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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group A. Cedik 3 Internet-Draft shipcloud GmbH 4 Intended status: Standards Track E. Wilde 5 Expires: October 1, 2020 Axway 6 March 30, 2020 8 Communicating Warning Information in HTTP APIs 9 draft-cedik-http-warning-01 11 Abstract 13 This document defines a new HTTP header field Content-Warning and a 14 standard response format for representing warning information in HTTP 15 APIs. 17 Note to Readers 19 This draft should be discussed on the rfc-interest mailing list 20 (). 22 Online access to all versions and files is available on GitHub 23 (). 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on October 1, 2020. 42 Copyright Notice 44 Copyright (c) 2020 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (https://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3 61 3. Content-Warning Header Field . . . . . . . . . . . . . . . . 3 62 4. The "embedded-warning" Content-Warning Type . . . . . . . . . 4 63 5. JSON Warning Format . . . . . . . . . . . . . . . . . . . . . 4 64 6. Example with HTTP Header Field and Embedded Warning . . . . . 5 65 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 66 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 67 8.1. HTTP Header Field Content-Warning . . . . . . . . . . . . 6 68 8.2. Content-Warning Type Registry . . . . . . . . . . . . . . 6 69 8.2.1. Registration Procedure . . . . . . . . . . . . . . . 6 70 8.2.2. Initial Registry Content . . . . . . . . . . . . . . 7 71 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 72 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 73 9.2. Informative References . . . . . . . . . . . . . . . . . 8 74 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8 75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 77 1. Introduction 79 Many current APIs are based on HTTP [RFC7230] as their application 80 protocol. Their response handling model is based on the assumption 81 that requests either are successful or they fail. In both cases 82 (success and failure) an HTTP status code [RFC7231] is returned to 83 convey either fact. 85 But response status is not always strictly either success or failure. 86 For example, there are cases where an underlying system returns a 87 response with data that cannot be defined as a clear error. API 88 providers who are integrating such a service might want to return a 89 success response nonetheless, but returning a HTTP status code of 90 e.g. 200 OK without any additional information is not the only 91 possible approach in this case. 93 As defined in the principles of Web architecture 94 [W3C.REC-webarch-20041215], agents that "recover from errors by 95 making a choice without the user's consent are not acting on the 96 user's behalf". Therefore APIs should be able to communicate what 97 has happened to their consumers, which then allows clients or users 98 to make more informed decisions. Note that this specification 99 specifically targets warnings and not errors, meaning that while it 100 may be useful for clients to understand the warning condition and act 101 on it, they also may choose to ignore it and treat the response as a 102 successful one. 104 This document defines a warning code and a standard response 105 structure for communicating and representing warning information in 106 HTTP APIs. The goal is to allow HTTP providers to have a 107 standardized way of communicating to their consumers that while the 108 response can be considered to represent success, there is warning 109 information available that they might want to take into account. 111 As a general guideline, warning information should be considered to 112 be any information that can be safely ignored (treating the response 113 as if it did not communicate or embed any warning information), but 114 that might help clients and users to make better decisions. 116 2. Notational Conventions 118 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 119 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 120 document are to be interpreted as described in [RFC2119]. 122 3. Content-Warning Header Field 124 The Content-Warning header field allows to represent different kinds 125 of warning information via HTTP. It is defined as a Structured 126 Header List [I-D.ietf-httpbis-header-structure]. Its ABNF is: 128 Content-Warning = sh-list 130 Each member of the list MUST have exactly the two parameters "type" 131 and "date". 133 The "type" parameter represents the warning that is being 134 signaled. Its value is defined as a sh-token and SHOULD be a type 135 that is registered in the Content-Warning type registry 136 Section 8.2. Clients SHOULD ignore Content-Warning types that 137 they do not know. 139 The "date" parameter defines the last occurrence of this warning 140 as a structured headers date as defined in 141 [I-D.ietf-binary-structured-headers] (e.g. "1581410465"). 143 4. The "embedded-warning" Content-Warning Type 145 This document introduces the Content-Warning Type "embedded-warning". 147 As mentioned in the introduction (Section 1), HTTP requests can be 148 successful or they can fail. They can also result in a state where 149 the original intent was satisfied, but a side effect happened that 150 should be conveyed back to the client. 152 To make it easier for clients to handle such an event, the Content- 153 Warning type "embedded-warning" MAY be returned. In this case, the 154 client MAY either treat the response according to its HTTP status 155 code, or in addition the client MAY use the embedded warning 156 information to understand the nature of the warning. 158 The "embedded-warning" type does not prescribe the way in which 159 warnings are represented. The assumption is that the response will 160 have embedded information that allows the client to learn about the 161 nature of the warning. The following section describes a JSON 162 structure that MAY be used to represent the warning. HTTP services 163 are free to use this or other formats to represent the warning 164 information they are embedding. 166 An exemplary Content-Warning header field looks like this: 168 Content-Warning: "embedded-warning"; 1590190500 170 5. JSON Warning Format 172 The JSON warning format uses the JSON format described in [RFC8259]. 