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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 INTERNET DRAFT Michiel B. de Jong 2 Document: draft-dejong-remotestorage-10 (independent) 3 F. Kooman 4 Intended Status: Proposed Standard (independent) 5 Expires: 7 June 2018 4 December 2017 7 remoteStorage 9 Abstract 11 This draft describes a protocol by which client-side applications, 12 running inside a web browser, can communicate with a data storage 13 server that is hosted on a different domain name. This way, the 14 provider of a web application need not also play the role of data 15 storage provider. The protocol supports storing, retrieving, and 16 removing individual documents, as well as listing the contents of an 17 individual folder, and access control is based on bearer tokens. 19 Status of this Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on 7 June 2018. 36 Copyright Notice 38 Copyright (c) 2017 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction...................................................2 54 2. Terminology....................................................3 55 3. Storage model..................................................3 56 4. Requests.......................................................4 57 5. Response codes.................................................7 58 6. Versioning.....................................................8 59 7. CORS headers...................................................8 60 8. Session description............................................9 61 9. Bearer tokens and access control...............................9 62 10. Application-first bearer token issuance.......................10 63 11. Storage-first bearer token issuance...........................12 64 12. Example wire transcripts......................................12 65 12.1. WebFinger................................................12 66 12.2. OAuth dialog form........................................13 67 12.3. OAuth dialog form submission.............................14 68 12.4. OPTIONS preflight........................................14 69 12.5. Initial PUT..............................................15 70 12.6. Subsequent PUT...........................................15 71 12.7. GET......................................................16 72 12.8. DELETE...................................................17 73 13. Distributed versioning........................................18 74 14. Security Considerations.......................................19 75 15. IANA Considerations...........................................20 76 16. Acknowledgments...............................................20 77 17. References....................................................20 78 17.1. Normative References.....................................20 79 17.2. Informative References...................................21 80 18. Authors' addresses............................................22 82 1. Introduction 84 Many services for data storage are available over the Internet. This 85 specification describes a vendor-independent interface for such 86 services. It is based on HTTPS, CORS and bearer tokens. The 87 metaphor for addressing data on the storage is that of folders 88 containing documents and subfolders. The actions the interface 89 exposes are: 91 * GET a folder: retrieve the names and current versions of the 92 documents and subfolders currently contained by the folder 94 * GET a document: retrieve its content type, current version, 95 and contents 97 * PUT a document: store a new version, its content type, and 98 contents, conditional on the current version 100 * DELETE a document: remove it from the storage, conditional on 101 the current version 103 * HEAD a folder or document: like GET, but omitting the response 104 body 106 The exact details of these five actions are described in this 107 specification. 109 2. Terminology 111 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 112 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 113 document are to be interpreted as described in RFC 2119 [WORDS]. 115 "SHOULD" and "SHOULD NOT" are appropriate when valid exceptions to a 116 general requirement are known to exist or appear to exist, and it is 117 infeasible or impractical to enumerate all of them. However, they 118 should not be interpreted as permitting implementors to fail to 119 implement the general requirement when such failure would result in 120 interoperability failure. 