idnits 2.17.1 draft-ietf-webpush-protocol-06.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 (June 14, 2016) is 2870 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 1214, 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reference: RFC 7232 (Obsoleted by RFC 9110) ** Obsolete normative reference: RFC 7540 (Obsoleted by RFC 9113) == Outdated reference: A later version (-09) exists of draft-ietf-webpush-encryption-02 == Outdated reference: A later version (-04) exists of draft-ietf-webpush-vapid-00 Summary: 7 errors (**), 0 flaws (~~), 5 warnings (==), 2 comments (--).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: December 16, 2016 B. Raymor, Ed. 6 Microsoft 7 June 14, 2016 9 Generic Event Delivery Using HTTP Push 10 draft-ietf-webpush-protocol-06 12 Abstract 14 A simple protocol for the delivery of realtime 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 December 16, 2016. 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 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 97 1. Introduction 99 Many applications on mobile and embedded devices require continuous 100 access to network communications so that real-time events - such as 101 incoming calls or messages - can be delivered (or "pushed") in a 102 timely fashion. These devices typically have limited power reserves, 103 so finding more efficient ways to serve application requirements 104 greatly benefits the application ecosystem. 106 One significant contributor to power usage is the radio. Radio 107 communications consume a significant portion of the energy budget on 108 a wireless device. 110 Uncoordinated use of persistent connections or sessions from multiple 111 applications can contribute to unnecessary use of the device radio, 112 since each independent session can incur its own overhead. In 113 particular, keep alive traffic used to ensure that middleboxes do not 114 prematurely time out sessions, can result in significant waste. 115 Maintenance traffic tends to dominate over the long term, since 116 events are relatively rare. 118 Consolidating all real-time events into a single session ensures more 119 efficient use of network and radio resources. A single service 120 consolidates all events, distributing those events to applications as 121 they arrive. This requires just one session, avoiding duplicated 122 overhead costs. 124 The W3C Push API [API] describes an API that enables the use of a 125 consolidated push service from web applications. This document 126 expands on that work by describing a protocol that can be used to: 128 o request the delivery of a push message to a user agent, 130 o create new push message delivery subscriptions, and 132 o monitor for new push messages. 134 A standardized method of event delivery is particularly important for 135 the W3C Push API, where application servers might need to use 136 multiple push services. The subscription, management and monitoring 137 functions are currently fulfilled by proprietary protocols; these are 138 adequate, but do not offer any of the advantages that standardization 139 affords. 141 This document intentionally does not describe how a push service is 142 discovered. Discovery of push services is left for future efforts, 143 if it turns out to be necessary at all. User agents are expected to 144 be configured with a URL for a push service. 146 1.1. Conventions and Terminology 148 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 149 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 150 document are to be interpreted as described in [RFC2119]. 152 This document defines the following terms: 154 application: Both the sender and ultimate consumer of push messages. 155 Many applications have components that are run on a user agent and 156 other components that run on servers. 158 application server: The component of an application that usually 159 runs on a server and requests the delivery of a push message. 161 push message subscription: A message delivery context that is 162 established between the user agent and the push service and shared 163 with the application server. All push messages are associated 164 with a push message subscription. 166 push message subscription set: A message delivery context that is 167 established between the user agent and the push service that 168 collects multiple push message subscriptions into a set. 170 push message: A message sent from an application server to a user 171 agent via a push service. 173 push message receipt: A message delivery confirmation sent from the 174 push service to the application server. 176 push service: A service that delivers push messages to user agents. 178 user agent: A device and software that is the recipient of push 179 messages. 181 Examples in this document use the HTTP/1.1 message format [RFC7230]. 182 Many of the exchanges can be completed using HTTP/1.1, where HTTP/2 183 is necessary, the more verbose frame format from [RFC7540] is used. 185 Examples do not include specific methods for push message encryption 186 or application server authentication because the protocol does not 187 define a mandatory system. The examples in Voluntary Application 188 Server Identification [I-D.ietf-webpush-vapid] and Message Encryption 189 for WebPush [I-D.ietf-webpush-encryption] demonstrate the approach 190 adopted by the W3C Push API [API] for its requirements. 192 2. Overview 194 A general model for push services includes three basic actors: a user 195 agent, a push service, and an application (server). 197 +-------+ +--------------+ +-------------+ 198 | UA | | Push Service | | Application | 199 +-------+ +--------------+ +-------------+ 200 | | | 201 | Subscribe | | 202 |--------------------->| | 203 | Monitor | | 204 |<====================>| | 205 | | | 206 | Distribute Push Resource | 207 |-------------------------------------------->| 208 | | | 209 : : : 210 | | Push Message | 211 | Push Message |<---------------------| 212 |<---------------------| | 213 | | | 215 At the very beginning of the process, a new message subscription is 216 created by the user agent and then distributed to its application 217 server. This subscription is the basis of all future interactions 218 between the actors. A subscription is used by the application server 219 to send messages to the push service for being delivered to the user 220 agent. It is used by the user agent to monitor the push service for 221 any incoming message. 223 To offer more control for authorization, a message subscription is 224 modeled as two resources with different capabilities: 226 o A subscription resource is used to receive messages from a 227 subscription and to delete a subscription. It is private to the 228 user agent. 230 o A push resource is used to send messages to a subscription. It is 231 public and shared by the user agent with its application server. 