173 It is intended to be used as a building block in the response schemas 174 of JSON-based APIs. 176 In many current designs of JSON-based HTTP APIs, services represent 177 response data as members of the returned JSON object. In order to 178 make it easier for consumers to identify information about warnings, 179 a top-level member is defined that contains all warning information 180 in a representation. A "warnings" member MUST encapsulate the 181 warnings that will be returned to the client. 183 When an condition occurs that can not be defined as a "hard error" 184 (i.e., that allows clients to continue treating the resulting 185 response as a success), additional information about this condition 186 can be returned to the API client. The "warnings" member MUST be an 187 array that is structured with one object for each and every warning 188 message that is returned to the client. 190 Entries in these individual objects follow the pattern described in 191 [RFC7807]. 193 When warnings are present the Content-Warning header field (as 194 defined in Section 3) SHOULD be set to indicate that warnings have be 195 returned. This way a client will not have to parse the response body 196 to find out whether a warnings member is present. 198 6. Example with HTTP Header Field and Embedded Warning 200 Since warnings do not have an effect on the returned HTTP status 201 code, the response status code SHOULD be in the 2xx range, indicating 202 that the intent of the API client was successful. 204 POST /example HTTP/1.1 205 Host: example.com 206 Accept: application/json 208 HTTP/1.1 200 OK 209 Content-Type: application/json 210 Content-Warning: "embedded-warning"; 1590190500 212 { 213 "request_id": "2326b087-d64e-43bd-a557-42171155084f", 214 "warnings": [ 215 { 216 "detail": "Street name was too long. It has been shortened...", 217 "instance": "https://example.com/shipments/3a186c51/msgs/c94d", 218 "status": "200", 219 "title": "Street name too long. It has been shortened.", 220 "type": "https://example.com/errors/shortened_entry" 221 }, 222 { 223 "detail": "City for this zipcode unknown. Code for shipment..", 224 "instance": "https://example.com/shipments/3a186c51/msgs/5927", 225 "status": "200", 226 "title": "City for zipcode unknown.", 227 "type": "https://example.com/errors/city_unknown" 228 } 229 ], 230 "id": "3a186c51d4281acb", 231 "carrier_tracking_no": "84168117830018", 232 "tracking_url": "http://example.com/3a186c51d", 233 "label_url": "http://example.com/shipping_label_3a186c51d.pdf", 234 "price": 3.4 235 } 237 7. Security Considerations 239 API providers need to exercise care when reporting warnings. 240 Malicious actors could use this information for orchestrating 241 attacks. Social engineering can also be a factor when warning 242 information is returned by the API. 244 8. IANA Considerations 246 8.1. HTTP Header Field Content-Warning 248 This specification registers the following entry in the Permanent 249 Message Header Field Names registry established by [RFC3864]: 251 o Header field name: Content-Warning 253 o Applicable protocol: HTTP 255 o Status: standard 257 o Author/Change Controller: IETF 259 o Specification document(s): [this document] 261 o Related information: 263 8.2. Content-Warning Type Registry 265 The "Content-Warning Type Registry" defines the namespace for new 266 Content-Warning types. This specification establishes a new registry 267 according to the guidelines given in [RFC8126]. This new registry 268 should not be included in an existing group of registries. 270 8.2.1. Registration Procedure 272 A registration MUST include the following fields: 274 o Content-Warning Type: Name of the Content-Warning Type 276 o Reference: Pointer to a specification text 278 The registration policy for this registry is "Specification Required" 279 as defined by [RFC8126], Section 4.6. They MUST follow the "sh- 280 token" syntax defined by [I-D.ietf-httpbis-header-structure]. 282 8.2.2. Initial Registry Content 284 The registry has been populated with the registered values shown 285 below: 287 +------------------------+----------------------------------+ 288 | Content-Warning Type | Reference | 289 +------------------------+----------------------------------+ 290 | embedded-warning | this RFC, Section 4 | 291 +------------------------+----------------------------------+ 293 9. References 295 9.1. Normative References 297 [I-D.ietf-binary-structured-headers] 298 Nottingham, M., "Binary Structured HTTP Headers", draft- 299 nottingham-binary-structured-headers-02 (work in 300 progress), March 2020. 302 [I-D.ietf-httpbis-header-structure] 303 Nottingham, M. and P. Kamp, "Structured Headers for HTTP", 304 draft-ietf-httpbis-header-structure-14 (work in progress), 305 October 2019. 307 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 308 Requirement Levels", BCP 14, RFC 2119, 309 DOI 10.17487/RFC2119, March 1997, 310 . 312 [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration 313 Procedures for Message Header Fields", BCP 90, RFC 3864, 314 DOI 10.17487/RFC3864, September 2004, 315 . 317 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 318 Protocol (HTTP/1.1): Message Syntax and Routing", 319 RFC 7230, DOI 10.17487/RFC7230, June 2014, 320 . 322 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 323 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 324 DOI 10.17487/RFC7231, June 2014, 325 . 327 [RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, 328 Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching", 329 RFC 7234, DOI 10.17487/RFC7234, June 2014, 330 . 332 [RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP 333 APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016, 334 . 336 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 337 Writing an IANA Considerations Section in RFCs", BCP 26, 338 RFC 8126, DOI 10.17487/RFC8126, June 2017, 339 . 341 [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data 342 Interchange Format", STD 90, RFC 8259, 343 DOI 10.17487/RFC8259, December 2017, 344 . 346 9.2. Informative References 348 [W3C.REC-webarch-20041215] 349 Jacobs, I. and N. Walsh, "Architecture of the World Wide 350 Web, Volume One", World Wide Web Consortium 351 Recommendation REC-webarch-20041215, December 2004, 352 . 354 Appendix A. Acknowledgements 356 Thanks for comments and suggestions provided by ... 358 Authors' Addresses 360 Andre Cedik 361 shipcloud GmbH 363 Email: andre.cedik@googlemail.com 365 Erik Wilde 366 Axway 368 Email: erik.wilde@dret.net 369 URI: http://dret.net/netdret/