122 3. Storage model 124 The server stores data in nodes that form a tree structure. 125 Internal nodes are called 'folders' and leaf nodes are called 126 'documents'. For a folder, the server stores references to nodes 127 contained in the folder, and it should be able to produce a list of 128 them, with for each contained item: 130 * item name 131 * item type (folder or document) 132 * current version 133 * content type 134 * content length 136 For a document, the server stores, and should be able to produce: 138 * current version 139 * content type 140 * content length 141 * content 143 4. Requests 145 Client-to-server requests SHOULD be made over HTTPS [HTTPS], and 146 servers MUST comply with HTTP/1.1 [HTTP]. Specifically, they 147 MUST support chunked transfer coding on PUT requests. Servers MAY 148 also offer an optional switch to HTTP/2 [HTTP/2]. 150 A request is considered successful if the HTTP response code is in 151 the 2xx range (e.g. 200 OK, 201 Created), and unsuccessful if an 152 error occurred or a condition was not met, e.g. response code 404 153 Not Found, 304 Not Modified. 155 The root folder of the storage tree is represented by the following 156 URL: 158 URI_ENCODE( '/' ) 160 Subsequently, let be the URL of a folder, i.e. ends 161 with a '/', then the URL of an item contained in it is: 163 URI_ENCODE( ) 165 for a document, or: 167 URI_ENCODE( '/' ) 169 for a folder. 171 Item names MAY contain all characters, before URI_ENCODE, except '/' 172 and the null character '\0' and MUST NOT have zero length. Item 173 names MUST NOT be equal to '.' or to '..', as those have a special 174 semantic in URIs (Section 5.2.4 of [URI]). 176 A document description is a map containing one string-valued 'ETag' 177 field, one string-valued 'Content-Type' and one integer-valued 178 'Content-Length' field. They represent the document's current 179 version, its content type, and its content length respectively. Note 180 that content length is measured in octets (bytes), not in 181 characters. 183 A folder description is a map containing a string-valued 'ETag' 184 field, representing the folder's current version. 186 A successful GET request to a folder MUST be responded to with a 187 JSON-LD [JSON-LD] document (content type 'application/ld+json'), 188 containing as its 'items' field a map in which contained documents 189 appear as entries to a document description, and 190 contained non-empty folders appear as entries '/' to a 191 folder description. It MUST also contain an '@context' field with 192 the value 'http://remotestorage.io/spec/folder-description'. For 193 instance: 195 { 196 "@context": "http://remotestorage.io/spec/folder-description", 197 "items": { 198 "abc": { 199 "ETag": "DEADBEEFDEADBEEFDEADBEEF", 200 "Content-Type": "image/jpeg", 201 "Content-Length": 82352 202 }, 203 "def/": { 204 "ETag": "1337ABCD1337ABCD1337ABCD" 205 } 206 } 207 } 209 GET requests to empty folders SHOULD be responded to with a folder 210 description with no items (the items field set to '{}'). However, an 211 empty folder MUST NOT be listed as an item in its parent folder. 213 PUT and DELETE requests only need to be made to documents, and never 214 to folders. A document PUT will make all ancestor folders along its 215 path become non-empty; deleting the last document from a subtree 216 will make that whole subtree become empty. Folders will therefore 217 show up in their parent folder descriptions if and only if their 218 subtree contains at least one document. 220 In contexts outside of this document, non-empty folders may be 221 called 'existent', while empty folders may be called 'non-existent'. 223 A successful GET request to a document SHOULD be responded to with 224 the full document contents in the body, the document's content type 225 in a 'Content-Type' header, its content length in octets (not in 226 characters) in a 'Content-Length' header, and the document's current 227 version as a strong ETag in an 'ETag' header. 