From 4d2747e4b8c8588b7d34d11dcd622e89b8babfde Mon Sep 17 00:00:00 2001
From: Daniel Watkins <daniel@daniel-watkins.co.uk>
Date: Fri, 29 Oct 2021 08:56:44 -0400
Subject: [PATCH] cformat.rs: reject %c args > 255 when byte formatting

This matches CPython's behaviour.  Thanks to @DimitrisJim for the
improved implementation here.
---
 vm/src/cformat.rs | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/vm/src/cformat.rs b/vm/src/cformat.rs
index 6fb383c71..6da6a1bbc 100644
--- a/vm/src/cformat.rs
+++ b/vm/src/cformat.rs
@@ -440,12 +440,9 @@ impl CFormatSpec {
             CFormatType::Character => {
                 if let Some(i) = obj.payload::<PyInt>() {
                     let ch = i
-                        .as_bigint()
-                        .to_u32()
-                        .and_then(std::char::from_u32)
-                        .ok_or_else(|| {
-                            vm.new_overflow_error("%c arg not in range(0x110000)".to_owned())
-                        })?;
+                        .try_to_primitive::<u8>(vm)
+                        .map_err(|_| vm.new_overflow_error("%c arg not in range(256)".to_owned()))?
+                        as char;
                     return Ok(self.format_char(ch).into_bytes());
                 }
                 if let Some(b) = obj.payload::<PyBytes>() {