HDFS-10705: libhdfs++: FileSystem should have a convenience no-args ctor. Contributed by James Clampffer.

hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/libhdfspp/include/hdfspp/hdfspp.h

@@ -155,18 +155,25 @@ class FileSystem {
    * initializes the RPC connections to the NameNode and returns an
    * FileSystem object.
    *
+   * Note: The FileSystem takes ownership of the IoService passed in the
+   * constructor.  The FileSystem destructor will call delete on it.
+   *
    * If user_name is blank, the current user will be used for a default.
    **/
-  static FileSystem * New(
+  static FileSystem *New(
       IoService *&io_service, const std::string &user_name, const Options &options);
 
-  virtual void Connect(const std::string &server,
-      const std::string &service,
+  /**
+   * Returns a new instance with default user and option, with the default IOService.
+   **/
+  static FileSystem *New();
+
+
+  virtual void Connect(const std::string &server, const std::string &service,
       const std::function<void(const Status &, FileSystem *)> &handler) = 0;
 
   /* Synchronous call of Connect */
-  virtual Status Connect(const std::string &server,
-      const std::string &service) = 0;
+  virtual Status Connect(const std::string &server, const std::string &service) = 0;
 
 
   /**

hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/libhdfspp/lib/fs/filesystem.cc

@@ -40,6 +40,9 @@ using ::asio::ip::tcp;
 
 static constexpr uint16_t kDefaultPort = 8020;
 
+// forward declarations
+const std::string get_effective_user_name(const std::string &);
+
 uint32_t FileSystem::GetDefaultFindMaxDepth() {
   return std::numeric_limits<uint32_t>::max();
 }
@@ -72,11 +75,21 @@ Status FileSystem::CheckValidReplication(uint16_t replication) {
  *                    FILESYSTEM BASE CLASS
  ****************************************************************************/
 
-FileSystem * FileSystem::New(
+FileSystem *FileSystem::New(
     IoService *&io_service, const std::string &user_name, const Options &options) {
   return new FileSystemImpl(io_service, user_name, options);
 }
 
+FileSystem *FileSystem::New() {
+  // No, this pointer won't be leaked.  The FileSystem takes ownership.
+  IoService *io_service = IoService::New();
+  if(!io_service)
+    return nullptr;
+  std::string user_name = get_effective_user_name("");
+  Options options;
+  return new FileSystemImpl(io_service, user_name, options);
+}
+
 /*****************************************************************************
  *                    FILESYSTEM IMPLEMENTATION
  ****************************************************************************/