Merge bitcoin#16562: Refactor message transport packaging

16d6113 Refactor message transport packaging (Jonas Schnelli)

Pull request description:

  This PR factors out transport packaging logic from `CConnman::PushMessage()`.
  It's similar to bitcoin#16202 (where we refactor deserialization).

  This allows implementing a new message transport protocol like BIP324.

ACKs for top commit:
  dongcarl:
    ACK 16d6113 FWIW
  ariard:
    Code review ACK 16d6113
  elichai:
    semiACK 16d6113 ran functional+unit tests.
  MarcoFalke:
    ACK 16d6113 🙎

Tree-SHA512: 8c2f8ab9f52e9b94327973ae15019a08109d5d9f9247492703a842827c5b5d634fc0411759e0bb316d824c586614b0220c2006410851933613bc143e58f7e6c1

src/net.cpp

@@ -720,6 +720,19 @@ CNetMessage V1TransportDeserializer::GetMessage(const CMessageHeader::MessageSta
     return msg;
 }
 
+void V1TransportSerializer::prepareForTransport(CSerializedNetMsg& msg, std::vector<unsigned char>& header) {
+    // create dbl-sha256 checksum
+    uint256 hash = Hash(msg.data.begin(), msg.data.end());
+
+    // create header
+    CMessageHeader hdr(Params().MessageStart(), msg.command.c_str(), msg.data.size());
+    memcpy(hdr.pchChecksum, hash.begin(), CMessageHeader::CHECKSUM_SIZE);
+
+    // serialize header
+    header.reserve(CMessageHeader::HEADER_SIZE);
+    CVectorWriter{SER_NETWORK, INIT_PROTO_VERSION, header, 0, hdr};
+}
+
 size_t CConnman::SocketSendData(CNode *pnode) const EXCLUSIVE_LOCKS_REQUIRED(pnode->cs_vSend)
 {
     auto it = pnode->vSendMsg.begin();
@@ -2814,6 +2827,7 @@ CNode::CNode(NodeId idIn, ServiceFlags nLocalServicesIn, int nMyStartingHeightIn
     }
 
     m_deserializer = MakeUnique<V1TransportDeserializer>(V1TransportDeserializer(Params().MessageStart(), SER_NETWORK, INIT_PROTO_VERSION));
+    m_serializer = MakeUnique<V1TransportSerializer>(V1TransportSerializer());
 }
 
 CNode::~CNode()
@@ -2829,16 +2843,12 @@ bool CConnman::NodeFullyConnected(const CNode* pnode)
 void CConnman::PushMessage(CNode* pnode, CSerializedNetMsg&& msg)
 {
     size_t nMessageSize = msg.data.size();
-    size_t nTotalSize = nMessageSize + CMessageHeader::HEADER_SIZE;
     LogPrint(BCLog::NET, "sending %s (%d bytes) peer=%d\n",  SanitizeString(msg.command), nMessageSize, pnode->GetId());
 
+    // make sure we use the appropriate network transport format
     std::vector<unsigned char> serializedHeader;
-    serializedHeader.reserve(CMessageHeader::HEADER_SIZE);
-    uint256 hash = Hash(msg.data.data(), msg.data.data() + nMessageSize);
-    CMessageHeader hdr(Params().MessageStart(), msg.command.c_str(), nMessageSize);
-    memcpy(hdr.pchChecksum, hash.begin(), CMessageHeader::CHECKSUM_SIZE);
-
-    CVectorWriter{SER_NETWORK, INIT_PROTO_VERSION, serializedHeader, 0, hdr};
+    pnode->m_serializer->prepareForTransport(msg, serializedHeader);
+    size_t nTotalSize = nMessageSize + serializedHeader.size();
 
     size_t nBytesSent = 0;
     {

src/net.h

@@ -787,12 +787,27 @@ class V1TransportDeserializer final : public TransportDeserializer
     CNetMessage GetMessage(const CMessageHeader::MessageStartChars& message_start, int64_t time) override;
 };
 
+/** The TransportSerializer prepares messages for the network transport
+ */
+class TransportSerializer {
+public:
+    // prepare message for transport (header construction, error-correction computation, payload encryption, etc.)
+    virtual void prepareForTransport(CSerializedNetMsg& msg, std::vector<unsigned char>& header) = 0;
+    virtual ~TransportSerializer() {}
+};
+
+class V1TransportSerializer  : public TransportSerializer {
+public:
+    void prepareForTransport(CSerializedNetMsg& msg, std::vector<unsigned char>& header) override;
+};
+
 /** Information about a peer */
 class CNode
 {
     friend class CConnman;
 public:
     std::unique_ptr<TransportDeserializer> m_deserializer;
+    std::unique_ptr<TransportSerializer> m_serializer;
 
     // socket
     std::atomic<ServiceFlags> nServices{NODE_NONE};