feat(usenet): implement full NNTP download pipeline

Complete usenet download support for unarr CLI: - NZB XML parser with password extraction from <head> meta - yEnc decoder with CRC32 verification - NNTP client with TLS, auth, and connection pool (up to 10 conns) - Segment downloader with parallel workers and progress reporting - Post-processing: par2 verify/repair, unrar/7z extraction with password support - Agent client methods: SearchNzbs, DownloadNzb, GetUsenetCredentials - UsenetDownloader implementing full Downloader interface - Daemon wiring: UsenetDownloader passed to Manager E2E tested: Oppenheimer 1080p (2.94 GB) downloaded via NNTP in 77.6s.
2026-03-28 21:12:12 +01:00 · 2026-03-28 21:12:12 +01:00 · e332c0a6e4
commit e332c0a6e4
parent 5f337eebd7
15 changed files with 3016 additions and 23 deletions
--- a/internal/usenet/download/downloader.go
+++ b/internal/usenet/download/downloader.go
@ -0,0 +1,308 @@
+package download
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+	"sort"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/torrentclaw/torrentclaw-cli/internal/ui"
+	"github.com/torrentclaw/torrentclaw-cli/internal/usenet/nntp"
+	"github.com/torrentclaw/torrentclaw-cli/internal/usenet/nzb"
+	"github.com/torrentclaw/torrentclaw-cli/internal/usenet/yenc"
+)
+
+// Progress is emitted during download.
+type Progress struct {
+	FileName        string
+	SegmentsDone    int
+	SegmentsTotal   int
+	BytesDownloaded int64
+	BytesTotal      int64
+	SpeedBps        int64
+}
+
+// Downloader orchestrates downloading all segments of NZB files via NNTP.
+type Downloader struct {
+	nntp *nntp.Client
+}
+
+// NewDownloader creates a usenet segment downloader.
+func NewDownloader(nntpClient *nntp.Client) *Downloader {
+	return &Downloader{nntp: nntpClient}
+}
+
+// DownloadFile downloads all segments of a single NZB file and assembles them.
+// Returns the path to the assembled file.
+func (d *Downloader) DownloadFile(ctx context.Context, file nzb.File, outputDir string, progressCh chan<- Progress) (string, error) {
+	fileName := file.Filename()
+	if fileName == "" {
+		fileName = fmt.Sprintf("usenet_%d", time.Now().UnixNano())
+	}
+
+	destPath := filepath.Join(outputDir, fileName)
+
+	// Ensure output directory exists
+	if err := os.MkdirAll(outputDir, 0o755); err != nil {
+		return "", fmt.Errorf("mkdir: %w", err)
+	}
+
+	totalBytes := file.TotalBytes()
+	totalSegs := len(file.Segments)
+
+	// Sort segments by number
+	segments := make([]nzb.Segment, len(file.Segments))
+	copy(segments, file.Segments)
+	sort.Slice(segments, func(i, j int) bool {
+		return segments[i].Number < segments[j].Number
+	})
+
+	// Create/open output file
+	outFile, err := os.Create(destPath)
+	if err != nil {
+		return "", fmt.Errorf("create file: %w", err)
+	}
+	defer outFile.Close()
+
+	// Pre-allocate file if we know the size
+	if totalBytes > 0 {
+		outFile.Truncate(totalBytes)
+	}
+
+	// Download segments using worker pool
+	var downloaded atomic.Int64
+	var segsDone atomic.Int32
+	startTime := time.Now()
+
+	// Create work channel
+	type segWork struct {
+		seg   nzb.Segment
+		index int
+	}
+	workCh := make(chan segWork, len(segments))
+	for i, seg := range segments {
+		workCh <- segWork{seg: seg, index: i}
+	}
+	close(workCh)
+
+	// Track file offsets for each segment (sequential assembly)
+	offsets := make([]int64, len(segments))
+	var offset int64
+	for i, seg := range segments {
+		offsets[i] = offset
+		offset += seg.Bytes
+	}
+
+	// Progress reporter goroutine
+	stopProgress := make(chan struct{})
+	go func() {
+		ticker := time.NewTicker(500 * time.Millisecond)
+		defer ticker.Stop()
+		for {
+			select {
+			case <-ticker.C:
+				dl := downloaded.Load()
+				elapsed := time.Since(startTime).Seconds()
+				var speed int64
+				if elapsed > 0 {
+					speed = int64(float64(dl) / elapsed)
+				}
+				if progressCh != nil {
+					select {
+					case progressCh <- Progress{
+						FileName:        fileName,
+						SegmentsDone:    int(segsDone.Load()),
+						SegmentsTotal:   totalSegs,
+						BytesDownloaded: dl,
+						BytesTotal:      totalBytes,
+						SpeedBps:        speed,
+					}:
+					default:
+					}
+				}
+			case <-stopProgress:
+				return
+			case <-ctx.Done():
+				return
+			}
+		}
+	}()
+
+	// Workers — one per NNTP connection
+	numWorkers := d.nntp.ActiveConnections()
+	if numWorkers <= 0 {
+		numWorkers = 1
+	}
+
+	errCh := make(chan error, 1)
+	var wg sync.WaitGroup
+
+	for w := 0; w < numWorkers; w++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for work := range workCh {
+				select {
+				case <-ctx.Done():
+					return
+				default:
+				}
+
+				data, err := d.downloadSegment(ctx, work.seg)
+				if err != nil {
+					select {
+					case errCh <- fmt.Errorf("segment %d (%s): %w", work.seg.Number, work.seg.MessageID, err):
+					default:
+					}
+					return
+				}
+
+				// Write decoded data at the correct offset
+				// WriteAt is safe for concurrent non-overlapping writes
+				_, writeErr := outFile.WriteAt(data, offsets[work.index])
+
+				if writeErr != nil {
+					select {
+					case errCh <- fmt.Errorf("write segment %d: %w", work.seg.Number, writeErr):
+					default:
+					}
+					return
+				}
+
+				downloaded.Add(int64(len(data)))
+				segsDone.Add(1)
+			}
+		}()
+	}
+
+	// Wait for all workers
+	wg.Wait()
+
+	// Stop progress reporter before sending final progress
+	close(stopProgress)
+
+	// Check for errors
+	select {
+	case err := <-errCh:
+		os.Remove(destPath)
+		return "", err
+	default:
+	}
+
+	// Check context cancellation
+	if ctx.Err() != nil {
+		os.Remove(destPath)
+		return "", ctx.Err()
+	}
+
+	// Final progress report
+	dl := downloaded.Load()
+	elapsed := time.Since(startTime).Seconds()
+	var speed int64
+	if elapsed > 0 {
+		speed = int64(float64(dl) / elapsed)
+	}
+	if progressCh != nil {
+		select {
+		case progressCh <- Progress{
+			FileName:        fileName,
+			SegmentsDone:    totalSegs,
+			SegmentsTotal:   totalSegs,
+			BytesDownloaded: dl,
+			BytesTotal:      totalBytes,
+			SpeedBps:        speed,
+		}:
+		default:
+		}
+	}
+
+	// Truncate to actual size (in case pre-allocation was larger)
+	actualSize := downloaded.Load()
+	if actualSize > 0 {
+		outFile.Truncate(actualSize)
+	}
+
+	log.Printf("[usenet] downloaded %s (%d segments, %s)", fileName, totalSegs, ui.FormatBytes(actualSize))
+	return destPath, nil
+}
+
+// DownloadNZB downloads content files from an NZB (rars or direct content).
+// Par2 files are NOT downloaded initially — they're only fetched on demand
+// if extraction fails (via DownloadPar2).
+// Returns a map of filename → filepath for all downloaded files.
+func (d *Downloader) DownloadNZB(ctx context.Context, n *nzb.NZB, outputDir string, progressCh chan<- Progress) (map[string]string, error) {
+	// Determine which files to download (NO par2 initially)
+	var filesToDownload []nzb.File
+
+	if n.HasRars() {
+		filesToDownload = n.RarFiles()
+	} else {
+		filesToDownload = n.ContentFiles()
+	}
+
+	if len(filesToDownload) == 0 {
+		return nil, fmt.Errorf("no downloadable files found in NZB")
+	}
+
+	results := make(map[string]string)
+
+	for _, file := range filesToDownload {
+		select {
+		case <-ctx.Done():
+			return results, ctx.Err()
+		default:
+		}
+
+		path, err := d.DownloadFile(ctx, file, outputDir, progressCh)
+		if err != nil {
+			return results, fmt.Errorf("download %s: %w", file.Filename(), err)
+		}
+		results[file.Filename()] = path
+	}
+
+	return results, nil
+}
+
+// DownloadPar2 downloads par2 parity files from the NZB.
+// Called on-demand when extraction/verification fails.
+func (d *Downloader) DownloadPar2(ctx context.Context, n *nzb.NZB, outputDir string, progressCh chan<- Progress) (map[string]string, error) {
+	par2Files := n.Par2Files()
+	if len(par2Files) == 0 {
+		return nil, fmt.Errorf("no par2 files in NZB")
+	}
+
+	results := make(map[string]string)
+	for _, file := range par2Files {
+		path, err := d.DownloadFile(ctx, file, outputDir, progressCh)
+		if err != nil {
+			log.Printf("[usenet] par2 download failed (non-fatal): %v", err)
+			continue
+		}
+		results[file.Filename()] = path
+	}
+	return results, nil
+}
+
+// downloadSegment downloads and decodes a single segment.
+func (d *Downloader) downloadSegment(ctx context.Context, seg nzb.Segment) ([]byte, error) {
+	// Download article body via NNTP
+	body, err := d.nntp.Body(ctx, seg.MessageID)
+	if err != nil {
+		return nil, fmt.Errorf("nntp body: %w", err)
+	}
+
+	// Decode yEnc
+	part, err := yenc.Decode(bytes.NewReader(body))
+	if err != nil {
+		return nil, fmt.Errorf("yenc decode: %w", err)
+	}
+
+	return part.Data, nil
+}
+
--- a/internal/usenet/download/e2e_test.go
+++ b/internal/usenet/download/e2e_test.go
@ -0,0 +1,177 @@
+package download_test
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/torrentclaw/torrentclaw-cli/internal/usenet/download"
+	"github.com/torrentclaw/torrentclaw-cli/internal/usenet/nntp"
+	"github.com/torrentclaw/torrentclaw-cli/internal/usenet/nzb"
+	"github.com/torrentclaw/torrentclaw-cli/internal/usenet/postprocess"
+)
+
+// TestE2EDownload is a real end-to-end test that downloads from Usenet.