233 It is expected that a unique subscription will be distributed to each 234 application; however, there are no inherent cardinality constraints 235 in the protocol. Multiple subscriptions might be created for the 236 same application, or multiple applications could use the same 237 subscription. Note however that sharing subscriptions has security 238 and privacy implications. 240 Subscriptions have a limited lifetime. They can also be terminated 241 by either the push service or user agent at any time. User agents 242 and application servers must be prepared to manage changes in 243 subscription state. 245 2.1. HTTP Resources 247 This protocol uses HTTP resources [RFC7230] and link relations 248 [RFC5988]. The following resources are defined: 250 push service: This resource is used to create push message 251 subscriptions (Section 4). A URL for the push service is 252 configured into user agents. 254 push message subscription: This resource provides read and delete 255 access for a message subscription. A user agent receives push 256 messages (Section 6) using a push message subscription. Every 257 push message subscription has exactly one push resource associated 258 with it. 260 push message subscription set: This resource provides read and 261 delete access for a collection of push message subscriptions. A 262 user agent receives push messages (Section 6.1) for all the push 263 message subscriptions in the set. A link relation of type 264 "urn:ietf:params:push:set" identifies a push message subscription 265 set. 267 push: An application server requests the delivery (Section 5) of a 268 push message using a push resource. A link relation of type 269 "urn:ietf:params:push" identifies a push resource. 271 push message: The push service creates a push message resource to 272 identify push messages that have been accepted for delivery 273 (Section 5). The push message resource is also deleted by the 274 user agent to acknowledge receipt (Section 6.2) of a push message. 276 receipt subscription: An application server receives delivery 277 confirmations (Section 5.1) for push messages using a receipt 278 subscription. A link relation of type 279 "urn:ietf:params:push:receipt" identifies a receipt subscription. 281 3. Connecting to the Push Service 283 The push service shares the same default port number (443/TCP) with 284 HTTPS, but MAY also advertise the IANA allocated TCP System Port 1001 285 using HTTP alternative services [RFC7838]. 287 While the default port (443) offers broad reachability 288 characteristics, it is most often used for web browsing scenarios 289 with a lower idle timeout than other ports configured in middleboxes. 290 For webpush scenarios, this would contribute to unnecessary radio 291 communications to maintain the connection on battery-powered devices. 293 Advertising the alternate port (1001) allows middleboxes to optimize 294 idle timeouts for connections specific to push scenarios with the 295 expectation that data exchange will be infrequent. 297 Middleboxes SHOULD comply with REQ-5 in [RFC5382] which requires that 298 "the value of the 'established connection idle-timeout' MUST NOT be 299 less than 2 hours 4 minutes". 301 4. Subscribing for Push Messages 303 A user agent sends a POST request to its configured push service 304 resource to create a new subscription. 306 POST /subscribe HTTP/1.1 307 Host: push.example.net 309 A 201 (Created) response indicates that the a push subscription was 310 created. A URI for the push message subscription resource that was 311 created in response to the request MUST be returned in the Location 312 header field. 314 The push service MUST provide a URI for the push resource 315 corresponding to the push message subscription in a link relation of 316 type "urn:ietf:params:push". 318 An application-specific method is used to distribute the push URI to 319 the application server. Confidentiality protection and application 320 server authentication MUST be used to ensure that this URI is not 321 disclosed to unauthorized recipients (Section 8.3). 323 HTTP/1.1 201 Created 324 Date: Thu, 11 Dec 2014 23:56:52 GMT 325 Link: ; 326 rel="urn:ietf:params:push" 327 Link: ; 328 rel="urn:ietf:params:push:set" 329 Location: https://push.example.net/subscription/LBhhw0OohO-Wl4Oi971UG 331 4.1. Collecting Subscriptions into Sets 333 Collecting multiple push message subscriptions into a subscription 334 set can represent a significant efficiency improvement for push 335 services and user agents. The push service MAY provide a URI for a 336 subscription set resource in a link relation of type 337 "urn:ietf:params:push:set". 339 When a subscription set is returned in a push message subscription 340 response, the user agent SHOULD include this subscription set in a 341 link relation of type "urn:ietf:params:push:set" in subsequent 342 requests to create new push message subscriptions. 344 A user agent MAY omit the subscription set if it is unable to receive 345 push messages in an aggregated way for the lifetime of the 346 subscription. This might be necessary if the user agent is 347 monitoring subscriptions on behalf of other push message receivers. 349 POST /subscribe HTTP/1.1 350 Host: push.example.net 351 Link: ; 352 rel="urn:ietf:params:push:set" 354 The push service SHOULD return the same subscription set in its 355 response, although it MAY return a new subscription set if it is 356 unable to reuse the one provided by the user agent. 358 HTTP/1.1 201 Created 359 Date: Thu, 11 Dec 2014 23:56:52 GMT 360 Link: ; 361 rel="urn:ietf:params:push" 362 Link: ; 363 rel="urn:ietf:params:push:set" 364 Location: https://push.example.net/subscription/i-nQ3A9Zm4kgSWg8_ZijV 366 A push service MUST return a 400 (Bad Request) status code for 367 requests which contain an invalid subscription set. A push service 368 MAY return a 429 (Too Many Requests) status code [RFC6585] to reject 369 requests which omit a subscription set. 371 How a push service detects that requests originate from the same user 372 agent is implementation-specific but could take ambient information 373 into consideration, such as the TLS connection, source IP address and 374 port. Implementers are reminded that some heuristics can produce 375 false positives and cause requests to be rejected incorrectly. 377 5. Requesting Push Message Delivery 379 An application server requests the delivery of a push message by 380 sending a HTTP POST request to a push resource distributed to the 381 application server by a user agent. The content of the push message 382 is included in the body of the request. 384 POST /push/JzLQ3raZJfFBR0aqvOMsLrt54w4rJUsV HTTP/1.1 385 Host: push.example.net 386 TTL: 15 387 Content-Type: text/plain;charset=utf8 388 Content-Length: 36 390 iChYuI3jMzt3ir20P8r_jgRR-dSuN182x7iB 392 A 201 (Created) response indicates that the push message was 393 accepted. A URI for the push message resource that was created in 394 response to the request MUST be returned in the Location header 395 field. This does not indicate that the message was delivered to the 396 user agent. 