fn copy_to()

in sgx_tstd/src/io/copy.rs [100:144]
37 lines of code
8 McCabe index (conditional complexity)

    fn copy_to<R: Read + ?Sized>(reader: &mut R, writer: &mut Self) -> Result<u64> {
        if writer.capacity() < DEFAULT_BUF_SIZE {
            return stack_buffer_copy(reader, writer);
        }

        let mut len = 0;
        let mut init = 0;

        loop {
            let buf = writer.buffer_mut();
            let mut read_buf: BorrowedBuf<'_> = buf.spare_capacity_mut().into();

            unsafe {
                // SAFETY: init is either 0 or the init_len from the previous iteration.
                read_buf.set_init(init);
            }

            if read_buf.capacity() >= DEFAULT_BUF_SIZE {
                let mut cursor = read_buf.unfilled();
                match reader.read_buf(cursor.reborrow()) {
                    Ok(()) => {
                        let bytes_read = cursor.written();

                        if bytes_read == 0 {
                            return Ok(len);
                        }

                        init = read_buf.init_len() - bytes_read;
                        len += bytes_read as u64;

                        // SAFETY: BorrowedBuf guarantees all of its filled bytes are init
                        unsafe { buf.set_len(buf.len() + bytes_read) };

                        // Read again if the buffer still has enough capacity, as BufWriter itself would do
                        // This will occur if the reader returns short reads
                    }
                    Err(ref e) if e.kind() == ErrorKind::Interrupted => {}
                    Err(e) => return Err(e),
                }
            } else {
                writer.flush_buf()?;
                init = 0;
            }
        }
    }