Want to get `transaction_hash` before submit, where are the source codes of `/construction/submit`

I think it’s possible to get the transaction_hash before /construction/submit (Construction · Rosetta)

After review the source code in https://github.com/dfinity/ic didn’t find it, I’m not sure it’s open source? and where is the code.


Is here the source code of generating the transaction_hash ic/lib.rs at 779549eccfcf61ac702dfc2ee6d76ffdc2db1f7f · dfinity/ic · GitHub

How can I specify the created_at_time