telegabber/calls/audio/capture.go

// optional offline-replay dump of the two media streams; gated by
// CALLS_CAPTURE_DIR (no-op when unset). big-endian throughout, ts is ms
// since writer construction.
// header: [magic 8B][ver u8=1][reserved 7B]
// PCM rec (tg->xmpp): [ts_ms i64][ssrc u32][len u32][pcm...]
// RTP rec (xmpp->tg): [ts_ms i64][ssrc u32][seq u16][rtp_ts u32][pt u8][len u32][opus...]
package audio

import (
	"encoding/binary"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"sync"
	"time"
)

const (
	captureEnvVar = "CALLS_CAPTURE_DIR"
	captureVer    = byte(1)
)

var (
	magicPCM = [8]byte{'T', 'G', 'C', 'A', 'P', 'P', 'C', 'M'}
	magicRTP = [8]byte{'T', 'G', 'C', 'A', 'P', 'R', 'T', 'P'}
)

// per-call file sink; nil-safe so call sites can stay branchless
type captureWriter struct {
	mu     sync.Mutex
	f      *os.File
	start  time.Time
	closed bool
}

// returns (nil, nil) when CALLS_CAPTURE_DIR is unset
func newCaptureWriter(name string, magic [8]byte) (*captureWriter, error) {
	dir := os.Getenv(captureEnvVar)
	if dir == "" {
		return nil, nil
	}
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return nil, fmt.Errorf("capture: mkdir %s: %w", dir, err)
	}
	path := filepath.Join(dir, name)
	f, err := os.Create(path)
	if err != nil {
		return nil, fmt.Errorf("capture: create %s: %w", path, err)
	}
	var hdr [16]byte
	copy(hdr[0:8], magic[:])
	hdr[8] = captureVer
	if _, err := f.Write(hdr[:]); err != nil {
		_ = f.Close()
		return nil, fmt.Errorf("capture: write header: %w", err)
	}
	return &captureWriter{f: f, start: time.Now()}, nil
}

func (w *captureWriter) writePCM(ssrc uint32, data []byte) {
	if w == nil {
		return
	}
	w.mu.Lock()
	defer w.mu.Unlock()
	if w.closed {
		return
	}
	var hdr [16]byte
	binary.BigEndian.PutUint64(hdr[0:8], uint64(time.Since(w.start).Milliseconds()))
	binary.BigEndian.PutUint32(hdr[8:12], ssrc)
	binary.BigEndian.PutUint32(hdr[12:16], uint32(len(data)))
	_, _ = w.f.Write(hdr[:])
	_, _ = w.f.Write(data)
}

func (w *captureWriter) writeRTP(ssrc uint32, seq uint16, rtpTS uint32, pt uint8, data []byte) {
	if w == nil {
		return
	}
	w.mu.Lock()
	defer w.mu.Unlock()
	if w.closed {
		return
	}
	var hdr [23]byte
	binary.BigEndian.PutUint64(hdr[0:8], uint64(time.Since(w.start).Milliseconds()))
	binary.BigEndian.PutUint32(hdr[8:12], ssrc)
	binary.BigEndian.PutUint16(hdr[12:14], seq)
	binary.BigEndian.PutUint32(hdr[14:18], rtpTS)
	hdr[18] = pt
	binary.BigEndian.PutUint32(hdr[19:23], uint32(len(data)))
	_, _ = w.f.Write(hdr[:])
	_, _ = w.f.Write(data)
}

func (w *captureWriter) close() {
	if w == nil {
		return
	}
	w.mu.Lock()
	defer w.mu.Unlock()
	if w.closed {
		return
	}
	w.closed = true
	_ = w.f.Close()
}

// one tg->xmpp record from a PCM capture file
type CapturedPCM struct {
	TimestampMs int64
	SSRC        uint32
	Data        []byte
}

func ReadPCMCapture(r io.Reader) ([]CapturedPCM, error) {
	if err := verifyMagic(r, magicPCM); err != nil {
		return nil, err
	}
	var out []CapturedPCM
	for {
		var hdr [16]byte
		_, err := io.ReadFull(r, hdr[:])
		if errors.Is(err, io.EOF) {
			return out, nil
		}
		if err != nil {
			return nil, err
		}
		rec := CapturedPCM{
			TimestampMs: int64(binary.BigEndian.Uint64(hdr[0:8])),
			SSRC:        binary.BigEndian.Uint32(hdr[8:12]),
		}
		length := binary.BigEndian.Uint32(hdr[12:16])
		rec.Data = make([]byte, length)
		if _, err := io.ReadFull(r, rec.Data); err != nil {
			return nil, err
		}
		out = append(out, rec)
	}
}

func verifyMagic(r io.Reader, want [8]byte) error {
	var hdr [16]byte
	if _, err := io.ReadFull(r, hdr[:]); err != nil {
		return fmt.Errorf("capture: read header: %w", err)
	}
	var got [8]byte
	copy(got[:], hdr[0:8])
	if got != want {
		return fmt.Errorf("capture: bad magic %q, want %q", string(got[:]), string(want[:]))
	}
	if hdr[8] != captureVer {
		return fmt.Errorf("capture: unsupported version %d", hdr[8])
	}
	return nil
}