idnits 2.17.1 draft-ietf-webpush-protocol-07.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 == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: An application server MAY include an Urgency header field in its request for push message delivery. This header field indicates the message urgency. The push service MUST not forward the Urgency header field to the user agent. A push message without the Urgency header field defaults to a value of "normal". -- The document date (July 8, 2016) is 2842 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFCthis' is mentioned on line 1215, but not defined -- Possible downref: Non-RFC (?) normative reference: ref. '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reference: RFC 7232 (Obsoleted by RFC 9110) ** Obsolete normative reference: RFC 7540 (Obsoleted by RFC 9113) == Outdated reference: A later version (-09) exists of draft-ietf-webpush-encryption-03 == Outdated reference: A later version (-04) exists of draft-ietf-webpush-vapid-01 Summary: 7 errors (**), 0 flaws (~~), 5 warnings (==), 2 comments (--).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 9, 2017 B. Raymor, Ed. 6 Microsoft 7 July 8, 2016 9 Generic Event Delivery Using HTTP Push 10 draft-ietf-webpush-protocol-07 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 9, 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 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 98 1. Introduction 100 Many applications on mobile and embedded devices require continuous 101 access to network communications so that real-time events - such as 102 incoming calls or messages - can be delivered (or "pushed") in a 103 timely fashion. These devices typically have limited power reserves, 104 so finding more efficient ways to serve application requirements 105 greatly benefits the application ecosystem. 107 One significant contributor to power usage is the radio. Radio 108 communications consume a significant portion of the energy budget on 109 a wireless device. 111 Uncoordinated use of persistent connections or sessions from multiple 112 applications can contribute to unnecessary use of the device radio, 113 since each independent session can incur its own overhead. In 114 particular, keep alive traffic used to ensure that middleboxes do not 115 prematurely time out sessions, can result in significant waste. 116 Maintenance traffic tends to dominate over the long term, since 117 events are relatively rare. 119 Consolidating all real-time events into a single session ensures more 120 efficient use of network and radio resources. A single service 121 consolidates all events, distributing those events to applications as 122 they arrive. This requires just one session, avoiding duplicated 123 overhead costs. 125 The W3C Push API [API] describes an API that enables the use of a 126 consolidated push service from web applications. This document 127 expands on that work by describing a protocol that can be used to: 129 o request the delivery of a push message to a user agent, 131 o create new push message delivery subscriptions, and 133 o monitor for new push messages. 135 A standardized method of event delivery is particularly important for 136 the W3C Push API, where application servers might need to use 137 multiple push services. The subscription, management and monitoring 138 functions are currently fulfilled by proprietary protocols; these are 139 adequate, but do not offer any of the advantages that standardization 140 affords. 142 This document intentionally does not describe how a push service is 143 discovered. Discovery of push services is left for future efforts, 144 if it turns out to be necessary at all. User agents are expected to 145 be configured with a URL for a push service. 147 1.1. Conventions and Terminology 149 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 150 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 151 document are to be interpreted as described in [RFC2119]. 153 This document defines the following terms: 155 application: Both the sender and ultimate consumer of push messages. 156 Many applications have components that are run on a user agent and 157 other components that run on servers. 159 application server: The component of an application that usually 160 runs on a server and requests the delivery of a push message. 162 push message subscription: A message delivery context that is 163 established between the user agent and the push service and shared 164 with the application server. All push messages are associated 165 with a push message subscription. 167 push message subscription set: A message delivery context that is 168 established between the user agent and the push service that 169 collects multiple push message subscriptions into a set. 171 push message: A message sent from an application server to a user 172 agent via a push service. 174 push message receipt: A message delivery confirmation sent from the 175 push service to the application server. 177 push service: A service that delivers push messages to user agents. 179 user agent: A device and software that is the recipient of push 180 messages. 182 Examples in this document use the HTTP/1.1 message format [RFC7230]. 183 Many of the exchanges can be completed using HTTP/1.1, where HTTP/2 184 is necessary, the more verbose frame format from [RFC7540] is used. 186 Examples do not include specific methods for push message encryption 187 or application server authentication because the protocol does not 188 define a mandatory system. The examples in Voluntary Application 189 Server Identification [I-D.ietf-webpush-vapid] and Message Encryption 190 for WebPush [I-D.ietf-webpush-encryption] demonstrate the approach 191 adopted by the W3C Push API [API] for its requirements. 193 2. Overview 195 A general model for push services includes three basic actors: a user 196 agent, a push service, and an application (server). 198 +-------+ +--------------+ +-------------+ 199 | UA | | Push Service | | Application | 200 +-------+ +--------------+ +-------------+ 201 | | | 202 | Subscribe | | 203 |--------------------->| | 204 | Monitor | | 205 |<====================>| | 206 | | | 207 | Distribute Push Resource | 208 |-------------------------------------------->| 209 | | | 210 : : : 211 | | Push Message | 212 | Push Message |<---------------------| 213 |<---------------------| | 214 | | | 216 At the very beginning of the process, a new message subscription is 217 created by the user agent and then distributed to its application 218 server. This subscription is the basis of all future interactions 219 between the actors. A subscription is used by the application server 220 to send messages to the push service for being delivered to the user 221 agent. It is used by the user agent to monitor the push service for 222 any incoming message. 