Support GCS as a history storage

README.md

@@ -421,6 +421,7 @@ The storage block has one label, which is a type of storage. Valid types are as
 
 - `local`: Save a history file to local filesystem.
 - `s3`: Save a history file to AWS S3.
+- `gcs`: Save a history file to GCS (Google Cloud Storage).
 
 If your cloud provider has not been supported yet, as a workaround, you can use `local` storage and synchronize a history file to your cloud storage with a wrapper script.
 
@@ -479,6 +480,31 @@ tfmigrate {
 }
 ```
 
+#### storage block (gcs)
+
+The `gcs` storage has the following attributes:
+
+- `bucket` (required): Name of the bucket.
+- `name` (required): Path to the migration history file.
+
+Note that this storage implementation refers the Application Default Credentials (ADC) for authentication.
+
+An example of configuration file is as follows.
+
+```hcl
+tfmigrate {
+  migration_dir = "./tfmigrate"
+  history {
+    storage "gcs" {
+      bucket = "tfstate-test"
+      name   = "tfmigrate/history.json"
+    }
+  }
+}
+```
+
+If you want to connect to an emulator instead of GCS, set the `STORAGE_EMULATOR_HOST` environment variable as required by the [Go library for GCS](https://pkg.go.dev/cloud.google.com/go/storage).
+
 ## Migration file
 
 You can write terraform state operations in HCL. The syntax of migration file is as follows:

config/storage.go

@@ -6,6 +6,7 @@ import (
 	"github.com/hashicorp/hcl/v2"
 	"github.com/hashicorp/hcl/v2/gohcl"
 	storage "github.com/minamijoyo/tfmigrate-storage"
+	"github.com/minamijoyo/tfmigrate-storage/gcs"
 	"github.com/minamijoyo/tfmigrate-storage/local"
 	"github.com/minamijoyo/tfmigrate-storage/mock"
 	"github.com/minamijoyo/tfmigrate-storage/s3"
@@ -37,6 +38,9 @@ func parseStorageBlock(b StorageBlock) (storage.Config, error) {
 	case "s3":
 		return parseS3StorageBlock(b)
 
+	case "gcs":
+		return parseGCSStorageBlock(b)
+
 	default:
 		return nil, fmt.Errorf("unknown history storage type: %s", b.Type)
 	}
@@ -74,3 +78,13 @@ func parseS3StorageBlock(b StorageBlock) (storage.Config, error) {
 
 	return &config, nil
 }
+
+func parseGCSStorageBlock(b StorageBlock) (storage.Config, error) {
+	var config gcs.Config
+	diags := gohcl.DecodeBody(b.Remain, nil, &config)
+	if diags.HasErrors() {
+		return nil, diags
+	}
+
+	return &config, nil
+}

config/storage_gcs_test.go

@@ -0,0 +1,101 @@
+package config
+
+import (
+	"reflect"
+	"testing"
+
+	storage "github.com/minamijoyo/tfmigrate-storage"
+	"github.com/minamijoyo/tfmigrate-storage/gcs"
+)
+
+func TestParseGCSStorageBlock(t *testing.T) {
+	cases := []struct {
+		desc   string
+		source string
+		want   storage.Config
+		ok     bool
+	}{
+		{
+			desc: "valid (required)",
+			source: `
+tfmigrate {
+  history {
+    storage "gcs" {
+      bucket = "tfmigrate-test"
+      name   = "tfmigrate/history.json"
+    }
+  }
+}
+`,
+			want: &gcs.Config{
+				Bucket: "tfmigrate-test",
+				Name:   "tfmigrate/history.json",
+			},
+			ok: true,
+		},
+		{
+			desc: "valid (with optional)",
+			source: `
+tfmigrate {
+  history {
+    storage "gcs" {
+      bucket   = "tfmigrate-test"
+      name     = "tfmigrate/history.json"
+    }
+  }
+}
+`,
+			want: &gcs.Config{
+				Bucket: "tfmigrate-test",
+				Name:   "tfmigrate/history.json",
+			},
+			ok: true,
+		},
+		{
+			desc: "missing required attribute (bucket)",
+			source: `
+tfmigrate {
+  history {
+    storage "gcs" {
+      name = "tfmigrate/history.json"
+    }
+  }
+}
+`,
+			want: nil,
+			ok:   false,
+		},
+		{
+			desc: "missing required attribute (name)",
+			source: `
+tfmigrate {
+  history {
+    storage "gcs" {
+      bucket = "tfmigrate-test"
+    }
+  }
+}
+`,
+			want: nil,
+			ok:   false,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.desc, func(t *testing.T) {
