refactor stream to remove a couple of race conditions

fixes #42

stream_frame_sorter_test.go

@@ -0,0 +1,49 @@
+package quic
+
+import (
+	"github.com/lucas-clemente/quic-go/frames"
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("StreamFrame sorter", func() {
+	var (
+		s streamFrameSorter
+	)
+
+	BeforeEach(func() {
+		s = streamFrameSorter{}
+	})
+
+	It("head returns nil when empty", func() {
+		Expect(s.Head()).To(BeNil())
+	})
+
+	It("inserts and pops a single frame", func() {
+		f := &frames.StreamFrame{}
+		s.Push(f)
+		Expect(s.Head()).To(Equal(f))
+		Expect(s.Pop()).To(Equal(f))
+		Expect(s.Head()).To(BeNil())
+	})
+
+	It("inserts two frames in order", func() {
+		f1 := &frames.StreamFrame{Offset: 1}
+		f2 := &frames.StreamFrame{Offset: 2}
+		s.Push(f1)
+		s.Push(f2)
+		Expect(s.Pop()).To(Equal(f1))
+		Expect(s.Pop()).To(Equal(f2))
+		Expect(s.Head()).To(BeNil())
+	})
+
+	It("inserts two frames out of order", func() {
+		f1 := &frames.StreamFrame{Offset: 1}
+		f2 := &frames.StreamFrame{Offset: 2}
+		s.Push(f2)
+		s.Push(f1)
+		Expect(s.Pop()).To(Equal(f1))
+		Expect(s.Pop()).To(Equal(f2))
+		Expect(s.Head()).To(BeNil())
+	})
+})