gotenberg/pkg/modules/exiftool/exiftool.go

package exiftool

import (
	"context"
	"errors"
	"fmt"
	"os"
	"os/exec"
	"reflect"
	"strings"
	"syscall"

	"github.com/barasher/go-exiftool"
	"go.uber.org/zap"

	"github.com/gotenberg/gotenberg/v8/pkg/gotenberg"
)

func init() {
	gotenberg.MustRegisterModule(new(ExifTool))
}

// ExifTool abstracts the CLI tool ExifTool and implements the
// [gotenberg.PdfEngine] interface.
type ExifTool struct {
	binPath string
}

// Descriptor returns [ExifTool]'s module descriptor.
func (engine *ExifTool) Descriptor() gotenberg.ModuleDescriptor {
	return gotenberg.ModuleDescriptor{
		ID:  "exiftool",
		New: func() gotenberg.Module { return new(ExifTool) },
	}
}

// Provision sets the module properties.
func (engine *ExifTool) Provision(ctx *gotenberg.Context) error {
	binPath, ok := os.LookupEnv("EXIFTOOL_BIN_PATH")
	if !ok {
		return errors.New("EXIFTOOL_BIN_PATH environment variable is not set")
	}

	engine.binPath = binPath

	return nil
}

// Validate validates the module properties.
func (engine *ExifTool) Validate() error {
	_, err := os.Stat(engine.binPath)
	if os.IsNotExist(err) {
		return fmt.Errorf("ExifTool binary path does not exist: %w", err)
	}

	return nil
}

// Debug returns additional debug data.
func (engine *ExifTool) Debug() map[string]any {
	debug := make(map[string]any)

	cmd := exec.Command(engine.binPath, "-ver") //nolint:gosec
	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}

	output, err := cmd.Output()
	if err != nil {
		debug["version"] = err.Error()
		return debug
	}

	debug["version"] = strings.TrimSpace(string(output))
	return debug
}

// Merge is not available in this implementation.
func (engine *ExifTool) Merge(ctx context.Context, logger *zap.Logger, inputPaths []string, outputPath string) error {
	return fmt.Errorf("merge PDFs with ExifTool: %w", gotenberg.ErrPdfEngineMethodNotSupported)
}

// Split is not available in this implementation.
func (engine *ExifTool) Split(ctx context.Context, logger *zap.Logger, mode gotenberg.SplitMode, inputPath, outputDirPath string) ([]string, error) {
	return nil, fmt.Errorf("split PDF with ExifTool: %w", gotenberg.ErrPdfEngineMethodNotSupported)
}

// Flatten is not available in this implementation.
func (engine *ExifTool) Flatten(ctx context.Context, logger *zap.Logger, inputPath string) error {
	return fmt.Errorf("flatten PDF with ExifTool: %w", gotenberg.ErrPdfEngineMethodNotSupported)
}

// Convert is not available in this implementation.
func (engine *ExifTool) Convert(ctx context.Context, logger *zap.Logger, formats gotenberg.PdfFormats, inputPath, outputPath string) error {
	return fmt.Errorf("convert PDF to '%+v' with ExifTool: %w", formats, gotenberg.ErrPdfEngineMethodNotSupported)
}

// ReadMetadata extracts the metadata of a given PDF file.
func (engine *ExifTool) ReadMetadata(ctx context.Context, logger *zap.Logger, inputPath string) (map[string]any, error) {
	exifTool, err := exiftool.NewExiftool(exiftool.SetExiftoolBinaryPath(engine.binPath))
	if err != nil {
		return nil, fmt.Errorf("new ExifTool: %w", err)
	}

	defer func(exifTool *exiftool.Exiftool) {
		err := exifTool.Close()
		if err != nil {
			logger.Error(fmt.Sprintf("close ExifTool: %v", err))
		}
	}(exifTool)

	fileMetadata := exifTool.ExtractMetadata(inputPath)
	if fileMetadata[0].Err != nil {
		return nil, fmt.Errorf("read metadata with ExitfTool: %w", fileMetadata[0].Err)
	}

	return fileMetadata[0].Fields, nil
}

// WriteMetadata writes the metadata into a given PDF file.
func (engine *ExifTool) WriteMetadata(ctx context.Context, logger *zap.Logger, metadata map[string]any, inputPath string) error {
	exifTool, err := exiftool.NewExiftool(exiftool.SetExiftoolBinaryPath(engine.binPath))
	if err != nil {
		return fmt.Errorf("new ExifTool: %w", err)
	}

	defer func(exifTool *exiftool.Exiftool) {
		err := exifTool.Close()
		if err != nil {
			logger.Error(fmt.Sprintf("close ExifTool: %v", err))
		}
	}(exifTool)

	fileMetadata := exifTool.ExtractMetadata(inputPath)
	if fileMetadata[0].Err != nil {
		return fmt.Errorf("read metadata with ExitfTool: %w", fileMetadata[0].Err)
	}

