implement native Deezer download/decrypt pipeline

Replace Deezer yt-dlp usage with native ARL session + media.get_url resolution, add BF_CBC_STRIPE decryption in downloader, and wire cipher-aware Deezer downloads through the main rip pipeline. Includes validation hardening and metadata/source-id improvements used by tagging flows.

internal/download/downloader.go

@@ -3,12 +3,15 @@ package download
 import (
 	"bufio"
 	"context"
+	"crypto/cipher"
+	"crypto/md5"
 	"fmt"
 	"io"
 	"net/http"
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"sync/atomic"
 
@@ -17,6 +20,8 @@ import (
 	"golang.org/x/term"
 
 	"streamrip-go/internal/netutil"
+
+	"golang.org/x/crypto/blowfish"
 )
 
 type Downloader struct {
@@ -56,6 +61,33 @@ func (d *Downloader) FileVideo(ctx context.Context, sourceURL, outputPath string
 	return d.file(ctx, sourceURL, outputPath, true, true)
 }
 
+func (d *Downloader) FileDeezerEncrypted(ctx context.Context, sourceURL, outputPath, trackID string) error {
+	if err := os.MkdirAll(filepath.Dir(outputPath), 0o755); err != nil {
+		return err
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, sourceURL, nil)
+	if err != nil {
+		return err
+	}
+	resp, err := d.http.Do(req)
+	if err != nil {
+		return err
+	}
+	defer func() { _ = resp.Body.Close() }()
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("download failed: status=%d", resp.StatusCode)
+	}
+	encrypted, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return err
+	}
+	plain, err := decryptDeezerBFCBCStripe(encrypted, trackID)
+	if err != nil {
+		return err
+	}
+	return os.WriteFile(outputPath, plain, 0o644)
+}
+
 func (d *Downloader) file(ctx context.Context, sourceURL, outputPath string, allowProgress bool, includeVideo bool) error {
 	if err := os.MkdirAll(filepath.Dir(outputPath), 0o755); err != nil {
 		return err
@@ -204,3 +236,60 @@ func isManifestResponse(contentType string, peek []byte) bool {
 	}
 	return false
 }
+
+const deezerBFChunkSize = 2048
+
+var deezerBFIV = []byte{0, 1, 2, 3, 4, 5, 6, 7}
+
+func decryptDeezerBFCBCStripe(in []byte, trackID string) ([]byte, error) {
+	block, err := blowfish.NewCipher(deriveDeezerBlowfishKey(trackID))
+	if err != nil {
+		return nil, err
+	}
+	out := make([]byte, len(in))
+	for i := 0; i*deezerBFChunkSize < len(in); i++ {
+		start := i * deezerBFChunkSize
+		end := start + deezerBFChunkSize
+		if end > len(in) {
+			end = len(in)
+		}
+		chunk := in[start:end]
+		if i%3 == 0 && len(chunk) == deezerBFChunkSize {
+			dec := make([]byte, len(chunk))
+			mode := cipher.NewCBCDecrypter(block, deezerBFIV)
+			mode.CryptBlocks(dec, chunk)
+			copy(out[start:end], dec)
+		} else {
+			copy(out[start:end], chunk)
+		}
+	}
+	return out, nil
+}
+
+func deriveDeezerBlowfishKey(trackID string) []byte {
+	sum := md5.Sum([]byte(trackID))
+	md5Hex := fmt.Sprintf("%x", sum)
+	secret := "g4el58wc0zvf9na1"
+	key := make([]byte, 16)
+	for i := 0; i < 16; i++ {
+		key[i] = md5Hex[i] ^ md5Hex[i+16] ^ secret[i]
+	}
+	return key
+}
+
+func normalizeDeezerTrackID(raw string) string {
+	trimmed := strings.TrimSpace(raw)
+	if trimmed == "" {
+		return ""
+	}
+	if _, err := strconv.Atoi(trimmed); err == nil {
+		return trimmed
+	}
+	parts := strings.Split(strings.Trim(trimmed, "/"), "/")
+	for i := len(parts) - 1; i >= 0; i-- {
+		if _, err := strconv.Atoi(parts[i]); err == nil {
+			return parts[i]
+		}
+	}
+	return trimmed
+}

internal/download/downloader_test.go

@@ -2,11 +2,14 @@ package download
 
 import (
 	"context"
+	"crypto/cipher"
 	"net/http"
 	"net/http/httptest"
 	"os"
 	"path/filepath"
 	"testing"
+
+	"golang.org/x/crypto/blowfish"
 )
 
 func TestDownloaderHasNoClientTimeout(t *testing.T) {
@@ -51,3 +54,33 @@ func TestManifestDetection(t *testing.T) {
 		t.Fatalf("did not expect flac to be manifest")
 	}
 }
+
+func TestNormalizeDeezerTrackID(t *testing.T) {
+	if got := normalizeDeezerTrackID("https://www.deezer.com/track/3135556"); got != "3135556" {
+		t.Fatalf("normalize track id = %q, want 3135556", got)
+	}
+}
+
+func TestDecryptDeezerBFCBCStripe(t *testing.T) {
+	trackID := "3135556"
+	plain := make([]byte, deezerBFChunkSize*2)
+	for i := range plain {
+		plain[i] = byte(i % 251)
+	}
+	enc := make([]byte, len(plain))
+	copy(enc, plain)
+	block, err := blowfish.NewCipher(deriveDeezerBlowfishKey(trackID))
+	if err != nil {
+		t.Fatalf("cipher error: %v", err)
+	}
+	cbc := cipher.NewCBCEncrypter(block, deezerBFIV)
+	cbc.CryptBlocks(enc[:deezerBFChunkSize], enc[:deezerBFChunkSize])
+
+	dec, err := decryptDeezerBFCBCStripe(enc, trackID)
+	if err != nil {
+		t.Fatalf("decrypt error: %v", err)
+	}
+	if len(dec) != len(plain) || string(dec) != string(plain) {
+		t.Fatalf("decrypted data mismatch")
+	}
+}