ffi: Assert that the read callback does not return more bytes than requested.

kinetiknz · kinetiknz · commit eb54606cdbfe · 2026-04-14T16:23:42.000+12:00
diff --git a/mp4parse_capi/src/lib.rs b/mp4parse_capi/src/lib.rs
@@ -499,6 +499,7 @@ impl Read for Mp4parseIo {
         }
         let rv = self.read.unwrap()(buf.as_mut_ptr(), buf.len(), self.userdata);
         if rv >= 0 {
+            assert!(rv as usize <= buf.len(), "read callback returned more bytes than buffer size");
             Ok(rv as usize)
         } else {
             Err(std::io::Error::other("I/O error in Mp4parseIo Read impl"))

Original file line number	Diff line number	Diff line change
`@@ -499,6 +499,7 @@ impl Read for Mp4parseIo {`
`499`	`499`	`}`
`500`	`500`	`let rv = self.read.unwrap()(buf.as_mut_ptr(), buf.len(), self.userdata);`
`501`	`501`	`if rv >= 0 {`
	`502`	`+ assert!(rv as usize <= buf.len(), "read callback returned more bytes than buffer size");`
`502`	`503`	`Ok(rv as usize)`
`503`	`504`	`} else {`
`504`	`505`	`Err(std::io::Error::other("I/O error in Mp4parseIo Read impl"))`