[lbry] contrib: add a helper script for generating snapshots

contrib/snapshot.sh

@@ -0,0 +1,63 @@
+#!/bin/sh
+
+read -r -d '' help << EOM
+snapshot.sh - helper script for generating snapshot from lbcd's app dir.
+
+The default output name "lbcd_snapshot_<height>_<lbcd_ver>_<date>.tar.zst"
+
+To extract the snapshot (data/mainter/):
+
+    zstd -d lbcd_snapshot_<height>_<lbcd_ver>_<date>.tar.zst | tar xf - -C <appdir>
+
+Default appdir of lbcd on different OSes:
+
+        Darwin)  "\${HOME}/Library/Application Support/Lbcd"
+        Linux)   "\${HOME}/.lbcd"
+        Windows) "%%LOCALAPPDATA%%/lbcd"
+
+Options:
+
+    -h Display this message.
+    -d Specify APPDIR to copy the snapshot from.
+
+    -o Specify the output filename of snapshot.
+    -b Specify the best block height of the snapshot. (ignored if -o is specified)
+    -l Specify git tag of the running lbcd. (ignored if -o is specified)
+    -t Specify the date when the snapshot is generated. (ignored if -o is specified)
+EOM
+
+while getopts o:d:b:l:t:h flag
+do
+    case "${flag}" in
+	h) printf "${help}\n\n"; exit 0;;
+        d) appdir=${OPTARG};;
+
+        o) snapshot=${OPTARG};;
+        b) height=${OPTARG};;
+        l) lbcd_ver=${OPTARG};;
+        t) date=${OPTARG};;
+    esac
+done
+
+if [ -z "$appdir" ]; then
+    case $(uname) in
+        Darwin)  appdir="${HOME}/Library/Application Support/Lbcd" ;;
+        Linux)   appdir="${HOME}/.lbcd" ;;
+        Windows) appdir="%LOCALAPPDATA%/lbcd" ;;
+    esac
+fi
+
+
+if [ -z ${snapshot} ]; then
+    git_repo=$(git rev-parse --show-toplevel)
+    [ -z "${height}" ] && height=$(go run ${git_repo}/claimtrie/cmd block best --showhash=false)
+    [ -z "${lbcd_ver}" ] && lbcd_ver=$(git describe --tags)
+    [ -z "${date}" ] && date=$(date  +"%Y-%m-%d")
+    snapshot="lbcd_snapshot_${height}_${lbcd_ver}_${date}.tar.zst"
+fi
+
+
+echo "Generating $snapshot ..."
+
+tar c -C "${appdir}" data/mainnet | zstd -9 --no-progress -o "${snapshot}"
+