idnits 2.17.1 draft-ietf-webpush-protocol-08.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (July 22, 2016) is 2834 days in the past. Is this intentional? 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'CAP-URI' ** Obsolete normative reference: RFC 2818 (Obsoleted by RFC 9110) ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) ** Obsolete normative reference: RFC 5988 (Obsoleted by RFC 8288) ** Obsolete normative reference: RFC 7230 (Obsoleted by RFC 9110, RFC 9112) ** Obsolete normative reference: RFC 7231 (Obsoleted by RFC 9110) ** Obsolete normative reference: RFC 7232 (Obsoleted by RFC 9110) ** Obsolete normative reference: RFC 7540 (Obsoleted by RFC 9113) == Outdated reference: A later version (-09) exists of draft-ietf-webpush-encryption-03 == Outdated reference: A later version (-04) exists of draft-ietf-webpush-vapid-01 Summary: 7 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 WEBPUSH M. Thomson 3 Internet-Draft Mozilla 4 Intended status: Standards Track E. Damaggio 5 Expires: January 23, 2017 B. Raymor, Ed. 6 Microsoft 7 July 22, 2016 9 Generic Event Delivery Using HTTP Push 10 draft-ietf-webpush-protocol-08 12 Abstract 14 A simple protocol for the delivery of real-time events to user agents 15 is described. This scheme uses HTTP/2 server push. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at http://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on January 23, 2017. 34 Copyright Notice 36 Copyright (c) 2016 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (http://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 52 1.1. Conventions and Terminology . . . . . . . . . . . . . . . 4 53 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5 54 2.1. HTTP Resources . . . . . . . . . . . . . . . . . . . . . 6 55 3. Connecting to the Push Service . . . . . . . . . . . . . . . 6 56 4. Subscribing for Push Messages . . . . . . . . . . . . . . . . 7 57 4.1. Collecting Subscriptions into Sets . . . . . . . . . . . 8 58 5. Requesting Push Message Delivery . . . . . . . . . . . . . . 9 59 5.1. Requesting Push Message Receipts . . . . . . . . . . . . 9 60 5.2. Push Message Time-To-Live . . . . . . . . . . . . . . . . 10 61 5.3. Push Message Urgency . . . . . . . . . . . . . . . . . . 12 62 5.4. Replacing Push Messages . . . . . . . . . . . . . . . . . 13 63 6. Receiving Push Messages for a Subscription . . . . . . . . . 14 64 6.1. Receiving Push Messages for a Subscription Set . . . . . 16 65 6.2. Acknowledging Push Messages . . . . . . . . . . . . . . . 17 66 6.3. Receiving Push Message Receipts . . . . . . . . . . . . . 18 67 7. Operational Considerations . . . . . . . . . . . . . . . . . 19 68 7.1. Load Management . . . . . . . . . . . . . . . . . . . . . 19 69 7.2. Push Message Expiration . . . . . . . . . . . . . . . . . 19 70 7.3. Subscription Expiration . . . . . . . . . . . . . . . . . 20 71 7.3.1. Subscription Set Expiration . . . . . . . . . . . . . 21 72 7.4. Implications for Application Reliability . . . . . . . . 21 73 7.5. Subscription Sets and Concurrent HTTP/2 streams . . . . . 21 74 8. Security Considerations . . . . . . . . . . . . . . . . . . . 22 75 8.1. Confidentiality from Push Service Access . . . . . . . . 22 76 8.2. Privacy Considerations . . . . . . . . . . . . . . . . . 22 77 8.3. Authorization . . . . . . . . . . . . . . . . . . . . . . 23 78 8.4. Denial of Service Considerations . . . . . . . . . . . . 24 79 8.5. Logging Risks . . . . . . . . . . . . . . . . . . . . . . 25 80 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 81 9.1. Header Field Registrations . . . . . . . . . . . . . . . 25 82 9.2. Link Relation URNs . . . . . . . . . . . . . . . . . . . 25 83 9.3. Service Name and Port Number Registration . . . . . . . . 27 84 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27 85 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 86 11.1. Normative References . . . . . . . . . . . . . . . . . . 28 87 11.2. Informative References . . . . . . . . . . . . . . . . . 29 88 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 29 89 A.1. Since draft-ietf-webpush-protocol-00 . . . . . . . . . . 30 90 A.2. Since draft-ietf-webpush-protocol-01 . . . . . . . . . . 30 91 A.3. Since draft-ietf-webpush-protocol-02 . . . . . . . . . . 30 92 A.4. Since draft-ietf-webpush-protocol-03 . . . . . . . . . . 30 93 A.5. Since draft-ietf-webpush-protocol-04 . . . . . . . . . . 30 94 A.6. Since draft-ietf-webpush-protocol-05 . . . . . . . . . . 31 95 A.7. Since draft-ietf-webpush-protocol-06 . . . . . . . . . . 31 96 A.8. Since draft-ietf-webpush-protocol-07 . . . . . . . . . . 31 98 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 100 1. Introduction 102 Many applications on mobile and embedded devices require continuous 103 access to network communications so that real-time events - such as 104 incoming calls or messages - can be delivered (or "pushed") in a 105 timely fashion. These devices typically have limited power reserves, 106 so finding more efficient ways to serve application requirements 107 greatly benefits the application ecosystem. 109 One significant contributor to power usage is the radio. Radio 110 communications consume a significant portion of the energy budget on 111 a wireless device. 113 Uncoordinated use of persistent connections or sessions from multiple 114 applications can contribute to unnecessary use of the device radio, 115 since each independent session can incur its own overhead. In 116 particular, keep alive traffic used to ensure that middleboxes do not 117 prematurely time out sessions, can result in significant waste. 118 Maintenance traffic tends to dominate over the long term, since 119 events are relatively rare. 121 Consolidating all real-time events into a single session ensures more 122 efficient use of network and radio resources. A single service 123 consolidates all events, distributing those events to applications as 124 they arrive. This requires just one session, avoiding duplicated 125 overhead costs. 127 The W3C Push API [API] describes an API that enables the use of a 128 consolidated push service from web applications. This document 129 expands on that work by describing a protocol that can be used to: 131 o request the delivery of a push message to a user agent, 133 o create new push message delivery subscriptions, and 135 o monitor for new push messages. 137 A standardized method of event delivery is particularly important for 138 the W3C Push API, where application servers might need to use 139 multiple push services. The subscription, management and monitoring 140 functions are currently fulfilled by proprietary protocols; these are 141 adequate, but do not offer any of the advantages that standardization 142 affords. 144 This document intentionally does not describe how a push service is 145 discovered. Discovery of push services is left for future efforts, 146 if it turns out to be necessary at all. User agents are expected to 147 be configured with a URL for a push service. 149 1.1. Conventions and Terminology 151 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 152 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 153 document are to be interpreted as described in [RFC2119]. 155 This document defines the following terms: 157 application: Both the sender and ultimate consumer of push messages. 