Merge #15654: net: Remove unused unsanitized user agent string CNode::strSubVer

fa8548c net: Remove unused unsanitized user agent string CNode::strSubVer (MarcoFalke)

Pull request description:

  I fail to see a use case for this unsanitized byte array. In fact this can easily be confused with `cleanSubVer` and be displayed to the user (or logged) by a simple typo that is hard to find in review.

  Further reading: https://btcinformation.org/en/developer-reference#version

ACKs for commit fa8548:
  promag:
    utACK fa8548c, good catch.
  practicalswift:
    utACK fa8548c
  sipa:
    utACK fa8548c

Tree-SHA512: 3c3ff1504d1583ad099df9a6aa761458a82ec48a58ef7aaa9b5679a5281dd1b59036ba2932ed708488951a565b669a3083ef70be5a58472ff8677b971162ae2f

Author: MarcoFalke

src/net.cpp

@@ -2627,7 +2627,6 @@ CNode::CNode(NodeId idIn, ServiceFlags nLocalServicesIn, int nMyStartingHeightIn
 {
     hSocket = hSocketIn;
     addrName = addrNameIn == "" ? addr.ToStringIPPort() : addrNameIn;
-    strSubVer = "";
     hashContinue = uint256();
     filterInventoryKnown.reset();
     pfilter = MakeUnique<CBloomFilter>();

src/net.h

@@ -53,7 +53,7 @@ static const unsigned int MAX_LOCATOR_SZ = 101;
 static const unsigned int MAX_ADDR_TO_SEND = 1000;
 /** Maximum length of incoming protocol messages (no message over 4 MB is currently acceptable). */
 static const unsigned int MAX_PROTOCOL_MESSAGE_LENGTH = 4 * 1000 * 1000;
-/** Maximum length of strSubVer in `version` message */
+/** Maximum length of the user agent string in `version` message */
 static const unsigned int MAX_SUBVERSION_LENGTH = 256;
 /** Maximum number of automatic outgoing nodes */
 static const int MAX_OUTBOUND_CONNECTIONS = 8;
@@ -650,12 +650,12 @@ class CNode
     // Bind address of our side of the connection
     const CAddress addrBind;
     std::atomic<int> nVersion{0};
-    // strSubVer is whatever byte array we read from the wire. However, this field is intended
-    // to be printed out, displayed to humans in various forms and so on. So we sanitize it and
-    // store the sanitized version in cleanSubVer. The original should be used when dealing with
-    // the network or wire types and the cleaned string used when displayed or logged.
-    std::string strSubVer GUARDED_BY(cs_SubVer), cleanSubVer GUARDED_BY(cs_SubVer);
-    CCriticalSection cs_SubVer; // used for both cleanSubVer and strSubVer
+    RecursiveMutex cs_SubVer;
+    /**
+     * cleanSubVer is a sanitized string of the user agent byte array we read
+     * from the wire. This cleaned string can safely be logged or displayed.
+     */
+    std::string cleanSubVer GUARDED_BY(cs_SubVer){};
     bool m_prefer_evict{false}; // This peer is preferred for eviction.
     bool fWhitelisted{false}; // This peer can bypass DoS banning.
     bool fFeeler{false}; // If true this node is being used as a short lived feeler.

src/net_processing.cpp

@@ -1843,7 +1843,6 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
         ServiceFlags nServices;
         int nVersion;
         int nSendVersion;
-        std::string strSubVer;
         std::string cleanSubVer;
         int nStartingHeight = -1;
         bool fRelay = true;
@@ -1880,6 +1879,7 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
         if (!vRecv.empty())
             vRecv >> addrFrom >> nNonce;
         if (!vRecv.empty()) {
+            std::string strSubVer;
             vRecv >> LIMITED_STRING(strSubVer, MAX_SUBVERSION_LENGTH);
             cleanSubVer = SanitizeString(strSubVer);
         }
@@ -1911,7 +1911,6 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
         pfrom->SetAddrLocal(addrMe);
         {
             LOCK(pfrom->cs_SubVer);
-            pfrom->strSubVer = strSubVer;
             pfrom->cleanSubVer = cleanSubVer;
         }
         pfrom->nStartingHeight = nStartingHeight;