Image#copy_memory returns an image wrapping NULL when libvips fails, and the next call segfaults #442

Summary

When vips_image_copy_memory() fails (for example because the source image cannot be decoded), it returns NULL. Vips::Image#copy_memory wraps that pointer in a Vips::Image without checking it, so instead of raising Vips::Error, the call returns an object whose pointer is NULL. The next operation on that object dereferences it and crashes the whole Ruby process with a segmentation fault, which cannot be rescued.

Versions

• ruby-vips 2.3.0 (also master as of 2026-10-15)
• libvips 8.16.1
• Ruby 4.0.7 (aarch64-linux, Debian, in Docker)
• also returns NULL with libvips 8.18.7 / Ruby 4.0.6 on macOS arm64

Reproduction

require "vips"

# A valid JPEG cut in half: the header is intact, so the load itself succeeds
# lazily, and decoding fails only when the pixels are computed.
jpeg = Vips::Image.black(256, 256).add(128).cast(:uchar).jpegsave_buffer
broken = jpeg.byteslice(0, jpeg.bytesize / 2)
image = Vips::Image.new_from_buffer(broken, "", fail_on: :error)

copy = image.copy_memory            # libvips fails and returns NULL
p copy.class                        # => Vips::Image
p copy.ptr.null?                    # => true
copy.width                          # segfault

Output:

(process:1): VIPS-WARNING **: error in tile 0 x 40
Vips::Image
true
/usr/local/bundle/ruby/4.0.0/gems/ruby-vips-2.3.0/lib/vips/image.rb:891: [BUG] Segmentation fault at 0x0000000000000050
ruby 4.0.7 (2026-09-15 revision 229531a6cf) +YJIT +PRISM [aarch64-linux]

-- Ruby level backtrace information ----------------------------------------
repro.rb:12:in '<main>'
.../ruby-vips-2.3.0/lib/vips/image.rb:891:in 'width'
.../ruby-vips-2.3.0/lib/vips/image.rb:891:in 'vips_image_get_width'

Expected behaviour

copy_memory raises Vips::Error with the libvips error message (here VipsJpeg: premature end of JPEG image), as other methods do when libvips fails.

Cause

lib/vips/image.rb:

def copy_memory
  new_image = Vips.vips_image_copy_memory self
  Vips::Image.new new_image
end

write_to_memory in the same file already checks for this case:

ptr = Vips.vips_image_write_to_memory self, len
raise Vips::Error if ptr.null?

Suggested fix

def copy_memory
  new_image = Vips.vips_image_copy_memory self
  raise Vips::Error if new_image.null?

  Vips::Image.new new_image
end

With that change, the reproduction above raises Vips::Error: VipsJpeg: premature end of JPEG image and the process keeps running.

Related

Same class of bug as #419 (fixed in #420), which added NULL checks to write_to_memory and others; copy_memory was missed.

Fix: #443