+// It requires:
+//   - NZB file at /tmp/oppenheimer-test.nzb
+//   - NNTP credentials in env: NNTP_USER, NNTP_PASS
+//   - Network access to reader.torrentclaw.com:563
+//
+// Run with: go test -v -run TestE2EDownload -tags e2e -timeout 30m ./internal/usenet/download/
+func TestE2EDownload(t *testing.T) {
+	if os.Getenv("NNTP_USER") == "" || os.Getenv("NNTP_PASS") == "" {
+		t.Skip("NNTP_USER and NNTP_PASS not set — skipping e2e test")
+	}
+
+	nzbPath := os.Getenv("NZB_FILE")
+	if nzbPath == "" {
+		nzbPath = "/tmp/oppenheimer-test.nzb"
+	}
+
+	// 1. Parse NZB
+	f, err := os.Open(nzbPath)
+	if err != nil {
+		t.Fatalf("open NZB: %v", err)
+	}
+	defer f.Close()
+
+	nzbFile, err := nzb.Parse(f)
+	if err != nil {
+		t.Fatalf("parse NZB: %v", err)
+	}
+
+	t.Logf("NZB: %d files, %d total segments, %.2f GB",
+		len(nzbFile.Files), nzbFile.TotalSegments(),
+		float64(nzbFile.TotalBytes())/1024/1024/1024)
+
+	if nzbFile.Password != "" {
+		t.Logf("NZB password: %s", nzbFile.Password)
+	}
+
+	t.Logf("Has rars: %v, Has par2: %v", nzbFile.HasRars(), nzbFile.HasPar2())
+
+	for _, file := range nzbFile.Files {
+		t.Logf("  %s — %d segments, %.1f MB",
+			file.Filename(), len(file.Segments),
+			float64(file.TotalBytes())/1024/1024)
+	}
+
+	// 2. Connect NNTP
+	client := nntp.NewClient(nntp.Config{
+		Host:           "reader.torrentclaw.com",
+		Port:           563,
+		SSL:            true,
+		TLSServerName:  "xsnews.nl",
+		Username:       os.Getenv("NNTP_USER"),
+		Password:       os.Getenv("NNTP_PASS"),
+		MaxConnections: 10,
+	})
+
+	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Minute)
+	defer cancel()
+
+	t.Log("Connecting NNTP (10 connections)...")
+	if err := client.Connect(ctx); err != nil {
+		t.Fatalf("NNTP connect: %v", err)
+	}
+	defer client.Close()
+	t.Logf("NNTP connected: %s", client.Status())
+
+	// 3. Download all files
+	outputDir, err := os.MkdirTemp("", "usenet-e2e-*")
+	if err != nil {
+		t.Fatalf("tmpdir: %v", err)
+	}
+	t.Logf("Output dir: %s", outputDir)
+	// Don't cleanup automatically — let user inspect
+	// defer os.RemoveAll(outputDir)
+
+	dl := download.NewDownloader(client)
+
+	progressCh := make(chan download.Progress, 64)
+	go func() {
+		for p := range progressCh {
+			pct := 0
+			if p.BytesTotal > 0 {
+				pct = int(float64(p.BytesDownloaded) / float64(p.BytesTotal) * 100)
+			}
+			fmt.Fprintf(os.Stderr, "\r  [%s] %d%% — %s/%s @ %s/s (%d/%d segs)  ",
+				p.FileName,
+				pct,
+				formatSize(p.BytesDownloaded),
+				formatSize(p.BytesTotal),
+				formatSize(p.SpeedBps),
+				p.SegmentsDone, p.SegmentsTotal)
+		}
+		fmt.Fprintln(os.Stderr)
+	}()
+
+	downloadedFiles, err := dl.DownloadNZB(ctx, nzbFile, outputDir, progressCh)
+	close(progressCh)
+	if err != nil {
+		t.Fatalf("download: %v", err)
+	}
+
+	t.Logf("Downloaded %d files:", len(downloadedFiles))
+	for name, path := range downloadedFiles {
+		fi, _ := os.Stat(path)
+		size := int64(0)
+		if fi != nil {
+			size = fi.Size()
+		}
+		t.Logf("  %s → %s (%.1f MB)", name, path, float64(size)/1024/1024)
+	}
+
+	// 4. Post-process
+	t.Log("Post-processing...")
+	result, err := postprocess.Process(outputDir, downloadedFiles, postprocess.Options{
+		Password: nzbFile.Password,
+		Cleanup:  true,
+	})
+	if err != nil {
+		t.Fatalf("post-process: %v", err)
+	}
+
+	t.Logf("Post-process result:")
+	t.Logf("  Final path: %s", result.FinalPath)
+	t.Logf("  Repaired: %v", result.Repaired)
+	t.Logf("  Extracted: %v", result.Extracted)
+	t.Logf("  Files: %v", result.Files)
+
+	// Verify final file exists and has size
+	if result.FinalPath != "" {
+		fi, err := os.Stat(result.FinalPath)
+		if err != nil {
+			t.Errorf("final file stat: %v", err)
+		} else {
+			t.Logf("  Final size: %.2f GB", float64(fi.Size())/1024/1024/1024)
+		}
+	}
+
+	// List all files in output dir
+	t.Log("Final directory contents:")
+	filepath.Walk(outputDir, func(path string, info os.FileInfo, err error) error {
+		if err != nil || info.IsDir() {
+			return nil
+		}
+		rel, _ := filepath.Rel(outputDir, path)
+		t.Logf("  %s (%.1f MB)", rel, float64(info.Size())/1024/1024)
+		return nil
+	})
+}
+
+func formatSize(b int64) string {
+	const unit = 1024
+	if b < unit {
+		return fmt.Sprintf("%d B", b)
+	}
+	div, exp := int64(unit), 0
+	for n := b / unit; n >= unit; n /= unit {
+		div *= unit
+		exp++
+	}
+	return fmt.Sprintf("%.1f %cB", float64(b)/float64(div), "KMGTPE"[exp])
+}
--- a/internal/usenet/nntp/client.go
+++ b/internal/usenet/nntp/client.go
@ -0,0 +1,386 @@
+package nntp
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"crypto/tls"
+	"fmt"
+	"io"
+	"net"
+	"net/textproto"
+	"sync"
+	"time"
+)
+
+// Config holds NNTP server connection parameters.
+type Config struct {
+	Host           string
+	Port           int
+	SSL            bool
+	TLSServerName  string // override for TLS cert validation (e.g., "xsnews.nl" when Host is a CNAME)
+	Username       string
+	Password       string
+	MaxConnections int // default 10
+}
+
+// Client manages a pool of authenticated NNTP connections.
+type Client struct {
+	cfg  Config
+	pool chan *conn
+	mu   sync.Mutex
+	open int
+	done chan struct{} // closed on Close()
+}
+
+// conn is a single NNTP connection.
+type conn struct {
+	tp     *textproto.Conn
+	raw    net.Conn
+	closed bool
+}
+
+// NewClient creates a new NNTP client (does not connect yet).
+func NewClient(cfg Config) *Client {
+	if cfg.MaxConnections <= 0 {
+		cfg.MaxConnections = 10
+	}
+	return &Client{
+		cfg:  cfg,
+		pool: make(chan *conn, cfg.MaxConnections),
+		done: make(chan struct{}),
+	}
+}
+
+// Connect opens and authenticates all connections in the pool.
+// Safe to call again after a previous Connect failure.
+func (c *Client) Connect(ctx context.Context) error {
+	// Reset done channel if previously closed (allows retry after failure)
+	select {
+	case <-c.done:
+		c.done = make(chan struct{})
+	default:
+	}
+
+	for i := 0; i < c.cfg.MaxConnections; i++ {
+		conn, err := c.dial(ctx)
+		if err != nil {
+			// Close any connections we already opened, but keep client reusable
+			c.drainPool()
+			return fmt.Errorf("nntp: connect %d/%d: %w", i+1, c.cfg.MaxConnections, err)
+		}
+		c.pool <- conn
+		c.mu.Lock()
+		c.open++
+		c.mu.Unlock()
+	}
+	return nil
+}
+
+// drainPool closes all connections in the pool without closing the done channel.
+func (c *Client) drainPool() {
+	for {
+		select {
+		case cn := <-c.pool:
+			c.closeConn(cn)
+		default:
+			c.mu.Lock()
+			c.open = 0
+			c.mu.Unlock()
+			return
+		}
+	}
+}
+
+// Body downloads the body of an NNTP article by message-ID.
+// Returns the raw body reader (typically yEnc encoded).
+// The caller MUST call release() when done reading.
+func (c *Client) Body(ctx context.Context, messageID string) ([]byte, error) {
+	cn, err := c.acquire(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	data, err := c.bodyOnConn(ctx, cn, messageID)
+	if err != nil {
+		// Connection might be broken, try to reconnect
+		cn2, reconErr := c.reconnect(ctx, cn)
+		if reconErr != nil {
+			c.discard(cn)
+			return nil, fmt.Errorf("nntp: body failed and reconnect failed: %w (original: %v)", reconErr, err)
+		}
+		// Retry once on the fresh connection
+		data, err = c.bodyOnConn(ctx, cn2, messageID)
+		if err != nil {
+			c.release(cn2)
+			return nil, err
+		}
+		c.release(cn2)
+		return data, nil
+	}
+
+	c.release(cn)
+	return data, nil
+}
+
+// ActiveConnections returns the number of open connections.
+func (c *Client) ActiveConnections() int {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	return c.open
+}
+
+// Close shuts down all connections in the pool.
