MXS-2015: Remove buffer iterator

The iterator to the buffer isn't really needed as the beginning of the
buffer can be used instead. This should make the code more robust. Changed
the internal buffer from a vector to a deque as the latter is more
appropriate for insertion on one end and consumption on the other.

connectors/cdc-connector/cdc_connector.cpp

@@ -186,7 +186,6 @@ Connection::Connection(const std::string& address,
     m_timeout(timeout),
     m_connected(false)
 {
-    m_buf_ptr = m_buffer.begin();
 }
 
 Connection::~Connection()
@@ -283,8 +282,9 @@ bool Connection::connect(const std::string& table, const std::string& gtid)
                 }
                 else
                 {
-                    m_error += ". Data received so far: ";
+                    m_error += ". Data received so far: '";
                     std::copy(m_buffer.begin(), m_buffer.end(), std::back_inserter(m_error));
+                    m_error += "'";
                 }
             }
         }
@@ -545,11 +545,13 @@ bool Connection::read_row(std::string& dest)
     {
         if (!m_buffer.empty())
         {
-            std::vector<char>::iterator it = std::find(m_buf_ptr, m_buffer.end(), '\n');
+            std::deque<char>::iterator it = std::find(m_buffer.begin(), m_buffer.end(), '\n');
+
             if (it != m_buffer.end())
             {
-                dest.assign(m_buf_ptr, it);
-                m_buf_ptr = it + 1;
+                dest.assign(m_buffer.begin(), it);
+                m_buffer.erase(m_buffer.begin(), std::next(it));
+                assert(m_buffer.empty() || m_buffer[0] != '\n');
                 break;
             }
         }
@@ -572,22 +574,14 @@ bool Connection::read_row(std::string& dest)
             break;
         }
 
-        if (!m_connected)
-        {
-            // This is here to work around a missing newline in MaxScale error messages
-            buf[rc] = '\0';
-
-            if (is_error(buf))
-            {
-                rval = false;
-                break;
-            }
-        }
-
-        m_buffer.erase(m_buffer.begin(), m_buf_ptr);
         assert(std::find(m_buffer.begin(), m_buffer.end(), '\n') == m_buffer.end());
-        m_buffer.insert(m_buffer.end(), buf, buf + rc);
-        m_buf_ptr = m_buffer.begin();
+        std::copy(buf, buf + rc, std::back_inserter(m_buffer));
+
+        if (is_error(&m_buffer[0]))
+        {
+            rval = false;
+            break;
+        }
     }
 
     if (is_error(dest.c_str()))

connectors/cdc-connector/cdc_connector.h

@@ -21,6 +21,7 @@
 #include <string>
 #include <tr1/memory>
 #include <vector>
+#include <deque>
 #include <map>
 #include <algorithm>
 #include <jansson.h>
@@ -137,8 +138,7 @@ private:
     SValueVector m_keys;
     SValueVector m_types;
     int m_timeout;
-    std::vector<char> m_buffer;
-    std::vector<char>::iterator m_buf_ptr;
+    std::deque<char> m_buffer;
     SRow m_first_row;
     bool m_connected;