Allow Users to change customized ldb tools' header in help printing

Summary: Closes https://github.com/facebook/rocksdb/pull/2018

Differential Revision: D4748448

Pulled By: siying

fbshipit-source-id: a54c2f9

include/rocksdb/ldb_tool.h

@@ -26,6 +26,8 @@ struct LDBOptions {
   // Key formatter that converts a slice to a readable string.
   // Default: Slice::ToString()
   std::shared_ptr<SliceFormatter> key_formatter;
+
+  std::string print_help_header = "ldb - RocksDB Tool";
 };
 
 class LDBTool {

include/rocksdb/utilities/ldb_cmd.h

@@ -239,7 +239,7 @@ class LDBCommand {
 
 class LDBCommandRunner {
  public:
-  static void PrintHelp(const char* exec_name);
+  static void PrintHelp(const LDBOptions& ldb_options, const char* exec_name);
 
   static void RunCommand(
       int argc, char** argv, Options options, const LDBOptions& ldb_options,

tools/ldb_tool.cc

@@ -12,10 +12,11 @@ namespace rocksdb {
 
 LDBOptions::LDBOptions() {}
 
-void LDBCommandRunner::PrintHelp(const char* exec_name) {
+void LDBCommandRunner::PrintHelp(const LDBOptions& ldb_options,
+                                 const char* exec_name) {
   std::string ret;
 
-  ret.append("ldb - LevelDB Tool");
+  ret.append(ldb_options.print_help_header);
   ret.append("\n\n");
   ret.append("commands MUST specify --" + LDBCommand::ARG_DB +
              "=<full_path_to_db_directory> when necessary\n");
@@ -91,7 +92,7 @@ void LDBCommandRunner::RunCommand(
     int argc, char** argv, Options options, const LDBOptions& ldb_options,
     const std::vector<ColumnFamilyDescriptor>* column_families) {
   if (argc <= 2) {
-    PrintHelp(argv[0]);
+    PrintHelp(ldb_options, argv[0]);
     exit(1);
   }
 
@@ -99,7 +100,7 @@ void LDBCommandRunner::RunCommand(
       argc, argv, options, ldb_options, column_families);
   if (cmdObj == nullptr) {
     fprintf(stderr, "Unknown command\n");
-    PrintHelp(argv[0]);
+    PrintHelp(ldb_options, argv[0]);
     exit(1);
   }