+func (c *Client) Close() error {
+	select {
+	case <-c.done:
+		return nil // already closed
+	default:
+		close(c.done)
+	}
+
+	// Drain pool and close connections
+	for {
+		select {
+		case cn := <-c.pool:
+			c.closeConn(cn)
+		default:
+			return nil
+		}
+	}
+}
+
+// --- Internal ---
+
+func (c *Client) dial(ctx context.Context) (*conn, error) {
+	addr := fmt.Sprintf("%s:%d", c.cfg.Host, c.cfg.Port)
+
+	dialer := &net.Dialer{Timeout: 30 * time.Second}
+
+	var rawConn net.Conn
+	var err error
+
+	if c.cfg.SSL {
+		// Use TLSServerName if set (e.g., cert is for xsnews.nl but host is reader.torrentclaw.com)
+		serverName := c.cfg.TLSServerName
+		if serverName == "" {
+			serverName = c.cfg.Host
+		}
+		tlsCfg := &tls.Config{
+			ServerName: serverName,
+			MinVersion: tls.VersionTLS12,
+		}
+		rawConn, err = tls.DialWithDialer(dialer, "tcp", addr, tlsCfg)
+	} else {
+		rawConn, err = dialer.DialContext(ctx, "tcp", addr)
+	}
+	if err != nil {
+		return nil, fmt.Errorf("dial %s: %w", addr, err)
+	}
+
+	tp := textproto.NewConn(rawConn)
+	cn := &conn{tp: tp, raw: rawConn}
+
+	// Read welcome banner (200 or 201)
+	code, msg, err := tp.ReadCodeLine(200)
+	if err != nil {
+		// Also accept 201 (posting not allowed)
+		if code != 201 {
+			rawConn.Close()
+			return nil, fmt.Errorf("welcome: %d %s: %w", code, msg, err)
+		}
+	}
+
+	// Authenticate
+	if c.cfg.Username != "" {
+		if err := c.auth(tp); err != nil {
+			rawConn.Close()
+			return nil, fmt.Errorf("auth: %w", err)
+		}
+	}
+
+	return cn, nil
+}
+
+func (c *Client) auth(tp *textproto.Conn) error {
+	id, err := tp.Cmd("AUTHINFO USER %s", c.cfg.Username)
+	if err != nil {
+		return err
+	}
+	tp.StartResponse(id)
+	code, msg, err := tp.ReadCodeLine(381)
+	tp.EndResponse(id)
+	if err != nil {
+		// 281 means no password required (unlikely but valid)
+		if code == 281 {
+			return nil
+		}
+		return fmt.Errorf("AUTHINFO USER: %d %s: %w", code, msg, err)
+	}
+
+	id, err = tp.Cmd("AUTHINFO PASS %s", c.cfg.Password)
+	if err != nil {
+		return err
+	}
+	tp.StartResponse(id)
+	code, msg, err = tp.ReadCodeLine(281)
+	tp.EndResponse(id)
+	if err != nil {
+		return fmt.Errorf("AUTHINFO PASS: %d %s: %w", code, msg, err)
+	}
+
+	return nil
+}
+
+func (c *Client) bodyOnConn(ctx context.Context, cn *conn, messageID string) ([]byte, error) {
+	// Set deadline from context
+	deadline, hasDeadline := ctx.Deadline()
+	if !hasDeadline {
+		deadline = time.Now().Add(60 * time.Second)
+	}
+	cn.raw.SetDeadline(deadline)
+	defer cn.raw.SetDeadline(time.Time{})
+
+	// Send BODY command
+	id, err := cn.tp.Cmd("BODY <%s>", messageID)
+	if err != nil {
+		return nil, fmt.Errorf("BODY cmd: %w", err)
+	}
+
+	cn.tp.StartResponse(id)
+	defer cn.tp.EndResponse(id)
+
+	// Read response code
+	code, msg, err := cn.tp.ReadCodeLine(222)
+	if err != nil {
+		if code == 430 {
+			return nil, &ArticleNotFoundError{MessageID: messageID}
+		}
+		return nil, fmt.Errorf("BODY response: %d %s: %w", code, msg, err)
+	}
+
+	// Read dot-terminated body
+	body, err := readDotBody(cn.tp.R)
+	if err != nil {
+		// Partial read leaves textproto in broken state — mark connection as dead
+		cn.closed = true
+		return nil, fmt.Errorf("read body: %w", err)
+	}
+
+	return body, nil
+}
+
+// readDotBody reads a dot-terminated text block from the NNTP server.
+// Lines beginning with a dot have the dot removed (dot-stuffing).
+// The final ".\r\n" line signals the end.
+func readDotBody(r *bufio.Reader) ([]byte, error) {
+	var buf bytes.Buffer
+
+	for {
+		line, err := r.ReadBytes('\n')
+		if err != nil {
+			if err == io.EOF {
+				break
+			}
+			return nil, err
+		}
+
+		// Trim trailing \r\n
+		line = bytes.TrimRight(line, "\r\n")
+
+		// Check for terminator: single dot
+		if len(line) == 1 && line[0] == '.' {
+			break
+		}
+
+		// Dot-unstuffing: remove leading dot if present
+		if len(line) > 0 && line[0] == '.' {
+			line = line[1:]
+		}
+
+		buf.Write(line)
+		buf.WriteByte('\n')
+	}
+
+	return buf.Bytes(), nil
+}
+
+func (c *Client) acquire(ctx context.Context) (*conn, error) {
+	for {
+		select {
+		case cn := <-c.pool:
+			if cn.closed {
+				c.mu.Lock()
+				c.open--
+				c.mu.Unlock()
+				continue // discard and try next
+			}
+			return cn, nil
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		case <-c.done:
+			return nil, fmt.Errorf("nntp: client closed")
+		}
+	}
+}
+
+func (c *Client) release(cn *conn) {
+	if cn == nil || cn.closed {
+		return
+	}
+	select {
+	case c.pool <- cn:
+	default:
+		// Pool full, close the connection
+		c.closeConn(cn)
+	}
+}
+
+func (c *Client) discard(cn *conn) {
+	c.closeConn(cn)
+	c.mu.Lock()
+	c.open--
+	c.mu.Unlock()
+}
+
+func (c *Client) reconnect(ctx context.Context, old *conn) (*conn, error) {
+	c.closeConn(old)
+	newConn, err := c.dial(ctx)
+	if err != nil {
+		c.mu.Lock()
+		c.open--
+		c.mu.Unlock()
+		return nil, err
+	}
+	return newConn, nil
+}
+
+func (c *Client) closeConn(cn *conn) {
+	if cn == nil || cn.closed {
+		return
+	}
+	cn.closed = true
+	// Best-effort QUIT
+	cn.tp.Cmd("QUIT")
+	cn.raw.Close()
+}
+
+// ArticleNotFoundError is returned when the server responds with 430.
+type ArticleNotFoundError struct {
+	MessageID string
+}
+
+func (e *ArticleNotFoundError) Error() string {
+	return fmt.Sprintf("nntp: article not found: %s", e.MessageID)
+}
+
+// Status returns a human-readable status string.
+func (c *Client) Status() string {
+	c.mu.Lock()
+	open := c.open
+	c.mu.Unlock()
+
+	pooled := len(c.pool)
+	return fmt.Sprintf("%d connections (%d pooled) to %s:%d", open, pooled, c.cfg.Host, c.cfg.Port)
+}
+
--- a/internal/usenet/nzb/parser.go
+++ b/internal/usenet/nzb/parser.go
@ -0,0 +1,365 @@
+package nzb
+
+import (
+	"encoding/xml"
+	"fmt"
+	"io"
+	"path/filepath"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+// NZB represents a parsed NZB file containing one or more files to download.
+type NZB struct {
+	Files    []File
+	Password string            // from <meta type="password"> in <head>
+	Meta     map[string]string // all <meta> entries from <head>
+}
+
+// File represents a single file within an NZB, composed of multiple segments.
+type File struct {
+	Poster   string
+	Date     int64
+	Subject  string
+	Groups   []string
+	Segments []Segment
+}
+
+// Segment represents a single NNTP article segment of a file.
+type Segment struct {
+	Bytes     int64
+	Number    int
+	MessageID string // message-id without angle brackets
+}
+
+// xmlNZB is the raw XML structure for parsing.
+type xmlNZB struct {
+	XMLName xml.Name  `xml:"nzb"`
+	Head    xmlHead   `xml:"head"`
+	Files   []xmlFile `xml:"file"`
+}
+
+type xmlHead struct {
+	Meta []xmlMeta `xml:"meta"`
+}
+
+type xmlMeta struct {
+	Type  string `xml:"type,attr"`
+	Value string `xml:",chardata"`
+}
+
+type xmlFile struct {
+	Poster   string        `xml:"poster,attr"`
+	Date     string        `xml:"date,attr"`
+	Subject  string        `xml:"subject,attr"`
+	Groups   xmlGroups     `xml:"groups"`
+	Segments xmlSegments   `xml:"segments"`
+}
+
+type xmlGroups struct {
+	Groups []string `xml:"group"`
+}
+
+type xmlSegments struct {
+	Segments []xmlSegment `xml:"segment"`
+}
+
+type xmlSegment struct {
+	Bytes     string `xml:"bytes,attr"`
+	Number    string `xml:"number,attr"`
+	MessageID string `xml:",chardata"`
+}
+
+// Parse reads and parses an NZB XML document from the given reader.
