dd: fix skip=n processing. add test.

Author: jgarzik

file/src/dd.rs

@@ -205,20 +205,21 @@ fn copy_convert_file(config: &Config) -> Result<(), Box<dyn std::error::Error>>
     let mut ibuf = vec![0u8; config.ibs];
     let mut obuf = vec![0u8; config.obs];
 
+    // Skip the specified number of bytes
+    let mut skipped = 0;
+    while skipped < config.skip {
+        let bytes_to_skip = std::cmp::min(config.skip - skipped, config.ibs);
+        let n = ifile.read(&mut ibuf[..bytes_to_skip])?;
+        if n == 0 {
+            break;
+        }
+        skipped += n;
+    }
+
     let mut count = 0;
-    let mut skip = config.skip;
     let mut seek = config.seek;
 
     loop {
-        if skip > 0 {
-            let n = ifile.read(&mut ibuf)?;
-            if n == 0 {
-                break;
-            }
-            skip -= n;
-            continue;
-        }
-
         if seek > 0 {
             let n = ifile.read(&mut ibuf)?;
             if n == 0 {

file/tests/dd-tests.rs

@@ -178,3 +178,28 @@ fn test_lcase_conversion() {
         expected_exit_code: 0,
     });
 }
+
+#[test]
+fn test_skip_n() {
+    let input_file_path = get_test_file_path("dd.ascii");
+
+    let mut input_file = File::open(input_file_path).expect("Unable to open input test file");
+    let mut input_data = Vec::new();
+    input_file
+        .read_to_end(&mut input_data)
+        .expect("Unable to read input test file");
+
+    let expected_output = b"world! {[ $&chars ]}\nAlas, poor Yorick, I knew him well.\n";
+
+    run_test_u8(TestPlanU8 {
+        cmd: String::from("dd"),
+        args: vec![
+            String::from("ibs=1"),
+            String::from("skip=7"), // Adjusting skip to 7 bytes to reach the correct output
+        ],
+        stdin_data: input_data,
+        expected_out: expected_output.to_vec(),
+        expected_err: Vec::new(),
+        expected_exit_code: 0,
+    });
+}