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'OVERVIEW' ** Obsolete normative reference: RFC 7230 (Obsoleted by RFC 9110, RFC 9112) ** Obsolete normative reference: RFC 7231 (Obsoleted by RFC 9110) ** Obsolete normative reference: RFC 7540 (Obsoleted by RFC 9113) -- No information found for draft-ietf-webtrans-http3-latest - is the name correct? -- Possible downref: Normative reference to a draft: ref. 'WEBTRANSPORT-H3' Summary: 4 errors (**), 0 flaws (~~), 2 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 webtrans A. Frindell 3 Internet-Draft Facebook Inc. 4 Intended status: Standards Track E. Kinnear 5 Expires: 26 August 2021 T. Pauly 6 Apple Inc. 7 V. Vasiliev 8 Google 9 G. Xie 10 Facebook Inc. 11 22 February 2021 13 WebTransport using HTTP/2 14 draft-kinnear-webtransport-http2-02 16 Abstract 18 WebTransport [OVERVIEW] is a protocol framework that enables clients 19 constrained by the Web security model to communicate with a remote 20 server using a secure multiplexed transport. This document describes 21 a WebTransport protocol that is based on HTTP/2 [RFC7540] and 22 provides support for unidirectional streams, bidirectional streams 23 and datagrams, all multiplexed within the same HTTP/2 connection. 25 Note to Readers 27 Discussion of this draft takes place on the WebTransport mailing list 28 (webtransport@ietf.org), which is archived at 29 . 31 The repository tracking the issues for this draft can be found at 32 . The 33 web API draft corresponding to this document can be found at 34 . 36 Status of This Memo 38 This Internet-Draft is submitted in full conformance with the 39 provisions of BCP 78 and BCP 79. 41 Internet-Drafts are working documents of the Internet Engineering 42 Task Force (IETF). Note that other groups may also distribute 43 working documents as Internet-Drafts. The list of current Internet- 44 Drafts is at https://datatracker.ietf.org/drafts/current/. 46 Internet-Drafts are draft documents valid for a maximum of six months 47 and may be updated, replaced, or obsoleted by other documents at any 48 time. It is inappropriate to use Internet-Drafts as reference 49 material or to cite them other than as "work in progress." 51 This Internet-Draft will expire on 26 August 2021. 53 Copyright Notice 55 Copyright (c) 2021 IETF Trust and the persons identified as the 56 document authors. All rights reserved. 58 This document is subject to BCP 78 and the IETF Trust's Legal 59 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 60 license-info) in effect on the date of publication of this document. 61 Please review these documents carefully, as they describe your rights 62 and restrictions with respect to this document. Code Components 63 extracted from this document must include Simplified BSD License text 64 as described in Section 4.e of the Trust Legal Provisions and are 65 provided without warranty as described in the Simplified BSD License. 67 Table of Contents 69 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 70 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 71 2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 3 72 3. Session Establishment . . . . . . . . . . . . . . . . . . . . 4 73 3.1. Establishing a Transport-Capable HTTP/2 Connection . . . 4 74 3.2. Extended CONNECT in HTTP/2 . . . . . . . . . . . . . . . 4 75 3.3. Creating a New Session . . . . . . . . . . . . . . . . . 4 76 3.4. Limiting the Number of Simultaneous Sessions . . . . . . 5 77 4. WebTransport Features . . . . . . . . . . . . . . . . . . . . 5 78 4.1. WT_STREAM Frame . . . . . . . . . . . . . . . . . . . . . 6 79 4.2. WT_DATAGRAM Frame . . . . . . . . . . . . . . . . . . . . 7 80 5. Session Termination . . . . . . . . . . . . . . . . . . . . . 8 81 6. Transport Properties . . . . . . . . . . . . . . . . . . . . 8 82 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 83 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 84 8.1. HTTP/2 SETTINGS Parameter Registration . . . . . . . . . 