Merge branch 'feature/vtop-fix' into feature/tcp

Add full TCP/IP stack implementation at L4 alongside UDP and ICMP.

Core Protocol Engine:
- TCP types in nettypes.pas (header, TCB, state enum, error codes,
  callbacks, OOO entry, socket structures)
- 3-way handshake (active & passive OPEN)
- Reliable data transfer with ACK and sequence number tracking
- Graceful close (FIN_WAIT, CLOSE_WAIT, LAST_ACK, TIME_WAIT)
- RST send/receive handling
- Retransmission with exponential backoff (max 5 attempts)
- Pseudo-header based checksum (RFC 793)

Server Support:
- LISTEN → SYN_RECEIVED → ESTABLISHED passive open path
- Listen backlog enforcement (configurable per-socket)
- accept() to retrieve established child connections

Robustness & Hardening:
- Delayed ACK timer (~200ms)
- Nagle's algorithm (buffer small sends while unACKed data pending)
- Jacobson/Karels RTT estimation with adaptive RTO
- Congestion control (slow start / congestion avoidance)
- Zero-window probing with exponential backoff
- MSS option negotiation in SYN/SYN-ACK (Kind=2, Len=4)
- Keep-alive (30s idle, 10s interval, 5 probes)
- Out-of-order segment reassembly (4-slot buffer)

Terminal & Testing:
- tcpconnect: active open + send "Hello, World!"
- tcplisten: passive open with syslog output
- tcphttp: HTTP/1.0 GET client

Also add push_trace() instrumentation to net, eth2, arp, ipv4,
icmp, udp, and dhcp entry points for call tracing, and register
tcp in net.init.

src/driver/net/l1/net.pas

@@ -100,8 +100,8 @@ end;
 
 procedure send(p_data : void; p_len : uint16);
 begin
-    //push_trace('net.send');
+    push_trace('net.send');
-    //writeToLogLn('L1: net.send');
+    writeToLogLn('L1/NET: send');
     if CBSend <> nil then CBSend(p_data, p_len);
     pop_trace;
 end;
@@ -111,8 +111,7 @@ var
     context : PPacketContext;
 
 begin
-    //push_trace('net.recv');
+    push_trace('net.recv');
-    //writeToLogLn('L1: net.recv');
     context:= newPacketContext;
     if CBNext <> nil then CBNext(p_data, p_len, context);
     freePacketContext(context);
@@ -129,6 +128,7 @@ end;
 procedure init;
 begin
     push_trace('net.init');
+    writeToLogLn('L1/NET: init');
     //l2
     eth2.register;
     //l3
@@ -136,6 +136,7 @@ begin
     ipv4.register;
     //l4
     icmp.register;
+    tcp.register;
     udp.register;
     //l5
     dhcp.register;

src/driver/net/l2/eth2.pas

@@ -46,6 +46,7 @@ var
 
 procedure registerTypePromisc(eType : uint16; RecvCB : TRecvCallback);
 begin
+    push_trace('eth2.registerTypePromisc');
     register;
     if EthTypes[eType] = nil then EthTypes[eType]:= RecvCB;
     Promisc[eType]:= true;
@@ -53,6 +54,7 @@ end;
 
 procedure registerType(eType : uint16; RecvCB : TRecvCallback);
 begin
+    push_trace('eth2.registerType');
     register;
     if EthTypes[eType] = nil then EthTypes[eType]:= RecvCB;
 end;
@@ -93,7 +95,7 @@ var
     buf        : puint8;
 
 begin
-    //writeToLogLn('    L2: eth2.recv');
+    push_trace('eth2.recv');
     buf:= puint8(p_data);
     
     Header:= PEthernetHeader(buf);
@@ -120,6 +122,7 @@ var
 begin
     push_trace('eth2.register');
     if not Registered then begin
+        writeToLogLn('    L2/ETH: register');
         for i:=0 to 65535 do begin
             EthTypes[i]:= nil;
             Promisc[i]:= false;

src/driver/net/l3/arp.pas

@@ -96,6 +96,7 @@ var
     hSize, pSize : uint8;
 
 begin
+    push_trace('arp.send');
     if p_context <> nil then begin
         buf:= kalloc(sizeof(TARPHeader));
         hdr:= PARPHeader(buf);
@@ -135,6 +136,8 @@ var
     context : PPacketContext;
 
 begin
+     push_trace('arp.sendGratuitous');
+     writeToLogLn('      L3/ARP: sendGratuitous');
      context:= newPacketContext;
      CopyIPv4(@getIPv4Config^.Address[0], @context^.IP.Destination[0]);
      CopyIPv4(@getIPv4Config^.Address[0], @context^.IP.Source[0]);
@@ -150,6 +153,7 @@ var
     CacheRecord : PARPCacheRecord;
 