224 To offer more control for authorization, a message subscription is 225 modeled as two resources with different capabilities: 227 o A subscription resource is used to receive messages from a 228 subscription and to delete a subscription. It is private to the 229 user agent. 231 o A push resource is used to send messages to a subscription. It is 232 public and shared by the user agent with its application server. 234 It is expected that a unique subscription will be distributed to each 235 application; however, there are no inherent cardinality constraints 236 in the protocol. Multiple subscriptions might be created for the 237 same application, or multiple applications could use the same 238 subscription. Note however that sharing subscriptions has security 239 and privacy implications. 241 Subscriptions have a limited lifetime. They can also be terminated 242 by either the push service or user agent at any time. User agents 243 and application servers must be prepared to manage changes in 244 subscription state. 246 2.1. HTTP Resources 248 This protocol uses HTTP resources [RFC7230] and link relations 249 [RFC5988]. The following resources are defined: 251 push service: This resource is used to create push message 252 subscriptions (Section 4). A URL for the push service is 253 configured into user agents. 255 push message subscription: This resource provides read and delete 256 access for a message subscription. A user agent receives push 257 messages (Section 6) using a push message subscription. Every 258 push message subscription has exactly one push resource associated 259 with it. 261 push message subscription set: This resource provides read and 262 delete access for a collection of push message subscriptions. A 263 user agent receives push messages (Section 6.1) for all the push 264 message subscriptions in the set. A link relation of type 265 "urn:ietf:params:push:set" identifies a push message subscription 266 set. 268 push: An application server requests the delivery (Section 5) of a 269 push message using a push resource. A link relation of type 270 "urn:ietf:params:push" identifies a push resource. 272 push message: The push service creates a push message resource to 273 identify push messages that have been accepted for delivery 274 (Section 5). The push message resource is also deleted by the 275 user agent to acknowledge receipt (Section 6.2) of a push message. 277 receipt subscription: An application server receives delivery 278 confirmations (Section 5.1) for push messages using a receipt 279 subscription. A link relation of type 280 "urn:ietf:params:push:receipt" identifies a receipt subscription. 282 3. Connecting to the Push Service 284 The push service shares the same default port number (443/TCP) with 285 HTTPS, but MAY also advertise the IANA allocated TCP System Port 1001 286 using HTTP alternative services [RFC7838]. 288 While the default port (443) offers broad reachability 289 characteristics, it is most often used for web browsing scenarios 290 with a lower idle timeout than other ports configured in middleboxes. 291 For webpush scenarios, this would contribute to unnecessary radio 292 communications to maintain the connection on battery-powered devices. 294 Advertising the alternate port (1001) allows middleboxes to optimize 295 idle timeouts for connections specific to push scenarios with the 296 expectation that data exchange will be infrequent. 298 Middleboxes SHOULD comply with REQ-5 in [RFC5382] which requires that 299 "the value of the 'established connection idle-timeout' MUST NOT be 300 less than 2 hours 4 minutes". 302 4. Subscribing for Push Messages 304 A user agent sends a POST request to its configured push service 305 resource to create a new subscription. 307 POST /subscribe HTTP/1.1 308 Host: push.example.net 310 A 201 (Created) response indicates that the a push subscription was 311 created. A URI for the push message subscription resource that was 312 created in response to the request MUST be returned in the Location 313 header field. 315 The push service MUST provide a URI for the push resource 316 corresponding to the push message subscription in a link relation of 317 type "urn:ietf:params:push". 319 An application-specific method is used to distribute the push URI to 320 the application server. Confidentiality protection and application 321 server authentication MUST be used to ensure that this URI is not 322 disclosed to unauthorized recipients (Section 8.3). 324 HTTP/1.1 201 Created 325 Date: Thu, 11 Dec 2014 23:56:52 GMT 326 Link: ; 327 rel="urn:ietf:params:push" 328 Link: ; 329 rel="urn:ietf:params:push:set" 330 Location: https://push.example.net/subscription/LBhhw0OohO-Wl4Oi971UG 332 4.1. Collecting Subscriptions into Sets 334 Collecting multiple push message subscriptions into a subscription 335 set can represent a significant efficiency improvement for push 336 services and user agents. The push service MAY provide a URI for a 337 subscription set resource in a link relation of type 338 "urn:ietf:params:push:set". 340 When a subscription set is returned in a push message subscription 341 response, the user agent SHOULD include this subscription set in a 342 link relation of type "urn:ietf:params:push:set" in subsequent 343 requests to create new push message subscriptions. 345 A user agent MAY omit the subscription set if it is unable to receive 346 push messages in an aggregated way for the lifetime of the 347 subscription. This might be necessary if the user agent is 348 monitoring subscriptions on behalf of other push message receivers. 350 POST /subscribe HTTP/1.1 351 Host: push.example.net 352 Link: ; 353 rel="urn:ietf:params:push:set" 355 The push service SHOULD return the same subscription set in its 356 response, although it MAY return a new subscription set if it is 357 unable to reuse the one provided by the user agent. 359 HTTP/1.1 201 Created 360 Date: Thu, 11 Dec 2014 23:56:52 GMT 361 Link: ; 362 rel="urn:ietf:params:push" 363 Link: ; 364 rel="urn:ietf:params:push:set" 365 Location: https://push.example.net/subscription/i-nQ3A9Zm4kgSWg8_ZijV 367 A push service MUST return a 400 (Bad Request) status code for 368 requests which contain an invalid subscription set. A push service 369 MAY return a 429 (Too Many Requests) status code [RFC6585] to reject 370 requests which omit a subscription set. 372 How a push service detects that requests originate from the same user 373 agent is implementation-specific but could take ambient information 374 into consideration, such as the TLS connection, source IP address and 375 port. Implementers are reminded that some heuristics can produce 376 false positives and cause requests to be rejected incorrectly. 378 5. Requesting Push Message Delivery 380 An application server requests the delivery of a push message by 381 sending a HTTP POST request to a push resource distributed to the 382 application server by a user agent. The content of the push message 383 is included in the body of the request. 