398 HTTP/1.1 201 Created 399 Date: Thu, 11 Dec 2014 23:56:55 GMT 400 Location: https://push.example.net/message/qDIYHNcfAIPP_5ITvURr-d6BGt 402 5.1. Requesting Push Message Receipts 404 An application server can include the Prefer header field [RFC7240] 405 with the "respond-async" preference to request confirmation from the 406 push service when a push message is delivered and then acknowledged 407 by the user agent. The push service MUST support delivery 408 confirmations. 410 POST /push/JzLQ3raZJfFBR0aqvOMsLrt54w4rJUsV HTTP/1.1 411 Host: push.example.net 412 Prefer: respond-async 413 TTL: 15 414 Content-Type: text/plain;charset=utf8 415 Content-Length: 36 417 iChYuI3jMzt3ir20P8r_jgRR-dSuN182x7iB 418 When the push service accepts the message for delivery with 419 confirmation, it MUST return a 202 (Accepted) response. A URI for 420 the push message resource that was created in response to the request 421 MUST be returned in the Location header field. The push service MUST 422 also provide a URI for the receipt subscription resource in a link 423 relation of type "urn:ietf:params:push:receipt". 425 HTTP/1.1 202 Accepted 426 Date: Thu, 11 Dec 2014 23:56:55 GMT 427 Link: ; 428 rel="urn:ietf:params:push:receipt" 429 Location: https://push.example.net/message/qDIYHNcfAIPP_5ITvURr-d6BGt 431 For subsequent receipt requests to the same origin [RFC6454], the 432 application server SHOULD include the returned receipt subscription 433 in a link relation of type "urn:ietf:params:push:receipt". This 434 gives the push service an option to aggregate the receipts. The push 435 service SHOULD return the same receipt subscription in its response, 436 although it MAY return a new receipt subscription if it is unable to 437 reuse the one provided by the application server. 439 An application server MAY omit the receipt subscription if it is 440 unable to receive receipts in an aggregated way for the lifetime of 441 the receipt subscription. This might be necessary if the application 442 server is monitoring receipt subscriptions on the behalf of other 443 push message senders. 445 A push service MUST return a 400 (Bad Request) status code for 446 requests which contain an invalid receipt subscription. If a push 447 service wishes to limit the number of receipt subscriptions that it 448 maintains, it MAY return a 429 (Too Many Requests) status code 449 [RFC6585] to reject receipt requests which omit a receipt 450 subscription. 452 5.2. Push Message Time-To-Live 454 A push service can improve the reliability of push message delivery 455 considerably by storing push messages for a period. User agents are 456 often only intermittently connected, and so benefit from having short 457 term message storage at the push service. 459 Delaying delivery might also be used to batch communication with the 460 user agent, thereby conserving radio resources. 462 Some push messages are not useful once a certain period of time 463 elapses. Delivery of messages after they have ceased to be relevant 464 is wasteful. For example, if the push message contains a call 465 notification, receiving a message after the caller has abandoned the 466 call is of no value; the application at the user agent is forced to 467 suppress the message so that it does not generate a useless alert. 469 An application server MUST include the TTL (Time-To-Live) header 470 field in its request for push message delivery. The TTL header field 471 contains a value in seconds that suggests how long a push message is 472 retained by the push service. 474 TTL = 1*DIGIT 476 A push service MUST return a 400 (Bad Request) status code in 477 response to requests that omit the TTL header field. 479 A push service MAY retain a push message for a shorter duration than 480 requested. It indicates this by returning a TTL header field in its 481 response with the actual TTL. This TTL value MUST be less than or 482 equal to the value provided by the application server. 484 Once the TTL period elapses, the push service MUST NOT attempt to 485 deliver the push message to the user agent. A push service might 486 adjust the TTL value to account for time accounting errors in 487 processing. For instance, distributing a push message within a 488 server cluster might accrue errors due to clock skew or propagation 489 delays. 491 A push service is not obligated to account for time spent by the 492 application server in sending a push message to the push service, or 493 delays incurred while sending a push message to the user agent. An 494 application server needs to account for transit delays in selecting a 495 TTL header field value. 497 A Push message with a zero TTL is immediately delivered if the user 498 agent is available to receive the message. After delivery, the push 499 service is permitted to immediately remove a push message with a zero 500 TTL. This might occur before the user agent acknowledges receipt of 501 the message by performing a HTTP DELETE on the push message resource. 502 Consequently, an application server cannot rely on receiving 503 acknowledgement receipts for zero TTL push messages. 505 If the user agent is unavailable, a push message with a zero TTL 506 expires and is never delivered. 508 5.3. Push Message Urgency 510 For a device that is battery-powered, it is often critical that it 511 remains dormant for extended periods. Radio communication in 512 particular consumes significant power and limits the length of time 513 that the device can operate. 515 To avoid consuming resources to receive trivial messages, it is 516 helpful if an application server can communicate the urgency of a 517 message and if the user agent can request that the push server only 518 forward messages of a specific urgency. 520 An application server MAY include an Urgency header field in its 521 request for push message delivery. This header field indicates the 522 message urgency. The push service MUST not forward the Urgency 523 header field to the user agent. A push message without the Urgency 524 header field defaults to a value of "normal". 526 A user agent MAY include the Urgency header field when monitoring for 527 push messages to indicate the lowest urgency of push messages that it 528 is willing to receive. A push service MUST NOT deliver push messages 529 with lower urgency than the value indicated by the user agent in its 530 monitoring request. Push messages of any urgency are delivered to a 531 user agent that does not include an Urgency header field when 532 monitoring for messages. 