Fix DMG mounting.

Library/Homebrew/cask/lib/hbc/container/dmg.rb

@@ -13,34 +13,38 @@ module Hbc
                               print_stderr: false).stdout.empty?
       end
 
-      attr_reader :mounts
-      def initialize(*args)
-        super(*args)
-        @mounts = []
-      end
-
       def extract
-        mount!
-        assert_mounts_found
-        extract_mounts
+        mount do |mounts|
+          begin
+            raise CaskError, "No mounts found in '#{@path}'; perhaps it is a bad DMG?" if mounts.empty?
+            mounts.each(&method(:extract_mount))
           ensure
-        eject!
+            mounts.each(&method(:eject))
+          end
+        end
       end
 
-      def mount!
-        plist = @command.run!("/usr/bin/hdiutil",
+      def mount
         # realpath is a failsafe against unusual filenames
-                              args:  %w[mount -plist -nobrowse -readonly -noidme -mountrandom /tmp] + [Pathname.new(@path).realpath],
-                              input: "y\n")
-                        .plist
-        @mounts = mounts_from_plist(plist)
+        path = Pathname.new(@path).realpath
+
+        Dir.mktmpdir do |unpack_dir|
+          cdr_path = Pathname.new(unpack_dir).join("#{path.basename(".dmg")}.cdr")
+
+          @command.run!("/usr/bin/hdiutil", args: ["convert", "-quiet", "-format", "UDTO", "-o", cdr_path, path])
+
+          plist = @command.run!("/usr/bin/hdiutil",
+                                args:  ["attach", "-plist", "-nobrowse", "-readonly", "-noidme", "-mountrandom", unpack_dir, cdr_path],
+                                input: "qy\n").plist
+
+          yield mounts_from_plist(plist)
+        end
       end
 
-      def eject!
-        @mounts.each do |mount|
+      def eject(mount)
         # realpath is a failsafe against unusual filenames
         mountpath = Pathname.new(mount).realpath
-          next unless mountpath.exist?
+        return unless mountpath.exist?
 
         begin
           tries ||= 3
@@ -60,14 +64,9 @@ module Hbc
           retry
         end
       end
-      end
 
       private
 
-      def extract_mounts
-        @mounts.each(&method(:extract_mount))
-      end
-
       def extract_mount(mount)
         Tempfile.open(["", ".bom"]) do |bomfile|
           bomfile.close
@@ -124,10 +123,6 @@ module Hbc
         return [] unless plist.respond_to?(:fetch)
         plist.fetch("system-entities", []).map { |e| e["mount-point"] }.compact
       end
-
-      def assert_mounts_found
-        raise CaskError, "No mounts found in '#{@path}'; perhaps it is a bad DMG?" if @mounts.empty?
-      end
     end
   end
 end

Library/Homebrew/test/cask/container/dmg_spec.rb

@@ -9,11 +9,12 @@ describe Hbc::Container::Dmg, :cask do
         Hbc::SystemCommand,
       )
 
+      dmg.mount do |mounts|
         begin
-        dmg.mount!
-        expect(dmg.mounts).not_to include nil
+          expect(mounts).not_to include nil
         ensure
-        dmg.eject!
+          mounts.each(&dmg.public_method(:eject))
+        end
       end
     end
   end