1// Package webmail implements a webmail client, serving html/js and providing an API for message actions and SSE endpoint for receiving real-time updates.

2package webmail

4// todo: should we be serving the messages/parts on a separate (sub)domain for user-content? to limit damage if the csp rules aren't enough.

6import (

7 "archive/zip"

8 "bytes"

9 "context"

10 "encoding/base64"

11 "encoding/json"

12 "errors"

13 "fmt"

14 "io"

15 "log/slog"

16 "mime"

17 "net/http"

18 "os"

19 "path/filepath"

20 "regexp"

21 "runtime/debug"

22 "strconv"

23 "strings"

25 _ "embed"

27 "golang.org/x/net/html"

29 "github.com/prometheus/client_golang/prometheus"

30 "github.com/prometheus/client_golang/prometheus/promauto"

32 "github.com/mjl-/bstore"

33 "github.com/mjl-/sherpa"

35 "github.com/mjl-/mox/message"

36 "github.com/mjl-/mox/metrics"

37 "github.com/mjl-/mox/mlog"

38 "github.com/mjl-/mox/mox-"

39 "github.com/mjl-/mox/moxio"

40 "github.com/mjl-/mox/store"

41 "github.com/mjl-/mox/webauth"

42 "github.com/mjl-/mox/webops"

43)

45var pkglog = mlog.New("webmail", nil)

47type ctxKey string

49// We pass the request to the sherpa handler so the TLS info can be used for

50// the Received header in submitted messages. Most API calls need just the

51// account name.

52var requestInfoCtxKey ctxKey = "requestInfo"

54type requestInfo struct {

55 Log mlog.Log

56 LoginAddress string

57 Account *store.Account // Nil only for methods Login and LoginPrep.

58 SessionToken store.SessionToken

59 Response http.ResponseWriter

60 Request *http.Request // For Proto and TLS connection state during message submit.

61}

63//go:embed webmail.html

64var webmailHTML []byte

66//go:embed webmail.js

67var webmailJS []byte

69//go:embed msg.html

70var webmailmsgHTML []byte

72//go:embed msg.js

73var webmailmsgJS []byte

75//go:embed text.html

76var webmailtextHTML []byte

78//go:embed text.js

79var webmailtextJS []byte

81var (

82 // Similar between ../webmail/webmail.go:/metricSubmission and ../smtpserver/server.go:/metricSubmission and ../webapisrv/server.go:/metricSubmission

83 metricSubmission = promauto.NewCounterVec(

84 prometheus.CounterOpts{

85 Name: "mox_webmail_submission_total",

86 Help: "Webmail message submission results, known values (those ending with error are server errors): ok, badfrom, messagelimiterror, recipientlimiterror, queueerror, storesenterror.",

87 },

88 []string{

89 "result",

90 },

91 )

92 metricServerErrors = promauto.NewCounterVec(

93 prometheus.CounterOpts{

94 Name: "mox_webmail_errors_total",

95 Help: "Webmail server errors, known values: dkimsign, submit.",

96 },

97 []string{

98 "error",

99 },

100 )

101 metricSSEConnections = promauto.NewGauge(

102 prometheus.GaugeOpts{

103 Name: "mox_webmail_sse_connections",

104 Help: "Number of active webmail SSE connections.",

105 },

106 )

107)

108

109func xcheckf(ctx context.Context, err error, format string, args ...any) {

110 if err == nil {

111 return

112 }

113 msg := fmt.Sprintf(format, args...)

114 errmsg := fmt.Sprintf("%s: %s", msg, err)

115 pkglog.WithContext(ctx).Errorx(msg, err)

116 code := "server:error"

117 if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {

118 code = "user:error"

119 }

120 panic(&sherpa.Error{Code: code, Message: errmsg})

121}

122

123func xcheckuserf(ctx context.Context, err error, format string, args ...any) {

124 if err == nil {

125 return

126 }

127 msg := fmt.Sprintf(format, args...)