385 POST /push/JzLQ3raZJfFBR0aqvOMsLrt54w4rJUsV HTTP/1.1 386 Host: push.example.net 387 TTL: 15 388 Content-Type: text/plain;charset=utf8 389 Content-Length: 36 391 iChYuI3jMzt3ir20P8r_jgRR-dSuN182x7iB 393 A 201 (Created) response indicates that the push message was 394 accepted. A URI for the push message resource that was created in 395 response to the request MUST be returned in the Location header 396 field. This does not indicate that the message was delivered to the 397 user agent. 399 HTTP/1.1 201 Created 400 Date: Thu, 11 Dec 2014 23:56:55 GMT 401 Location: https://push.example.net/message/qDIYHNcfAIPP_5ITvURr-d6BGt 403 5.1. Requesting Push Message Receipts 405 An application server can include the Prefer header field [RFC7240] 406 with the "respond-async" preference to request confirmation from the 407 push service when a push message is delivered and then acknowledged 408 by the user agent. The push service MUST support delivery 409 confirmations. 411 POST /push/JzLQ3raZJfFBR0aqvOMsLrt54w4rJUsV HTTP/1.1 412 Host: push.example.net 413 Prefer: respond-async 414 TTL: 15 415 Content-Type: text/plain;charset=utf8 416 Content-Length: 36 418 iChYuI3jMzt3ir20P8r_jgRR-dSuN182x7iB 419 When the push service accepts the message for delivery with 420 confirmation, it MUST return a 202 (Accepted) response. A URI for 421 the push message resource that was created in response to the request 422 MUST be returned in the Location header field. The push service MUST 423 also provide a URI for the receipt subscription resource in a link 424 relation of type "urn:ietf:params:push:receipt". 426 HTTP/1.1 202 Accepted 427 Date: Thu, 11 Dec 2014 23:56:55 GMT 428 Link: ; 429 rel="urn:ietf:params:push:receipt" 430 Location: https://push.example.net/message/qDIYHNcfAIPP_5ITvURr-d6BGt 432 For subsequent receipt requests to the same origin [RFC6454], the 433 application server SHOULD include the returned receipt subscription 434 in a link relation of type "urn:ietf:params:push:receipt". This 435 gives the push service an option to aggregate the receipts. The push 436 service SHOULD return the same receipt subscription in its response, 437 although it MAY return a new receipt subscription if it is unable to 438 reuse the one provided by the application server. 440 An application server MAY omit the receipt subscription if it is 441 unable to receive receipts in an aggregated way for the lifetime of 442 the receipt subscription. This might be necessary if the application 443 server is monitoring receipt subscriptions on the behalf of other 444 push message senders. 446 A push service MUST return a 400 (Bad Request) status code for 447 requests which contain an invalid receipt subscription. If a push 448 service wishes to limit the number of receipt subscriptions that it 449 maintains, it MAY return a 429 (Too Many Requests) status code 450 [RFC6585] to reject receipt requests which omit a receipt 451 subscription. 453 5.2. Push Message Time-To-Live 455 A push service can improve the reliability of push message delivery 456 considerably by storing push messages for a period. User agents are 457 often only intermittently connected, and so benefit from having short 458 term message storage at the push service. 460 Delaying delivery might also be used to batch communication with the 461 user agent, thereby conserving radio resources. 463 Some push messages are not useful once a certain period of time 464 elapses. Delivery of messages after they have ceased to be relevant 465 is wasteful. For example, if the push message contains a call 466 notification, receiving a message after the caller has abandoned the 467 call is of no value; the application at the user agent is forced to 468 suppress the message so that it does not generate a useless alert. 470 An application server MUST include the TTL (Time-To-Live) header 471 field in its request for push message delivery. The TTL header field 472 contains a value in seconds that suggests how long a push message is 473 retained by the push service. 475 TTL = 1*DIGIT 477 A push service MUST return a 400 (Bad Request) status code in 478 response to requests that omit the TTL header field. 480 A push service MAY retain a push message for a shorter duration than 481 requested. It indicates this by returning a TTL header field in its 482 response with the actual TTL. This TTL value MUST be less than or 483 equal to the value provided by the application server. 485 Once the TTL period elapses, the push service MUST NOT attempt to 486 deliver the push message to the user agent. A push service might 487 adjust the TTL value to account for time accounting errors in 488 processing. For instance, distributing a push message within a 489 server cluster might accrue errors due to clock skew or propagation 490 delays. 492 A push service is not obligated to account for time spent by the 493 application server in sending a push message to the push service, or 494 delays incurred while sending a push message to the user agent. An 495 application server needs to account for transit delays in selecting a 496 TTL header field value. 498 A Push message with a zero TTL is immediately delivered if the user 499 agent is available to receive the message. After delivery, the push 500 service is permitted to immediately remove a push message with a zero 501 TTL. This might occur before the user agent acknowledges receipt of 502 the message by performing a HTTP DELETE on the push message resource. 503 Consequently, an application server cannot rely on receiving 504 acknowledgement receipts for zero TTL push messages. 506 If the user agent is unavailable, a push message with a zero TTL 507 expires and is never delivered. 509 5.3. Push Message Urgency 511 For a device that is battery-powered, it is often critical that it 512 remains dormant for extended periods. Radio communication in 513 particular consumes significant power and limits the length of time 514 that the device can operate. 516 To avoid consuming resources to receive trivial messages, it is 517 helpful if an application server can communicate the urgency of a 518 message and if the user agent can request that the push server only 519 forward messages of a specific urgency. 521 An application server MAY include an Urgency header field in its 522 request for push message delivery. This header field indicates the 523 message urgency. The push service MUST not forward the Urgency 524 header field to the user agent. A push message without the Urgency 525 header field defaults to a value of "normal". 527 A user agent MAY include the Urgency header field when monitoring for 528 push messages to indicate the lowest urgency of push messages that it 529 is willing to receive. A push service MUST NOT deliver push messages 530 with lower urgency than the value indicated by the user agent in its 531 monitoring request. Push messages of any urgency are delivered to a 532 user agent that does not include an Urgency header field when 533 monitoring for messages. 