move to consul freeport implementation

vendor/github.com/hashicorp/consul/lib/freeport/freeport.go

@@ -0,0 +1,131 @@
+// Package freeport provides a helper for allocating free ports across multiple
+// processes on the same machine.
+package freeport
+
+import (
+	"fmt"
+	"math/rand"
+	"net"
+	"sync"
+	"time"
+
+	"github.com/mitchellh/go-testing-interface"
+)
+
+const (
+	// blockSize is the size of the allocated port block. ports are given out
+	// consecutively from that block with roll-over for the lifetime of the
+	// application/test run.
+	blockSize = 500
+
+	// maxBlocks is the number of available port blocks.
+	// lowPort + maxBlocks * blockSize must be less than 65535.
+	maxBlocks = 30
+
+	// lowPort is the lowest port number that should be used.
+	lowPort = 10000
+
+	// attempts is how often we try to allocate a port block
+	// before giving up.
+	attempts = 10
+)
+
+var (
+	// firstPort is the first port of the allocated block.
+	firstPort int
+
+	// lockLn is the system-wide mutex for the port block.
+	lockLn net.Listener
+
+	// mu guards nextPort
+	mu sync.Mutex
+
+	// port is the last allocated port.
+	port int
+)
+
+func init() {
+	if lowPort+maxBlocks*blockSize > 65535 {
+		panic("freeport: block size too big or too many blocks requested")
+	}
+
+	rand.Seed(time.Now().UnixNano())
+	firstPort, lockLn = alloc()
+}
+
+// alloc reserves a port block for exclusive use for the lifetime of the
+// application. lockLn serves as a system-wide mutex for the port block and is
+// implemented as a TCP listener which is bound to the firstPort and which will
+// be automatically released when the application terminates.
+func alloc() (int, net.Listener) {
+	for i := 0; i < attempts; i++ {
+		block := int(rand.Int31n(int32(maxBlocks)))
+		firstPort := lowPort + block*blockSize
+		ln, err := net.ListenTCP("tcp", tcpAddr("127.0.0.1", firstPort))
+		if err != nil {
+			continue
+		}
+		// log.Printf("[DEBUG] freeport: allocated port block %d (%d-%d)", block, firstPort, firstPort+blockSize-1)
+		return firstPort, ln
+	}
+	panic("freeport: cannot allocate port block")
+}
+
+func tcpAddr(ip string, port int) *net.TCPAddr {
+	return &net.TCPAddr{IP: net.ParseIP(ip), Port: port}
+}
+
+// Get wraps the Free function and panics on any failure retrieving ports.
+func Get(n int) (ports []int) {
+	ports, err := Free(n)
+	if err != nil {
+		panic(err)
+	}
+
+	return ports
+}
+
+// GetT is suitable for use when retrieving unused ports in tests. If there is
+// an error retrieving free ports, the test will be failed.
+func GetT(t testing.T, n int) (ports []int) {
+	ports, err := Free(n)
+	if err != nil {
+		t.Fatalf("Failed retrieving free port: %v", err)
+	}
+
+	return ports
+}
+
+// Free returns a list of free ports from the allocated port block. It is safe
+// to call this method concurrently. Ports have been tested to be available on
+// 127.0.0.1 TCP but there is no guarantee that they will remain free in the
+// future.
+func Free(n int) (ports []int, err error) {
+	mu.Lock()
+	defer mu.Unlock()
+
+	if n > blockSize-1 {
+		return nil, fmt.Errorf("freeport: block size too small")
+	}
+
+	for len(ports) < n {
+		port++
+
+		// roll-over the port
+		if port < firstPort+1 || port >= firstPort+blockSize {
+			port = firstPort + 1
+		}
+
+		// if the port is in use then skip it
+		ln, err := net.ListenTCP("tcp", tcpAddr("127.0.0.1", port))
+		if err != nil {
+			// log.Println("[DEBUG] freeport: port already in use: ", port)
+			continue
+		}
+		ln.Close()
+
+		ports = append(ports, port)
+	}
+	// log.Println("[DEBUG] freeport: free ports:", ports)
+	return ports, nil
+}