 begin
+     push_trace('arp.sendRequestGateway');
      context:= newPacketContext;
      CacheRecord:= findCacheRecordByIP(@getIPv4Config^.Gateway[0]);
      if CacheRecord <> nil then begin
@@ -168,6 +172,8 @@ var
     CacheRecord : PARPCacheRecord;
 
 begin
+     push_trace('arp.sendRequest');
+     writeToLogLn('      L3/ARP: sendRequest');
      context:= newPacketContext;
      CopyIPv4(ip, @context^.IP.Destination[0]);
      CopyIPv4(@getIPv4Config^.Address[0], @context^.IP.Source[0]);
@@ -184,6 +190,7 @@ var
     CacheRecord : PARPCacheRecord;
 
 begin
+    push_trace('arp.resolveIP');
     CacheRecord:= findCacheRecordByIP(ip);
     resolveIP:= nil;
     if CacheRecord = nil then begin
@@ -203,6 +210,7 @@ var
     context      : PPacketContext;
 
 begin
+    push_trace('arp.recv');
     { Get our converted Header }
     Header:= PARPHeader(p_data);
     AHeader.Hardware_Type:= (Header^.Hardware_Type_Hi SHL 8) + Header^.Hardware_Type_Lo;
@@ -298,6 +306,7 @@ procedure register;
 begin
     push_trace('arp.register');
     if not Registered then begin
+        writeToLogLn('      L3/ARP: register');
         Cache:= LL_New(sizeof(TARPCacheRecord));
         eth2.registerTypePromisc($0806, @recv);
         stdio.registerCommand('ARP', @terminal_command_arp, 'Get ARP Table.');

src/driver/net/l3/ipv4.pas

@@ -46,7 +46,9 @@ var
 
 function  getIPv4Config : PIPv4Configuration;
 begin
+    push_trace('ipv4.getIPv4Config');
     getIPv4Config:= @Config;
+    pop_trace;
 end;
 
 procedure send(p_data : void; p_len : uint16; p_context : PPacketContext);
@@ -57,6 +59,7 @@ var
     buffer : void;
 
 begin
+    push_trace('ipv4.send');
     inc(CurrentID);
     Header.version:= 4;
     Header.header_len:= 5;
@@ -84,6 +87,7 @@ begin
     memcpy(uint32(p_data), uint32(Buffer) + (Header.header_len * 4), p_len);
     eth2.send(Buffer, (Header.header_len * 4) + p_len, $0800, p_context);
     kfree(Buffer);
+    pop_trace;
 end;
 
 procedure recv(p_data : void; p_len : uint16; p_context : PPacketContext);
@@ -95,6 +99,7 @@ var
     len     : uint16;
 
 begin
+    push_trace('ipv4.recv');
     Header:= PIPV4Header(p_data);
     AHeader.version:= Header^.version;
     AHeader.header_len:= Header^.header_len;
@@ -195,6 +200,7 @@ var
 begin
     push_trace('ipv4.register');
     if not Registered then begin
+        writeToLogLn('      L3/IPv4: register');
         for i:=0 to 255 do begin
             Protocols[i]:= nil;
         end;
@@ -213,6 +219,7 @@ end;
 
 procedure registerProtocol(Protocol_ID : uint8; recv_callback : TRecvCallback);
 begin
+    push_trace('ipv4.registerProtocol');
     register;
     if Protocols[Protocol_ID] = nil then Protocols[Protocol_ID]:= recv_callback;
     pop_trace;

src/driver/net/l4/icmp.pas

@@ -23,7 +23,7 @@ interface
 
 uses
     bios_data_area,
-    lmemorymanager,
+    lmemorymanager, tracer,
     net, nettypes, netutils, ipv4, arp, util;
 
 type
@@ -55,6 +55,7 @@ var
     i : uint8;
 
 begin
+    push_trace('icmp.nextInactiveHandler');
     nextInactiveHandler:= 0;
     for i:=1 to 255 do begin
         if not Handlers[i].Active then begin
@@ -80,6 +81,8 @@ var
     Size     : uint32;
 
 begin
+    push_trace('icmp.sendICMPRequest');
+    writeToLogLn('        L4/ICMP: sendICMPRequest');
     handle:= nextInactiveHandler;
     Handlers[handle].Active:= true;
     Handlers[handle].OnReply:= OnRep;
@@ -135,6 +138,8 @@ var
     Handle : uint8;
 
