[RocksDB] allow LDB tool to have customized key formatter

Summary: Currently ldb tool dump keys either in ascii format or hex format - neither is ideal if the key has a binary structure and is not readable in ascii. This diff also allows LDB tool to be customized in ways beyond DB options.

Test Plan: verify that key formatter works with some simple db with binary key.

Reviewers: sdong, ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D19209

include/rocksdb/ldb_tool.h

@@ -4,13 +4,32 @@
 // of patent rights can be found in the PATENTS file in the same directory.
 #ifndef ROCKSDB_LITE
 #pragma once
+#include <string>
 #include "rocksdb/options.h"
 
 namespace rocksdb {
 
+// An interface for converting a slice to a readable string
+class SliceFormatter {
+ public:
+  virtual ~SliceFormatter() {}
+  virtual std::string Format(const Slice& s) const = 0;
+};
+
+// Options for customizing ldb tool (beyond the DB Options)
+struct LDBOptions {
+  // Create LDBOptions with default values for all fields
+  LDBOptions();
+
+  // Key formatter that converts a slice to a readable string.
+  // Default: Slice::ToString()
+  std::shared_ptr<SliceFormatter> key_formatter;
+};
+
 class LDBTool {
  public:
-  void Run(int argc, char** argv, Options = Options());
+  void Run(int argc, char** argv, Options db_options= Options(),
+           const LDBOptions& ldb_options = LDBOptions());
 };
 
 } // namespace rocksdb