访问net / http响应的基础套接字

Question

I'm new to Go and evaluating it for a project.

I'm trying to write a custom handler to serve files with net/http. I can't use the default http.FileServer() handler because I need to have access to the underlying socket (the internal net.Conn) so I can perform some informational platform specific "syscall" calls on it (mainly TCP_INFO).

More precisly: I need to access the underlying socket of the http.ResponseWriter in the handler function:

func myHandler(w http.ResponseWriter, r *http.Request) {
...
// I need the net.Conn of w
...
}

used in

http.HandleFunc("/", myHandler)

Is there a way to this. I looked at how websocket.Upgrade does this but it uses Hijack() which is 'too much' because then I have to code 'speaking http' over the raw tcp socket I get. I just want a reference to the socket and not taking over completely.

Answer 1

After Issue #30694 is completed, it looks like Go 1.13 will probably support storing the net.Conn in the Request Context, which makes this fairly clean and simple:

package main

import (
  "net/http"
  "context"
  "net"
  "log"
)

type contextKey struct {
  key string
}
var ConnContextKey = &contextKey{"http-conn"}
func SaveConnInContext(ctx context.Context, c net.Conn) (context.Context) {
  return context.WithValue(ctx, ConnContextKey, c)
}
func GetConn(r *http.Request) (net.Conn) {
  return r.Context().Value(ConnContextKey).(net.Conn)
}

func main() {
  http.HandleFunc("/", myHandler)

  server := http.Server{
    Addr: ":8080",
    ConnContext: SaveConnInContext,
  }
  server.ListenAndServe()
}

func myHandler(w http.ResponseWriter, r *http.Request) {
  conn := GetConn(r)
  ...
}

Until then ... For a server listening on a TCP port, net.Conn.RemoteAddr().String() is unique for each connection and is available to the http.Handler as r.RemoteAddr, so it can be used as a key to a global map of Conns:

package main
import (
  "net/http"
  "net"
  "fmt"
  "log"
)

var conns = make(map[string]net.Conn)
func ConnStateEvent(conn net.Conn, event http.ConnState) {
  if event == http.StateActive {
    conns[conn.RemoteAddr().String()] = conn
  } else if event == http.StateHijacked || event == http.StateClosed {
    delete(conns, conn.RemoteAddr().String())
  }
}
func GetConn(r *http.Request) (net.Conn) {
  return conns[r.RemoteAddr]
}

func main() {
  http.HandleFunc("/", myHandler)

  server := http.Server{
    Addr: ":8080",
    ConnState: ConnStateEvent,
  }
  server.ListenAndServe()
}

func myHandler(w http.ResponseWriter, r *http.Request) {
  conn := GetConn(r)
  ...
}

For a server listening on a UNIX socket, net.Conn.RemoteAddr().String() is always "@", so the above doesn't work. To make this work, we can override net.Listener.Accept(), and use that to override net.Conn.RemoteAddr().String() so that it returns a unique string for each connection:

package main

import (
  "net/http"
  "net"
  "os"
  "golang.org/x/sys/unix"
  "fmt"
  "log"
)

func main() {
  http.HandleFunc("/", myHandler)

  listenPath := "/var/run/go_server.sock"
  l, err := NewUnixListener(listenPath)
  if err != nil {
    log.Fatal(err)
  }
  defer os.Remove(listenPath)

  server := http.Server{
    ConnState: ConnStateEvent,
  }
  server.Serve(NewConnSaveListener(l))
}

func myHandler(w http.ResponseWriter, r *http.Request) {
  conn := GetConn(r)
  if unixConn, isUnix := conn.(*net.UnixConn); isUnix {
    f, _ := unixConn.File()
    pcred, _ := unix.GetsockoptUcred(int(f.Fd()), unix.SOL_SOCKET, unix.SO_PEERCRED)
    f.Close()
    log.Printf("Remote UID: %d", pcred.Uid)
  }
}

var conns = make(map[string]net.Conn)
type connSaveListener struct {
  net.Listener
}
func NewConnSaveListener(wrap net.Listener) (net.Listener) {
  return connSaveListener{wrap}
}
func (self connSaveListener) Accept() (net.Conn, error) {
  conn, err := self.Listener.Accept()
  ptrStr := fmt.Sprintf("%d", &conn)
  conns[ptrStr] = conn
  return remoteAddrPtrConn{conn, ptrStr}, err
}
func GetConn(r *http.Request) (net.Conn) {
  return conns[r.RemoteAddr]
}
func ConnStateEvent(conn net.Conn, event http.ConnState) {
  if event == http.StateHijacked || event == http.StateClosed {
    delete(conns, conn.RemoteAddr().String())
  }
}
type remoteAddrPtrConn struct {
  net.Conn
  ptrStr string
}
func (self remoteAddrPtrConn) RemoteAddr() (net.Addr) {
  return remoteAddrPtr{self.ptrStr}
}
type remoteAddrPtr struct {
  ptrStr string
}
func (remoteAddrPtr) Network() (string) {
  return ""
}
func (self remoteAddrPtr) String() (string) {
  return self.ptrStr
}

func NewUnixListener(path string) (net.Listener, error) {
  if err := unix.Unlink(path); err != nil && !os.IsNotExist(err) {
    return nil, err
  }
  mask := unix.Umask(0777)
  defer unix.Umask(mask)

  l, err := net.Listen("unix", path)
  if err != nil {
    return nil, err
  }

  if err := os.Chmod(path, 0660); err != nil {
    l.Close()
    return nil, err
  }

  return l, nil
}