Add GCP migration binary.

cmd/experimental/migrate/gcp/main.go

@@ -0,0 +1,94 @@
+// Copyright 2025 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.
+
+// gcp-migrate is a command-line tool for migrating data from a tlog-tiles
+// compliant log, into a Tessera log instance.
+package main
+
+import (
+	"context"
+	"encoding/base64"
+	"flag"
+	"net/url"
+	"strconv"
+	"strings"
+
+	"github.com/transparency-dev/trillian-tessera/client"
+	"github.com/transparency-dev/trillian-tessera/cmd/experimental/migrate/internal"
+	"github.com/transparency-dev/trillian-tessera/storage/gcp"
+	"k8s.io/klog/v2"
+)
+
+var (
+	bucket  = flag.String("bucket", "", "Bucket to use for storing log")
+	listen  = flag.String("listen", ":2024", "Address:port to listen on")
+	spanner = flag.String("spanner", "", "Spanner resource URI ('projects/.../...')")
+
+	sourceURL  = flag.String("source_url", "", "Base URL for the source log.")
+	numWorkers = flag.Int("num_workers", 30, "Number of migration worker goroutines.")
+)
+
+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)
+	if err != nil {
+		klog.Exitf("Failed to create HTTP fetcher: %v", err)
+	}
+	sourceCP, err := src.ReadCheckpoint(ctx)
+	if err != nil {
+		klog.Exitf("fetch initial source checkpoint: %v", err)
+	}
+	bits := strings.Split(string(sourceCP), "\n")
+	sourceSize, err := strconv.ParseUint(bits[1], 10, 64)
+	if err != nil {
+		klog.Exitf("invalid CP size %q: %v", bits[1], err)
+	}
+	sourceRoot, err := base64.StdEncoding.DecodeString(bits[2])
+	if err != nil {
+		klog.Exitf("invalid checkpoint roothash %q: %v", bits[2], err)
+	}
+
+	// Create our Tessera storage backend:
+	gcpCfg := storageConfigFromFlags()
+	driver, err := gcp.NewMigrationTarget(ctx, gcpCfg, internal.BundleHasher)
+	if err != nil {
+		klog.Exitf("Failed to create new GCP storage: %v", err)
+	}
+
+	if err := internal.Migrate(context.Background(), *numWorkers, sourceSize, sourceRoot, src.ReadEntryBundle, driver); 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,
+	}
+}