158 Many applications have components that are run on a user agent and 159 other components that run on servers. 161 application server: The component of an application that usually 162 runs on a server and requests the delivery of a push message. 164 push message subscription: A message delivery context that is 165 established between the user agent and the push service and shared 166 with the application server. All push messages are associated 167 with a push message subscription. 169 push message subscription set: A message delivery context that is 170 established between the user agent and the push service that 171 collects multiple push message subscriptions into a set. 173 push message: A message sent from an application server to a user 174 agent via a push service. 176 push message receipt: A message delivery confirmation sent from the 177 push service to the application server. 179 push service: A service that delivers push messages to user agents. 181 user agent: A device and software that is the recipient of push 182 messages. 184 Examples in this document use the HTTP/1.1 message format [RFC7230]. 185 Many of the exchanges can be completed using HTTP/1.1. Where HTTP/2 186 is necessary, the more verbose frame format from [RFC7540] is used. 188 Examples do not include specific methods for push message encryption 189 or application server authentication because the protocol does not 190 define a mandatory system. The examples in Voluntary Application 191 Server Identification [I-D.ietf-webpush-vapid] and Message Encryption 192 for WebPush [I-D.ietf-webpush-encryption] demonstrate the approach 193 adopted by the W3C Push API [API] for its requirements. 195 2. Overview 197 A general model for push services includes three basic actors: a user 198 agent, a push service, and an application (server). 200 +-------+ +--------------+ +-------------+ 201 | UA | | Push Service | | Application | 202 +-------+ +--------------+ +-------------+ 203 | | | 204 | Subscribe | | 205 |--------------------->| | 206 | Monitor | | 207 |<====================>| | 208 | | | 209 | Distribute Push Resource | 210 |-------------------------------------------->| 211 | | | 212 : : : 213 | | Push Message | 214 | Push Message |<---------------------| 215 |<---------------------| | 216 | | | 218 At the very beginning of the process, a new message subscription is 219 created by the user agent and then distributed to its application 220 server. This subscription is the basis of all future interactions 221 between the actors. A subscription is used by the application server 222 to send messages to the push service for being delivered to the user 223 agent. It is used by the user agent to monitor the push service for 224 any incoming message. 226 To offer more control for authorization, a message subscription is 227 modeled as two resources with different capabilities: 229 o A subscription resource is used to receive messages from a 230 subscription and to delete a subscription. It is private to the 231 user agent. 233 o A push resource is used to send messages to a subscription. It is 234 public and shared by the user agent with its application server. 236 It is expected that a unique subscription will be distributed to each 237 application; however, there are no inherent cardinality constraints 238 in the protocol. Multiple subscriptions might be created for the 239 same application, or multiple applications could use the same 240 subscription. Note however that sharing subscriptions has security 241 and privacy implications. 243 Subscriptions have a limited lifetime. They can also be terminated 244 by either the push service or user agent at any time. User agents 245 and application servers must be prepared to manage changes in 246 subscription state. 248 2.1. HTTP Resources 250 This protocol uses HTTP resources [RFC7230] and link relations 251 [RFC5988]. The following resources are defined: 253 push service: This resource is used to create push message 254 subscriptions (Section 4). A URL for the push service is 255 configured into user agents. 257 push message subscription: This resource provides read and delete 258 access for a message subscription. A user agent receives push 259 messages (Section 6) using a push message subscription. Every 260 push message subscription has exactly one push resource associated 261 with it. 263 push message subscription set: This resource provides read and 264 delete access for a collection of push message subscriptions. A 265 user agent receives push messages (Section 6.1) for all the push 266 message subscriptions in the set. A link relation of type 267 "urn:ietf:params:push:set" identifies a push message subscription 268 set. 270 push: An application server requests the delivery (Section 5) of a 271 push message using a push resource. A link relation of type 272 "urn:ietf:params:push" identifies a push resource. 274 push message: The push service creates a push message resource to 275 identify push messages that have been accepted for delivery 276 (Section 5). The push message resource is also deleted by the 277 user agent to acknowledge receipt (Section 6.2) of a push message. 279 receipt subscription: An application server receives delivery 280 confirmations (Section 5.1) for push messages using a receipt 281 subscription. A link relation of type 282 "urn:ietf:params:push:receipt" identifies a receipt subscription. 284 3. Connecting to the Push Service 286 The push service shares the same default port number (443/TCP) with 287 HTTPS, but MAY also advertise the IANA allocated TCP System Port 1001 288 using HTTP alternative services [RFC7838]. 290 While the default port (443) offers broad reachability 291 characteristics, it is most often used for web browsing scenarios 292 with a lower idle timeout than other ports configured in middleboxes. 293 For webpush scenarios, this would contribute to unnecessary radio 294 communications to maintain the connection on battery-powered devices. 296 Advertising the alternate port (1001) allows middleboxes to optimize 297 idle timeouts for connections specific to push scenarios with the 298 expectation that data exchange will be infrequent. 300 Middleboxes SHOULD comply with REQ-5 in [RFC5382] which requires that 301 "the value of the 'established connection idle-timeout' MUST NOT be 302 less than 2 hours 4 minutes". 304 4. Subscribing for Push Messages 306 A user agent sends a POST request to its configured push service 307 resource to create a new subscription. 309 POST /subscribe HTTP/1.1 310 Host: push.example.net 312 A 201 (Created) response indicates that the a push subscription was 313 created. A URI for the push message subscription resource that was 314 created in response to the request MUST be returned in the Location 315 header field. 317 The push service MUST provide a URI for the push resource 318 corresponding to the push message subscription in a link relation of 319 type "urn:ietf:params:push". 321 An application-specific method is used to distribute the push URI to 322 the application server. Confidentiality protection and application 323 server authentication MUST be used to ensure that this URI is not 324 disclosed to unauthorized recipients (Section 8.3). 