make a pdf doc of an image

cairo-test.rb

require 'base64'
require 'cairo'
require 'stringio'

png_b64 = <<END
iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAC7mlDQ1BJQ0Mg
UHJvZmlsZQAAeAGFVM9rE0EU/jZuqdAiCFprDrJ4kCJJWatoRdQ2/RFiawzb
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k/qv8RGw/bBS+fmsUtl+ThrWgZf6b8C8/UXAeIuJAAAACXBIWXMAAAsTAAAL
EwEAmpwYAAAADUlEQVQIHWO4ffv2fwAItwORKePmcwAAAABJRU5ErkJggg==
END

pdf_surface = Cairo::PDFSurface.new('a.pdf', 100, 100)
pdf_context = Cairo::Context.new(pdf_surface)
image = Cairo::ImageSurface.from_png(StringIO.new(Base64.decode64(png_b64)))

pdf_surface.set_size(image.width, image.height)

pdf_context.set_source(image)
pdf_context.paint
pdf_context.show_page

pdf_surface.finish