9 85 8.2. Frame Type Registration . . . . . . . . . . . . . . . . . 9 86 8.3. HTTP/2 Error Code Registry . . . . . . . . . . . . . . . 10 87 8.4. Examples . . . . . . . . . . . . . . . . . . . . . . . . 10 88 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 89 9.1. Normative References . . . . . . . . . . . . . . . . . . 12 90 9.2. Informative References . . . . . . . . . . . . . . . . . 13 91 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 14 92 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 94 1. Introduction 96 Currently, the only mechanism in HTTP/2 for server to client 97 communication is server push. That is, servers can initiate 98 unidirectional push promised streams to clients, but clients cannot 99 respond to them; they can only accept them or discard them. 100 Additionally, intermediaries along the path may have different server 101 push policies and may not forward push promised streams to the 102 downstream client. This best effort mechanism is not sufficient to 103 reliably deliver messages from servers to clients, limiting server to 104 client use-cases such as chat messages or notifications. 106 Several techniques have been developed to workaround these 107 limitations: long polling [RFC6202], WebSocket [RFC8441], and 108 tunneling using the CONNECT method. All of these approaches have 109 limitations. 111 This document defines a mechanism for multiplexing non-HTTP data with 112 HTTP/2 in a manner that conforms with the WebTransport protocol 113 requirements and semantics [OVERVIEW]. Using the mechanism described 114 here, multiple WebTransport instances can be multiplexed 115 simultaneously with regular HTTP traffic on the same HTTP/2 116 connection. 118 1.1. Terminology 120 The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 121 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 122 "OPTIONAL" in this document are to be interpreted as described in BCP 123 14 [RFC2119] [RFC8174] when, and only when, they appear in all 124 capitals, as shown here. 126 This document follows terminology defined in Section 1.2 of 127 [OVERVIEW]. Note that this document distinguishes between a 128 WebTransport server and an HTTP/2 server. An HTTP/2 server is the 129 server that terminates HTTP/2 connections; a WebTransport server is 130 an application that accepts WebTransport sessions, which can be 131 accessed via an HTTP/2 server. 133 2. Protocol Overview 135 WebTransport servers are identified by a pair of authority value and 136 path value (defined in [RFC3986] Sections 3.2 and 3.3 137 correspondingly). 139 When an HTTP/2 connection is established, both the client and server 140 have to send a SETTINGS_ENABLE_WEBTRANSPORT setting in order to 141 indicate that they both support WebTransport over HTTP/2. 143 WebTransport sessions are initiated inside a given HTTP/2 connection 144 by the client, who sends an extended CONNECT request [RFC8441]. If 145 the server accepts the request, an WebTransport session is 146 established. The resulting stream will be further referred to as a 147 _CONNECT stream_, and its stream ID is used to uniquely identify a 148 given WebTransport session within the connection. The ID of the 149 CONNECT stream that established a given WebTransport session will be 150 further referred to as a _Session ID_. 152 After the session is established, the peers can exchange data using 153 the following mechanisms: 155 * Both client and server can create a bidirectional or 156 unidirectional stream using a new HTTP/2 extension frame 157 (WT_STREAM) 159 * A datagram can be sent using a new HTTP/2 extension frame 160 WT_DATAGRAM. 162 A WebTransport session is terminated when the CONNECT stream that 163 created it is closed. 165 3. Session Establishment 167 3.1. Establishing a Transport-Capable HTTP/2 Connection 169 In order to indicate support for WebTransport, both the client and 170 the server MUST send a SETTINGS_ENABLE_WEBTRANSPORT value set to "1" 171 in their SETTINGS frame. Endpoints MUST NOT use any WebTransport- 172 related functionality unless the parameter has been negotiated. 