+			config, err := ParseConfigurationFile("test.hcl", []byte(tc.source))
+			if tc.ok && err != nil {
+				t.Fatalf("unexpected err: %s", err)
+			}
+			if !tc.ok && err == nil {
+				t.Fatalf("expected to return an error, but no error, got: %#v", config)
+			}
+			if tc.ok {
+				got := config.History.Storage
+				if !reflect.DeepEqual(got, tc.want) {
+					t.Errorf("got: %#v, want: %#v", got, tc.want)
+				}
+			}
+		})
+	}
+}

docker-compose.yml

@@ -13,8 +13,10 @@ services:
       # Use the same filesystem to avoid a checksum mismatch error
       # or a file busy error caused by asynchronous IO.
       TF_PLUGIN_CACHE_DIR: "/tmp/plugin-cache"
+      STORAGE_EMULATOR_HOST: "http://fake-gcs-server:4443"
     depends_on:
       - localstack
+      - fake-gcs-server
 
   localstack:
     image: localstack/localstack:1.0.3
@@ -28,7 +30,14 @@ services:
     volumes:
       - "./scripts/localstack:/docker-entrypoint-initaws.d"  # initialize scripts on startup
 
+  fake-gcs-server:
+    image: fsouza/fake-gcs-server:1.38
+    ports:
+      - "4443:4443"
+    command: -scheme http
+
   dockerize:
     image: powerman/dockerize:0.16.3
     depends_on:
       - localstack
+      - fake-gcs-server

go.mod

@@ -4,24 +4,33 @@ go 1.19
 
 require (
 	github.com/davecgh/go-spew v1.1.1
-	github.com/google/go-cmp v0.5.2
+	github.com/google/go-cmp v0.5.8
 	github.com/hashicorp/go-version v1.3.0
 	github.com/hashicorp/hcl/v2 v2.6.0
 	github.com/hashicorp/logutils v1.0.0
 	github.com/mattn/go-shellwords v1.0.10
-	github.com/minamijoyo/tfmigrate-storage v0.0.0-20220325144224-f6ba9f1d2224
+	github.com/minamijoyo/tfmigrate-storage v0.0.0-20220824073652-6dd8f2fd2948
 	github.com/mitchellh/cli v1.1.1
 	github.com/spf13/pflag v1.0.2
 )
 
 require (
+	cloud.google.com/go v0.102.1 // indirect
+	cloud.google.com/go/compute v1.7.0 // indirect
+	cloud.google.com/go/iam v0.3.0 // indirect
+	cloud.google.com/go/storage v1.25.0 // indirect
 	github.com/agext/levenshtein v1.2.1 // indirect
 	github.com/apparentlymart/go-textseg v1.0.0 // indirect
 	github.com/apparentlymart/go-textseg/v12 v12.0.0 // indirect
 	github.com/armon/go-radix v0.0.0-20180808171621-7fddfc383310 // indirect
 	github.com/aws/aws-sdk-go v1.43.22 // indirect
 	github.com/bgentry/speakeasy v0.1.0 // indirect
 	github.com/fatih/color v1.7.0 // indirect
+	github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e // indirect
+	github.com/golang/protobuf v1.5.2 // indirect
+	github.com/google/uuid v1.3.0 // indirect
+	github.com/googleapis/enterprise-certificate-proxy v0.1.0 // indirect
+	github.com/googleapis/gax-go/v2 v2.4.0 // indirect
 	github.com/hashicorp/aws-sdk-go-base v1.1.0 // indirect
 	github.com/hashicorp/errwrap v1.0.0 // indirect
 	github.com/hashicorp/go-cleanhttp v0.5.0 // indirect
@@ -33,7 +42,15 @@ require (
 	github.com/mitchellh/go-wordwrap v0.0.0-20150314170334-ad45545899c7 // indirect
 	github.com/posener/complete v1.1.1 // indirect
 	github.com/zclconf/go-cty v1.2.0 // indirect
-	golang.org/x/sys v0.0.0-20211216021012-1d35b9e2eb4e // indirect
+	go.opencensus.io v0.23.0 // indirect
+	golang.org/x/net v0.0.0-20220624214902-1bab6f366d9e // indirect
+	golang.org/x/oauth2 v0.0.0-20220622183110-fd043fe589d2 // indirect
+	golang.org/x/sys v0.0.0-20220624220833-87e55d714810 // indirect
 	golang.org/x/text v0.3.7 // indirect
-	golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 // indirect
+	golang.org/x/xerrors v0.0.0-20220609144429-65e65417b02f // indirect
+	google.golang.org/api v0.88.0 // indirect
+	google.golang.org/appengine v1.6.7 // indirect
+	google.golang.org/genproto v0.0.0-20220720214146-176da50484ac // indirect
+	google.golang.org/grpc v1.48.0 // indirect
+	google.golang.org/protobuf v1.28.0 // indirect
 )