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tailscale/portlist/poller.go

123 lines
3.4 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
// This file contains the code related to the Poller type and its methods.
// The hot loop to keep efficient is Poller.Run.
package portlist
import (
"errors"
"fmt"
"runtime"
"sync"
"time"
"golang.org/x/exp/slices"
"tailscale.com/envknob"
)
var (
newOSImpl func(includeLocalhost bool) osImpl // if non-nil, constructs a new osImpl.
pollInterval = 5 * time.Second // default; changed by some OS-specific init funcs
debugDisablePortlist = envknob.RegisterBool("TS_DEBUG_DISABLE_PORTLIST")
)
// PollInterval is the recommended OS-specific interval
// to wait between *Poller.Poll method calls.
func PollInterval() time.Duration {
return pollInterval
}
// Poller scans the systems for listening ports periodically and sends
// the results to C.
type Poller struct {
// IncludeLocalhost controls whether services bound to localhost are included.
//
// This field should only be changed before calling Run.
IncludeLocalhost bool
// os, if non-nil, is an OS-specific implementation of the portlist getting
// code. When non-nil, it's responsible for getting the complete list of
// cached ports complete with the process name. That is, when set,
// addProcesses is not used.
// A nil values means we don't have code for getting the list on the current
// operating system.
os osImpl
initOnce sync.Once // guards init of os
initErr error
// scatch is memory for Poller.getList to reuse between calls.
scratch []Port
prev List // most recent data, not aliasing scratch
}
// osImpl is the OS-specific implementation of getting the open listening ports.
type osImpl interface {
Close() error
// AppendListeningPorts appends to base (which must have length 0 but
// optional capacity) the list of listening ports. The Port struct should be
// populated as completely as possible. Another pass will not add anything
// to it.
//
// The appended ports should be in a sorted (or at least stable) order so
// the caller can cheaply detect when there are no changes.
AppendListeningPorts(base []Port) ([]Port, error)
}
func (p *Poller) setPrev(pl List) {
// Make a copy, as the pass in pl slice aliases pl.scratch and we don't want
// that to except to the caller.
p.prev = slices.Clone(pl)
}
// init initializes the Poller by ensuring it has an underlying
// OS implementation and is not turned off by envknob.
func (p *Poller) init() {
switch {
case debugDisablePortlist():
p.initErr = errors.New("portlist disabled by envknob")
case newOSImpl == nil:
p.initErr = errors.New("portlist poller not implemented on " + runtime.GOOS)
default:
p.os = newOSImpl(p.IncludeLocalhost)
}
}
// Close closes the Poller.
func (p *Poller) Close() error {
if p.initErr != nil {
return p.initErr
}
if p.os == nil {
return nil
}
return p.os.Close()
}
// Poll returns the list of listening ports, if changed from
// a previous call as indicated by the changed result.
func (p *Poller) Poll() (ports []Port, changed bool, err error) {
p.initOnce.Do(p.init)
if p.initErr != nil {
return nil, false, fmt.Errorf("error initializing poller: %w", p.initErr)
}
pl, err := p.getList()
if err != nil {
return nil, false, err
}
if pl.equal(p.prev) {
return nil, false, nil
}
p.setPrev(pl)
return p.prev, true, nil
}
func (p *Poller) getList() (List, error) {
var err error
p.scratch, err = p.os.AppendListeningPorts(p.scratch[:0])
return p.scratch, err
}