+func Parse(r io.Reader) (*NZB, error) {
+	var raw xmlNZB
+	dec := xml.NewDecoder(r)
+	if err := dec.Decode(&raw); err != nil {
+		return nil, fmt.Errorf("nzb: xml decode: %w", err)
+	}
+
+	if len(raw.Files) == 0 {
+		return nil, fmt.Errorf("nzb: no files found")
+	}
+
+	nzb := &NZB{
+		Files: make([]File, 0, len(raw.Files)),
+		Meta:  make(map[string]string),
+	}
+
+	// Parse <head> meta entries
+	for _, m := range raw.Head.Meta {
+		if m.Type != "" {
+			nzb.Meta[m.Type] = strings.TrimSpace(m.Value)
+		}
+	}
+	nzb.Password = nzb.Meta["password"]
+
+	for _, rf := range raw.Files {
+		date, _ := strconv.ParseInt(rf.Date, 10, 64)
+
+		segs := make([]Segment, 0, len(rf.Segments.Segments))
+		for _, rs := range rf.Segments.Segments {
+			bytes, _ := strconv.ParseInt(rs.Bytes, 10, 64)
+			num, _ := strconv.Atoi(rs.Number)
+			msgID := strings.TrimSpace(rs.MessageID)
+			// Strip angle brackets if present
+			msgID = strings.TrimPrefix(msgID, "<")
+			msgID = strings.TrimSuffix(msgID, ">")
+
+			if msgID == "" {
+				continue
+			}
+
+			segs = append(segs, Segment{
+				Bytes:     bytes,
+				Number:    num,
+				MessageID: msgID,
+			})
+		}
+
+		if len(segs) == 0 {
+			continue
+		}
+
+		nzb.Files = append(nzb.Files, File{
+			Poster:   rf.Poster,
+			Date:     date,
+			Subject:  rf.Subject,
+			Groups:   rf.Groups.Groups,
+			Segments: segs,
+		})
+	}
+
+	if len(nzb.Files) == 0 {
+		return nil, fmt.Errorf("nzb: no valid files with segments found")
+	}
+
+	return nzb, nil
+}
+
+// ParseBytes parses an NZB from a byte slice.
+func ParseBytes(data []byte) (*NZB, error) {
+	return Parse(strings.NewReader(string(data)))
+}
+
+// TotalBytes returns the total size of all segments across all files.
+func (n *NZB) TotalBytes() int64 {
+	var total int64
+	for _, f := range n.Files {
+		total += f.TotalBytes()
+	}
+	return total
+}
+
+// TotalSegments returns the total number of segments across all files.
+func (n *NZB) TotalSegments() int {
+	var total int
+	for _, f := range n.Files {
+		total += len(f.Segments)
+	}
+	return total
+}
+
+// ContentFiles returns files that are likely content (video, audio, images),
+// excluding par2, nfo, sfv, nzb, and sample files.
+func (n *NZB) ContentFiles() []File {
+	var result []File
+	for _, f := range n.Files {
+		name := f.Filename()
+		if isMetadataFile(name) || isSampleFile(name) {
+			continue
+		}
+		result = append(result, f)
+	}
+	return result
+}
+
+// Par2Files returns only par2 parity files.
+func (n *NZB) Par2Files() []File {
+	var result []File
+	for _, f := range n.Files {
+		ext := strings.ToLower(filepath.Ext(f.Filename()))
+		if ext == ".par2" {
+			result = append(result, f)
+		}
+	}
+	return result
+}
+
+// RarFiles returns rar archive files (.rar, .rNN, .NNN).
+func (n *NZB) RarFiles() []File {
+	var result []File
+	for _, f := range n.Files {
+		if isRarFile(f.Filename()) {
+			result = append(result, f)
+		}
+	}
+	return result
+}
+
+// LargestFile returns the file with the most total bytes.
+// Returns nil if NZB has no files.
+func (n *NZB) LargestFile() *File {
+	if len(n.Files) == 0 {
+		return nil
+	}
+	largest := &n.Files[0]
+	for i := 1; i < len(n.Files); i++ {
+		if n.Files[i].TotalBytes() > largest.TotalBytes() {
+			largest = &n.Files[i]
+		}
+	}
+	return largest
+}
+
+// IsObfuscated returns true if the NZB filenames appear to be obfuscated
+// (random strings instead of meaningful names).
+func (n *NZB) IsObfuscated() bool {
+	for _, f := range n.Files {
+		name := f.Filename()
+		if name == "" {
+			continue
+		}
+		base := strings.TrimSuffix(name, filepath.Ext(name))
+		// Check if base name is mostly hex/random chars (obfuscated)
+		if len(base) > 10 && isHexLike(base) {
+			return true
+		}
+	}
+	return false
+}
+
+// HasRars returns true if the NZB contains rar archive files.
+func (n *NZB) HasRars() bool {
+	for _, f := range n.Files {
+		if isRarFile(f.Filename()) {
+			return true
+		}
+	}
+	return false
+}
+
+// HasPar2 returns true if the NZB contains par2 parity files.
+func (n *NZB) HasPar2() bool {
+	for _, f := range n.Files {
+		ext := strings.ToLower(filepath.Ext(f.Filename()))
+		if ext == ".par2" {
+			return true
+		}
+	}
+	return false
+}
+
+// TotalBytes returns the sum of all segment sizes in this file.
+func (f *File) TotalBytes() int64 {
+	var total int64
+	for _, s := range f.Segments {
+		total += s.Bytes
+	}
+	return total
+}
+
+// subjectFilenameRe matches the filename in a typical Usenet subject line.
+// Examples:
+//   "Movie.2024.1080p.mkv" yEnc (1/50)
+//   [PRiVATE]-[#a]- "file.rar" yEnc (01/99)
+var subjectFilenameRe = regexp.MustCompile(`"([^"]+)"`)
+
+// Filename extracts the filename from the subject line.
+// Falls back to the raw subject if no quoted filename is found.
+func (f *File) Filename() string {
+	m := subjectFilenameRe.FindStringSubmatch(f.Subject)
+	if len(m) >= 2 {
+		return m[1]
+	}
+	// Fallback: try to extract something useful
+	return sanitizeFilename(f.Subject)
+}
+
+// Extension returns the lowercase file extension (e.g., ".mkv", ".rar").
+func (f *File) Extension() string {
+	return strings.ToLower(filepath.Ext(f.Filename()))
+}
+
+// isMetadataFile returns true for non-content files.
+func isMetadataFile(name string) bool {
+	ext := strings.ToLower(filepath.Ext(name))
+	switch ext {
+	case ".par2", ".nfo", ".sfv", ".nzb", ".txt", ".jpg", ".png", ".url":
+		return true
+	}
+	return false
+}
+
+// isSampleFile returns true for sample/preview files.
+// Matches filenames containing "sample" as a word boundary (e.g., "movie.sample.mkv", "Sample/video.mkv").
+func isSampleFile(name string) bool {
+	lower := strings.ToLower(name)
+	// Match "sample" preceded and followed by non-alphanumeric (word boundary)
+	idx := strings.Index(lower, "sample")
+	if idx < 0 {
+		return false
+	}
+	// Check it's not part of a larger word (e.g., "resampled")
+	if idx > 0 && isAlphaNum(lower[idx-1]) {
+		return false
+	}
+	end := idx + 6
+	if end < len(lower) && isAlphaNum(lower[end]) {
+		return false
+	}
+	return true
+}
+
+func isAlphaNum(b byte) bool {
+	return (b >= 'a' && b <= 'z') || (b >= '0' && b <= '9')
+}
+
+// isRarFile returns true for rar archive files.
+func isRarFile(name string) bool {
+	lower := strings.ToLower(name)
+	ext := filepath.Ext(lower)
+	if ext == ".rar" {
+		return true
+	}
+	// Match .r00, .r01, ..., .r99 and .s00, .s01
+	if len(ext) == 4 && (ext[1] == 'r' || ext[1] == 's') {
+		_, err := strconv.Atoi(ext[2:])
+		return err == nil
+	}
+	// Match .001, .002, etc (split rar)
+	if len(ext) == 4 {
+		_, err := strconv.Atoi(ext[1:])
+		return err == nil
+	}
+	return false
+}
+
+// isHexLike returns true if the string looks like random hex/obfuscated.
+func isHexLike(s string) bool {
+	hexChars := 0
+	for _, c := range s {
+		if (c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F') {
+			hexChars++
+		}
+	}
+	return float64(hexChars)/float64(len(s)) > 0.8
+}
+
+var yencPartRe = regexp.MustCompile(`\s*\(\d+/\d+\)\s*`)
+
+// sanitizeFilename removes characters that are invalid in filenames.
