fix: avoid char-boundary panic in NBReader::try_read

src/reader.rs

@@ -203,11 +203,9 @@ impl NBReader {
     pub fn try_read(&mut self) -> Option<char> {
         // discard eventual errors, EOF will be handled in read_until correctly
         let _ = self.read_into_buffer();
-        if !self.buffer.is_empty() {
-            self.buffer.drain(..1).last()
-        } else {
-            None
-        }
+        let first = self.buffer.chars().next()?;
+        self.buffer.drain(..first.len_utf8());
+        Some(first)
     }
 }
 
@@ -457,4 +455,21 @@ mod tests {
         assert_eq!(None, r.try_read());
         assert_eq!(None, r.try_read());
     }
+
+    #[test]
+    fn test_try_read_multibyte() {
+        let f = io::Cursor::new("\u{c3}");
+        let mut r = NBReader::new(f, Options::default());
+        // pump bytes from the reader thread into the buffer
+        let mut chars = String::new();
+        for _ in 0..10 {
+            if let Some(c) = r.try_read() {
+                chars.push(c);
+            }
+            thread::sleep(time::Duration::from_millis(5));
+        }
+        // Each raw byte is cast to a char before reaching the buffer, so the two
+        // UTF-8 bytes of "\u{c3}" surface as separate Latin-1 chars.
+        assert_eq!(chars, "\u{c3}\u{83}");
+    }
 }