535 Urgency = 1#(urgency-option) 536 urgency-option = ("very-low" / "low" / "normal" / "high") 538 In order of increasing urgency: 540 +----------+-----------------------------+--------------------------+ 541 | Urgency | Device State | Application Scenario | 542 +----------+-----------------------------+--------------------------+ 543 | very-low | On power and wifi | Advertisements | 544 | low | On either power or wifi | Topic updates | 545 | normal | On neither power nor wifi | Chat or Calendar Message | 546 | high | Low battery | Incoming phone call or | 547 | | | time-sensitive alert | 548 +----------+-----------------------------+--------------------------+ 550 Table 1: Table of Urgency Values 552 Multiple values for the Urgency header field MUST NOT be included in 553 requests; otherwise, the push service MUST return a 400 (Bad Request) 554 status code. 556 5.4. Replacing Push Messages 558 A push message that has been stored by the push service can be 559 replaced with new content. If the user agent is offline during the 560 time that the push messages are sent, updating a push message avoids 561 the situation where outdated or redundant messages are sent to the 562 user agent. 564 Only push messages that have been assigned a topic can be replaced. 565 A push message with a topic replaces any outstanding push message 566 with an identical topic. 568 A push message topic is a string carried in a Topic header field. A 569 topic is used to correlate push messages sent to the same 570 subscription and does not convey any other semantics. 572 The grammar for the Topic header field uses the "token" rule defined 573 in [RFC7230]. 575 Topic = token 577 For use with this protocol, the Topic header field MUST be restricted 578 to no more than 32 characters from the URL and filename safe Base 64 579 alphabet [RFC4648]. A push service that receives a request with a 580 Topic header field that does not meet these constraints MUST return a 581 400 (Bad Request) status code to the application server. 583 A push message replacement request creates a new push message 584 resource and simultaneously deletes any existing message resource 585 that has a matching topic. Delivery receipts for the deleted message 586 SHOULD be suppressed. 588 The replacement request also replaces the stored TTL, Urgency, and 589 any receipt subscription associated with the previous message in the 590 matching topic. 592 A push message with a topic that is not shared by an outstanding 593 message to the same subscription is stored or delivered as normal. 595 For example, the following message could cause an existing message to 596 be replaced: 598 POST /push/JzLQ3raZJfFBR0aqvOMsLrt54w4rJUsV HTTP/1.1 599 Host: push.example.net 600 TTL: 600 601 Topic: upd 602 Content-Type: text/plain;charset=utf8 603 Content-Length: 36 605 ZuHSZPKa2b1jtOKLGpWrcrn8cNqt0iVQyroF 607 If the push service identifies an outstanding push message with a 608 topic of "upd", then that message resource is deleted. A 201 609 (Created) response indicates that the push message replacement was 610 accepted. A URI for the new push message resource that was created 611 in response to the request is included in the Location header field. 613 HTTP/1.1 201 Created 614 Date: Thu, 11 Dec 2014 23:57:02 GMT 615 Location: https://push.example.net/message/qDIYHNcfAIPP_5ITvURr-d6BGt 617 The value of the Topic header field MUST NOT be forwarded to user 618 agents. Its value is neither encrypted nor authenticated. 620 6. Receiving Push Messages for a Subscription 622 A user agent requests the delivery of new push messages by making a 623 GET request to a push message subscription resource. The push 624 service does not respond to this request, it instead uses HTTP/2 625 server push [RFC7540] to send the contents of push messages as they 626 are sent by application servers. 628 A user agent MAY include a Urgency header field in its request. The 629 push service MUST NOT deliver messages with lower urgency than the 630 value of the header field as defined in the Table of Urgency Values. 632 Each push message is pushed as the response to a synthesized GET 633 request sent in a PUSH_PROMISE. This GET request is made to the push 634 message resource that was created by the push service when the 635 application server requested message delivery. The response headers 636 SHOULD provide a URI for the push resource corresponding to the push 637 message subscription in a link relation of type 638 "urn:ietf:params:push". The response body is the entity body from 639 the most recent request sent to the push resource by the application 640 server. 642 The following example request is made over HTTP/2. 644 HEADERS [stream 7] +END_STREAM +END_HEADERS 645 :method = GET 646 :path = /subscription/LBhhw0OohO-Wl4Oi971UG 647 :authority = push.example.net 649 The push service permits the request to remain outstanding. When a 650 push message is sent by an application server, a server push is 651 generated in association with the initial request. The response for 652 the server push includes the push message. 654 PUSH_PROMISE [stream 7; promised stream 4] +END_HEADERS 655 :method = GET 656 :path = /message/qDIYHNcfAIPP_5ITvURr-d6BGt 657 :authority = push.example.net 659 HEADERS [stream 4] +END_HEADERS 660 :status = 200 661 date = Thu, 11 Dec 2014 23:56:56 GMT 662 last-modified = Thu, 11 Dec 2014 23:56:55 GMT 663 cache-control = private 664 :link = ; 665 rel="urn:ietf:params:push" 666 content-type = text/plain;charset=utf8 667 content-length = 36 669 DATA [stream 4] +END_STREAM 670 iChYuI3jMzt3ir20P8r_jgRR-dSuN182x7iB 672 HEADERS [stream 7] +END_STREAM +END_HEADERS 673 :status = 200 675 A user agent can also request the contents of the push message 676 subscription resource immediately by including a Prefer header field 677 [RFC7240] with a "wait" preference set to "0". In response to this 678 request, the push service MUST generate a server push for all push 679 messages that have not yet been delivered. 681 A 204 (No Content) status code with no associated server pushes 682 indicates that no messages are presently available. This could be 683 because push messages have expired. 685 6.1. Receiving Push Messages for a Subscription Set 687 There are minor differences between receiving push messages for a 688 subscription and a subscription set. If a subscription set is 689 available, the user agent SHOULD use the subscription set to monitor 690 for push messages rather than individual push message subscriptions. 692 A user agent requests the delivery of new push messages for a 693 collection of push message subscriptions by making a GET request to a 694 push message subscription set resource. The push service does not 695 respond to this request, it instead uses HTTP/2 server push [RFC7540] 696 to send the contents of push messages as they are sent by application 697 servers. 