Guard against incorrect read_buf_exact implementations

joshtriplett · joshtriplett · commit 199f30844688 · 2025-11-12T23:12:37.000-08:00
diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
@@ -1278,6 +1278,8 @@ pub trait Read {
         let mut buf = [MaybeUninit::uninit(); N];
         let mut borrowed_buf = BorrowedBuf::from(buf.as_mut_slice());
         self.read_buf_exact(borrowed_buf.unfilled())?;
+        // Guard against incorrect `read_buf_exact` implementations.
+        assert_eq!(borrowed_buf.len(), N);
         Ok(unsafe { MaybeUninit::array_assume_init(buf) })
     }
 }

Original file line number	Diff line number	Diff line change
`@@ -1278,6 +1278,8 @@ pub trait Read {`
`1278`	`1278`	`let mut buf = [MaybeUninit::uninit(); N];`
`1279`	`1279`	`let mut borrowed_buf = BorrowedBuf::from(buf.as_mut_slice());`
`1280`	`1280`	`self.read_buf_exact(borrowed_buf.unfilled())?;`
	`1281`	+ // Guard against incorrect `read_buf_exact` implementations.
	`1282`	`+ assert_eq!(borrowed_buf.len(), N);`
`1281`	`1283`	`Ok(unsafe { MaybeUninit::array_assume_init(buf) })`
`1282`	`1284`	`}`
`1283`	`1285`	`}`