9 files changed, 140 insertions, 17 deletions

diff --git a/README.md b/README.md
index 94c727d..4843f5c 100644
--- a/README.md
+++ b/README.md
@@ -355,7 +355,8 @@ Other options worth knowing:
 
 ```bash
 -datadir=PATH    # wallet and chain data elsewhere
--port=N          # P2P listen port, default 8433
+-testnet         # isolated test network datadir, port 18433, and message magic
+-port=N          # P2P listen port, default 8433; testnet default 18433
 -socks=HOST:PORT # SOCKS5 for outbound Nostr, .btf relay, and onion peer dials
 -tor[=HOST:PORT] # Tor mode; default local Tor SOCKS5 proxy is 127.0.0.1:9050
 -managedtor[=PATH] # start Tor, create a hidden service, advertise its onion
diff --git a/src/Makefile b/src/Makefile
index b83ff58..ab0b307 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -193,6 +193,7 @@ tests: test_bip32 bitflash-node
         ./bitflash-node -selftest=wallet-crypto
         ./bitflash-node -selftest=wallet-encrypt
         ./bitflash-node -selftest=net-message
+        ./bitflash-node -selftest=network-params
         ./bitflash-node -selftest=consensus-limits
         ./bitflash-node -selftest=pool-stratum
         ./bitflash-node -selftest=parse-money
diff --git a/src/main.cpp b/src/main.cpp
index 5bd4028..6fd8c82 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -2497,11 +2497,21 @@ string GetAppDir()
     {
         return ".";
     }
-    static bool fMkdirDone;
-    if (!fMkdirDone)
+    static string strCreatedBaseDir;
+    if (strCreatedBaseDir != strDir)
     {
-        fMkdirDone = true;
         _mkdir(strDir.c_str());
+        strCreatedBaseDir = strDir;
+    }
+    if (IsTestNet())
+    {
+        strDir += "/testnet";
+        static string strCreatedTestnetDir;
+        if (strCreatedTestnetDir != strDir)
+        {
+            _mkdir(strDir.c_str());
+            strCreatedTestnetDir = strDir;
+        }
     }
     return strDir;
 }
diff --git a/src/main_gui.cpp b/src/main_gui.cpp
index 943799f..0a961bf 100644
--- a/src/main_gui.cpp
+++ b/src/main_gui.cpp
@@ -118,7 +118,7 @@ static void PrintUsage()
     printf("            wallet-crypto, wallet-encrypt, wallet-portability,\n");
     printf("            net-message,\n");
     printf("            consensus-limits, pool-stratum,\n");
-    printf("            parse-money, socks5-proxy, or managed-tor\n");
+    printf("            parse-money, network-params, socks5-proxy, or managed-tor\n");
     printf("\n");
     printf("Mining mode:\n");
     printf("  /operator\n");
@@ -143,7 +143,8 @@ static void PrintUsage()
     printf("  /onionservice=HOST.onion:PORT  (advertise this node's Tor hidden service)\n");
     printf("\n");
     printf("Network:\n");
-    printf("  /port=N                    (P2P listen port, default 8433)\n");
+    printf("  /testnet                   (isolated test network datadir, port, and magic)\n");
+    printf("  /port=N                    (P2P listen port, default 8433; testnet 18433)\n");
     printf("  /socks=HOST:PORT           (SOCKS5 proxy for Nostr, .btf relay, and onion dials)\n");
     printf("  /tor[=HOST:PORT]           (Tor mode; default SOCKS5 proxy is 127.0.0.1:9050)\n");
     printf("  /managedtor[=PATH]         (start Tor, create a hidden service, advertise its onion)\n");
@@ -205,6 +206,8 @@ static void ParseStartupArguments(int argc, char* argv[])
     if (arg(argc,argv,"/datadir") || arg(argc,argv,"-datadir"))
         strSetDataDir = argval2(argc, argv, "/datadir", "-datadir");
 
+    SelectNetworkParams(arg(argc, argv, "/testnet") || arg(argc, argv, "-testnet"));
+
