Call Workflow
This diagram shows the call execution flow: starting with request_preimage, passing through validation
(signature, nonce, mortality, fee payment), then pre-dispatch checks, followed by dispatch which emits events: Requested and modifies storage: StatusFor, RequestStatusFor, and finally post-dispatch where ExtrinsicSuccess is emitted and fees are settled.
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Used by: validatorsdevelopers
The Big Picture
Signals governance mechanism needs this.
Use Cases
- Mark preimage as in-use
From Chain Metadata
Request a preimage be uploaded to the chain without paying any fees or deposits. If the preimage requests has already been provided on-chain, we unreserve any deposit a user may have paid, and take the control of the preimage out of their hands.
Input Parameters
| # | Name | Type | Description |
|---|---|---|---|
| 0 | hash | H256 T::Hash | hash: Cryptographic hash (32 bytes) |
Permissions
Origin
Unknown
Required Role
Permission data inferred from metadata. May be incomplete.
Requirements
- Hash provided
Effects
Events Emitted
Storage Modified
Postconditions
- Preimage marked as requested
Side Effects
- Emits Requested
Code Examples
import { createClient, Binary } from "polkadot-api";
import { getWsProvider } from "polkadot-api/ws";
import { sub } from "@polkadot-api/descriptors"; // generated by: npx papi add sub -w wss://entrypoint-finney.opentensor.ai:443
const client = createClient(getWsProvider("wss://entrypoint-finney.opentensor.ai:443"));
const api = client.getTypedApi(sub);
// Build request_preimage call (typed, named args)
const hash = "0x0000000000000000000000000000000000000000000000000000000000000000";
const tx = api.tx.Preimage.request_preimage({
hash,
});Runtime Info
- Pallet Index
- 14
- Call Index
- 2
- First Version
- v133
- Current Version
- v411