[object/fuzz] Update fuzz target open_file

- remove group length elements before writing
- assume that writing back should not fail
- tweak target to keep corpus when the fuzz does not fail

object/fuzz/fuzz_targets/open_file.rs

@@ -1,18 +1,29 @@
 #![no_main]
-use libfuzzer_sys::fuzz_target;
+use libfuzzer_sys::{fuzz_target, Corpus};
 use std::error::Error;
 
-fuzz_target!(|data: &[u8]| {
-    let _ = fuzz(data);
+fuzz_target!(|data: &[u8]| -> Corpus {
+    match fuzz(data) {
+        Ok(_) => Corpus::Keep,
+        Err(_) => Corpus::Reject,
+    }
 });
 
 fn fuzz(data: &[u8]) -> Result<(), Box<dyn Error>> {
     // deserialize random bytes
-    let obj = dicom_object::from_reader(data)?;
+    let mut obj = dicom_object::OpenFileOptions::new()
+        .read_preamble(dicom_object::file::ReadPreamble::Auto)
+        .odd_length_strategy(dicom_object::file::OddLengthStrategy::Fail)
+        .from_reader(data)?;
 
+    // remove group length elements
+    for g in 0..=0x07FF {
+        obj.remove_element(dicom_object::Tag(g, 0x0000));
+    }
     // serialize object back to bytes
     let mut bytes = Vec::new();
-    obj.write_all(&mut bytes)?;
+    obj.write_all(&mut bytes)
+        .expect("writing DICOM file should always be successful");
 
     // deserialize back to object
     let obj2 = dicom_object::from_reader(bytes.as_slice())