     if (arg(argc,argv,"/debug") || arg(argc,argv,"-debug"))
         fDebug = true;
 
diff --git a/src/makefile.mingw b/src/makefile.mingw
index 55f186b..910e025 100644
--- a/src/makefile.mingw
+++ b/src/makefile.mingw
@@ -116,6 +116,7 @@ tests: test_bip32.exe bitflash.exe
         ./bitflash.exe -selftest=wallet-backend-default
         ./bitflash.exe -selftest=wallet-convert
         ./bitflash.exe -selftest=net-message
+        ./bitflash.exe -selftest=network-params
         ./bitflash.exe -selftest=consensus-limits
         ./bitflash.exe -selftest=pool-stratum
         ./bitflash.exe -selftest=socks5-proxy
diff --git a/src/net.cpp b/src/net.cpp
index 4603d2d..ecfd565 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -50,10 +50,14 @@ static int BtfPoll(BtfPollFd* pfd, unsigned int nfd, int nTimeoutMs)
 //
 // Global state variables
 //
+static const char pchMainnetMessageStart[4] = { 0xbf, 0x20, 0x5c, 0xfd };
+static const char pchTestnetMessageStart[4] = { (char)0xce, (char)0xe2, (char)0xc0, (char)0xff };
+static bool fTestNet = false;
+char pchMessageStart[4] = { 0xbf, 0x20, 0x5c, 0xfd };
 bool fClient = false;
 uint64 nLocalServices = (fClient ? 0 : NODE_NETWORK);
-CAddress addrLocalHost(0, DEFAULT_PORT, nLocalServices);
-unsigned short nListenPort = DEFAULT_PORT; // local P2P port (tunable via /port)
+CAddress addrLocalHost(0, GetDefaultPort(), nLocalServices);
+unsigned short nListenPort = GetDefaultPort(); // local P2P port (tunable via /port)
 CNode nodeLocalHost(INVALID_SOCKET, CAddress("127.0.0.1", nLocalServices));
 CNode* pnodeLocalHost = &nodeLocalHost;
 bool fShutdown = false;
@@ -90,6 +94,29 @@ static int64 nBtfHandshakeSilent = 0;
 static string strBtfLastDialFail;
 static string strBtfLastHandshakeTimeout;
 
+bool IsTestNet()
+{
+    return fTestNet;
+}
+
+unsigned short GetDefaultPort()
+{
+    return htons(fTestNet ? TESTNET_PORT : MAINNET_PORT);
+}
+
+void SelectNetworkParams(bool fTestNetIn)
+{
+    if (fTestNet == fTestNetIn)
+        return;
+
+    fTestNet = fTestNetIn;
+    memcpy(pchMessageStart,
+           fTestNet ? pchTestnetMessageStart : pchMainnetMessageStart,
+           sizeof(pchMessageStart));
+    nListenPort = GetDefaultPort();
+    addrLocalHost.port = nListenPort;
+}
+
 void BtfChurnNoteResolveAttempt()
 {
     CRITICAL_BLOCK(cs_btfChurn)
@@ -288,6 +315,7 @@ string GetDiagnosticsText()
     int nMedian = GetPeerMedianHeight();
 
     str += "Bitflash node diagnostics\n";
+    str += strprintf("  network           %s\n", IsTestNet() ? "testnet" : "mainnet");
     str += strprintf("  uptime            %s\n",
                      FormatAge(nNodeStartTime ? nNow - nNodeStartTime : -1).c_str());
     if (nMedian < 0)
diff --git a/src/net.h b/src/net.h
index e3d4a93..56f1341 100644
--- a/src/net.h
+++ b/src/net.h
@@ -13,7 +13,8 @@ class CBlockIndex;
 
 
 
-static const unsigned short DEFAULT_PORT = htons(8433);
+static const unsigned short MAINNET_PORT = 8433;
+static const unsigned short TESTNET_PORT = 18433;
 static const unsigned int PUBLISH_HOPS = 5;
 enum
 {
@@ -26,6 +27,9 @@ enum
 
 
 bool GetMyExternalIP(unsigned int& ipRet);
+bool IsTestNet();
+unsigned short GetDefaultPort();
+void SelectNetworkParams(bool fTestNetIn);
 CNode* ConnectNodeBtf(const string& strBtfAddr);
 CNode* ConnectNodeBtfResolved(const string& strBtfAddr, const string& strMeeting,
                               const string& strOnion, const unsigned char enc_pub[32],
@@ -219,15 +223,17 @@ void CheckForShutdown(int n);
 // The message start string is designed to be unlikely to occur in normal data.
