net: Add and document network messages in protocol.h

- Avoids string typos (by making the compiler check)
- Makes it easier to grep for handling/generation of a certain message type
- Refer directly to documentation by following the symbol in IDE
- Move list of valid message types to protocol.cpp:
    protocol.cpp is a more appropriate place for this, and having
    the array there makes it easier to keep things consistent.

Github-Pull: #7181
Rebased-From: 9bbe71b641e2fc985daf127988a14a67c99da50a

5 files changed, 281 insertions, 63 deletions

diff --git a/src/alert.cpp b/src/alert.cpp
index 91e54a9178..b705069407 100644
--- a/src/alert.cpp
+++ b/src/alert.cpp
@@ -138,7 +138,7 @@ bool CAlert::RelayTo(CNode* pnode) const
             AppliesToMe() ||
             GetAdjustedTime() < nRelayUntil)
         {
-            pnode->PushMessage("alert", *this);
+            pnode->PushMessage(NetMsgType::ALERT, *this);
             return true;
         }
     }
diff --git a/src/main.cpp b/src/main.cpp
index d6fadd10b2..d965f67a7b 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -4171,14 +4171,14 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
                     if (!ReadBlockFromDisk(block, (*mi).second, consensusParams))
                         assert(!"cannot load block from disk");
                     if (inv.type == MSG_BLOCK)
-                        pfrom->PushMessage("block", block);
+                        pfrom->PushMessage(NetMsgType::BLOCK, block);
                     else // MSG_FILTERED_BLOCK)
                     {
                         LOCK(pfrom->cs_filter);
                         if (pfrom->pfilter)
                         {
                             CMerkleBlock merkleBlock(block, *pfrom->pfilter);
-                            pfrom->PushMessage("merkleblock", merkleBlock);
+                            pfrom->PushMessage(NetMsgType::MERKLEBLOCK, merkleBlock);
                             // CMerkleBlock just contains hashes, so also push any transactions in the block the client did not see
                             // This avoids hurting performance by pointlessly requiring a round-trip
                             // Note that there is currently no way for a node to request any single transactions we didn't send here -
@@ -4187,7 +4187,7 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
                             // however we MUST always provide at least what the remote peer needs
                             typedef std::pair<unsigned int, uint256> PairType;
                             BOOST_FOREACH(PairType& pair, merkleBlock.vMatchedTxn)
-                                pfrom->PushMessage("tx", block.vtx[pair.first]);
+                                pfrom->PushMessage(NetMsgType::TX, block.vtx[pair.first]);
                         }
                         // else
                             // no response
@@ -4201,7 +4201,7 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
                         // wait for other stuff first.
                         vector<CInv> vInv;
                         vInv.push_back(CInv(MSG_BLOCK, chainActive.Tip()->GetBlockHash()));
-                        pfrom->PushMessage("inv", vInv);
+                        pfrom->PushMessage(NetMsgType::INV, vInv);
                         pfrom->hashContinue.SetNull();
                     }
                 }
@@ -4224,7 +4224,7 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
                         CDataStream ss(SER_NETWORK, PROTOCOL_VERSION);
                         ss.reserve(1000);
                         ss << tx;
-                        pfrom->PushMessage("tx", ss);
+                        pfrom->PushMessage(NetMsgType::TX, ss);
                         pushed = true;
                     }
                 }
@@ -4251,7 +4251,7 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
         // do that because they want to know about (and store and rebroadcast and
         // risk analyze) the dependencies of transactions relevant to them, without
         // having to download the entire memory pool.
-        pfrom->PushMessage("notfound", vNotFound);
+        pfrom->PushMessage(NetMsgType::NOTFOUND, vNotFound);
     }
 }
 