229 Note that the use of strong ETags prohibits changing the response 230 body based on request headers; in particular, the server will not be 231 able to serve the same document uncompressed to some clients and 232 compressed to other clients when requested, since the two bodies 233 would not be identical byte-for-byte. 235 Servers MAY support Content-Range headers [RANGE] on GET requests, 236 but whether or not they do SHOULD be announced both through the 237 "http://tools.ietf.org/html/rfc7233" option mentioned below in 238 section 10 and through the HTTP 'Accept-Ranges' response header. 240 A successful PUT request to a document MUST result in: 242 * the request body being stored as the document's new content, 243 * parent and further ancestor folders being silently created as 244 necessary, with the document (name and version) being added to 245 its parent folder, and each folder added to its subsequent 246 parent, 247 * the value of its Content-Type header being stored as the 248 document's new content type, 249 * its version being updated, as well as that of its parent folder 250 and further ancestor folders, using a strong validator [HTTP, 251 section 7.2]. 253 If no valid Content-Type header was received as part of a PUT 254 request, the server MAY refuse to process the request, and instead 255 respond with a descriptive error message in the body, as well as a 256 http response code from the 4xx range. 258 RemoteStorage does not place any restrictions on the value of 259 Content-Type other than what is defined in [HTTP, section 3.1.1.5]. 261 The response MUST contain a strong ETag header, with the document's 262 new version (for instance a hash of its contents) as its value. 264 A successful DELETE request to a document MUST result in: 266 * the deletion of that document from the storage, and from its 267 parent folder, 268 * silent deletion of the parent folder if it is left empty by 269 this, and so on for further ancestor folders, 270 * the version of its parent folder being updated, as well as that 271 of further ancestor folders. 273 A successful HEAD request SHOULD be responded to like to the 274 equivalent GET request, but omitting the response body. 276 A successful OPTIONS request SHOULD be responded to as described in 277 the CORS section below. 279 5. Response codes 281 Response codes SHOULD be given as defined by [HTTP, section 6] and 282 [BEARER, section 3.1]. The following is a non-normative list of 283 status codes that are likely to occur in practice: 285 * 500 if an internal server error occurred, 286 * 429 if the client makes too frequent requests or is suspected 287 of malicious activity, 288 * 414 if the request URI is too long, 289 * 416 if Range requests are supported by the server and the Range 290 request can not be satisfied, 291 * 401 for all requests that require a valid bearer token and 292 where no valid one was sent (see also [BEARER, section 293 3.1]), 294 * 403 for all requests that have insufficient scope, e.g. 295 accessing a for which no scope was obtained, or 296 accessing data outside the user's , 297 * 404 for all DELETE, GET and HEAD requests to documents that do 298 not exist on the storage, 299 * 304 for a conditional GET request whose precondition 300 fails (see "Versioning" below), 301 * 409 for a PUT request where any folder name in the path 302 clashes with an existing document's name at the same 303 level, or where the document name coincides with an 304 existing folder's name at the same level. 305 * 412 for a conditional PUT or DELETE request whose precondition 306 fails (see "Versioning" below), 307 * 507 in case the account is over its storage quota, 308 * 4xx for all malformed requests, e.g. reserved characters in the 309 path [URI, section 2.2], as well as for all PUT and DELETE 310 requests to folders, 311 * 2xx for all successful requests. 313 Clients SHOULD also handle the case where a response takes too long 314 to arrive, or where no response is received at all. 316 6. Versioning 318 All successful GET, HEAD, PUT and DELETE requests MUST return an 319 'ETag' header [HTTP] with, in the case of GET and HEAD the current 320 version, in the case of PUT, the new version, and in case of DELETE, 321 the version that was deleted. All successful GET requests MUST 322 return a 'Cache-Control: no-cache' header. PUT and DELETE requests 323 MAY have an 'If-Match' request header [COND], and MUST fail with a 324 412 response code if that does not match the document's current 325 version. 