326 HTTP/1.1 201 Created 327 Date: Thu, 11 Dec 2014 23:56:52 GMT 328 Link: ; 329 rel="urn:ietf:params:push" 330 Link: ; 331 rel="urn:ietf:params:push:set" 332 Location: https://push.example.net/subscription/LBhhw0OohO-Wl4Oi971UG 334 4.1. Collecting Subscriptions into Sets 336 Collecting multiple push message subscriptions into a subscription 337 set can represent a significant efficiency improvement for push 338 services and user agents. The push service MAY provide a URI for a 339 subscription set resource in a link relation of type 340 "urn:ietf:params:push:set". 342 When a subscription set is returned in a push message subscription 343 response, the user agent SHOULD include this subscription set in a 344 link relation of type "urn:ietf:params:push:set" in subsequent 345 requests to create new push message subscriptions. 347 A user agent MAY omit the subscription set if it is unable to receive 348 push messages in an aggregated way for the lifetime of the 349 subscription. This might be necessary if the user agent is 350 monitoring subscriptions on behalf of other push message receivers. 352 POST /subscribe HTTP/1.1 353 Host: push.example.net 354 Link: ; 355 rel="urn:ietf:params:push:set" 357 The push service SHOULD return the same subscription set in its 358 response, although it MAY return a new subscription set if it is 359 unable to reuse the one provided by the user agent. 361 HTTP/1.1 201 Created 362 Date: Thu, 11 Dec 2014 23:56:52 GMT 363 Link: ; 364 rel="urn:ietf:params:push" 365 Link: ; 366 rel="urn:ietf:params:push:set" 367 Location: https://push.example.net/subscription/i-nQ3A9Zm4kgSWg8_ZijV 369 A push service MUST return a 400 (Bad Request) status code for 370 requests which contain an invalid subscription set. A push service 371 MAY return a 429 (Too Many Requests) status code [RFC6585] to reject 372 requests which omit a subscription set. 374 How a push service detects that requests originate from the same user 375 agent is implementation-specific but could take ambient information 376 into consideration, such as the TLS connection, source IP address and 377 port. Implementers are reminded that some heuristics can produce 378 false positives and cause requests to be rejected incorrectly. 380 5. Requesting Push Message Delivery 382 An application server requests the delivery of a push message by 383 sending a HTTP POST request to a push resource distributed to the 384 application server by a user agent. The content of the push message 385 is included in the body of the request. 387 POST /push/JzLQ3raZJfFBR0aqvOMsLrt54w4rJUsV HTTP/1.1 388 Host: push.example.net 389 TTL: 15 390 Content-Type: text/plain;charset=utf8 391 Content-Length: 36 393 iChYuI3jMzt3ir20P8r_jgRR-dSuN182x7iB 395 A 201 (Created) response indicates that the push message was 396 accepted. A URI for the push message resource that was created in 397 response to the request MUST be returned in the Location header 398 field. This does not indicate that the message was delivered to the 399 user agent. 401 HTTP/1.1 201 Created 402 Date: Thu, 11 Dec 2014 23:56:55 GMT 403 Location: https://push.example.net/message/qDIYHNcfAIPP_5ITvURr-d6BGt 405 5.1. Requesting Push Message Receipts 407 An application server can include the Prefer header field [RFC7240] 408 with the "respond-async" preference to request confirmation from the 409 push service when a push message is delivered and then acknowledged 410 by the user agent. The push service MUST support delivery 411 confirmations. 413 POST /push/JzLQ3raZJfFBR0aqvOMsLrt54w4rJUsV HTTP/1.1 414 Host: push.example.net 415 Prefer: respond-async 416 TTL: 15 417 Content-Type: text/plain;charset=utf8 418 Content-Length: 36 420 iChYuI3jMzt3ir20P8r_jgRR-dSuN182x7iB 421 When the push service accepts the message for delivery with 422 confirmation, it MUST return a 202 (Accepted) response. A URI for 423 the push message resource that was created in response to the request 424 MUST be returned in the Location header field. The push service MUST 425 also provide a URI for the receipt subscription resource in a link 426 relation of type "urn:ietf:params:push:receipt". 428 HTTP/1.1 202 Accepted 429 Date: Thu, 11 Dec 2014 23:56:55 GMT 430 Link: ; 431 rel="urn:ietf:params:push:receipt" 432 Location: https://push.example.net/message/qDIYHNcfAIPP_5ITvURr-d6BGt 434 For subsequent receipt requests to the same origin [RFC6454], the 435 application server SHOULD include the returned receipt subscription 436 in a link relation of type "urn:ietf:params:push:receipt". This 437 gives the push service an option to aggregate the receipts. The push 438 service SHOULD return the same receipt subscription in its response, 439 although it MAY return a new receipt subscription if it is unable to 440 reuse the one provided by the application server. 442 An application server MAY omit the receipt subscription if it is 443 unable to receive receipts in an aggregated way for the lifetime of 444 the receipt subscription. This might be necessary if the application 445 server is monitoring receipt subscriptions on the behalf of other 446 push message senders. 448 A push service MUST return a 400 (Bad Request) status code for 449 requests which contain an invalid receipt subscription. If a push 450 service wishes to limit the number of receipt subscriptions that it 451 maintains, it MAY return a 429 (Too Many Requests) status code 452 [RFC6585] to reject receipt requests which omit a receipt 453 subscription. 455 5.2. Push Message Time-To-Live 457 A push service can improve the reliability of push message delivery 458 considerably by storing push messages for a period. User agents are 459 often only intermittently connected, and so benefit from having short 460 term message storage at the push service. 462 Delaying delivery might also be used to batch communication with the 463 user agent, thereby conserving radio resources. 465 Some push messages are not useful once a certain period of time 466 elapses. Delivery of messages after they have ceased to be relevant 467 is wasteful. For example, if the push message contains a call 468 notification, receiving a message after the caller has abandoned the 469 call is of no value; the application at the user agent is forced to 470 suppress the message so that it does not generate a useless alert. 472 An application server MUST include the TTL (Time-To-Live) header 473 field in its request for push message delivery. The TTL header field 474 contains a value in seconds that suggests how long a push message is 475 retained by the push service. 477 TTL = 1*DIGIT 479 A push service MUST return a 400 (Bad Request) status code in 480 response to requests that omit the TTL header field. 482 A push service MAY retain a push message for a shorter duration than 483 requested. It indicates this by returning a TTL header field in its 484 response with the actual TTL. This TTL value MUST be less than or 485 equal to the value provided by the application server. 487 Once the TTL period elapses, the push service MUST NOT attempt to 488 deliver the push message to the user agent. A push service might 489 adjust the TTL value to account for time accounting errors in 490 processing. For instance, distributing a push message within a 491 server cluster might accrue errors due to clock skew or propagation 492 delays. 