+func sanitizeFilename(s string) string {
+	// Remove yEnc part indicators like (01/50)
+	s = yencPartRe.ReplaceAllString(s, "")
+	// Remove yEnc keyword
+	s = strings.ReplaceAll(s, "yEnc", "")
+	s = strings.TrimSpace(s)
+	// Remove invalid path chars
+	for _, c := range []string{"/", "\\", ":", "*", "?", "\"", "<", ">", "|"} {
+		s = strings.ReplaceAll(s, c, "_")
+	}
+	return s
+}
--- a/internal/usenet/nzb/parser_test.go
+++ b/internal/usenet/nzb/parser_test.go
@ -0,0 +1,269 @@
+package nzb
+
+import (
+	"strings"
+	"testing"
+)
+
+const testNZB = `<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE nzb PUBLIC "-//newzBin//DTD NZB 1.1//EN" "http://www.newzbin.com/DTD/nzb/nzb-1.1.dtd">
+<nzb xmlns="http://www.newzbin.com/DTD/2003/nzb">
+  <file poster="user@example.com" date="1700000000" subject="Movie.2024.1080p.BluRay.x264-GROUP [01/50] - &quot;Movie.2024.1080p.BluRay.x264-GROUP.mkv&quot; yEnc (1/3200)">
+    <groups>
+      <group>alt.binaries.movies</group>
+      <group>alt.binaries.multimedia</group>
+    </groups>
+    <segments>
+      <segment bytes="768000" number="1">abc123@news.example.com</segment>
+      <segment bytes="768000" number="2">def456@news.example.com</segment>
+      <segment bytes="512000" number="3">ghi789@news.example.com</segment>
+    </segments>
+  </file>
+  <file poster="user@example.com" date="1700000000" subject="Movie.2024.1080p.BluRay.x264-GROUP [02/50] - &quot;Movie.2024.1080p.BluRay.x264-GROUP.nfo&quot; yEnc (1/1)">
+    <groups>
+      <group>alt.binaries.movies</group>
+    </groups>
+    <segments>
+      <segment bytes="4096" number="1">nfo001@news.example.com</segment>
+    </segments>
+  </file>
+  <file poster="user@example.com" date="1700000000" subject="Movie.2024.1080p.BluRay.x264-GROUP [03/50] - &quot;Movie.2024.1080p.BluRay.x264-GROUP.par2&quot; yEnc (1/1)">
+    <groups>
+      <group>alt.binaries.movies</group>
+    </groups>
+    <segments>
+      <segment bytes="32768" number="1">par001@news.example.com</segment>
+    </segments>
+  </file>
+</nzb>`
+
+const testNZBWithRars = `<?xml version="1.0" encoding="UTF-8"?>
+<nzb xmlns="http://www.newzbin.com/DTD/2003/nzb">
+  <file poster="bot@example.com" date="1700000000" subject="[PRiVATE]-[#a]- &quot;Movie.2024.rar&quot; yEnc (01/99)">
+    <groups><group>alt.binaries.movies</group></groups>
+    <segments>
+      <segment bytes="768000" number="1">rar001@example</segment>
+      <segment bytes="768000" number="2">rar002@example</segment>
+    </segments>
+  </file>
+  <file poster="bot@example.com" date="1700000000" subject="[PRiVATE]-[#a]- &quot;Movie.2024.r00&quot; yEnc (01/99)">
+    <groups><group>alt.binaries.movies</group></groups>
+    <segments>
+      <segment bytes="768000" number="1">r00001@example</segment>
+    </segments>
+  </file>
+  <file poster="bot@example.com" date="1700000000" subject="[PRiVATE]-[#a]- &quot;Movie.2024.r01&quot; yEnc (01/99)">
+    <groups><group>alt.binaries.movies</group></groups>
+    <segments>
+      <segment bytes="768000" number="1">r01001@example</segment>
+    </segments>
+  </file>
+  <file poster="bot@example.com" date="1700000000" subject="[PRiVATE]-[#a]- &quot;Movie.2024.par2&quot; yEnc (1/1)">
+    <groups><group>alt.binaries.movies</group></groups>
+    <segments>
+      <segment bytes="32768" number="1">par001@example</segment>
+    </segments>
+  </file>
+</nzb>`
+
+func TestParse(t *testing.T) {
+	nzb, err := Parse(strings.NewReader(testNZB))
+	if err != nil {
+		t.Fatalf("Parse failed: %v", err)
+	}
+
+	if len(nzb.Files) != 3 {
+		t.Fatalf("expected 3 files, got %d", len(nzb.Files))
+	}
+
+	// First file — the MKV
+	f := nzb.Files[0]
+	if f.Poster != "user@example.com" {
+		t.Errorf("poster: got %q", f.Poster)
+	}
+	if f.Date != 1700000000 {
+		t.Errorf("date: got %d", f.Date)
+	}
+	if len(f.Groups) != 2 {
+		t.Errorf("groups: got %d", len(f.Groups))
+	}
+	if f.Groups[0] != "alt.binaries.movies" {
+		t.Errorf("group[0]: got %q", f.Groups[0])
+	}
+	if len(f.Segments) != 3 {
+		t.Errorf("segments: got %d", len(f.Segments))
+	}
+
+	seg := f.Segments[0]
+	if seg.Bytes != 768000 {
+		t.Errorf("seg bytes: got %d", seg.Bytes)
+	}
+	if seg.Number != 1 {
+		t.Errorf("seg number: got %d", seg.Number)
+	}
+	if seg.MessageID != "abc123@news.example.com" {
+		t.Errorf("seg msgid: got %q", seg.MessageID)
+	}
+}
+
+func TestParseBytes(t *testing.T) {
+	nzb, err := ParseBytes([]byte(testNZB))
+	if err != nil {
+		t.Fatalf("ParseBytes failed: %v", err)
+	}
+	if len(nzb.Files) != 3 {
+		t.Fatalf("expected 3 files, got %d", len(nzb.Files))
+	}
+}
+
+func TestTotalBytes(t *testing.T) {
+	nzb, _ := ParseBytes([]byte(testNZB))
+	// 768000 + 768000 + 512000 + 4096 + 32768
+	expected := int64(768000 + 768000 + 512000 + 4096 + 32768)
+	if got := nzb.TotalBytes(); got != expected {
+		t.Errorf("TotalBytes: got %d, want %d", got, expected)
+	}
+}
+
+func TestTotalSegments(t *testing.T) {
+	nzb, _ := ParseBytes([]byte(testNZB))
+	if got := nzb.TotalSegments(); got != 5 {
+		t.Errorf("TotalSegments: got %d, want 5", got)
+	}
+}
+
+func TestContentFiles(t *testing.T) {
+	nzb, _ := ParseBytes([]byte(testNZB))
+	content := nzb.ContentFiles()
+	if len(content) != 1 {
+		t.Fatalf("ContentFiles: got %d, want 1", len(content))
+	}
+	if content[0].Filename() != "Movie.2024.1080p.BluRay.x264-GROUP.mkv" {
+		t.Errorf("content filename: got %q", content[0].Filename())
+	}
+}
+
+func TestPar2Files(t *testing.T) {
+	nzb, _ := ParseBytes([]byte(testNZB))
+	par2 := nzb.Par2Files()
+	if len(par2) != 1 {
+		t.Fatalf("Par2Files: got %d, want 1", len(par2))
+	}
+}
+
+func TestLargestFile(t *testing.T) {
+	nzb, _ := ParseBytes([]byte(testNZB))
+	largest := nzb.LargestFile()
+	if largest == nil {
+		t.Fatal("LargestFile returned nil")
+	}
+	if largest.Filename() != "Movie.2024.1080p.BluRay.x264-GROUP.mkv" {
+		t.Errorf("largest file: got %q", largest.Filename())
+	}
+}
+
+func TestFilename(t *testing.T) {
+	tests := []struct {
+		subject  string
+		expected string
+	}{
+		{
+			`Movie.2024.1080p [01/50] - "Movie.2024.1080p.mkv" yEnc (1/3200)`,
+			"Movie.2024.1080p.mkv",
+		},
+		{
+			`[PRiVATE]-[#a]- "file.rar" yEnc (01/99)`,
+			"file.rar",
+		},
+		{
+			`Some subject without quotes (1/1)`,
+			"Some subject without quotes",
+		},
+	}
+
+	for _, tt := range tests {
+		f := File{Subject: tt.subject}
+		if got := f.Filename(); got != tt.expected {
+			t.Errorf("Filename(%q) = %q, want %q", tt.subject, got, tt.expected)
+		}
+	}
+}
+
+func TestExtension(t *testing.T) {
+	f := File{Subject: `"Movie.2024.1080p.BluRay.x264-GROUP.mkv" yEnc (1/3200)`}
+	if got := f.Extension(); got != ".mkv" {
+		t.Errorf("Extension: got %q, want .mkv", got)
+	}
+}
+
+func TestHasRars(t *testing.T) {
+	nzb, _ := ParseBytes([]byte(testNZBWithRars))
+	if !nzb.HasRars() {
+		t.Error("HasRars: expected true")
+	}
+	if !nzb.HasPar2() {
+		t.Error("HasPar2: expected true")
+	}
+}
+
+func TestRarFiles(t *testing.T) {
+	nzb, _ := ParseBytes([]byte(testNZBWithRars))
+	rars := nzb.RarFiles()
+	if len(rars) != 3 {
+		t.Fatalf("RarFiles: got %d, want 3", len(rars))
+	}
+}
+
+func TestIsRarFile(t *testing.T) {
+	tests := []struct {
+		name string
+		want bool
+	}{
+		{"file.rar", true},
+		{"file.r00", true},
+		{"file.r99", true},
+		{"file.s00", true},
+		{"file.001", true},
+		{"file.mkv", false},
+		{"file.par2", false},
+		{"file.nfo", false},
+	}
+	for _, tt := range tests {
+		if got := isRarFile(tt.name); got != tt.want {
+			t.Errorf("isRarFile(%q) = %v, want %v", tt.name, got, tt.want)
+		}
+	}
+}
+
+func TestParseEmpty(t *testing.T) {
+	_, err := Parse(strings.NewReader(`<?xml version="1.0"?><nzb xmlns="http://www.newzbin.com/DTD/2003/nzb"></nzb>`))
+	if err == nil {
+		t.Error("expected error for empty NZB")
+	}
+}
+
+func TestParseInvalidXML(t *testing.T) {
+	_, err := Parse(strings.NewReader("not xml"))
+	if err == nil {
+		t.Error("expected error for invalid XML")
+	}
+}
+
+func TestStripAngleBrackets(t *testing.T) {
+	nzbXML := `<?xml version="1.0"?>
+<nzb xmlns="http://www.newzbin.com/DTD/2003/nzb">
+  <file poster="test" date="0" subject="&quot;test.bin&quot; (1/1)">
+    <groups><group>alt.test</group></groups>
+    <segments>
+      <segment bytes="100" number="1">&lt;angle@brackets.com&gt;</segment>
+    </segments>
+  </file>
+</nzb>`
+	nzb, err := ParseBytes([]byte(nzbXML))
+	if err != nil {
+		t.Fatalf("Parse failed: %v", err)
+	}
+	if nzb.Files[0].Segments[0].MessageID != "angle@brackets.com" {
+		t.Errorf("MessageID not stripped: got %q", nzb.Files[0].Segments[0].MessageID)
+	}
+}
--- a/internal/usenet/postprocess/extract.go
+++ b/internal/usenet/postprocess/extract.go
@ -0,0 +1,224 @@
+package postprocess
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"regexp"
+	"strings"
+)
+
+// ExtractorType identifies which extraction tool is available.
+type ExtractorType string
+
+const (
+	ExtractorNone  ExtractorType = ""
+	ExtractorUnrar ExtractorType = "unrar"
+	Extractor7z    ExtractorType = "7z"
+)
+
+// FindExtractor checks which archive extractor is available in PATH.