327 All successful requests MUST return an 'ETag' header [HTTP] with, in 328 the case of GET, the current version, in the case of PUT, the new 329 version, and in case of DELETE, the version that was deleted. All 330 successful GET requests MUST return an 'Cache-Control: no-cache' 331 header. PUT and DELETE requests MAY have an 'If-Match' request 332 header [COND], and MUST fail with a 412 response code if that 333 does not match the document's current version. 335 GET requests MAY have a comma-separated list of revisions in an 336 'If-None-Match' header [COND], and SHOULD be responded to with a 304 337 response if that list includes the document or folder's current 338 version. A PUT request MAY have an 'If-None-Match: *' header [COND], 339 in which case it MUST fail with a 412 response code if the document 340 already exists. 342 A provider MAY offer version rollback functionality to its users, 343 but this specification does not define the interface for that. 345 7. CORS headers 347 All responses MUST carry CORS headers [CORS]. The server MUST also 348 reply to preflight OPTIONS requests as per CORS. 350 8. Session description 352 The information that a client needs to receive in order to be able 353 to connect to a server SHOULD reach the client as described in the 354 'bearer token issuance' sections below. It consists of: 356 * , consisting of 'https://' followed by a server 357 host, and optionally a server port and a path prefix as per 358 [IRI]. Examples: 359 * 'https://example.com' (host only) 360 * 'https://example.com:8080' (host and port) 361 * 'https://example.com/path/to/storage' (host, port and 362 path prefix; note there is no trailing slash) 363 * as per [OAUTH]. The token SHOULD be hard to 364 guess and SHOULD NOT be reused from one client to another. It 365 can however be reused in subsequent interactions with the same 366 client, as long as that client is still trusted. Example: 367 'ofb24f1ac3973e70j6vts19qr9v2eei' 368 * , always 'draft-dejong-remotestorage-10' for this 369 alternative version of the specification. 371 The client can make its requests using HTTPS with CORS and bearer 372 tokens, to the URL that is the concatenation of with 373 '/' plus one or more '/' strings indicating a path in the 374 folder tree, followed by zero or one strings, indicating 375 a document. For example, if is 376 "https://storage.example.com/bob", then to retrieve the folder 377 contents of the /public/documents/ folder, or to retrieve a 378 'draft.txt' document from that folder, the client would make 379 requests to, respectively: 381 * https://storage.example.com/bob/public/documents/ 382 * https://storage.example.com/bob/public/documents/draft.txt 384 9. Bearer tokens and access control 386 A bearer token represents one or more access scopes. These access 387 scopes are represented as strings of the form , 388 where the string SHOULD be lower-case alphanumerical, other 389 than the reserved word 'public', and can be ':r' or ':rw'. 390 The access the bearer token gives is the sum of its access scopes, 391 with each access scope representing the following permissions: 393 '*:rw') any request, 395 '*:r') any GET or HEAD request, 397 ':rw') any requests to paths relative to 398 that start with '/' '/' or 399 '/public/' '/', 401 ':r') any GET or HEAD requests to paths relative to 402 that start with 403 '/' '/' or '/public/' '/', 405 As a special exceptions, GET and HEAD requests to a document (but 406 not a folder) whose path starts with '/public/' are always allowed. 407 They, as well as OPTIONS requests, can be made without a bearer 408 token. Unless [KERBEROS] is used (see section 10 below), all other 409 requests SHOULD present a bearer token with sufficient access scope, 410 using a header of the following form (no double quotes here): 412 Authorization: Bearer 414 In addition, providing the access token via a HTTP query parameter 415 for GET requests MAY be supported by the server, although its use 416 is not recommended, due to its security deficiencies; see [BEARER, 417 section 2.3]. If supported, this SHOULD be announce through the 418 "http://tools.ietf.org/html/rfc6750#section-2.3" WebFinger property 419 as per section 10 below. 