494 A push service is not obligated to account for time spent by the 495 application server in sending a push message to the push service, or 496 delays incurred while sending a push message to the user agent. An 497 application server needs to account for transit delays in selecting a 498 TTL header field value. 500 A Push message with a zero TTL is immediately delivered if the user 501 agent is available to receive the message. After delivery, the push 502 service is permitted to immediately remove a push message with a zero 503 TTL. This might occur before the user agent acknowledges receipt of 504 the message by performing a HTTP DELETE on the push message resource. 505 Consequently, an application server cannot rely on receiving 506 acknowledgement receipts for zero TTL push messages. 508 If the user agent is unavailable, a push message with a zero TTL 509 expires and is never delivered. 511 5.3. Push Message Urgency 513 For a device that is battery-powered, it is often critical that it 514 remains dormant for extended periods. Radio communication in 515 particular consumes significant power and limits the length of time 516 that the device can operate. 518 To avoid consuming resources to receive trivial messages, it is 519 helpful if an application server can communicate the urgency of a 520 message and if the user agent can request that the push server only 521 forward messages of a specific urgency. 523 An application server MAY include an Urgency header field in its 524 request for push message delivery. This header field indicates the 525 message urgency. The push service MUST NOT forward the Urgency 526 header field to the user agent. A push message without the Urgency 527 header field defaults to a value of "normal". 529 A user agent MAY include the Urgency header field when monitoring for 530 push messages to indicate the lowest urgency of push messages that it 531 is willing to receive. A push service MUST NOT deliver push messages 532 with lower urgency than the value indicated by the user agent in its 533 monitoring request. Push messages of any urgency are delivered to a 534 user agent that does not include an Urgency header field when 535 monitoring for messages. 537 Urgency = 1#(urgency-option) 538 urgency-option = ("very-low" / "low" / "normal" / "high") 540 In order of increasing urgency: 542 +----------+-----------------------------+--------------------------+ 543 | Urgency | Device State | Application Scenario | 544 +----------+-----------------------------+--------------------------+ 545 | very-low | On power and wifi | Advertisements | 546 | low | On either power or wifi | Topic updates | 547 | normal | On neither power nor wifi | Chat or Calendar Message | 548 | high | Low battery | Incoming phone call or | 549 | | | time-sensitive alert | 550 +----------+-----------------------------+--------------------------+ 552 Table 1: Table of Urgency Values 554 Multiple values for the Urgency header field MUST NOT be included in 555 requests; otherwise, the push service MUST return a 400 (Bad Request) 556 status code. 558 5.4. Replacing Push Messages 560 A push message that has been stored by the push service can be 561 replaced with new content. If the user agent is offline during the 562 time that the push messages are sent, updating a push message avoids 563 the situation where outdated or redundant messages are sent to the 564 user agent. 566 Only push messages that have been assigned a topic can be replaced. 567 A push message with a topic replaces any outstanding push message 568 with an identical topic. 570 A push message topic is a string carried in a Topic header field. A 571 topic is used to correlate push messages sent to the same 572 subscription and does not convey any other semantics. 574 The grammar for the Topic header field uses the "token" rule defined 575 in [RFC7230]. 577 Topic = token 579 For use with this protocol, the Topic header field MUST be restricted 580 to no more than 32 characters from the URL and filename safe Base 64 581 alphabet [RFC4648]. A push service that receives a request with a 582 Topic header field that does not meet these constraints MUST return a 583 400 (Bad Request) status code to the application server. 585 A push message replacement request creates a new push message 586 resource and simultaneously deletes any existing message resource 587 that has a matching topic. Delivery receipts for the deleted message 588 SHOULD be suppressed. 590 The replacement request also replaces the stored TTL, Urgency, and 591 any receipt subscription associated with the previous message in the 592 matching topic. 594 A push message with a topic that is not shared by an outstanding 595 message to the same subscription is stored or delivered as normal. 597 For example, the following message could cause an existing message to 598 be replaced: 600 POST /push/JzLQ3raZJfFBR0aqvOMsLrt54w4rJUsV HTTP/1.1 601 Host: push.example.net 602 TTL: 600 603 Topic: upd 604 Content-Type: text/plain;charset=utf8 605 Content-Length: 36 607 ZuHSZPKa2b1jtOKLGpWrcrn8cNqt0iVQyroF 609 If the push service identifies an outstanding push message with a 610 topic of "upd", then that message resource is deleted. A 201 611 (Created) response indicates that the push message replacement was 612 accepted. A URI for the new push message resource that was created 613 in response to the request is included in the Location header field. 615 HTTP/1.1 201 Created 616 Date: Thu, 11 Dec 2014 23:57:02 GMT 617 Location: https://push.example.net/message/qDIYHNcfAIPP_5ITvURr-d6BGt 619 The value of the Topic header field MUST NOT be forwarded to user 620 agents. Its value is neither encrypted nor authenticated. 622 6. Receiving Push Messages for a Subscription 624 A user agent requests the delivery of new push messages by making a 625 GET request to a push message subscription resource. The push 626 service does not respond to this request, it instead uses HTTP/2 627 server push [RFC7540] to send the contents of push messages as they 628 are sent by application servers. 630 A user agent MAY include a Urgency header field in its request. The 631 push service MUST NOT deliver messages with lower urgency than the 632 value of the header field as defined in the Table of Urgency Values. 634 Each push message is pushed as the response to a synthesized GET 635 request sent in a PUSH_PROMISE. This GET request is made to the push 636 message resource that was created by the push service when the 637 application server requested message delivery. The response headers 638 SHOULD provide a URI for the push resource corresponding to the push 639 message subscription in a link relation of type 640 "urn:ietf:params:push". The response body is the entity body from 641 the most recent request sent to the push resource by the application 642 server. 644 The following example request is made over HTTP/2. 646 HEADERS [stream 7] +END_STREAM +END_HEADERS 647 :method = GET 648 :path = /subscription/LBhhw0OohO-Wl4Oi971UG 649 :authority = push.example.net 651 The push service permits the request to remain outstanding. When a 652 push message is sent by an application server, a server push is 653 generated in association with the initial request. The response for 654 the server push includes the push message. 