534 Urgency = 1#(urgency-option) 535 urgency-option = ("very-low" / "low" / "normal" / "high") 537 In order of increasing urgency: 539 +----------+-----------------------------+--------------------------+ 540 | Urgency | Device State | Application Scenario | 541 +----------+-----------------------------+--------------------------+ 542 | very-low | On power and wifi | Advertisements | 543 | low | On either power or wifi | Topic updates | 544 | normal | On neither power nor wifi | Chat or Calendar Message | 545 | high | Low battery | Incoming phone call or | 546 | | | time-sensitive alert | 547 +----------+-----------------------------+--------------------------+ 549 Table 1: Table of Urgency Values 551 Multiple values for the Urgency header field MUST NOT be included in 552 requests; otherwise, the push service MUST return a 400 (Bad Request) 553 status code. 555 5.4. Replacing Push Messages 557 A push message that has been stored by the push service can be 558 replaced with new content. If the user agent is offline during the 559 time that the push messages are sent, updating a push message avoids 560 the situation where outdated or redundant messages are sent to the 561 user agent. 563 Only push messages that have been assigned a topic can be replaced. 564 A push message with a topic replaces any outstanding push message 565 with an identical topic. 567 A push message topic is a string carried in a Topic header field. A 568 topic is used to correlate push messages sent to the same 569 subscription and does not convey any other semantics. 571 The grammar for the Topic header field uses the "token" rule defined 572 in [RFC7230]. 574 Topic = token 576 For use with this protocol, the Topic header field MUST be restricted 577 to no more than 32 characters from the URL and filename safe Base 64 578 alphabet [RFC4648]. A push service that receives a request with a 579 Topic header field that does not meet these constraints MUST return a 580 400 (Bad Request) status code to the application server. 582 A push message replacement request creates a new push message 583 resource and simultaneously deletes any existing message resource 584 that has a matching topic. Delivery receipts for the deleted message 585 SHOULD be suppressed. 587 The replacement request also replaces the stored TTL, Urgency, and 588 any receipt subscription associated with the previous message in the 589 matching topic. 591 A push message with a topic that is not shared by an outstanding 592 message to the same subscription is stored or delivered as normal. 594 For example, the following message could cause an existing message to 595 be replaced: 597 POST /push/JzLQ3raZJfFBR0aqvOMsLrt54w4rJUsV HTTP/1.1 598 Host: push.example.net 599 TTL: 600 600 Topic: upd 601 Content-Type: text/plain;charset=utf8 602 Content-Length: 36 604 ZuHSZPKa2b1jtOKLGpWrcrn8cNqt0iVQyroF 606 If the push service identifies an outstanding push message with a 607 topic of "upd", then that message resource is deleted. A 201 608 (Created) response indicates that the push message replacement was 609 accepted. A URI for the new push message resource that was created 610 in response to the request is included in the Location header field. 612 HTTP/1.1 201 Created 613 Date: Thu, 11 Dec 2014 23:57:02 GMT 614 Location: https://push.example.net/message/qDIYHNcfAIPP_5ITvURr-d6BGt 616 The value of the Topic header field MUST NOT be forwarded to user 617 agents. Its value is neither encrypted nor authenticated. 619 6. Receiving Push Messages for a Subscription 621 A user agent requests the delivery of new push messages by making a 622 GET request to a push message subscription resource. The push 623 service does not respond to this request, it instead uses HTTP/2 624 server push [RFC7540] to send the contents of push messages as they 625 are sent by application servers. 627 A user agent MAY include a Urgency header field in its request. The 628 push service MUST NOT deliver messages with lower urgency than the 629 value of the header field as defined in the Table of Urgency Values. 631 Each push message is pushed as the response to a synthesized GET 632 request sent in a PUSH_PROMISE. This GET request is made to the push 633 message resource that was created by the push service when the 634 application server requested message delivery. The response headers 635 SHOULD provide a URI for the push resource corresponding to the push 636 message subscription in a link relation of type 637 "urn:ietf:params:push". The response body is the entity body from 638 the most recent request sent to the push resource by the application 639 server. 641 The following example request is made over HTTP/2. 643 HEADERS [stream 7] +END_STREAM +END_HEADERS 644 :method = GET 645 :path = /subscription/LBhhw0OohO-Wl4Oi971UG 646 :authority = push.example.net 648 The push service permits the request to remain outstanding. When a 649 push message is sent by an application server, a server push is 650 generated in association with the initial request. The response for 651 the server push includes the push message. 653 PUSH_PROMISE [stream 7; promised stream 4] +END_HEADERS 654 :method = GET 655 :path = /message/qDIYHNcfAIPP_5ITvURr-d6BGt 656 :authority = push.example.net 658 HEADERS [stream 4] +END_HEADERS 659 :status = 200 660 date = Thu, 11 Dec 2014 23:56:56 GMT 661 last-modified = Thu, 11 Dec 2014 23:56:55 GMT 662 cache-control = private 663 :link = ; 664 rel="urn:ietf:params:push" 665 content-type = text/plain;charset=utf8 666 content-length = 36 668 DATA [stream 4] +END_STREAM 669 iChYuI3jMzt3ir20P8r_jgRR-dSuN182x7iB 671 HEADERS [stream 7] +END_STREAM +END_HEADERS 672 :status = 200 674 A user agent can also request the contents of the push message 675 subscription resource immediately by including a Prefer header field 676 [RFC7240] with a "wait" preference set to "0". In response to this 677 request, the push service MUST generate a server push for all push 678 messages that have not yet been delivered. 680 A 204 (No Content) status code with no associated server pushes 681 indicates that no messages are presently available. This could be 682 because push messages have expired. 684 6.1. Receiving Push Messages for a Subscription Set 686 There are minor differences between receiving push messages for a 687 subscription and a subscripion set. If a subscription set is 688 available, the user agent SHOULD use the subscription set to monitor 689 for push messages rather than individual push message subscriptions. 691 A user agent requests the delivery of new push messages for a 692 collection of push message subscriptions by making a GET request to a 693 push message subscription set resource. The push service does not 694 respond to this request, it instead uses HTTP/2 server push [RFC7540] 695 to send the contents of push messages as they are sent by application 696 servers. 698 A user agent MAY include a Urgency header field in its request. The 699 push service MUST NOT deliver messages with lower urgency than the 700 value of the header field as defined in the Table of Urgency Values. 