Merge pull request #908 from devlights/add-tcp-select-syscall

Author: devlights

examples/socket/tcp_select_syscall/.gitignore

@@ -0,0 +1 @@
+app

examples/socket/tcp_select_syscall/README.md

@@ -0,0 +1,31 @@
+# これは何？
+
+[golang.org/sys/unix](https://pkg.go.dev/golang.org/x/sys/unix) を使って、[select(2)](https://ja.manpages.org/select/2)を呼び出し
+
+対象となるソケットファイルディスクリプタが読み取り可能な状態であるかを確認して処理するサンプルです。
+
+
+```sh
+$ task
+task: [build] go build -o app .
+task: [run] ./app -server &
+task: [run] sleep 0.5
+task: [run] ./app
+10:01:00.206680 [C] select(2) -- not readable(fd=6)
+10:01:00.216917 [C] select(2) -- not readable(fd=6)
+10:01:00.227016 [C] select(2) -- not readable(fd=6)
+10:01:00.237166 [C] select(2) -- not readable(fd=6)
+10:01:00.247262 [C] select(2) -- not readable(fd=6)
+10:01:00.257365 [C] select(2) -- not readable(fd=6)
+10:01:00.267527 [C] select(2) -- not readable(fd=6)
+10:01:00.277664 [C] select(2) -- not readable(fd=6)
+10:01:00.287777 [C] select(2) -- not readable(fd=6)
+10:01:00.296891 [S] send data
+10:01:00.297322 [C] recv hello
+10:01:00.297369 [C] shutdown(SHUT_WR)
+10:01:00.297405 [C] close
+10:01:00.297458 [S] disconnect
+10:01:00.297523 [S] close
+task: [run] sleep 0.5
+task: [run] pkill app
+```

examples/socket/tcp_select_syscall/Taskfile.yml

@@ -0,0 +1,20 @@
+# https://taskfile.dev
+
+version: '3'
+
+tasks:
+  default:
+    cmds:
+      - task: build
+      - task: run
+  build:
+    cmds:
+      - go build -o app .
+  run:
+    cmds:
+      - ./app -server &
+      - sleep 0.5
+      - ./app
+      - sleep 0.5
+      - pkill app
+    ignore_error: true

examples/socket/tcp_select_syscall/fd.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+// SocketFd は、ソケットファイルディスクリプタを表します。
+type SocketFd int
+
+// Readable は、select(2)を呼び出し読み込み可能かどうかを判定します。
+func (me SocketFd) Readable(sec, usec time.Duration) (bool, error) {
+	fd := int(me)
+	if fd < 0 || fd >= unix.FD_SETSIZE {
+		return false, fmt.Errorf("invalid file descriptor: out of range %d (FD_SETSIZE = %d)", fd, unix.FD_SETSIZE)
+	}
+
+	rfds := &unix.FdSet{}
+	rfds.Zero()
+	rfds.Set(fd)
+
+	timeout := &unix.Timeval{
+		Sec:  int64(sec.Seconds()),
+		Usec: usec.Microseconds(),
+	}
+
+	n, err := unix.Select(fd+1, rfds, nil, nil, timeout)
+	if err != nil {
+		if errors.Is(err, unix.EINTR) {
+			return false, nil
+		}
+		return false, err
+	}
+
+	return n > 0 && rfds.IsSet(fd), nil
+}

examples/socket/tcp_select_syscall/main.go

@@ -0,0 +1,172 @@
+package main
+
+import (
+	"errors"
+	"flag"
+	"io"
+	"log"
+	"net"
+	"time"
+)
+
+type (
+	Args struct {
+		IsServer bool
+	}
+)
+
+var (
+	args Args
+)
+
+func init() {
+	flag.BoolVar(&args.IsServer, "server", false, "server mode")
+}
+
+func main() {
+	log.SetFlags(log.Lmicroseconds)
+	flag.Parse()
+
+	if err := run(); err != nil {
+		panic(err)
+	}
+}
+
+func run() error {
+	var err error
+	switch args.IsServer {
+	case true:
+		err = runServer()
+	default:
+		err = runClient()
+	}
+
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func runServer() error {
+	ln, err := net.Listen("tcp", ":8888")
+	if err != nil {
+		return err
+	}
+	defer ln.Close()
+
+	errCh := make(chan error)
+	defer close(errCh)
+
+	for {
+		select {
+		case e := <-errCh:
+			return e
+		default:
+		}
+
+		err = ln.(*net.TCPListener).SetDeadline(time.Now().Add(1 * time.Second))
+		if err != nil {
+			return err
+		}
+
+		conn, err := ln.Accept()
+		if err != nil {
+			if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
+				continue
+			}
+
+			return err
+		}
+
+		go func(conn net.Conn) {
+			defer func() {
+				conn.Close()
+				log.Println("[S] close")
+			}()
+
+			time.Sleep(100 * time.Millisecond)
+			{
+				log.Println("[S] send data")
+				if _, err := conn.Write([]byte("hello")); err != nil {
+					errCh <- err
+				}
+
+				buf := make([]byte, 1)
+				for {
+					_, err := conn.Read(buf)
+					if err != nil {
+						if errors.Is(err, io.EOF) {
+							log.Println("[S] disconnect")
+							break
+						}
+
+						errCh <- err
+					}
+				}
+			}
+		}(conn)
+	}
+}
+
+func runClient() error {
+	conn, err := net.Dial("tcp", ":8888")
+	if err != nil {
+		return err
+	}
+	defer func() {
+		conn.Close()
+		log.Println("[C] close")
+	}()
+
+	//
+	// select(2) を使って読み込み可能かを判定
+	// select(2)に指定するFDは、net.TCPConn.File() から取得する
+	//
+	tcpConn, _ := conn.(*net.TCPConn)
+	file, err := tcpConn.File()
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	var (
+		fd   = SocketFd(file.Fd())
+		buf  = make([]byte, 10)
+		sec  = 0 * time.Second
+		usec = 10 * time.Millisecond
+	)
+	for {
+		readable, err := fd.Readable(sec, usec)
+		if err != nil {
+			return err
+		}
+
+		if !readable {
+			log.Printf("[C] select(2) -- not readable(fd=%d)", int(fd))
+			continue
+		}
+
+		clear(buf)
+		n, err := conn.Read(buf)
+		if err != nil {
+			if errors.Is(err, io.EOF) {
+				log.Println("[C] disconnect")
+				break
+			}
+
+			return err
+		}
+		log.Printf("[C] recv %s", buf[:n])
+
+		err = conn.(*net.TCPConn).CloseWrite()
+		if err != nil {
+			return err
+		}
+		log.Println("[C] shutdown(SHUT_WR)")
+
+		break
+	}
+
+	return nil
+}