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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 CoRE Working Group A. Castellani 3 Internet-Draft University of Padova 4 Intended status: Informational S. Loreto 5 Expires: April 28, 2017 Ericsson 6 A. Rahman 7 InterDigital Communications, LLC 8 T. Fossati 9 Nokia 10 E. Dijk 11 Philips Lighting 12 October 25, 2016 14 Guidelines for HTTP-to-CoAP Mapping Implementations 15 draft-ietf-core-http-mapping-16 17 Abstract 19 This document provides reference information for implementing a 20 cross-protocol network proxy that performs translation from the HTTP 21 protocol to CoAP (Constrained Application Protocol). This will 22 enable a HTTP client to access resources on a CoAP server through the 23 proxy. This document describes how a HTTP request is mapped to a 24 CoAP request, and then how a CoAP response is mapped back to a HTTP 25 response. This includes guidelines for status code, URI, and media 26 type mappings, as well as additional interworking advice. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at http://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on April 28, 2017. 45 Copyright Notice 47 Copyright (c) 2016 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (http://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 3. HTTP-to-CoAP Proxy . . . . . . . . . . . . . . . . . . . . . 5 65 4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 6 66 5. URI Mapping . . . . . . . . . . . . . . . . . . . . . . . . . 7 67 5.1. URI Terminology . . . . . . . . . . . . . . . . . . . . . 8 68 5.2. Null Mapping . . . . . . . . . . . . . . . . . . . . . . 8 69 5.3. Default Mapping . . . . . . . . . . . . . . . . . . . . . 8 70 5.3.1. Optional Scheme Omission . . . . . . . . . . . . . . 9 71 5.3.2. Encoding Caveats . . . . . . . . . . . . . . . . . . 9 72 5.4. URI Mapping Template . . . . . . . . . . . . . . . . . . 10 73 5.4.1. Simple Form . . . . . . . . . . . . . . . . . . . . . 10 74 5.4.2. Enhanced Form . . . . . . . . . . . . . . . . . . . . 11 75 5.5. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 13 76 5.5.1. Examples . . . . . . . . . . . . . . . . . . . . . . 13 77 6. Media Type Mapping . . . . . . . . . . . . . . . . . . . . . 15 78 6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 15 79 6.2. 'application/coap-payload' Media Type . . . . . . . . . . 16 80 6.3. Loose Media Type Mapping . . . . . . . . . . . . . . . . 17 81 6.4. Media Type to Content Format Mapping Algorithm . . . . . 18 82 6.5. Content Transcoding . . . . . . . . . . . . . . . . . . . 19 83 6.5.1. General . . . . . . . . . . . . . . . . . . . . . . . 19 84 6.5.2. CoRE Link Format . . . . . . . . . . . . . . . . . . 20 85 6.5.3. Diagnostic Messages . . . . . . . . . . . . . . . . . 21 86 7. Response Code Mapping . . . . . . . . . . . . . . . . . . . . 21 87 8. Additional Mapping Guidelines . . . . . . . . . . . . . . . . 24 88 8.1. Caching and Congestion Control . . . . . . . . . . . . . 24 89 8.2. Cache Refresh via Observe . . . . . . . . . . . . . . . . 24 90 8.3. Use of CoAP Blockwise Transfer . . . . . . . . . . . . . 25 91 8.4. CoAP Multicast . . . . . . . . . . . . . . . . . . . . . 26 92 8.5. Timeouts . . . . . . . . . . . . . . . . . . . . . . . . 26 94 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 95 9.1. New 'core.hc' Resource Type . . . . . . . . . . . . . . . 27 96 9.2. New 'coap-payload' Internet Media Type . . . . . . . . . 27 97 10. Security Considerations . . . . . . . . . . . . . . . . . . . 28 98 10.1. Multicast . . . . . . . . . . . . . . . . . . . . . . . 29 99 10.2. Traffic Overflow . . . . . . . . . . . . . . . . . . . . 29 100 10.3. Handling Secured Exchanges . . . . . . . . . . . . . . . 30 101 10.4. URI Mapping . . . . . . . . . . . . . . . . . . . . . . 30 102 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 31 103 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 104 12.1. Normative References . . . . . . . . . . . . . . . . . . 31 105 12.2. Informative References . . . . . . . . . . . . . . . . . 33 106 Appendix A. Media Type Mapping Source Code . . . . . . . . . . . 34 107 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 38 108 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42 110 1. Introduction 112 CoAP (Constrained Application Protocol) [RFC7252] has been designed 113 with the twofold aim to be an application protocol specialized for 114 constrained environments and to be easily used in Representational 115 State Transfer (REST) [REST] based architectures such as the Web. 116 The latter goal has led to defining CoAP to easily interoperate with 117 HTTP [RFC7230] through an intermediary proxy which performs cross- 118 protocol conversion. 120 Section 10 of [RFC7252] describes the fundamentals of the CoAP-to- 121 HTTP and the HTTP-to-CoAP cross-protocol mapping process. However, 122 [RFC7252] focuses on the basic mapping of request methods and simple 123 response code mapping between HTTP and CoAP, while leaving many 124 details of the cross-protocol proxy for future definition. 125 Therefore, a primary goal of this informational document is to define 126 a consistent set of guidelines that an HTTP-to-CoAP proxy 127 implementation should adhere to. The key benefit to adhering to such 128 guidelines is to reduce variation between proxy implementations, 129 thereby increasing interoperability between an HTTP client and a CoAP 130 server independent of the proxy that implements the cross-protocol 131 mapping. (For example, a proxy conforming to these guidelines made 132 by vendor A can be easily replaced by a proxy from vendor B that also 133 conforms to the guidelines.) 135 This document describes HTTP mappings that apply to protocol elements 136 defined in the base CoAP specification [RFC7252]. It is up to CoAP 137 protocol extensions (new methods, response codes, options, content- 138 formats) to describe their own HTTP mappings, if applicable. 140 This document is organized as follows: 142 o Section 2 defines proxy terminology; 144 o Section 3 introduces the HTTP-to-CoAP proxy; 146 o Section 4 lists use cases in which HTTP clients need to contact 147 CoAP servers; 149 o Section 5 introduces a null, default and advanced HTTP-to-CoAP URI 150 mapping syntax; 152 o Section 6 describes how to map HTTP media types to CoAP content 153 formats and vice versa; 155 o Section 7 describes how to map CoAP responses to HTTP responses; 157 o Section 8 describes additional mapping guidelines related to 158 caching, congestion, timeouts, etc.; 160 o Section 10 discusses possible security impact of HTTP-to-CoAP 161 protocol mapping. 163 2. Terminology 165 The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 166 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 167 "OPTIONAL" in this document are to be interpreted as described in 168 [RFC2119]. 170 This specification requires readers to be familiar with the 171 vocabulary and concepts discussed in [RFC7228], in particular the 172 terms "Constrained Nodes" and "Constrained Networks". In addition, 173 this specification makes use of the following terms: 175 HC Proxy 176 A proxy performing a cross-protocol mapping, in the context of 177 this document an HTTP-to-CoAP (HC) mapping. Specifically, the HC 178 proxy acts as an HTTP server and a CoAP client. The HC Proxy can 179 take on the role of a Forward, Reverse or Interception Proxy. 181 Forward Proxy (or Forward HC Proxy) 182 A message forwarding agent that is selected by the HTTP client, 183 usually via local configuration rules, to receive requests for 184 some type(s) of absolute URI and to attempt to satisfy those 185 requests via translation to the protocol indicated by the 186 absolute URI. The user decides (is willing) to use the proxy as 187 the forwarding/de-referencing agent for a predefined subset of 188 the URI space. In [RFC7230] this is called a Proxy. [RFC7252] 189 defines Forward-Proxy similarly. 191 Reverse Proxy (or Reverse HC Proxy) 192 As in [RFC7230], a receiving agent that acts as a layer above 193 some other server(s) and translates the received requests to the 194 underlying server's protocol. A Reverse HC Proxy behaves as an 195 origin (HTTP) server on its connection from the HTTP client. The 196 HTTP client uses the "origin-form" (Section 5.3.1 of [RFC7230]) 197 as a request-target URI. (Note that a Reverse Proxy appears to 198 an HTTP client as an origin server while a Forward Proxy does 199 not. So, when communicating with a Reverse Proxy a client may be 200 unaware it is communicating with a proxy at all.) 202 Interception Proxy (or Interception HC Proxy) 203 As in [RFC3040], a proxy that receives inbound HTTP traffic flows 204 through the process of traffic redirection; transparent to the 205 HTTP client. 207 3. HTTP-to-CoAP Proxy 209 A HC proxy is accessed by an HTTP client that needs to access a 210 resource on a CoAP server. The HC proxy handles the HTTP request by 211 mapping it to the equivalent CoAP request, which is then forwarded to 212 the appropriate CoAP server. The received CoAP response is then 213 mapped to an appropriate HTTP response and finally sent back to the 214 originating HTTP client. 216 See Figure 1 for an example deployment scenario. Here a HC proxy is 217 located at the boundary of the Constrained Network domain, to avoid 218 sending any HTTP traffic into the Constrained Network and to avoid 219 any CoAP multicast traffic outside the Constrained Network. A DNS 220 server (not shown) is used by the HTTP Client to resolve the IP 221 address of the HC proxy and optionally also used by the HC proxy to 222 resolve IP addresses of CoAP servers. 