Merge #20048: chainparams: do not log signet startup messages for other chains

6fccad7f71 signet: do not log signet startup messages for other chains (Jon Atack)

Pull request description:

  The following signet startup messages are printed to the debug log immediately on node startup for all chains. This behavior occurs on master as a side effect after the merge of #20014. This PR removes the first message and moves the signet derived magic logging to `init.cpp`.
  ```
  $ ./src/bitcoind
  2020-09-30T14:25:15Z Using default signet network
  2020-09-30T14:25:15Z Signet derived magic (message start): 0a03cf40
  2020-09-30T14:25:15Z Bitcoin Core version v0.20.99.0 ...
  ```

ACKs for top commit:
  MarcoFalke:
    ACK 6fccad7f71
  kallewoof:
    utACK 6fccad7f71
  hebasto:
    ACK 6fccad7f71

Tree-SHA512: 33821dce89b24caf7b7c1ecb41e572ecfb26e6958a1316d359ff240e6ef97c4a1f2cf1b4b974596b252815f9df23960ce385c132ebdbc855bbe6123c3b0b003a

src/chainparams.cpp

@@ -265,7 +265,6 @@ public:
         vSeeds.clear();
 
         if (!args.IsArgSet("-signetchallenge")) {
-            LogPrintf("Using default signet network\n");
             bin = ParseHex("512103ad5e0edad18cb1f0fc0d28a3d4f1f3e445640337489abb10404f2d1e086be430210359ef5021964fe22d6f8e05b2463c9540ce96883fe3b278760f048f5189f2e6c452ae");
             vSeeds.emplace_back("178.128.221.177");
             vSeeds.emplace_back("2a01:7c8:d005:390::5");
@@ -327,7 +326,6 @@ public:
         h << consensus.signet_challenge;
         uint256 hash = h.GetHash();
         memcpy(pchMessageStart, hash.begin(), 4);
-        LogPrintf("Signet derived magic (message start): %s\n", HexStr({pchMessageStart, pchMessageStart + 4}));
 
         nDefaultPort = 38333;
         nPruneAfterHeight = 1000;

src/init.cpp

@@ -37,6 +37,7 @@
 #include <policy/fees.h>
 #include <policy/policy.h>
 #include <policy/settings.h>
+#include <protocol.h>
 #include <rpc/blockchain.h>
 #include <rpc/register.h>
 #include <rpc/server.h>
@@ -966,6 +967,9 @@ bool AppInitParameterInteraction(const ArgsManager& args)
     // specified in default section of config file, but not overridden
     // on the command line or in this network's section of the config file.
     std::string network = args.GetChainName();
+    if (network == CBaseChainParams::SIGNET) {
+        LogPrintf("Signet derived magic (message start): %s\n", HexStr(chainparams.MessageStart()));
+    }
     bilingual_str errors;
     for (const auto& arg : args.GetUnsuitableSectionOnlyArgs()) {
         errors += strprintf(_("Config setting for %s only applied on %s network when in [%s] section.") + Untranslated("\n"), arg, network, network);

test/functional/feature_signet.py

@@ -65,6 +65,10 @@ class SignetBasicTest(BitcoinTestFramework):
 
         assert_equal(self.nodes[4].submitblock(signet_blocks[0]), 'bad-signet-blksig')
 
+        self.log.info("test that signet logs the network magic on node start")
+        with self.nodes[0].assert_debug_log(["Signet derived magic (message start)"]):
+            self.restart_node(0)
+
 
 if __name__ == '__main__':
     SignetBasicTest().main()