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[package]
name = "eth_signer_example"
version = "0.1.0"
edition = "2021"

[dependencies]
anyhow = { version = "1.0.80", features = ["backtrace"] }
subxt = "0.34.0"
tokio = { version = "1.36.0", features = ["rt-multi-thread", "macros"] }
codec = { package = "parity-scale-codec", version = "3.6.9", features = ["derive"] }

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Constructing and Signing Extrinsics

Substrate is configurable enough that extrinsics can take any format, in theory. In practice, runtimes tend to use our UncheckedExtrinsic type to represent extrinsics. In Polkadot, this is configured here at the time of writing.

What follows is a description of how extrinsics based on this type are encoded into bytes. These bytes can then be submitted to a chain for inclusion in a block (this is how we make changes to the state of a chain), and are ultimately stored in the body of a block.

Encoding an Extrinsic

At a high level, all extrinsics are formed from concatenating some details together, ie:

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import * as dapp from "@polkadot/extension-dapp";
import { Keyring } from "@polkadot/ui-keyring";
import {
  mnemonicGenerate,
  cryptoWaitReady,
  signatureVerify,
  decodeAddress,
} from "@polkadot/util-crypto";
import { stringToU8a, u8aToHex, stringToHex, hexToU8a } from "@polkadot/util";

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function aggregateAndDebounce<A, B>(
    // Take some val and the current aggregated vals in and return next aggregated vals
    aggregate: (val: A, vals: B) => B,
    // This is called waitMs after the some values are given
    debounced: (val: B) => void,
    // This produces an initial state for the aggregated vals, to start from/
    initialVals: () => B,
    // How long to wait until calling the debounce
    waitMs: number
): (val: A) => void {

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/**
 * A PromiseQueue, enforcing that no more than `maxTasks` number of tasks
 * are running at a given time. 
 */
class PromiseQueue<T> {
    // How many tasks are allowed to run concurrently?
    #maxTasks: number;
    // How many tasks are currently running concurrently?
    #runningTasks: number = 0;
    // The queued tasks waiting to run

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{-# LANGUAGE DataKinds, TypeOperators, FlexibleContexts, GeneralizedNewtypeDeriving, TypeFamilies #-}

module Main where

import qualified Database as Database
import qualified Data.Map as Map

import Network.Wai (Request, requestHeaders)
import Network.Wai.Handler.Warp (run)
import Control.Applicative ((<$>), (<*>))