perf(fuzz): Improves code coverage of fuzzers

Updates fuzz target to include;
- A round trip writer
- A slice reader
- Pretty printing, debug and display code

Author: nathaniel-brough

fuzz/fuzz_targets/fuzz_target_1.rs

@@ -1,44 +1,98 @@
 #![no_main]
 use libfuzzer_sys::fuzz_target;
+use std::hint::black_box;
 
-use quick_xml::events::Event;
-use quick_xml::reader::Reader;
+use quick_xml::{events::Event, reader::Reader, writer::Writer};
 use std::io::Cursor;
 
-fuzz_target!(|data: &[u8]| {
-    // fuzzed code goes here
-    let cursor = Cursor::new(data);
-    let mut reader = Reader::from_reader(cursor);
+macro_rules! debug_format {
+    ($x:expr) => {
+        let _unused = std::hint::black_box(format!("{:?}", $x));
+    };
+}
+
+fn round_trip<R>(reader: &mut Reader<R>) -> ()
+where
+    R: std::io::BufRead,
+{
+    let mut writer = Writer::new(Cursor::new(Vec::new()));
     let mut buf = vec![];
+    let reader = reader
+        .expand_empty_elements(true)
+        .trim_text(true)
+        .trim_text_end(true);
     loop {
-        match reader.read_event_into(&mut buf) {
+        let event_result = reader.read_event_into(&mut buf);
+        if let Ok(ref event) = event_result {
+            let _event = black_box(event.borrow());
+            let _event = black_box(event.as_ref());
+            debug_format!(event);
+            debug_format!(writer.write_event(event));
+        }
+        match event_result {
             Ok(Event::Start(ref e)) | Ok(Event::Empty(ref e)) => {
+                debug_format!(e);
+                debug_format!(e.name());
                 for a in e.attributes() {
+                    debug_format!(a);
                     if a.ok().map_or(false, |a| a.unescape_value().is_err()) {
                         break;
                     }
                 }
             }
-            Ok(Event::Text(ref e)) | Ok(Event::Comment(ref e))
+            Ok(Event::Text(ref e))
+            | Ok(Event::Comment(ref e))
             | Ok(Event::PI(ref e))
             | Ok(Event::DocType(ref e)) => {
-                if e.unescape().is_err() {
+                debug_format!(e);
+                if let Err(err) = e.unescape() {
+                    debug_format!(err);
                     break;
                 }
             }
             Ok(Event::CData(e)) => {
-                if e.escape().is_err() {
+                if let Err(err) = e.escape() {
+                    let _displayed = black_box(format!("{}", err));
+                    debug_format!(err);
                     break;
                 }
             }
             Ok(Event::Decl(ref e)) => {
-                let _ = e.version();
-                let _ = e.encoding();
-                let _ = e.standalone();
+                debug_format!(e);
+                let _ = black_box(e.version());
+                let _ = black_box(e.encoding());
+                let _ = black_box(e.standalone());
+            }
+            Ok(Event::End(e)) => {
+                debug_format!(e.local_name());
+                let name = e.name();
+                debug_format!(name);
+                debug_format!(name.prefix());
+                debug_format!(name.local_name());
+                debug_format!(name.decompose());
+                debug_format!(name.as_namespace_binding());
+                debug_format!(e);
+            }
+            Err(e) => {
+                debug_format!(e);
+                break;
             }
-            Ok(Event::End(_)) => (),
-            Ok(Event::Eof) | Err(..) => break,
+            Ok(Event::Eof) => break,
         }
         buf.clear();
     }
+    let _round_trip = std::hint::black_box(writer.into_inner().into_inner());
+}
+
+fuzz_target!(|data: &[u8]| {
+    // From reader
+    let cursor = Cursor::new(data);
+    let mut reader = Reader::from_reader(cursor);
+    _ = std::hint::black_box(round_trip(&mut reader));
+
+    // From str
+    if let Ok(s) = std::str::from_utf8(data) {
+        let mut reader = Reader::from_str(s);
+        _ = std::hint::black_box(round_trip(&mut reader));
+    }
 });