Function otxn_field 

pub unsafe extern "C" fn otxn_field(
    write_ptr: u32,
    write_len: u32,
    field_id: u32,
) -> i64

Retrieve a field from the originating transaction in its raw serialized form. @param write_ptr A buffer to output the field into @param write_len The length of the buffer. @param field_if The field code of the field being requested @return The number of bytes written to write_ptr or a negative integer if an error occured.