From a5a7021fedbf52b36289e56105fdc01a3ecab8c1 Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Fri, 15 Apr 2016 16:00:15 +0700
Subject: [PATCH] basic ACK frame parsing

---
 ack_frame.go | 86 +++++++++++++++++++++++++++++++++++++++++++++++-----
 session.go   |  7 +++++
 2 files changed, 86 insertions(+), 7 deletions(-)

diff --git a/ack_frame.go b/ack_frame.go
index 4de785531..a77b84a6e 100644
--- a/ack_frame.go
+++ b/ack_frame.go
@@ -9,18 +9,90 @@ import (
 // An AckFrame in QUIC
 type AckFrame struct {
 	Entropy         byte
-	LargestObserved uint32 // TODO: change to uint64
+	LargestObserved uint64
+	DelayTime       uint16 // Todo: properly interpret this value as described in the specification
 }
 
-// WriteAckFrame writes an ack frame.
+// Write writes an ACK frame.
 func (f *AckFrame) Write(b *bytes.Buffer) error {
 	typeByte := uint8(0x48)
 	b.WriteByte(typeByte)
 	b.WriteByte(f.Entropy)
-	utils.WriteUint32(b, f.LargestObserved)
-	utils.WriteUint16(b, 1) // TODO: Ack delay time
-	b.WriteByte(0x01)       // Just one timestamp
-	b.WriteByte(0x00)       // Largest observed
-	utils.WriteUint32(b, 0) // First timestamp
+	utils.WriteUint32(b, uint32(f.LargestObserved)) // TODO: send the correct length
+	utils.WriteUint16(b, 1)                         // TODO: Ack delay time
+	b.WriteByte(0x01)                               // Just one timestamp
+	b.WriteByte(0x00)                               // Largest observed
+	utils.WriteUint32(b, 0)                         // First timestamp
 	return nil
 }
+
+// ParseAckFrame reads an ACK frame
+func ParseAckFrame(r *bytes.Reader, typeByte byte) (*AckFrame, error) {
+	frame := &AckFrame{}
+
+	if typeByte&0x20 == 0x20 {
+		panic("NACK ranges not yet implemented.")
+	}
+	if typeByte&0x10 == 0x10 {
+		panic("truncated ACKs not yet implemented.")
+	}
+
+	var largestObservedLen uint8 = 2 * ((typeByte & 0x0C) >> 2)
+	if largestObservedLen == 0 {
+		largestObservedLen = 1
+	}
+
+	var missingSequenceNumberDeltaLen uint8 = 2 * (typeByte & 0x03)
+	if missingSequenceNumberDeltaLen == 0 {
+		missingSequenceNumberDeltaLen = 1
+	}
+
+	var err error
+	frame.Entropy, err = r.ReadByte()
+	if err != nil {
+		return nil, err
+	}
+
+	frame.LargestObserved, err = utils.ReadUintN(r, largestObservedLen)
+	if err != nil {
+		return nil, err
+	}
+
+	frame.DelayTime, err = utils.ReadUint16(r)
+	if err != nil {
+		return nil, err
+	}
+
+	numTimestampByte, err := r.ReadByte()
+	if err != nil {
+		return nil, err
+	}
+	numTimestamp := uint8(numTimestampByte)
+
+	// Delta Largest observed
+	_, err = r.ReadByte()
+	if err != nil {
+		return nil, err
+	}
+
+	// First Timestamp
+	_, err = utils.ReadUint32(r)
+	if err != nil {
+		return nil, err
+	}
+
+	for i := 0; i < int(numTimestamp)-1; i++ {
+		// Delta Largest observed
+		_, err = r.ReadByte()
+		if err != nil {
+			return nil, err
+		}
+		// Time Since Previous Timestamp
+		_, err := utils.ReadUint16(r)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return frame, nil
+}
diff --git a/session.go b/session.go
index 7a146edc0..95323c7fd 100644
--- a/session.go
+++ b/session.go
@@ -88,6 +88,13 @@ func (s *Session) HandlePacket(addr *net.UDPAddr, publicHeaderBinary []byte, pub
 			}
 		} else if typeByte&0xC0 == 0x40 { // ACK
 			fmt.Println("Detected ACK")
+			frame, err := ParseAckFrame(r, typeByte)
+			if err != nil {
+				return err
+			}
+
+			fmt.Printf("%#v\n", frame)
+
 			continue // not yet implemented
 		} else if typeByte&0xE0 == 0x20 { // CONGESTION_FEEDBACK
 			fmt.Println("Detected CONGESTION_FEEDBACK")