702 Each push message is pushed as the response to a synthesized GET 703 request sent in a PUSH_PROMISE. This GET request is made to the push 704 message resource that was created by the push service when the 705 application server requested message delivery. The synthetic request 706 MUST provide a URI for the push resource corresponding to the push 707 message subscription in a link relation of type 708 "urn:ietf:params:push". This enables the user agent to differentiate 709 the source of the message. The response body is the entity body from 710 the most recent request sent to the push resource by an application 711 server. 713 The following example request is made over HTTP/2. 715 HEADERS [stream 7] +END_STREAM +END_HEADERS 716 :method = GET 717 :path = /subscription-set/4UXwi2Rd7jGS7gp5cuutF8ZldnEuvbOy 718 :authority = push.example.net 720 The push service permits the request to remain outstanding. When a 721 push message is sent by an application server, a server push is 722 generated in association with the initial request. The server push's 723 response includes the push message. 725 PUSH_PROMISE [stream 7; promised stream 4] +END_HEADERS 726 :method = GET 727 :path = /message/qDIYHNcfAIPP_5ITvURr-d6BGt 728 :authority = push.example.net 729 :link = ; 730 rel="urn:ietf:params:push" 732 HEADERS [stream 4] +END_HEADERS 733 :status = 200 734 date = Thu, 11 Dec 2014 23:56:56 GMT 735 last-modified = Thu, 11 Dec 2014 23:56:55 GMT 736 cache-control = private 737 content-type = text/plain;charset=utf8 738 content-length = 36 740 DATA [stream 4] +END_STREAM 741 iChYuI3jMzt3ir20P8r_jgRR-dSuN182x7iB 743 HEADERS [stream 7] +END_STREAM +END_HEADERS 744 :status = 200 746 A user agent can request the contents of the push message 747 subscription set resource immediately by including a Prefer header 748 field [RFC7240] with a "wait" preference set to "0". In response to 749 this request, the push service MUST generate a server push for all 750 push messages that have not yet been delivered. 752 A 204 (No Content) status code with no associated server pushes 753 indicates that no messages are presently available. This could be 754 because push messages have expired. 756 6.2. Acknowledging Push Messages 758 To ensure that a push message is properly delivered to the user agent 759 at least once, the user agent MUST acknowledge receipt of the message 760 by performing a HTTP DELETE on the push message resource. 762 DELETE /message/qDIYHNcfAIPP_5ITvURr-d6BGt HTTP/1.1 763 Host: push.example.net 764 If the push service receives the acknowledgement and the application 765 has requested a delivery receipt, the push service MUST return a 204 766 (No Content) response to the application server monitoring the 767 receipt subscription. 769 If the push service does not receive the acknowledgement within a 770 reasonable amount of time, then the message is considered to be not 771 yet delivered. The push service SHOULD continue to retry delivery of 772 the message until its advertised expiration. 774 The push service MAY cease to retry delivery of the message prior to 775 its advertised expiration due to scenarios such as an unresponsive 776 user agent or operational constraints. If the application has 777 requested a delivery receipt, then the push service MUST return a 410 778 (Gone) response to the application server monitoring the receipt 779 subscription. 781 6.3. Receiving Push Message Receipts 783 The application server requests the delivery of receipts from the 784 push service by making a HTTP GET request to the receipt subscription 785 resource. The push service does not respond to this request, it 786 instead uses HTTP/2 server push [RFC7540] to send push receipts when 787 messages are acknowledged (Section 6.2) by the user agent. 789 Each receipt is pushed as the response to a synthesized GET request 790 sent in a PUSH_PROMISE. This GET request is made to the same push 791 message resource that was created by the push service when the 792 application server requested message delivery. The response includes 793 a status code indicating the result of the message delivery and 794 carries no data. 796 The following example request is made over HTTP/2. 798 HEADERS [stream 13] +END_STREAM +END_HEADERS 799 :method = GET 800 :path = /receipt-subscription/3ZtI4YVNBnUUZhuoChl6omUvG4ZM 801 :authority = push.example.net 803 The push service permits the request to remain outstanding. When the 804 user agent acknowledges the message, the push service pushes a 805 delivery receipt to the application server. A 204 (No Content) 806 status code confirms that the message was delivered and acknowledged. 808 PUSH_PROMISE [stream 13; promised stream 82] +END_HEADERS 809 :method = GET 810 :path = /message/qDIYHNcfAIPP_5ITvURr-d6BGt 811 :authority = push.example.net 813 HEADERS [stream 82] +END_STREAM 814 +END_HEADERS 815 :status = 204 816 date = Thu, 11 Dec 2014 23:56:56 GMT 818 If the user agent fails to acknowledge the receipt of the push 819 message and the push service ceases to retry delivery of the message 820 prior to its advertised expiration, then the push service MUST push a 821 failure response with a status code of 410 (Gone). 823 7. Operational Considerations 825 7.1. Load Management 827 A push service is likely to have to maintain a very large number of 828 open TCP connections. Effective management of those connections can 829 depend on being able to move connections between server instances. 831 A user agent MUST support the 307 (Temporary Redirect) status code 832 [RFC7231], which can be used by a push service to redistribute load 833 at the time that a new subscription is requested. 835 A server that wishes to redistribute load can do so using HTTP 836 alternative services [RFC7838]. HTTP alternative services allows for 837 redistribution of load while maintaining the same URIs for various 838 resources. A user agent can ensure a graceful transition by using 839 the GOAWAY frame once it has established a replacement connection. 841 7.2. Push Message Expiration 843 Storage of push messages based on the TTL header field comprises a 844 potentially significant amount of storage for a push service. A push 845 service is not obligated to store messages indefinitely. A push 846 service is able to indicate how long it intends to retain a message 847 to an application server using the TTL header field (Section 5.2). 849 A user agent that does not actively monitor for push messages will 850 not receive messages that expire during that interval. 852 Push messages that are stored and have not been delivered to a user 853 agent are delivered when the user agent recommences monitoring. 854 Stored push messages SHOULD include a Last-Modified header field 855 (Section 2.2 of [RFC7232]) indicating when delivery was requested by 856 an application server. 