224 Constrained Network 225 .-------------------. 226 / .------. \ 227 / | CoAP | \ 228 / |server| \ 229 || '------' || 230 || || 231 .--------. HTTP Request .------------. CoAP Req .------. || 232 | HTTP |---------------->|HTTP-to-CoAP|----------->| CoAP | || 233 | Client |<----------------| Proxy |<-----------|Server| || 234 '--------' HTTP Response '------------' CoAP Resp '------' || 235 || || 236 || .------. || 237 || | CoAP | || 238 \ |server| .------. / 239 \ '------' | CoAP | / 240 \ |server| / 241 \ '------' / 242 '-----------------' 244 Figure 1: HTTP-To-CoAP Proxy Deployment Scenario 246 Normative requirements on the translation of HTTP requests to CoAP 247 requests and of the CoAP responses back to HTTP responses are defined 248 in Section 10.2 of [RFC7252]. However, [RFC7252] focuses on the 249 basic mapping of request methods and simple response code mapping 250 between HTTP and CoAP, and leaves many details of the cross-protocol 251 HC proxy for future definition. This document provides additional 252 guidelines and more details for the implementation of a HC Proxy, 253 which should be followed in addition to the normative requirements. 254 Note that the guidelines apply to all forms of an HC proxy (i.e., 255 Reverse, Forward, Intercepting) unless explicitly otherwise noted. 257 4. Use Cases 259 To illustrate a few situations in which HTTP to CoAP protocol 260 translation may be used, three use cases are described below. 262 1. Legacy building control application without CoAP: A building 263 control application that uses HTTP but not CoAP can check the 264 status of CoAP sensors and/or control actuators via a HC proxy. 266 2. Making sensor data available to 3rd parties on the Web: For 267 demonstration or public interest purposes, a HC proxy may be 268 configured to expose the contents of a CoAP sensor to the world 269 via the web (HTTP and/or HTTPS). Some sensors may only accept 270 secure 'coaps' requests, therefore the proxy is configured to 271 translate requests to those devices accordingly. The HC proxy is 272 furthermore configured to only pass through GET requests in order 273 to protect the constrained network. 275 3. Smartphone and home sensor: A smartphone can access directly a 276 CoAP home sensor using a mutually authenticated 'https' request, 277 provided its home router runs a HC proxy and is configured with 278 the appropriate certificate. An HTML5 [W3C.REC-html5-20141028] 279 application on the smartphone can provide a friendly UI using the 280 standard (HTTP) networking functions of HTML5. 282 A key point in the above use cases is the expected nature of the URI 283 to be used by the HTTP client initiating the HTTP request to the HC 284 proxy. Specifically, in use case #1, there will be no 'coap' or 285 'coaps' related information embedded in the HTTP URI as it is a 286 legacy HTTP client sending the request. Use case #2 is also expected 287 to be similar. In contrast, in use case #3, it is likely that the 288 HTTP client will specifically embed 'coap' or 'coaps' related 289 information in the HTTP URI of the HTTP request to the HC proxy. 291 5. URI Mapping 293 Though, in principle, a CoAP URI could be directly used by a HTTP 294 client to de-reference a CoAP resource through a HC proxy, the 295 reality is that all major web browsers, networking libraries and 296 command line tools do not allow making HTTP requests using URIs with 297 a scheme 'coap' or 'coaps'. 299 Thus, there is a need for web applications to embed or "pack" a CoAP 300 URI into a HTTP URI so that it can be (non-destructively) transported 301 from the HTTP client to the HC proxy. The HC proxy can then "unpack" 302 the CoAP URI and finally de-reference it via a CoAP request to the 303 target Server. 305 URI Mapping is the term used in this document to describe the process 306 through which the URI of a CoAP resource is transformed into an HTTP 307 URI so that: 309 o The requesting HTTP client can handle it; 311 o The receiving HC proxy can extract the intended CoAP URI 312 unambiguously. 314 To this end, the remainder of this section will identify: 316 o The default mechanism to map a CoAP URI into a HTTP URI; 317 o The URI template format to express a class of CoAP-HTTP URI 318 mapping functions; 320 o The discovery mechanism based on CoRE Link Format [RFC6690] 321 through which clients of a HC proxy can dynamically discover 322 information about the supported URI Mapping Template(s), as well 323 as the URI where the HC proxy function is anchored. 325 5.1. URI Terminology 327 In the remainder of this section, the following terms will be used 328 with a distinctive meaning: 330 HC Proxy URI: 331 URI which refers to the HC proxy function. It conforms to 332 syntax defined in Section 2.7 of [RFC7230]. 334 Target CoAP URI: 335 URI which refers to the (final) CoAP resource that has to be 336 de-referenced. It conforms to syntax defined in Section 6 of 337 [RFC7252]. Specifically, its scheme is either 'coap' or 338 'coaps'. 340 Hosting HTTP URI: 341 URI that conforms to syntax in Section 2.7 of [RFC7230]. Its 342 authority component refers to a HC proxy, whereas path (and 343 query) component(s) embed the information used by a HC proxy 344 to extract the Target CoAP URI. 346 5.2. Null Mapping 348 The null mapping is the case where there is no Target CoAP URI 349 appended to the HC Proxy URI. In other words, it is a "pure" HTTP 350 URI that is sent to the HC Proxy. This would typically occur in 351 situations like Use Case #1 described in Section 4, and the Proxy 352 would typically be a Reverse Proxy. In this scenario, the HC Proxy 353 will determine through its own private algorithms what the Target 354 CoAP URI should be. 356 5.3. Default Mapping 358 The default mapping is for the Target CoAP URI to be appended as-is 359 (with the only caveat discussed in Section 5.3.2) to the HC Proxy 360 URI, to form the Hosting HTTP URI. This is the Effective Request URI 361 (see section 5.5 of [RFC7230]) that will then be sent by the HTTP 362 client in the HTTP request to the HC proxy. 364 For example: given a HC Proxy URI https://p.example.com/hc/ and a 365 Target CoAP URI coap://s.example.com/light, the resulting Hosting 366 HTTP URI would be https://p.example.com/hc/coap://s.example.com/ 367 light. 369 Provided a correct Target CoAP URI, the Hosting HTTP URI resulting 370 from the default mapping will be a syntactically valid HTTP URI. 371 Furthermore, the Target CoAP URI can always be extracted 372 unambiguously from the Hosting HTTP URI. 374 There is no default for the HC Proxy URI. Therefore, it is either 375 known in advance, e.g., as a configuration preset, or dynamically 376 discovered using the mechanism described in Section 5.5. 378 The default URI mapping function SHOULD be implemented and SHOULD be 379 activated by default in a HC proxy, unless there are valid reasons, 380 e.g., application specific, to use a different mapping function. 382 5.3.1. Optional Scheme Omission 384 When constructing a Hosting HTTP URI by embedding a Target CoAP URI, 385 the scheme (i.e., 'coap' or 'coaps'), the scheme component delimiter 386 (":"), and the double slash ("//") preceding the authority MAY be 387 omitted if a local default - not defined by this document - applies. 388 If no prior mutual agreement exists between the client and the HC 389 proxy, then a Target CoAP URI without the scheme component is 390 syntactically incorrect, and therefore: 392 o It MUST NOT be emitted by clients; 394 o It MUST elicit a suitable client error status (i.e., 4xx) by the 395 HC proxy. 397 5.3.2. Encoding Caveats 399 When the authority of the Target CoAP URI is given as an IPv6address, 400 then the surrounding square brackets must be percent-encoded in the 401 Hosting HTTP URI, in order to comply with the syntax defined in 402 Section 3.3. of [RFC3986] for a URI path segment. E.g.: 403 coap://[2001:db8::1]/light?on becomes 404 https://p.example.com/hc/coap://%5B2001:db8::1%5D/light?on. (Note 405 that the percent-encoded square brackets shall be reverted to their 406 non-percent-encoded form when the HC proxy unpacks the Target CoAP 407 URI.) 409 Everything else can be safely copied verbatim from the Target CoAP 410 URI to the Hosting HTTP URI. 412 5.4. URI Mapping Template 414 This section defines a format for the URI template [RFC6570] used by 415 a HC proxy to inform its clients about the expected syntax for the 416 Hosting HTTP URI. This will then be used by the HTTP client to 417 construct the Effective Request URI to be sent in the HTTP request to 418 the HC proxy. 420 When instantiated, an URI Mapping Template is always concatenated to 421 a HC Proxy URI provided by the HC proxy via discovery (see 422 Section 5.5), or by other means. 424 A simple form (Section 5.4.1) and an enhanced form (Section 5.4.2) 425 are provided to fit different users' requirements. 427 Both forms are expressed as level 2 URI templates [RFC6570] to take 428 care of the expansion of values that are allowed to include reserved 429 URI characters. The syntax of all URI formats is specified in this 430 section in Augmented Backus-Naur Form (ABNF) [RFC5234]. 432 5.4.1. Simple Form 434 The simple form MUST be used for mappings where the Target CoAP URI 435 is going to be copied (using rules of Section 5.3.2) at some fixed 436 position into the Hosting HTTP URI. 438 The "tu" template variable is intended to be used in a template 439 definition to represent a Target CoAP URI: 441 tu = [ ( "coap:" / "coaps:" ) "//" ] host [ ":" port ] path-abempty 442 [ "?" query ] 444 Note that the same considerations as in Section 5.3.1 apply, in that 445 the CoAP scheme may be omitted from the Hosting HTTP URI. 447 5.4.1.1. Examples 449 All the following examples (given as a specific URI mapping template, 450 a Target CoAP URI, and the produced Hosting HTTP URI) use 451 https://p.example.com/hc/ as the HC Proxy URI. Note that these 452 examples all define mapping templates that deviate from the default 453 template of Section 5.3 to be able to illustrate the use of the above 454 template variables. 