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

Author: kinetiknz

mp4parse_capi/src/lib.rs

@@ -543,6 +543,10 @@ 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"))