699 A user agent MAY include a Urgency header field in its request. The 700 push service MUST NOT deliver messages with lower urgency than the 701 value of the header field as defined in the Table of Urgency Values. 703 Each push message is pushed as the response to a synthesized GET 704 request sent in a PUSH_PROMISE. This GET request is made to the push 705 message resource that was created by the push service when the 706 application server requested message delivery. The synthetic request 707 MUST provide a URI for the push resource corresponding to the push 708 message subscription in a link relation of type 709 "urn:ietf:params:push". This enables the user agent to differentiate 710 the source of the message. The response body is the entity body from 711 the most recent request sent to the push resource by an application 712 server. 714 The following example request is made over HTTP/2. 716 HEADERS [stream 7] +END_STREAM +END_HEADERS 717 :method = GET 718 :path = /subscription-set/4UXwi2Rd7jGS7gp5cuutF8ZldnEuvbOy 719 :authority = push.example.net 721 The push service permits the request to remain outstanding. When a 722 push message is sent by an application server, a server push is 723 generated in association with the initial request. The server push's 724 response includes the push message. 726 PUSH_PROMISE [stream 7; promised stream 4] +END_HEADERS 727 :method = GET 728 :path = /message/qDIYHNcfAIPP_5ITvURr-d6BGt 729 :authority = push.example.net 730 :link = ; 731 rel="urn:ietf:params:push" 733 HEADERS [stream 4] +END_HEADERS 734 :status = 200 735 date = Thu, 11 Dec 2014 23:56:56 GMT 736 last-modified = Thu, 11 Dec 2014 23:56:55 GMT 737 cache-control = private 738 content-type = text/plain;charset=utf8 739 content-length = 36 741 DATA [stream 4] +END_STREAM 742 iChYuI3jMzt3ir20P8r_jgRR-dSuN182x7iB 744 HEADERS [stream 7] +END_STREAM +END_HEADERS 745 :status = 200 747 A user agent can request the contents of the push message 748 subscription set resource immediately by including a Prefer header 749 field [RFC7240] with a "wait" preference set to "0". In response to 750 this request, the push service MUST generate a server push for all 751 push messages that have not yet been delivered. 753 A 204 (No Content) status code with no associated server pushes 754 indicates that no messages are presently available. This could be 755 because push messages have expired. 757 6.2. Acknowledging Push Messages 759 To ensure that a push message is properly delivered to the user agent 760 at least once, the user agent MUST acknowledge receipt of the message 761 by performing a HTTP DELETE on the push message resource. 763 DELETE /message/qDIYHNcfAIPP_5ITvURr-d6BGt HTTP/1.1 764 Host: push.example.net 765 If the push service receives the acknowledgement and the application 766 has requested a delivery receipt, the push service MUST return a 204 767 (No Content) response to the application server monitoring the 768 receipt subscription. 770 If the push service does not receive the acknowledgement within a 771 reasonable amount of time, then the message is considered to be not 772 yet delivered. The push service SHOULD continue to retry delivery of 773 the message until its advertised expiration. 775 The push service MAY cease to retry delivery of the message prior to 776 its advertised expiration due to scenarios such as an unresponsive 777 user agent or operational constraints. If the application has 778 requested a delivery receipt, then the push service MUST return a 410 779 (Gone) response to the application server monitoring the receipt 780 subscription. 782 6.3. Receiving Push Message Receipts 784 The application server requests the delivery of receipts from the 785 push service by making a HTTP GET request to the receipt subscription 786 resource. The push service does not respond to this request, it 787 instead uses HTTP/2 server push [RFC7540] to send push receipts when 788 messages are acknowledged (Section 6.2) by the user agent. 790 Each receipt is pushed as the response to a synthesized GET request 791 sent in a PUSH_PROMISE. This GET request is made to the same push 792 message resource that was created by the push service when the 793 application server requested message delivery. The response includes 794 a status code indicating the result of the message delivery and 795 carries no data. 797 The following example request is made over HTTP/2. 799 HEADERS [stream 13] +END_STREAM +END_HEADERS 800 :method = GET 801 :path = /receipt-subscription/3ZtI4YVNBnUUZhuoChl6omUvG4ZM 802 :authority = push.example.net 804 The push service permits the request to remain outstanding. When the 805 user agent acknowledges the message, the push service pushes a 806 delivery receipt to the application server. A 204 (No Content) 807 status code confirms that the message was delivered and acknowledged. 809 PUSH_PROMISE [stream 13; promised stream 82] +END_HEADERS 810 :method = GET 811 :path = /message/qDIYHNcfAIPP_5ITvURr-d6BGt 812 :authority = push.example.net 814 HEADERS [stream 82] +END_STREAM 815 +END_HEADERS 816 :status = 204 817 date = Thu, 11 Dec 2014 23:56:56 GMT 819 If the user agent fails to acknowledge the receipt of the push 820 message and the push service ceases to retry delivery of the message 821 prior to its advertised expiration, then the push service MUST push a 822 failure response with a status code of 410 (Gone). 824 7. Operational Considerations 826 7.1. Load Management 828 A push service is likely to have to maintain a very large number of 829 open TCP connections. Effective management of those connections can 830 depend on being able to move connections between server instances. 832 A user agent MUST support the 307 (Temporary Redirect) status code 833 [RFC7231], which can be used by a push service to redistribute load 834 at the time that a new subscription is requested. 836 A server that wishes to redistribute load can do so using HTTP 837 alternative services [RFC7838]. HTTP alternative services allows for 838 redistribution of load while maintaining the same URIs for various 839 resources. A user agent can ensure a graceful transition by using 840 the GOAWAY frame once it has established a replacement connection. 842 7.2. Push Message Expiration 844 Storage of push messages based on the TTL header field comprises a 845 potentially significant amount of storage for a push service. A push 846 service is not obligated to store messages indefinitely. A push 847 service is able to indicate how long it intends to retain a message 848 to an application server using the TTL header field (Section 5.2). 850 A user agent that does not actively monitor for push messages will 851 not receive messages that expire during that interval. 853 Push messages that are stored and have not been delivered to a user 854 agent are delivered when the user agent recommences monitoring. 