Add IsDirectory() to Env and FS (#6711)

Summary:
IsDirectory() is a common API to check whether a path is a regular file or
directory.
POSIX: call stat() and use S_ISDIR(st_mode)
Windows: PathIsDirectoryA() and PathIsDirectoryW()
HDFS: FileSystem.IsDirectory()
Java: File.IsDirectory()
...
Pull Request resolved: facebook/rocksdb#6711

Test Plan: make check

Reviewed By: anand1976

Differential Revision: D21053520

Pulled By: riversand963

fbshipit-source-id: 680aadfd8ce982b63689190cf31b3145d5a89e27
Signed-off-by: Changlong Chen <levisonchen@live.cn>

env/composite_env_wrapper.h

@@ -492,6 +492,12 @@ class CompositeEnvWrapper : public Env {
     return file_system_->NewLogger(fname, io_opts, result, &dbg);
   }
 
+  Status IsDirectory(const std::string& path, bool* is_dir) override {
+    IOOptions io_opts;
+    IODebugContext dbg;
+    return file_system_->IsDirectory(path, io_opts, is_dir, &dbg);
+  }
+
 #if !defined(OS_WIN) && !defined(ROCKSDB_NO_DYNAMIC_EXTENSION)
   Status LoadLibrary(const std::string& lib_name,
                      const std::string& search_path,
@@ -1081,6 +1087,10 @@ class LegacyFileSystemWrapper : public FileSystem {
                         uint64_t* diskfree, IODebugContext* /*dbg*/) override {
     return status_to_io_status(target_->GetFreeSpace(path, diskfree));
   }
+  IOStatus IsDirectory(const std::string& path, const IOOptions& /*options*/,
+                       bool* is_dir, IODebugContext* /*dbg*/) override {
+    return status_to_io_status(target_->IsDirectory(path, is_dir));
+  }
 
  private:
   Env* target_;

env/fs_posix.cc

@@ -877,6 +877,28 @@ class PosixFileSystem : public FileSystem {
     return IOStatus::OK();
   }
 
+  IOStatus IsDirectory(const std::string& path, const IOOptions& /*opts*/,
+                       bool* is_dir, IODebugContext* /*dbg*/) override {
+    // First open
+    int fd = -1;
+    int flags = cloexec_flags(O_RDONLY, nullptr);
+    {
+      IOSTATS_TIMER_GUARD(open_nanos);
+      fd = open(path.c_str(), flags);
+    }
+    if (fd < 0) {
+      return IOError("While open for IsDirectory()", path, errno);
+    }
+    struct stat sbuf;
+    if (fstat(fd, &sbuf) < 0) {
+      return IOError("While doing stat for IsDirectory()", path, errno);
+    }
+    if (nullptr != is_dir) {
+      *is_dir = S_ISDIR(sbuf.st_mode);
+    }
+    return IOStatus::OK();
+  }
+
   FileOptions OptimizeForLogWrite(const FileOptions& file_options,
                                  const DBOptions& db_options) const override {
     FileOptions optimized = file_options;