2b:null 2c:["$","title",null,{"children":"Maker Spell Tracing | jpark | Observable"}] 31:T4ed,md` The idea -- adopted from ethtx -- is that, using Parity's [trace call](https://wiki.parity.io/JSONRPC-trace-module#trace_call) method, we can simulate calling \`cast\` on a spell *as if* it were executable at the current block. Then we use the resulting trace to create state diffs. The temptation, if one were trying this for the first time, might be to simulate a call to \`cast\` itself. But if we do that, we'll get reversions from either 1) the spell not having the hat or 2) from the action not having awaited the GSM delay. This runs up against the limitations of \`trace_call\`: it does let us send a transaction from _any_ addresses, but it doesn't allow us to freely change storage variables. Instead, we should call the \`exec\` method (shown below) on the [pause proxy](https://github.com/dapphub/ds-pause/blob/53700f6fb648911ab18ac080e97c5dfd2aa03f2e/src/pause.sol#L109). Its auth blocks anyone but the ds-pause from calling it, but, as mentioned, we're free to set ds-pause as the \`msg.sender\` in our call. And, ultimately, the pause proxy is [the one authorized](https://github.com/makerdao/dss-auth-viz/blob/master/out/graph-mainnet-deployment.svg) on the core contracts (so it's always eventually called by a \`spell.cast\` anyway). `32:T4cb,md`### Notes 1. If the spell doesn't conform to the standard abi, we'd need to find \`usr\` and \`fax\` another way. One such method is to search the contract code for the \`pause.exec\` method selector. Another is to fetch the solidity from etherscan and search it (if it isn't available, the spell should be flagged on the frontend). Enumerating these strategies is outside the scope of this notebook, but my sense as of writing this is that there are several, but none are foolproof. So, however it is done, warnings and disclaimers should be added to fronteds. 2. For a practical frontend, additional validation regarding which spells have already been executed, which ones have been queued, and which ones are still queueable would be required. 3. One limitation of this approach is that any actions taken outside of \`pause.exec\` will not be captured. Because the proxy is the one with auth on MCD contracts, all the core contract changes should go through it. But, some setup may be done in \`spell.schedule\`, for example, and that wouldn't be seen. 4. This is only possible with parity nodes where the [tracing api](https://wiki.parity.io/JSONRPC-trace-module) is enabled. For this demo, we use ${rpcTracingUrl}.`33:Taf6,makerSpellAbi = [ { inputs: [], payable: false, stateMutability: "nonpayable", type: "constructor" }, { constant: true, inputs: [], name: "action", outputs: [{ internalType: "address", name: "", type: "address" }], payable: false, stateMutability: "view", type: "function" }, { constant: false, inputs: [], name: "cast", outputs: [], payable: false, stateMutability: "nonpayable", type: "function" }, { constant: true, inputs: [], name: "description", outputs: [{ internalType: "string", name: "", type: "string" }], payable: false, stateMutability: "view", type: "function" }, { constant: true, inputs: [], name: "done", outputs: [{ internalType: "bool", name: "", type: "bool" }], payable: false, stateMutability: "view", type: "function" }, { constant: true, inputs: [], name: "eta", outputs: [{ internalType: "uint256", name: "", type: "uint256" }], payable: false, stateMutability: "view", type: "function" }, { constant: true, inputs: [], name: "expiration", outputs: [{ internalType: "uint256", name: "", type: "uint256" }], payable: false, stateMutability: "view", type: "function" }, { constant: true, inputs: [], name: "newMkrOracle", outputs: [ { internalType: "contract NewMkrOracle", name: "", type: "address" } ], payable: false, stateMutability: "view", type: "function" }, { constant: true, inputs: [], name: "pause", outputs: [ { internalType: "contract DSPauseAbstract", name: "", type: "address" } ], payable: false, stateMutability: "view", type: "function" }, { constant: true, inputs: [], name: "saiMom", outputs: [ { internalType: "contract SaiMomAbstract", name: "", type: "address" } ], payable: false, stateMutability: "view", type: "function" }, { constant: true, inputs: [], name: "saiSlayer", outputs: [ { internalType: "contract SaiSlayer", name: "", type: "address" } ], payable: false, stateMutability: "view", type: "function" }, { constant: false, inputs: [], name: "schedule", outputs: [], payable: false, stateMutability: "nonpayable", type: "function" }, { constant: true, inputs: [], name: "sig", outputs: [{ internalType: "bytes", name: "", type: "bytes" }], payable: false, stateMutability: "view", type: "function" }, { constant: true, inputs: [], name: "tag", outputs: [{ internalType: "bytes32", name: "", type: "bytes32" }], payable: false, stateMutability: "view", type: "function" } ]34:[{"id":"a2b075e796621089b5779a7230e51ff85791414fd591c1a2c207a94c5b3bfcd58fabbb57ef26c029a159d9aff4cc5b93b156b9ad4d2b6b6f0e8ce8390fedc925","href":"https://static.observableusercontent.com/files/a2b075e796621089b5779a7230e51ff85791414fd591c1a2c207a94c5b3bfcd58fabbb57ef26c029a159d9aff4cc5b93b156b9ad4d2b6b6f0e8ce8390fedc925","name":"ethtx-state-diff.png","type":"image/png","lastModified":1588101168767.141,"size":107908}] 2f:{"id":"4b32d8dcb88d3d8f","slug":"maker-spell-tracing","title":"Maker Spell Tracing","thumbnail":"f3269e41939c495ed3f19c790cba39336a2bbe9e0922b5ff96f3bea437e5d961","access_level":"public","create_time":"$D2020-04-28T16:11:52.505Z","update_time":"$D2021-11-16T00:22:16.110Z","view_time":null,"first_public_time":"$D2020-05-30T05:10:29.651Z","fork":false,"stars":1,"starred":false,"owner":{"type":"team","id":"75a1153b1f93cd48","login":"jparklev","name":"jpark","avatar_url":"https://avatars-next.observableusercontent.com/9af5c11e007fc5f66f9624cbfc1bad0fd8296d28d64126149eb0992f07ac46b3","tier":"starter_2024"},"version":1344,"publish_version":1344,"role":null,"authored":false,"authors":[{"type":"individual","id":"50a8beb6caf2400d","login":"jparklev","name":"jpark","avatar_url":"https://avatars-next.observableusercontent.com/9af5c11e007fc5f66f9624cbfc1bad0fd8296d28d64126149eb0992f07ac46b3","tier":null}],"members":[{"type":"individual","id":"50a8beb6caf2400d","login":"jparklev","name":"jpark","avatar_url":"https://avatars-next.observableusercontent.com/9af5c11e007fc5f66f9624cbfc1bad0fd8296d28d64126149eb0992f07ac46b3","tier":null,"role":"editor"}],"comments":[],"custom_thumbnail":false,"trashed":false,"subscribed":null,"forks":1,"collection":null,"type":"notebook","body":{"title":"Maker Spell Tracing","cells":[{"id":0,"value":"md`# Maker Spell Tracing`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":146,"value":"md`This notebook demonstrates how one might create state diffs akin to [catflip](https://catflip.co/changelog) ([@destiner](https://github.com/Destiner)) or [ethtx](https://ethtx.info/) ([@Exef](https://github.com/Exef), [@tmierzwa](https://github.com/tmierzwa), [@krzkaczor](https://github.com/krzkaczor)) for not-yet-executed [spells](https://docs.makerdao.com/smart-contract-modules/governance-module/spell-detailed-documentation) (ie, Maker governance proposals).`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":183,"value":"$31","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":654,"value":"(hljs,\nmd`\n~~~solidity\nfunction exec(address usr, bytes memory fax)\n public auth\n returns (bytes memory out)\n{\n bool ok;\n (ok, out) = usr.delegatecall(fax);\n require(ok, \"ds-pause-delegatecall-error\");\n}\n~~~`)","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":191,"value":"md`tl;dr we'll send a \\`trace_call\\` request with the following params:\n* **from** as the **ds pause address** \n* **to** as the **pause proxy address**\n* **data** as the **calldata for the pause proxy that calling cast on an authorized spell would generate**`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":397,"value":"md`To help create the mental image, here's the ethtx state diff for a previously executed spell. The idea is to create exactly this, but for spells that haven't yet been executed.`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":393,"value":"FileAttachment(\"ethtx-state-diff.png\").image()","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":453,"value":"md`---`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":250,"value":"md`\n# Demo`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":98,"value":"!isValidAddress(spellAddress) && !!spellAddress\n ? html`Please enter a valid address`\n : md`First, we need a spell address. For a list of spells currently in chief, you can check the \"Executive Votes\" section of mkrgov.science (where you can click the icon next to any of the titles to copy the address).