Restore DNS Round Robin Behavior (#134)

connection.go

@@ -40,6 +40,7 @@ import (
 	"database/sql/driver"
 	"encoding/binary"
 	"fmt"
+	"math/rand"
 	"net"
 	"net/url"
 	"os"
@@ -277,18 +278,39 @@ func (v *connection) establishSocketConnection() (net.Conn, error) {
 	// Failover: loop to try all hosts in the list
 	err_msg := ""
 	for i := 0; i < len(v.connHostsList); i++ {
-		// net.Dial will resolve the host to multiple IP addresses,
-		// and try each IP address in order until one succeeds.
-		conn, err := net.Dial("tcp", v.connHostsList[i])
+		host, port, err := net.SplitHostPort(v.connHostsList[i])
 		if err != nil {
-			err_msg += fmt.Sprintf("\n  '%s': %s", v.connHostsList[i], err.Error())
-		} else {
-			if len(err_msg) != 0 {
-				connectionLogger.Debug("Failed to establish a connection to %s", err_msg)
+			// no host-port pair identified
+			err_msg += fmt.Sprintf("\n  '%s': %s", host, err.Error())
+			continue
+		}
+		ips, err := net.LookupIP(host)
+		if err != nil {
+			// failed to resolve any IPs from host
+			err_msg += fmt.Sprintf("\n  '%s': %s", host, err.Error())
+			continue
+		}
+		r := rand.New(rand.NewSource(time.Now().Unix()))
+		for _, j := range r.Perm(len(ips)) {
+			// j comes from random permutation of indexes - ips[j] will access a random resolved ip
+			ip := net.IP.String(ips[j])
+			if strings.HasPrefix(ip, "::") {
+				//handle IPV6 shorthand
+				ip = "[" + ip + "]"
 			}
-			connectionLogger.Debug("Established socket connection to %s", v.connHostsList[i])
-			v.connHostsList = v.connHostsList[i:]
-			return conn, err
+			addrString := ip + ":" + string(port)
+		    conn, err := net.Dial("tcp", addrString)
+
+		    if err != nil {
+		    	err_msg += fmt.Sprintf("\n  '%s': %s", v.connHostsList[i], err.Error())
+		    } else {
+		    	if len(err_msg) != 0 {
+		    		connectionLogger.Debug("Failed to establish a connection to %s", err_msg)
+		    	}
+		    	connectionLogger.Debug("Established socket connection to %s", addrString)
+		    	v.connHostsList = v.connHostsList[i:]
+		    	return conn, err
+		    }
 		}
 	}
 	// All of the hosts failed

driver_test.go

@@ -60,6 +60,7 @@ var (
 	ctx                   context.Context
 )
 
+// The following assert functions compensate for Go having no native assertions
 func assertTrue(t *testing.T, v bool) {
 	t.Helper()