@@ -4268,9 +4268,9 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
 
 
     if (!(nLocalServices & NODE_BLOOM) &&
-              (strCommand == "filterload" ||
-               strCommand == "filteradd" ||
-               strCommand == "filterclear"))
+              (strCommand == NetMsgType::FILTERLOAD ||
+               strCommand == NetMsgType::FILTERADD ||
+               strCommand == NetMsgType::FILTERCLEAR))
     {
         if (pfrom->nVersion >= NO_BLOOM_VERSION) {
             Misbehaving(pfrom->GetId(), 100);
@@ -4282,12 +4282,12 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    if (strCommand == "version")
+    if (strCommand == NetMsgType::VERSION)
     {
         // Each connection can only send one version message
         if (pfrom->nVersion != 0)
         {
-            pfrom->PushMessage("reject", strCommand, REJECT_DUPLICATE, string("Duplicate version message"));
+            pfrom->PushMessage(NetMsgType::REJECT, strCommand, REJECT_DUPLICATE, string("Duplicate version message"));
             Misbehaving(pfrom->GetId(), 1);
             return false;
         }
@@ -4301,7 +4301,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         {
             // disconnect from peers older than this proto version
             LogPrintf("peer=%d using obsolete version %i; disconnecting\n", pfrom->id, pfrom->nVersion);
-            pfrom->PushMessage("reject", strCommand, REJECT_OBSOLETE,
+            pfrom->PushMessage(NetMsgType::REJECT, strCommand, REJECT_OBSOLETE,
                                strprintf("Version must be %d or greater", MIN_PEER_PROTO_VERSION));
             pfrom->fDisconnect = true;
             return false;
@@ -4346,7 +4346,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         UpdatePreferredDownload(pfrom, State(pfrom->GetId()));
 
         // Change version
-        pfrom->PushMessage("verack");
+        pfrom->PushMessage(NetMsgType::VERACK);
         pfrom->ssSend.SetVersion(min(pfrom->nVersion, PROTOCOL_VERSION));
 
         if (!pfrom->fInbound)
@@ -4369,7 +4369,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             // Get recent addresses
             if (pfrom->fOneShot || pfrom->nVersion >= CADDR_TIME_VERSION || addrman.size() < 1000)
             {
-                pfrom->PushMessage("getaddr");
+                pfrom->PushMessage(NetMsgType::GETADDR);
                 pfrom->fGetAddr = true;
             }
             addrman.Good(pfrom->addr);
@@ -4413,7 +4413,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "verack")
+    else if (strCommand == NetMsgType::VERACK)
     {
         pfrom->SetRecvVersion(min(pfrom->nVersion, PROTOCOL_VERSION));
 
@@ -4428,12 +4428,12 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             // We send this to non-NODE NETWORK peers as well, because even
             // non-NODE NETWORK peers can announce blocks (such as pruning
             // nodes)
-            pfrom->PushMessage("sendheaders");
+            pfrom->PushMessage(NetMsgType::SENDHEADERS);
         }
     }
 
 
-    else if (strCommand == "addr")
+    else if (strCommand == NetMsgType::ADDR)
     {
         vector<CAddress> vAddr;
         vRecv >> vAddr;
@@ -4499,14 +4499,14 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             pfrom->fDisconnect = true;
     }
 
-    else if (strCommand == "sendheaders")
+    else if (strCommand == NetMsgType::SENDHEADERS)
     {
         LOCK(cs_main);
         State(pfrom->GetId())->fPreferHeaders = true;
     }
 
 
-    else if (strCommand == "inv")
+    else if (strCommand == NetMsgType::INV)
     {
         vector<CInv> vInv;
         vRecv >> vInv;
@@ -4547,7 +4547,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                     // time the block arrives, the header chain leading up to it is already validated. Not
                     // doing this will result in the received block being rejected as an orphan in case it is
                     // not a direct successor.
-                    pfrom->PushMessage("getheaders", chainActive.GetLocator(pindexBestHeader), inv.hash);
+                    pfrom->PushMessage(NetMsgType::GETHEADERS, chainActive.GetLocator(pindexBestHeader), inv.hash);
                     CNodeState *nodestate = State(pfrom->GetId());
                     if (CanDirectFetch(chainparams.GetConsensus()) &&
                         nodestate->nBlocksInFlight < MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
@@ -4577,11 +4577,11 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         }
 
         if (!vToFetch.empty())
-            pfrom->PushMessage("getdata", vToFetch);
+            pfrom->PushMessage(NetMsgType::GETDATA, vToFetch);
     }
 