174 3.2. Extended CONNECT in HTTP/2 176 [RFC8441] defines an extended CONNECT method in Section 4, enabled by 177 the SETTINGS_ENABLE_CONNECT_PROTOCOL parameter. An endpoint doesn 178 not need to send both SETTINGS_ENABLE_CONNECT_PROTOCOL and 179 SETTINGS_ENABLE_WEBTRANSPORT; the SETTINGS_ENABLE_WEBTRANSPORT 180 setting implies that an endpoint supports extended CONNECT. 182 3.3. Creating a New Session 184 As WebTransport sessions are established over HTTP/2, they are 185 identified using the "https" URI scheme [RFC7230]. 187 In order to create a new WebTransport session, a client can send an 188 HTTP CONNECT request. The ":protocol" pseudo-header field 189 ([RFC8441]) MUST be set to "webtransport" (Section 7.1 190 [WEBTRANSPORT-H3]). The ":scheme" field MUST be "https". Both the 191 ":authority" and the ":path" value MUST be set; those fields indicate 192 the desired WebTransport server. An "Origin" header [RFC6454] MUST 193 be provided within the request. 195 Upon receiving an extended CONNECT request with a ":protocol" field 196 set to "webtransport", the HTTP/2 server can check if it has a 197 WebTransport server associated with the specified ":authority" and 198 ":path" values. If it does not, it SHOULD reply with status code 404 199 (Section 6.5.4, [RFC7231]). If it does, it MAY accept the session by 200 replying with status code 200. The WebTransport server MUST verify 201 the "Origin" header to ensure that the specified origin is allowed to 202 access the server in question. 204 From the client's perspective, a WebTransport session is established 205 when the client receives a 200 response. From the server's 206 perspective, a session is established once it sends a 200 response. 207 Both endpoints MUST NOT open any streams or send any datagrams on a 208 given session before that session is established. 210 3.4. Limiting the Number of Simultaneous Sessions 212 From the flow control perspective, WebTransport sessions count 213 against the stream flow control just like regular HTTP requests, 214 since they are established via an HTTP CONNECT request. This 215 document does not make any effort to introduce a separate flow 216 control mechanism for sessions, nor to separate HTTP requests from 217 WebTransport data streams. If the server needs to limit the rate of 218 incoming requests, it has alternative mechanisms at its disposal: 220 * "HTTP_STREAM_REFUSED" error code defined in [RFC7540] indicates to 221 the receiving HTTP/2 stack that the request was not processed in 222 any way. 224 * HTTP status code 429 indicates that the request was rejected due 225 to rate limiting [RFC6585]. Unlike the previous method, this 226 signal is directly propagated to the application. 228 4. WebTransport Features 230 WebTransport over HTTP/2 provides the following features described in 231 [OVERVIEW]: unidirectional streams, bidirectional streams and 232 datagrams, initiated by either endpoint. 234 Session IDs are used to demultiplex streams and datagrams belonging 235 to different WebTransport sessions. On the wire, session IDs are 236 encoded using a 31-bit integer field. 238 4.1. WT_STREAM Frame 240 A new HTTP/2 frame called WT_STREAM is introduced for either endpoint 241 to establish WebTransport streams. WT_STREAM frames can be sent on a 242 stream in the "idle", "reserved (local)", "open", or "half-closed 243 (remote)" state. 245 0 1 2 3 246 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 247 +---------------+ 248 |Pad Length? (8)| 249 +-+-------------+-----------------------------------------------+ 250 |R| Session ID (31) | 251 +-+-------------------------------------------------------------+ 252 | Padding (*) ... 253 +---------------------------------------------------------------+ 255 Figure 1: WT_STREAM Frame Format 257 The WT_STREAM frame define the following fields: 259 Pad Length: An 8-bit field containing the length of the frame padding 260 in units of octets. This field is conditional (as signified by a "?" 