`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":61,"value":"viewof spellAddress = text({\n submit: \"Go\",\n description: \"Enter a spell address to get started\",\n size: 50\n})","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":468,"value":"md`---`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":219,"value":"md`\n### Generating the calldata\n\nTo generate the calldata, we'll need:\n1. the \\`exec\\` function signature\n2. the contract to be delegate called [${Object.assign(\n html`usr`,\n {\n onclick: () => scrollToElement(\"usr\", 'span')\n }\n)}] _<- click to have it highlighted_\n3. the calldata for the delegatecall [${Object.assign(\n html`fax`,\n {\n onclick: () => scrollToElement(\"fax\", 'span')\n }\n)}]\n\n(1) we already have by hashing \\`exec(address,bytes)\\`. For (2) & (3), we can read the \\`action\\` and \\`sig\\` storage variables from the dss spells since, if you follow the calls, that's what ends up being passed to \\`proxy.exec\\`. \n${Object.assign(\n html`^{[note 1]`,\n {\n onclick: () =>\n scrollToElement(\"If the spell doesn't conform to the standard abi\", 'p')\n }\n)}}\n`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":169,"value":"md`With our spell, we'll create an ethers contract object using a generic dss spell abi`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":42,"value":"spellContract = new ethers.Contract(\n validatedSpellAddress,\n makerSpellAbi,\n provider\n)","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":172,"value":"md`Next, let's fetch the values`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":240,"value":"usr = spellContract.action()","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":243,"value":"fax = spellContract.sig()","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":293,"value":"!fax || !usr\n ? html`either \\`sig\\` or \\`action\\` not found for the given spell`\n : html`both \\`sig\\` and \\`action\\` have been found for the given spell ✔️`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":339,"value":"md`Then we can encode the \\`pauseProxy.exec\\` call using a convenient ethers encoding utility that needs only abi fragments`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":1074,"value":"pauseProxyCalldata = new ethers.utils.Interface([\n \"function exec(address, bytes)\"\n]).encodeFunctionData('exec', [usr, fax])","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":215,"value":"md`### Making the request\nNow we just need to make the request with the right parameters. Here's what that looks like:`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":47,"value":"traceCallResult = {\n const resp = await d3.json(rpcTracingUrl, {\n method: 'POST',\n headers: {\n Accept: 'application/json',\n 'Content-Type': 'application/json'\n },\n body: JSON.stringify({\n jsonrpc: '2.0',\n method: 'trace_call',\n params: [\n {\n from: addresses.dsPause,\n to: addresses.dsPauseProxy,\n data: pauseProxyCalldata\n },\n [\"trace\", \"stateDiff\"]\n ],\n id: 1\n })\n });\n return resp.result;\n}","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":893,"value":"md`If there's a \\`stateDiff\\` object in the response, then it worked 🥳 We won't do it here, but the next step would be to parse the storage keys and contract addresses using known smart contract semantics. [ethtx](https://ethtx.info/) actually does exactly this already, so we can simply pass our object directly into its parser.`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":1040,"value":"md`---`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":372,"value":"$32","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":18,"value":"md`---\n# Appendix\n---`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":28,"value":"md`### Utils`","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":49,"value":"rpcTracingUrl = \"https://eth-mainnet.alchemyapi.io/jsonrpc/Z8mVj3Mv-Ejd-S97690_uHhlg8nZmvHl\"","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":10,"value":"provider = {\n if (\n typeof window.ethereum !== 'undefined' &&\n parseInt(window.ethereum.chainId) === 1\n ) {\n window.ethereum.autoRefreshOnNetworkChange = false;\n return new ethers.providers.Web3Provider(window.ethereum);\n } else {\n return new ethers.providers.InfuraProvider();\n }\n}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":102,"value":"function isValidAddress(address) {\n return /^0x([A-Fa-f0-9]{40})$/.test(address);\n}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":661,"value":"html`