Add a script for downloading mithril snapshots

Also mention using mithril in the ledger-state README

Author: neilmayhew

libs/ledger-state/README.md

@@ -30,8 +30,14 @@ curl -O -J https://book.play.dev.cardano.org/environments/mainnet/conway-genesis
 
 Download or build copies of `cardano-node` and `cardano-cli`. A convenient way of doing this is to download the assets from one of the `cardano-node` [releases](https://github.com/IntersectMBO/cardano-node/releases) on GitHub. The Linux executables are statically linked, so will run on any system.
 
+Download a snapshot of the node db using [mithril](https://mithril.network/doc/manual/getting-started/bootstrap-cardano-node/#bootstrap-a-cardano-node-from-a-testnet-mithril-cardano-db-snapshot). This will greatly speed up the process of syncing the node. There's a convenient nix-based script for doing it in `scripts/mithril-download.sh`:
+
+```shell
+$ scripts/mithril-download.sh -d "${CARDANO_DATA}/db" mainnet
 ```
 
+Note that you will need to get a snapshot that's compatible with the version of `cardano-node` you're using.
+
 Start the node and wait for it to fully sync
 
 ```shell

scripts/mithril-download.sh

@@ -0,0 +1,73 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# Author: [email protected]
+
+export NETWORK=mainnet
+export UNPACK_DIR=cardano-db
+export MITHRIL_VERSION=2513.0
+
+usage()
+{
+	cat <<-EOF
+		Usage: $(basename "$0") [-h] [-d DIR] [-v VERSION] NETWORK
+		  Download cardano-db using mithril
+
+		Options:
+		  -h          Show this help text
+		  -d DIR      Unpack the DB into DIR (default: $UNPACK_DIR)
+		  -v VERSION  Use version VERSION of the mithril client (default: $MITHRIL_VERSION)
+
+		Arguments:
+		  NETWORK     Download the DB for NETWORK (default: $NETWORK)
+	EOF
+
+	exit "${1:-0}"
+}
+
+while getopts hd:v: OPT
+do
+	case "$OPT" in
+		\?) usage 1 >&2;;
+		h)  usage;;
+		d)  UNPACK_DIR=$OPTARG;;
+		v)  MITHRIL_VERSION=$OPTARG;;
+	esac
+done
+
+shift $((OPTIND - 1))
+
+case $# in
+	0) ;;
+	1) NETWORK=$1;;
+	*) usage 2 >&2;;
+esac
+
+case "$NETWORK" in
+	"mainnet") MITHRIL_NETWORK="release-mainnet" ;;
+	"preprod") MITHRIL_NETWORK="release-preprod" ;;
+	"preview") MITHRIL_NETWORK="pre-release-preview" ;;
+	*) echo >&2 "fatal: invalid NETWORK value: $NETWORK"; exit 1 ;;
+esac
+export MITHRIL_NETWORK
+
+export AGGREGATOR_ENDPOINT="https://aggregator.${MITHRIL_NETWORK}.api.mithril.network/aggregator"
+
+# shellcheck disable=SC2016
+nix shell \
+		"github:input-output-hk/mithril/${MITHRIL_VERSION}#mithril-client-cli" \
+		nixpkgs#jq \
+		nixpkgs#bash \
+		nixpkgs#curl \
+		--command bash -c '
+	set -euo pipefail
+
+	SNAPSHOT_DIGEST=$(mithril-client cardano-db snapshot list --json | jq -r ".[0].digest")
+
+	GENESIS_VERIFICATION_KEY=$(curl -fsSL "https://raw.githubusercontent.com/input-output-hk/mithril/${MITHRIL_VERSION}/mithril-infra/configuration/${MITHRIL_NETWORK}/genesis.vkey")
+	export GENESIS_VERIFICATION_KEY
+
+	set -x
+	mithril-client cardano-db download "$SNAPSHOT_DIGEST" --download-dir "$UNPACK_DIR"
+'