656 PUSH_PROMISE [stream 7; promised stream 4] +END_HEADERS 657 :method = GET 658 :path = /message/qDIYHNcfAIPP_5ITvURr-d6BGt 659 :authority = push.example.net 661 HEADERS [stream 4] +END_HEADERS 662 :status = 200 663 date = Thu, 11 Dec 2014 23:56:56 GMT 664 last-modified = Thu, 11 Dec 2014 23:56:55 GMT 665 cache-control = private 666 :link = ; 667 rel="urn:ietf:params:push" 668 content-type = text/plain;charset=utf8 669 content-length = 36 671 DATA [stream 4] +END_STREAM 672 iChYuI3jMzt3ir20P8r_jgRR-dSuN182x7iB 674 HEADERS [stream 7] +END_STREAM +END_HEADERS 675 :status = 200 677 A user agent can also request the contents of the push message 678 subscription resource immediately by including a Prefer header field 679 [RFC7240] with a "wait" preference set to "0". In response to this 680 request, the push service MUST generate a server push for all push 681 messages that have not yet been delivered. 683 A 204 (No Content) status code with no associated server pushes 684 indicates that no messages are presently available. This could be 685 because push messages have expired. 687 6.1. Receiving Push Messages for a Subscription Set 689 There are minor differences between receiving push messages for a 690 subscription and a subscription set. If a subscription set is 691 available, the user agent SHOULD use the subscription set to monitor 692 for push messages rather than individual push message subscriptions. 694 A user agent requests the delivery of new push messages for a 695 collection of push message subscriptions by making a GET request to a 696 push message subscription set resource. The push service does not 697 respond to this request, it instead uses HTTP/2 server push [RFC7540] 698 to send the contents of push messages as they are sent by application 699 servers. 701 A user agent MAY include a Urgency header field in its request. The 702 push service MUST NOT deliver messages with lower urgency than the 703 value of the header field as defined in the Table of Urgency Values. 705 Each push message is pushed as the response to a synthesized GET 706 request sent in a PUSH_PROMISE. This GET request is made to the push 707 message resource that was created by the push service when the 708 application server requested message delivery. The synthetic request 709 MUST provide a URI for the push resource corresponding to the push 710 message subscription in a link relation of type 711 "urn:ietf:params:push". This enables the user agent to differentiate 712 the source of the message. The response body is the entity body from 713 the most recent request sent to the push resource by an application 714 server. 716 The following example request is made over HTTP/2. 718 HEADERS [stream 7] +END_STREAM +END_HEADERS 719 :method = GET 720 :path = /subscription-set/4UXwi2Rd7jGS7gp5cuutF8ZldnEuvbOy 721 :authority = push.example.net 723 The push service permits the request to remain outstanding. When a 724 push message is sent by an application server, a server push is 725 generated in association with the initial request. The server push's 726 response includes the push message. 728 PUSH_PROMISE [stream 7; promised stream 4] +END_HEADERS 729 :method = GET 730 :path = /message/qDIYHNcfAIPP_5ITvURr-d6BGt 731 :authority = push.example.net 732 :link = ; 733 rel="urn:ietf:params:push" 735 HEADERS [stream 4] +END_HEADERS 736 :status = 200 737 date = Thu, 11 Dec 2014 23:56:56 GMT 738 last-modified = Thu, 11 Dec 2014 23:56:55 GMT 739 cache-control = private 740 content-type = text/plain;charset=utf8 741 content-length = 36 743 DATA [stream 4] +END_STREAM 744 iChYuI3jMzt3ir20P8r_jgRR-dSuN182x7iB 746 HEADERS [stream 7] +END_STREAM +END_HEADERS 747 :status = 200 749 A user agent can request the contents of the push message 750 subscription set resource immediately by including a Prefer header 751 field [RFC7240] with a "wait" preference set to "0". In response to 752 this request, the push service MUST generate a server push for all 753 push messages that have not yet been delivered. 755 A 204 (No Content) status code with no associated server pushes 756 indicates that no messages are presently available. This could be 757 because push messages have expired. 759 6.2. Acknowledging Push Messages 761 To ensure that a push message is properly delivered to the user agent 762 at least once, the user agent MUST acknowledge receipt of the message 763 by performing a HTTP DELETE on the push message resource. 765 DELETE /message/qDIYHNcfAIPP_5ITvURr-d6BGt HTTP/1.1 766 Host: push.example.net 767 If the push service receives the acknowledgement and the application 768 has requested a delivery receipt, the push service MUST return a 204 769 (No Content) response to the application server monitoring the 770 receipt subscription. 772 If the push service does not receive the acknowledgement within a 773 reasonable amount of time, then the message is considered to be not 774 yet delivered. The push service SHOULD continue to retry delivery of 775 the message until its advertised expiration. 777 The push service MAY cease to retry delivery of the message prior to 778 its advertised expiration due to scenarios such as an unresponsive 779 user agent or operational constraints. If the application has 780 requested a delivery receipt, then the push service MUST return a 410 781 (Gone) response to the application server monitoring the receipt 782 subscription. 784 6.3. Receiving Push Message Receipts 786 The application server requests the delivery of receipts from the 787 push service by making a HTTP GET request to the receipt subscription 788 resource. The push service does not respond to this request, it 789 instead uses HTTP/2 server push [RFC7540] to send push receipts when 790 messages are acknowledged (Section 6.2) by the user agent. 792 Each receipt is pushed as the response to a synthesized GET request 793 sent in a PUSH_PROMISE. This GET request is made to the same push 794 message resource that was created by the push service when the 795 application server requested message delivery. The response includes 796 a status code indicating the result of the message delivery and 797 carries no data. 799 The following example request is made over HTTP/2. 801 HEADERS [stream 13] +END_STREAM +END_HEADERS 802 :method = GET 803 :path = /receipt-subscription/3ZtI4YVNBnUUZhuoChl6omUvG4ZM 804 :authority = push.example.net 806 The push service permits the request to remain outstanding. When the 807 user agent acknowledges the message, the push service pushes a 808 delivery receipt to the application server. A 204 (No Content) 809 status code confirms that the message was delivered and acknowledged. 811 PUSH_PROMISE [stream 13; promised stream 82] +END_HEADERS 812 :method = GET 813 :path = /message/qDIYHNcfAIPP_5ITvURr-d6BGt 814 :authority = push.example.net 816 HEADERS [stream 82] +END_STREAM 817 +END_HEADERS 818 :status = 204 819 date = Thu, 11 Dec 2014 23:56:56 GMT 821 If the user agent fails to acknowledge the receipt of the push 822 message and the push service ceases to retry delivery of the message 823 prior to its advertised expiration, then the push service MUST push a 824 failure response with a status code of 410 (Gone). 826 7. Operational Considerations 828 7.1. Load Management 830 A push service is likely to have to maintain a very large number of 831 open TCP connections. Effective management of those connections can 832 depend on being able to move connections between server instances. 