261 in the diagram) and is only present if the PADDED flag is set. 263 Session ID: An unsigned 31-bit integer that identifies the stream 264 Connect Stream for this Web Transport stream. The Session ID MUST be 265 MUST be an open stream negotiated via the extended CONNECT protocol 266 with a ":protocol" value of "webtransport". 268 The WT_STREAM frame defines the following flags: 270 UNIDIRECTIONAL (0x1): When set, the stream begins in the "half-closed 271 (remote)" state at the sender, and in the "half-closed (local)" state 272 at the receiver. 274 As with all HTTP/2 streams, WebTransport streams initiated by a 275 client have odd stream IDs and those initiated by a server have even 276 stream IDs. 278 The recipient MUST respond with a stream error of type 279 WT_STREAM_ERROR if the specified WebTransport Connect Stream does not 280 exist, is not a stream established via extended CONNECT to use the 281 "webtransport" protocol, or if it is in the "closed" or "half-closed 282 (remote)" stream state. 284 4.2. WT_DATAGRAM Frame 286 A new HTTP/2 frame called WT_DATAGRAM is introduced for either 287 endpoint to transmit a datagram. WT_DATAGRAM frames are sent with 288 Stream Identifier 0. 290 0 1 2 3 291 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 292 +---------------+ 293 |Pad Length? (8)| 294 +-+-------------+-----------------------------------------------+ 295 |R| Session ID (31) | 296 +-+-------------------------------------------------------------+ 297 | Data (*) ... 298 +---------------------------------------------------------------+ 299 | Padding (*) ... 300 +---------------------------------------------------------------+ 302 Figure 2: WT_DATAGRAM Frame Format 304 The WT_DATAGRAM frame define the following fields: 306 Pad Length: An 8-bit field containing the length of the frame padding 307 in units of octets. This field is conditional (as signified by a "?" 308 in the diagram) and is only present if the PADDED flag is set. 310 Session ID: An unsigned 31-bit integer that identifies the stream 311 Connect Stream for this Web Transport stream. The Session ID MUST be 312 MUST be an open stream negotiated via the extended CONNECT protocol 313 with a ":protocol" value of "webtransport". 315 Data: Application data. The amount of data is the remainder of the 316 frame payload after subtracting the length of the other fields that 317 are present. 319 The WT_DATAGRAM frame does not define any flags. 321 The recipient MAY respond with a stream error of type WT_STREAM_ERROR 322 if the specified WebTransport Connect Stream does not exist, is not a 323 stream established via extended CONNECT to use the "webtransport" 324 protocol, or if it is in the "closed" or "half-closed (remote)" 325 stream state. 327 The data in WT_DATAGRAM frames is not subject to flow control. The 328 receiver MAY discard this data if it does not have sufficient space 329 to buffer it. 331 An intermediary could forward the data in a WT_DATAGRAM frame over 332 another protocol, such as WebTransport over HTTP/3. In QUIC, a 333 datagram frame can span at most one packet. Because of that, the 334 applications have to know the maximum size of the datagram they can 335 send. However, when proxying the datagrams, the hop-by-hop MTUs can 336 vary. 338 5. Session Termination 340 An WebTransport session over HTTP/2 is terminated when either 341 endpoint closes the stream associated with the CONNECT request that 342 initiated the session. Upon learning about the session being 343 terminated, the endpoint MUST stop sending new datagrams and reset 344 all of the streams associated with the session. 346 6. Transport Properties 348 The WebTransport framework [OVERVIEW] defines a set of optional 349 transport properties that clients can use to determine the presence 350 of features which might allow additional optimizations beyond the 351 common set of properties available via all WebTransport protocols. 