 
-    else if (strCommand == "getdata")
+    else if (strCommand == NetMsgType::GETDATA)
     {
         vector<CInv> vInv;
         vRecv >> vInv;
@@ -4602,7 +4602,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "getblocks")
+    else if (strCommand == NetMsgType::GETBLOCKS)
     {
         CBlockLocator locator;
         uint256 hashStop;
@@ -4646,7 +4646,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "getheaders")
+    else if (strCommand == NetMsgType::GETHEADERS)
     {
         CBlockLocator locator;
         uint256 hashStop;
@@ -4691,11 +4691,11 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         // headers message). In both cases it's safe to update
         // pindexBestHeaderSent to be our tip.
         nodestate->pindexBestHeaderSent = pindex ? pindex : chainActive.Tip();
-        pfrom->PushMessage("headers", vHeaders);
+        pfrom->PushMessage(NetMsgType::HEADERS, vHeaders);
     }
 
 
-    else if (strCommand == "tx")
+    else if (strCommand == NetMsgType::TX)
     {
         // Stop processing the transaction early if
         // We are in blocks only mode and peer is either not whitelisted or whitelistalwaysrelay is off
@@ -4824,7 +4824,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                 pfrom->id,
                 FormatStateMessage(state));
             if (state.GetRejectCode() < REJECT_INTERNAL) // Never send AcceptToMemoryPool's internal codes over P2P
-                pfrom->PushMessage("reject", strCommand, (unsigned char)state.GetRejectCode(),
+                pfrom->PushMessage(NetMsgType::REJECT, strCommand, (unsigned char)state.GetRejectCode(),
                                    state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), inv.hash);
             if (nDoS > 0)
                 Misbehaving(pfrom->GetId(), nDoS);
@@ -4833,7 +4833,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "headers" && !fImporting && !fReindex) // Ignore headers received while importing
+    else if (strCommand == NetMsgType::HEADERS && !fImporting && !fReindex) // Ignore headers received while importing
     {
         std::vector<CBlockHeader> headers;
 
@@ -4881,7 +4881,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             // TODO: optimize: if pindexLast is an ancestor of chainActive.Tip or pindexBestHeader, continue
             // from there instead.
             LogPrint("net", "more getheaders (%d) to end to peer=%d (startheight:%d)\n", pindexLast->nHeight, pfrom->id, pfrom->nStartingHeight);
-            pfrom->PushMessage("getheaders", chainActive.GetLocator(pindexLast), uint256());
+            pfrom->PushMessage(NetMsgType::GETHEADERS, chainActive.GetLocator(pindexLast), uint256());
         }
 
         bool fCanDirectFetch = CanDirectFetch(chainparams.GetConsensus());
@@ -4926,7 +4926,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                             pindexLast->GetBlockHash().ToString(), pindexLast->nHeight);
                 }
                 if (vGetData.size() > 0) {
-                    pfrom->PushMessage("getdata", vGetData);
+                    pfrom->PushMessage(NetMsgType::GETDATA, vGetData);
                 }
             }
         }
@@ -4934,7 +4934,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         CheckBlockIndex(chainparams.GetConsensus());
     }
 
-    else if (strCommand == "block" && !fImporting && !fReindex) // Ignore blocks received while importing
+    else if (strCommand == NetMsgType::BLOCK && !fImporting && !fReindex) // Ignore blocks received while importing
     {
         CBlock block;
         vRecv >> block;
@@ -4954,7 +4954,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         int nDoS;
         if (state.IsInvalid(nDoS)) {
             assert (state.GetRejectCode() < REJECT_INTERNAL); // Blocks are never rejected with internal reject codes
-            pfrom->PushMessage("reject", strCommand, (unsigned char)state.GetRejectCode(),
+            pfrom->PushMessage(NetMsgType::REJECT, strCommand, (unsigned char)state.GetRejectCode(),
                                state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), inv.hash);
             if (nDoS > 0) {
                 LOCK(cs_main);
@@ -4970,7 +4970,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     // to users' AddrMan and later request them by sending getaddr messages.
     // Making nodes which are behind NAT and can only make outgoing connections ignore
     // the getaddr message mitigates the attack.
-    else if ((strCommand == "getaddr") && (pfrom->fInbound))
+    else if ((strCommand == NetMsgType::GETADDR) && (pfrom->fInbound))
     {
         pfrom->vAddrToSend.clear();
         vector<CAddress> vAddr = addrman.GetAddr();
@@ -4979,7 +4979,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "mempool")
+    else if (strCommand == NetMsgType::MEMPOOL)
     {
         if (CNode::OutboundTargetReached(false) && !pfrom->fWhitelisted)
         {
@@ -5002,16 +5002,16 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             }
             vInv.push_back(inv);
             if (vInv.size() == MAX_INV_SZ) {
-                pfrom->PushMessage("inv", vInv);
+                pfrom->PushMessage(NetMsgType::INV, vInv);
                 vInv.clear();
             }
         }
         if (vInv.size() > 0)
-            pfrom->PushMessage("inv", vInv);
+            pfrom->PushMessage(NetMsgType::INV, vInv);
     }
 
