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// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package socktest provides utilities for socket testing.
package socktest
import (
// A Switch represents a callpath point switch for socket system
// calls.
type Switch struct {
once sync.Once
fmu sync.RWMutex
fltab map[FilterType]Filter
smu sync.RWMutex
sotab Sockets
stats stats
func (sw *Switch) init() {
sw.fltab = make(map[FilterType]Filter)
sw.sotab = make(Sockets)
sw.stats = make(stats)
// Stats returns a list of per-cookie socket statistics.
func (sw *Switch) Stats() []Stat {
var st []Stat
for _, s := range sw.stats {
ns := *s
st = append(st, ns)
return st
// Sockets returns mappings of socket descriptor to socket status.
func (sw *Switch) Sockets() Sockets {
tab := make(Sockets, len(sw.sotab))
for i, s := range sw.sotab {
tab[i] = s
return tab
// A Cookie represents a 3-tuple of a socket; address family, socket
// type and protocol number.
type Cookie uint64
// Family returns an address family.
func (c Cookie) Family() int { return int(c >> 48) }
// Type returns a socket type.
func (c Cookie) Type() int { return int(c << 16 >> 32) }
// Protocol returns a protocol number.
func (c Cookie) Protocol() int { return int(c & 0xff) }
func cookie(family, sotype, proto int) Cookie {
return Cookie(family)<<48 | Cookie(sotype)&0xffffffff<<16 | Cookie(proto)&0xff
// A Status represents the status of a socket.
type Status struct {
Cookie Cookie
Err error // error status of socket system call
SocketErr error // error status of socket by SO_ERROR
func (so Status) String() string {
return fmt.Sprintf("(%s, %s, %s): syscallerr=%v socketerr=%v", familyString(so.Cookie.Family()), typeString(so.Cookie.Type()), protocolString(so.Cookie.Protocol()), so.Err, so.SocketErr)
// A Stat represents a per-cookie socket statistics.
type Stat struct {
Family int // address family
Type int // socket type
Protocol int // protocol number
Opened uint64 // number of sockets opened
Connected uint64 // number of sockets connected
Listened uint64 // number of sockets listened
Accepted uint64 // number of sockets accepted
Closed uint64 // number of sockets closed
OpenFailed uint64 // number of sockets open failed
ConnectFailed uint64 // number of sockets connect failed
ListenFailed uint64 // number of sockets listen failed
AcceptFailed uint64 // number of sockets accept failed
CloseFailed uint64 // number of sockets close failed
func (st Stat) String() string {
return fmt.Sprintf("(%s, %s, %s): opened=%d connected=%d listened=%d accepted=%d closed=%d openfailed=%d connectfailed=%d listenfailed=%d acceptfailed=%d closefailed=%d", familyString(st.Family), typeString(st.Type), protocolString(st.Protocol), st.Opened, st.Connected, st.Listened, st.Accepted, st.Closed, st.OpenFailed, st.ConnectFailed, st.ListenFailed, st.AcceptFailed, st.CloseFailed)
type stats map[Cookie]*Stat
func (st stats) getLocked(c Cookie) *Stat {
s, ok := st[c]
if !ok {
s = &Stat{Family: c.Family(), Type: c.Type(), Protocol: c.Protocol()}
st[c] = s
return s
// A FilterType represents a filter type.
type FilterType int
const (
FilterSocket FilterType = iota // for Socket
FilterConnect // for Connect or ConnectEx
FilterListen // for Listen
FilterAccept // for Accept, Accept4 or AcceptEx
FilterGetsockoptInt // for GetsockoptInt
FilterClose // for Close or Closesocket
// A Filter represents a socket system call filter.
// It will only be executed before a system call for a socket that has
// an entry in internal table.
// If the filter returns a non-nil error, the execution of system call
// will be canceled and the system call function returns the non-nil
// error.
// It can return a non-nil AfterFilter for filtering after the
// execution of the system call.
type Filter func(*Status) (AfterFilter, error)
func (f Filter) apply(st *Status) (AfterFilter, error) {
if f == nil {
return nil, nil
return f(st)
// An AfterFilter represents a socket system call filter after an
// execution of a system call.
// It will only be executed after a system call for a socket that has
// an entry in internal table.
// If the filter returns a non-nil error, the system call function
// returns the non-nil error.
type AfterFilter func(*Status) error
func (f AfterFilter) apply(st *Status) error {
if f == nil {
return nil
return f(st)
// Set deploys the socket system call filter f for the filter type t.
func (sw *Switch) Set(t FilterType, f Filter) {
sw.fltab[t] = f