 begin
+    push_trace('icmp.recv');
+    writeToLogLn('        L4/ICMP: recv');
     Header:= PICMPHeader(p_data);
     //writehexlnWND(Header^.ICMP_Type, getTerminalHWND); 
     case Header^.ICMP_Type of
@@ -243,6 +248,8 @@ var
     i : uint32;
 
 begin
+    push_trace('icmp.register');
+    writeToLogLn('        L4/ICMP: register');
     for i:=0 to 255 do begin
         Handlers[i].Active:= false;
         Handlers[i].OnError:= nil;

src/driver/net/l4/udp.pas

@@ -25,7 +25,7 @@ uses
     lmemorymanager,
     nettypes, netutils,
     ipv4, net,
-    util;
+    tracer, util;
 
 procedure register();
 function bind(bindContext : PUDPBindContext) : TUDPError;
@@ -71,6 +71,7 @@ begin
             nullend:= true;
         end;
         pseudoBuffer:= kalloc(sizeof(TUDPPseudoHeader) + pseudoSize);
+        push_trace('udp.CalculateChecksum');
         pseudoBuffer8:= puint8(pseudoBuffer);
         pseudoBuffer16:= puint16(pseudoBuffer);
         pseudoBuffer32:= puint32(pseudoBuffer);
@@ -118,6 +119,7 @@ var
 
 
 begin
+    push_trace('udp.send');
     if udpContext <> nil then begin
         size:= p_len + sizeof(TUDPHeader);
         buffer:= kalloc(size);
@@ -152,6 +154,7 @@ var
     context : PUDPBindContext;
 
 begin
+    push_trace('udp.bind');
     result:= tueGenericError;
     if bindContext <> nil then begin
         if Ports[bindContext^.port] = nil then begin
@@ -174,6 +177,7 @@ var
     context : PUDPBindContext;
 
 begin
+    push_trace('udp.unbind');
     result:= tueGenericError;
     if bindContext <> nil then begin
         context:= Ports[bindContext^.port];
@@ -203,6 +207,7 @@ var
     size    : uint16;
 
 begin
+    push_trace('udp.ProcessPacket');
     header:= PUDPHeader(p_data);
     if Ports[switchendian16(header^.DstPort)] <> nil then begin
         context:= PUDPPacketContext(kalloc(sizeof(TUDPPacketContext)));
@@ -245,6 +250,8 @@ var
     Checksum      : uint32;
 
 begin
+    push_trace('udp.register');
+    writeToLogLn('        L4/UDP: register');
     for i:=0 to 65535 do begin
         Ports[i]:= nil;
     end;

src/driver/net/l5/dhcp.pas

@@ -415,7 +415,7 @@ end;
 
 procedure processPacket_NAK(Header : PDHCPHeader; Options : PDHCPOptions);
 begin
-    syslog.logln('DHCP', 'Process NAK.'); 
+    writeToLogLn('          L5/DHCP: Process NAK.');
     { Server provided a NAK, NULL configuration ready for next DISCOVER/Request } 
     nullConfiguration();  
 end;
@@ -429,7 +429,7 @@ var
     cfgopt : void;
 
 begin
-    syslog.logln('DHCP', 'Process ACK.');
+    writeToLogLn('          L5/DHCP: Process ACK.');
     getIPv4Config^.UP:= false;
     
     //Copy new address
@@ -484,7 +484,7 @@ Var
 
 begin
     syslog.logln('DHCP', 'Process OFFER.');  
-
+    writeToLogLn('          L5/DHCP: Process OFFER.');
     { Check the Transaction ID matches our stored ID, discard if not. }
     if Header^.Transaction_ID = Configuration^.Transaction then begin
         syslog.logln('DHCP', 'XID Match');
@@ -566,6 +566,7 @@ var
 
 begin
     tracer.push_trace('dhcp.processPacket.enter');
+    writeToLogLn('          L5/DHCP: processPacket');
     syslog.logln('DHCP','processPacket');
     
     { Give access to header values & process to correct endianness. }
@@ -636,6 +637,7 @@ var
 
 begin
     tracer.push_trace('dhcp.DHCPDiscover.begin');
+    writeToLogLn('          L5/DHCP: DHCPDiscover');
     { Ensure we have a socket bound. }
     if Socket <> nil then begin    
         { Clear any current configuration }
@@ -711,6 +713,7 @@ var
 
 begin
     tracer.push_trace('dhcp.register');
+    writeToLogLn('          L5/DHCP: register');
     syslog.logln('DHCP', 'Register begin.');
     
     { Kalloc our Configuration Data }