 
-    else if (strCommand == "ping")
+    else if (strCommand == NetMsgType::PING)
     {
         if (pfrom->nVersion > BIP0031_VERSION)
         {
@@ -5028,12 +5028,12 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             // it, if the remote node sends a ping once per second and this node takes 5
             // seconds to respond to each, the 5th ping the remote sends would appear to
             // return very quickly.
-            pfrom->PushMessage("pong", nonce);
+            pfrom->PushMessage(NetMsgType::PONG, nonce);
         }
     }
 
 
-    else if (strCommand == "pong")
+    else if (strCommand == NetMsgType::PONG)
     {
         int64_t pingUsecEnd = nTimeReceived;
         uint64_t nonce = 0;
@@ -5090,7 +5090,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (fAlerts && strCommand == "alert")
+    else if (fAlerts && strCommand == NetMsgType::ALERT)
     {
         CAlert alert;
         vRecv >> alert;
@@ -5121,7 +5121,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "filterload")
+    else if (strCommand == NetMsgType::FILTERLOAD)
     {
         CBloomFilter filter;
         vRecv >> filter;
@@ -5140,7 +5140,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "filteradd")
+    else if (strCommand == NetMsgType::FILTERADD)
     {
         vector<unsigned char> vData;
         vRecv >> vData;
@@ -5160,7 +5160,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "filterclear")
+    else if (strCommand == NetMsgType::FILTERCLEAR)
     {
         LOCK(pfrom->cs_filter);
         delete pfrom->pfilter;
@@ -5169,7 +5169,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
     }
 
 
-    else if (strCommand == "reject")
+    else if (strCommand == NetMsgType::REJECT)
     {
         if (fDebug) {
             try {
@@ -5179,7 +5179,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                 ostringstream ss;
                 ss << strMsg << " code " << itostr(ccode) << ": " << strReason;
 
-                if (strMsg == "block" || strMsg == "tx")
+                if (strMsg == NetMsgType::BLOCK || strMsg == NetMsgType::TX)
                 {
                     uint256 hash;
                     vRecv >> hash;
@@ -5287,7 +5287,7 @@ bool ProcessMessages(CNode* pfrom)
         }
         catch (const std::ios_base::failure& e)
         {
-            pfrom->PushMessage("reject", strCommand, REJECT_MALFORMED, string("error parsing message"));
+            pfrom->PushMessage(NetMsgType::REJECT, strCommand, REJECT_MALFORMED, string("error parsing message"));
             if (strstr(e.what(), "end of data"))
             {
                 // Allow exceptions from under-length message on vRecv
@@ -5355,11 +5355,11 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
             pto->nPingUsecStart = GetTimeMicros();
             if (pto->nVersion > BIP0031_VERSION) {
                 pto->nPingNonceSent = nonce;
-                pto->PushMessage("ping", nonce);
+                pto->PushMessage(NetMsgType::PING, nonce);
             } else {
                 // Peer is too old to support ping command with nonce, pong will never arrive.
                 pto->nPingNonceSent = 0;
-                pto->PushMessage("ping");
+                pto->PushMessage(NetMsgType::PING);
             }
         }
 
@@ -5401,14 +5401,14 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
                     // receiver rejects addr messages larger than 1000
                     if (vAddr.size() >= 1000)
                     {
-                        pto->PushMessage("addr", vAddr);
+                        pto->PushMessage(NetMsgType::ADDR, vAddr);
                         vAddr.clear();
                     }
                 }
             }
             pto->vAddrToSend.clear();
             if (!vAddr.empty())
-                pto->PushMessage("addr", vAddr);
+                pto->PushMessage(NetMsgType::ADDR, vAddr);
         }
 
         CNodeState &state = *State(pto->GetId());
@@ -5428,7 +5428,7 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
         }
 
