From d2899a4378a4b2b68c2a221239f822146f4f51b5 Mon Sep 17 00:00:00 2001
From: Kleissner <peter@kleissner.investments>
Date: Wed, 20 Oct 2021 10:20:56 +0200
Subject: [PATCH] Initial Transfer message encoding. Embedded UDT
 implementation to follow. Documentation of file transfer to follow in
 upcoming Whitepaper update.

---
 protocol/Message Encoding Announcement.go |   5 +-
 protocol/Message Encoding Transfer.go     | 110 ++++++++++++++++++++++
 2 files changed, 113 insertions(+), 2 deletions(-)
 create mode 100644 protocol/Message Encoding Transfer.go

diff --git a/protocol/Message Encoding Announcement.go b/protocol/Message Encoding Announcement.go
index 5d87054..8b39009 100644
--- a/protocol/Message Encoding Announcement.go	
+++ b/protocol/Message Encoding Announcement.go	
@@ -115,12 +115,13 @@ func DecodeAnnouncement(msg *MessageRaw) (result *MessageAnnouncement, err error
 
 	// INFO_STORE
 	if result.Actions&(1<<ActionInfoStore) > 0 {
-		files, read, valid := decodeInfoStore(data)
+		files, _, valid := decodeInfoStore(data)
 		if !valid {
 			return nil, errors.New("announcement: INFO_STORE invalid data")
 		}
 
-		data = data[read:]
+		// commented out because never used
+		//data = data[read:]
 		result.InfoStoreFiles = files
 	}
 
diff --git a/protocol/Message Encoding Transfer.go b/protocol/Message Encoding Transfer.go
new file mode 100644
index 0000000..ab5cff8
--- /dev/null
+++ b/protocol/Message Encoding Transfer.go	
@@ -0,0 +1,110 @@
+/*
+File Name:  Message Encoding Transfer.go
+Copyright:  2021 Peernet s.r.o.
+Author:     Peter Kleissner
+
+Transfer message encoding:
+Offset  Size   Info
+0       1      Control
+1       1      Transfer Protocol
+2       32     File Hash
+34      ?      Embedded protocol data
+
+*/
+
+package protocol
+
+import (
+	"encoding/binary"
+	"errors"
+
+	"github.com/btcsuite/btcd/btcec"
+)
+
+// MessageTransfer is the decoded transfer message.
+// It is sent to initiate a file transfer, and to send data as part of a file transfer. The actual file data is encapsulated via UDT.
+type MessageTransfer struct {
+	*MessageRaw              // Underlying raw message.
+	Control           uint8  // Control. See TransferControlX.
+	TransferProtocol  uint8  // Embedded transfer protocol: 0 = UDT
+	Hash              []byte // Hash of the file to transfer.
+	Offset            uint64 // Offset to start reading at. Only TransferControlRequestStart.
+	Limit             uint64 // Limit (count of bytes) to read starting at the offset. Only TransferControlRequestStart.
+	EmbeddedPacketRaw []byte // Embedded packet. Only TransferControlActive.
+}
+
+const (
+	TransferControlRequestStart = 0 // Request start transfer of file. Data at byte 34 is offset and limit to read, each 8 bytes.
+	TransferControlNotAvailable = 1 // Requested file not available
+	TransferControlActive       = 2 // Active file transfer
+	TransferControlTerminate    = 3 // Terminate
+)
+
+const transferPayloadHeaderSize = 34
+
+// DecodeTransfer decodes a transfer message
+func DecodeTransfer(msg *MessageRaw) (result *MessageTransfer, err error) {
+	if len(msg.Payload) < transferPayloadHeaderSize {
+		return nil, errors.New("transfer: invalid minimum length")
+	}
+
+	result = &MessageTransfer{
+		MessageRaw: msg,
+		Hash:       make([]byte, HashSize),
+	}
+
+	result.Control = msg.Payload[0]
+	result.TransferProtocol = msg.Payload[1]
+	copy(result.Hash, msg.Payload[2:2+HashSize])
+
+	switch result.Control {
+	case TransferControlRequestStart:
+		// Offset and Limit must be provided after the header.
+		if len(msg.Payload) < transferPayloadHeaderSize+16 {
+			return nil, errors.New("transfer: invalid minimum length")
+		}
+
+		result.Offset = binary.LittleEndian.Uint64(msg.Payload[34 : 34+8])
+		result.Limit = binary.LittleEndian.Uint64(msg.Payload[42 : 42+8])
+
+	case TransferControlActive:
+		result.EmbeddedPacketRaw = msg.Payload[34:]
+
+	}
+
+	return nil, nil
+}
+
+// TransferMaxEmbedSize is the maximum size of embedded data inside the Transfer message.
+const TransferMaxEmbedSize = udpMaxPacketSize - PacketLengthMin - transferPayloadHeaderSize
+
+// EncodeTransfer encodes a transfer message. The embedded packet size must be smaller than TransferMaxEmbedSize.
+func EncodeTransfer(senderPrivateKey *btcec.PrivateKey, embeddedPacketRaw []byte, control, transferProtocol uint8, hash []byte, offset, limit uint64) (packetRaw []byte, err error) {
+	if control == TransferControlRequestStart && len(embeddedPacketRaw) != 0 {
+		return nil, errors.New("transfer encode: payload not allowed in start")
+	} else if isPacketSizeExceed(TransferMaxEmbedSize, len(embeddedPacketRaw)) {
+		return nil, errors.New("transfer encode: embedded packet too big")
+	}
+
+	packetSize := transferPayloadHeaderSize
+	if control == TransferControlRequestStart {
+		packetSize += 16
+	} else if control == TransferControlActive {
+		packetSize += len(embeddedPacketRaw)
+	}
+
+	raw := make([]byte, packetSize)
+
+	raw[0] = control
+	raw[1] = transferProtocol
+	copy(raw[2:2+HashSize], hash)
+
+	if control == TransferControlRequestStart {
+		binary.LittleEndian.PutUint64(raw[34:34+8], offset)
+		binary.LittleEndian.PutUint64(raw[42:42+8], limit)
+	} else if control == TransferControlActive {
+		copy(raw[34:34+len(embeddedPacketRaw)], embeddedPacketRaw)
+	}
+
+	return raw, nil
+}