copydoc
+  virtual const SingleDataField* getField(ssize_t fieldIndex) const {
+    if (isIgnored() || fieldIndex > 0) {
+      return nullptr;
+    }
+    return const_cast<SingleDataField*>(this);
+  }
+
+  /**
+   * Return the data type definition.
+   * @return the data type definition.
+   */
+  const DataType* getDataType() const { return m_dataType; }
+
   /**
    * Dump the common prefix field settings to the output (name and part type).
    * @param prependFieldSeparator whether to start with a @a FIELD_SEPARATOR.
@@ -658,6 +679,9 @@ class DataFieldSet : public DataField {
   // @copydoc
   string getName(ssize_t fieldIndex) const override;
 
+  // @copydoc
+  const SingleDataField* getField(ssize_t fieldIndex) const override;
+
   // @copydoc
   result_t derive(const string& name, PartType partType, int divisor,
       const map<unsigned int, string>& values, map<string, string>* attributes,

src/lib/ebus/message.h

@@ -285,6 +285,13 @@ class Message : public AttributedItem {
    */
   string getFieldName(ssize_t fieldIndex) const { return m_data->getName(fieldIndex); }
 
+  /**
+   * Get the specified field.
+   * @param fieldIndex the index of the field (excluding ignored fields).
+   * @return the field, or @a nullptr if not available.
+   */
+  const SingleDataField* getField(ssize_t fieldIndex) const { return m_data->getField(fieldIndex); }
+
   /**
    * Get whether this is a write message.
    * @return whether this is a write message.