use crystal for generating tempfile name

src/tempfile.cr

@@ -39,14 +39,14 @@ require "c/stdlib"
 # Tempfile.new("foo", ".png").path # => "/tmp/foo.ulBCPS.png"
 # ```
 class Tempfile < IO::FileDescriptor
+  OPEN_FLAGS = LibC::O_EXCL | LibC::O_RDWR | LibC::O_CREAT |
+               LibC::S_IRUSR | LibC::S_IWUSR
   # Creates a `Tempfile` with the given filename and extension.
   def initialize(name, extension = nil)
     tmpdir = self.class.dirname + File::SEPARATOR
-    @path = "#{tmpdir}#{name}.XXXXXX#{extension}"
-    fileno = LibC.mkstemp(@path)
-    if fileno == -1
-      raise Errno.new("mkstemp")
-    end
+    @path = build_path(name, extension)
+    fileno = LibC.open(@path, OPEN_FLAGS)
+
     super(fileno, blocking: true)
   end
 
@@ -96,4 +96,15 @@ class Tempfile < IO::FileDescriptor
   def unlink
     delete
   end
+
+  private def build_path(name, extension = nil)
+    result = String.build do |io|
+      io << name
+      io << Time.now.to_s("%Y%m%d")
+      io << "#{Process.pid}-#{rand(0x100000000).to_s(36)}"
+      io << extension
+    end
+
+    result.check_no_null_byte
+  end
 end