456 1. Target CoAP URI is a query argument of the Hosting HTTP URI: 458 ?target_uri={+tu} 460 coap://s.example.com/light 462 => https://p.example.com/hc/?target_uri=coap://s.example.com/light 464 whereas 466 coaps://s.example.com/light 468 => https://p.example.com/hc/?target_uri=coaps://s.example.com/light 470 2. Target CoAP URI in the path component of the Hosting HTTP URI: 472 forward/{+tu} 474 coap://s.example.com/light 476 => https://p.example.com/hc/forward/coap://s.example.com/light 478 whereas 480 coaps://s.example.com/light 482 => https://p.example.com/hc/forward/coaps://s.example.com/light 484 3. 'coap' URI is a query argument of the Hosting HTTP URI; client 485 decides to omit scheme because a default scheme is agreed 486 beforehand between client and proxy: 488 ?coap_uri={+tu} 490 coap://s.example.com/light 492 => https://p.example.com/hc/?coap_uri=s.example.com/light 494 5.4.2. Enhanced Form 496 The enhanced form can be used to express more sophisticated mappings 497 of the Target CoAP URI into the Hosting HTTP URI, i.e., mappings that 498 do not fit into the simple form. 500 There MUST be at most one instance of each of the following template 501 variables in a template definition: 503 s = "coap" / "coaps" ; from [RFC7252], Sections 6.1 and 6.2 504 hp = host [":" port] ; from [RFC3986], Sections 3.2.2 and 3.2.3 505 p = path-abempty ; from [RFC3986], Section 3.3 506 q = query ; from [RFC3986], Section 3.4 507 qq = [ "?" query ] ; qq is empty if and only if 'query' is empty 509 The qq form is used when the path and the (optional) query components 510 are to be copied verbatim from the Target CoAP URI into the Hosting 511 HTTP URI, i.e., as "{+p}{+qq}". Instead, the q form is used when the 512 query and path are mapped as separate entities, e.g., as in 513 "coap_path={+p}&coap_query={+q}". 515 5.4.2.1. Examples 517 All the following examples (given as a specific URI mapping template, 518 a Target CoAP URI, and the produced Hosting HTTP URI) use 519 https://p.example.com/hc/ as the HC Proxy URI. 521 1. Target CoAP URI components in path segments, and optional query 522 in query component: 524 {+s}/{+hp}{+p}{+qq} 526 coap://s.example.com/light 528 => https://p.example.com/hc/coap/s.example.com/light 530 whereas 532 coap://s.example.com/light?on 534 => https://p.example.com/hc/coap/s.example.com/light?on 536 2. Target CoAP URI components split in individual query arguments: 538 ?s={+s}&hp={+hp}&p={+p}&q={+q} 540 coap://s.example.com/light 542 => https://p.example.com/hc/?s=coap&hp=s.example.com&p=/light&q= 544 whereas 546 coaps://s.example.com/light?on 548 => https://p.example.com/hc/?s=coaps&hp=s.example.com&p=/light&q=on 550 5.5. Discovery 552 In order to accommodate site specific needs while allowing third 553 parties to discover the proxy function, the HC proxy SHOULD publish 554 information related to the location and syntax of the HC proxy 555 function using the CoRE Link Format [RFC6690] interface. 557 To this aim a new Resource Type, "core.hc", is defined in this 558 document. It can be used as the value for the "rt" attribute in a 559 query to the /.well-known/core in order to locate the URI where the 560 HC proxy function is anchored, i.e., the HC Proxy URI. 562 Along with it, the new target attribute "hct" is defined in this 563 document. This attribute MAY be returned in a "core.hc" link to 564 provide the URI Mapping Template associated to the mapping resource. 565 The default template given in Section 5.3, i.e., {+tu}, MUST be 566 assumed if no "hct" attribute is found in the returned link. If a 567 "hct" attribute is present in the returned link, then a client MUST 568 use it to create the Hosting HTTP URI. 570 The URI mapping SHOULD be discoverable (as specified in [RFC6690]) on 571 both the HTTP and the CoAP side of the HC proxy, with one important 572 difference: on the CoAP side the link associated to the "core.hc" 573 resource needs an explicit anchor referring to the HTTP origin 574 [RFC6454], while on the HTTP interface the link context is already 575 the HTTP origin carried in the request's Host header, and doesn't 576 have to be made explicit. 578 5.5.1. Examples 580 o The first example exercises the CoAP interface, and assumes that 581 the default template, {+tu}, is used. For example, in use case #3 582 in section Section 4, the smartphone may discover the public HC 583 proxy before leaving the home network. Then when outside the home 584 network, the smartphone will be able to query the appropriate home 585 sensor. 587 Req: GET coap://[ff02::1]/.well-known/core?rt=core.hc 589 Res: 2.05 Content 590 ;anchor="https://p.example.com";rt="core.hc" 592 o The second example - also on the CoAP side of the HC proxy - uses 593 a custom template, i.e., one where the CoAP URI is carried inside 594 the query component, thus the returned link carries the URI 595 template to be used in an explicit "hct" attribute: 597 Req: GET coap://[ff02::1]/.well-known/core?rt=core.hc 599 Res: 2.05 Content 600 ;anchor="https://p.example.com"; 601 rt="core.hc";hct="?uri={+tu}" 603 On the HTTP side, link information can be serialized in more than one 604 way: 606 o using the 'application/link-format' content type: 608 Req: GET /.well-known/core?rt=core.hc HTTP/1.1 609 Host: p.example.com 611 Res: HTTP/1.1 200 OK 612 Content-Type: application/link-format 613 Content-Length: 18 615 ;rt="core.hc" 617 o using the 'application/link-format+json' content type as defined 618 in [I-D.ietf-core-links-json]: 620 Req: GET /.well-known/core?rt=core.hc HTTP/1.1 621 Host: p.example.com 623 Res: HTTP/1.1 200 OK 624 Content-Type: application/link-format+json 625 Content-Length: 31 627 [{"href":"/hc/","rt":"core.hc"}] 629 o using the Link header: 631 Req: GET /.well-known/core?rt=core.hc HTTP/1.1 632 Host: p.example.com 634 Res: HTTP/1.1 200 OK 635 Link: ;rt="core.hc" 637 6. Media Type Mapping 639 6.1. Overview 641 A HC proxy needs to translate HTTP media types (Section 3.1.1.1 of 642 [RFC7231]) and content encodings (Section 3.1.2.2 of [RFC7231]) into 643 CoAP content formats (Section 12.3 of [RFC7252]) and vice versa. 645 Media type translation can happen in GET, PUT or POST requests going 646 from HTTP to CoAP, and in 2.xx (i.e., successful) responses going 647 from CoAP to HTTP. Specifically, PUT and POST need to map both the 648 Content-Type and Content-Encoding HTTP headers into a single CoAP 649 Content-Format option, whereas GET needs to map Accept and Accept- 650 Encoding HTTP headers into a single CoAP Accept option. To generate 651 the HTTP response, the CoAP Content-Format option is mapped back to a 652 suitable HTTP Content-Type and Content-Encoding combination. 654 An HTTP request carrying a Content-Type and Content-Encoding 655 combination which the HC proxy is unable to map to an equivalent CoAP 656 Content-Format, SHALL elicit a 415 (Unsupported Media Type) response 657 by the HC proxy. 659 On the content negotiation side, failure to map Accept and Accept-* 660 headers SHOULD be silently ignored: the HC proxy SHOULD therefore 661 forward as a CoAP request with no Accept option. The HC proxy thus 662 disregards the Accept/Accept-* header fields by treating the response 663 as if it is not subject to content negotiation, as mentioned in 664 Sections 5.3.* of [RFC7231]. However, a HC proxy implementation is 665 free to attempt mapping a single Accept header in a GET request to 666 multiple CoAP GET requests, each with a single Accept option, which 667 are then tried in sequence until one succeeds. Note that an HTTP 668 Accept */* MUST be mapped to a CoAP request without Accept option. 670 While the CoAP to HTTP direction has always a well defined mapping 671 (with the exception examined in Section 6.2), the HTTP to CoAP 672 direction is more problematic because the source set, i.e., 673 potentially 1000+ IANA registered media types, is much bigger than 674 the destination set, i.e., the mere 6 values initially defined in 675 Section 12.3 of [RFC7252]. 677 Depending on the tight/loose coupling with the application(s) for 678 which it proxies, the HC proxy could implement different media type 679 mappings. 681 When tightly coupled, the HC proxy knows exactly which content 682 formats are supported by the applications, and can be strict when 683 enforcing its forwarding policies in general, and the media type 684 mapping in particular. 686 On the other hand, when the HC proxy is a general purpose application 687 layer gateway, being too strict could significantly reduce the amount 688 of traffic that it would be able to successfully forward. In this 689 case, the "loose" media type mapping detailed in Section 6.3 MAY be 690 implemented. 692 The latter grants more evolution of the surrounding ecosystem, at the 693 cost of allowing more attack surface. In fact, as a result of such 694 strategy, payloads would be forwarded more liberally across the 695 unconstrained/constrained network boundary of the communication path. 697 6.2. 