128 errmsg := fmt.Sprintf("%s: %s", msg, err)

129 pkglog.WithContext(ctx).Errorx(msg, err)

130 panic(&sherpa.Error{Code: "user:error", Message: errmsg})

131}

132

133func xdbwrite(ctx context.Context, acc *store.Account, fn func(tx *bstore.Tx)) {

134 err := acc.DB.Write(ctx, func(tx *bstore.Tx) error {

135 fn(tx)

136 return nil

137 })

138 xcheckf(ctx, err, "transaction")

139}

140

141func xdbread(ctx context.Context, acc *store.Account, fn func(tx *bstore.Tx)) {

142 err := acc.DB.Read(ctx, func(tx *bstore.Tx) error {

143 fn(tx)

144 return nil

145 })

146 xcheckf(ctx, err, "transaction")

147}

148

149var webmailFile = &mox.WebappFile{

150 HTML: webmailHTML,

151 JS: webmailJS,

152 HTMLPath: filepath.FromSlash("webmail/webmail.html"),

153 JSPath: filepath.FromSlash("webmail/webmail.js"),

154}

155

156// Serve content, either from a file, or return the fallback data. Caller

157// should already have set the content-type. We use this to return a file from

158// the local file system (during development), or embedded in the binary (when

159// deployed).

160func serveContentFallback(log mlog.Log, w http.ResponseWriter, r *http.Request, path string, fallback []byte) {

161 f, err := os.Open(path)

162 if err == nil {

163 defer f.Close()

164 st, err := f.Stat()

165 if err == nil {

166 http.ServeContent(w, r, "", st.ModTime(), f)

167 return

168 }

169 }

170 http.ServeContent(w, r, "", mox.FallbackMtime(log), bytes.NewReader(fallback))

171}

172

173func init() {

174 mox.NewWebmailHandler = func(maxMsgSize int64, basePath string, isForwarded bool, accountPath string) http.Handler {

175 return http.HandlerFunc(Handler(maxMsgSize, basePath, isForwarded, accountPath))

176 }

177}

178

179// Handler returns a handler for the webmail endpoints, customized for the max

180// message size coming from the listener and cookiePath.

181func Handler(maxMessageSize int64, cookiePath string, isForwarded bool, accountPath string) func(w http.ResponseWriter, r *http.Request) {

182 sh, err := makeSherpaHandler(maxMessageSize, cookiePath, isForwarded)

183 return func(w http.ResponseWriter, r *http.Request) {

184 if err != nil {

185 http.Error(w, "500 - internal server error - cannot handle requests", http.StatusInternalServerError)

186 return

187 }

188 handle(sh, isForwarded, accountPath, w, r)

189 }

190}

191

192func handle(apiHandler http.Handler, isForwarded bool, accountPath string, w http.ResponseWriter, r *http.Request) {

193 ctx := r.Context()

194 log := pkglog.WithContext(ctx).With(slog.String("userauth", ""))

195

196 // Server-sent event connection, for all initial data (list of mailboxes), list of

197 // messages, and all events afterwards. Authenticated through a single use token in

198 // the query string, which it got from a Token API call.

199 if r.URL.Path == "/events" {

200 serveEvents(ctx, log, accountPath, w, r)

201 return

202 }

203

204 defer func() {

205 x := recover()

206 if x == nil {

207 return

208 }

209 err, ok := x.(*sherpa.Error)

210 if !ok {

211 log.WithContext(ctx).Error("handle panic", slog.Any("err", x))

212 debug.PrintStack()

213 metrics.PanicInc(metrics.Webmailhandle)

214 panic(x)

215 }

216 if strings.HasPrefix(err.Code, "user:") {

217 log.Debugx("webmail user error", err)

218 http.Error(w, "400 - bad request - "+err.Message, http.StatusBadRequest)

219 } else {

220 log.Errorx("webmail server error", err)

221 http.Error(w, "500 - internal server error - "+err.Message, http.StatusInternalServerError)

222 }

223 }()

224

225 switch r.URL.Path {

226 case "/":

227 switch r.Method {

228 case "GET", "HEAD":

229 h := w.Header()

230 h.Set("X-Frame-Options", "deny")

231 h.Set("Referrer-Policy", "same-origin")

232 webmailFile.Serve(ctx, log, w, r)

233 default:

234 http.Error(w, "405 - method not allowed - use get", http.StatusMethodNotAllowed)

235 }

236 return

237

238 case "/msg.js", "/text.js":

239 switch r.Method {

240 default:

241 http.Error(w, "405 - method not allowed - use get", http.StatusMethodNotAllowed)

242 return

243 case "GET", "HEAD":

244 }

245

246 path := filepath.Join("webmail", r.URL.Path[1:])

247 var fallback = webmailmsgJS

248 if r.URL.Path == "/text.js" {

249 fallback = webmailtextJS

250 }

251

252 w.Header().Set("Content-Type", "application/javascript; charset=utf-8")

253 serveContentFallback(log, w, r, path, fallback)

254 return

255 }

256

257 isAPI := strings.HasPrefix(r.URL.Path, "/api/")

258 // Only allow POST for calls, they will not work cross-domain without CORS.

