Add GCP migrate tool

cmd/experimental/migrate/gcp/main.go

@@ -0,0 +1,73 @@
+// Copyright 2024 The Tessera authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// posix-migrate is a command-line tool for migrating data from a tlog-tiles
+// compliant log, into a Tessera log instance.
+package main
+
+import (
+	"context"
+	"flag"
+	"net/url"
+
+	"github.com/transparency-dev/trillian-tessera/client"
+	"github.com/transparency-dev/trillian-tessera/cmd/experimental/migrate/internal/migrate"
+	"github.com/transparency-dev/trillian-tessera/storage/gcp"
+	"k8s.io/klog/v2"
+)
+
+var (
+	bucket    = flag.String("bucket", "", "Bucket to use for storing log")
+	spanner   = flag.String("spanner", "", "Spanner resource URI ('projects/.../...')")
+	sourceURL = flag.String("source_url", "", "Base URL for the source log.")
+	stateDB   = flag.String("state_database", "migrate.sttate", "File to use for the temporary file used to track migration state.")
+)
+
+func main() {
+	klog.InitFlags(nil)
+	flag.Parse()
+	ctx := context.Background()
+
+	srcURL, err := url.Parse(*sourceURL)
+	if err != nil {
+		klog.Exitf("Invalid --source_url %q: %v", *sourceURL, err)
+	}
+	src, err := client.NewHTTPFetcher(srcURL, nil)
+
+	// Create our Tessera storage backend:
+	gcpCfg := storageConfigFromFlags()
+	st, err := gcp.NewMigrationTarget(ctx, gcpCfg)
+	if err != nil {
+		klog.Exitf("Failed to create new GCP storage: %v", err)
+	}
+
+	if err := migrate.Migrate(context.Background(), *stateDB, src.ReadCheckpoint, src.ReadTile, src.ReadEntryBundle, st); err != nil {
+		klog.Exitf("Migrate failed: %v", err)
+	}
+}
+
+// storageConfigFromFlags returns a gcp.Config struct populated with values
+// provided via flags.
+func storageConfigFromFlags() gcp.Config {
+	if *bucket == "" {
+		klog.Exit("--bucket must be set")
+	}
+	if *spanner == "" {
+		klog.Exit("--spanner must be set")
+	}
+	return gcp.Config{
+		Bucket:  *bucket,
+		Spanner: *spanner,
+	}
+}