feat!: remove MockTUFClient (#135)

* feat! remove MockTUFClient

*Breaking*
- use LocalPolicyDir and nil TUFClient instead

Other:
- add stateful Verifier

pkg/tuf/mock.go

@@ -1,67 +1,5 @@
 package tuf
 
-import (
-	"io"
-	"os"
-	"path/filepath"
-
-	"github.com/docker/attest/internal/util"
-)
-
-type MockTufClient struct {
-	srcPath string
-	dstPath string
-}
-
-func NewMockTufClient(srcPath string, dstPath string) *MockTufClient {
-	if srcPath == "" {
-		panic("srcPath must be set")
-	}
-	if dstPath == "" {
-		panic("dstPath must be set")
-	}
-	return &MockTufClient{
-		srcPath: srcPath,
-		dstPath: dstPath,
-	}
-}
-
-func (dc *MockTufClient) DownloadTarget(target string, filePath string) (file *TargetFile, err error) {
-	targetPath := filepath.Join(dc.srcPath, target)
-	src, err := os.Open(targetPath)
-	if err != nil {
-		return nil, err
-	}
-	defer src.Close()
-
-	var dstFilePath string
-	if filePath == "" {
-		dstFilePath = filepath.Join(dc.dstPath, filepath.FromSlash(target))
-	} else {
-		dstFilePath = filePath
-	}
-
-	err = os.MkdirAll(filepath.Dir(dstFilePath), os.ModePerm)
-	if err != nil {
-		return nil, err
-	}
-	dst, err := os.Create(dstFilePath)
-	if err != nil {
-		return nil, err
-	}
-	defer dst.Close()
-
-	// reading from tee will read from src and write to dst at the same time
-	tee := io.TeeReader(src, dst)
-
-	b, err := io.ReadAll(tee)
-	if err != nil {
-		return nil, err
-	}
-
-	return &TargetFile{ActualFilePath: dstFilePath, TargetURI: targetPath, Data: b, Digest: util.SHA256Hex(b)}, nil
-}
-
 type MockVersionChecker struct {
 	err error
 }

pkg/tuf/tuf.go

@@ -1,7 +1,6 @@
 package tuf
 
 import (
-	"context"
 	"errors"
 	"fmt"
 	"io/fs"
@@ -21,24 +20,6 @@ import (
 	"github.com/theupdateframework/go-tuf/v2/metadata/updater"
 )
 
-type tufCtxKeyType struct{}
-
-var DownloaderCtxKey tufCtxKeyType
-
-// WithDownloader sets Downloader in context.
-func WithDownloader(ctx context.Context, downloader Downloader) context.Context {
-	return context.WithValue(ctx, DownloaderCtxKey, downloader)
-}
-
-// GetDownloader returns the Downloader from context and `true` if it exists, otherwise `nil` and `false`.
-func GetDownloader(ctx context.Context) (Downloader, bool) {
-	t, ok := ctx.Value(DownloaderCtxKey).(Downloader)
-	if !ok {
-		return nil, false
-	}
-	return t, true
-}
-
 type Source string
 
 const (