259 if isAPI && r.URL.Path != "/api/" && r.Method != "POST" {

260 http.Error(w, "405 - method not allowed - use post", http.StatusMethodNotAllowed)

261 return

262 }

263

264 var loginAddress, accName string

265 var sessionToken store.SessionToken

266 // All other URLs, except the login endpoint require some authentication.

267 if r.URL.Path != "/api/LoginPrep" && r.URL.Path != "/api/Login" {

268 var ok bool

269 isExport := r.URL.Path == "/export"

270 requireCSRF := isAPI || isExport

271 accName, sessionToken, loginAddress, ok = webauth.Check(ctx, log, webauth.Accounts, "webmail", isForwarded, w, r, isAPI, requireCSRF, isExport)

272 if !ok {

273 // Response has been written already.

274 return

275 }

276 }

277

278 if isAPI {

279 var acc *store.Account

280 if accName != "" {

281 log = log.With(slog.String("account", accName))

282 var err error

283 acc, err = store.OpenAccount(log, accName)

284 if err != nil {

285 log.Errorx("open account", err)

286 http.Error(w, "500 - internal server error - error opening account", http.StatusInternalServerError)

287 return

288 }

289 defer func() {

290 err := acc.Close()

291 log.Check(err, "closing account")

292 }()

293 }

294 reqInfo := requestInfo{log, loginAddress, acc, sessionToken, w, r}

295 ctx = context.WithValue(ctx, requestInfoCtxKey, reqInfo)

296 apiHandler.ServeHTTP(w, r.WithContext(ctx))

297 return

298 }

299

300 // We are now expecting the following URLs:

301 // .../export

302 // .../msg/<msgid>/{attachments.zip,parsedmessage.js,raw}

303 // .../msg/<msgid>/{,msg}{text,html,htmlexternal}

304 // .../msg/<msgid>/{view,viewtext,download}/<partid>

305

306 if r.URL.Path == "/export" {

307 webops.Export(log, accName, w, r)

308 return

309 }

310

311 if !strings.HasPrefix(r.URL.Path, "/msg/") {

312 http.NotFound(w, r)

313 return

314 }

315

316 t := strings.Split(r.URL.Path[len("/msg/"):], "/")

317 if len(t) < 2 {

318 http.NotFound(w, r)

319 return

320 }

321

322 id, err := strconv.ParseInt(t[0], 10, 64)

323 if err != nil || id == 0 {

324 http.NotFound(w, r)

325 return

326 }

327

328 // Many of the requests need either a message or a parsed part. Make it easy to

329 // fetch/prepare and cleanup. We only do all the work when the request seems legit

330 // (valid HTTP route and method).

331 xprepare := func() (acc *store.Account, m store.Message, msgr *store.MsgReader, p message.Part, cleanup func(), ok bool) {

332 if r.Method != "GET" {

333 http.Error(w, "405 - method not allowed - post required", http.StatusMethodNotAllowed)

334 return

335 }

336

337 defer func() {

338 if ok {

339 return

340 }

341 if msgr != nil {

342 err := msgr.Close()

343 log.Check(err, "closing message reader")

344 msgr = nil

345 }

346 if acc != nil {

347 err := acc.Close()

348 log.Check(err, "closing account")

349 acc = nil

350 }

351 }()

352

353 var err error

354

355 acc, err = store.OpenAccount(log, accName)

356 xcheckf(ctx, err, "open account")

357

358 m = store.Message{ID: id}

359 err = acc.DB.Get(ctx, &m)

360 if err == bstore.ErrAbsent || err == nil && m.Expunged {

361 http.NotFound(w, r)

362 return

363 }

364 xcheckf(ctx, err, "get message")

365

366 msgr = acc.MessageReader(m)

367

368 p, err = m.LoadPart(msgr)

369 xcheckf(ctx, err, "load parsed message")

370

371 cleanup = func() {

372 err := msgr.Close()

373 log.Check(err, "closing message reader")

374 err = acc.Close()

375 log.Check(err, "closing account")

376 }

377 ok = true

378 return

379 }

380

381 h := w.Header()

382

383 // We set a Content-Security-Policy header that is as strict as possible, depending

384 // on the type of message/part/html/js. We have to be careful because we are

385 // returning data that is coming in from external places. E.g. HTML could contain

386 // javascripts that we don't want to execute, especially not on our domain. We load

387 // resources in an iframe. The CSP policy starts out with default-src 'none' to

388 // disallow loading anything, then start allowing what is safe, such as inlined

389 // datauri images and inline styles. Data can only be loaded when the request is

390 // coming from the same origin (so other sites cannot include resources

391 // (messages/parts)).

