From 971bb3e901aad5d4f04a651e3e2a75161d3a4e2a Mon Sep 17 00:00:00 2001
From: Josh Lehan <krellan@krellan.net>
Date: Thu, 22 Aug 2013 04:34:33 -0700
Subject: Added ping time measurement. New RPC "ping" command to request ping.
 Implemented "pong" message handler. New "pingtime" field in getpeerinfo, to
 provide results to user. New "pingwait" field, to show pings still in flight,
 to better see newly lagging peers.

---
 src/main.cpp | 85 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 81 insertions(+), 4 deletions(-)

(limited to 'src/main.cpp')

diff --git a/src/main.cpp b/src/main.cpp
index 8df288380a..9cf21a2a1f 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -3861,6 +3861,63 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv)
     }
 
 
+    else if (strCommand == "pong")
+    {
+        int64 pingUsecEnd = GetTimeMicros();
+        uint64 nonce = 0;
+        size_t nAvail = vRecv.in_avail();
+        bool bPingFinished = false;
+        std::string sProblem;
+        
+        if (nAvail >= sizeof(nonce)) {
+            vRecv >> nonce;
+        
+            // Only process pong message if there is an outstanding ping (old ping without nonce should never pong)
+            if (pfrom->nPingNonceSent != 0) {
+                if (nonce == pfrom->nPingNonceSent) {
+                    // Matching pong received, this ping is no longer outstanding
+                    bPingFinished = true;
+                    int64 pingUsecTime = pingUsecEnd - pfrom->nPingUsecStart;
+                    if (pingUsecTime > 0) {
+                        // Successful ping time measurement, replace previous
+                        pfrom->nPingUsecTime = pingUsecTime;
+                    } else {
+                        // This should never happen
+                        sProblem = "Timing mishap";
+                    }
+                } else {
+                    // Nonce mismatches are normal when pings are overlapping
+                    sProblem = "Nonce mismatch";
+                    if (nonce == 0) {
+                        // This is most likely a bug in another implementation somewhere, cancel this ping
+                        bPingFinished = true;
+                        sProblem = "Nonce zero";
+                    }
+                }
+            } else {
+                sProblem = "Unsolicited pong without ping";
+            }
+        } else {
+            // This is most likely a bug in another implementation somewhere, cancel this ping
+            bPingFinished = true;
+            sProblem = "Short payload";
+        }
+        
+        if (!(sProblem.empty())) {
+            LogPrint("net", "pong %s %s: %s, %"PRI64x" expected, %"PRI64x" received, %zu bytes\n"
+                , pfrom->addr.ToString().c_str()
+                , pfrom->strSubVer.c_str()
+                , sProblem.c_str()
+                , pfrom->nPingNonceSent
+                , nonce
+                , nAvail);
+        }
+        if (bPingFinished) {
+            pfrom->nPingNonceSent = 0;
+        }
+    }
+    
+    
     else if (strCommand == "alert")
     {
         CAlert alert;
@@ -4082,14 +4139,34 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
         if (pto->nVersion == 0)
             return true;
 
-        // Keep-alive ping. We send a nonce of zero because we don't use it anywhere
-        // right now.
+        //
+        // Message: ping
+        //
+        bool pingSend = false;
+        if (pto->fPingQueued) {
+            // RPC ping request by user
+            pingSend = true;
+        }
         if (pto->nLastSend && GetTime() - pto->nLastSend > 30 * 60 && pto->vSendMsg.empty()) {
+            // Ping automatically sent as a keepalive
+            pingSend = true;
+        }
+        if (pingSend) {
             uint64 nonce = 0;
-            if (pto->nVersion > BIP0031_VERSION)
+            while (nonce == 0) {
+                RAND_bytes((unsigned char*)&nonce, sizeof(nonce));
+            }
+            pto->nPingNonceSent = nonce;
+            pto->fPingQueued = false;
+            if (pto->nVersion > BIP0031_VERSION) {
+                // Take timestamp as close as possible before transmitting ping
+                pto->nPingUsecStart = GetTimeMicros();
                 pto->PushMessage("ping", nonce);
-            else
+            } else {
+                // Peer is too old to support ping command with nonce, pong will never arrive, disable timing
+                pto->nPingUsecStart = 0;
                 pto->PushMessage("ping");
+            }
         }
 
         // Start block sync
-- 
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