+func FindExtractor() (ExtractorType, string) {
+	if path, err := exec.LookPath("unrar"); err == nil {
+		return ExtractorUnrar, path
+	}
+	if path, err := exec.LookPath("7z"); err == nil {
+		return Extractor7z, path
+	}
+	return ExtractorNone, ""
+}
+
+// Extract extracts an archive using the best available tool.
+// password is optional — pass "" if not needed.
+// Returns the list of extracted file paths.
+func Extract(archivePath string, outputDir string, password string) ([]string, error) {
+	extType, extPath := FindExtractor()
+	if extType == ExtractorNone {
+		return nil, fmt.Errorf("no archive extractor found (install unrar or 7z)")
+	}
+
+	switch extType {
+	case ExtractorUnrar:
+		return extractUnrar(extPath, archivePath, outputDir, password)
+	case Extractor7z:
+		return extract7z(extPath, archivePath, outputDir, password)
+	default:
+		return nil, fmt.Errorf("unknown extractor: %s", extType)
+	}
+}
+
+// extractUnrar extracts using unrar.
+func extractUnrar(unrarPath, archivePath, outputDir, password string) ([]string, error) {
+	args := []string{"x", "-o+", "-y"}
+	if password != "" {
+		args = append(args, "-p"+password)
+	} else {
+		args = append(args, "-p-") // no password, skip asking
+	}
+	args = append(args, archivePath, outputDir+"/")
+
+	cmd := exec.Command(unrarPath, args...)
+	cmd.Dir = outputDir
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		// Check for password error
+		outStr := string(output)
+		if strings.Contains(outStr, "wrong password") || strings.Contains(outStr, "Incorrect password") {
+			return nil, &PasswordError{Archive: archivePath}
+		}
+		return nil, fmt.Errorf("unrar: %w\n%s", err, output)
+	}
+
+	return listExtractedFiles(outputDir, archivePath)
+}
+
+// extract7z extracts using 7z.
+func extract7z(szPath, archivePath, outputDir, password string) ([]string, error) {
+	args := []string{"x", "-y", "-o" + outputDir}
+	if password != "" {
+		args = append(args, "-p"+password)
+	} else {
+		args = append(args, "-p") // empty password
+	}
+	args = append(args, archivePath)
+
+	cmd := exec.Command(szPath, args...)
+	cmd.Dir = outputDir
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		outStr := string(output)
+		if strings.Contains(outStr, "Wrong password") || strings.Contains(outStr, "incorrect password") {
+			return nil, &PasswordError{Archive: archivePath}
+		}
+		return nil, fmt.Errorf("7z: %w\n%s", err, output)
+	}
+
+	return listExtractedFiles(outputDir, archivePath)
+}
+
+// IsPasswordProtected checks if a rar archive requires a password.
+func IsPasswordProtected(archivePath string) bool {
+	extType, extPath := FindExtractor()
+	if extType == ExtractorNone {
+		return false
+	}
+
+	switch extType {
+	case ExtractorUnrar:
+		cmd := exec.Command(extPath, "t", "-p-", archivePath)
+		output, err := cmd.CombinedOutput()
+		if err != nil {
+			outStr := string(output)
+			return strings.Contains(outStr, "password") || strings.Contains(outStr, "encrypted")
+		}
+	case Extractor7z:
+		cmd := exec.Command(extPath, "t", "-p", archivePath)
+		output, err := cmd.CombinedOutput()
+		if err != nil {
+			outStr := string(output)
+			return strings.Contains(outStr, "Wrong password") || strings.Contains(outStr, "encrypted")
+		}
+	}
+	return false
+}
+
+// listExtractedFiles returns new files in outputDir that aren't the archive itself.
+func listExtractedFiles(dir, archivePath string) ([]string, error) {
+	archiveBase := filepath.Base(archivePath)
+	archiveDir := filepath.Dir(archivePath)
+	var files []string
+
+	err := filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return nil // skip errors
+		}
+		if info.IsDir() {
+			return nil
+		}
+		base := filepath.Base(path)
+		// Skip archive files themselves
+		if isArchiveFile(base) && filepath.Dir(path) == archiveDir {
+			return nil
+		}
+		if base == archiveBase {
+			return nil
+		}
+		files = append(files, path)
+		return nil
+	})
+	return files, err
+}
+
+// Cleanup removes archive and parity files from a directory.
+func Cleanup(dir string) error {
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		return err
+	}
+
+	for _, entry := range entries {
+		if entry.IsDir() {
+			continue
+		}
+		name := entry.Name()
+		if isCleanupTarget(name) {
+			path := filepath.Join(dir, name)
+			log.Printf("[usenet] cleanup: removing %s", name)
+			os.Remove(path)
+		}
+	}
+	return nil
+}
+
+// isArchiveFile returns true for rar/split archive files.
+func isArchiveFile(name string) bool {
+	lower := strings.ToLower(name)
+	ext := filepath.Ext(lower)
+
+	if ext == ".rar" {
+		return true
+	}
+	// .r00, .r01, ... .r99, .s00, etc.
+	if len(ext) == 4 && (ext[1] == 'r' || ext[1] == 's') {
+		return isNumeric(ext[2:])
+	}
+	// .001, .002, etc.
+	if len(ext) == 4 && isNumeric(ext[1:]) {
+		return true
+	}
+	return false
+}
+
+// isCleanupTarget returns true for files that should be removed after extraction.
+var cleanupExts = regexp.MustCompile(`(?i)\.(par2|nfo|sfv|nzb|srr|srs|jpg|png|txt|url)$`)
+var cleanupRarParts = regexp.MustCompile(`(?i)\.(rar|r\d{2}|s\d{2}|\d{3})$`)
+
+func isCleanupTarget(name string) bool {
+	if cleanupExts.MatchString(name) {
+		return true
+	}
+	if cleanupRarParts.MatchString(name) {
+		return true
+	}
+	return false
+}
+
+func isNumeric(s string) bool {
+	for _, c := range s {
+		if c < '0' || c > '9' {
+			return false
+		}
+	}
+	return len(s) > 0
+}
+
+// PasswordError indicates the archive requires a password.
+type PasswordError struct {
+	Archive string
+}
+
+func (e *PasswordError) Error() string {
+	return fmt.Sprintf("archive is password protected: %s", e.Archive)
+}
--- a/internal/usenet/postprocess/par2.go
+++ b/internal/usenet/postprocess/par2.go
@ -0,0 +1,65 @@
+package postprocess
+
+import (
+	"fmt"
+	"log"
+	"os/exec"
+	"strings"
+)
+
+// Par2Available checks if par2cmdline is installed.
+func Par2Available() bool {
+	_, err := exec.LookPath("par2")
+	return err == nil
+}
+
+// Par2Verify verifies files using a par2 file.
+// Returns nil if verification passes, error otherwise.
+func Par2Verify(par2File string) error {
+	if !Par2Available() {
+		log.Printf("[usenet] par2 not installed, skipping verification")
+		return nil
+	}
+
+	cmd := exec.Command("par2", "verify", par2File)
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		outStr := string(output)
+		// Check if repair is possible
+		if strings.Contains(outStr, "Repair is possible") {
+			return &Par2RepairableError{Par2File: par2File}
+		}
+		if strings.Contains(outStr, "Repair is not possible") {
+			return fmt.Errorf("par2: verification failed and repair not possible:\n%s", outStr)
+		}
+		return fmt.Errorf("par2 verify: %w\n%s", err, outStr)
+	}
+
+	log.Printf("[usenet] par2: verification OK")
+	return nil
+}
+
+// Par2Repair attempts to repair files using par2 parity data.
+func Par2Repair(par2File string) error {
+	if !Par2Available() {
+		return fmt.Errorf("par2 not installed")
+	}
+
+	cmd := exec.Command("par2", "repair", par2File)
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		return fmt.Errorf("par2 repair: %w\n%s", err, output)
+	}
+
+	log.Printf("[usenet] par2: repair successful")
+	return nil
+}
+
+// Par2RepairableError indicates verification failed but repair is possible.
+type Par2RepairableError struct {
+	Par2File string
+}
+
+func (e *Par2RepairableError) Error() string {
+	return fmt.Sprintf("par2: verification failed, repair possible: %s", e.Par2File)
+}
--- a/internal/usenet/postprocess/pipeline.go
+++ b/internal/usenet/postprocess/pipeline.go
@ -0,0 +1,229 @@
+package postprocess
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+	"regexp"
+	"sort"
+	"strings"
+)
+
+// Result holds the outcome of post-processing.
+type Result struct {
+	FinalPath string   // path to the main content file (e.g., the video)
+	Files     []string // all final files
+	Repaired  bool     // whether par2 repair was needed
+	Extracted bool     // whether archive extraction was performed
+}
+
+// Options configures post-processing behavior.
+type Options struct {
+	Password string // password for encrypted archives (empty = none)
+	Cleanup  bool   // remove intermediate files after extraction
+}
+
+// Process runs the full post-processing pipeline on downloaded usenet files.
+// Steps: par2 verify → par2 repair → extract archives → cleanup → find main file.
+func Process(dir string, downloadedFiles map[string]string, opts Options) (*Result, error) {
+	result := &Result{}
+
+	// Step 1: Par2 verification and repair
+	par2File := findPar2File(downloadedFiles)
+	if par2File != "" {
+		err := Par2Verify(par2File)
+		if err != nil {
+			if _, ok := err.(*Par2RepairableError); ok {
+				log.Printf("[usenet] attempting par2 repair...")