392 //

393 // We want to load resources in sandbox-mode, causing the page to be loaded as from

394 // a different origin. If sameOrigin is set, we have a looser CSP policy:

395 // allow-same-origin is set so resources are loaded as coming from this same

396 // origin. This is needed for the msg* endpoints that render a message, where we

397 // load the message body in a separate iframe again (with stricter CSP again),

398 // which we need to access for its inner height. If allowSelfScript is also set

399 // (for "msgtext"), the CSP leaves out the sandbox entirely.

400 //

401 // If allowExternal is set, we allow loading image, media (audio/video), styles and

402 // fronts from external URLs as well as inline URI's. By default we don't allow any

403 // loading of content, except inlined images (we do that ourselves for images

404 // embedded in the email), and we allow inline styles (which are safely constrained

405 // to an iframe).

406 //

407 // If allowSelfScript is set, inline scripts and scripts from our origin are

408 // allowed. Used to display a message including header. The header is rendered with

409 // javascript, the content is rendered in a separate iframe with a CSP that doesn't

410 // have allowSelfScript.

411 headers := func(sameOrigin, allowExternal, allowSelfScript, allowSelfImg bool) {

412 // allow-popups is needed to make opening links in new tabs work.

413 sb := "sandbox allow-popups allow-popups-to-escape-sandbox; "

414 if sameOrigin && allowSelfScript {

415 // Sandbox with both allow-same-origin and allow-script would not provide security,

416 // and would give warning in console about that.

417 sb = ""

418 } else if sameOrigin {

419 sb = "sandbox allow-popups allow-popups-to-escape-sandbox allow-same-origin; "

420 }

421 script := ""

422 if allowSelfScript {

423 script = "; script-src 'unsafe-inline' 'self'; frame-src 'self'; connect-src 'self'"

424 }

425 var csp string

426 if allowExternal {

427 csp = sb + "frame-ancestors 'self'; default-src 'none'; img-src data: http: https: 'unsafe-inline'; style-src 'unsafe-inline' data: http: https:; font-src data: http: https: 'unsafe-inline'; media-src 'unsafe-inline' data: http: https:" + script

428 } else if allowSelfImg {

429 csp = sb + "frame-ancestors 'self'; default-src 'none'; img-src data: 'self'; style-src 'unsafe-inline'" + script

430 } else {

431 csp = sb + "frame-ancestors 'self'; default-src 'none'; img-src data:; style-src 'unsafe-inline'" + script

432 }

433 h.Set("Content-Security-Policy", csp)

434 h.Set("X-Frame-Options", "sameorigin") // Duplicate with CSP, but better too much than too little.

435 h.Set("X-Content-Type-Options", "nosniff")

436 h.Set("Referrer-Policy", "no-referrer")

437 }

438

439 switch {

440 case len(t) == 2 && t[1] == "attachments.zip":

441 acc, m, msgr, p, cleanup, ok := xprepare()

442 if !ok {

443 return

444 }

445 defer cleanup()

446 state := msgState{acc: acc, m: m, msgr: msgr, part: &p}

447 // note: state is cleared by cleanup

448

449 mi, err := messageItem(log, m, &state)

450 xcheckf(ctx, err, "parsing message")

451

452 headers(false, false, false, false)

453 h.Set("Content-Type", "application/zip")

454 h.Set("Cache-Control", "no-store, max-age=0")

455 var subjectSlug string

456 if p.Envelope != nil {

457 s := p.Envelope.Subject

458 s = strings.ToLower(s)

459 s = regexp.MustCompile("[^a-z0-9_.-]").ReplaceAllString(s, "-")

460 s = regexp.MustCompile("--*").ReplaceAllString(s, "-")

461 s = strings.TrimLeft(s, "-")

462 s = strings.TrimRight(s, "-")

463 if s != "" {

464 s = "-" + s

465 }

466 subjectSlug = s

467 }

468 filename := fmt.Sprintf("email-%d-attachments-%s%s.zip", m.ID, m.Received.Format("20060102-150405"), subjectSlug)

469 cd := mime.FormatMediaType("attachment", map[string]string{"filename": filename})

470 h.Set("Content-Disposition", cd)

471

472 zw := zip.NewWriter(w)

473 names := map[string]bool{}

474 for _, a := range mi.Attachments {

475 ap := a.Part

476 name := tryDecodeParam(log, ap.ContentTypeParams["name"])

477 if name == "" {

478 // We don't check errors, this is all best-effort.