'application/coap-payload' Media Type 699 If the HC proxy receives a CoAP response with a Content-Format that 700 it does not recognize (e.g., because the value has been registered 701 after the proxy has been deployed, or the CoAP server uses an 702 experimental value which is not registered), then the HC proxy SHALL 703 return a generic "application/coap-payload" media type with numeric 704 parameter "cf" as defined in Section 9.2. 706 For example, the CoAP content format '60' ("application/cbor") would 707 be represented by "application/coap-payload;cf=60", if the HC Proxy 708 doesn't recognize the content format '60'. 710 A HTTP client may use the media type "application/coap-payload" as a 711 means to send a specific content format to a CoAP server via a HC 712 Proxy if the client has determined that the HC Proxy does not 713 directly support the type mapping it needs. This case may happen 714 when dealing for example with newly registered, yet to be registered, 715 or experimental CoAP content formats. However, unless explicitly 716 configured to allow pass-through of unknown content formats, the HC 717 proxy SHOULD NOT forward requests carrying a Content-Type or Accept 718 header with an "application/coap-payload", and return an appropriate 719 client error instead. 721 6.3. Loose Media Type Mapping 723 By structuring the type information in a super-class (e.g., "text") 724 followed by a finer grained sub-class (e.g., "html"), and optional 725 parameters (e.g., "charset=utf-8"), Internet media types provide a 726 rich and scalable framework for encoding the type of any given 727 entity. 729 This approach is not applicable to CoAP, where Content Formats 730 conflate an Internet media type (potentially with specific 731 parameters) and a content encoding into one small integer value. 733 To remedy this loss of flexibility, we introduce the concept of a 734 "loose" media type mapping, where media types that are 735 specializations of a more generic media type can be aliased to their 736 super-class and then mapped (if possible) to one of the CoAP content 737 formats. For example, "application/soap+xml" can be aliased to 738 "application/xml", which has a known conversion to CoAP. In the 739 context of this "loose" media type mapping, "application/octet- 740 stream" can be used as a fallback when no better alias is found for a 741 specific media type. 743 Table 1 defines the default lookup table for the "loose" media type 744 mapping. It is expected that an implementation can refine it either 745 given application-specific knowledge, or because new Content-Formats 746 are defined. Given an input media type, the table returns its best 747 generalized media type using the most specific match i.e., the table 748 entries are compared to the input in top to bottom order until an 749 entry matches. 751 +-----------------------------+--------------------------+ 752 | Internet media type pattern | Generalized media type | 753 +-----------------------------+--------------------------+ 754 | application/*+xml | application/xml | 755 | application/*+json | application/json | 756 | application/*+cbor | application/cbor | 757 | text/xml | application/xml | 758 | text/* | text/plain | 759 | */* | application/octet-stream | 760 +-----------------------------+--------------------------+ 762 Table 1: Media type generalization lookup table 764 The "loose" media type mapping is an OPTIONAL feature. 765 Implementations supporting this kind of mapping should provide a 766 flexible way to define the set of media type generalizations allowed. 768 6.4. Media Type to Content Format Mapping Algorithm 770 This section defines the algorithm used to map an HTTP Internet media 771 type to its correspondent CoAP content format; it can be used as a 772 building block for translating HTTP Content-Type and Accept headers 773 into CoAP Content-Format and Accept Options. 775 The algorithm uses an IANA-maintained table, "CoAP Content-Formats", 776 as established by Section 12.3 of [RFC7252] plus, possibly, any 777 locally defined extension of it. Optionally, the table and lookup 778 mechanism described in Section 6.3 can be used if the implementation 779 chooses so. 781 Note that the algorithm assumes an "identity" Content-Encoding and 782 expects the resource body has been already successfully content- 783 decoded or transcoded to the desired format. 785 In the following (Figure 2): 787 o media_type is the media type to translate; 789 o coap_cf_registry is a lookup table matching the CoAP Content 790 Format Registry; 792 o loose_mapper is an optional lookup table describing the loose 793 media type mappings (e.g., the one defined in Table 1); 795 The full source code is provided in Appendix A. 797 def mt2cf(media_type, encoding=None, 798 coap_cf_registry=CoAPContentFormatRegistry(), 799 loose_mapper=None): 800 """Return a CoAP Content-Format given an Internet Media Type and 801 its optional encoding. The current (as of 2016/10/24) CoAP 802 Content Format Registry is supplied by default. An optional 803 'loose-mapping' implementation can be supplied by the caller.""" 804 assert media_type is not None 805 assert coap_cf_registry is not None 807 # Lookup the CoAP Content-Formats registry 808 content_format = coap_cf_registry.lookup(media_type, encoding) 810 # If an exact match is not found and a loose mapper has been 811 # supplied, try to use it to get a media type with which to 812 # re-try the CoAP Content-Formats registry lookup. 813 if content_format is None and loose_mapper is not None: 814 content_format = coap_cf_registry.lookup( 815 loose_mapper.lookup(media_type), encoding) 817 return content_format 819 Figure 2 821 6.5. Content Transcoding 823 6.5.1. General 825 Payload content transcoding (e.g., see steps 11-14 of Figure 2) is an 826 OPTIONAL feature. Implementations supporting this feature should 827 provide a flexible way to define the set of transcodings allowed. 829 As noted in Section 6.4, the process of mapping the media type can 830 have side effects on the forwarded entity body. This may be caused 831 by the removal or addition of a specific content encoding, or because 832 the HC proxy decides to transcode the representation to a different 833 (compatible) format. The latter proves useful when an optimized 834 version of a specific format exists. For example a XML-encoded 835 resource could be transcoded to Efficient XML Interchange (EXI) 836 format, or a JSON-encoded resource into CBOR [RFC7049], effectively 837 achieving compression without losing any information. 839 However, there are a few important factors to keep in mind when 840 enabling a transcoding function: 842 1. Maliciously crafted inputs coming from the HTTP side might 843 inflate in size (see for example Section 4.2 of [RFC7049]), 844 therefore creating a security threat for both the HC proxy and 845 the target resource; 847 2. Transcoding can lose information in non-obvious ways. For 848 example, encoding a XML document using schema-informed EXI 849 encoding leads to a loss of information when the destination does 850 not know the exact schema version used by the encoder. That 851 means that whenever the HC proxy transcodes an application/XML to 852 application/EXI in-band metadata could be lost. 854 3. When content-type is mapped, there is a risk that the content 855 with the destination type would have malware not active in the 856 source type. 858 Therefore, it is crucial that these risks are well understood and 859 carefully weighed against the actual benefits before deploying the 860 transcoding function. 862 6.5.2. CoRE Link Format 864 The CoRE Link Format [RFC6690] is a set of links (i.e., URIs and 865 their formal relationships) which is carried as content payload in a 866 CoAP response. These links usually include CoAP URIs that might be 867 translated by the HC proxy to the correspondent HTTP URIs using the 868 implemented URI mapping function (see Section 5). Such a process 869 would inspect the forwarded traffic and attempt to re-write the body 870 of resources with an application/link-format media type, mapping the 871 embedded CoAP URIs to their HTTP counterparts. Some potential issues 872 with this approach are: 874 1. The client may be interested to retrieve original (unaltered) 875 CoAP payloads through the HC proxy, not modified versions. 877 2. Tampering with payloads is incompatible with resources that are 878 integrity protected (although this is a problem with transcoding 879 in general). 881 3. The HC proxy needs to fully understand [RFC6690] syntax and 882 semantics, otherwise there is an inherent risk to corrupt the 883 payloads. 885 Therefore, CoRE Link Format payload should only be transcoded at the 886 risk and discretion of the proxy implementer. 888 6.5.3. Diagnostic Messages 890 CoAP responses may, in certain error cases, contain a diagnostic 891 message in the payload explaining the error situation, as described 892 in Section 5.5.2 of [RFC7252]. If present, the CoAP response 893 diagnostic payload SHOULD be copied in the HTTP response body. The 894 CoAP diagnostic message MUST NOT be copied into the HTTP reason- 895 phrase, since it potentially contains CR-LF characters which are 896 incompatible with HTTP reason-phrase syntax. 898 7. Response Code Mapping 900 Table 2 defines the HTTP response status codes to which each CoAP 901 response code SHOULD be mapped. Multiple appearances of a HTTP 902 status code in the second column indicates multiple equivalent HTTP 903 responses are possible based on the same CoAP response code, 904 depending on the conditions cited in the Notes (third column and text 905 below table). 