858 A GET request to a push message subscription resource with only 859 expired messages results in a response as though no push message was 860 ever sent. 862 Push services might need to limit the size and number of stored push 863 messages to avoid overloading. To limit the size of messages, the 864 push service MAY return a 413 (Payload Too Large) status code 865 [RFC7231] in response to requests that include an entity body that is 866 too large. Push services MUST NOT return a 413 status code in 867 responses to an entity body that is 4k (4096 bytes) or less in size. 869 To limit the number of stored push messages, the push service MAY 870 either expire messages prior to their advertised Time-To-Live or 871 reduce their advertised Time-To-Live. 873 7.3. Subscription Expiration 875 In some cases, it may be necessary to terminate subscriptions so that 876 they can be refreshed. This applies to both push message 877 subscriptions and receipt subscriptions. 879 A push service MAY expire a subscription at any time. If there are 880 outstanding requests to an expired push message subscription resource 881 (Section 6) from a user agent or to an expired receipt subscription 882 resource (Section 6.3) from an application server, this MUST be 883 signaled by returning a 404 (Not Found) status code. 885 A push service MUST return a 404 (Not Found) status code if an 886 application server attempts to send a push message to an expired push 887 message subscription. 889 A user agent can remove its push message subscription by sending a 890 DELETE request to the corresponding URI. An application server can 891 remove its receipt subscription by sending a DELETE request to the 892 corresponding URI. 894 7.3.1. Subscription Set Expiration 896 A push service MAY expire a subscription set at any time and MUST 897 also expire all push message subscriptions in the set. If a user 898 agent has an outstanding request to a push subscription set 899 (Section 6.1) this MUST be signaled by returning a 404 (Not Found) 900 status code. 902 A user agent can request that a subscription set be removed by 903 sending a DELETE request to the subscription set URI. This MUST also 904 remove all push message subscriptions in the set. 906 If a specific push message subscription that is a member of a 907 subscription set is expired or removed, then it MUST also be removed 908 from its subscription set. 910 7.4. Implications for Application Reliability 912 A push service that does not support reliable delivery over 913 intermittent network connections or failing applications on devices, 914 forces the device to acknowledge receipt directly to the application 915 server, incurring additional power drain in order to establish 916 (usually secure) connections to the individual application servers. 918 Push message reliability can be important if messages contain 919 information critical to the state of an application. Repairing state 920 can be expensive, particularly for devices with limited 921 communications capacity. Knowing that a push message has been 922 correctly received avoids retransmissions, polling, and state 923 resynchronization. 925 The availability of push message delivery receipts ensures that the 926 application developer is not tempted to create alternative mechanisms 927 for message delivery in case the push service fails to deliver a 928 critical message. Setting up a polling mechanism or a backup 929 messaging channel in order to compensate for these shortcomings 930 negates almost all of the advantages a push service provides. 932 However, reliability might not be necessary for messages that are 933 transient (e.g. an incoming call) or messages that are quickly 934 superceded (e.g. the current number of unread emails). 936 7.5. Subscription Sets and Concurrent HTTP/2 streams 938 If the push service requires that the user agent use push message 939 subscription sets, then it MAY limit the number of concurrently 940 active streams with the SETTINGS_MAX_CONCURRENT_STREAMS parameter 941 within a HTTP/2 SETTINGS frame [RFC7540]. The user agent MAY be 942 limited to one concurrent stream to manage push message subscriptions 943 and one concurrent stream for each subscription set returned by the 944 push service. This could force the user agent to serialize 945 subscription requests to the push service. 947 8. Security Considerations 949 This protocol MUST use HTTP over TLS [RFC2818]. This includes any 950 communications between user agent and push service, plus 951 communications between the application and the push service. All 952 URIs therefore use the "https" scheme. This provides confidentiality 953 and integrity protection for subscriptions and push messages from 954 external parties. 956 Applications using this protocol MUST use mechanisms that provide 957 confidentiality, integrity and data origin authentication. The 958 application server sending the push message and the application on 959 the user agent that receives it are frequently just different 960 instances of the same application, so no standardized protocol is 961 needed to establish a proper security context. The distribution of 962 subscription information from the user agent to its application 963 server also offers a convenient medium for key agreement. 965 8.1. Confidentiality from Push Service Access 967 The protection afforded by TLS does not protect content from the push 968 service. Without additional safeguards, a push service can inspect 969 and modify the message content. 971 For its requirements, the W3C Push API [API] has adopted Message 972 Encryption for WebPush [I-D.ietf-webpush-encryption] to secure the 973 content of messages from the push service. Other scenarios can be 974 addressed by similar policies. 976 The Topic header field exposes information that allows more granular 977 correlation of push messages on the same subject. This might be used 978 to aid traffic analysis of push messages by the push service. 980 8.2. Privacy Considerations 982 Push message confidentiality does not ensure that the identity of who 983 is communicating and when they are communicating is protected. 984 However, the amount of information that is exposed can be limited. 986 The URIs provided for push resources MUST NOT provide any basis to 987 correlate communications for a given user agent. It MUST NOT be 988 possible to correlate any two push resource URIs based solely on 989 their contents. This allows a user agent to control correlation 990 across different applications, or over time. 992 Similarly, the URIs provided by the push service to identify a push 993 message MUST NOT provide any information that allows for correlation 994 across subscriptions. Push message URIs for the same subscription 995 MAY contain information that would allow correlation with the 996 associated subscription or other push messages for that subscription. 