834 A user agent MUST support the 307 (Temporary Redirect) status code 835 [RFC7231], which can be used by a push service to redistribute load 836 at the time that a new subscription is requested. 838 A server that wishes to redistribute load can do so using HTTP 839 alternative services [RFC7838]. HTTP alternative services allows for 840 redistribution of load while maintaining the same URIs for various 841 resources. A user agent can ensure a graceful transition by using 842 the GOAWAY frame once it has established a replacement connection. 844 7.2. Push Message Expiration 846 Storage of push messages based on the TTL header field comprises a 847 potentially significant amount of storage for a push service. A push 848 service is not obligated to store messages indefinitely. A push 849 service is able to indicate how long it intends to retain a message 850 to an application server using the TTL header field (Section 5.2). 852 A user agent that does not actively monitor for push messages will 853 not receive messages that expire during that interval. 855 Push messages that are stored and have not been delivered to a user 856 agent are delivered when the user agent recommences monitoring. 857 Stored push messages SHOULD include a Last-Modified header field 858 (Section 2.2 of [RFC7232]) indicating when delivery was requested by 859 an application server. 861 A GET request to a push message subscription resource with only 862 expired messages results in a response as though no push message was 863 ever sent. 865 Push services might need to limit the size and number of stored push 866 messages to avoid overloading. To limit the size of messages, the 867 push service MAY return a 413 (Payload Too Large) status code 868 [RFC7231] in response to requests that include an entity body that is 869 too large. Push services MUST NOT return a 413 status code in 870 responses to an entity body that is 4096 bytes or less in size. 872 To limit the number of stored push messages, the push service MAY 873 either expire messages prior to their advertised Time-To-Live or 874 reduce their advertised Time-To-Live. 876 7.3. Subscription Expiration 878 In some cases, it may be necessary to terminate subscriptions so that 879 they can be refreshed. This applies to both push message 880 subscriptions and receipt subscriptions. 882 A push service MAY expire a subscription at any time. If there are 883 outstanding requests to an expired push message subscription resource 884 (Section 6) from a user agent or to an expired receipt subscription 885 resource (Section 6.3) from an application server, this MUST be 886 signaled by returning a 404 (Not Found) status code. 888 A push service MUST return a 404 (Not Found) status code if an 889 application server attempts to send a push message to an expired push 890 message subscription. 892 A user agent can remove its push message subscription by sending a 893 DELETE request to the corresponding URI. An application server can 894 remove its receipt subscription by sending a DELETE request to the 895 corresponding URI. 897 7.3.1. Subscription Set Expiration 899 A push service MAY expire a subscription set at any time and MUST 900 also expire all push message subscriptions in the set. If a user 901 agent has an outstanding request to a push subscription set 902 (Section 6.1) this MUST be signaled by returning a 404 (Not Found) 903 status code. 905 A user agent can request that a subscription set be removed by 906 sending a DELETE request to the subscription set URI. This MUST also 907 remove all push message subscriptions in the set. 909 If a specific push message subscription that is a member of a 910 subscription set is expired or removed, then it MUST also be removed 911 from its subscription set. 913 7.4. Implications for Application Reliability 915 A push service that does not support reliable delivery over 916 intermittent network connections or failing applications on devices, 917 forces the device to acknowledge receipt directly to the application 918 server, incurring additional power drain in order to establish 919 (usually secure) connections to the individual application servers. 921 Push message reliability can be important if messages contain 922 information critical to the state of an application. Repairing state 923 can be expensive, particularly for devices with limited 924 communications capacity. Knowing that a push message has been 925 correctly received avoids retransmissions, polling, and state 926 resynchronization. 928 The availability of push message delivery receipts ensures that the 929 application developer is not tempted to create alternative mechanisms 930 for message delivery in case the push service fails to deliver a 931 critical message. Setting up a polling mechanism or a backup 932 messaging channel in order to compensate for these shortcomings 933 negates almost all of the advantages a push service provides. 935 However, reliability might not be necessary for messages that are 936 transient (e.g. an incoming call) or messages that are quickly 937 superceded (e.g. the current number of unread emails). 939 7.5. Subscription Sets and Concurrent HTTP/2 streams 941 If the push service requires that the user agent use push message 942 subscription sets, then it MAY limit the number of concurrently 943 active streams with the SETTINGS_MAX_CONCURRENT_STREAMS parameter 944 within a HTTP/2 SETTINGS frame [RFC7540]. The user agent MAY be 945 limited to one concurrent stream to manage push message subscriptions 946 and one concurrent stream for each subscription set returned by the 947 push service. This could force the user agent to serialize 948 subscription requests to the push service. 950 8. Security Considerations 952 This protocol MUST use HTTP over TLS [RFC2818]. This includes any 953 communications between user agent and push service, plus 954 communications between the application and the push service. All 955 URIs therefore use the "https" scheme. This provides confidentiality 956 and integrity protection for subscriptions and push messages from 957 external parties. 959 Applications using this protocol MUST use mechanisms that provide 960 confidentiality, integrity and data origin authentication. The 961 application server sending the push message and the application on 962 the user agent that receives it are frequently just different 963 instances of the same application, so no standardized protocol is 964 needed to establish a proper security context. The distribution of 965 subscription information from the user agent to its application 966 server also offers a convenient medium for key agreement. 968 8.1. Confidentiality from Push Service Access 970 The protection afforded by TLS does not protect content from the push 971 service. Without additional safeguards, a push service can inspect 972 and modify the message content. 974 For its requirements, the W3C Push API [API] has adopted Message 975 Encryption for WebPush [I-D.ietf-webpush-encryption] to secure the 976 content of messages from the push service. Other scenarios can be 977 addressed by similar policies. 979 The Topic header field exposes information that allows more granular 980 correlation of push messages on the same subject. This might be used 981 to aid traffic analysis of push messages by the push service. 983 8.2. Privacy Considerations 985 Push message confidentiality does not ensure that the identity of who 986 is communicating and when they are communicating is protected. 