Add option to select an IP randomly instead of using the order provided by getaddrinfo, which is proximity based.

include/amqpcpp/linux_tcp/tcpconnection.h

@@ -192,8 +192,9 @@ public:
      *  Constructor
      *  @param  handler         User implemented handler object
      *  @param  hostname        The address to connect to
+     *  @param  random          Randomly select one of the IP addresses that belong to the hostname
      */
-    TcpConnection(TcpHandler *handler, const Address &address);
+    TcpConnection(TcpHandler *handler, const Address &address, bool random = false);
     
     /**
      *  No copying

src/linux_tcp/addressinfo.h

@@ -1,12 +1,17 @@
 /**
  *  AddressInfo.h
  *
- *  Utility wrapper arround "getAddressInfo()"
+ *  Utility wrapper around "getAddressInfo()"
  *
  *  @author Emiel Bruijntjes <emiel.bruijntjes@copernica.com>
  *  @copyright 2015 Copernica BV
  */
 
+/**
+ *  Dependencies
+ */
+#include <sys/time.h>
+
 /**
  *  Include guard
  */
@@ -35,8 +40,9 @@ public:
      *  Constructor
      *  @param  hostname
      *  @param  port
+     *  @param  randomOrder
      */
-    AddressInfo(const char *hostname, uint16_t port = 5672)
+    AddressInfo(const char *hostname, uint16_t port = 5672, bool randomOrder = false)
     {
         // store portnumber in buffer
         auto portnumber = std::to_string(port);
@@ -63,6 +69,25 @@ public:
             // store in vector
             _v.push_back(current);
         }
+
+        // Do we want to have a random order of the addresses?
+        // This may be useful since getaddrinfo is sorting the addresses on proximity
+        // (e.g. https://lists.debian.org/debian-glibc/2007/09/msg00347.html),
+        // which may break loadbalancing..
+        if (randomOrder)
+        {
+            // We need to seed the random number generator. Normally time is taken
+            // for this. Since we want to have randomness within a second we use
+            // more precision via timeval
+            struct timeval time; 
+            gettimeofday(&time, nullptr);
+
+            // We seed with the precision of miliseconds. 
+            srand((time.tv_sec * 1000) + (time.tv_usec / 1000));  
+
+            // shuffle the vector.    
+            std::random_shuffle(_v.begin(), _v.end());
+        }
     }
 
     /**
@@ -99,4 +124,3 @@ public:
  *  End of namespace
  */
 }
-

src/linux_tcp/tcpconnection.cpp

@@ -23,10 +23,11 @@ namespace AMQP {
  *  Constructor
  *  @param  handler         User implemented handler object
  *  @param  hostname        The address to connect to
+ *  @param  random          Randomly select one of the IP addresses that belong to the hostname
  */
-TcpConnection::TcpConnection(TcpHandler *handler, const Address &address) :
+TcpConnection::TcpConnection(TcpHandler *handler, const Address &address, bool random) :
     _handler(handler),
-    _state(new TcpResolver(this, address.hostname(), address.port(), address.secure(), address.option("connectTimeout", 5))),
+    _state(new TcpResolver(this, address.hostname(), address.port(), address.secure(), address.option("connectTimeout", 5), random)),
     _connection(this, address.login(), address.vhost()) 
 {
     // tell the handler
@@ -286,4 +287,3 @@ void TcpConnection::onLost(TcpState *state)
  *  End of namespace
  */
 }
-

src/linux_tcp/tcpresolver.h

@@ -85,6 +85,12 @@ private:
      */
     std::thread _thread;
 
+    /**
+     *  Do we want to have random ordering
+     *  @var bool
+     */
+    bool _random;
+
 
     /**
      *  Run the thread
@@ -98,7 +104,7 @@ private:
             if (_secure && !OpenSSL::valid()) throw std::runtime_error("Secure connection cannot be established: libssl.so cannot be loaded");
             
             // get address info
-            AddressInfo addresses(_hostname.data(), _port);
+            AddressInfo addresses(_hostname.data(), _port, _random);
     
             // the pollfd structure, needed for poll()
             pollfd fd;
@@ -188,13 +194,15 @@ public:
      *  @param  portnumber  The portnumber for the lookup
      *  @param  secure      Do we need a secure tls connection when ready?
      *  @param  timeout     timeout per connection attempt
+     *  @param  random      Do we want to have random oredering of the address of the host to connect to
      */
-    TcpResolver(TcpParent *parent, std::string hostname, uint16_t port, bool secure, int timeout) : 
+    TcpResolver(TcpParent *parent, std::string hostname, uint16_t port, bool secure, int timeout, bool random) : 
         TcpExtState(parent), 
         _hostname(std::move(hostname)),
         _secure(secure),
         _port(port),
-        _timeout(timeout)
+        _timeout(timeout),
+        _random(random)
     {
         // tell the event loop to monitor the filedescriptor of the pipe
         parent->onIdle(this, _pipe.in(), readable);