         BOOST_FOREACH(const CBlockReject& reject, state.rejects)
-            pto->PushMessage("reject", (string)"block", reject.chRejectCode, reject.strRejectReason, reject.hashBlock);
+            pto->PushMessage(NetMsgType::REJECT, (string)NetMsgType::BLOCK, reject.chRejectCode, reject.strRejectReason, reject.hashBlock);
         state.rejects.clear();
 
         // Start block sync
@@ -5451,7 +5451,7 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
                 if (pindexStart->pprev)
                     pindexStart = pindexStart->pprev;
                 LogPrint("net", "initial getheaders (%d) to peer=%d (startheight:%d)\n", pindexStart->nHeight, pto->id, pto->nStartingHeight);
-                pto->PushMessage("getheaders", chainActive.GetLocator(pindexStart), uint256());
+                pto->PushMessage(NetMsgType::GETHEADERS, chainActive.GetLocator(pindexStart), uint256());
             }
         }
 
@@ -5551,7 +5551,7 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
                     LogPrint("net", "%s: sending header %s to peer=%d\n", __func__,
                             vHeaders.front().GetHash().ToString(), pto->id);
                 }
-                pto->PushMessage("headers", vHeaders);
+                pto->PushMessage(NetMsgType::HEADERS, vHeaders);
                 state.pindexBestHeaderSent = pBestIndex;
             }
             pto->vBlockHashesToAnnounce.clear();
@@ -5594,14 +5594,14 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
                 vInv.push_back(inv);
                 if (vInv.size() >= 1000)
                 {
-                    pto->PushMessage("inv", vInv);
+                    pto->PushMessage(NetMsgType::INV, vInv);
                     vInv.clear();
                 }
             }
             pto->vInventoryToSend = vInvWait;
         }
         if (!vInv.empty())
-            pto->PushMessage("inv", vInv);
+            pto->PushMessage(NetMsgType::INV, vInv);
 
         // Detect whether we're stalling
         int64_t nNow = GetTimeMicros();
@@ -5670,7 +5670,7 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
                 vGetData.push_back(inv);
                 if (vGetData.size() >= 1000)
                 {
-                    pto->PushMessage("getdata", vGetData);
+                    pto->PushMessage(NetMsgType::GETDATA, vGetData);
                     vGetData.clear();
                 }
             } else {
@@ -5680,7 +5680,7 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
             pto->mapAskFor.erase(pto->mapAskFor.begin());
         }
         if (!vGetData.empty())
-            pto->PushMessage("getdata", vGetData);
+            pto->PushMessage(NetMsgType::GETDATA, vGetData);
 
     }
     return true;
diff --git a/src/net.cpp b/src/net.cpp
index a8aa97feec..e4db60aec4 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -459,7 +459,7 @@ void CNode::PushVersion()
         LogPrint("net", "send version message: version %d, blocks=%d, us=%s, them=%s, peer=%d\n", PROTOCOL_VERSION, nBestHeight, addrMe.ToString(), addrYou.ToString(), id);
     else
         LogPrint("net", "send version message: version %d, blocks=%d, us=%s, peer=%d\n", PROTOCOL_VERSION, nBestHeight, addrMe.ToString(), id);
-    PushMessage("version", PROTOCOL_VERSION, nLocalServices, nTime, addrYou, addrMe,
+    PushMessage(NetMsgType::VERSION, PROTOCOL_VERSION, nLocalServices, nTime, addrYou, addrMe,
                 nLocalHostNonce, strSubVersion, nBestHeight, !GetBoolArg("-blocksonly", DEFAULT_BLOCKSONLY));
 }
 
diff --git a/src/protocol.cpp b/src/protocol.cpp
index dd855aa33a..5d3ae87de8 100644
--- a/src/protocol.cpp
+++ b/src/protocol.cpp
@@ -12,13 +12,67 @@
 # include <arpa/inet.h>
 #endif
 
