Extract state from db (#3889)

tools/extractor/BUILD.bazel

@@ -0,0 +1,20 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["main.go"],
+    importpath = "github.com/prysmaticlabs/prysm/tools/extractor",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//beacon-chain/core/state/interop:go_default_library",
+        "//beacon-chain/db:go_default_library",
+        "//beacon-chain/db/filters:go_default_library",
+        "//shared/featureconfig:go_default_library",
+    ],
+)
+
+go_binary(
+    name = "extractor",
+    embed = [":go_default_library"],
+    visibility = ["//visibility:public"],
+)

tools/extractor/main.go

@@ -0,0 +1,51 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+
+	"github.com/prysmaticlabs/prysm/beacon-chain/core/state/interop"
+	"github.com/prysmaticlabs/prysm/beacon-chain/db"
+	"github.com/prysmaticlabs/prysm/beacon-chain/db/filters"
+	"github.com/prysmaticlabs/prysm/shared/featureconfig"
+)
+
+var (
+	// Required fields
+	datadir = flag.String("datadir", "", "Path to data directory.")
+
+	state = flag.Uint("state", 0, "Extract state at this slot.")
+
+)
+
+func init() {
+	fc := featureconfig.Get()
+	fc.WriteSSZStateTransitions = true
+	featureconfig.Init(fc)
+}
+
+func main() {
+	flag.Parse()
+	fmt.Println("Starting process...")
+	d, err := db.NewDB(*datadir)
+	if err != nil {
+		panic(err)
+	}
+	ctx := context.Background()
+	slot := uint64(*state)
+	roots, err := d.BlockRoots(ctx, filters.NewFilter().SetStartSlot(slot).SetEndSlot(slot))
+	if err != nil {
+		panic(err)
+	}
+	if len(roots) != 1 {
+		fmt.Printf("Expected 1 block root for slot %d, got %d roots", *state, len(roots))
+	}
+	s, err := d.State(ctx, roots[0])
+	if err != nil {
+		panic(err)
+	}
+
+	interop.WriteStateToDisk(s)
+	fmt.Println("done")
+}