minstrel/internal/api/leveled_stream.go

package api

import (
	"context"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"net/http"
	"os"
	"strconv"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/jackc/pgx/v5/pgtype"

	"git.fabledsword.com/bvandeusen/minstrel/internal/apierror"
	"git.fabledsword.com/bvandeusen/minstrel/internal/auth"
	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
	"git.fabledsword.com/bvandeusen/minstrel/internal/library"
)

// The leveled stream: a track rendered with the user's loudness
// gain applied, for the Sonos and UPnP speakers that fetch their own audio.
// See internal/library/leveled.go for how it is rendered.

// SignLeveledStreamToken signs a leveled stream URL. The gain is part of what
// is signed, so a speaker's URL cannot be edited into a different render.
// The message cannot collide with SignStreamToken's "<id>|<exp>": a plain
// token does not open a leveled stream, nor the reverse.
func SignLeveledStreamToken(secret []byte, trackID string, exp int64, g library.LeveledGain) string {
	mac := hmac.New(sha256.New, secret)
	lim := 0
	if g.Limiter {
		lim = 1
	}
	_, _ = fmt.Fprintf(mac, "%s|%d|leveled|%d|%d", trackID, exp, g.CentiDB, lim)
	return hex.EncodeToString(mac.Sum(nil))
}

// VerifyLeveledStreamToken checks a token from SignLeveledStreamToken, and
// that it has not expired.
func VerifyLeveledStreamToken(secret []byte, trackID string, exp int64, g library.LeveledGain, token string) bool {
	if time.Now().Unix() > exp {
		return false
	}
	return hmac.Equal([]byte(SignLeveledStreamToken(secret, trackID, exp, g)), []byte(token))
}

// leveledStreamPath is the leveled stream's path. It ends in .flac because
// Sonos reads the format from the URL's extension.
func leveledStreamPath(trackID pgtype.UUID) string {
	return "/api/tracks/" + uuidToString(trackID) + "/leveled.flac"
}

// leveledQuery is the query string a leveled URL carries.
func leveledQuery(g library.LeveledGain, token string, exp int64) string {
	lim := "0"
	if g.Limiter {
		lim = "1"
	}
	return "?g=" + strconv.Itoa(g.CentiDB) + "&lim=" + lim +
		"&token=" + token + "&exp=" + strconv.FormatInt(exp, 10)
}

// leveledGainFor is the render request for one track under the user's
// preference. Unity when leveling is off or the track is unmeasured, which
// the caller answers with the plain stream.
func (h *handlers) leveledGainFor(ctx context.Context, userID, trackID pgtype.UUID, asAlbum bool) (library.LeveledGain, error) {
	q := dbq.New(h.pool)
	prefs, err := library.LoadNormalizationPrefs(ctx, q, userID)
	if err != nil {
		return library.LeveledGain{}, err
	}
	gains, err := library.ReplayGainForTracks(ctx, q, []pgtype.UUID{trackID})
	if err != nil {
		return library.LeveledGain{}, err
	}
	return library.NewLeveledGain(library.LeveledGainDB(prefs, gains[trackID], asAlbum), prefs.Boost), nil
}

// parseLeveledGain reads ?g= and ?lim= from a leveled URL.
func parseLeveledGain(r *http.Request) (library.LeveledGain, bool) {
	c, err := strconv.Atoi(r.URL.Query().Get("g"))
	if err != nil {
		return library.LeveledGain{}, false
	}
	lim := r.URL.Query().Get("lim")
	if lim != "0" && lim != "1" {
		return library.LeveledGain{}, false
	}
	g := library.LeveledGain{CentiDB: c, Limiter: lim == "1"}
	return g, g.Valid()
}

// handleGetLeveledStream implements GET /api/tracks/{id}/leveled.flac. It
// accepts a session, like the plain stream, or a leveled token: the gain in
// the query must be the one the token was signed for.
func (h *handlers) handleGetLeveledStream(w http.ResponseWriter, r *http.Request) {
	rawID := chi.URLParam(r, "id")
	g, ok := parseLeveledGain(r)
	if !h.leveledAuthOk(r, rawID, g, ok) {
		writeErr(w, apierror.ErrUnauthorized)
		return
	}
	if !ok {
		writeErr(w, apierror.BadRequest("invalid_gain", "g and lim must describe a valid gain"))
		return
	}
	if h.leveled == nil {
		writeErr(w, &apierror.Error{Status: http.StatusServiceUnavailable, Code: "leveling_unavailable",
			Message: "leveled streams are not available on this server"})
		return
	}
	track, apiErr := resolveByID(r, "id", dbq.New(h.pool).GetTrackByID, "track")
	if apiErr != nil {
		writeErr(w, apiErr)
		return
	}
	path, err := h.leveled.Path(r.Context(), library.LeveledSource{
		TrackID: rawID, Path: track.FilePath, DurationMs: track.DurationMs,
	}, g)
	switch {
	case errors.Is(err, library.ErrLeveledSourceMissing):
		writeErr(w, &apierror.Error{Status: http.StatusNotFound, Code: "not_found", Message: "track file not found"})
		return
	case r.Context().Err() != nil:
		return // the speaker hung up; the render carries on for its retry
	case err != nil:
		writeErrWithLog(w, h.logger, "leveled stream: render failed", apierror.InternalMsg("render failed", err))
		return
	}
	f, err := os.Open(path)
	if err != nil {
		// Evicted between render and open: rare, and the speaker retries.
		writeErrWithLog(w, h.logger, "leveled stream: open render", apierror.InternalMsg("server error", err))
		return
	}
	defer func() { _ = f.Close() }()
	info, err := f.Stat()
	if err != nil {
		writeErrWithLog(w, h.logger, "leveled stream: stat render", apierror.InternalMsg("server error", err))
		return
	}
	w.Header().Set("Content-Type", "audio/flac")
	w.Header().Set("Accept-Ranges", "bytes")
	w.Header().Set("Cache-Control", "private, max-age=86400")
	http.ServeContent(w, r, "leveled.flac", info.ModTime(), f)
}

// leveledAuthOk mirrors streamAuthOk: a session, or a token signed over this
// track and this gain. A malformed gain fails the token path, since there is
// nothing it could have been signed over.
func (h *handlers) leveledAuthOk(r *http.Request, trackID string, g library.LeveledGain, gainOK bool) bool {
	if _, ok := auth.UserFromContext(r.Context()); ok {
		return true
	}
	if !gainOK {
		return false
	}
	tok := r.URL.Query().Get("token")
	exp, err := strconv.ParseInt(r.URL.Query().Get("exp"), 10, 64)
	if tok == "" || err != nil {
		return false
	}
	return VerifyLeveledStreamToken(h.streamSecret, trackID, exp, g, tok)
}