479 h, _ := ap.Header()

480 disposition := h.Get("Content-Disposition")

481 _, params, _ := mime.ParseMediaType(disposition)

482 name = tryDecodeParam(log, params["filename"])

483 }

484 if name != "" {

485 name = filepath.Base(name)

486 }

487 mt := strings.ToLower(ap.MediaType + "/" + ap.MediaSubType)

488 if name == "" || names[name] {

489 ext := filepath.Ext(name)

490 if ext == "" {

491 // Handle just a few basic types.

492 extensions := map[string]string{

493 "text/plain": ".txt",

494 "text/html": ".html",

495 "image/jpeg": ".jpg",

496 "image/png": ".png",

497 "image/gif": ".gif",

498 "application/zip": ".zip",

499 }

500 ext = extensions[mt]

501 if ext == "" {

502 ext = ".bin"

503 }

504 }

505 var stem string

506 if name != "" && strings.HasSuffix(name, ext) {

507 stem = strings.TrimSuffix(name, ext)

508 } else {

509 stem = "attachment"

510 for _, index := range a.Path {

511 stem += fmt.Sprintf("-%d", index)

512 }

513 }

514 name = stem + ext

515 seq := 0

516 for names[name] {

517 seq++

518 name = stem + fmt.Sprintf("-%d", seq) + ext

519 }

520 }

521 names[name] = true

522

523 fh := zip.FileHeader{

524 Name: name,

525 Modified: m.Received,

526 }

527 nodeflate := map[string]bool{

528 "application/x-bzip2": true,

529 "application/zip": true,

530 "application/x-zip-compressed": true,

531 "application/gzip": true,

532 "application/x-gzip": true,

533 "application/vnd.rar": true,

534 "application/x-rar-compressed": true,

535 "application/x-7z-compressed": true,

536 }

537 // Sniff content-type as well for compressed data.

538 buf := make([]byte, 512)

539 n, _ := io.ReadFull(ap.Reader(), buf)

540 var sniffmt string

541 if n > 0 {

542 sniffmt = strings.ToLower(http.DetectContentType(buf[:n]))

543 }

544 deflate := ap.MediaType != "VIDEO" && ap.MediaType != "AUDIO" && (ap.MediaType != "IMAGE" || ap.MediaSubType == "BMP") && !nodeflate[mt] && !nodeflate[sniffmt]

545 if deflate {

546 fh.Method = zip.Deflate

547 }

548 // We cannot return errors anymore: we have already sent an application/zip header.

549 if zf, err := zw.CreateHeader(&fh); err != nil {

550 log.Check(err, "adding to zip file")

551 return

552 } else if _, err := io.Copy(zf, ap.Reader()); err != nil {

553 log.Check(err, "writing to zip file")

554 return

555 }

556 }

557 err = zw.Close()

558 log.Check(err, "final write to zip file")

559

560 // Raw display of a message, as text/plain.

561 case len(t) == 2 && t[1] == "raw":

562 _, _, msgr, p, cleanup, ok := xprepare()

563 if !ok {

564 return

565 }

566 defer cleanup()

567

568 // We intentially use text/plain. We certainly don't want to return a format that

569 // browsers or users would think of executing. We do set the charset if available

570 // on the outer part. If present, we assume it may be relevant for other parts. If

571 // not, there is not much we could do better...

572 headers(false, false, false, false)

573 ct := "text/plain"

574 params := map[string]string{}

575 if charset := p.ContentTypeParams["charset"]; charset != "" {

576 params["charset"] = charset

577 }

578 h.Set("Content-Type", mime.FormatMediaType(ct, params))

579 h.Set("Cache-Control", "no-store, max-age=0")

580

581 _, err := io.Copy(w, &moxio.AtReader{R: msgr})

582 log.Check(err, "writing raw")

583

584 case len(t) == 2 && (t[1] == "msgtext" || t[1] == "msghtml" || t[1] == "msghtmlexternal"):

585 // msg.html has a javascript tag with message data, and javascript to render the

586 // message header like the regular webmail.html and to load the message body in a

587 // separate iframe with a separate request with stronger CSP.

