Reimplemented MIX file reader/writer

lib/ww_mix.rb

@@ -0,0 +1,280 @@
+require "digest"
+require "stringio"
+
+class W3DHub
+  # Reimplementating MIX1 reader/writer with years more
+  # experience working with these formats and having then
+  # advantage of being able to reference the renegade source
+  # code :)
+  class WWMix
+    MIX1_HEADER = 0x3158494D
+    MIX2_HEADER = 0x3258494D
+
+    MixHeader = Struct.new(
+      :mime_type, # int32
+      :file_data_offset, # int32
+      :file_names_offset, # int32
+      :_reserved # int32
+    )
+
+    EntryInfoHeader = Struct.new(
+      :crc32, # uint32
+      :content_offset, # uint32
+      :content_length # uint32
+    )
+
+    class Entry
+      attr_accessor :path, :name, :info, :blob, :is_blob
+
+      def initialize(name:, path:, info:, blob: nil)
+        @name = name
+        @path = path
+        @info = info
+        @blob = blob
+
+        @info.content_length = blob.size if blob?
+      end
+
+      def blob?
+        @blob
+      end
+
+      def calculate_crc32
+        Digest::CRC32.hexdigest(@name.upcase).upcase.to_i(16)
+      end
+
+      # Write entry's data to stream.
+      # Caller is responsible for ensuring stream is valid for writing
+      def copy_to(stream)
+        if blob?
+          return false if @blob.size.zero?
+
+          stream.write(blob)
+          return true
+        else
+          if read
+            stream.write(@blob)
+            @blob = nil
+            return true
+          end
+        end
+
+        false
+      end
+
+      def read
+        return false unless File.exist?(@path)
+        return false if File.directory?(@path)
+        return false if File.size(@path) < @info.content_offset + @info.content_length
+
+        @blob = File.binread(@path, @info.content_length, @info.content_offset)
+
+        true
+      end
+    end
+
+    attr_reader :path, :encrypted, :entries, :error_reason
+
+    def initialize(path:, encrypted: false)
+      @path = path
+      @encrypted = encrypted
+      @entries = []
+
+      @error_reason = ""
+    end
+
+    # Load entries from MIX file. Entry data is NOT loaded.
+    # @return true on success or false on failure. Check m_error_reason for why.
+    def load
+      unless File.exist?(@path)
+        @error_reason = format("Path does not exist: %s", @path)
+        return false
+      end
+
+      if File.directory?(@path)
+        @error_reason = format("Path is a directory: %s", @path)
+        return false
+      end
+
+      File.open(@path, "rb") do |f|
+        header = MixHeader.new(0, 0, 0, 0)
+        header.mime_type = read_i32(f)
+        header.file_data_offset = read_i32(f)
+        header.file_names_offset = read_i32(f)
+        header._reserved = read_i32(f)
+
+        unless header.mime_type == MIX1_HEADER || header.mime_type == MIX2_HEADER
+          @error_reason = format("Invalid mime type: %d", header.mime_type)
+          return false
+        end
+
+        @encrypted = header.mime_type == MIX2_HEADER
+
+        # Read entry info
+        f.pos = header.file_data_offset
+        file_count = read_i32(f)
+
+        file_count.times do |i|
+          entry_info = EntryInfoHeader.new(0, 0, 0)
+          entry_info.crc32 = read_u32(f)
+          entry_info.content_offset = read_u32(f)
+          entry_info.content_length = read_u32(f)
+
+          @entries << Entry.new(name: "", path: @path, info: entry_info)
+        end
+
+        # Read entry names
+        f.pos = header.file_names_offset
+        file_count = read_i32(f)
+
+        file_count.times do |i|
+          @entries[i].name = read_string(f)
+        end
+      end
+
+      true
+    end
+
+    def save
+      unless @entries.size.positive?
+        @error_reason = "No entries to write."
+        return false
+      end
+
+      if File.directory?(@path)
+        @error_reason = format("Path is a directory: %s", @path)
+        return false
+      end
+
+      File.open(@path, "wb") do |f|
+        header = MixHeader.new(encrypted? ? MIX2_HEADER : MIX1_HEADER, 0, 0, 0)
+
+        # write mime type
+        write_i32(f, header.mime_type)
+
+        f.pos = 16
+
+        # sort entries by crc32 of their name
+        sort_entries
+
+        # write file blobs
+        @entries.each do |entry|
+          # store current io position
+          pos = f.pos
+
+          # copy entry to stream
+          entry.copy_to(f)
+
+          # update entry with new offset
+          entry.info.content_offset = pos
+
+          # add alignment padding
+          padding = (-f.pos & 7)
+          padding.times do |i|
+            write_u8(f, 0)
+          end
+        end
+
+        # Save file data offset
+        header.file_data_offset = f.pos
+
+        # write number of entries
+        write_i32(f, @entries.size)
+
+        # write entries file data
+        @entries.each do |entry|
+          write_u32(f, entry.info.crc32)
+          write_u32(f, entry.info.content_offset)
+          write_u32(f, entry.info.content_length)
+        end
+
+        # save file names offset
+        header.file_names_offset = f.pos
+
+        # write number of entries
+        write_i32(f, @entries.size)
+
+        # write entry names
+        @entries.each do |entry|
+          write_string(f, entry.name)
+        end
+
+        # jump to io_position 4
+        f.pos = 4
+        # write rest of header
+
+        write_i32(f, header.file_data_offset)
+        write_i32(f, header.file_names_offset)
+        write_i32(f, header._reserved)
+      end
+
+      true
+    end
+
+    def valid?
+      # ALL entries MUST have unique case-insensitive names
+      @entries.each do |a|
+        @entries.each do |b|
+          next if a == b
+
+          return false if a.name.upcase == b.name.upcase
+        end
+      end
+
+      true
+    end
+
+    def encrypted?
+      @encrypted
+    end
+
+    def add_file(path:)
+      return false unless File.exist?(path)
+      return false if File.directory?(path)
+
+      info = EntryInfoHeader.new(0, 0, File.size(path))
+      @entries << Entry.new(name: File.basename(path), path: path, info: info)
+
+      true
+    end
+
+    def add_blob(path:, blob:)
+      info = EntryInfoHeader.new(0, 0, blob.size)
+      @entries << Entry.new(name: File.basename(path), path: path, info: info, blob: blob)
+      into.crc32 = @entries.last.calculate_crc32
+
+      true
+    end
+
+    def add_entry(entry:)
+      @entries << entry
+
+      true
+    end
+
+    def sort_entries
+      return false if @entries.any? { |e| e.info.crc32 == 0 }
+
+      @entries.sort! { |a, b| a.info.crc32 <=> b.info.crc32 }
+
+      true
+    end
+
+    def read_i32(f) = f.read(4).unpack1("l")
+    def read_u32(f) = f.read(4).unpack1("L")
+    def read_u8(f) = f.read(1).unpack1("c")
+    def read_string(f)
+      f.read(read_u8(f)).strip
+    end
+
+    def write_i32(f, value) = f.write([value].pack("l"))
+    def write_u32(f, value) = f.write([value].pack("L"))
+    def write_u8(f, value) = f.write([value].pack("c"))
+    def write_string(f, string)
+      length = string.size + 1 # include null byte
+      write_u8(f, length)
+      f.write(string)
+      write_u8(f, 0) # null byte
+    end
+  end
+end