f simplify loop and nit

Author: valentinewallace

lightning/src/util/chacha20poly1305rfc.rs

@@ -77,8 +77,8 @@ mod real_chachapoly {
 		// below.
 		pub(super) fn encrypt_in_place(&mut self, input_output: &mut [u8]) {
 			debug_assert!(self.finished == false);
-			self.data_len += input_output.len();
 			self.cipher.process_in_place(input_output);
+			self.data_len += input_output.len();
 			self.mac.input(input_output);
 		}
 
@@ -132,14 +132,12 @@ impl<'a, W: Writer> Writer for ChaChaPolyWriter<'a, W> {
 	// complete.
 	fn write_all(&mut self, src: &[u8]) -> Result<(), io::Error> {
 		let mut src_idx = 0;
-		let mut write_buffer = [0; 8192];
-		let mut bytes_written = (&mut write_buffer[..]).write(&src[src_idx..]).expect("In-memory writes can't fail");
-		while bytes_written != 0 {
+		while src.len() - src_idx > 0 {
+			let mut write_buffer = [0; 8192];
+			let bytes_written = (&mut write_buffer[..]).write(&src[src_idx..]).expect("In-memory writes can't fail");
 			self.chacha.encrypt_in_place(&mut write_buffer[..bytes_written]);
 			self.write.write_all(&write_buffer[..bytes_written])?;
 			src_idx += bytes_written;
-			write_buffer = [0; 8192];
-			bytes_written = (&mut write_buffer[..]).write(&src[src_idx..]).expect("In-memory writes can't fail");
 		}
 		Ok(())
 	}