352 Below are details about support in Http2Transport for those 353 properties. 355 Stream Independence: Http2Transport does not support stream 356 independence, as HTTP/2 inherently has head of line blocking. 358 Partial Reliability: Http2Transport does not support partial 359 reliability, as HTTP/2 retransmits any lost data. This means that 360 any datagrams sent via Http2Transport will be retransmitted 361 regardless of the preference of the application. The receiver is 362 permitted to drop them, however, if it is unable to buffer them. 364 Pooling Support: Http2Transport supports pooling, as multiple 365 transports using Http2Transport may share the same underlying 366 HTTP/2 connection and therefore share a congestion controller and 367 other transport context. 369 Connection Mobility: Http2Transport does not support connection 370 mobility, unless an underlying transport protocol that supports 371 multipath or migration, such as MPTCP [RFC7540], is used 372 underneath HTTP/2 and TLS. Without such support, Http2Transport 373 connections cannot survive network transitions. 375 7. Security Considerations 377 WebTransport over HTTP/2 satisfies all of the security requirements 378 imposed by [OVERVIEW] on WebTransport protocols, thus providing a 379 secure framework for client-server communication in cases when the 380 client is potentially untrusted. 382 WebTransport over HTTP/2 requires explicit opt-in through the use of 383 HTTP SETTINGS; this avoids potential protocol confusion attacks by 384 ensuring the HTTP/2 server explicitly supports it. It also requires 385 the use of the Origin header, providing the server with the ability 386 to deny access to Web-based clients that do not originate from a 387 trusted origin. 389 Just like HTTP traffic going over HTTP/2, WebTransport pools traffic 390 to different origins within a single connection. Different origins 391 imply different trust domains, meaning that the implementations have 392 to treat each transport as potentially hostile towards others on the 393 same connection. One potential attack is a resource exhaustion 394 attack: since all of the transports share both congestion control and 395 flow control context, a single client aggressively using up those 396 resources can cause other transports to stall. The user agent thus 397 SHOULD implement a fairness scheme that ensures that each transport 398 within connection gets a reasonable share of controlled resources; 399 this applies both to sending data and to opening new streams. 401 8. IANA Considerations 403 8.1. HTTP/2 SETTINGS Parameter Registration 405 The following entry is added to the "HTTP/2 Settings" registry 406 established by [RFC7540]: 408 The "SETTINGS_ENABLE_WEBTRANSPORT" parameter indicates that the 409 specified HTTP/2 connection is WebTransport-capable. 411 Setting Name: ENABLE_WEBTRANSPORT 413 Value: 0x2b603742 415 Default: 0 417 Specification: This document 419 8.2. Frame Type Registration 421 The following entries are added to the "HTTP/2 Frame Type" registry 422 established by [RFC7540]: 424 The "WT_STREAM" frame allows HTTP/2 client- and server-initiated 425 unidirectional and bidirectional streams to be used by WebTransport: 427 Code: 0xTBD 429 Frame Type: WEBTRANSPORT_STREAM 431 Specification: This document 433 The "WT_DATAGRAM" frame allows HTTP/2 client and server to exchange 434 datagrams used by WebTransport: 436 Code: 0xTBD 438 Frame Type: WEBTRANSPORT_DATAGRAM 440 Specification: This document 442 8.3. HTTP/2 Error Code Registry 444 The following entries are added to the "HTTP/2 Error Code" registry 445 that was established by Section 11.2 of [RFC7540]. 447 Name: WT_STREAM_ERROR 449 Code: 0xTBD 451 Description: Invalid use of WT_STREAM frame 453 Specification: _RFC Editor: Please fill in this value with the RFC 454 number for this document_ 456 8.4. Examples 458 An example of negotiating a WebTransport Stream on an HTTP/2 459 connection follows. This example is intended to closely follow the 460 example in Section 5.1 of [RFC8441] to help illustrate the 461 differences defined in this document. 