421 10. Application-first bearer token issuance 423 To make a remoteStorage server available as 'the remoteStorage of 424 the person identified by ', exactly one link of the following 425 format SHOULD be added to the WebFinger record [WEBFINGER] for 426 : 428 { 429 "href": , 430 "rel": "http://tools.ietf.org/id/draft-dejong-remotestorage", 431 "properties": { 432 "http://remotestorage.io/spec/version": , 433 "http://tools.ietf.org/html/rfc6749#section-4.2": , 434 "...": "...", 435 } 436 } 438 A common way of identifying persons as at is through a 439 URI of the format "acct:@". Persons who use a personal 440 domain name, not shared with any other users, can be identified by 441 a URI of the format "http:///" (see [WEBFINGER, section 4.1]). 443 Here and are as per "Session 444 description" above, and SHOULD be either null or a 445 URL where an OAuth 2.0 implicit-grant flow dialog [OAUTH] is 446 presented. 448 If is a URL, the user can supply their credentials 449 for accessing the account (how, is out of scope), and allow or 450 reject a request by the connecting application to obtain a bearer 451 token for a certain list of access scopes. Note that an account 452 will often belong to just one human user, but may also belong to a 453 group of multiple users (the remoteStorage of at ). 455 If is null, the client will not have a way to obtain 456 an access token, and SHOULD send all requests without Authorization 457 header, and rely on Kerberos [KERBEROS] instead for requests that 458 would normally be sent with a bearer token, but servers SHOULD NOT 459 impose any such access barriers for resources that would normally 460 not require an access token. 462 The '...' ellipses indicate that more properties may be present. 463 Non-breaking examples that have been proposed so far, include a 464 "http://tools.ietf.org/html/rfc6750#section-2.3" property, set to 465 the string value "true" if the server supports passing the bearer 466 token in the URI query parameter as per section 2.3 of [BEARER], 467 instead of in the request header. 469 Another example is "http://tools.ietf.org/html/rfc7233" with a 470 string value of "GET" if Content-Range headers are supported for 471 GET requests as per [RANGE]. 473 Both these proposals are non-breaking extensions, since the client 474 will have a way to work around it if these features are not present 475 (e.g. retrieve the protected resource asynchronously in the first 476 case, or request the entire resource in the second case). 478 A "http://remotestorage.io/spec/web-authoring" property has been 479 proposed with a string value of the fully qualified domain name to 480 which web authoring content is published if the server supports web 481 authoring as per [AUTHORING]. Note that this extension is a breaking 482 extension in the sense that it divides users into "haves", whose 483 remoteStorage accounts allow them to author web content, and 484 "have-nots", whose remoteStorage account does not support this 485 functionality. 487 The server MAY expire bearer tokens, and MAY require the user to 488 register applications as OAuth clients before first use; if no 489 client registration is required, the server MUST ignore the value of 490 the client_id parameter in favor of relying on the origin of the 491 redirect_uri parameter for unique client identification. See section 492 4 of [ORIGIN] for computing the origin. 494 11. Storage-first bearer token issuance 496 To request that the application connects to the user account 497 ' ' , providers MAY redirect to applications with a 498 'remotestorage' field in the URL fragment, with the user account as 499 value. 501 The appplication MUST make sure this request is intended by the 502 user. It SHOULD ask for confirmation from the user whether they want 503 to connect to the given provider account. After confirmation, it 504 SHOULD connect to the given provider account, as defined in Section 505 10. 507 If the 'remotestorage' field exists in the URL fragment, the 508 application SHOULD ignore any other parameters such as 509 'access_token' or 'state', to ensure compatibility with servers 510 that implement older versions of this specification. 512 12. Example wire transcripts 514 The following examples are not normative ("\" indicates a line was 515 wrapped). 