1 files changed, 78 insertions, 0 deletions
diff --git a/src/rocksdb/utilities/merge_operators/string_append/stringappend.cc b/src/rocksdb/utilities/merge_operators/string_append/stringappend.cc
new file mode 100644
index 000000000..5092cabcb
--- /dev/null
+++ b/src/rocksdb/utilities/merge_operators/string_append/stringappend.cc
@@ -0,0 +1,78 @@
+/**
+ * A MergeOperator for rocksdb that implements string append.
+ * @author Deon Nicholas (dnicholas@fb.com)
+ * Copyright 2013 Facebook
+ */
+
+#include "stringappend.h"
+
+#include <assert.h>
+
+#include <memory>
+
+#include "rocksdb/merge_operator.h"
+#include "rocksdb/slice.h"
+#include "rocksdb/utilities/options_type.h"
+#include "utilities/merge_operators.h"
+
+namespace ROCKSDB_NAMESPACE {
+namespace {
+static std::unordered_map<std::string, OptionTypeInfo>
+    stringappend_merge_type_info = {
+#ifndef ROCKSDB_LITE
+        {"delimiter",
+         {0, OptionType::kString, OptionVerificationType::kNormal,
+          OptionTypeFlags::kNone}},
+#endif  // ROCKSDB_LITE
+};
+}  // namespace
+// Constructor: also specify the delimiter character.
+StringAppendOperator::StringAppendOperator(char delim_char)
+    : delim_(1, delim_char) {
+  RegisterOptions("Delimiter", &delim_, &stringappend_merge_type_info);
+}
+
+StringAppendOperator::StringAppendOperator(const std::string& delim)
+    : delim_(delim) {
+  RegisterOptions("Delimiter", &delim_, &stringappend_merge_type_info);
+}
+
+// Implementation for the merge operation (concatenates two strings)
+bool StringAppendOperator::Merge(const Slice& /*key*/,
+                                 const Slice* existing_value,
+                                 const Slice& value, std::string* new_value,
+                                 Logger* /*logger*/) const {
+  // Clear the *new_value for writing.
+  assert(new_value);
+  new_value->clear();
+
+  if (!existing_value) {
+    // No existing_value. Set *new_value = value
+    new_value->assign(value.data(), value.size());
+  } else {
+    // Generic append (existing_value != null).
+    // Reserve *new_value to correct size, and apply concatenation.
+    new_value->reserve(existing_value->size() + delim_.size() + value.size());
+    new_value->assign(existing_value->data(), existing_value->size());
+    new_value->append(delim_);
+    new_value->append(value.data(), value.size());
+  }
+
+  return true;
+}
+
+std::shared_ptr<MergeOperator> MergeOperators::CreateStringAppendOperator() {
+  return std::make_shared<StringAppendOperator>(',');
+}
+
+std::shared_ptr<MergeOperator> MergeOperators::CreateStringAppendOperator(
+    char delim_char) {
+  return std::make_shared<StringAppendOperator>(delim_char);
+}
+
+std::shared_ptr<MergeOperator> MergeOperators::CreateStringAppendOperator(
+    const std::string& delim) {
+  return std::make_shared<StringAppendOperator>(delim);
+}
+
+}  // namespace ROCKSDB_NAMESPACE