987 However, the amount of information that is exposed can be limited. 989 The URIs provided for push resources MUST NOT provide any basis to 990 correlate communications for a given user agent. It MUST NOT be 991 possible to correlate any two push resource URIs based solely on 992 their contents. This allows a user agent to control correlation 993 across different applications, or over time. 995 Similarly, the URIs provided by the push service to identify a push 996 message MUST NOT provide any information that allows for correlation 997 across subscriptions. Push message URIs for the same subscription 998 MAY contain information that would allow correlation with the 999 associated subscription or other push messages for that subscription. 1001 User and device information MUST NOT be exposed through a push or 1002 push message URI. 1004 In addition, push URIs established by the same user agent or push 1005 message URIs for the same subscription MUST NOT include any 1006 information that allows them to be correlated with the user agent. 1008 Note: This need not be perfect as long as the resulting anonymity 1009 set ([RFC6973], Section 6.1.1) is sufficiently large. A push URI 1010 necessarily identifies a push service or a single server instance. 1011 It is also possible that traffic analysis could be used to 1012 correlate subscriptions. 1014 A user agent MUST be able to create new subscriptions with new 1015 identifiers at any time. 1017 8.3. Authorization 1019 This protocol does not define how a push service establishes whether 1020 a user agent is permitted to create a subscription, or whether push 1021 messages can be delivered to the user agent. A push service MAY 1022 choose to authorize requests based on any HTTP-compatible 1023 authorization method available, of which there are numerous options. 1024 The authorization process and any associated credentials are expected 1025 to be configured in the user agent along with the URI for the push 1026 service. 1028 Authorization is managed using capability URLs for the push message 1029 subscription, push, and receipt subscription resources ([CAP-URI]). 1030 A capability URL grants access to a resource based solely on 1031 knowledge of the URL. 1033 Capability URLs are used for their "easy onward sharing" and "easy 1034 client API" properties. These make it possible to avoid relying on 1035 relationships between push services and application servers, with the 1036 protocols necessary to build and support those relationships. 1038 Capability URLs act as bearer tokens. Knowledge of a push message 1039 subscription URI implies authorization to either receive push 1040 messages or delete the subscription. Knowledge of a push URI implies 1041 authorization to send push messages. Knowledge of a push message URI 1042 allows for reading and acknowledging that specific message. 1043 Knowledge of a receipt subscription URI implies authorization to 1044 receive push receipts. 1046 Encoding a large amount of random entropy (at least 120 bits) in the 1047 path component ensures that it is difficult to successfully guess a 1048 valid capability URL. 1050 8.4. Denial of Service Considerations 1052 A user agent can control where valid push messages originate by 1053 limiting the distribution of push URIs to authorized application 1054 servers. Ensuring that push URIs are hard to guess ensures that only 1055 application servers that have received a push URI can use it. 1057 Push messages that are not successfully authenticated by the user 1058 agent will not be delivered, but this can present a denial of service 1059 risk. Even a relatively small volume of push messages can cause 1060 battery-powered devices to exhaust power reserves. 1062 To address this case, the W3C Push API [API] has adopted Voluntary 1063 Application Server Identification [I-D.ietf-webpush-vapid], which 1064 allows a user agent to restrict a subscription to a specific 1065 application server. The push service can then identify and reject 1066 unwanted messages without contacting the user agent. 1068 A malicious application with a valid push URI could use the greater 1069 resources of a push service to mount a denial of service attack on a 1070 user agent. Push services SHOULD limit the rate at which push 1071 messages are sent to individual user agents. 1073 A push service MAY return a 429 (Too Many Requests) status code 1074 [RFC6585] when an application server has exceeded its rate limit for 1075 push message delivery to a push resource. The push service SHOULD 1076 also include a Retry-After header [RFC7231] to indicate how long the 1077 application server is requested to wait before it makes another 1078 request to the push resource. 1080 A push service or user agent MAY also terminate subscriptions 1081 (Section 7.3) that receive too many push messages. 1083 A push service is also able to deny service to user agents. 1084 Intentional failure to deliver messages is difficult to distinguish 1085 from faults, which might occur due to transient network errors, 1086 interruptions in user agent availability, or genuine service outages. 1088 8.5. Logging Risks 1090 Server request logs can reveal subscription-related URIs or 1091 relationships between subscription-related URIs for the same user 1092 agent. Limitations on log retention and strong access control 1093 mechanisms can ensure that URIs are not revealed to unauthorized 1094 entities. 1096 9. IANA Considerations 1098 This protocol defines new HTTP header fields in Section 9.1. New 1099 link relation types are identified using the URNs defined in 1100 Section 9.2. Port registration is defined in Section 9.3 1102 9.1. Header Field Registrations 1104 HTTP header fields are registered within the "Message Headers" 1105 registry maintained at . 1108 This document defines the following HTTP header fields, so their 1109 associated registry entries shall be added according to the permanent 1110 registrations below ([RFC3864]): 1112 +-------------------+----------+----------+--------------+ 1113 | Header Field Name | Protocol | Status | Reference | 1114 +-------------------+----------+----------+--------------+ 1115 | TTL | http | standard | Section 5.2 | 1116 | Urgency | http | standard | Section 5.3 | 1117 | Topic | http | standard | Section 5.4 | 1118 +-------------------+----------+----------+--------------+ 1120 The change controller is: "IETF (iesg@ietf.org) - Internet 1121 Engineering Task Force". 1123 9.2. Link Relation URNs 1125 This document registers URNs for use in identifying link relation 1126 types. These are added to a new "Web Push Identifiers" registry 1127 according to the procedures in Section 4 of [RFC3553]; the 1128 corresponding "push" sub-namespace is entered in the "IETF URN Sub- 1129 namespace for Registered Protocol Parameter Identifiers" registry. 1131 The "Web Push Identifiers" registry operates under the IETF Review 1132 policy [RFC5226]. 1134 Registry name: Web Push Identifiers 1135 URN Prefix: urn:ietf:params:push 1137 Specification: (this document) 1139 Repository: [Editor/IANA note: please include a link to the final 1140 registry location.] 1142 Index value: Values in this registry are URNs or URN prefixes that 1143 start with the prefix "urn:ietf:params:push". Each is registered 1144 independently. 