907 +-----------------------------+-----------------------------+-------+ 908 | CoAP Response Code | HTTP Status Code | Notes | 909 +-----------------------------+-----------------------------+-------+ 910 | 2.01 Created | 201 Created | 1 | 911 | 2.02 Deleted | 200 OK | 2 | 912 | | 204 No Content | 2 | 913 | 2.03 Valid | 304 Not Modified | 3 | 914 | | 200 OK | 4 | 915 | 2.04 Changed | 200 OK | 2 | 916 | | 204 No Content | 2 | 917 | 2.05 Content | 200 OK | | 918 | 4.00 Bad Request | 400 Bad Request | | 919 | 4.01 Unauthorized | 403 Forbidden | 5 | 920 | 4.02 Bad Option | 400 Bad Request | 6 | 921 | 4.02 Bad Option | 500 Internal Server Error | 6 | 922 | 4.03 Forbidden | 403 Forbidden | | 923 | 4.04 Not Found | 404 Not Found | | 924 | 4.05 Method Not Allowed | 400 Bad Request | 7 | 925 | 4.06 Not Acceptable | 406 Not Acceptable | | 926 | 4.12 Precondition Failed | 412 Precondition Failed | | 927 | 4.13 Request Ent. Too Large | 413 Request Repr. Too Large | | 928 | 4.15 Unsupported Media Type | 415 Unsupported Media Type | | 929 | 5.00 Internal Server Error | 500 Internal Server Error | | 930 | 5.01 Not Implemented | 501 Not Implemented | | 931 | 5.02 Bad Gateway | 502 Bad Gateway | | 932 | 5.03 Service Unavailable | 503 Service Unavailable | 8 | 933 | 5.04 Gateway Timeout | 504 Gateway Timeout | | 934 | 5.05 Proxying Not Supported | 502 Bad Gateway | 9 | 935 +-----------------------------+-----------------------------+-------+ 937 Table 2: CoAP-HTTP Response Code Mappings 939 Notes: 941 1. A CoAP server may return an arbitrary format payload along with 942 this response. If present, this payload MUST be returned as 943 entity in the HTTP 201 response. Section 7.3.2 of [RFC7231] does 944 not put any requirement on the format of the entity. (In the 945 past, [RFC2616] did.) 947 2. The HTTP code is 200 or 204 respectively for the case that a CoAP 948 server returns a payload or not. [RFC7231] Section 5.3 requires 949 code 200 in case a representation of the action result is 950 returned for DELETE/POST/PUT, and code 204 if not. Hence, a 951 proxy MUST transfer any CoAP payload contained in a CoAP 2.02 952 response to the HTTP client using a 200 OK response. 954 3. HTTP code 304 (Not Modified) is sent if the HTTP client performed 955 a conditional HTTP request and the CoAP server responded with 956 2.03 (Valid) to the corresponding CoAP validation request. Note 957 that Section 4.1 of [RFC7232] puts some requirements on header 958 fields that must be present in the HTTP 304 response. 960 4. A 200 response to a CoAP 2.03 occurs only when the HC proxy, for 961 efficiency reasons, is running a local cache. An unconditional 962 HTTP GET which produces a cache-hit, could trigger a re- 963 validation (i.e., a conditional GET) on the CoAP side. The proxy 964 receiving 2.03 updates the freshness of its cached representation 965 and returns it to the HTTP client. 967 5. A HTTP 401 Unauthorized (Section 3.1 of [RFC7235]) response is 968 not applicable because there is no equivalent in CoAP of WWW- 969 Authenticate which is mandatory in a HTTP 401 response. 971 6. If the proxy has a way to determine that the Bad Option is due to 972 the straightforward mapping of a client request header into a 973 CoAP option, then returning HTTP 400 (Bad Request) is 974 appropriate. In all other cases, the proxy MUST return HTTP 500 975 (Internal Server Error) stating its inability to provide a 976 suitable translation to the client's request. 978 7. A CoAP 4.05 (Method Not Allowed) response SHOULD normally be 979 mapped to a HTTP 400 (Bad Request) code, because the HTTP 405 980 response would require specifying the supported methods - which 981 are generally unknown. In this case the HC Proxy SHOULD also 982 return a HTTP reason-phrase in the HTTP status line that starts 983 with the string "CoAP server returned 4.05" in order to 984 facilitate troubleshooting. However, if the HC proxy has more 985 granular information about the supported methods for the 986 requested resource (e.g., via a Resource Directory 987 ([I-D.ietf-core-resource-directory])) then it MAY send back a 988 HTTP 405 (Method Not Allowed) with a properly filled in "Allow" 989 response-header field (Section 7.4.1 of [RFC7231]). 991 8. The value of the HTTP "Retry-After" response-header field is 992 taken from the value of the CoAP Max-Age Option, if present. 994 9. This CoAP response can only happen if the proxy itself is 995 configured to use a CoAP forward-proxy (Section 5.7 of [RFC7252]) 996 to execute some, or all, of its CoAP requests. 998 8. Additional Mapping Guidelines 1000 8.1. Caching and Congestion Control 1002 A HC proxy should cache CoAP responses, and reply whenever applicable 1003 with a cached representation of the requested resource. 1005 If the HTTP client drops the connection after the HTTP request was 1006 made, a HC proxy should wait for the associated CoAP response and 1007 cache it if possible. Subsequent requests to the HC proxy for the 1008 same resource can use the result present in cache, or, if a response 1009 has still to come, the HTTP requests will wait on the open CoAP 1010 request. 1012 According to [RFC7252], a proxy must limit the number of outstanding 1013 requests to a given CoAP server to NSTART. To limit the amount of 1014 aggregate traffic to a constrained network, the HC proxy should also 1015 put a limit on the number of concurrent CoAP requests pending on the 1016 same constrained network; further incoming requests may either be 1017 queued or dropped (returning 503 Service Unavailable). This limit 1018 and the proxy queueing/dropping behavior should be configurable. 1020 Highly volatile resources that are being frequently requested may be 1021 observed [RFC7641] by the HC proxy to keep their cached 1022 representation fresh while minimizing the amount of CoAP traffic in 1023 the constrained network. See Section 8.2. 1025 8.2. Cache Refresh via Observe 1027 There are cases where using the CoAP observe protocol [RFC7641] to 1028 handle proxy cache refresh is preferable to the validation mechanism 1029 based on ETag as defined in [RFC7252]. Such scenarios include sleepy 1030 CoAP nodes - with possibly high variance in requests' distribution - 1031 which would greatly benefit from a server driven cache update 1032 mechanism. Ideal candidates for CoAP observe are also crowded or 1033 very low throughput networks, where reduction of the total number of 1034 exchanged messages is an important requirement. 1036 This subsection aims at providing a practical evaluation method to 1037 decide whether refreshing a cached resource R is more efficiently 1038 handled via ETag validation or by establishing an observation on R. 1039 The idea being that the HC proxy proactively installs an observation 1040 on a "popular enough" resource and actively monitors: 1042 a. Its update pattern on the CoAP side; and 1044 b. The request pattern on the HTTP side; 1045 and uses the formula below to determine whether the observation 1046 should be kept alive or shut down. 1048 Let T_R be the mean time between two client requests to resource R, 1049 let T_C be the mean time between two representation changes of R, and 1050 let M_R be the mean number of CoAP messages per second exchanged to 1051 and from resource R. If we assume that the initial cost for 1052 establishing the observation is negligible, an observation on R 1053 reduces M_R if and only if T_R < 2*T_C with respect to using ETag 1054 validation, that is if and only if the mean arrival rate of requests 1055 for resource R is greater than half the change rate of R. 1057 When observing the resource R, M_R is always upper bounded by 2/T_C. 1059 8.3. Use of CoAP Blockwise Transfer 1061 A HC proxy SHOULD support CoAP blockwise transfers [RFC7959] to allow 1062 transport of large CoAP payloads while avoiding excessive link-layer 1063 fragmentation in constrained networks, and to cope with small 1064 datagram buffers in CoAP end-points as described in [RFC7252] 1065 Section 4.6. 1067 A HC proxy SHOULD attempt to retry a payload-carrying CoAP PUT or 1068 POST request with blockwise transfer if the destination CoAP server 1069 responded with 4.13 (Request Entity Too Large) to the original 1070 request. A HC proxy SHOULD attempt to use blockwise transfer when 1071 sending a CoAP PUT or POST request message that is larger than 1072 BLOCKWISE_THRESHOLD bytes. The value of BLOCKWISE_THRESHOLD is 1073 implementation-specific, for example it can be: 1075 o Calculated based on a known or typical UDP datagram buffer size 1076 for CoAP end-points, or 1078 o Set to N times the known size of a link-layer frame in a 1079 constrained network where e.g., N=5, or 1081 o Preset to a known IP MTU value, or 1083 o Set to a known Path MTU value. 1085 The value BLOCKWISE_THRESHOLD, or the parameters from which it is 1086 calculated, should be configurable in a proxy implementation. The 1087 maximum block size the proxy will attempt to use in CoAP requests 1088 should also be configurable. 1090 The HC proxy SHOULD detect CoAP end-points not supporting blockwise 1091 transfers. This can be done by checking for a 4.02 (Bad Option) 1092 response returned by an end-point in response to a CoAP request with 1093 a Block* Option, and subsequent absence of the 4.02 in response to 1094 the same request without Block* Options. This allows the HC proxy to 1095 be more efficient, not attempting repeated blockwise transfers to 1096 CoAP servers that do not support it. 1098 8.4. CoAP Multicast 1100 A HC proxy MAY support CoAP multicast. If it does, the HC proxy 1101 sends out a multicast CoAP request if the Target CoAP URI's authority 1102 is a multicast IP literal or resolves to a multicast IP address. If 1103 the HC proxy does not support CoAP multicast, it SHOULD respond 403 1104 (Forbidden) to any valid HTTP request that maps to a CoAP multicast 1105 request. 