+				if repairErr := Par2Repair(par2File); repairErr != nil {
+					log.Printf("[usenet] par2 repair failed: %v", repairErr)
+				} else {
+					result.Repaired = true
+				}
+			} else {
+				log.Printf("[usenet] par2 verification error: %v", err)
+			}
+		}
+	}
+
+	// Step 2: Find and extract archives
+	rarFile := findFirstRar(downloadedFiles)
+	if rarFile != "" {
+		log.Printf("[usenet] extracting archive: %s", filepath.Base(rarFile))
+
+		// Check if password-protected
+		if opts.Password == "" && IsPasswordProtected(rarFile) {
+			return nil, &PasswordError{Archive: rarFile}
+		}
+
+		extracted, err := Extract(rarFile, dir, opts.Password)
+		if err != nil {
+			if _, ok := err.(*PasswordError); ok {
+				return nil, err
+			}
+			return nil, fmt.Errorf("extraction failed: %w", err)
+		}
+
+		result.Extracted = true
+		result.Files = extracted
+
+		// Step 3: Cleanup archive + par2 files
+		if opts.Cleanup {
+			Cleanup(dir)
+		}
+	} else {
+		// No archives — content files are the final files
+		for _, path := range downloadedFiles {
+			if !isCleanupTarget(filepath.Base(path)) {
+				result.Files = append(result.Files, path)
+			}
+		}
+
+		// Cleanup metadata files
+		if opts.Cleanup {
+			for name, path := range downloadedFiles {
+				lower := strings.ToLower(name)
+				ext := filepath.Ext(lower)
+				if ext == ".par2" || ext == ".nfo" || ext == ".sfv" || ext == ".nzb" {
+					log.Printf("[usenet] cleanup: removing %s", name)
+					os.Remove(path)
+				}
+			}
+		}
+	}
+
+	// Step 4: Find main content file (largest video file)
+	result.FinalPath = findMainFile(dir, result.Files)
+
+	if result.FinalPath == "" && len(result.Files) > 0 {
+		result.FinalPath = result.Files[0]
+	}
+
+	return result, nil
+}
+
+// findPar2File returns the path of the main .par2 file (not volume sets).
+func findPar2File(files map[string]string) string {
+	var mainPar2 string
+	var smallestSize int64 = -1
+
+	for name, path := range files {
+		ext := strings.ToLower(filepath.Ext(name))
+		if ext != ".par2" {
+			continue
+		}
+		// The main par2 file is typically the smallest one (index file)
+		// Volume par2 files are larger (contain recovery data)
+		fi, err := os.Stat(path)
+		if err != nil {
+			continue
+		}
+		if smallestSize < 0 || fi.Size() < smallestSize {
+			smallestSize = fi.Size()
+			mainPar2 = path
+		}
+	}
+	return mainPar2
+}
+
+// firstRarRe matches the first volume of a multi-part rar set.
+// Patterns: .part01.rar, .part1.rar, or just .rar (single/first volume)
+var firstRarRe = regexp.MustCompile(`(?i)\.part0*1\.rar$`)
+
+// findFirstRar returns the path to the first rar volume.
+// For multi-part rars (part01.rar, part02.rar...), returns part01 specifically.
+func findFirstRar(files map[string]string) string {
+	// Priority 1: Find explicitly named first part (part01.rar, part1.rar)
+	for _, path := range files {
+		if firstRarRe.MatchString(path) {
+			return path
+		}
+	}
+
+	// Priority 2: Find the shortest-named .rar file (usually the first volume)
+	var rarFiles []struct {
+		name string
+		path string
+	}
+	for name, path := range files {
+		if strings.HasSuffix(strings.ToLower(name), ".rar") {
+			rarFiles = append(rarFiles, struct {
+				name string
+				path string
+			}{name, path})
+		}
+	}
+	if len(rarFiles) > 0 {
+		sort.Slice(rarFiles, func(i, j int) bool {
+			return len(rarFiles[i].name) < len(rarFiles[j].name)
+		})
+		return rarFiles[0].path
+	}
+
+	// Priority 3: .001 split format
+	for name, path := range files {
+		if strings.HasSuffix(strings.ToLower(name), ".001") {
+			return path
+		}
+	}
+	return ""
+}
+
+// findMainFile finds the largest video file in the directory or file list.
+func findMainFile(dir string, files []string) string {
+	videoExts := map[string]bool{
+		".mkv": true, ".mp4": true, ".avi": true, ".mov": true,
+		".wmv": true, ".flv": true, ".m4v": true, ".ts": true,
+		".webm": true,
+	}
+
+	var bestPath string
+	var bestSize int64
+
+	// First try from the explicit file list
+	for _, path := range files {
+		ext := strings.ToLower(filepath.Ext(path))
+		if !videoExts[ext] {
+			continue
+		}
+		fi, err := os.Stat(path)
+		if err != nil {
+			continue
+		}
+		if fi.Size() > bestSize {
+			bestSize = fi.Size()
+			bestPath = path
+		}
+	}
+
+	if bestPath != "" {
+		return bestPath
+	}
+
+	// Fallback: scan directory
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		return ""
+	}
+	for _, entry := range entries {
+		if entry.IsDir() {
+			continue
+		}
+		ext := strings.ToLower(filepath.Ext(entry.Name()))
+		if !videoExts[ext] {
+			continue
+		}
+		fi, err := entry.Info()
+		if err != nil {
+			continue
+		}
+		if fi.Size() > bestSize {
+			bestSize = fi.Size()
+			bestPath = filepath.Join(dir, entry.Name())
+		}
+	}
+
+	return bestPath
+}
+
--- a/internal/usenet/yenc/decode.go
+++ b/internal/usenet/yenc/decode.go
@ -0,0 +1,210 @@
+package yenc
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"hash/crc32"
+	"io"
+	"strconv"
+	"strings"
+)
+
+// Part represents a decoded yEnc part (one NNTP article body).
+type Part struct {
+	Name   string // filename from =ybegin
+	Number int    // part number (1-based)
+	Total  int    // total parts (from =ybegin total=N)
+	Begin  int64  // byte offset start (from =ypart begin=N, 1-based)
+	End    int64  // byte offset end (from =ypart end=N, inclusive)
+	Size   int64  // total file size (from =ybegin size=N)
+	CRC32  uint32 // CRC32 of this part's data (from =yend pcrc32)
+	Data   []byte // decoded binary data
+}
+
+// Decode reads a yEnc encoded article body and returns the decoded part.
+// The reader should contain the raw article body (after NNTP BODY response).
+func Decode(r io.Reader) (*Part, error) {
+	scanner := bufio.NewScanner(r)
+	scanner.Buffer(make([]byte, 0, 1024*1024), 10*1024*1024) // up to 10MB per article
+
+	part := &Part{}
+
+	// Phase 1: Find and parse =ybegin header
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.HasPrefix(line, "=ybegin ") {
+			parseYBegin(part, line)
+			break
+		}
+	}
+	if part.Name == "" && part.Size == 0 {
+		return nil, fmt.Errorf("yenc: no =ybegin header found")
+	}
+
+	// Phase 2: Find optional =ypart header (for multipart)
+	// Peek at next line
+	if scanner.Scan() {
+		line := scanner.Text()
+		if strings.HasPrefix(line, "=ypart ") {
+			parseYPart(part, line)
+		} else {
+			// Not a ypart line, decode it as data
+			part.Data = append(part.Data, decodeLine(line)...)
+		}
+	}
+
+	// Phase 3: Decode data lines until =yend
+	hasher := crc32.NewIEEE()
+	// Hash data we already decoded (if any from non-ypart line)
+	if len(part.Data) > 0 {
+		hasher.Write(part.Data)
+	}
+
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		if strings.HasPrefix(line, "=yend") {
+			parseYEnd(part, line)
+			break
+		}
+
+		decoded := decodeLine(line)
+		hasher.Write(decoded)
+		part.Data = append(part.Data, decoded...)
+	}
+
+	if err := scanner.Err(); err != nil {
+		return nil, fmt.Errorf("yenc: read error: %w", err)
+	}
+
+	// Verify CRC32 if provided
+	if part.CRC32 != 0 {
+		computed := hasher.Sum32()
+		if computed != part.CRC32 {
+			return nil, fmt.Errorf("yenc: CRC32 mismatch: expected %08x, got %08x", part.CRC32, computed)
+		}
+	}
+
+	return part, nil
+}
+
+// DecodeBytes decodes a yEnc encoded byte slice.
+func DecodeBytes(data []byte) (*Part, error) {
+	return Decode(bytes.NewReader(data))
+}
+
+// decodeLine decodes a single line of yEnc data.
+// yEnc encoding: each byte = (original + 42) % 256
+// Escape character '=' followed by next byte: (escapedByte - 64 - 42) % 256
+func decodeLine(line string) []byte {
+	out := make([]byte, 0, len(line))
+	escaped := false
+
+	for i := 0; i < len(line); i++ {
+		b := line[i]
+
+		if escaped {
+			// Escaped byte: subtract 106 (42 + 64)
+			out = append(out, b-106)
+			escaped = false
+			continue
+		}
+
+		if b == '=' {
+			escaped = true
+			continue
+		}
+
+		// Normal byte: subtract 42
+		out = append(out, b-42)
+	}
+
+	return out
+}
+
+// parseYBegin parses "=ybegin part=1 total=50 line=128 size=768000 name=file.mkv"
+func parseYBegin(p *Part, line string) {
+	p.Number = getIntParam(line, "part")
+	p.Total = getIntParam(line, "total")
+	p.Size = int64(getIntParam(line, "size"))
+
+	// Name is special: it's everything after "name=" to end of line
+	if idx := strings.Index(line, "name="); idx >= 0 {
+		p.Name = strings.TrimSpace(line[idx+5:])
+	}
+}
+
+// parseYPart parses "=ypart begin=1 end=768000"
+func parseYPart(p *Part, line string) {
+	p.Begin = int64(getIntParam(line, "begin"))
+	p.End = int64(getIntParam(line, "end"))
+}
+
+// parseYEnd parses "=yend size=768000 part=1 pcrc32=ABCD1234 crc32=ABCD1234"
+func parseYEnd(p *Part, line string) {
+	// pcrc32 is the CRC of this part; crc32 is the CRC of the whole file (only on last part)
+	if hex := getHexParam(line, "pcrc32"); hex != 0 {
+		p.CRC32 = hex
+	} else if hex := getHexParam(line, "crc32"); hex != 0 && p.Total <= 1 {
+		// For single-part files, crc32 is the only CRC
+		p.CRC32 = hex
+	}
+}
+
+// getIntParam extracts an integer parameter from a yEnc header line.