463 [[ From Client ]] [[ From Server ]] 465 SETTINGS 466 SETTINGS_ENABLE_WEBTRANSPORT = 1 468 SETTINGS 469 SETTINGS_ENABLE_WEBTRANSPORT = 1 471 HEADERS + END_HEADERS 472 Stream ID = 3 473 :method = CONNECT 474 :protocol = webtransport 475 :scheme = https 476 :path = / 477 :authority = server.example.com 478 origin: server.example.com 480 HEADERS + END_HEADERS 481 Stream ID = 3 482 :status = 200 484 WT_STREAM 485 Stream ID = 5 486 Session ID = 3 488 DATA 489 Stream ID = 5 490 WebTransport Data 492 DATA + END_STREAM 493 Stream ID = 5 494 WebTransport Data 496 DATA + END_STREAM 497 Stream ID = 5 498 WebTransport Data 500 An example of the server initiating a WebTransport Stream follows. 501 The only difference here is the endpoint that sends the first 502 WT_STREAM frame. 504 [[ From Client ]] [[ From Server ]] 506 SETTINGS 507 SETTINGS_ENABLE_WEBTRANSPORT = 1 509 SETTINGS 510 SETTINGS_ENABLE_WEBTRANSPORT = 1 512 HEADERS + END_HEADERS 513 Stream ID = 3 514 :method = CONNECT 515 :protocol = webtransport 516 :scheme = https 517 :path = / 518 :authority = server.example.com 519 origin: server.example.com 520 HEADERS + END_HEADERS 521 Stream ID = 3 522 :status = 200 524 WT_STREAM 525 Stream ID = 2 526 Session ID = 3 528 DATA 529 Stream ID = 2 530 WebTransport Data 532 DATA + END_STREAM 533 Stream ID = 2 534 WebTransport Data 536 DATA + END_STREAM 537 Stream ID = 2 538 WebTransport Data 540 9. References 542 9.1. Normative References 544 [OVERVIEW] Vasiliev, V., "The WebTransport Protocol Framework", Work 545 in Progress, Internet-Draft, draft-ietf-webtrans-overview- 546 latest, . 549 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 550 Requirement Levels", BCP 14, RFC 2119, 551 DOI 10.17487/RFC2119, March 1997, 552 . 554 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 555 Resource Identifier (URI): Generic Syntax", STD 66, 556 RFC 3986, DOI 10.17487/RFC3986, January 2005, 557 . 559 [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, 560 DOI 10.17487/RFC6454, December 2011, 561 . 563 [RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status 564 Codes", RFC 6585, DOI 10.17487/RFC6585, April 2012, 565 . 567 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 568 Protocol (HTTP/1.1): Message Syntax and Routing", 569 RFC 7230, DOI 10.17487/RFC7230, June 2014, 570 . 572 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 573 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 574 DOI 10.17487/RFC7231, June 2014, 575 . 577 [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext 578 Transfer Protocol Version 2 (HTTP/2)", RFC 7540, 579 DOI 10.17487/RFC7540, May 2015, 580 . 582 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 583 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 584 May 2017, . 586 [RFC8441] McManus, P., "Bootstrapping WebSockets with HTTP/2", 587 RFC 8441, DOI 10.17487/RFC8441, September 2018, 588 . 590 [WEBTRANSPORT-H3] 591 Vasiliev, V., "WebTransport over HTTP/3", Work in 592 Progress, Internet-Draft, draft-ietf-webtrans- 593 http3-latest, . 596 9.2. Informative References 598 [RFC6202] Loreto, S., Saint-Andre, P., Salsano, S., and G. Wilkins, 599 "Known Issues and Best Practices for the Use of Long 600 Polling and Streaming in Bidirectional HTTP", RFC 6202, 601 DOI 10.17487/RFC6202, April 2011, 602 . 604 Acknowledgments 606 Thanks to Anthony Chivetta, Joshua Otto, and Valentin Pistol for 607 their contributions in the design and implementation of this work. 609 Authors' Addresses 611 Alan Frindell 612 Facebook Inc. 614 Email: afrind@fb.com 616 Eric Kinnear 617 Apple Inc. 618 One Apple Park Way 619 Cupertino, California 95014, 620 United States of America 622 Email: ekinnear@apple.com 624 Tommy Pauly 625 Apple Inc. 626 One Apple Park Way 627 Cupertino, California 95014, 628 United States of America 630 Email: tpauly@apple.com 632 Victor Vasiliev 633 Google 635 Email: vasilvv@google.com 637 Guowu Xie 638 Facebook Inc. 640 Email: woo@fb.com