Class: Kithe::ExiftoolCharacterization

Inherits:
Object
  • Object
show all
Defined in:
app/characterization/kithe/exiftool_characterization.rb,
app/characterization/kithe/exiftool_characterization/result.rb

Overview

Can run an installed ‘exiftool` command line, and return results as a JSON hash. exiftool needs to be installed. This version developed against exiftool 12.60

Results are extended with exact command-line arguments given to exiftool in key ‘Kithe:CliArgs` as an array of Strings.

We ask exiftool to check for validation errors, and output them too, although they are output in exiftool json with kind of inconvenient key patterns.

Results can be parsed with accompanying Kithe::Exiftool::Characterization::Result class – in future, if different versions or invocations of exiftool produce different hash results, we can provide different Results parsers, and a switching method to choose right one based on exiftool version and args embedded in results.

In cases of errors where exiftool returns errors in hash, hash is still returned, no raise!

  • exiftool needs to be installed

  • Runs with -G0:4 so keys might look like ‘EXIF:BitsPerSample` or in some cases have a `Copy1` or `Copy2` in there, like `XMP:Copy1:Make`. The `g4` arg results in that `Copy1`, necessary to get multiple validation warnings all included, but a bit annoying when it puts in extraneous `Copy1` for singular results sometimes too.

Examples:

hash = Kithe::ExiftoolCharacterization.new.call(file_path)

presenter = Kithe::ExiftoolCharacterization.presenter_for(hash)
presenter.bits_per_sample
presenter.make
presenter.model
presenter.exiftool_validation_warnings # Array of strings

Defined Under Namespace

Classes: Result

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#file_path ⇒ Object

Returns the value of attribute file_path.



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# File 'app/characterization/kithe/exiftool_characterization.rb', line 40

def file_path
  @file_path
end

Class Method Details

.presenter_for(hash) ⇒ Object

Returns a nice presenter object with methods that get out metadata we are interested in – in the future, might return differnet classes for specific data, looking at ‘Exiftool:Version` or `Kithe:CliArgs` keys to switch.

Parameters:

  • hash (Hash) —

    a hash returned by ExiftoolCharacterization.call

Returns:

  • a presenter



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# File 'app/characterization/kithe/exiftool_characterization.rb', line 49

def self.presenter_for(hash)
  Kithe::ExiftoolCharacterization::Result.new(hash)
end

Instance Method Details

#call(file_path) ⇒ Object

Parameters:

  • file_path (String) —

    path to a local file



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# File 'app/characterization/kithe/exiftool_characterization.rb', line 55

def call(file_path)
  cmd = TTY::Command.new(printer: :null)

  exiftool_args = [
    "-All",       # all tags
    "--File:All",  # EXCEPT not "File" group tags,
    "-duplicates", # include duplicate values
    "-validate",   # include some validation errors
    "-json",       # json output

    # with exif group names as key prefixes eg "ICC_Profile:ProfileDescription"
    # But also with weird `:Copy1`, `:Copy2` appended for multiples, which we need
    # for `ExifTool:Warning` from `-validate`, to get all of them, that's what the :4 does.
    #
    # https://exiftool.org/forum/index.php?topic=15194.0
    "-G0:4"
  ]

  # exiftool may return a non-zero exit for a corrupt file -- we don't want to raise,
  # it's still usually returning a nice json hash with error message, just store that
  # in the exiftool_result area anyway!
  result = cmd.run!(
    exiftool_command,
    *exiftool_args,
    file_path.to_s)


  if result.out.blank? && result.failed?
    raise ArgumentError.new("#{self.class}: #{result.err}")
  end

  # Returns an array of hashes
  # decimal_class: String needed so exiftool version number like `12.60` doesn't
  # wind up truncated to 12.6 as a ruby float!
  result_hash = JSON.parse(result.out, decimal_class: String).first

  # Let's add our invocation options, as a record
  result_hash["Kithe:CliArgs"] = exiftool_args

  result_hash
end