588 acc, m, msgr, p, cleanup, ok := xprepare()

589 if !ok {

590 return

591 }

592 defer cleanup()

593

594 state := msgState{acc: acc, m: m, msgr: msgr, part: &p}

595 // note: state is cleared by cleanup

596

597 pm, err := parsedMessage(log, m, &state, true, true)

598 xcheckf(ctx, err, "getting parsed message")

599 if t[1] == "msgtext" && len(pm.Texts) == 0 || t[1] != "msgtext" && !pm.HasHTML {

600 http.Error(w, "400 - bad request - no such part", http.StatusBadRequest)

601 return

602 }

603

604 sameorigin := true

605 loadExternal := t[1] == "msghtmlexternal"

606 allowSelfScript := true

607 headers(sameorigin, loadExternal, allowSelfScript, false)

608 h.Set("Content-Type", "text/html; charset=utf-8")

609 h.Set("Cache-Control", "no-store, max-age=0")

610

611 path := filepath.FromSlash("webmail/msg.html")

612 fallback := webmailmsgHTML

613 serveContentFallback(log, w, r, path, fallback)

614

615 case len(t) == 2 && t[1] == "parsedmessage.js":

616 // Used by msg.html, for the msg* endpoints, for the data needed to show all data

617 // except the message body.

618 // This is js with data inside instead so we can load it synchronously, which we do

619 // to get a "loaded" event after the page was actually loaded.

620

621 acc, m, msgr, p, cleanup, ok := xprepare()

622 if !ok {

623 return

624 }

625 defer cleanup()

626 state := msgState{acc: acc, m: m, msgr: msgr, part: &p}

627 // note: state is cleared by cleanup

628

629 pm, err := parsedMessage(log, m, &state, true, true)

630 xcheckf(ctx, err, "parsing parsedmessage")

631 pmjson, err := json.Marshal(pm)

632 xcheckf(ctx, err, "marshal parsedmessage")

633

634 m.MsgPrefix = nil

635 m.ParsedBuf = nil

636 mi := MessageItem{m, pm.envelope, pm.attachments, pm.isSigned, pm.isEncrypted, pm.firstLine, false}

637 mijson, err := json.Marshal(mi)

638 xcheckf(ctx, err, "marshal messageitem")

639

640 headers(false, false, false, false)

641 h.Set("Content-Type", "application/javascript; charset=utf-8")

642 h.Set("Cache-Control", "no-store, max-age=0")

643

644 _, err = fmt.Fprintf(w, "window.messageItem = %s;\nwindow.parsedMessage = %s;\n", mijson, pmjson)

645 log.Check(err, "writing parsedmessage.js")

646

647 case len(t) == 2 && t[1] == "text":

648 // Returns text.html whichs loads the message data with a javascript tag and

649 // renders just the text content with the same code as webmail.html. Used by the

650 // iframe in the msgtext endpoint. Not used by the regular webmail viewer, it

651 // renders the text itself, with the same shared js code.

652 acc, m, msgr, p, cleanup, ok := xprepare()

653 if !ok {

654 return

655 }

656 defer cleanup()

657

658 state := msgState{acc: acc, m: m, msgr: msgr, part: &p}

659 // note: state is cleared by cleanup

660

661 pm, err := parsedMessage(log, m, &state, true, true)

662 xcheckf(ctx, err, "parsing parsedmessage")

663

664 if len(pm.Texts) == 0 {

665 http.Error(w, "400 - bad request - no text part in message", http.StatusBadRequest)

666 return

667 }

668

669 // Needed for inner document height for outer iframe height in separate message view.

670 sameorigin := true

671 allowSelfScript := true

672 allowSelfImg := true

673 headers(sameorigin, false, allowSelfScript, allowSelfImg)

674 h.Set("Content-Type", "text/html; charset=utf-8")

675 h.Set("Cache-Control", "no-store, max-age=0")

676

677 // We typically return the embedded file, but during development it's handy to load

678 // from disk.

679 path := filepath.FromSlash("webmail/text.html")

680 fallback := webmailtextHTML

681 serveContentFallback(log, w, r, path, fallback)

682

683 case len(t) == 2 && (t[1] == "html" || t[1] == "htmlexternal"):

684 // Returns the first HTML part, with "cid:" URIs replaced with an inlined datauri

685 // if the referenced Content-ID attachment can be found.

686 _, _, _, p, cleanup, ok := xprepare()

687 if !ok {

688 return

689 }

690 defer cleanup()

691

692 setHeaders := func() {

693 // Needed for inner document height for outer iframe height in separate message

694 // view. We only need that when displaying as a separate message on the msghtml*

695 // endpoints. When displaying in the regular webmail, we don't need to know the

696 // inner height so we load it as different origin, which should be safer.

697 sameorigin := r.URL.Query().Get("sameorigin") == "true"

698 allowExternal := strings.HasSuffix(t[1], "external")

699 headers(sameorigin, allowExternal, false, false)

700

701 h.Set("Content-Type", "text/html; charset=utf-8")

702 h.Set("Cache-Control", "no-store, max-age=0")

703 }

704

705 // todo: skip certain html parts? e.g. with content-disposition: attachment?

