Improve dynamic port selection

.gitignore

@@ -56,3 +56,5 @@ TODO.md
 .terraform
 *.tfstate*
 rkt-*
+
+.idea/

nomad/structs/network.go

@@ -2,7 +2,6 @@ package structs
 
 import (
 	"fmt"
-	"math/rand"
 	"net"
 	"sync"
 )
@@ -183,6 +182,8 @@ func (idx *NetworkIndex) AssignNetwork(ask *NetworkResource) (out *NetworkResour
 			return
 		}
 
+		used := idx.UsedPorts[ipStr]
+
 		// Check if any of the reserved ports are in use
 		for _, port := range ask.ReservedPorts {
 			// Guard against invalid port
@@ -192,7 +193,6 @@ func (idx *NetworkIndex) AssignNetwork(ask *NetworkResource) (out *NetworkResour
 			}
 
 			// Check if in use
-			used := idx.UsedPorts[ipStr]
 			if used != nil && used.Check(uint(port.Value)) {
 				err = fmt.Errorf("reserved port collision")
 				return
@@ -208,28 +208,19 @@ func (idx *NetworkIndex) AssignNetwork(ask *NetworkResource) (out *NetworkResour
 			DynamicPorts:  ask.DynamicPorts,
 		}
 
-		// Check if we need to generate any ports
-		for i := 0; i < len(ask.DynamicPorts); i++ {
-			attempts := 0
-		PICK:
-			attempts++
-			if attempts > maxRandPortAttempts {
-				err = fmt.Errorf("dynamic port selection failed")
-				return
-			}
+		portRange := PortsFromRange(MinDynamicPort, MaxDynamicPort)
+		usedPorts := PortsFromBitmap(used, 0, maxValidPort-1)
+		availablePorts := portRange.Difference(usedPorts)
+		availablePorts = availablePorts.Difference(ask.ReservedPorts)
+		availablePorts = availablePorts.ShufflePorts()
 
-			randPort := MinDynamicPort + rand.Intn(MaxDynamicPort-MinDynamicPort)
-			used := idx.UsedPorts[ipStr]
-			if used != nil && used.Check(uint(randPort)) {
-				goto PICK
-			}
+		if len(availablePorts) < len(offer.DynamicPorts) {
+			err = fmt.Errorf("dynamic port selection failed - insufficient available ports")
+			return
+		}
 
-			for _, ports := range [][]Port{offer.ReservedPorts, offer.DynamicPorts} {
-				if isPortReserved(ports, randPort) {
-					goto PICK
-				}
-			}
-			offer.DynamicPorts[i].Value = randPort
+		for i := 0; i < len(offer.DynamicPorts); i++ {
+			offer.DynamicPorts[i].Value = availablePorts[i].Value
 		}
 
 		// Stop, we have an offer!
@@ -240,7 +231,6 @@ func (idx *NetworkIndex) AssignNetwork(ask *NetworkResource) (out *NetworkResour
 	return
 }
 
-// IntContains scans an integer slice for a value
 func isPortReserved(haystack []Port, needle int) bool {
 	for _, item := range haystack {
 		if item.Value == needle {

nomad/structs/structs.go

@@ -10,6 +10,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"math/rand"
 	"path/filepath"
 	"reflect"
 	"regexp"
@@ -835,15 +836,87 @@ type Port struct {
 	Value int `mapstructure:"static"`
 }
 
+// implement sort interface for Ports
+type Ports []Port
+
+func (slice Ports) Len() int {
+	return len(slice)
+}
+
+func (slice Ports) Less(i, j int) bool {
+	return slice[i].Value < slice[j].Value
+}
+
+func (slice Ports) Swap(i, j int) {
+	slice[i], slice[j] = slice[j], slice[i]
+}
+
+func (slice Ports) ShufflePorts() Ports {
+	dest := make(Ports, len(slice))
+	perm := rand.Perm(len(slice))
+	for i, v := range perm {
+		dest[v] = slice[i]
+	}
+	return dest
+}
+
+func (minuend Ports) Difference(subtrahend Ports) Ports {
+	makeSet := func(ports Ports) map[int]Port {
+		portMap := make(map[int]Port, len(ports))
+		for _, port := range ports {
+			portMap[port.Value] = port
+		}
+
+		return portMap
+	}
+
+	var results Ports
+
+	minuendSet := makeSet(minuend)
+	subtrahendSet := makeSet(subtrahend)
+
+	for value, port := range minuendSet {
+		if _, ok := subtrahendSet[value]; !ok {
+			results = append(results, port)
+		}
+	}
+
+	return results
+}
+
+func PortsFromRange(i, j int) Ports {
+	dest := make(Ports, j-i)
+	for k := 0; k < j-i; k++ {
+		dest[k] = Port{Label: string(i + k), Value: i + k}
+	}
+	return dest
+}
+
+func PortsFromBitmap(portmap Bitmap, i, j int) Ports {
+	var results Ports
+
+	for k := i; k <= j; k++ {
+		if portmap.Check(uint(k)) {
+			newPort := Port{
+				Label: string(k),
+				Value: k,
+			}
+			results = append(results, newPort)
+		}
+	}
+
+	return results
+}
+
 // NetworkResource is used to represent available network
 // resources
 type NetworkResource struct {
 	Device        string // Name of the device
 	CIDR          string // CIDR block of addresses
 	IP            string // IP address
 	MBits         int    // Throughput
-	ReservedPorts []Port // Reserved ports
-	DynamicPorts  []Port // Dynamically assigned ports
+	ReservedPorts Ports  // Reserved ports
+	DynamicPorts  Ports  // Dynamically assigned ports
 }
 
 // MeetsMinResources returns an error if the resources specified are less than