855 Stored push messages SHOULD include a Last-Modified header field 856 (Section 2.2 of [RFC7232]) indicating when delivery was requested by 857 an application server. 859 A GET request to a push message subscription resource with only 860 expired messages results in a response as though no push message was 861 ever sent. 863 Push services might need to limit the size and number of stored push 864 messages to avoid overloading. To limit the size of messages, the 865 push service MAY return a 413 (Payload Too Large) status code 866 [RFC7231] in response to requests that include an entity body that is 867 too large. Push services MUST NOT return a 413 status code in 868 responses to an entity body that is 4k (4096 bytes) or less in size. 870 To limit the number of stored push messages, the push service MAY 871 either expire messages prior to their advertised Time-To-Live or 872 reduce their advertised Time-To-Live. 874 7.3. Subscription Expiration 876 In some cases, it may be necessary to terminate subscriptions so that 877 they can be refreshed. This applies to both push message 878 subscriptions and receipt subscriptions. 880 A push service MAY expire a subscription at any time. If there are 881 outstanding requests to an expired push message subscription resource 882 (Section 6) from a user agent or to an expired receipt subscription 883 resource (Section 6.3) from an application server, this MUST be 884 signaled by returning a 404 (Not Found) status code. 886 A push service MUST return a 404 (Not Found) status code if an 887 application server attempts to send a push message to an expired push 888 message subscription. 890 A user agent can remove its push message subscription by sending a 891 DELETE request to the corresponding URI. An application server can 892 remove its receipt subscription by sending a DELETE request to the 893 corresponding URI. 895 7.3.1. Subscription Set Expiration 897 A push service MAY expire a subscription set at any time and MUST 898 also expire all push message subscriptions in the set. If a user 899 agent has an outstanding request to a push subscription set 900 (Section 6.1) this MUST be signaled by returning a 404 (Not Found) 901 status code. 903 A user agent can request that a subscription set be removed by 904 sending a DELETE request to the subscription set URI. This MUST also 905 remove all push message subscriptions in the set. 907 If a specific push message subscription that is a member of a 908 subscription set is expired or removed, then it MUST also be removed 909 from its subscription set. 911 7.4. Implications for Application Reliability 913 A push service that does not support reliable delivery over 914 intermittent network connections or failing applications on devices, 915 forces the device to acknowledge receipt directly to the application 916 server, incurring additional power drain in order to establish 917 (usually secure) connections to the individual application servers. 919 Push message reliability can be important if messages contain 920 information critical to the state of an application. Repairing state 921 can be expensive, particularly for devices with limited 922 communications capacity. Knowing that a push message has been 923 correctly received avoids retransmissions, polling, and state 924 resynchronization. 926 The availability of push message delivery receipts ensures that the 927 application developer is not tempted to create alternative mechanisms 928 for message delivery in case the push service fails to deliver a 929 critical message. Setting up a polling mechanism or a backup 930 messaging channel in order to compensate for these shortcomings 931 negates almost all of the advantages a push service provides. 933 However, reliability might not be necessary for messages that are 934 transient (e.g. an incoming call) or messages that are quickly 935 superceded (e.g. the current number of unread emails). 937 7.5. Subscription Sets and Concurrent HTTP/2 streams 939 If the push service requires that the user agent use push message 940 subscription sets, then it MAY limit the number of concurrently 941 active streams with the SETTINGS_MAX_CONCURRENT_STREAMS parameter 942 within a HTTP/2 SETTINGS frame [RFC7540]. The user agent MAY be 943 limited to one concurrent stream to manage push message subscriptions 944 and one concurrent stream for each subscription set returned by the 945 push service. This could force the user agent to serialize 946 subscription requests to the push service. 948 8. Security Considerations 950 This protocol MUST use HTTP over TLS [RFC2818]. This includes any 951 communications between user agent and push service, plus 952 communications between the application and the push service. All 953 URIs therefore use the "https" scheme. This provides confidentiality 954 and integrity protection for subscriptions and push messages from 955 external parties. 957 Applications using this protocol MUST use mechanisms that provide 958 confidentiality, integrity and data origin authentication. The 959 application server sending the push message and the application on 960 the user agent that receives it are frequently just different 961 instances of the same application, so no standardized protocol is 962 needed to establish a proper security context. The distribution of 963 subscription information from the user agent to its application 964 server also offers a convenient medium for key agreement. 966 8.1. Confidentiality from Push Service Access 968 The protection afforded by TLS does not protect content from the push 969 service. Without additional safeguards, a push service can inspect 970 and modify the message content. 972 For its requirements, the W3C Push API [API] has adopted Message 973 Encryption for WebPush [I-D.ietf-webpush-encryption] to secure the 974 content of messages from the push service. Other scenarios can be 975 addressed by similar policies. 977 The Topic header field exposes information that allows more granular 978 correlation of push messages on the same subject. This might be used 979 to aid traffic analysis of push messages by the push service. 981 8.2. Privacy Considerations 983 Push message confidentiality does not ensure that the identity of who 984 is communicating and when they are communicating is protected. 985 However, the amount of information that is exposed can be limited. 987 The URIs provided for push resources MUST NOT provide any basis to 988 correlate communications for a given user agent. It MUST NOT be 989 possible to correlate any two push resource URIs based solely on 990 their contents. This allows a user agent to control correlation 991 across different applications, or over time. 993 Similarly, the URIs provided by the push service to identify a push 994 message MUST NOT provide any information that allows for correlation 995 across subscriptions. Push message URIs for the same subscription 996 MAY contain information that would allow correlation with the 997 associated subscription or other push messages for that subscription. 