rsser/outputs/nntp/nntp.go

package nntp

import (
	"bufio"
	"encoding/base64"
	"fmt"
	"log/slog"
	"net"
	"strings"
	"time"

	"go.dev.pztrn.name/rsser/configuration"
	"go.dev.pztrn.name/rsser/outputs"
)

type nntp struct {
	cfg  *configuration.Config
	conn net.Conn
	br   *bufio.Reader
	bw   *bufio.Writer
}

// New creates new simple NNTP client. Connection will be established only for sending posts.
func New(cfg *configuration.Config) (outputs.Output, error) {
	c := &nntp{
		cfg: cfg,
	}

	return c, nil
}

func (c *nntp) establishConnection() error {
	if c.conn != nil {
		return nil
	}

	//nolint:noctx
	conn, err := net.DialTimeout(
		"tcp",
		c.cfg.Outputs.NNTP.Address,
		time.Second*time.Duration(c.cfg.Outputs.NNTP.ConnectTimeout),
	)
	if err != nil {
		return fmt.Errorf("establishConnection: %w", err)
	}

	c.conn = conn
	c.br = bufio.NewReader(c.conn)
	c.bw = bufio.NewWriter(c.conn)

	// Waiting for hello (200/201).
	line, err := c.readLine()
	if err != nil {
		_ = conn.Close()

		return fmt.Errorf("no greeting from server: %w", err)
	}

	if !strings.HasPrefix(line, "200") && !strings.HasPrefix(line, "201") {
		_ = conn.Close()

		//nolint:err113
		return fmt.Errorf("unexpected greeting: %s", line)
	}

	if err := c.authInfo(); err != nil {
		//nolint:err113
		return fmt.Errorf("auth failed: %s", line)
	}

	return nil
}

func (c *nntp) authInfo() error {
	resp, err := c.sendCommand("AUTHINFO USER " + c.cfg.Outputs.NNTP.Username)
	if err != nil {
		return err
	}

	if !strings.HasPrefix(resp, "381") { // 381 = send PASS
		// Some servers immediately giving 281 (success) or 480 (fail)
		if strings.HasPrefix(resp, "281") {
			return nil // уже авторизованы
		}

		//nolint:err113
		return fmt.Errorf("AUTHINFO USER failed: %s", resp)
	}

	resp, err = c.sendCommand("AUTHINFO PASS " + c.cfg.Outputs.NNTP.Password)
	if err != nil {
		return err
	}

	if !strings.HasPrefix(resp, "281") {
		//nolint:err113
		return fmt.Errorf("AUTHINFO PASS failed: %s", resp)
	}

	return nil
}

func (c *nntp) Do(dest, feedName, url, title, body string) error {
	headers := map[string]string{
		"From":                      "\"" + feedName + "\" <" + c.cfg.Outputs.NNTP.Username + "@mail.invalid",
		"Newsgroups":                dest,
		"Subject":                   c.encodeSubjectB(title),
		"Date":                      time.Now().UTC().Format(time.RFC1123),
		"Content-Type":              "text/plain; charset=UTF-8; format=flowed",
		"Content-Transfer-Encoding": "7bit",
	}

	body = "URL: " + url + "\n\n" + body

	if err := c.postArticle(headers, body); err != nil {
		return fmt.Errorf("Do: %w", err)
	}

	return nil
}

func (c *nntp) doubleDot(s string) string {
	var result strings.Builder

	scanner := bufio.NewScanner(strings.NewReader(s))
	for scanner.Scan() {
		line := scanner.Text()
		if len(line) > 0 && line[0] == '.' {
			result.WriteString("..")
			result.WriteString(line[1:])
		} else {
			result.WriteString(line)
		}

		result.WriteByte('\n')
	}

	return result.String()
}

func (c *nntp) encodeSubjectB(s string) string {
	b := base64.StdEncoding.EncodeToString([]byte(s))

	return fmt.Sprintf("=?utf-8?B?%s?=", b)
}

func (c *nntp) Name() string {
	return "nntp"
}

func (c *nntp) postArticle(headers map[string]string, body string) error {
	if err := c.establishConnection(); err != nil {
		return fmt.Errorf("PostArticle: %w", err)
	}

	resp, err := c.sendCommand("POST")
	if err != nil {
		return err
	}

	if !strings.HasPrefix(resp, "340") { // 340 = ready to accept article
		//nolint:err113
		return fmt.Errorf("POST not accepted by server: %s", resp)
	}

	// Заголовки
	for k, v := range headers {
		_, _ = fmt.Fprintf(c.bw, "%s: %s\r\n", k, v)
	}

	_, _ = fmt.Fprint(c.bw, "\r\n")

	// Article body: double starting dot (RFC).
	processedBody := c.doubleDot(body)
	_, _ = fmt.Fprint(c.bw, processedBody)
	_, _ = fmt.Fprintln(c.bw, ".")

	if flushErr := c.bw.Flush(); flushErr != nil {
		return fmt.Errorf("PostArticle: %w", flushErr)
	}

	finalResp, err := c.readLine()
	if err != nil {
		return err
	}

	if !strings.HasPrefix(finalResp, "240") {
		//nolint:err113
		return fmt.Errorf("article not accepted: %s", finalResp)
	}

	slog.Info("Article posted successfully", "resp", finalResp)

	return nil
}

func (c *nntp) readLine() (string, error) {
	b, err := c.br.ReadBytes('\n')
	if err != nil {
		return "", fmt.Errorf("readLine: %w", err)
	}

	s := strings.TrimRight(string(b), "\r\n")

	return s, nil
}

func (c *nntp) sendCommand(cmd string) (string, error) {
	_, err := fmt.Fprintf(c.bw, "%s\r\n", cmd)
	if err != nil {
		return "", fmt.Errorf("readLine: %w", err)
	}

	if err := c.bw.Flush(); err != nil {
		return "", fmt.Errorf("readLine: %w", err)
	}

	return c.readLine()
}