+namespace NetMsgType {
+const char *VERSION="version";
+const char *VERACK="verack";
+const char *ADDR="addr";
+const char *INV="inv";
+const char *GETDATA="getdata";
+const char *MERKLEBLOCK="merkleblock";
+const char *GETBLOCKS="getblocks";
+const char *GETHEADERS="getheaders";
+const char *TX="tx";
+const char *HEADERS="headers";
+const char *BLOCK="block";
+const char *GETADDR="getaddr";
+const char *MEMPOOL="mempool";
+const char *PING="ping";
+const char *PONG="pong";
+const char *ALERT="alert";
+const char *NOTFOUND="notfound";
+const char *FILTERLOAD="filterload";
+const char *FILTERADD="filteradd";
+const char *FILTERCLEAR="filterclear";
+const char *REJECT="reject";
+const char *SENDHEADERS="sendheaders";
+};
+
 static const char* ppszTypeName[] =
 {
-    "ERROR",
-    "tx",
-    "block",
-    "filtered block"
+    "ERROR", // Should never occur
+    NetMsgType::TX,
+    NetMsgType::BLOCK,
+    "filtered block" // Should never occur
+};
+
+/** All known message types. Keep this in the same order as the list of
+ * messages above and in protocol.h.
+ */
+const static std::string allNetMessageTypes[] = {
+    NetMsgType::VERSION,
+    NetMsgType::VERACK,
+    NetMsgType::ADDR,
+    NetMsgType::INV,
+    NetMsgType::GETDATA,
+    NetMsgType::MERKLEBLOCK,
+    NetMsgType::GETBLOCKS,
+    NetMsgType::GETHEADERS,
+    NetMsgType::TX,
+    NetMsgType::HEADERS,
+    NetMsgType::BLOCK,
+    NetMsgType::GETADDR,
+    NetMsgType::MEMPOOL,
+    NetMsgType::PING,
+    NetMsgType::PONG,
+    NetMsgType::ALERT,
+    NetMsgType::NOTFOUND,
+    NetMsgType::FILTERLOAD,
+    NetMsgType::FILTERADD,
+    NetMsgType::FILTERCLEAR,
+    NetMsgType::REJECT,
+    NetMsgType::SENDHEADERS
 };
+const static std::vector<std::string> allNetMessageTypesVec(allNetMessageTypes, allNetMessageTypes+ARRAYLEN(allNetMessageTypes));
 
 CMessageHeader::CMessageHeader(const MessageStartChars& pchMessageStartIn)
 {
@@ -140,3 +194,8 @@ std::string CInv::ToString() const
 {
     return strprintf("%s %s", GetCommand(), hash.ToString());
 }
+
+const std::vector<std::string> &getAllNetMessageTypes()
+{
+    return allNetMessageTypesVec;
+}
diff --git a/src/protocol.h b/src/protocol.h
index 50aeaf44ba..b84c78baca 100644
--- a/src/protocol.h
+++ b/src/protocol.h
@@ -65,6 +65,165 @@ public:
     unsigned int nChecksum;
 };
 
