Source.new_from_memory: keep a ref to the memory area

vips_source_new_from_memory() aliases the caller's buffer rather than
copying it -- vips_blob_new(NULL, data, length), NULL free_fn -- so
libvips reads it for as long as the source is alive. We kept no Ruby
reference to it, so nothing stopped the GC from freeing it first.

Mirrors Image.new_from_memory, which already does this.

Also answers and removes the FIXME: Image.new_from_buffer does not need
a ref. It goes through GValue#set for Vips::BLOB_TYPE, which g_mallocs
its own block, memcpys into it and hands libvips ownership via
vips_value_set_blob(..., GLib::G_FREE, ...).

Author: Jeremy Daer

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## master
 
+* `Source.new_from_memory` keeps a reference to the memory area, which libvips
+  aliases rather than copies
+
 ## Version 2.3.0 (2025-12-10)
 
 * move library_name out of the global namespace and into FFI [jcupitt]

lib/vips/source.rb

@@ -70,6 +70,9 @@ def self.new_from_file(filename)
     # Create a new source from an area of memory. Memory areas can be
     # strings, arrays and so forth -- anything that supports bytesize.
     #
+    # libvips does not copy the memory area, so the source keeps a reference
+    # to it and will hold it alive for as long as the source is alive.
+    #
     # Pass sources to {Image.new_from_source} to load images from
     # them.
     #
@@ -79,10 +82,14 @@ def self.new_from_memory(data)
       ptr = Vips.vips_source_new_from_memory data, data.bytesize
       raise Vips::Error if ptr.null?
 
-      # FIXME do we need to keep a ref to the underlying memory area? what
-      # about Image.new_from_buffer? Does that need a secret ref too?
+      source = Vips::Source.new ptr
 
-      Vips::Source.new ptr
+      # vips_source_new_from_memory() aliases the memory area rather than
+      # copying it, so we must keep a secret ref to stop it being freed while
+      # the source is alive. See {Image.new_from_memory}.
+      source.references << data
+
+      source
     end
   end
 end

spec/connection_spec.rb

@@ -26,6 +26,21 @@
     expect(source)
   end
 
+  it "can load an image from a memory source after the caller drops its ref" do
+    source = Vips::Source.new_from_memory File.binread(simg("wagon.jpg"))
+
+    # the secret ref inside source is now the only thing keeping the string
+    # alive ... GC to try to trigger a segv if new_from_memory didn't take one
+    GC.start
+
+    image = Vips::Image.new_from_source source, ""
+
+    expect(image.width).to eq(685)
+    expect(image.height).to eq(478)
+    expect(image.bands).to eq(3)
+    expect(image.avg).to be_within(0.001).of(109.789)
+  end
+
   it "sources have filenames and nicks" do
     source = Vips::Source.new_from_file simg("wagon.jpg")