anyhttp/anyhttp.go
Balakrishnan Balasubramanian bbef4be4a7 Refactor environment parsing
Systemd environment variables LISTEN* are unset by default and saved for
future calls
2023-04-30 23:37:46 -04:00

246 lines
6.0 KiB
Go

// Package anyhttp has helpers to serve http from unix sockets and systemd socket activated fds
package anyhttp
import (
"errors"
"fmt"
"io/fs"
"net"
"net/http"
"os"
"strconv"
"strings"
"sync"
"syscall"
)
// UnixSocketConfig has the configuration for Unix socket
type UnixSocketConfig struct {
// Absolute or relative path of socket, e.g. /run/app.sock
SocketPath string
// Socket file permission
SocketMode fs.FileMode
// Whether to delete existing socket before creating new one
RemoveExisting bool
}
// DefaultUnixSocketConfig has defaults for UnixSocketConfig
var DefaultUnixSocketConfig = UnixSocketConfig{
SocketMode: 0666,
RemoveExisting: true,
}
// NewUnixSocketConfig creates a UnixSocketConfig with the default values and the socketPath passed
func NewUnixSocketConfig(socketPath string) UnixSocketConfig {
usc := DefaultUnixSocketConfig
usc.SocketPath = socketPath
return usc
}
type sysdEnvData struct {
pid int
fdNames []string
fdNamesStr string
numFds int
}
var sysdEnvParser = struct {
sysdOnce sync.Once
data sysdEnvData
err error
}{}
func parse() (sysdEnvData, error) {
p := &sysdEnvParser
p.sysdOnce.Do(func() {
p.data.pid, p.err = strconv.Atoi(os.Getenv("LISTEN_PID"))
if p.err != nil {
p.err = fmt.Errorf("invalid LISTEN_PID, err: %w", p.err)
return
}
p.data.numFds, p.err = strconv.Atoi(os.Getenv("LISTEN_FDS"))
if p.err != nil {
p.err = fmt.Errorf("invalid LISTEN_FDS, err: %w", p.err)
return
}
p.data.fdNamesStr = os.Getenv("LISTEN_FDNAMES")
p.data.fdNames = strings.Split(p.data.fdNamesStr, ":")
})
return p.data, p.err
}
// SysdConfig has the configuration for the socket activated fd
type SysdConfig struct {
// Integer value starting at 0. Either index or name is required
FDIndex *int
// Name configured via FileDescriptorName or the default socket file name. Either index or name is required
FDName *string
// Check process PID matches LISTEN_PID
CheckPID bool
// Unsets the LISTEN* environment variables, so they don't get passed to any child processes
UnsetEnv bool
}
// DefaultSysdConfig has the default values for SysdConfig
var DefaultSysdConfig = SysdConfig{
CheckPID: true,
UnsetEnv: true,
}
// NewSysDConfigWithFDIdx creates SysdConfig with defaults and fdIdx
func NewSysDConfigWithFDIdx(fdIdx int) SysdConfig {
sysc := DefaultSysdConfig
sysc.FDIndex = &fdIdx
return sysc
}
// NewSysDConfigWithFDName creates SysdConfig with defaults and fdName
func NewSysDConfigWithFDName(fdName string) SysdConfig {
sysc := DefaultSysdConfig
sysc.FDName = &fdName
return sysc
}
// GetListener returns the unix socket listener
func (u *UnixSocketConfig) GetListener() (net.Listener, error) {
if u.RemoveExisting {
if err := os.Remove(u.SocketPath); err != nil && !errors.Is(err, fs.ErrNotExist) {
return nil, err
}
}
l, err := net.Listen("unix", u.SocketPath)
if err != nil {
return nil, err
}
if err = os.Chmod(u.SocketPath, u.SocketMode); err != nil {
return nil, err
}
return l, nil
}
// StartFD is the starting file descriptor number
const StartFD = 3
func makeFdListener(fd int, name string) (net.Listener, error) {
fdFile := os.NewFile(uintptr(fd), name)
l, err := net.FileListener(fdFile)
if err != nil {
return nil, err
}
syscall.CloseOnExec(fd)
return l, nil
}
// GetListener returns the FileListener created with socketed activated fd
func (s *SysdConfig) GetListener() (net.Listener, error) {
if s.UnsetEnv {
defer UnsetSystemdListenVars()
}
envData, err := parse()
if err != nil {
return nil, err
}
if s.CheckPID {
if envData.pid != os.Getpid() {
return nil, fmt.Errorf("unexpected PID, current:%v, LISTEN_PID: %v", os.Getpid(), envData.pid)
}
}
if s.FDIndex != nil {
idx := *s.FDIndex
if idx < 0 || idx >= envData.numFds {
return nil, fmt.Errorf("invalid fd index, expected between 0 and %v, got: %v", envData.numFds, idx)
}
fd := StartFD + idx
if idx < len(envData.fdNames) {
return makeFdListener(fd, envData.fdNames[idx])
}
return makeFdListener(fd, fmt.Sprintf("sysdfd_%d", fd))
}
if s.FDName != nil {
for idx, name := range envData.fdNames {
if name == *s.FDName {
fd := StartFD + idx
return makeFdListener(fd, name)
}
}
return nil, fmt.Errorf("fdName not found: %q, LISTEN_FDNAMES:%q", *s.FDName, envData.fdNamesStr)
}
return nil, errors.New("neither FDIndex nor FDName set")
}
// UnknownAddress Error is returned when address does not match any known syntax
type UnknownAddress struct{}
func (u UnknownAddress) Error() string {
return "unknown address"
}
// GetListener gets a unix or systemd socket listener
func GetListener(addr string) (net.Listener, error) {
if strings.HasPrefix(addr, "unix/") {
usc := NewUnixSocketConfig(strings.TrimPrefix(addr, "unix/"))
return usc.GetListener()
}
if strings.HasPrefix(addr, "sysd/fdidx/") {
idx, err := strconv.Atoi(strings.TrimPrefix(addr, "sysd/fdidx/"))
if err != nil {
return nil, fmt.Errorf("invalid fdidx, addr:%q err: %w", addr, err)
}
sysdc := NewSysDConfigWithFDIdx(idx)
return sysdc.GetListener()
}
if strings.HasPrefix(addr, "sysd/fdname/") {
sysdc := NewSysDConfigWithFDName(strings.TrimPrefix(addr, "sysd/fdname/"))
return sysdc.GetListener()
}
return nil, UnknownAddress{}
}
// ListenAndServe is the drop-in replacement for `http.ListenAndServe`.
// Supports unix and systemd sockets in addition
func ListenAndServe(addr string, h http.Handler) error {
listener, err := GetListener(addr)
if _, isUnknown := err.(UnknownAddress); err != nil && !isUnknown {
return err
}
if listener != nil {
return http.Serve(listener, h)
}
if port, err := strconv.Atoi(addr); err == nil {
if port > 0 && port < 65536 {
return http.ListenAndServe(fmt.Sprintf(":%v", port), h)
}
return fmt.Errorf("invalid port: %v", port)
}
return http.ListenAndServe(addr, h)
}
// UnsetSystemdListenVars unsets the LISTEN* environment variables so they are not passed to any child processes
func UnsetSystemdListenVars() {
_ = os.Unsetenv("LISTEN_PID")
_ = os.Unsetenv("LISTEN_FDS")
_ = os.Unsetenv("LISTEN_FDNAMES")
}