1146 New registrations in the "Web Push Identifiers" are encouraged to 1147 include the following information: 1149 URN: A complete URN or URN prefix. 1151 Description: A summary description. 1153 Specification: A reference to a specification describing the 1154 semantics of the URN or URN prefix. 1156 Contact: Email for the person or group making the registration. 1158 Index value: As described in [RFC3553], URN prefixes that are 1159 registered include a description of how the URN is constructed. 1160 This is not applicable for specific URNs. 1162 These values are entered as the initial content of the "Web Push 1163 Identifiers" registry. 1165 URN: urn:ietf:params:push 1167 Description: This link relation type is used to identify a resource 1168 for sending push messages. 1170 Specification: (this document) 1172 Contact: The Web Push WG (webpush@ietf.org) 1174 URN: urn:ietf:params:push:set 1176 Description: This link relation type is used to identify a 1177 collection of push message subscriptions. 1179 Specification: (this document) 1181 Contact: The Web Push WG (webpush@ietf.org) 1182 URN: urn:ietf:params:push:receipt 1184 Description: This link relation type is used to identify a resource 1185 for receiving delivery confirmations for push messages. 1187 Specification: (this document) 1189 Contact: The Web Push WG (webpush@ietf.org) 1191 9.3. Service Name and Port Number Registration 1193 Service names and port numbers are registered within the "Service 1194 Name and Transport Protocol Port Number Registry" maintained at 1195 . 1198 IANA is requested to assign the System Port number 1001 and the 1199 service name "webpush" in accordance with [RFC6335]. 1201 Service Name. 1202 webpush 1204 Transport Protocol. 1205 tcp 1207 Assignee. 1208 IESG (iesg@ietf.org) 1210 Contact. 1211 The Web Push WG (webpush@ietf.org) 1213 Description. 1214 HTTP Web Push 1216 Reference. 1217 [RFCthis] 1219 Port Number. 1220 1001 1222 10. Acknowledgements 1224 Significant technical input to this document has been provided by Ben 1225 Bangert, Peter Beverloo, Kit Cambridge, JR Conlin, Lucas Jenns, 1226 Matthew Kaufman, Costin Manolache, Mark Nottingham, Idel Pivnitskiy, 1227 Robert Sparks, Darshak Thakore and many others. 1229 11. References 1231 11.1. Normative References 1233 [CAP-URI] Tennison, J., "Good Practices for Capability URLs", FPWD 1234 capability-urls, February 2014, 1235 . 1237 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1238 Requirement Levels", BCP 14, RFC 2119, March 1997. 1240 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 1242 [RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An 1243 IETF URN Sub-namespace for Registered Protocol 1244 Parameters", BCP 73, RFC 3553, June 2003. 1246 [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration 1247 Procedures for Message Header Fields", BCP 90, RFC 3864, 1248 September 2004. 1250 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 1251 Encodings", RFC 4648, October 2006. 1253 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1254 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1255 May 2008. 1257 [RFC5382] Biswas, K., Ford, B., Sivakumar, S., and P. Srisuresh, 1258 "NAT Behavioral Requirements for TCP", RFC 5382, October 1259 2008. 1261 [RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010. 1263 [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. 1264 Cheshire, "Internet Assigned Numbers Authority (IANA) 1265 Procedures for the Management of the Service Name and 1266 Transport Protocol Port Number Registry", RFC 6335, August 1267 2011. 1269 [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, December 1270 2011. 1272 [RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status 1273 Codes", RFC 6585, April 2012. 1275 [RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol 1276 (HTTP/1.1): Message Syntax and Routing", RFC 7230, June 1277 2014. 1279 [RFC7231] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol 1280 (HTTP/1.1): Semantics and Content", RFC 7231, June 2014. 1282 [RFC7232] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol 1283 (HTTP/1.1): Conditional Requests", RFC 7232, June 2014. 1285 [RFC7240] Snell, J., "Prefer Header for HTTP", RFC 7240, June 2014. 1287 [RFC7540] Belshe, M., Peon, R., and M. Thomson, "Hypertext Transfer 1288 Protocol Version 2", RFC 7540, May 2015. 1290 [RFC7838] Nottingham, M., McManus, P., and J. Reschke, "HTTP 1291 Alternative Services", RFC 7838, April 2016. 1293 11.2. Informative References 1295 [API] van Ouwerkerk, M., Thomson, M., Sullivan, B., and E. 1296 Fullea, "W3C Push API", ED push-api, July 2016, 1297 . 1299 [I-D.ietf-webpush-encryption] 1300 Thomson, M., "Message Encryption for Web Push", draft- 1301 ietf-webpush-encryption-03 (work in progress), March 2016, 1302 . 1305 [I-D.ietf-webpush-vapid] 1306 Thomson, M. and P. Beverloo, "Voluntary Application Server 1307 Identification for Web Push", draft-ietf-webpush-vapid-01 1308 (work in progress), April 2016, 1309 . 1312 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 1313 Morris, J., Hansen, M., and R. Smith, "Privacy 1314 Considerations for Internet Protocols", RFC 6973, July 1315 2013. 1317 Appendix A. Change Log 1319 [[The RFC Editor is requested to remove this section at 1320 publication.]] 1322 A.1. Since draft-ietf-webpush-protocol-00 1324 Editorial changes for Push Message Time-To-Live 1326 Editorial changes for Push Acknowledgements 1328 Removed subscription expiration based on HTTP cache headers 1330 A.2. Since draft-ietf-webpush-protocol-01 1332 Added Subscription Sets 1334 Added System Port as an alternate service with guidance for idle 1335 timeouts 1337 Finalized status codes for acknowledgements 1339 Editorial changes for Rate Limits 1341 A.3. Since draft-ietf-webpush-protocol-02 1343 Added explicit correlation for Subscription Sets 1345 Added Push Message Updates (message collapsing) 1347 Renamed the push:receipt link relation to push:receipts and 1348 transitioned the Push-Receipt header field to the push:receipt link 1349 relation type 1351 A.4. Since draft-ietf-webpush-protocol-03 1353 An application server MUST include the TTL (Time-To-Live) header 1354 field in its request for push message delivery. 1356 Added Push Message Urgency header field 1358 A.5. Since draft-ietf-webpush-protocol-04 1360 Simplified design for Push Receipts and eliminated the 1361 urn:ietf:params:push:receipts link relation 1363 Clarified Security Considerations section and added informative 1364 references to Message Encryption and Voluntary Application Server 1365 Identification 1367 A.6. Since draft-ietf-webpush-protocol-05 1369 Addressed feedback from Working Group Last Call 1371 A.7. Since draft-ietf-webpush-protocol-06 1373 Updated informative references to W3C Push API, Message Encryption, 1374 and Voluntary Application Server Identification 1376 A.8. Since draft-ietf-webpush-protocol-07 1378 Minor editorial changes 1380 Authors' Addresses 1382 Martin Thomson 1383 Mozilla 1384 331 E Evelyn Street 1385 Mountain View, CA 94041 1386 US 1388 Email: martin.thomson@gmail.com 1390 Elio Damaggio 1391 Microsoft 1392 One Microsoft Way 1393 Redmond, WA 98052 1394 US 1396 Email: elioda@microsoft.com 1398 Brian Raymor (editor) 1399 Microsoft 1400 One Microsoft Way 1401 Redmond, WA 98052 1402 US 1404 Email: brian.raymor@microsoft.com