999 User and device information MUST NOT be exposed through a push or 1000 push message URI. 1002 In addition, push URIs established by the same user agent or push 1003 message URIs for the same subscription MUST NOT include any 1004 information that allows them to be correlated with the user agent. 1006 Note: This need not be perfect as long as the resulting anonymity 1007 set ([RFC6973], Section 6.1.1) is sufficiently large. A push URI 1008 necessarily identifies a push service or a single server instance. 1009 It is also possible that traffic analysis could be used to 1010 correlate subscriptions. 1012 A user agent MUST be able to create new subscriptions with new 1013 identifiers at any time. 1015 8.3. Authorization 1017 This protocol does not define how a push service establishes whether 1018 a user agent is permitted to create a subscription, or whether push 1019 messages can be delivered to the user agent. A push service MAY 1020 choose to authorize requests based on any HTTP-compatible 1021 authorization method available, of which there are numerous options. 1022 The authorization process and any associated credentials are expected 1023 to be configured in the user agent along with the URI for the push 1024 service. 1026 Authorization is managed using capability URLs for the push message 1027 subscription, push, and receipt subscription resources ([CAP-URI]). 1028 A capability URL grants access to a resource based solely on 1029 knowledge of the URL. 1031 Capability URLs are used for their "easy onward sharing" and "easy 1032 client API" properties. These make it possible to avoid relying on 1033 relationships between push services and application servers, with the 1034 protocols necessary to build and support those relationships. 1036 Capability URLs act as bearer tokens. Knowledge of a push message 1037 subscription URI implies authorization to either receive push 1038 messages or delete the subscription. Knowledge of a push URI implies 1039 authorization to send push messages. Knowledge of a push message URI 1040 allows for reading and acknowledging that specific message. 1041 Knowledge of a receipt subscription URI implies authorization to 1042 receive push receipts. 1044 Encoding a large amount of random entropy (at least 120 bits) in the 1045 path component ensures that it is difficult to successfully guess a 1046 valid capability URL. 1048 8.4. Denial of Service Considerations 1050 A user agent can control where valid push messages originate by 1051 limiting the distribution of push URIs to authorized application 1052 servers. Ensuring that push URIs are hard to guess ensures that only 1053 application servers that have received a push URI can use it. 1055 Push messages that are not successfully authenticated by the user 1056 agent will not be delivered, but this can present a denial of service 1057 risk. Even a relatively small volume of push messages can cause 1058 battery-powered devices to exhaust power reserves. 1060 To address this case, the W3C Push API [API] has adopted Voluntary 1061 Application Server Identification [I-D.ietf-webpush-vapid], which 1062 allows a user agent to restrict a subscription to a specific 1063 application server. The push service can then identity and reject 1064 unwanted messages without contacting the user agent. 1066 A malicious application with a valid push URI could use the greater 1067 resources of a push service to mount a denial of service attack on a 1068 user agent. Push services SHOULD limit the rate at which push 1069 messages are sent to individual user agents. 1071 A push service MAY return a 429 (Too Many Requests) status code 1072 [RFC6585] when an application server has exceeded its rate limit for 1073 push message delivery to a push resource. The push service SHOULD 1074 also include a Retry-After header [RFC7231] to indicate how long the 1075 application server is requested to wait before it makes another 1076 request to the push resource. 1078 A push service or user agent MAY also terminate subscriptions 1079 (Section 7.3) that receive too many push messages. 1081 A push service is also able to deny service to user agents. 1082 Intentional failure to deliver messages is difficult to distinguish 1083 from faults, which might occur due to transient network errors, 1084 interruptions in user agent availability, or genuine service outages. 1086 8.5. Logging Risks 1088 Server request logs can reveal subscription-related URIs or 1089 relationships between subscription-related URIs for the same user 1090 agent. Limitations on log retention and strong access control 1091 mechanisms can ensure that URIs are not revealed to unauthorized 1092 entities. 1094 9. IANA Considerations 1096 This protocol defines new HTTP header fields in Section 9.1. New 1097 link relation types are identified using the URNs defined in 1098 Section 9.2. Port registration is defined in Section 9.3 1100 9.1. Header Field Registrations 1102 HTTP header fields are registered within the "Message Headers" 1103 registry maintained at . 1106 This document defines the following HTTP header fields, so their 1107 associated registry entries shall be added according to the permanent 1108 registrations below ([RFC3864]): 1110 +-------------------+----------+----------+--------------+ 1111 | Header Field Name | Protocol | Status | Reference | 1112 +-------------------+----------+----------+--------------+ 1113 | TTL | http | standard | Section 5.2 | 1114 | Urgency | http | standard | Section 5.3 | 1115 | Topic | http | standard | Section 5.4 | 1116 +-------------------+----------+----------+--------------+ 1118 The change controller is: "IETF (iesg@ietf.org) - Internet 1119 Engineering Task Force". 1121 9.2. Link Relation URNs 1123 This document registers URNs for use in identifying link relation 1124 types. These are added to a new "Web Push Identifiers" registry 1125 according to the procedures in Section 4 of [RFC3553]; the 1126 corresponding "push" sub-namespace is entered in the "IETF URN Sub- 1127 namespace for Registered Protocol Parameter Identifiers" registry. 1129 The "Web Push Identifiers" registry operates under the IETF Review 1130 policy [RFC5226]. 1132 Registry name: Web Push Identifiers 1133 URN Prefix: urn:ietf:params:push 1135 Specification: (this document) 1137 Repository: [Editor/IANA note: please include a link to the final 1138 registry location.] 1140 Index value: Values in this registry are URNs or URN prefixes that 1141 start with the prefix "urn:ietf:params:push". Each is registered 1142 independently. 1144 New registrations in the "Web Push Identifiers" are encouraged to 1145 include the following information: 1147 URN: A complete URN or URN prefix. 1149 Description: A summary description. 1151 Specification: A reference to a specification describing the 1152 semantics of the URN or URN prefix. 