+func getIntParam(line, key string) int {
+	prefix := key + "="
+	idx := strings.Index(line, prefix)
+	if idx < 0 {
+		return 0
+	}
+	start := idx + len(prefix)
+	end := start
+	for end < len(line) && line[end] >= '0' && line[end] <= '9' {
+		end++
+	}
+	if end == start {
+		return 0
+	}
+	v, _ := strconv.Atoi(line[start:end])
+	return v
+}
+
+// getHexParam extracts a hex parameter (like CRC32) from a yEnc header line.
+// Uses word-boundary matching to avoid "pcrc32" matching "crc32".
+func getHexParam(line, key string) uint32 {
+	prefix := key + "="
+	idx := strings.Index(line, prefix)
+	if idx < 0 {
+		return 0
+	}
+	// Ensure we're matching the exact key, not a suffix (e.g., "crc32" should not match "pcrc32")
+	if idx > 0 && line[idx-1] != ' ' && line[idx-1] != '\t' {
+		// Try finding another occurrence after this one
+		rest := line[idx+1:]
+		nextIdx := strings.Index(rest, prefix)
+		if nextIdx < 0 {
+			return 0
+		}
+		idx = idx + 1 + nextIdx
+		if idx > 0 && line[idx-1] != ' ' && line[idx-1] != '\t' {
+			return 0
+		}
+	}
+	start := idx + len(prefix)
+	end := start
+	for end < len(line) && ((line[end] >= '0' && line[end] <= '9') ||
+		(line[end] >= 'a' && line[end] <= 'f') ||
+		(line[end] >= 'A' && line[end] <= 'F')) {
+		end++
+	}
+	if end == start {
+		return 0
+	}
+	v, err := strconv.ParseUint(line[start:end], 16, 32)
+	if err != nil {
+		return 0
+	}
+	return uint32(v)
+}
--- a/internal/usenet/yenc/decode_test.go
+++ b/internal/usenet/yenc/decode_test.go
@ -0,0 +1,208 @@
+package yenc
+
+import (
+	"bytes"
+	"encoding/hex"
+	"fmt"
+	"hash/crc32"
+	"strings"
+	"testing"
+)
+
+func TestDecodeLine(t *testing.T) {
+	// yEnc: each byte = (original + 42) % 256
+	// So to encode byte 0x00, we store 0x2A (42)
+	// To encode byte 0x01, we store 0x2B (43)
+
+	// Encode "Hello" manually:
+	// H=72 → 72+42=114='r'
+	// e=101 → 101+42=143='\x8f'
+	// l=108 → 108+42=150='\x96'
+	// l=108 → same
+	// o=111 → 111+42=153='\x99'
+	input := string([]byte{114, 143, 150, 150, 153})
+	decoded := decodeLine(input)
+	if string(decoded) != "Hello" {
+		t.Errorf("decodeLine: got %q, want %q", string(decoded), "Hello")
+	}
+}
+
+func TestDecodeLineWithEscape(t *testing.T) {
+	// Escaped characters: =\x00 (NUL), =\n (LF), =\r (CR), == (=)
+	// Escape: '=' followed by byte, decoded as (byte - 64 - 42) = (byte - 106)
+
+	// To encode byte 0x00 (NUL): escape it → '=' + (0 + 42 + 64) = '=' + 106 = '=' + 'j'
+	input := "=j" // should decode to 0x00
+	decoded := decodeLine(input)
+	if len(decoded) != 1 || decoded[0] != 0x00 {
+		t.Errorf("escape decode: got %v, want [0x00]", decoded)
+	}
+}
+
+func TestDecodeSimpleArticle(t *testing.T) {
+	// Create a simple yEnc encoded article
+	original := []byte("Hello, World! This is a test of yEnc encoding.")
+	encoded := encodeForTest(original)
+
+	crc := crc32.ChecksumIEEE(original)
+
+	article := fmt.Sprintf("=ybegin line=128 size=%d name=test.txt\r\n%s\r\n=yend size=%d crc32=%08x\r\n",
+		len(original), encoded, len(original), crc)
+
+	part, err := Decode(strings.NewReader(article))
+	if err != nil {
+		t.Fatalf("Decode failed: %v", err)
+	}
+
+	if part.Name != "test.txt" {
+		t.Errorf("Name: got %q, want %q", part.Name, "test.txt")
+	}
+	if part.Size != int64(len(original)) {
+		t.Errorf("Size: got %d, want %d", part.Size, len(original))
+	}
+	if !bytes.Equal(part.Data, original) {
+		t.Errorf("Data mismatch:\n  got:  %s\n  want: %s", hex.EncodeToString(part.Data), hex.EncodeToString(original))
+	}
+}
+
+func TestDecodeMultipart(t *testing.T) {
+	original := []byte("Part one data here")
+	encoded := encodeForTest(original)
+
+	crc := crc32.ChecksumIEEE(original)
+
+	article := fmt.Sprintf("=ybegin part=1 total=3 line=128 size=1000 name=movie.mkv\r\n"+
+		"=ypart begin=1 end=%d\r\n"+
+		"%s\r\n"+
+		"=yend size=%d part=1 pcrc32=%08x\r\n",
+		len(original), encoded, len(original), crc)
+
+	part, err := Decode(strings.NewReader(article))
+	if err != nil {
+		t.Fatalf("Decode failed: %v", err)
+	}
+
+	if part.Number != 1 {
+		t.Errorf("Number: got %d, want 1", part.Number)
+	}
+	if part.Total != 3 {
+		t.Errorf("Total: got %d, want 3", part.Total)
+	}
+	if part.Begin != 1 {
+		t.Errorf("Begin: got %d, want 1", part.Begin)
+	}
+	if part.End != int64(len(original)) {
+		t.Errorf("End: got %d, want %d", part.End, len(original))
+	}
+	if part.Name != "movie.mkv" {
+		t.Errorf("Name: got %q", part.Name)
+	}
+	if !bytes.Equal(part.Data, original) {
+		t.Error("Data mismatch")
+	}
+}
+
+func TestDecodeCRC32Mismatch(t *testing.T) {
+	original := []byte("test data")
+	encoded := encodeForTest(original)
+
+	article := fmt.Sprintf("=ybegin line=128 size=%d name=test.bin\r\n%s\r\n=yend size=%d crc32=deadbeef\r\n",
+		len(original), encoded, len(original))
+
+	_, err := Decode(strings.NewReader(article))
+	if err == nil {
+		t.Error("expected CRC32 mismatch error")
+	}
+	if !strings.Contains(err.Error(), "CRC32 mismatch") {
+		t.Errorf("unexpected error: %v", err)
+	}
+}
+
+func TestDecodeNoHeader(t *testing.T) {
+	_, err := Decode(strings.NewReader("just some random data\r\n"))
+	if err == nil {
+		t.Error("expected error for missing header")
+	}
+}
+
+func TestDecodeBytes(t *testing.T) {
+	original := []byte("quick test")
+	encoded := encodeForTest(original)
+	crc := crc32.ChecksumIEEE(original)
+
+	article := fmt.Sprintf("=ybegin line=128 size=%d name=q.bin\r\n%s\r\n=yend size=%d crc32=%08x\r\n",
+		len(original), encoded, len(original), crc)
+
+	part, err := DecodeBytes([]byte(article))
+	if err != nil {
+		t.Fatalf("DecodeBytes failed: %v", err)
+	}
+	if !bytes.Equal(part.Data, original) {
+		t.Error("Data mismatch")
+	}
+}
+
+func TestDecodeBinaryData(t *testing.T) {
+	// Test with all byte values 0-255
+	original := make([]byte, 256)
+	for i := range original {
+		original[i] = byte(i)
+	}
+
+	encoded := encodeForTest(original)
+	crc := crc32.ChecksumIEEE(original)
+
+	article := fmt.Sprintf("=ybegin line=128 size=%d name=binary.bin\r\n%s\r\n=yend size=%d crc32=%08x\r\n",
+		len(original), encoded, len(original), crc)
+
+	part, err := Decode(strings.NewReader(article))
+	if err != nil {
+		t.Fatalf("Decode failed: %v", err)
+	}
+	if !bytes.Equal(part.Data, original) {
+		t.Errorf("Binary data mismatch: got %d bytes, want %d", len(part.Data), len(original))
+	}
+}
+
+func TestGetIntParam(t *testing.T) {
+	line := "=ybegin part=5 total=100 line=128 size=768000 name=file.mkv"
+	if v := getIntParam(line, "part"); v != 5 {
+		t.Errorf("part: got %d", v)
+	}
+	if v := getIntParam(line, "total"); v != 100 {
+		t.Errorf("total: got %d", v)
+	}
+	if v := getIntParam(line, "size"); v != 768000 {
+		t.Errorf("size: got %d", v)
+	}
+	if v := getIntParam(line, "missing"); v != 0 {
+		t.Errorf("missing: got %d", v)
+	}
+}
+
+func TestGetHexParam(t *testing.T) {
+	line := "=yend size=1000 pcrc32=ABCD1234 crc32=deadbeef"
+	if v := getHexParam(line, "pcrc32"); v != 0xABCD1234 {
+		t.Errorf("pcrc32: got %08x, want ABCD1234", v)
+	}
+	if v := getHexParam(line, "crc32"); v != 0xdeadbeef {
+		t.Errorf("crc32: got %08x, want deadbeef", v)
+	}
+}
+
+// encodeForTest encodes data using yEnc for testing purposes.
+func encodeForTest(data []byte) string {
+	var buf bytes.Buffer
+	for _, b := range data {
+		encoded := byte((int(b) + 42) % 256)
+		// Escape special bytes: NUL, LF, CR, '=', '.'
+		switch encoded {
+		case 0x00, 0x0A, 0x0D, 0x3D, 0x2E:
+			buf.WriteByte('=')
+			buf.WriteByte(byte((int(encoded) + 64) % 256))
+		default:
+			buf.WriteByte(encoded)
+		}
+	}
+	return buf.String()
+}