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verify.go
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verify.go
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// Copyright 2021 The Sigstore Authors.
//
// 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 dockerfile
import (
"bufio"
"context"
"errors"
"flag"
"fmt"
"io"
"os"
"strings"
"github.com/sigstore/cosign/cmd/cosign/cli/verify"
)
// VerifyCommand verifies a signature on a supplied container image
// nolint
type VerifyDockerfileCommand struct {
verify.VerifyCommand
BaseOnly bool
}
// Exec runs the verification command
func (c *VerifyDockerfileCommand) Exec(ctx context.Context, args []string) error {
if len(args) != 1 {
return flag.ErrHelp
}
dockerfile, err := os.Open(args[0])
if err != nil {
return fmt.Errorf("could not open Dockerfile: %w", err)
}
defer dockerfile.Close()
images, err := getImagesFromDockerfile(dockerfile)
if err != nil {
return fmt.Errorf("failed extracting images from Dockerfile: %w", err)
}
if len(images) == 0 {
return errors.New("no images found in Dockerfile")
}
if c.BaseOnly {
images = images[len(images)-1:]
}
fmt.Fprintf(os.Stderr, "Extracted image(s): %s\n", strings.Join(images, ", "))
return c.VerifyCommand.Exec(ctx, images)
}
func getImagesFromDockerfile(dockerfile io.Reader) ([]string, error) {
var images []string
fileScanner := bufio.NewScanner(dockerfile)
for fileScanner.Scan() {
line := strings.TrimSpace(fileScanner.Text())
if strings.HasPrefix(strings.ToUpper(line), "FROM") {
switch image := getImageFromLine(line); image {
case "scratch":
fmt.Fprintln(os.Stderr, "- scratch image ignored")
default:
images = append(images, image)
}
}
}
if err := fileScanner.Err(); err != nil {
return nil, err
}
return images, nil
}
func getImageFromLine(line string) string {
line = strings.TrimPrefix(line, "FROM") // Remove "FROM" prefix
line = os.ExpandEnv(line) // Substitute templated vars
fields := strings.Fields(line)
for i := len(fields) - 1; i > 0; i-- {
// Remove the "AS" portion of line
if strings.EqualFold(fields[i], "AS") {
fields = fields[:i]
break
}
}
return fields[len(fields)-1] // The image should be the last portion of the line that remains
}