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`recv_buf` does not handle the MSG_PEEK flag correctly: it keeps calling `recv` until all requested bytes are available or an error occurs. The problem is how it calculates the number of bytes read: MSG_PEEK doesn't consume any bytes and will re-read the same bytes from the buffer head, so summing the return value every time is wrong. Moreover, MSG_PEEK doesn't consume the bytes in the buffer, so if more bytes are requested than are available, the loop will never terminate, because `recv` will never return EOF. For this reason, we need to compare the number of bytes read with the number of bytes expected. Add a check: if the MSG_PEEK flag is present, update the byte counter and break out of the loop only after at least the expected number of bytes have been received; otherwise, retry after a short delay to avoid consuming too many CPU cycles. This allows us to simplify the `test_stream_credit_update_test` by reusing `recv_buf`, like some other tests already do. Suggested-by: Stefano Garzarella <sgarzare@redhat.com> Signed-off-by: Luigi Leonardi <leonardi@redhat.com> Reviewed-by: Stefano Garzarella <sgarzare@redhat.com> Link: https://patch.msgid.link/20260415-fix_peek-v4-2-8207e872759e@redhat.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>