998 User and device information MUST NOT be exposed through a push or 999 push message URI. 1001 In addition, push URIs established by the same user agent or push 1002 message URIs for the same subscription MUST NOT include any 1003 information that allows them to be correlated with the user agent. 1005 Note: This need not be perfect as long as the resulting anonymity 1006 set ([RFC6973], Section 6.1.1) is sufficiently large. A push URI 1007 necessarily identifies a push service or a single server instance. 1008 It is also possible that traffic analysis could be used to 1009 correlate subscriptions. 1011 A user agent MUST be able to create new subscriptions with new 1012 identifiers at any time. 1014 8.3. Authorization 1016 This protocol does not define how a push service establishes whether 1017 a user agent is permitted to create a subscription, or whether push 1018 messages can be delivered to the user agent. A push service MAY 1019 choose to authorize requests based on any HTTP-compatible 1020 authorization method available, of which there are numerous options. 1021 The authorization process and any associated credentials are expected 1022 to be configured in the user agent along with the URI for the push 1023 service. 1025 Authorization is managed using capability URLs for the push message 1026 subscription, push, and receipt subscription resources ([CAP-URI]). 1027 A capability URL grants access to a resource based solely on 1028 knowledge of the URL. 1030 Capability URLs are used for their "easy onward sharing" and "easy 1031 client API" properties. These make it possible to avoid relying on 1032 relationships between push services and application servers, with the 1033 protocols necessary to build and support those relationships. 1035 Capability URLs act as bearer tokens. Knowledge of a push message 1036 subscription URI implies authorization to either receive push 1037 messages or delete the subscription. Knowledge of a push URI implies 1038 authorization to send push messages. Knowledge of a push message URI 1039 allows for reading and acknowledging that specific message. 1040 Knowledge of a receipt subscription URI implies authorization to 1041 receive push receipts. 1043 Encoding a large amount of random entropy (at least 120 bits) in the 1044 path component ensures that it is difficult to successfully guess a 1045 valid capability URL. 1047 8.4. Denial of Service Considerations 1049 A user agent can control where valid push messages originate by 1050 limiting the distribution of push URIs to authorized application 1051 servers. Ensuring that push URIs are hard to guess ensures that only 1052 application servers that have received a push URI can use it. 1054 Push messages that are not successfully authenticated by the user 1055 agent will not be delivered, but this can present a denial of service 1056 risk. Even a relatively small volume of push messages can cause 1057 battery-powered devices to exhaust power reserves. 1059 To address this case, the W3C Push API [API] has adopted Voluntary 1060 Application Server Identification [I-D.ietf-webpush-vapid], which 1061 allows a user agent to restrict a subscription to a specific 1062 application server. The push service can then identity and reject 1063 unwanted messages without contacting the user agent. 1065 A malicious application with a valid push URI could use the greater 1066 resources of a push service to mount a denial of service attack on a 1067 user agent. Push services SHOULD limit the rate at which push 1068 messages are sent to individual user agents. 1070 A push service MAY return a 429 (Too Many Requests) status code 1071 [RFC6585] when an application server has exceeded its rate limit for 1072 push message delivery to a push resource. The push service SHOULD 1073 also include a Retry-After header [RFC7231] to indicate how long the 1074 application server is requested to wait before it makes another 1075 request to the push resource. 1077 A push service or user agent MAY also terminate subscriptions 1078 (Section 7.3) that receive too many push messages. 1080 A push service is also able to deny service to user agents. 1081 Intentional failure to deliver messages is difficult to distinguish 1082 from faults, which might occur due to transient network errors, 1083 interruptions in user agent availability, or genuine service outages. 1085 8.5. Logging Risks 1087 Server request logs can reveal subscription-related URIs or 1088 relationships between subscription-related URIs for the same user 1089 agent. Limitations on log retention and strong access control 1090 mechanisms can ensure that URIs are not revealed to unauthorized 1091 entities. 1093 9. IANA Considerations 1095 This protocol defines new HTTP header fields in Section 9.1. New 1096 link relation types are identified using the URNs defined in 1097 Section 9.2. Port registration is defined in Section 9.3 1099 9.1. Header Field Registrations 1101 HTTP header fields are registered within the "Message Headers" 1102 registry maintained at . 1105 This document defines the following HTTP header fields, so their 1106 associated registry entries shall be added according to the permanent 1107 registrations below ([RFC3864]): 1109 +-------------------+----------+----------+--------------+ 1110 | Header Field Name | Protocol | Status | Reference | 1111 +-------------------+----------+----------+--------------+ 1112 | TTL | http | standard | Section 5.2 | 1113 | Urgency | http | standard | Section 5.3 | 1114 | Topic | http | standard | Section 5.4 | 1115 +-------------------+----------+----------+--------------+ 1117 The change controller is: "IETF (iesg@ietf.org) - Internet 1118 Engineering Task Force". 1120 9.2. Link Relation URNs 1122 This document registers URNs for use in identifying link relation 1123 types. These are added to a new "Web Push Identifiers" registry 1124 according to the procedures in Section 4 of [RFC3553]; the 1125 corresponding "push" sub-namespace is entered in the "IETF URN Sub- 1126 namespace for Registered Protocol Parameter Identifiers" registry. 1128 The "Web Push Identifiers" registry operates under the IETF Review 1129 policy [RFC5226]. 1131 Registry name: Web Push Identifiers 1132 URN Prefix: urn:ietf:params:push 1134 Specification: (this document) 1136 Repository: [Editor/IANA note: please include a link to the final 1137 registry location.] 1139 Index value: Values in this registry are URNs or URN prefixes that 1140 start with the prefix "urn:ietf:params:push". Each is registered 1141 independently. 1143 New registrations in the "Web Push Identifiers" are encouraged to 1144 include the following information: 1146 URN: A complete URN or URN prefix. 1148 Description: A summary description. 