initial

attrsum.go

@@ -0,0 +1,238 @@
+package main
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"errors"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"path/filepath"
+	"time"
+
+	base58 "github.com/mr-tron/base58/base58"
+	"github.com/multiformats/go-multihash"
+	"github.com/pkg/xattr"
+	"github.com/spf13/cobra"
+)
+
+const (
+	// Extended-attribute keys
+	checksumKey = "berlin.sneak.app.attrsum.checksum"
+	sumTimeKey  = "berlin.sneak.app.attrsum.sumtime"
+)
+
+var verbose bool
+
+func main() {
+	rootCmd := &cobra.Command{
+		Use:   "attrsum",
+		Short: "Compute and verify file checksums via xattrs",
+	}
+
+	rootCmd.PersistentFlags().BoolVarP(
+		&verbose, "verbose", "v", false, "enable verbose output",
+	)
+
+	rootCmd.AddCommand(newSumCmd())
+	rootCmd.AddCommand(newCheckCmd())
+
+	if err := rootCmd.Execute(); err != nil {
+		log.Fatal(err)
+	}
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Sum operations
+///////////////////////////////////////////////////////////////////////////////
+
+func newSumCmd() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "sum",
+		Short: "Checksum maintenance operations",
+	}
+
+	addCmd := &cobra.Command{
+		Use:   "add <directory>",
+		Short: "Write checksums for files missing them",
+		Args:  cobra.ExactArgs(1),
+		RunE: func(_ *cobra.Command, args []string) error {
+			return ProcessSumAdd(args[0])
+		},
+	}
+
+	updateCmd := &cobra.Command{
+		Use:   "update <directory>",
+		Short: "Refresh checksums when file modified",
+		Args:  cobra.ExactArgs(1),
+		RunE: func(_ *cobra.Command, args []string) error {
+			return ProcessSumUpdate(args[0])
+		},
+	}
+
+	cmd.AddCommand(addCmd, updateCmd)
+	return cmd
+}
+
+// ProcessSumAdd writes checksum & sumtime only when checksum is absent.
+func ProcessSumAdd(dir string) error {
+	return walkAndProcess(dir, func(path string, info os.FileInfo) error {
+		if hasXattr(path, checksumKey) {
+			if verbose {
+				log.Printf("skip existing %s", path)
+			}
+			return nil
+		}
+		return writeChecksumAndTime(path)
+	})
+}
+
+// ProcessSumUpdate recalculates checksum when file mtime exceeds stored
+// sumtime (or when attributes are missing / malformed).
+func ProcessSumUpdate(dir string) error {
+	return walkAndProcess(dir, func(path string, info os.FileInfo) error {
+		needUpdate := false
+		t, err := readSumTime(path)
+		if err != nil || info.ModTime().After(t) {
+			needUpdate = true
+		}
+		if needUpdate {
+			if verbose {
+				log.Printf("update %s", path)
+			}
+			return writeChecksumAndTime(path)
+		}
+		return nil
+	})
+}
+
+func writeChecksumAndTime(path string) error {
+	hash, err := fileMultihash(path)
+	if err != nil {
+		return err
+	}
+	if err := xattr.Set(path, checksumKey, hash); err != nil {
+		return fmt.Errorf("set checksum attr: %w", err)
+	}
+	nowStr := time.Now().UTC().Format(time.RFC3339Nano)
+	if err := xattr.Set(path, sumTimeKey, []byte(nowStr)); err != nil {
+		return fmt.Errorf("set sumtime attr: %w", err)
+	}
+	return nil
+}
+
+func readSumTime(path string) (time.Time, error) {
+	b, err := xattr.Get(path, sumTimeKey)
+	if err != nil {
+		return time.Time{}, err
+	}
+	return time.Parse(time.RFC3339Nano, string(b))
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Check operation
+///////////////////////////////////////////////////////////////////////////////
+
+func newCheckCmd() *cobra.Command {
+	var cont bool
+
+	cmd := &cobra.Command{
+		Use:   "check <directory>",
+		Short: "Verify stored checksums against file contents",
+		Args:  cobra.ExactArgs(1),
+		RunE: func(_ *cobra.Command, args []string) error {
+			return ProcessCheck(args[0], cont)
+		},
+	}
+
+	cmd.Flags().BoolVar(&cont, "continue", false,
+		"continue after errors and report each file")
+	return cmd
+}
+
+// ProcessCheck verifies checksums and exits non-zero on first error unless
+// --continue is supplied.
+func ProcessCheck(dir string, cont bool) error {
+	exitErr := errors.New("verification failed")
+
+	err := walkAndProcess(dir, func(path string, info os.FileInfo) error {
+		exp, err := xattr.Get(path, checksumKey)
+		if err != nil {
+			if errors.Is(err, xattr.ENOATTR) {
+				log.Printf("ERROR missing xattr %s", path)
+				if cont {
+					return nil
+				}
+				return exitErr
+			}
+			return err
+		}
+
+		act, err := fileMultihash(path)
+		if err != nil {
+			return err
+		}
+
+		if !bytes.Equal(exp, act) {
+			log.Printf("ERROR checksum mismatch %s", path)
+			if cont {
+				return nil
+			}
+			return exitErr
+		}
+		if cont {
+			fmt.Printf("OK %s\n", path)
+		}
+		return nil
+	})
+
+	if err != nil {
+		if errors.Is(err, exitErr) {
+			return exitErr
+		}
+		return err
+	}
+	return nil
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Helpers
+///////////////////////////////////////////////////////////////////////////////
+
+func walkAndProcess(root string, fn func(string, os.FileInfo) error) error {
+	return filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+		if info.IsDir() {
+			return nil
+		}
+		return fn(path, info)
+	})
+}
+
+func hasXattr(path, key string) bool {
+	_, err := xattr.Get(path, key)
+	return err == nil
+}
+
+// fileMultihash returns the base58-encoded SHA-2-256 multihash of the file.
+func fileMultihash(path string) ([]byte, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	h := sha256.New()
+	if _, err := io.Copy(h, f); err != nil {
+		return nil, err
+	}
+
+	mh, err := multihash.Encode(h.Sum(nil), multihash.SHA2_256)
+	if err != nil {
+		return nil, err
+	}
+	return []byte(base58.Encode(mh)), nil
+}