From 4806807caaa9da92485de856dd8e03f5e3e33a7e Mon Sep 17 00:00:00 2001
From: Lucas Clemente <lucas@clemente.io>
Date: Sun, 24 Apr 2016 12:24:13 +0200
Subject: [PATCH] initial hybrid slow start implementation

---
 congestion/cubic_test.go             |  2 +-
 congestion/hybrid_slow_start.go      | 25 +++++++++++++++
 congestion/hybrid_slow_start_test.go | 47 ++++++++++++++++++++++++++++
 3 files changed, 73 insertions(+), 1 deletion(-)
 create mode 100644 congestion/hybrid_slow_start.go
 create mode 100644 congestion/hybrid_slow_start_test.go

diff --git a/congestion/cubic_test.go b/congestion/cubic_test.go
index 4533f4434..0f4531252 100644
--- a/congestion/cubic_test.go
+++ b/congestion/cubic_test.go
@@ -70,7 +70,7 @@ var _ = Describe("Cubic", func() {
 		Expect(current_cwnd).To(Equal(expected_cwnd))
 	})
 
-	// TODO: Test copied form Chromium has no assertions
+	// TODO: Test copied from Chromium has no assertions
 	It("has increasing cwnd stats during convex region", func() {
 		rtt_min := 100 * time.Millisecond
 		current_cwnd := uint64(10)
diff --git a/congestion/hybrid_slow_start.go b/congestion/hybrid_slow_start.go
new file mode 100644
index 000000000..0d31b8fb8
--- /dev/null
+++ b/congestion/hybrid_slow_start.go
@@ -0,0 +1,25 @@
+package congestion
+
+import "time"
+
+// HybridSlowStart implements the TCP hybrid slow start algorithm
+type HybridSlowStart struct {
+	endPacketNumber      uint64
+	lastSentPacketNumber uint64
+	started              bool
+	currentMinRTT        time.Duration
+	rttSampleCount       uint32
+}
+
+// StartReceiveRound is called for the start of each receive round (burst) in the slow start phase.
+func (s *HybridSlowStart) StartReceiveRound(last_sent uint64) {
+	s.endPacketNumber = last_sent
+	s.currentMinRTT = 0
+	s.rttSampleCount = 0
+	s.started = true
+}
+
+// IsEndOfRound returns true if this ack is the last packet number of our current slow start round.
+func (s *HybridSlowStart) IsEndOfRound(ack uint64) bool {
+	return s.endPacketNumber < ack
+}
diff --git a/congestion/hybrid_slow_start_test.go b/congestion/hybrid_slow_start_test.go
new file mode 100644
index 000000000..f45686832
--- /dev/null
+++ b/congestion/hybrid_slow_start_test.go
@@ -0,0 +1,47 @@
+package congestion_test
+
+import (
+	"github.com/lucas-clemente/quic-go/congestion"
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("Hybrid slow start", func() {
+	var (
+		slowStart congestion.HybridSlowStart
+	)
+
+	BeforeEach(func() {
+		slowStart = congestion.HybridSlowStart{}
+	})
+
+	It("works in a simple case", func() {
+		packet_number := uint64(1)
+		end_packet_number := uint64(3)
+		slowStart.StartReceiveRound(end_packet_number)
+
+		packet_number++
+		Expect(slowStart.IsEndOfRound(packet_number)).To(BeFalse())
+
+		// Test duplicates.
+		Expect(slowStart.IsEndOfRound(packet_number)).To(BeFalse())
+
+		packet_number++
+		Expect(slowStart.IsEndOfRound(packet_number)).To(BeFalse())
+		packet_number++
+		Expect(slowStart.IsEndOfRound(packet_number)).To(BeTrue())
+
+		// Test without a new registered end_packet_number;
+		packet_number++
+		Expect(slowStart.IsEndOfRound(packet_number)).To(BeTrue())
+
+		end_packet_number = 20
+		slowStart.StartReceiveRound(end_packet_number)
+		for packet_number < end_packet_number {
+			packet_number++
+			Expect(slowStart.IsEndOfRound(packet_number)).To(BeFalse())
+		}
+		packet_number++
+		Expect(slowStart.IsEndOfRound(packet_number)).To(BeTrue())
+	})
+})