internal/modules/modules.go

// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package modules assists in working with modules, e.g.,
// downloading a module via a Go proxy client.
package modules

import (
	"archive/zip"
	"context"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"

	"golang.org/x/pkgsite-metrics/internal/derrors"
	"golang.org/x/pkgsite-metrics/internal/log"
	"golang.org/x/pkgsite-metrics/internal/proxy"
)

// Download fetches module at version via proxyClient and writes the modules
// down to disk at dir.
func Download(ctx context.Context, module, version, dir string, proxyClient *proxy.Client, stripModulePrefix bool) error {
	zipr, err := proxyClient.Zip(ctx, module, version)
	if err != nil {
		return fmt.Errorf("%v: %w", err, derrors.ProxyError)
	}
	log.Debugf(ctx, "writing module zip: %s@%s", module, version)
	stripPrefix := ""
	if stripModulePrefix {
		stripPrefix = module + "@" + version + "/"
	}
	if err := writeZip(zipr, dir, stripPrefix); err != nil {
		return fmt.Errorf("%v: %w", err, derrors.ScanModuleOSError)
	}
	return nil
}

func writeZip(r *zip.Reader, destination, stripPrefix string) error {
	for _, f := range r.File {
		name := strings.TrimPrefix(f.Name, stripPrefix)
		fpath := filepath.Join(destination, name)
		if !strings.HasPrefix(fpath, filepath.Clean(destination)+string(os.PathSeparator)) {
			return fmt.Errorf("%s is an illegal filepath", fpath)
		}
		if f.FileInfo().IsDir() {
			if err := os.MkdirAll(fpath, os.ModePerm); err != nil {
				return err
			}
			continue
		}
		if err := os.MkdirAll(filepath.Dir(fpath), os.ModePerm); err != nil {
			return err
		}
		outFile, err := os.OpenFile(fpath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, f.Mode())
		if err != nil {
			return err
		}
		rc, err := f.Open()
		if err != nil {
			return err
		}
		if _, err := io.Copy(outFile, rc); err != nil {
			return err
		}
		if err := outFile.Close(); err != nil {
			return err
		}
		if err := rc.Close(); err != nil {
			return err
		}
	}
	return nil
}