commit ee11d4c8187a2ec638390e0047e9a380098aa935
Author: Aurélie DELHAIE <aureliedelhaie3@gmail.com>
Date:   Sat Aug 23 14:31:15 2025 +0200

    first commit

diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..daeab24
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module test
+
+go 1.25
\ No newline at end of file
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..4049747
--- /dev/null
+++ b/main.go
@@ -0,0 +1,12 @@
+package main
+
+import (
+	"test/pkg/client"
+)
+
+func main() {
+	cli := client.New("172.0.0.42", 80)
+	if err := cli.SendSMS("0782092003", "salut toi comment tu vas ?"); err != nil {
+		panic(err)
+	}
+}
diff --git a/pkg/client/client.go b/pkg/client/client.go
new file mode 100644
index 0000000..0a4c6f2
--- /dev/null
+++ b/pkg/client/client.go
@@ -0,0 +1,156 @@
+package client
+
+import (
+	"crypto/md5"
+	"encoding/hex"
+	"fmt"
+	"io"
+	"net"
+	"strings"
+)
+
+type (
+	Client struct {
+		addr string
+	}
+
+	Payload interface {
+		WriteTo(server io.Writer) (int64, error)
+		Len() int64
+	}
+
+	PayloadStrict struct {
+		data string
+	}
+
+	PayloadCloser struct {
+		data   string
+		closer byte
+	}
+
+	Command byte
+)
+
+const (
+	Send Command = 1
+)
+
+func (p PayloadCloser) WriteTo(server io.Writer) (int64, error) {
+	n1, err := server.Write([]byte(p.data))
+	if err != nil {
+		return int64(n1), err
+	}
+	n2, err := server.Write([]byte{p.closer})
+	if err != nil {
+		return int64(n1 + n2), err
+	}
+	return int64(n1 + n2), nil
+}
+
+func (p PayloadCloser) Len() int64 {
+	return int64(len(p.data) + 1)
+}
+
+func (p PayloadStrict) WriteTo(server io.Writer) (int64, error) {
+	n, err := server.Write([]byte(p.data))
+	return int64(n), err
+}
+
+func (p PayloadStrict) Len() int64 {
+	return int64(len(p.data))
+}
+
+func New(ip string, port int) *Client {
+	return &Client{
+		addr: fmt.Sprintf("%s:%d", ip, port),
+	}
+}
+
+func (c *Client) SendSMS(phoneNumber, msg string) error {
+	if len(msg) > 140 {
+		return fmt.Errorf("message too long")
+	}
+	conn, err := net.Dial("tcp", c.addr)
+	if err != nil {
+		return fmt.Errorf("failed to connect: %w", err)
+	}
+	defer conn.Close()
+
+	m := md5.New()
+	m.Write([]byte(msg))
+	hash := hex.EncodeToString(m.Sum(nil))
+
+	if err := c.Send(conn, Send, PayloadStrict{phoneNumber}, PayloadStrict{hash}, PayloadCloser{msg, 1}); err != nil {
+		return fmt.Errorf("failed to send data: %w", err)
+	}
+
+	resp, err := c.ReadAll(conn)
+	if err != nil {
+		return err
+	}
+
+	if len(resp) == 0 {
+		return fmt.Errorf("empty message: the server stop responding")
+	}
+	fmt.Println(resp)
+
+	return nil
+}
+
+func (c *Client) Send(server net.Conn, cmd Command, payload ...Payload) error {
+	if err := c.SendCommand(server, cmd); err != nil {
+		return err
+	}
+
+	for _, data := range payload {
+		n, err := data.WriteTo(server)
+		if err != nil {
+			return fmt.Errorf("failed to send phone number: %w", err)
+		}
+
+		if n != data.Len() {
+			return fmt.Errorf("network error: broken pipe")
+		}
+	}
+
+	return nil
+}
+
+func (c *Client) SendCommand(server net.Conn, cmd Command) error {
+	n, err := server.Write([]byte{byte(cmd)})
+	if err != nil {
+		return fmt.Errorf("failed to send command: %w", err)
+	}
+
+	if n != 1 {
+		return fmt.Errorf("failed to send command: broken pipe")
+	}
+	return nil
+}
+
+func (c *Client) ReadAll(server net.Conn) (string, error) {
+	var err error
+	var data []byte
+	var message string
+	waiting := true
+	for {
+		data, err = io.ReadAll(server)
+		if err != nil {
+			return "", fmt.Errorf("failed to received response: %w", err)
+		}
+		if len(data) == 0 {
+			if !waiting {
+				break
+			}
+		} else {
+			waiting = false
+			message += string(data)
+		}
+	}
+
+	if strings.HasPrefix(message, "error:") {
+		return "", fmt.Errorf("%s", message)
+	}
+
+	return message, nil
+}