1107 Details related to supporting CoAP multicast are currently out of 1108 scope of this document since in a proxy scenario a HTTP client 1109 typically expects to receive a single response, not multiple. 1110 However, a HC proxy that implements CoAP multicast may include 1111 application-specific functions to aggregate multiple CoAP responses 1112 into a single HTTP response. We suggest using the "application/http" 1113 internet media type (Section 8.3.2 of [RFC7230]) to enclose a set of 1114 one or more HTTP response messages, each representing the mapping of 1115 one CoAP response. 1117 For further considerations related to the handling of multicast 1118 requests, see Section 10.1. 1120 8.5. Timeouts 1122 If the CoAP server takes a long time in responding, the HTTP client 1123 or any other proxy in between may timeout. Further discussion of 1124 timeouts in HTTP is available in Section 6.2.4 of [RFC7230]. 1126 A HC proxy MUST define an internal timeout for each pending CoAP 1127 request, because the CoAP server may silently die before completing 1128 the request. Assuming the Proxy uses confirmable CoAP requests, such 1129 timeout value T SHOULD be at least 1131 T = MAX_RTT + MAX_SERVER_RESPONSE_DELAY 1133 where MAX_RTT is defined in [RFC7252] and MAX_SERVER_RESPONSE_DELAY 1134 is defined in [RFC7390]. 1136 9. IANA Considerations 1137 9.1. New 'core.hc' Resource Type 1139 This document registers a new Resource Type (rt=) Link Target 1140 Attribute, 'core.hc', in the "Resource Type (rt=) Link Target 1141 Attribute Values" subregistry under the "Constrained RESTful 1142 Environments (CoRE) Parameters" registry. 1144 Attribute Value: core.hc 1146 Description: HTTP to CoAP mapping base resource. 1148 Reference: See Section 5.5. 1150 9.2. New 'coap-payload' Internet Media Type 1152 This document defines the "application/coap-payload" media type with 1153 a single parameter "cf". This media type represents any payload that 1154 a CoAP message can carry, having a content format that can be 1155 identified by an integer in range 0-65535 corresponding to a CoAP 1156 Content-Format parameter ([RFC7252], Section 12.3). The parameter 1157 "cf" is the integer defining the CoAP content format. 1159 Type name: application 1161 Subtype name: coap-payload 1163 Required parameters: cf (CoAP Content-Format integer in range 0-65535 1164 denoting the content format of the CoAP payload carried, as defined 1165 by the "CoAP Content-Formats" subregistry that is part of the 1166 "Constrained RESTful Environments (CoRE) Parameters" registry.) 1168 Optional parameters: None 1170 Encoding considerations: Common use is BINARY. The specific CoAP 1171 content format encoding considerations for the selected Content- 1172 Format (cf parameter) apply. The encoding can vary based on the 1173 value of the cf parameter. 1175 Security considerations: The specific CoAP content format security 1176 considerations for the selected Content-Format (cf parameter) apply. 1178 Interoperability considerations: This media type can never be used 1179 directly in CoAP messages because there is no means available to 1180 encode the mandatory 'cf' parameter in CoAP. 1182 Published specification: (this I-D - TBD) 1184 Applications that use this media type: HTTP-to-CoAP Proxies. 1186 Fragment identifier considerations: CoAP does not support URI 1187 fragments; therefore a CoAP payload fragment cannot be identified. 1188 Fragments are not applicable for this media type. 1190 Additional information: 1192 Deprecated alias names for this type: N/A 1194 Magic number(s): N/A 1196 File extension(s): N/A 1198 Macintosh file type code(s): N/A 1200 Person and email address to contact for further information: 1202 Esko Dijk ("esko@ieee.org") 1204 Intended usage: COMMON 1206 Restrictions on usage: 1208 An application (or user) can only use this media type if it has to 1209 represent a CoAP payload of which the specified CoAP Content-Format 1210 is an unrecognized number; such that a proper translation directly to 1211 the equivalent HTTP media type is not possible. 1213 Author: CoRE WG 1215 Change controller: IETF 1217 Provisional registration: No 1219 10. Security Considerations 1221 The security concerns raised in Section 9.2 of [RFC7230] also apply 1222 to the HC proxy scenario. 1224 A HC proxy deployed at the boundary of a constrained network is an 1225 easy single point of failure for reducing availability. As such, 1226 special care should be taken in designing, developing and operating 1227 it, keeping in mind that, in most cases, it has fewer limitations 1228 than the constrained devices it is serving. 1230 The correctness of the request parsing in general (including any 1231 content transcoding), and of the URI translation process in 1232 particular, is essential to the security of the HC proxy function. 1233 This is especially true when the internal network hosts devices with 1234 genuinely limited capabilities. The quality of implementation and 1235 operation - i.e., careful implementation and/or selection of the 1236 third party libraries, sane configuration defaults, an expedite way 1237 to upgrade a running instance, etc. - is therefore an essential 1238 attribute of the HC proxy. For this purpose, see also Sections 9.3, 1239 9.4, 9.5 and 9.6 of [RFC7230] for well known issues related to HTTP 1240 request parsing, and section 11.1 of [RFC7252] for an overview of 1241 CoAP specific concerns related to URI processing - in particular the 1242 potential impact on access control mechanisms that are based on URIs. 1244 The following sub paragraphs categorize and discuss a set of specific 1245 security issues related to the translation, caching and forwarding 1246 functionality exposed by a HC proxy. 1248 10.1. Multicast 1250 Multicast requests impose a non-trivial cost on the constrained 1251 network and endpoints, and might be exploited as a DoS attack vector 1252 (see also Section 10.2). From a privacy perspective, they can be 1253 used to gather detailed information about the resources hosted in the 1254 constrained network. For example, an outsider that is able to 1255 successfully query the /.well-known/core could obtain a comprehensive 1256 list of the target's home appliances and devices. From a security 1257 perspective, they can be used to carry out a network reconnaissance 1258 attack to gather information about possible vulnerabilities that 1259 could be exploited at a later point in time. For these reasons, it 1260 is RECOMMENDED that requests to multicast resources are access 1261 controlled with a default-deny policy. It is RECOMMENDED that the 1262 requestor of a multicast resource be strongly authenticated. If 1263 privacy and / or security are first class requirements, for example 1264 whenever the HTTP request transits through the public Internet, the 1265 request SHOULD be transported over a mutually authenticated and 1266 encrypted TLS connection. 1268 10.2. Traffic Overflow 1270 Due to the typically constrained nature of CoAP nodes, particular 1271 attention should be given to the implementation of traffic reduction 1272 mechanisms (see Section 8.1), because inefficient proxy 1273 implementations can be targeted by unconstrained Internet attackers. 1274 Bandwidth or complexity involved in such attacks is very low. 1276 An amplification attack to the constrained network may be triggered 1277 by a multicast request generated by a single HTTP request which is 1278 mapped to a CoAP multicast resource, as discussed in Section 11.3 of 1279 [RFC7252]. 1281 The risk likelihood of this amplification technique is higher than an 1282 amplification attack carried out by a malicious constrained device 1283 (e.g., ICMPv6 flooding, like Packet Too Big, or Parameter Problem on 1284 a multicast destination [RFC4732]), since it does not require direct 1285 access to the constrained network. 1287 The feasibility of this attack which disrupts availability of the 1288 targeted CoAP server can be limited by access controlling the exposed 1289 multicast resources, so that only known/authorized users can access 1290 such URIs. 1292 10.3. Handling Secured Exchanges 1294 An HTTP request can be sent to the HC proxy over a secured 1295 connection. However, there may not always exist a secure connection 1296 mapping to CoAP. For example, a secure distribution method for 1297 multicast traffic is complex and may not be implemented (see 1298 [RFC7390]). 1300 A HC proxy should implement rules for security context translations. 1301 For example all 'https' unicast requests are translated to 'coaps' 1302 requests, or 'https' requests are translated to unsecured 'coap' 1303 requests. Another rule could specify the security policy and 1304 parameters used for DTLS sessions [RFC7925]. Such rules will largely 1305 depend on the application and network context in which the HC proxy 1306 operates. These rules should be configurable. 1308 It is RECOMMENDED that, by default, accessing a 'coaps' URI is only 1309 allowed from a corresponding 'https' URI. 1311 By default, a HC proxy SHOULD reject any secured CoAP client request 1312 (i.e., one with a 'coaps' scheme) if there is no configured security 1313 policy mapping. This recommendation may be relaxed in case the 1314 destination network is believed to be secured by other means. 1315 Assuming that CoAP nodes are isolated behind a firewall as in the HC 1316 proxy deployment shown in Figure 1, the HC proxy may be configured to 1317 translate the incoming HTTPS request using plain CoAP (NoSec mode). 