Add socket/tcp_io_readfull example

examples/socket/tcp_io_readfull/.gitignore

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

examples/socket/tcp_io_readfull/README.md

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+# io.ReadFull()のサンプル
+
+```sh
+$ task
+task: [build] go build -o app .
+task: [run] ./app -timeout 100ms
+03:01:14.980749 [C] recv start
+03:01:15.081186 netErr.Timeout()
+task: [run] ./app -timeout 3s
+03:01:15.091656 [C] recv start
+03:01:15.592085 io.ErrUnexpectedEOF
+task: [run] ./app -length 10 -timeout 3s
+03:01:15.602765 [C] recv start
+03:01:15.602902 [C] data=(hhhh)
+03:01:15.602912 [C] data=(hhhh)
+03:01:16.103520 io.ErrUnexpectedEOF
+task: [run] ./app -bufsize 6 -length 12 -timeout 3s
+03:01:16.113780 [C] recv start
+03:01:16.113887 [C] data=(hhhhhh)
+03:01:16.113901 [C] data=(hhhhhh)
+03:01:16.614526 io.EOF
+```
+
+
+- [io.ReadFull](https://pkg.go.dev/io@latest#ReadFull)

examples/socket/tcp_io_readfull/Taskfile.yml

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+# https://taskfile.dev
+
+version: '3'
+
+tasks:
+  default:
+    cmds:
+      - task: build
+      - task: run
+  build:
+    cmds:
+      - go build -o app .
+  run:
+    cmds:
+      - ./app -timeout 100ms
+      - ./app -timeout 3s
+      - ./app -length 10 -timeout 3s
+      - ./app -bufsize 6 -length 12 -timeout 3s

examples/socket/tcp_io_readfull/main.go

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+package main
+
+import (
+	"errors"
+	"flag"
+	"io"
+	"log"
+	"net"
+	"strings"
+	"time"
+)
+
+type (
+	Args struct {
+		bufsize int
+		length  int
+		timeout time.Duration
+	}
+)
+
+var (
+	args Args
+)
+
+func init() {
+	flag.IntVar(&args.bufsize, "bufsize", 4, "bufsize")
+	flag.IntVar(&args.length, "length", 2, "length")
+	flag.DurationVar(&args.timeout, "timeout", 1*time.Second, "timeout")
+}
+
+func main() {
+	log.SetFlags(log.Lmicroseconds)
+	flag.Parse()
+
+	ln, err := net.Listen("tcp", ":8888")
+	if err != nil {
+		panic(err)
+	}
+	defer ln.Close()
+
+	go func() {
+		conn, err := ln.Accept()
+		if err != nil {
+			if errors.Is(err, net.ErrClosed) {
+				return
+			}
+			panic(err)
+		}
+		defer conn.Close()
+
+		buf := []byte(strings.Repeat("h", args.length))
+		_, err = conn.Write(buf)
+		if err != nil {
+			panic(err)
+		}
+
+		time.Sleep(500 * time.Millisecond)
+	}()
+
+	if err := run(); err != nil {
+		panic(err)
+	}
+}
+
+func run() error {
+	conn, err := net.Dial("tcp", ":8888")
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+
+	log.Println("[C] recv start")
+	{
+		buf := make([]byte, args.bufsize)
+		for {
+			clear(buf)
+
+			err = conn.SetReadDeadline(time.Now().Add(args.timeout))
+			if err != nil {
+				return err
+			}
+
+			n, err := io.ReadFull(conn, buf)
+			if err != nil {
+				switch {
+				case errors.Is(err, io.EOF):
+					log.Println("io.EOF")
+					return nil
+				case errors.Is(err, io.ErrUnexpectedEOF):
+					log.Println("io.ErrUnexpectedEOF")
+					return nil
+				default:
+					var netErr net.Error
+					if errors.As(err, &netErr) && netErr.Timeout() {
+						log.Println("netErr.Timeout()")
+						return nil
+					}
+				}
+
+				return err
+			}
+
+			log.Printf("[C] data=(%s)", buf[:n])
+		}
+	}
+}