706 var done bool

707 var usePart func(p *message.Part, parents []*message.Part)

708 usePart = func(p *message.Part, parents []*message.Part) {

709 if done {

710 return

711 }

712 mt := p.MediaType + "/" + p.MediaSubType

713 switch mt {

714 case "TEXT/HTML":

715 done = true

716 err := inlineSanitizeHTML(log, setHeaders, w, p, parents)

717 if err != nil {

718 http.Error(w, "400 - bad request - "+err.Error(), http.StatusBadRequest)

719 }

720 return

721 }

722 parents = append(parents, p)

723 for _, sp := range p.Parts {

724 usePart(&sp, parents)

725 }

726 }

727 usePart(&p, nil)

728

729 if !done {

730 http.Error(w, "400 - bad request - no html part in message", http.StatusBadRequest)

731 }

732

733 case len(t) == 3 && (t[1] == "view" || t[1] == "viewtext" || t[1] == "download"):

734 // View any part, as referenced in the last element path. "0" is the whole message,

735 // 0.0 is the first subpart, etc. "view" returns it with the content-type from the

736 // message (could be dangerous, but we set strict CSP headers), "viewtext" returns

737 // data with a text/plain content-type so the browser will attempt to display it,

738 // and "download" adds a content-disposition header causing the browser the

739 // download the file.

740 _, _, _, p, cleanup, ok := xprepare()

741 if !ok {

742 return

743 }

744 defer cleanup()

745

746 paths := strings.Split(t[2], ".")

747 if len(paths) == 0 || paths[0] != "0" {

748 http.NotFound(w, r)

749 return

750 }

751 ap := p

752 for _, e := range paths[1:] {

753 index, err := strconv.ParseInt(e, 10, 32)

754 if err != nil || index < 0 || int(index) >= len(ap.Parts) {

755 http.NotFound(w, r)

756 return

757 }

758 ap = ap.Parts[int(index)]

759 }

760

761 headers(false, false, false, false)

762 var ct string

763 if t[1] == "viewtext" {

764 ct = "text/plain"

765 } else {

766 ct = strings.ToLower(ap.MediaType + "/" + ap.MediaSubType)

767 }

768 h.Set("Content-Type", ct)

769 h.Set("Cache-Control", "no-store, max-age=0")

770 if t[1] == "download" {

771 name := tryDecodeParam(log, ap.ContentTypeParams["name"])

772 if name == "" {

773 // We don't check errors, this is all best-effort.

774 h, _ := ap.Header()

775 disposition := h.Get("Content-Disposition")

776 _, params, _ := mime.ParseMediaType(disposition)

777 name = tryDecodeParam(log, params["filename"])

778 }

779 if name == "" {

780 name = "attachment.bin"

781 }

782 cd := mime.FormatMediaType("attachment", map[string]string{"filename": name})

783 h.Set("Content-Disposition", cd)

784 }

785

786 _, err := io.Copy(w, ap.Reader())

787 if err != nil && !moxio.IsClosed(err) {

788 log.Errorx("copying attachment", err)

789 }

790 default:

791 http.NotFound(w, r)

792 }

793}

794

795// inlineSanitizeHTML writes the part as HTML, with "cid:" URIs for html "src"

796// attributes inlined and with potentially dangerous tags removed (javascript). The

797// sanitizing is just a first layer of defense, CSP headers block execution of

798// scripts. If the HTML becomes too large, an error is returned. Before writing

799// HTML, setHeaders is called to write the required headers for content-type and

800// CSP. On error, setHeader is not called, no output is written and the caller

801// should write an error response.

802func inlineSanitizeHTML(log mlog.Log, setHeaders func(), w io.Writer, p *message.Part, parents []*message.Part) error {

803 // Prepare cids if there is a chance we will use them.

804 cids := map[string]*message.Part{}

805 for _, parent := range parents {

806 if parent.MediaType+"/"+parent.MediaSubType == "MULTIPART/RELATED" && p.DecodedSize < 2*1024*1024 {

807 for i, rp := range parent.Parts {

808 if rp.ContentID != "" {

809 cids[strings.ToLower(rp.ContentID)] = &parent.Parts[i]

810 }

811 }

812 }

813 }

814

815 node, err := html.Parse(p.ReaderUTF8OrBinary())

816 if err != nil {

817 return fmt.Errorf("parsing html: %v", err)

818 }

819

820 // We track size, if it becomes too much, we abort and still copy as regular html.