1319 10.4. URI Mapping 1321 The following risks related to the URI mapping described in Section 5 1322 and its use by HC proxies have been identified: 1324 DoS attack on the constrained/CoAP network. 1325 Mitigation: by default deny any Target CoAP URI whose authority is 1326 (or maps to) a multicast address. Then explicitly white-list 1327 multicast resources/authorities that are allowed to be de- 1328 referenced. See also Section 8.4. 1330 Leaking information on the constrained/CoAP network resources and 1331 topology. 1332 Mitigation: by default deny any Target CoAP URI (especially 1333 /.well-known/core is a resource to be protected), and then 1334 explicitly white-list resources that are allowed to be seen from 1335 outside. 1337 The internal CoAP Target resource is totally transparent from 1338 outside. 1339 Mitigation: implement a HTTPS-only interface, which makes the 1340 Target CoAP URI totally opaque to a passive attacker. 1342 11. Acknowledgments 1344 An initial version of Table 2 in Section 7 has been provided in 1345 revision -05 of the CoRE CoAP I-D. Special thanks to Peter van der 1346 Stok for countless comments and discussions on this document, that 1347 contributed to its current structure and text. 1349 Thanks to Abhijan Bhattacharyya, Alexey Melnikov, Brian Frank, 1350 Carsten Bormann, Christian Amsuess, Christian Groves, Cullen 1351 Jennings, Dorothy Gellert, Francesco Corazza, Francis Dupont, Hannes 1352 Tschofenig, Jaime Jimenez, Kathleen Moriarty, Kepeng Li, Kerry Lynn, 1353 Klaus Hartke, Larry Masinter, Linyi Tian, Michele Rossi, Michele 1354 Zorzi, Nicola Bui, Peter Saint-Andre, Sean Leonard, Spencer Dawkins, 1355 Stephen Farrell, Suresh Krishnan, Zach Shelby for helpful comments 1356 and discussions that have shaped the document. 1358 The research leading to these results has received funding from the 1359 European Community's Seventh Framework Programme [FP7/2007-2013] 1360 under grant agreement n.251557. 1362 12. References 1364 12.1. Normative References 1366 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1367 Requirement Levels", BCP 14, RFC 2119, 1368 DOI 10.17487/RFC2119, March 1997, 1369 . 1371 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 1372 Resource Identifier (URI): Generic Syntax", STD 66, 1373 RFC 3986, DOI 10.17487/RFC3986, January 2005, 1374 . 1376 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 1377 Specifications: ABNF", STD 68, RFC 5234, 1378 DOI 10.17487/RFC5234, January 2008, 1379 . 1381 [RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M., 1382 and D. Orchard, "URI Template", RFC 6570, 1383 DOI 10.17487/RFC6570, March 2012, 1384 . 1386 [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link 1387 Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, 1388 . 1390 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 1391 Protocol (HTTP/1.1): Message Syntax and Routing", 1392 RFC 7230, DOI 10.17487/RFC7230, June 2014, 1393 . 1395 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 1396 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 1397 DOI 10.17487/RFC7231, June 2014, 1398 . 1400 [RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 1401 Protocol (HTTP/1.1): Conditional Requests", RFC 7232, 1402 DOI 10.17487/RFC7232, June 2014, 1403 . 1405 [RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 1406 Protocol (HTTP/1.1): Authentication", RFC 7235, 1407 DOI 10.17487/RFC7235, June 2014, 1408 . 1410 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 1411 Application Protocol (CoAP)", RFC 7252, 1412 DOI 10.17487/RFC7252, June 2014, 1413 . 1415 [RFC7641] Hartke, K., "Observing Resources in the Constrained 1416 Application Protocol (CoAP)", RFC 7641, 1417 DOI 10.17487/RFC7641, September 2015, 1418 . 1420 [RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in 1421 the Constrained Application Protocol (CoAP)", RFC 7959, 1422 DOI 10.17487/RFC7959, August 2016, 1423 . 1425 12.2. Informative References 1427 [I-D.ietf-core-links-json] 1428 Li, K., Rahman, A., and C. Bormann, "Representing CoRE 1429 Formats in JSON and CBOR", draft-ietf-core-links-json-06 1430 (work in progress), July 2016. 1432 [I-D.ietf-core-resource-directory] 1433 Shelby, Z., Koster, M., Bormann, C., and P. Stok, "CoRE 1434 Resource Directory", draft-ietf-core-resource-directory-08 1435 (work in progress), July 2016. 1437 [REST] Fielding, R., "Architectural Styles and the Design of 1438 Network-based Software Architectures", PhD 1439 Dissertation, University of California, Irvine, 1440 ISBN 0-599-87118-0, 2000. 1442 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 1443 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 1444 Transfer Protocol -- HTTP/1.1", RFC 2616, 1445 DOI 10.17487/RFC2616, June 1999, 1446 . 1448 [RFC3040] Cooper, I., Melve, I., and G. Tomlinson, "Internet Web 1449 Replication and Caching Taxonomy", RFC 3040, 1450 DOI 10.17487/RFC3040, January 2001, 1451 . 1453 [RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet 1454 Denial-of-Service Considerations", RFC 4732, 1455 DOI 10.17487/RFC4732, December 2006, 1456 . 1458 [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, 1459 DOI 10.17487/RFC6454, December 2011, 1460 . 1462 [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object 1463 Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, 1464 October 2013, . 1466 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1467 Constrained-Node Networks", RFC 7228, 1468 DOI 10.17487/RFC7228, May 2014, 1469 . 1471 [RFC7390] Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for 1472 the Constrained Application Protocol (CoAP)", RFC 7390, 1473 DOI 10.17487/RFC7390, October 2014, 1474 . 1476 [RFC7925] Tschofenig, H., Ed. and T. Fossati, "Transport Layer 1477 Security (TLS) / Datagram Transport Layer Security (DTLS) 1478 Profiles for the Internet of Things", RFC 7925, 1479 DOI 10.17487/RFC7925, July 2016, 1480 . 1482 [W3C.REC-html5-20141028] 1483 Hickson, I., Berjon, R., Faulkner, S., Leithead, T., 1484 Navara, E., O'Connor, E., and S. Pfeiffer, "HTML5", W3C 1485 Recommendation REC-html5-20141028, 2014, 1486 . 1488 Appendix A. Media Type Mapping Source Code 1490 #!/usr/bin/env python 1492 import unittest 1493 import re 1495 class CoAPContentFormatRegistry(object): 1496 """Map an Internet media type (and optional inherent encoding) to a 1497 CoAP content format. 1498 """ 1499 TEXT_PLAIN = 0 1500 LINK_FORMAT = 40 1501 XML = 41 1502 OCTET_STREAM = 42 1503 EXI = 47 1504 JSON = 50 1505 CBOR = 60 1506 GROUP_JSON = 256 1508 # http://www.iana.org/assignments/core-parameters/core-parameters.xhtml 1509 # as of 2016/10/24. 1510 LOOKUP_TABLE = { 1511 ("text/plain;charset=utf-8", None): TEXT_PLAIN, 1512 ("application/link-format", None): LINK_FORMAT, 1513 ("application/xml", None): XML, 1514 ("application/octet-stream", None): OCTET_STREAM, 1515 ("application/exi", None): EXI, 1516 ("application/json", None): JSON, 1517 ("application/cbor", None): CBOR, 1518 ("application/coap-group+json", "utf-8"): GROUP_JSON, 1519 } 1521 def lookup(self, media_type, encoding): 1522 """Return the CoAP Content Format matching the supplied 1523 media type (and optional encoding), or None if no 1524 match can be found.""" 1525 return CoAPContentFormatRegistry.LOOKUP_TABLE.get( 1526 (media_type, encoding), None) 1528 class LooseMediaTypeMapper(object): 1529 # Order matters in this table: more specific types have higher rank 1530 # compared to less specific types. 1531 # This code only performs a shallow validation of acceptable 1532 # characters, and assumes overall validation of media type and 1533 # subtype has been done beforehand. 1534 LOOKUP_TABLE = [ 1535 (re.compile("application/.+\+xml$"), "application/xml"), 1536 (re.compile("application/.+\+json$"), "application/json"), 1537 (re.compile("application/.+\+cbor$"), "application/cbor"), 1538 (re.compile("text/xml$"), "application/xml"), 1539 (re.compile("text/[a-z\.\-\+]+$"), "text/plain;charset=utf-8"), 1540 (re.compile("[a-z]+/[a-z\.\-\+]+$"), "application/octet-stream") 1541 ] 1543 def lookup(self, media_type): 1544 """Return the best loose media type match available using 1545 the contents of LOOKUP_TABLE.""" 1546 for entry in LooseMediaTypeMapper.LOOKUP_TABLE: 1547 if entry[0].match(media_type) is not None: 1548 return entry[1] 1549 return None 1551 def mt2cf(media_type, encoding=None, 1552 coap_cf_registry=CoAPContentFormatRegistry(), 1553 loose_mapper=None): 1554 """Return a CoAP Content-Format given an Internet Media Type and 1555 its optional encoding. The current (as of 2016/10/24) CoAP 1556 Content Format Registry is supplied by default. An optional 1557 'loose-mapping' implementation can be supplied by the caller.""" 1558 assert media_type is not None 1559 assert coap_cf_registry is not None 1561 # Lookup the CoAP Content-Formats registry 1562 content_format = coap_cf_registry.lookup(media_type, encoding) 1563 # If an exact match is not found and a loose mapper has been 1564 # supplied, try to use it to get a media type with which to 1565 # re-try the CoAP Content-Formats registry lookup. 