Class: Fontisan::Parsers::DfontParser

Inherits:
Object
  • Object
show all
Defined in:
lib/fontisan/parsers/dfont_parser.rb

Overview

Parser for Apple dfont (Data Fork Font) resource fork format.

dfont files store resource fork data in the data fork, containing TrueType or OpenType SFNT data embedded in a resource fork structure.

Examples:

Extract SFNT from dfont

File.open("font.dfont", "rb") do |io|
  sfnt_data = DfontParser.extract_sfnt(io)
  # sfnt_data is raw SFNT binary
end

Defined Under Namespace

Classes: ResourceHeader, ResourceReference, ResourceType

Class Method Summary collapse

Class Method Details

.dfont?(io) ⇒ Boolean

Check if file is valid dfont resource fork

Parameters:

  • io (IO) —

    Open file handle

Returns:

  • (Boolean) 


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# File 'lib/fontisan/parsers/dfont_parser.rb', line 81

def self.dfont?(io)
  io.rewind
  header_bytes = io.read(16)
  io.rewind

  return false if header_bytes.nil? || header_bytes.length < 16

  # Basic sanity check on resource fork structure
  data_offset = header_bytes[0..3].unpack1("N")
  map_offset = header_bytes[4..7].unpack1("N")

  data_offset.positive? && map_offset > data_offset
end

.extract_resource_data(io, header, resource_info) ⇒ String

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Extract resource data at specific offset

Parameters:

  • io (IO) —

    Open file handle

  • header (ResourceHeader) —

    Parsed header

  • resource_info (Hash) —

    Resource info with :offset

Returns:

  • (String) —

    Raw SFNT binary data



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# File 'lib/fontisan/parsers/dfont_parser.rb', line 173

def self.extract_resource_data(io, header, resource_info)
  # Calculate absolute offset to resource data
  # The offset in the reference is relative to the start of the resource data section
  data_offset = header.resource_data_offset + resource_info[:offset]

  io.seek(data_offset)

  # Read data length (first 4 bytes of resource data)
  data_length = io.read(4).unpack1("N")

  # Read the actual data
  io.read(data_length)
end

.extract_sfnt(io, index: 0) ⇒ String

Extract SFNT data from dfont file

Parameters:

  • io (IO) —

    Open file handle

  • index (Integer) (defaults to: 0) —

    Font index for multi-font suitcases (default: 0)

Returns:

  • (String) —

    Raw SFNT binary data

Raises:



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# File 'lib/fontisan/parsers/dfont_parser.rb', line 51

def self.extract_sfnt(io, index: 0)
  header = parse_header(io)
  sfnt_resources = find_sfnt_resources(io, header)

  if sfnt_resources.empty?
    raise InvalidFontError, "No sfnt resources found in dfont file"
  end

  if index >= sfnt_resources.length
    raise InvalidFontError,
          "Font index #{index} out of range (dfont has #{sfnt_resources.length} fonts)"
  end

  extract_resource_data(io, header, sfnt_resources[index])
end

.find_sfnt_resources(io, header) ⇒ Array<Hash>

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Find all sfnt resources in resource map

Parameters:

  • io (IO) —

    Open file handle

  • header (ResourceHeader) —

    Parsed header

Returns:

  • (Array<Hash>) —

    Array of resource info hashes with :id and :offset



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# File 'lib/fontisan/parsers/dfont_parser.rb', line 114

def self.find_sfnt_resources(io, header)
  # Seek to resource map
  io.seek(header.resource_map_offset)

  # Skip resource map header (22 bytes reserved + 4 bytes attributes + 2 bytes type list offset + 2 bytes name list offset)
  # The actual layout is:
  # - Bytes 0-15: Copy of resource header (16 bytes)
  # - Bytes 16-19: Reserved for handle to next resource map (4 bytes)
  # - Bytes 20-21: Reserved for file reference number (2 bytes)
  # - Bytes 22-23: Resource file attributes (2 bytes)
  # - Bytes 24-25: Offset to type list (2 bytes)
  # - Bytes 26-27: Offset to name list (2 bytes)
  io.seek(header.resource_map_offset + 24)

  # Read type list offset (relative to start of resource map)
  type_list_offset = io.read(2).unpack1("n")

  # Seek to type list
  io.seek(header.resource_map_offset + type_list_offset)

  # Read number of types minus 1
  type_count_minus_1 = io.read(2).unpack1("n")
  type_count = type_count_minus_1 + 1

  # Find 'sfnt' type in type list
  sfnt_type = nil
  type_count.times do
    type_entry = ResourceType.read(io)

    if type_entry.type_code == "sfnt"
      sfnt_type = type_entry
      break
    end
  end

  return [] unless sfnt_type

  # Read reference list for sfnt resources
  reference_list_offset = header.resource_map_offset + type_list_offset + sfnt_type.reference_list_offset
  io.seek(reference_list_offset)

  resource_count = sfnt_type.resource_count_minus_1 + 1
  resources = []

  resource_count.times do
    ref = ResourceReference.read(io)
    resources << { id: ref.resource_id, offset: ref.data_offset }
  end

  resources
end

.parse_header(io) ⇒ ResourceHeader

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Parse resource fork header

Parameters:

  • io (IO) —

    Open file handle

Returns:

Raises:



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# File 'lib/fontisan/parsers/dfont_parser.rb', line 101

def self.parse_header(io)
  io.rewind
  ResourceHeader.read(io)
rescue BinData::ValidityError => e
  raise InvalidFontError, "Invalid dfont resource header: #{e.message}"
end

.sfnt_count(io) ⇒ Integer

Count number of sfnt resources (fonts) in dfont

Parameters:

  • io (IO) —

    Open file handle

Returns:

  • (Integer) —

    Number of fonts



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# File 'lib/fontisan/parsers/dfont_parser.rb', line 71

def self.sfnt_count(io)
  header = parse_header(io)
  sfnt_resources = find_sfnt_resources(io, header)
  sfnt_resources.length
end