1154 Contact: Email for the person or group making the registration. 1156 Index value: As described in [RFC3553], URN prefixes that are 1157 registered include a description of how the URN is constructed. 1158 This is not applicable for specific URNs. 1160 These values are entered as the initial content of the "Web Push 1161 Identifiers" registry. 1163 URN: urn:ietf:params:push 1165 Description: This link relation type is used to identify a resource 1166 for sending push messages. 1168 Specification: (this document) 1170 Contact: The Web Push WG (webpush@ietf.org) 1172 URN: urn:ietf:params:push:set 1174 Description: This link relation type is used to identify a 1175 collection of push message subscriptions. 1177 Specification: (this document) 1179 Contact: The Web Push WG (webpush@ietf.org) 1180 URN: urn:ietf:params:push:receipt 1182 Description: This link relation type is used to identify a resource 1183 for receiving delivery confirmations for push messages. 1185 Specification: (this document) 1187 Contact: The Web Push WG (webpush@ietf.org) 1189 9.3. Service Name and Port Number Registration 1191 Service names and port numbers are registered within the "Service 1192 Name and Transport Protocol Port Number Registry" maintained at 1193 . 1196 IANA is requested to assign the System Port number 1001 and the 1197 service name "webpush" in accordance with [RFC6335]. 1199 Service Name. 1200 webpush 1202 Transport Protocol. 1203 tcp 1205 Assignee. 1206 IESG (iesg@ietf.org) 1208 Contact. 1209 The Web Push WG (webpush@ietf.org) 1211 Description. 1212 HTTP Web Push 1214 Reference. 1215 [RFCthis] 1217 Port Number. 1218 1001 1220 10. Acknowledgements 1222 Significant technical input to this document has been provided by Ben 1223 Bangert, Peter Beverloo, Kit Cambridge, JR Conlin, Matthew Kaufman, 1224 Costin Manolache, Mark Nottingham, Idel Pivnitskiy, Robert Sparks, 1225 Darshak Thakore and many others. 1227 11. References 1229 11.1. Normative References 1231 [CAP-URI] Tennison, J., "Good Practices for Capability URLs", FPWD 1232 capability-urls, February 2014, 1233 . 1235 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1236 Requirement Levels", BCP 14, RFC 2119, March 1997. 1238 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 1240 [RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An 1241 IETF URN Sub-namespace for Registered Protocol 1242 Parameters", BCP 73, RFC 3553, June 2003. 1244 [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration 1245 Procedures for Message Header Fields", BCP 90, RFC 3864, 1246 September 2004. 1248 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 1249 Encodings", RFC 4648, October 2006. 1251 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1252 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1253 May 2008. 1255 [RFC5382] Biswas, K., Ford, B., Sivakumar, S., and P. Srisuresh, 1256 "NAT Behavioral Requirements for TCP", RFC 5382, October 1257 2008. 1259 [RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010. 1261 [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. 1262 Cheshire, "Internet Assigned Numbers Authority (IANA) 1263 Procedures for the Management of the Service Name and 1264 Transport Protocol Port Number Registry", RFC 6335, August 1265 2011. 1267 [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, December 1268 2011. 1270 [RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status 1271 Codes", RFC 6585, April 2012. 1273 [RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol 1274 (HTTP/1.1): Message Syntax and Routing", RFC 7230, June 1275 2014. 1277 [RFC7231] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol 1278 (HTTP/1.1): Semantics and Content", RFC 7231, June 2014. 1280 [RFC7232] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol 1281 (HTTP/1.1): Conditional Requests", RFC 7232, June 2014. 1283 [RFC7240] Snell, J., "Prefer Header for HTTP", RFC 7240, June 2014. 1285 [RFC7540] Belshe, M., Peon, R., and M. Thomson, "Hypertext Transfer 1286 Protocol Version 2", RFC 7540, May 2015. 1288 [RFC7838] Nottingham, M., McManus, P., and J. Reschke, "HTTP 1289 Alternative Services", RFC 7838, April 2016. 1291 11.2. Informative References 1293 [API] van Ouwerkerk, M., Thomson, M., Sullivan, B., and E. 1294 Fullea, "W3C Push API", ED push-api, July 2016, 1295 . 1297 [I-D.ietf-webpush-encryption] 1298 Thomson, M., "Message Encryption for Web Push", draft- 1299 ietf-webpush-encryption-03 (work in progress), March 2016, 1300 . 1303 [I-D.ietf-webpush-vapid] 1304 Thomson, M. and P. Beverloo, "Voluntary Application Server 1305 Identification for Web Push", draft-ietf-webpush-vapid-01 1306 (work in progress), April 2016, 1307 . 1310 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 1311 Morris, J., Hansen, M., and R. Smith, "Privacy 1312 Considerations for Internet Protocols", RFC 6973, July 1313 2013. 1315 Appendix A. Change Log 1317 [[The RFC Editor is requested to remove this section at 1318 publication.]] 1320 A.1. Since draft-ietf-webpush-protocol-00 1322 Editorial changes for Push Message Time-To-Live 1324 Editorial changes for Push Acknowledgements 1326 Removed subscription expiration based on HTTP cache headers 1328 A.2. Since draft-ietf-webpush-protocol-01 1330 Added Subscription Sets 1332 Added System Port as an alternate service with guidance for idle 1333 timeouts 1335 Finalized status codes for acknowledgements 1337 Editorial changes for Rate Limits 1339 A.3. Since draft-ietf-webpush-protocol-02 1341 Added explicit correlation for Subscription Sets 1343 Added Push Message Updates (message collapsing) 1345 Renamed the push:receipt link relation to push:receipts and 1346 transitioned the Push-Receipt header field to the push:receipt link 1347 relation type 1349 A.4. Since draft-ietf-webpush-protocol-03 1351 An application server MUST include the TTL (Time-To-Live) header 1352 field in its request for push message delivery. 1354 Added Push Message Urgency header field 1356 A.5. Since draft-ietf-webpush-protocol-04 1358 Simplified design for Push Receipts and eliminated the 1359 urn:ietf:params:push:receipts link relation 1361 Clarified Security Considerations section and added informative 1362 references to Message Encryption and Voluntary Application Server 1363 Identification 1365 A.6. Since draft-ietf-webpush-protocol-05 1367 Addressed feedback from Working Group Last Call 1369 A.7. Since draft-ietf-webpush-protocol-06 1371 Updated informative references to W3C Push API, Message Encryption, 1372 and Voluntary Application Server Identification 1374 Authors' Addresses 1376 Martin Thomson 1377 Mozilla 1378 331 E Evelyn Street 1379 Mountain View, CA 94041 1380 US 1382 Email: martin.thomson@gmail.com 1384 Elio Damaggio 1385 Microsoft 1386 One Microsoft Way 1387 Redmond, WA 98052 1388 US 1390 Email: elioda@microsoft.com 1392 Brian Raymor (editor) 1393 Microsoft 1394 One Microsoft Way 1395 Redmond, WA 98052 1396 US 1398 Email: brian.raymor@microsoft.com