821 var totalSize int64

822 if err := inlineNode(node, cids, &totalSize); err != nil {

823 return fmt.Errorf("inline cid uris in html nodes: %w", err)

824 }

825 sanitizeNode(node)

826 setHeaders()

827 err = html.Render(w, node)

828 log.Check(err, "writing html")

829 return nil

830}

831

832// We inline cid: URIs into data: URIs. If a cid is missing in the

833// multipart/related, we ignore the error and continue with other HTML nodes. It

834// will probably just result in a "broken image". We limit the max size we

835// generate. We only replace "src" attributes that start with "cid:". A cid URI

836// could theoretically occur in many more places, like link href, and css url().

837// That's probably not common though. Let's wait for someone to need it.

838func inlineNode(node *html.Node, cids map[string]*message.Part, totalSize *int64) error {

839 for i, a := range node.Attr {

840 if a.Key != "src" || !caselessPrefix(a.Val, "cid:") || a.Namespace != "" {

841 continue

842 }

843 cid := a.Val[4:]

844 ap := cids["<"+strings.ToLower(cid)+">"]

845 if ap == nil {

846 // Missing cid, can happen with email, no need to stop returning data.

847 continue

848 }

849 *totalSize += ap.DecodedSize

850 if *totalSize >= 10*1024*1024 {

851 return fmt.Errorf("html too large")

852 }

853 var sb strings.Builder

854 if _, err := fmt.Fprintf(&sb, "data:%s;base64,", strings.ToLower(ap.MediaType+"/"+ap.MediaSubType)); err != nil {

855 return fmt.Errorf("writing datauri: %v", err)

856 }

857 w := base64.NewEncoder(base64.StdEncoding, &sb)

858 if _, err := io.Copy(w, ap.Reader()); err != nil {

859 return fmt.Errorf("writing base64 datauri: %v", err)

860 }

861 node.Attr[i].Val = sb.String()

862 }

863 for node = node.FirstChild; node != nil; node = node.NextSibling {

864 if err := inlineNode(node, cids, totalSize); err != nil {

865 return err

866 }

867 }

868 return nil

869}

870

871func caselessPrefix(k, pre string) bool {

872 return len(k) >= len(pre) && strings.EqualFold(k[:len(pre)], pre)

873}

874

875var targetable = map[string]bool{

876 "a": true,

877 "area": true,

878 "form": true,

879 "base": true,

880}

881

882// sanitizeNode removes script elements, on* attributes, javascript: href

883// attributes, adds target="_blank" to all links and to a base tag.

884func sanitizeNode(node *html.Node) {

885 i := 0

886 var haveTarget, haveRel bool

887 for i < len(node.Attr) {

888 a := node.Attr[i]

889 // Remove dangerous attributes.

890 if strings.HasPrefix(a.Key, "on") || a.Key == "href" && caselessPrefix(a.Val, "javascript:") || a.Key == "src" && caselessPrefix(a.Val, "data:text/html") {

891 copy(node.Attr[i:], node.Attr[i+1:])

892 node.Attr = node.Attr[:len(node.Attr)-1]

893 continue

894 }

895 if a.Key == "target" {

896 node.Attr[i].Val = "_blank"

897 haveTarget = true

898 }

899 if a.Key == "rel" && targetable[node.Data] {

900 node.Attr[i].Val = "noopener noreferrer"

901 haveRel = true

902 }

903 i++

904 }

905 // Ensure target attribute is set for elements that can have it.

906 if !haveTarget && node.Type == html.ElementNode && targetable[node.Data] {

907 node.Attr = append(node.Attr, html.Attribute{Key: "target", Val: "_blank"})

908 haveTarget = true

909 }

910 if haveTarget && !haveRel {

911 node.Attr = append(node.Attr, html.Attribute{Key: "rel", Val: "noopener noreferrer"})

912 }

913

914 parent := node

915 node = node.FirstChild

916 var haveBase bool

917 for node != nil {

918 // Set next now, we may remove cur, which clears its NextSibling.

919 cur := node

920 node = node.NextSibling

921

922 // Remove script elements.

923 if cur.Type == html.ElementNode && cur.Data == "script" {

924 parent.RemoveChild(cur)

925 continue

926 }

927 sanitizeNode(cur)

928 }

929 if parent.Type == html.ElementNode && parent.Data == "head" && !haveBase {

930 n := html.Node{Type: html.ElementNode, Data: "base", Attr: []html.Attribute{{Key: "target", Val: "_blank"}, {Key: "rel", Val: "noopener noreferrer"}}}

931 parent.AppendChild(&n)

932 }

933}

934