Reuse ifmap xmpp message string for tracing

Pass a reference to std:string to SendUpdate so that it can be passed
on to XmppChannel::Send and then on to XmppConnection::Send, which can
now use the provided string (changed via bug number 1607132) instead
of constructing a new one from the data pointer.

Change-Id: If94a1cf63ab07a9ba9703bc5e54a6e177835217b
Partial-Bug: 1602347

src/ifmap/ifmap_encoder.cc

@@ -112,8 +112,3 @@ void IFMapMessage::Reset() {
     op_type_ = NONE;
     Open();
 }
-
-const char * IFMapMessage::c_str() const {
-    assert(!str_.empty());
-    return str_.c_str();
-}

src/ifmap/ifmap_encoder.h

@@ -25,7 +25,7 @@ class IFMapMessage {
     bool IsEmpty();
     void Reset();
 
-    const char *c_str() const;
+    const std::string &get_string() const { return str_; }
 
 private:
     enum Op {

src/ifmap/ifmap_update_sender.cc

@@ -262,7 +262,7 @@ void IFMapUpdateSender::SendUpdate(BitSet send_set, BitSet *blocked_set) {
         message_->Close();
 
         // Send the string version of the message to the client.
-        send_result = client->SendUpdate(message_->c_str());
+        send_result = client->SendUpdate(message_->get_string());
 
         // Keep track of all the clients whose buffers are full. 
         if (!send_result) {

src/ifmap/ifmap_xmpp.cc

@@ -113,7 +113,8 @@ IFMapXmppChannel::IFMapSender::IFMapSender(IFMapXmppChannel *parent)
 
 bool IFMapXmppChannel::IFMapSender::SendUpdate(const std::string &msg) {
     bool sent = parent_->channel_->Send(
-        (const uint8_t *)msg.data(), msg.size(), xmps::CONFIG,
+        reinterpret_cast<const uint8_t *>(msg.data()), msg.size(), &msg,
+        xmps::CONFIG,
         boost::bind(&IFMapXmppChannel::WriteReadyCb, parent_, _1));
 
     if (sent) {