+/**
+ * Bitcoin protocol message types. When adding new message types, don't forget
+ * to update allNetMessageTypes in protocol.cpp.
+ */
+namespace NetMsgType {
+
+/**
+ * The version message provides information about the transmitting node to the
+ * receiving node at the beginning of a connection.
+ * @see https://bitcoin.org/en/developer-reference#version
+ */
+extern const char *VERSION;
+/**
+ * The verack message acknowledges a previously-received version message,
+ * informing the connecting node that it can begin to send other messages.
+ * @see https://bitcoin.org/en/developer-reference#verack
+ */
+extern const char *VERACK;
+/**
+ * The addr (IP address) message relays connection information for peers on the
+ * network.
+ * @see https://bitcoin.org/en/developer-reference#addr
+ */
+extern const char *ADDR;
+/**
+ * The inv message (inventory message) transmits one or more inventories of
+ * objects known to the transmitting peer.
+ * @see https://bitcoin.org/en/developer-reference#inv
+ */
+extern const char *INV;
+/**
+ * The getdata message requests one or more data objects from another node.
+ * @see https://bitcoin.org/en/developer-reference#getdata
+ */
+extern const char *GETDATA;
+/**
+ * The merkleblock message is a reply to a getdata message which requested a
+ * block using the inventory type MSG_MERKLEBLOCK.
+ * @since protocol version 70001 as described by BIP37.
+ * @see https://bitcoin.org/en/developer-reference#merkleblock
+ */
+extern const char *MERKLEBLOCK;
+/**
+ * The getblocks message requests an inv message that provides block header
+ * hashes starting from a particular point in the block chain.
+ * @see https://bitcoin.org/en/developer-reference#getblocks
+ */
+extern const char *GETBLOCKS;
+/**
+ * The getheaders message requests a headers message that provides block
+ * headers starting from a particular point in the block chain.
+ * @since protocol version 31800.
+ * @see https://bitcoin.org/en/developer-reference#getheaders
+ */
+extern const char *GETHEADERS;
+/**
+ * The tx message transmits a single transaction.
+ * @see https://bitcoin.org/en/developer-reference#tx
+ */
+extern const char *TX;
+/**
+ * The headers message sends one or more block headers to a node which
+ * previously requested certain headers with a getheaders message.
+ * @since protocol version 31800.
+ * @see https://bitcoin.org/en/developer-reference#headers
+ */
+extern const char *HEADERS;
+/**
+ * The block message transmits a single serialized block.
+ * @see https://bitcoin.org/en/developer-reference#block
+ */
+extern const char *BLOCK;
+/**
+ * The getaddr message requests an addr message from the receiving node,
+ * preferably one with lots of IP addresses of other receiving nodes.
+ * @see https://bitcoin.org/en/developer-reference#getaddr
+ */
+extern const char *GETADDR;
+/**
+ * The mempool message requests the TXIDs of transactions that the receiving
+ * node has verified as valid but which have not yet appeared in a block.
+ * @since protocol version 60002.
+ * @see https://bitcoin.org/en/developer-reference#mempool
+ */
+extern const char *MEMPOOL;
+/**
+ * The ping message is sent periodically to help confirm that the receiving
+ * peer is still connected.
+ * @see https://bitcoin.org/en/developer-reference#ping
+ */
+extern const char *PING;
+/**
+ * The pong message replies to a ping message, proving to the pinging node that
+ * the ponging node is still alive.
+ * @since protocol version 60001 as described by BIP31.
+ * @see https://bitcoin.org/en/developer-reference#pong
+ */
+extern const char *PONG;
+/**
+ * The alert message warns nodes of problems that may affect them or the rest
+ * of the network.
+ * @since protocol version 311.
+ * @see https://bitcoin.org/en/developer-reference#alert
+ */
+extern const char *ALERT;
+/**
+ * The notfound message is a reply to a getdata message which requested an
+ * object the receiving node does not have available for relay.
+ * @ince protocol version 70001.
+ * @see https://bitcoin.org/en/developer-reference#notfound
+ */
+extern const char *NOTFOUND;
+/**
+ * The filterload message tells the receiving peer to filter all relayed
+ * transactions and requested merkle blocks through the provided filter.
+ * @since protocol version 70001 as described by BIP37.
+ *   Only available with service bit NODE_BLOOM since protocol version
+ *   70011 as described by BIP111.
+ * @see https://bitcoin.org/en/developer-reference#filterload
+ */
+extern const char *FILTERLOAD;
+/**
+ * The filteradd message tells the receiving peer to add a single element to a
+ * previously-set bloom filter, such as a new public key.
+ * @since protocol version 70001 as described by BIP37.
+ *   Only available with service bit NODE_BLOOM since protocol version
+ *   70011 as described by BIP111.
+ * @see https://bitcoin.org/en/developer-reference#filteradd
+ */
+extern const char *FILTERADD;
+/**
+ * The filterclear message tells the receiving peer to remove a previously-set
+ * bloom filter.
+ * @since protocol version 70001 as described by BIP37.
+ *   Only available with service bit NODE_BLOOM since protocol version
+ *   70011 as described by BIP111.
+ * @see https://bitcoin.org/en/developer-reference#filterclear
+ */
+extern const char *FILTERCLEAR;
+/**
+ * The reject message informs the receiving node that one of its previous
+ * messages has been rejected.
+ * @since protocol version 70002 as described by BIP61.
+ * @see https://bitcoin.org/en/developer-reference#reject
+ */
+extern const char *REJECT;
+/**
+ * Indicates that a node prefers to receive new block announcements via a
+ * "headers" message rather than an "inv".
+ * @since protocol version 70012 as described by BIP130.
+ * @see https://bitcoin.org/en/developer-reference#sendheaders
+ */
+extern const char *SENDHEADERS;
+
+};
+
+/* Get a vector of all valid message types (see above) */
+const std::vector<std::string> &getAllNetMessageTypes();
+
 /** nServices flags */
 enum {
     // NODE_NETWORK means that the node is capable of serving the block chain. It is currently