1566 if content_format is None and loose_mapper is not None: 1567 content_format = coap_cf_registry.lookup( 1568 loose_mapper.lookup(media_type), encoding) 1570 return content_format 1572 class TestMT2CF(unittest.TestCase): 1574 def testMissingContentType(self): 1575 with self.assertRaises(AssertionError): 1576 mt2cf(None) 1578 def testMissingContentFormatRegistry(self): 1579 with self.assertRaises(AssertionError): 1580 mt2cf(None, coap_cf_registry=None) 1582 def testTextPlain(self): 1583 self.assertEqual(mt2cf("text/plain;charset=utf-8"), 1584 CoAPContentFormatRegistry.TEXT_PLAIN) 1586 def testLinkFormat(self): 1587 self.assertEqual(mt2cf("application/link-format"), 1588 CoAPContentFormatRegistry.LINK_FORMAT) 1590 def testXML(self): 1591 self.assertEqual(mt2cf("application/xml"), 1592 CoAPContentFormatRegistry.XML) 1594 def testOctetStream(self): 1595 self.assertEqual(mt2cf("application/octet-stream"), 1596 CoAPContentFormatRegistry.OCTET_STREAM) 1598 def testEXI(self): 1599 self.assertEqual(mt2cf("application/exi"), 1600 CoAPContentFormatRegistry.EXI) 1602 def testJSON(self): 1603 self.assertEqual(mt2cf("application/json"), 1604 CoAPContentFormatRegistry.JSON) 1606 def testCBOR(self): 1607 self.assertEqual(mt2cf("application/cbor"), 1608 CoAPContentFormatRegistry.CBOR) 1610 def testCoAPGroupJSON(self): 1611 self.assertEqual(mt2cf("application/coap-group+json", 1612 "utf-8"), 1613 CoAPContentFormatRegistry.GROUP_JSON) 1615 def testUnknownMediaType(self): 1616 self.assertFalse(mt2cf("unknown/media-type")) 1618 def testLooseXML1(self): 1619 self.assertEqual( 1620 mt2cf( 1621 "application/somesubtype+xml", 1622 loose_mapper=LooseMediaTypeMapper()), 1623 CoAPContentFormatRegistry.XML) 1625 def testLooseXML2(self): 1626 self.assertEqual( 1627 mt2cf( 1628 "text/xml", 1629 loose_mapper=LooseMediaTypeMapper()), 1630 CoAPContentFormatRegistry.XML) 1632 def testLooseJSON(self): 1633 self.assertEqual( 1634 mt2cf( 1635 "application/somesubtype+json", 1636 loose_mapper=LooseMediaTypeMapper()), 1637 CoAPContentFormatRegistry.JSON) 1639 def testLooseCBOR(self): 1640 self.assertEqual( 1641 mt2cf( 1642 "application/somesubtype+cbor", 1643 loose_mapper=LooseMediaTypeMapper()), 1644 CoAPContentFormatRegistry.CBOR) 1646 def testLooseText(self): 1647 self.assertEqual( 1648 mt2cf( 1649 "text/somesubtype", 1650 loose_mapper=LooseMediaTypeMapper()), 1651 CoAPContentFormatRegistry.TEXT_PLAIN) 1653 def testLooseUnknown(self): 1654 self.assertEqual( 1655 mt2cf( 1656 "application/somesubtype-of-some-sort+format", 1657 loose_mapper=LooseMediaTypeMapper()), 1659 CoAPContentFormatRegistry.OCTET_STREAM) 1661 def testLooseInvalidStartsWithNonAlpha(self): 1662 self.assertFalse( 1663 mt2cf( 1664 " application/somesubtype", 1665 loose_mapper=LooseMediaTypeMapper())) 1667 def testLooseInvalidEndsWithUnexpectedChar(self): 1668 self.assertFalse( 1669 mt2cf( 1670 "application/somesubtype ", 1671 loose_mapper=LooseMediaTypeMapper())) 1673 def testLooseInvalidUnexpectedCharInTheMiddle(self): 1674 self.assertFalse( 1675 mt2cf( 1676 "application /somesubtype", 1677 loose_mapper=LooseMediaTypeMapper())) 1679 def testLooseInvalidNoSubType1(self): 1680 self.assertFalse( 1681 mt2cf( 1682 "application", 1683 loose_mapper=LooseMediaTypeMapper())) 1685 def testLooseInvalidNoSubType2(self): 1686 self.assertFalse( 1687 mt2cf( 1688 "application/", 1689 loose_mapper=LooseMediaTypeMapper())) 1691 if __name__ == "__main__": 1692 unittest.main(verbosity=2) 1694 Appendix B. Change Log 1696 [Note to RFC Editor: Please remove this section before publication.] 1698 Changes from ietf-15 to ietf-16 (Apps-Dir review): 1700 o Larry Masinter's comments. 1702 Changes from ietf-14 to ietf-15 (IESG review): 1704 o Kathleen Moriarty's DISCUSS and COMMENT; 1705 o Stephen Farrell's COMMENT; 1707 o Suresh Krishnan DISCUSS; 1709 o Spencer Dawkins' DISCUSS and COMMENT; 1711 Changes from ietf-13 to ietf-14: 1713 o Addressed Gen-ART and AD review comments. 1715 Changes from ietf-12 to ietf-13 (Christian Amsuess' comments): 1717 o More missing slashes in URI mapping template examples. 1719 Changes from ietf-11 to ietf-12 (2nd WGLC): 1721 o Addressed a few editorial issues (including a clarification on 1722 when to use qq vs q in the URI mapping template). 1724 o Fixed missing slash in one template example. 1726 o Added para about the need for future CoAP protocol elements to 1727 define their own HTTP mappings. 1729 Changes from ietf-10 to ietf-11 (Chair review): 1731 o Removed cu/su distinction from the URI mapping template. 1733 o Addressed a few editorial issues. 1735 Changes from ietf-09 to ietf-10: 1737 o Addressed Ticket #401 - Clarified that draft covers not only 1738 Reverse HC Proxy but that many parts also apply to Forward and 1739 Interception Proxies. 1741 o Clarified that draft concentrates on the HTTP-to-CoAP mapping 1742 direction (i.e., the HC proxy is a HTTP server and a CoAP client). 1744 o Clarified the "null mapping" case where no CoAP URI information is 1745 embedded in the HTTP request URI. 1747 o Moved multicast related security text to the "Security 1748 Considerations" to consolidate all security information in one 1749 location. 1751 o Removed references to "placement" of proxy (e.g., server-side vs 1752 client-side) as is confusing and provides little added value. 1754 o Fixed version numbers on references that were corrupted in last 1755 revision due to outdated xml2rfc conversion tool local cache. 1757 o Various editorial improvements. 1759 Changes from ietf-08 to ietf-09: 1761 o Clean up requirements language as per Klaus' comment. 1763 Changes from ietf-07 to ietf-08: 1765 o Addressed WGLC review comments from Klaus Hartke as per the 1766 correspondence of March 9, 2016 on the CORE WG mailing list. 1768 Changes from ietf-06 to ietf-07: 1770 o Addressed Ticket #384 - Section 5.4.1 describes briefly 1771 (informative) how to discover CoAP resources from an HTTP client. 1773 o Addressed Ticket #378 - For HTTP media type to CoAP content format 1774 mapping and vice versa: a new draft (TBD) may be proposed in CoRE 1775 which describes an approach for automatic updating of the media 1776 type mapping. This was noted in Section 6.1 but is otherwise 1777 outside the scope of this draft. 1779 o Addressed Ticket #377 - Added IANA section that defines a new HTTP 1780 media type "application/coap-payload" and created new Section 6.2 1781 on how to use it. 1783 o Addressed Ticket #376 - Updated Table 2 (and corresponding note 7) 1784 to indicate that a CoAP 4.05 (Method Not Allowed) Response Code 1785 should be mapped to a HTTP 400 (Bad Request). 1787 o Added note to comply to ABNF when translating CoAP diagnostic 1788 payload to reason-phrase in Section 6.5.3. 1790 Changes from ietf-05 to ietf-06: 1792 o Fully restructured the draft, bringing introductory text more to 1793 the front and allocating main sections to each of the key topics; 1794 addressing Ticket #379; 1796 o Addressed Ticket #382, fix of enhanced form URI template 1797 definition of q in Section 5.3.2; 1799 o Addressed Ticket #381, found a mapping 4.01 to 401 Unauthorized in 1800 Section 7; 1802 o Addressed Ticket #380 (Add IANA registration for "core.hc" 1803 Resource Type) in Section 9; 1805 o Addressed Ticket #376 (CoAP 4.05 response can't be translated to 1806 HTTP 405 by HC proxy) in Section 7 by use of empty 'Allow' header; 1808 o Removed details on the pros and cons of HC proxy placement 1809 options; 1811 o Addressed review comments of Carsten Bormann; 1813 o Clarified failure in mapping of HTTP Accept headers (Section 6.3); 1815 o Clarified detection of CoAP servers not supporting blockwise 1816 (Section 8.3); 1818 o Changed CoAP request timeout min value to MAX_RTT + 1819 MAX_SERVER_RESPONSE_DELAY (Section 8.6); 1821 o Added security section item (Section 10.3) related to use of CoAP 1822 blockwise transfers; 1824 o Many editorial improvements. 1826 Changes from ietf-04 to ietf-05: 1828 o Addressed Ticket #366 (Mapping of CoRE Link Format payloads to be 1829 valid in HTTP Domain?) in Section 6.3.3.2 (Content Transcoding - 1830 CORE Link Format); 1832 o Addressed Ticket #375 (Add requirement on mapping of CoAP 1833 diagnostic payload) in Section 6.3.3.3 (Content Transcoding - 1834 Diagnostic Messages); 1836 o Addressed comment from Yusuke (http://www.ietf.org/mail- 1837 archive/web/core/current/msg05491.html) in Section 6.3.3.1 1838 (Content Transcoding - General); 1840 o Various editorial improvements. 1842 Changes from ietf-03 to ietf-04: 1844 o Expanded use case descriptions in Section 4; 1846 o Fixed/enhanced discovery examples in Section 5.4.1; 1847 o Addressed Ticket #365 (Add text on media type conversion by HTTP- 1848 CoAP proxy) in new Section 6.3.1 (Generalized media type mapping) 1849 and new Section 6.3.2 (Content translation); 1851 o Updated HTTPBis WG draft references to recently published RFC 1852 numbers. 1854 o Various editorial improvements. 1856 Changes from ietf-02 to ietf-03: 1858 o Closed Ticket #351 "Add security implications of proposed default 1859 HTTP-CoAP URI mapping"; 1861 o Closed Ticket #363 "Remove CoAP scheme in default HTTP-CoAP URI 1862 mapping"; 1864 o Closed Ticket #364 "Add discovery of HTTP-CoAP mapping 1865 resource(s)". 1867 Changes from ietf-01 to ietf-02: 1869 o Selection of single default URI mapping proposal as proposed to WG 1870 mailing list 2013-10-09. 1872 Changes from ietf-00 to ietf-01: 1874 o Added URI mapping proposals to Section 4 as per the Email 1875 proposals to WG mailing list from Esko. 1877 Authors' Addresses 1879 Angelo P. Castellani 1880 University of Padova 1881 Via Gradenigo 6/B 1882 Padova 35131 1883 Italy 1885 Email: angelo@castellani.net 1887 Salvatore Loreto 1888 Ericsson 1889 Hirsalantie 11 1890 Jorvas 02420 1891 Finland 1893 Email: salvatore.loreto@ericsson.com 1894 Akbar Rahman 1895 InterDigital Communications, LLC 1896 1000 Sherbrooke Street West 1897 Montreal H3A 3G4 1898 Canada 1900 Phone: +1 514 585 0761 1901 Email: Akbar.Rahman@InterDigital.com 1903 Thomas Fossati 1904 Nokia 1905 3 Ely Road 1906 Milton, Cambridge CB24 6DD 1907 UK 1909 Email: thomas.fossati@nokia.com 1911 Esko Dijk 1912 Philips Lighting 1913 High Tech Campus 7 1914 Eindhoven 5656 AE 1915 The Netherlands 1917 Email: esko.dijk@philips.com