This document outlines some advanced techniques for generating, signing, and sending Azimuth-related transactions from within Urbit itself. It's strongly discouraged to do this unless you're very confident as Azimuth transactions are permanent and will cost ETH to complete. However, until you upload a signed transaction to the blockchain no transaction will take place so it's safe to explore these tools. It will also be very helpful to have at least a rudimentary understanding of Hoon in order to read and modify parts of the code.
These tools are currently only available for layer 1 transactions. Tooling for layer 2 transactions is forthcoming.
First you will want to boot a fakezod. You can do this with your live running ship but at this time this will need you to modify the code so it's best to do this on a ship you can make mistakes on.
Be sure to have mounted your base desk so you can easily edit files on it. The first edit that will probably need to be made is in app/claz.hoon. The listed url will need to be changed to a valid Ethereum endpoint. infura.io provides an Ethereum API that you can use.
The second change that may potentially be needed is to modify the gas limit. This number here is the maximum number of gas units that will be used. In future this will be configurable but for now you may need to change this manually. For a guide to what to set it to you can use the constants in bridge as a guide based on what action you are going to be performing. The maximum cost of your transaction will be the maximum gas units multiplied by the gwei you're going to set later. You'll need at least this much in your account.
Once you have made these changes be sure to run |commit %base to get them into your ship.
Next run |start %claz after which you'll be able to generate transactions.
:claz [%generate %/spawn/eth-txs %mainnet author %single %spawn ~ship to]
Here we have an example of generating a transaction to spawn a ship. Something to note is that for this to be successful you'll need to actually have the right to spawn the ship in question. Let's break down the command.
%generate is how all commands to claz are going to start.
%/spawn/eth-txs is simply the path for the output file
%mainnet specifies which network this is going to sent out on. Other options are possible including the test-net %ropsten.
author here is an Ethereum address that is issuing the transaction. It will need to be written in @ux notation, e.g. 0x3b17.d097.d9dd.711e.4ef8.517a.bbf1.8b2b.a643.81fe.
%single specifies what kind of batch that will be created. If you are going to do multiple transactions you will need to either set this to %more followed by a list of batches, or generate the next transaction after having submitted the previous one to the blockchain.
[%spawn ~ship to] is the transaction we want to issue. The arguments are will vary based on the transaction. ~ship will be the ship to be spawned. to is the Ethereum address to spawn the ship to.
You will want to read /sur/claz.hoon. This will contain more details about the various kinds of transactions you can perform particularly ++call
After running this command you should find a csv file at the output path you specified. You can examine this file to learn how they are constructed. You are able to modify the nonces, gas limit and price without changing the functionality of the transaction but it's not important for this guide.
This file can now be signed and uploaded. At this point, you can transfer this file to an airgapped machine which has your keys, if you want. If you choose to do that you will need to download the urbit binary as well as the most recent pill file or a copy of the fakezod pier you have already booted.
For this guide, we'll continue on the same ship.
Run |start %eth-sender and then you can use it to sign the transaction file.
:eth-sender [%sign %/spawn-signed/txt %/spawn/eth-txs %/mykey/txt ~[40 80]]
Let's break this down again.
%sign is the action we are going to perform here. eth-sender can also be used to submit batches of transactions to the network in various ways, but details on that are outside of the scope of this guide.
%/spawn-signed/txt is the path to the output file.
%/spawn/eth-txs is the path to the transaction file we generated earlier. It will need to be accessible so don't forget to |commit %base if you moved it to a different pier.
%/mykey/txt is the path to your private key file. It should contain your private key beginning with 0x and followed by a hex string with no dots, and where capital letters are fine. This file is most likely the reason you will want to use an airgapped machine so that your private key never touches a networked computer. Opsec is left to the reader.
~[40 80] is a list of gas prices, in gwei; a signed transaction file will be created for each one listed. Here we just specify 40 and 80 gwei. You may want to adjust this list based on current Ethereum network traffic and your time preference for the transactions.
Now you should have one file in your pier for each gwei costs.
To actually transmit the transaction, paste the contents of one of these files into https://etherscan.io/pushTx or whatever other transmission system you would like to use. This is the action that will actually cost you ETH and perform the transaction on the network. Only do this step if you want to actually perform the action.