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flash.go
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flash.go
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// Copyright 2020 Google LLC. 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.
// Package dummy provides a fake device to demo flashing firmware.
package dummy
import (
"encoding/json"
"fmt"
"os"
"path/filepath"
"github.com/google/trillian-examples/binary_transparency/firmware/api"
"github.com/google/trillian-examples/binary_transparency/firmware/cmd/flash_tool/devices"
)
const (
bundlePath = "bundle.json"
firmwarePath = "firmware.bin"
)
// Device is a fake device using the local filesystem for storage.
type Device struct {
// bundle holds all the update data except the firmware image.
bundle api.ProofBundle
storage string
}
var _ devices.Device = Device{}
// New creates a new dummy device instance using data from flags.
// TODO(al): figure out how/whether to remove the flag from in here.
func New(storage string) (*Device, error) {
dStat, err := os.Stat(storage)
if err != nil {
return nil, fmt.Errorf("unable to stat device storage dir %q: %w", storage, err)
}
if !dStat.Mode().IsDir() {
return nil, fmt.Errorf("device storage %q is not a directory", storage)
}
d := &Device{
storage: storage,
}
fPath := filepath.Join(storage, bundlePath)
f, err := os.OpenFile(fPath, os.O_RDONLY, os.ModePerm)
if err != nil {
if os.IsNotExist(err) {
return d, devices.ErrNeedsInit(fmt.Errorf("couldn't read bundle file %q: %w", fPath, err))
}
return d, fmt.Errorf("failed to read bundle file %q: %w", fPath, err)
}
defer func() {
_ = f.Close()
}()
err = json.NewDecoder(f).Decode(&d.bundle)
return d, err
}
// DeviceCheckpoint returns the latest log checkpoint stored on the device.
func (d Device) DeviceCheckpoint() ([]byte, error) {
return d.bundle.Checkpoint, nil
}
// ApplyUpdate applies the firmware update to the dummy device.
// The firmware image is stored in the dummy state directory in the firmware.bin file,
// and the rest of the update bundle is stored in the bundle.json file.
func (d Device) ApplyUpdate(u api.UpdatePackage) error {
fwFile := filepath.Join(d.storage, firmwarePath)
bundleFile := filepath.Join(d.storage, bundlePath)
if err := os.WriteFile(bundleFile, u.ProofBundle, os.ModePerm); err != nil {
return fmt.Errorf("failed to write proof bundle to %q: %q", bundleFile, err)
}
fw := u.FirmwareImage
if err := os.WriteFile(fwFile, fw, os.ModePerm); err != nil {
return fmt.Errorf("failed to write firmware image to %q: %q", fwFile, err)
}
return nil
}