1150 Specification: A reference to a specification describing the 1151 semantics of the URN or URN prefix. 1153 Contact: Email for the person or group making the registration. 1155 Index value: As described in [RFC3553], URN prefixes that are 1156 registered include a description of how the URN is constructed. 1157 This is not applicable for specific URNs. 1159 These values are entered as the initial content of the "Web Push 1160 Identifiers" registry. 1162 URN: urn:ietf:params:push 1164 Description: This link relation type is used to identify a resource 1165 for sending push messages. 1167 Specification: (this document) 1169 Contact: The Web Push WG (webpush@ietf.org) 1171 URN: urn:ietf:params:push:set 1173 Description: This link relation type is used to identify a 1174 collection of push message subscriptions. 1176 Specification: (this document) 1178 Contact: The Web Push WG (webpush@ietf.org) 1179 URN: urn:ietf:params:push:receipt 1181 Description: This link relation type is used to identify a resource 1182 for receiving delivery confirmations for push messages. 1184 Specification: (this document) 1186 Contact: The Web Push WG (webpush@ietf.org) 1188 9.3. Service Name and Port Number Registration 1190 Service names and port numbers are registered within the "Service 1191 Name and Transport Protocol Port Number Registry" maintained at 1192 . 1195 IANA is requested to assign the System Port number 1001 and the 1196 service name "webpush" in accordance with [RFC6335]. 1198 Service Name. 1199 webpush 1201 Transport Protocol. 1202 tcp 1204 Assignee. 1205 IESG (iesg@ietf.org) 1207 Contact. 1208 The Web Push WG (webpush@ietf.org) 1210 Description. 1211 HTTP Web Push 1213 Reference. 1214 [RFCthis] 1216 Port Number. 1217 1001 1219 10. Acknowledgements 1221 Significant technical input to this document has been provided by Ben 1222 Bangert, Peter Beverloo, Kit Cambridge, JR Conlin, Matthew Kaufman, 1223 Costin Manolache, Mark Nottingham, Idel Pivnitskiy, Robert Sparks, 1224 Darshak Thakore and many others. 1226 11. References 1228 11.1. Normative References 1230 [CAP-URI] Tennison, J., "Good Practices for Capability URLs", FPWD 1231 capability-urls, February 2014, 1232 . 1234 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1235 Requirement Levels", BCP 14, RFC 2119, March 1997. 1237 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 1239 [RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An 1240 IETF URN Sub-namespace for Registered Protocol 1241 Parameters", BCP 73, RFC 3553, June 2003. 1243 [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration 1244 Procedures for Message Header Fields", BCP 90, RFC 3864, 1245 September 2004. 1247 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 1248 Encodings", RFC 4648, October 2006. 1250 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1251 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1252 May 2008. 1254 [RFC5382] Biswas, K., Ford, B., Sivakumar, S., and P. Srisuresh, 1255 "NAT Behavioral Requirements for TCP", RFC 5382, October 1256 2008. 1258 [RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010. 1260 [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. 1261 Cheshire, "Internet Assigned Numbers Authority (IANA) 1262 Procedures for the Management of the Service Name and 1263 Transport Protocol Port Number Registry", RFC 6335, August 1264 2011. 1266 [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, December 1267 2011. 1269 [RFC6585] Nottingham, M. and R. Fielding, "Additional HTTP Status 1270 Codes", RFC 6585, April 2012. 1272 [RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol 1273 (HTTP/1.1): Message Syntax and Routing", RFC 7230, June 1274 2014. 1276 [RFC7231] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol 1277 (HTTP/1.1): Semantics and Content", RFC 7231, June 2014. 1279 [RFC7232] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol 1280 (HTTP/1.1): Conditional Requests", RFC 7232, June 2014. 1282 [RFC7240] Snell, J., "Prefer Header for HTTP", RFC 7240, June 2014. 1284 [RFC7540] Belshe, M., Peon, R., and M. Thomson, "Hypertext Transfer 1285 Protocol Version 2", RFC 7540, May 2015. 1287 [RFC7838] Nottingham, M., McManus, P., and J. Reschke, "HTTP 1288 Alternative Services", RFC 7838, April 2016. 1290 11.2. Informative References 1292 [API] van Ouwerkerk, M., Thomson, M., Sullivan, B., and E. 1293 Fullea, "W3C Push API", ED push-api, January 2016, 1294 . 1296 [I-D.ietf-webpush-encryption] 1297 Thomson, M., "Message Encryption for Web Push", draft- 1298 ietf-webpush-encryption-02 (work in progress), March 2016, 1299 . 1302 [I-D.ietf-webpush-vapid] 1303 Thomson, M. and P. Beverloo, "Voluntary Application Server 1304 Identification for Web Push", draft-ietf-webpush-vapid-00 1305 (work in progress), April 2016, 1306 . 1309 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 1310 Morris, J., Hansen, M., and R. Smith, "Privacy 1311 Considerations for Internet Protocols", RFC 6973, July 1312 2013. 1314 Appendix A. Change Log 1316 [[The RFC Editor is requested to remove this section at 1317 publication.]] 1319 A.1. Since draft-ietf-webpush-protocol-00 1321 Editorial changes for Push Message Time-To-Live 1323 Editorial changes for Push Acknowledgements 1325 Removed subscription expiration based on HTTP cache headers 1327 A.2. Since draft-ietf-webpush-protocol-01 1329 Added Subscription Sets 1331 Added System Port as an alternate service with guidance for idle 1332 timeouts 1334 Finalized status codes for acknowledgements 1336 Editorial changes for Rate Limits 1338 A.3. Since draft-ietf-webpush-protocol-02 1340 Added explicit correlation for Subscription Sets 1342 Added Push Message Updates (message collapsing) 1344 Renamed the push:receipt link relation to push:receipts and 1345 transitioned the Push-Receipt header field to the push:receipt link 1346 relation type 1348 A.4. Since draft-ietf-webpush-protocol-03 1350 An application server MUST include the TTL (Time-To-Live) header 1351 field in its request for push message delivery. 1353 Added Push Message Urgency header field 1355 A.5. Since draft-ietf-webpush-protocol-04 1357 Simplified design for Push Receipts and eliminated the 1358 urn:ietf:params:push:receipts link relation 1360 Clarified Security Considerations section and added informative 1361 references to Message Encryption and Voluntary Application Server 1362 Identification 1364 A.6. Since draft-ietf-webpush-protocol-05 1366 Addressed feedback from Working Group Last Call 1368 Authors' Addresses 1370 Martin Thomson 1371 Mozilla 1372 331 E Evelyn Street 1373 Mountain View, CA 94041 1374 US 1376 Email: martin.thomson@gmail.com 1378 Elio Damaggio 1379 Microsoft 1380 One Microsoft Way 1381 Redmond, WA 98052 1382 US 1384 Email: elioda@microsoft.com 1386 Brian Raymor (editor) 1387 Microsoft 1388 One Microsoft Way 1389 Redmond, WA 98052 1390 US 1392 Email: brian.raymor@microsoft.com