 // The characters are rarely used upper ascii, not valid as UTF-8, and produce
 // a large 4-byte int at any alignment.
-// Magic bytes unique to the Bitflash network (0xbf = "BF"). Second byte bumped
-// to 0x20 for the 2026 stable relaunch so the old test chain can't interfere.
-static const char pchMessageStart[4] = { 0xbf, 0x20, 0x5c, 0xfd };
+// Magic bytes unique to the selected Bitflash network. Mainnet uses 0xbf =
+// "BF"; testnet swaps the whole sequence so a test node cannot handshake with
+// mainnet before consensus-level testnet activation exists.
+extern char pchMessageStart[4];
 
 class CMessageHeader
 {
 public:
     enum { COMMAND_SIZE=12 };
-    char pchMessageStart[sizeof(::pchMessageStart)];
+    enum { MESSAGE_START_SIZE=4 };
+    char pchMessageStart[MESSAGE_START_SIZE];
     char pchCommand[COMMAND_SIZE];
     unsigned int nMessageSize;
 
@@ -318,7 +324,7 @@ public:
         nServices = 0;
         memcpy(pchReserved, pchIPv4, sizeof(pchReserved));
         ip = 0;
-        port = DEFAULT_PORT;
+        port = GetDefaultPort();
         nTime = GetAdjustedTime();
         nLastFailed = 0;
     }
@@ -348,7 +354,7 @@ public:
         nServices = nServicesIn;
         memcpy(pchReserved, pchIPv4, sizeof(pchReserved));
         ip = 0;
-        port = DEFAULT_PORT;
+        port = GetDefaultPort();
         nTime = GetAdjustedTime();
         nLastFailed = 0;
 
diff --git a/src/readme.txt b/src/readme.txt
index 752be66..5d62791 100644
--- a/src/readme.txt
+++ b/src/readme.txt
@@ -41,7 +41,8 @@ The resulting executable is src/bitflash.exe.
 
 Command-line options (in addition to the original ones)
 -------------------------------------------------------
-  /port=N        listen on P2P port N (default 8433)
+  /testnet       use isolated test network datadir, port 18433, and message magic
+  /port=N        listen on P2P port N (default 8433; testnet default 18433)
   /socks=HOST:PORT
                  route outbound Nostr, .btf rendezvous, and direct onion peer
                  dials through a SOCKS5 proxy, e.g. /socks=127.0.0.1:9050 for local Tor
diff --git a/src/selftest.cpp b/src/selftest.cpp
index dc9936e..30bd28e 100644
--- a/src/selftest.cpp
+++ b/src/selftest.cpp
@@ -3076,6 +3076,76 @@ static int RunNetMessageSelfTest()
     return nFail == 0 ? 0 : 1;
 }
 
+static int RunNetworkParamsSelfTest()
+{
+    fflush(stdout);
+    printf("network-params self-test\n");
+
+    int nFail = 0;
+    std::string strOldDataDir = strSetDataDir;
+    try
+    {
+        SelectNetworkParams(false);
+        nFail += Check(!IsTestNet(), "starts on mainnet after explicit selection") ? 0 : 1;
+        nFail += Check(ntohs(GetDefaultPort()) == MAINNET_PORT,
+                       "mainnet default P2P port is 8433") ? 0 : 1;
+        CAddress mainAddr("127.0.0.1");
+        nFail += Check(mainAddr.port == htons(MAINNET_PORT),
+                       "mainnet address parsing uses the mainnet default port") ? 0 : 1;
+        CMessageHeader mainHeader("ping", 0);
+        char mainMagic[4];
+        memcpy(mainMagic, mainHeader.pchMessageStart, sizeof(mainMagic));
+
+        SelectNetworkParams(true);
