Add simple du example

examples/du.rs

@@ -0,0 +1,36 @@
+extern crate jwalk;
+
+use jwalk::{DirEntry, Error, WalkDirGeneric};
+use std::env;
+use std::fs::Metadata;
+
+fn main() {
+    let path = env::args().skip(1).next().unwrap_or("./".to_owned());
+    let mut total: u64 = 0;
+
+    for dir_entry_result in WalkDirGeneric::<((), Option<u64>)>::new(&path).process_read_dir(
+        |_, _, _, dir_entry_results| {
+            dir_entry_results.iter_mut().for_each(|dir_entry_result| {
+                if let Ok(dir_entry) = dir_entry_result {
+                    if !dir_entry.file_type.is_dir() {
+                        dir_entry.client_state =
+                            Some(dir_entry.metadata().map(|m| m.len()).unwrap_or_default());
+                    }
+                }
+            })
+        },
+    ) {
+        match dir_entry_result {
+            Ok(dir_entry) => {
+                if let Some(len) = &dir_entry.client_state {
+                    total += len;
+                }
+            }
+            Err(error) => {
+                println!("Read dir_entry error: {}", error);
+            }
+        }
+    }
+
+    println!("path: {} total bytes: {}", path, total);
+}