open-consul/lib/freeport/freeport.go

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// 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 = 1500
// 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
// once is used to do the initialization on the first call to retrieve free
// ports
once sync.Once
// port is the last allocated port.
port int
)
// initialize is used to initialize freeport.
func initialize() {
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")
}
// Reserve a port block
once.Do(initialize)
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
}