	// Define a list of derived, system, or computed tags that ExifTool
	// extracts but should never be written back. Writing these can break PDF/A
	// compliance (e.g., PageCount -> prism:pageCount) or cause side effects
	// (e.g., FileModifyDate).
	derivedTags := []string{
		"PageCount",           // Causes prism:pageCount injection
		"Linearized",          // Computed status; writing it may invalidate structure
		"PDFVersion",          // Header version; should not be manually forced via metadata
		"MIMEType",            // Read-only derived
		"FileType",            // Read-only derived
		"FileTypeExtension",   // Read-only derived
		"FileSize",            // System attribute
		"FileModifyDate",      // System attribute
		"FileAccessDate",      // System attribute
		"FileInodeChangeDate", // System attribute
		"FilePermissions",     // System attribute
		"FileName",            // Writing this triggers a file rename in ExifTool
		"Directory",           // System attribute
		"ExifToolVersion",     // Tool metadata
		"Error",               // Extraction error messages
		"Warning",             // Extraction warning messages
	}

	for _, tag := range derivedTags {
		delete(fileMetadata[0].Fields, tag)
	}

	for key, value := range metadata {
		switch val := value.(type) {
		case string:
			fileMetadata[0].SetString(key, val)
		case []string:
			fileMetadata[0].SetStrings(key, val)
		case []any:
			// See https://github.com/gotenberg/gotenberg/issues/1048.
			strs := make([]string, len(val))
			for i, entry := range val {
				if str, ok := entry.(string); ok {
					strs[i] = str
					continue
				}
				return fmt.Errorf("write PDF metadata with ExifTool: %s %+v %s %w", key, val, reflect.TypeFor[[]any](), gotenberg.ErrPdfEngineMetadataValueNotSupported)
			}
			fileMetadata[0].SetStrings(key, strs)
		case bool:
			fileMetadata[0].SetString(key, fmt.Sprintf("%t", val))
		case int:
			fileMetadata[0].SetInt(key, int64(val))
		case int64:
			fileMetadata[0].SetInt(key, val)
		case float32:
			fileMetadata[0].SetFloat(key, float64(val))
		case float64:
			fileMetadata[0].SetFloat(key, val)
		// TODO: support more complex cases, e.g., arrays and nested objects
		// 	(limitations in underlying library).
		default:
			return fmt.Errorf("write PDF metadata with ExifTool: %s %+v %s %w", key, val, reflect.TypeOf(val), gotenberg.ErrPdfEngineMetadataValueNotSupported)
		}
	}

	exifTool.WriteMetadata(fileMetadata)
	if fileMetadata[0].Err != nil {
		return fmt.Errorf("write PDF metadata with ExifTool: %w", fileMetadata[0].Err)
	}

	return nil
}

// PageCount returns the number of pages in a PDF file using ExifTool.
func (engine *ExifTool) PageCount(ctx context.Context, logger *zap.Logger, inputPath string) (int, error) {
	metadata, err := engine.ReadMetadata(ctx, logger, inputPath)
	if err != nil {
		return 0, fmt.Errorf("read metadata with ExifTool: %w", err)
	}

	pageCountValue, ok := metadata["PageCount"]
	if !ok {
		return 0, errors.New("PageCount not found in metadata")
	}

	switch val := pageCountValue.(type) {
	case int:
		return val, nil
	case int64:
		return int(val), nil
	case float64:
		return int(val), nil
	case string:
		var res int
		_, err := fmt.Sscanf(val, "%d", &res)
		if err != nil {
			return 0, fmt.Errorf("parse PageCount string '%s': %w", val, err)
		}
		return res, nil
	default:
		return 0, fmt.Errorf("unexpected PageCount type '%T'", pageCountValue)
	}
}

// WriteBookmarks is not available in this implementation.
func (engine *ExifTool) WriteBookmarks(ctx context.Context, logger *zap.Logger, inputPath string, bookmarks []gotenberg.Bookmark) error {
	return fmt.Errorf("write PDF bookmarks with ExifTool: %w", gotenberg.ErrPdfEngineMethodNotSupported)
}

// ReadBookmarks is not available in this implementation.
func (engine *ExifTool) ReadBookmarks(ctx context.Context, logger *zap.Logger, inputPath string) ([]gotenberg.Bookmark, error) {
	return nil, fmt.Errorf("read PDF bookmarks with ExifTool: %w", gotenberg.ErrPdfEngineMethodNotSupported)
}

// Encrypt is not available in this implementation.
func (engine *ExifTool) Encrypt(ctx context.Context, logger *zap.Logger, inputPath, userPassword, ownerPassword string) error {
	return fmt.Errorf("encrypt PDF using ExifTool: %w", gotenberg.ErrPdfEncryptionNotSupported)
}

// EmbedFiles is not available in this implementation.
func (engine *ExifTool) EmbedFiles(ctx context.Context, logger *zap.Logger, filePaths []string, inputPath string) error {
	return fmt.Errorf("embed files with ExifTool: %w", gotenberg.ErrPdfEngineMethodNotSupported)
}

// Watermark is not available in this implementation.
func (engine *ExifTool) Watermark(ctx context.Context, logger *zap.Logger, inputPath string, stamp gotenberg.Stamp) error {
	return fmt.Errorf("watermark PDF with ExifTool: %w", gotenberg.ErrPdfEngineMethodNotSupported)
}

// Stamp is not available in this implementation.
func (engine *ExifTool) Stamp(ctx context.Context, logger *zap.Logger, inputPath string, stamp gotenberg.Stamp) error {
	return fmt.Errorf("stamp PDF with ExifTool: %w", gotenberg.ErrPdfEngineMethodNotSupported)
}

// Interface guards.
var (
	_ gotenberg.Module      = (*ExifTool)(nil)
	_ gotenberg.Provisioner = (*ExifTool)(nil)
	_ gotenberg.Validator   = (*ExifTool)(nil)
	_ gotenberg.Debuggable  = (*ExifTool)(nil)
	_ gotenberg.PdfEngine   = (*ExifTool)(nil)
)