+        nFail += Check(IsTestNet(), "testnet selection is sticky") ? 0 : 1;
+        nFail += Check(ntohs(GetDefaultPort()) == TESTNET_PORT,
+                       "testnet default P2P port is 18433") ? 0 : 1;
+        CAddress testAddr("127.0.0.1");
+        nFail += Check(testAddr.port == htons(TESTNET_PORT),
+                       "testnet address parsing uses the testnet default port") ? 0 : 1;
+        CMessageHeader testHeader("ping", 0);
+        nFail += Check(memcmp(mainMagic, testHeader.pchMessageStart, sizeof(mainMagic)) != 0,
+                       "testnet message magic differs from mainnet") ? 0 : 1;
+
+        std::string tmp;
+        if (!MakeTempDir(tmp))
+        {
+            nFail += Check(false, "creates a temporary data directory") ? 0 : 1;
+        }
+        else
+        {
+            strSetDataDir = tmp;
+            SelectNetworkParams(false);
+            std::string mainDir = GetAppDir();
+            SelectNetworkParams(true);
+            std::string testDir = GetAppDir();
+            nFail += Check(mainDir == tmp,
+                           "mainnet uses the selected data directory") ? 0 : 1;
+            nFail += Check(testDir == tmp + "/testnet",
+                           "testnet stores data below a testnet subdirectory") ? 0 : 1;
+            RemoveTree(tmp);
+        }
+    }
+    catch (const std::exception& e)
+    {
+        printf("  FAIL exception: %s\n", e.what());
+        nFail++;
+    }
+    catch (...)
+    {
+        printf("  FAIL unknown exception\n");
+        nFail++;
+    }
+
+    strSetDataDir = strOldDataDir;
+    SelectNetworkParams(false);
+
+    printf("%s (%d failure%s)\n", nFail == 0 ? "ALL TESTS PASSED" : "TESTS FAILED",
+           nFail, nFail == 1 ? "" : "s");
+    fflush(stdout);
+    return nFail == 0 ? 0 : 1;
+}
+
 static CBlock MakeSizedConsensusBlock(size_t nScriptBytes)
 {
     CTransaction tx;
@@ -3517,6 +3587,8 @@ int RunSelfTest(const std::string& name)
         return RunWalletPortabilitySelfTest();
     if (name == "net-message")
         return RunNetMessageSelfTest();
+    if (name == "network-params")
+        return RunNetworkParamsSelfTest();
     if (name == "consensus-limits")
         return RunConsensusLimitsSelfTest();
     if (name == "pool-stratum")
@@ -3529,6 +3601,6 @@ int RunSelfTest(const std::string& name)
         return RunManagedTorSelfTest();
 
     printf("Unknown self-test '%s'\n", name.c_str());
-    printf("Known self-tests: wallet-keypool, wallet-hd, wallet-format, wallet-storage-sanity, db-env-reopen, wallet-sqlite, wallet-sqlite-migration, wallet-crypto, wallet-encrypt, wallet-sqlite-encrypt, wallet-backend-default, wallet-convert, wallet-portability, net-message, consensus-limits, pool-stratum, parse-money, socks5-proxy, managed-tor\n");
+    printf("Known self-tests: wallet-keypool, wallet-hd, wallet-format, wallet-storage-sanity, db-env-reopen, wallet-sqlite, wallet-sqlite-migration, wallet-crypto, wallet-encrypt, wallet-sqlite-encrypt, wallet-backend-default, wallet-convert, wallet-portability, net-message, network-params, consensus-limits, pool-stratum, parse-money, socks5-proxy, managed-tor\n");
     return 1;
 }