op-challenger: Support file: URLs to download prestates from. (#12441)

* op-challenger: Introduce --prestates-url to specify prestates source for all game types at once.

* op-challenger: Add required config validation for asterisc kona.

Allow specify both prestate and prestates url to allow overriding. Prestate takes priority.

* op-challenger: Introduce vm-flag to make default with overrides pattern easier.

* op-challenger: Add vm type info to override flags.

* op-challenger: Support file: URLs to download prestates from.

Makes it possible to support multiple prestates without needing a HTTP server.

op-challenger/game/fault/trace/prestates/multi.go

@@ -69,20 +69,11 @@ func (m *MultiPrestateProvider) fetchPrestate(ctx context.Context, hash common.H
 		return fmt.Errorf("error creating prestate dir: %w", err)
 	}
 	prestateUrl := m.baseUrl.JoinPath(hash.Hex() + fileType)
-	tCtx, cancel := context.WithTimeout(ctx, time.Minute)
-	defer cancel()
-	req, err := http.NewRequestWithContext(tCtx, "GET", prestateUrl.String(), nil)
-	if err != nil {
-		return fmt.Errorf("failed to create prestate request: %w", err)
-	}
-	resp, err := http.DefaultClient.Do(req)
+	in, err := m.fetch(ctx, prestateUrl)
 	if err != nil {
-		return fmt.Errorf("failed to fetch prestate from %v: %w", prestateUrl, err)
-	}
-	defer resp.Body.Close()
-	if resp.StatusCode != http.StatusOK {
-		return fmt.Errorf("%w from url %v: status %v", ErrPrestateUnavailable, prestateUrl, resp.StatusCode)
+		return err
 	}
+	defer in.Close()
 	tmpFile := dest + ".tmp" + fileType // Preserve the file type extension so state decoding is applied correctly
 	out, err := ioutil.NewAtomicWriter(tmpFile, 0o644)
 	if err != nil {
@@ -92,7 +83,7 @@ func (m *MultiPrestateProvider) fetchPrestate(ctx context.Context, hash common.H
 		// If errors occur, try to clean up without renaming the file into its final destination as Close() would do
 		_ = out.Abort()
 	}()
-	if _, err := io.Copy(out, resp.Body); err != nil {
+	if _, err := io.Copy(out, in); err != nil {
 		return fmt.Errorf("failed to write file %v: %w", dest, err)
 	}
 	if err := out.Close(); err != nil {
@@ -110,3 +101,29 @@ func (m *MultiPrestateProvider) fetchPrestate(ctx context.Context, hash common.H
 	}
 	return nil
 }
+
+func (m *MultiPrestateProvider) fetch(ctx context.Context, prestateUrl *url.URL) (io.ReadCloser, error) {
+	if prestateUrl.Scheme == "file" {
+		path := prestateUrl.Path
+		in, err := os.OpenFile(path, os.O_RDONLY, 0o644)
+		if errors.Is(err, os.ErrNotExist) {
+			return nil, fmt.Errorf("%w unavailable from path %v", ErrPrestateUnavailable, path)
+		}
+		return in, err
+	}
+	tCtx, cancel := context.WithTimeout(ctx, time.Minute)
+	defer cancel()
+	req, err := http.NewRequestWithContext(tCtx, "GET", prestateUrl.String(), nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create prestate request: %w", err)
+	}
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("failed to fetch prestate from %v: %w", prestateUrl, err)
+	}
+	if resp.StatusCode != http.StatusOK {
+		_ = resp.Body.Close() // Not returning the body so make a best effort to close it now.
+		return nil, fmt.Errorf("%w from url %v: status %v", ErrPrestateUnavailable, prestateUrl, resp.StatusCode)
+	}
+	return resp.Body, nil
+}

op-challenger/game/fault/trace/prestates/multi_test.go

@@ -18,7 +18,7 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func TestDownloadPrestate(t *testing.T) {
+func TestDownloadPrestateHTTP(t *testing.T) {
 	for _, ext := range supportedFileTypes {
 		t.Run(ext, func(t *testing.T) {
 			dir := t.TempDir()
@@ -38,6 +38,28 @@ func TestDownloadPrestate(t *testing.T) {
 	}
 }
 
+func TestDownloadPrestateFile(t *testing.T) {
+	for _, ext := range supportedFileTypes {
+		t.Run(ext, func(t *testing.T) {
+			sourceDir := t.TempDir()
+			dir := t.TempDir()
+			hash := common.Hash{0xaa}
+			sourcePath := filepath.Join(sourceDir, hash.Hex()+ext)
+			expectedContent := "/" + hash.Hex() + ext
+			require.NoError(t, os.WriteFile(sourcePath, []byte(expectedContent), 0600))
+			provider := NewMultiPrestateProvider(parseURL(t, "file:"+sourceDir), dir, &stubStateConverter{hash: hash})
+			path, err := provider.PrestatePath(context.Background(), hash)
+			require.NoError(t, err)
+			in, err := os.Open(path)
+			require.NoError(t, err)
+			defer in.Close()
+			content, err := io.ReadAll(in)
+			require.NoError(t, err)
+			require.Equal(t, expectedContent, string(content))
+		})
+	}
+}
+
 func TestCreateDirectory(t *testing.T) {
 	for _, ext := range supportedFileTypes {
 		t.Run(ext, func(t *testing.T) {