Include a list of connections in the HTTP-TPC performance marker.

src/XrdTpc/XrdTpcMultistream.cc

@@ -264,7 +264,7 @@ int TPCHandler::RunCurlWithStreamsImpl(XrdHttpExtReq &req, State &state,
         time_t now = time(NULL);
         time_t next_marker = last_marker + m_marker_period;
         if (now >= next_marker) {
-            if (SendPerfMarker(req, current_offset)) {
+            if (SendPerfMarker(req, handles, current_offset)) {
                 return -1;
             }
             last_marker = now;

src/XrdTpc/XrdTpcState.cc

@@ -253,3 +253,27 @@ bool State::Finalize()
     return m_stream->Finalize();
 }
 
+std::string State::GetConnectionDescription()
+{
+    char *curl_ip = NULL;
+    CURLcode rc = curl_easy_getinfo(m_curl, CURLINFO_PRIMARY_IP, &curl_ip);
+    if ((rc != CURLE_OK) || !curl_ip) {
+        return "";
+    }
+    long curl_port = 0;
+    rc = curl_easy_getinfo(m_curl, CURLINFO_PRIMARY_PORT, &curl_port);
+    if ((rc != CURLE_OK) || !curl_port) {
+        return "";
+    }
+    std::stringstream ss;
+    // libcurl returns IPv6 addresses of the form:
+    //    2600:900:6:1301:5054:ff:fe0b:9cba:8000
+    // However the HTTP-TPC spec says to use the form
+    //   [2600:900:6:1301:5054:ff:fe0b:9cba:8000]
+    // Hence, we add '[' and ']' whenever a ':' is seen.
+    if (NULL == strchr(curl_ip, ':'))
+        ss << "tcp:" << curl_ip << ":" << curl_port;
+    else
+        ss << "tcp:[" << curl_ip << "]:" << curl_port;
+    return ss.str();
+}

src/XrdTpc/XrdTpcState.hh

@@ -90,6 +90,12 @@ public:
     // not all buffers have been reordered by the underlying stream.
     bool Finalize();
 
+    // Retrieve the description of the remote connection; is of the form:
+    //   tcp:129.93.3.4:1234
+    //   tcp:[2600:900:6:1301:268a:7ff:fef6:a590]:2345
+    // This is meant to facilitate the monitoring via the performance markers.
+    std::string GetConnectionDescription();
+
 private:
     bool InstallHandlers(CURL *curl);
 

src/XrdTpc/XrdTpcTPC.cc

@@ -238,14 +238,61 @@ int TPCHandler::DetermineXferSize(CURL *curl, XrdHttpExtReq &req, State &state,
     return 0;
 }
 
-int TPCHandler::SendPerfMarker(XrdHttpExtReq &req, off_t bytes_transferred) {
+int TPCHandler::SendPerfMarker(XrdHttpExtReq &req, TPC::State &state) {
+    std::stringstream ss;
+    const std::string crlf = "\n";
+    ss << "Perf Marker" << crlf;
+    ss << "Timestamp: " << time(NULL) << crlf;
+    ss << "Stripe Index: 0" << crlf;
+    ss << "Stripe Bytes Transferred: " << state.BytesTransferred() << crlf;
+    ss << "Total Stripe Count: 1" << crlf;
+    // Include the TCP connection associated with this transfer; used by
+    // the TPC client for monitoring purposes.
+    std::string desc = state.GetConnectionDescription();
+    if (!desc.empty())
+        ss << "RemoteConnections: " << desc << crlf;
+    ss << "End" << crlf;
+
+    return req.ChunkResp(ss.str().c_str(), 0);
+}
+
+int TPCHandler::SendPerfMarker(XrdHttpExtReq &req, std::vector<State*> &state,
+    off_t bytes_transferred)
+{
+    // The 'performance marker' format is largely derived from how GridFTP works
+    // (e.g., the concept of `Stripe` is not quite so relevant here).  See:
+    //    https://twiki.cern.ch/twiki/bin/view/LCG/HttpTpcTechnical
+    // Example marker:
+    //    Perf Marker\n
+    //    Timestamp: 1537788010\n
+    //    Stripe Index: 0\n
+    //    Stripe Bytes Transferred: 238745\n
+    //    Total Stripe Count: 1\n
+    //    RemoteConnections: tcp:129.93.3.4:1234,tcp:[2600:900:6:1301:268a:7ff:fef6:a590]:2345\n
+    //    End\n
+    //
     std::stringstream ss;
     const std::string crlf = "\n";
     ss << "Perf Marker" << crlf;
     ss << "Timestamp: " << time(NULL) << crlf;
     ss << "Stripe Index: 0" << crlf;
     ss << "Stripe Bytes Transferred: " << bytes_transferred << crlf;
     ss << "Total Stripe Count: 1" << crlf;
+    // Build a list of TCP connections associated with this transfer; used by
+    // the TPC client for monitoring purposes.
+    bool first = true;
+    std::stringstream ss2;
+    for (std::vector<State*>::const_iterator iter = state.begin();
+        iter != state.end(); iter++)
+    {
+        std::string desc = (*iter)->GetConnectionDescription();
+        if (!desc.empty()) {
+            ss2 << (first ? "" : ",") << desc;
+            first = false;
+        }
+    }
+    if (!first)
+        ss << "RemoteConnections: " << ss2.str() << crlf;
     ss << "End" << crlf;
 
     return req.ChunkResp(ss.str().c_str(), 0);
@@ -291,7 +338,7 @@ int TPCHandler::RunCurlWithUpdates(CURL *curl, XrdHttpExtReq &req, State &state,
         time_t now = time(NULL);
         time_t next_marker = last_marker + m_marker_period;
         if (now >= next_marker) {
-            if (SendPerfMarker(req, state.BytesTransferred())) {
+            if (SendPerfMarker(req, state)) {
                 curl_multi_remove_handle(multi_handle, curl);
                 curl_easy_cleanup(curl);
                 curl_multi_cleanup(multi_handle);

src/XrdTpc/XrdTpcTPC.hh

@@ -42,7 +42,13 @@ private:
     int DetermineXferSize(CURL *curl, XrdHttpExtReq &req, TPC::State &state,
                           bool &success);
 
-    int SendPerfMarker(XrdHttpExtReq &req, off_t bytes_transferred);
+    // Send a 'performance marker' back to the TPC client, informing it of our
+    // progress.  The TPC client will use this information to determine whether
+    // the transfer is making sufficient progress and/or other monitoring info
+    // (such as whether the transfer is happening over IPv4, IPv6, or both).
+    int SendPerfMarker(XrdHttpExtReq &req, TPC::State &state);
+    int SendPerfMarker(XrdHttpExtReq &req, std::vector<State*> &state,
+        off_t bytes_transferred);
 
     // Perform the libcurl transfer, periodically sending back chunked updates.
     int RunCurlWithUpdates(CURL *curl, XrdHttpExtReq &req, TPC::State &state,