use std instead of custom reader

src/de.rs

@@ -213,15 +213,15 @@ impl<R: Read> Deserializer<R> {
         &mut self,
         header: Header,
     ) -> Result<String> {
-        let mut reader = ReadWithQuotes::new(self.reader_with_limit(header)?);
+        let mut reader = read_with_quotes(self.reader_with_limit(header)?);
         Ok(crate::json::parse_json(&mut reader)?)
     }
 
     fn read_json5_compatible_string(
         &mut self,
         header: Header,
     ) -> Result<String> {
-        let mut reader = ReadWithQuotes::new(self.reader_with_limit(header)?);
+        let mut reader = read_with_quotes(self.reader_with_limit(header)?);
         Ok(crate::json::parse_json5(&mut reader)?)
     }
 
@@ -261,67 +261,8 @@ impl<R: Read> Deserializer<R> {
     }
 }
 
-/// A reader wrapped that adds double quotes around the original text
-struct ReadWithQuotes<R: Read> {
-    reader: R,
-    started: bool,
-    finished: bool,
-}
-
-impl<R: Read> ReadWithQuotes<R> {
-    fn new(reader: R) -> Self {
-        Self {
-            reader,
-            started: false,
-            finished: false,
-        }
-    }
-}
-
-impl<R: Read> Read for ReadWithQuotes<R> {
-    fn read(&mut self, mut buf: &mut [u8]) -> std::io::Result<usize> {
-        let mut len = 0;
-
-        if buf.is_empty() || self.finished {
-            return Ok(0);
-        }
-
-        if !self.started {
-            buf[0] = b'"';
-            self.started = true;
-            buf = &mut buf[1..];
-            len = 1;
-        }
-
-        let read = self.reader.read(buf)?;
-        len += read;
-        if read < buf.len() {
-            buf[read] = b'"';
-            len += 1;
-            self.finished = true;
-        }
-        Ok(len)
-    }
-}
-
-#[test]
-fn test_read_with_quotes() {
-    let input = b"Hello, world!";
-    let mut buffer = String::new();
-    ReadWithQuotes::new(&input[..])
-        .read_to_string(&mut buffer)
-        .unwrap();
-    assert_eq!(buffer, "\"Hello, world!\"");
-    // now harder: read little by little
-    let mut adapter = ReadWithQuotes::new(&b"x"[..]);
-    let mut b = [0u8];
-    adapter.read(&mut b).unwrap();
-    assert_eq!(b[0], b'"');
-    adapter.read(&mut b).unwrap();
-    assert_eq!(b[0], b'x');
-    adapter.read(&mut b).unwrap();
-    assert_eq!(b[0], b'"');
-    assert_eq!(adapter.read(&mut b).unwrap(), 0);
+fn read_with_quotes(r: impl Read) -> impl Read {
+    b"\"".chain(r).chain(&b"\""[..])
 }
 
 fn usize_conversion(e: std::num::TryFromIntError) -> Error {