Module: OllamaChat::Utils::PNGMetadataExtractor

Extended by:
UTF8Converter
Includes:
UTF8Converter
Defined in:
lib/ollama_chat/utils/png_metadata_extractor.rb

Overview

Extracts embedded metadata from PNG image files, such as character profiles, ComfyUI workflows, and prompts stored in 'tEXt' chunks.

Class Method Summary collapse

Methods included from UTF8Converter

convert_to_utf8

Class Method Details

.decode_character(text) ⇒ String?

Decodes a Base64 encoded character profile and validates it as JSON.

Parameters:

  • text (String) —

    The raw 'chara' metadata value.

Returns:

  • (String, nil) —

    The decoded JSON string if valid, otherwise nil.



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# File 'lib/ollama_chat/utils/png_metadata_extractor.rb', line 64

def decode_character(text)
  return nil unless text

  begin
    decoded = Base64.decode64(text)
    decoded = convert_to_utf8(decoded)
    JSON.parse(decoded) # Validation check
    decoded
  rescue JSON::ParserError, ArgumentError
    nil
  end
end

.extract_all(io) ⇒ Hash?

Extracts all 'tEXt' chunk metadata from the provided IO object.

Parameters:

  • io (IO) —

    An IO-like object providing access to the PNG binary data.

Returns:

  • (Hash, nil) —

    A hash of { keyword => text } if a valid PNG is found, otherwise nil.



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# File 'lib/ollama_chat/utils/png_metadata_extractor.rb', line 16

def extract_all(io)
  data = if io.respond_to?(:binmode)
           io.binmode
           io.read
         elsif io.respond_to?(:binread)
           io.binread
         else
           return nil
         end

  # PNG Signature is 8 bytes: \x89PNG\r\n\x1a\n
  pos = 8
  metadata = {}

  while pos < data.length
    # 1. Read Length (4 bytes, Big Endian)
    length = data[pos, 4]&.unpack1('L>')
    break unless length

    pos += 4

    # 2. Read Chunk Type (4 bytes)
    type = data[pos, 4]
    pos += 4

    # 3. Read Chunk Data
    chunk_data = data[pos, length]
    pos += length

    # 4. Skip CRC (4 bytes)
    pos += 4

    if type == 'tEXt'
      # tEXt chunks are formatted as: Keyword + NULL Byte + Text
      keyword, text = chunk_data.split("\x00", 2)
      metadata[keyword] = text if keyword
    end
  end

  metadata.empty? ? nil : metadata
ensure
  io.ask_and_send(:rewind)
end

.extract_character(io) ⇒ String?

Convenience method to extract a character profile from a PNG. Maintained for backward compatibility with existing call sites.

Parameters:

  • io (IO) —

    An IO-like object providing access to the PNG binary data.

Returns:

  • (String, nil) —

    The decoded JSON string if found and valid, otherwise nil.



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# File 'lib/ollama_chat/utils/png_metadata_extractor.rb', line 107

def extract_character(io)
  metadata = extract_all(io) or return
  decode_character(metadata['chara'])
end

.parse_a1111_parameters(text) ⇒ Hash?

Parses Automatic1111 / Stable Diffusion WebUI parameters metadata.

Parameters:

  • text (String) —

    The raw 'parameters' metadata value.

Returns:

  • (Hash, nil) —

    A hash containing :prompt, :negative_prompt, and :settings.



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# File 'lib/ollama_chat/utils/png_metadata_extractor.rb', line 81

def parse_a1111_parameters(text)
  text or return

  lines = text.split("\n")
  result = { prompt: lines[0], negative_prompt: nil, settings: {} }

  lines[1..].each do |line|
    if line.start_with?('Negative prompt: ')
      result[:negative_prompt] = line.sub('Negative prompt: ', '')
    else
      # Parse comma-separated key-value pairs (e.g., "Steps: 20, Sampler: Euler")
      line.split(', ').each do |pair|
        key, value = pair.split(': ', 2)
        result[:settings][key.downcase.to_sym] = value if key && value
      end
    end
  end

  result
end