517 12.1. WebFinger 519 In application-first, an in-browser application might issue the 520 following request, using XMLHttpRequest and CORS: 522 GET /.well-known/webfinger?resource=acct:michiel@michielbdejon\ 523 g.com HTTP/1.1 524 Host: michielbdejong.com 526 and the server's response might look like this: 528 HTTP/1.1 200 OK 529 Access-Control-Allow-Origin: * 530 Content-Type: application/jrd+json 532 { 533 "links":[{ 534 "href": "https://michielbdejong.com:7678/inbox", 535 "rel": "post-me-anything" 536 }, { 537 "href": "https://michielbdejong.com/me.jpg", 538 "rel": "avatar" 539 }, { 540 "href": "https://3pp.io:4439/storage/michiel", 541 "rel": "http://tools.ietf.org/id/draft-dejong-remotestorag\ 542 e", 543 "properties": { 544 "http://remotestorage.io/spec/version": "draft-dejong-re\ 545 motestorage-10", 546 "http://tools.ietf.org/html/rfc6749#section-4.2": "https\ 547 ://3pp.io:4439/oauth/michiel", 548 "http://tools.ietf.org/html/rfc6750#section-2.3": null, 549 "http://tools.ietf.org/html/rfc7233": null, 550 "http://remotestorage.io/spec/web-authoring": null 551 } 552 }] 553 } 555 12.2. OAuth dialog form 557 Once the in-browser application has discovered the server's OAuth 558 end-point, it will typically redirect the user to this URL, in 559 order to obtain a bearer token. Say the application is hosted on 560 https://drinks-unhosted.5apps.com/ and wants read-write access to 561 the account's "myfavoritedrinks" scope: 563 GET /oauth/michiel?redirect_uri=https%3A%2F%2Fdrinks-unhosted.5\ 564 apps.com%2F&scope=myfavoritedrinks%3Arw&client_id=https%3A%2F%2Fdrinks-\ 565 unhosted.5apps.com&response_type=token HTTP/1.1 566 Host: 3pp.io 568 The server's response might look like this (truncated for brevity): 570 HTTP/1.1 200 OK 572 573 574 575 Allow access? 576 ... 578 12.3. OAuth dialog form submission 580 When the user submits the form, the request would look something 581 like this: 583 POST /oauth HTTP/1.1 584 Host: 3pp.io:4439 585 Origin: https://3pp.io:4439 586 Content-Type: application/x-www-form-urlencoded 587 Referer: https://3pp.io:4439/oauth/michiel?redirect_uri=https%3\ 588 A%2F%2Fdrinks-unhosted.5apps.com%2F&scope=myfavoritedrinks%3Arw&client_\ 589 id=https%3A%2F%2Fdrinks-unhosted.5apps.com&response_type=token 591 client_id=https%3A%2F%2Fdrinks-unhosted.5apps.com&redirect_uri=\ 592 https%3A%2F%2Fdrinks-unhosted.5apps.com%2F&response_type=token&scope=my\ 593 favoritedrinks%3Arw&username=michiel&password=something&allow=Al\ 594 low 596 To which the server could respond with a 302 redirect, back to the 597 origin of the requesting application: 599 HTTP/1.1 302 Found 600 Location: https://drinks-unhosted.5apps.com/#access_token=j2YnG\ 601 tXjzzzHNjkd1CJxoQubA1o%3D&token_type=bearer 603 12.4. OPTIONS preflight 605 When an in-browser application makes a cross-origin request which 606 may affect the server-state, the browser will make a preflight 607 request first, with the OPTIONS verb, for instance: 609 OPTIONS /storage/michiel/myfavoritedrinks/ HTTP/1.1 610 Host: 3pp.io:4439 611 Access-Control-Request-Method: GET 612 Origin: https://drinks-unhosted.5apps.com 613 Access-Control-Request-Headers: Authorization 614 Referer: https://drinks-unhosted.5apps.com/ 616 To which the server can for instance respond: 618 HTTP/1.1 200 OK 619 Access-Control-Allow-Origin: https://drinks-unhosted.5apps.com 620 Access-Control-Allow-Methods: GET, PUT, DELETE 621 Access-Control-Allow-Headers: Authorization, Content-Length, Co\ 622 ntent-Type, Origin, X-Requested-With, If-Match, If-None-Match 624 12.5. Initial PUT 626 An initial PUT may contain an 'If-None-Match: *' header, like this: 628 PUT /storage/michiel/myfavoritedrinks/test HTTP/1.1 629 Host: 3pp.io:4439 630 Content-Length: 91 631 Origin: https://drinks-unhosted.5apps.com 632 Authorization: Bearer j2YnGtXjzzzHNjkd1CJxoQubA1o= 633 Content-Type: application/json; charset=UTF-8 634 Referer: https://drinks-unhosted.5apps.com/? 635 If-None-Match: * 637 {"name":"test","@context":"http://remotestorage.io/spec/modules\ 638 /myfavoritedrinks/drink"} 640 And the server may respond with either a 201 Created or a 200 OK 641 status: 643 HTTP/1.1 201 Created 644 Access-Control-Allow-Origin: https://drinks-unhosted.5apps.com 645 ETag: "1382694045000" 647 12.6. Subsequent PUT 648 A subsequent PUT may contain an 'If-Match' header referring to the 649 ETag previously returned, like this: 651 PUT /storage/michiel/myfavoritedrinks/test HTTP/1.1 652 Host: 3pp.io:4439 653 Content-Length: 91 654 Origin: https://drinks-unhosted.5apps.com 655 Authorization: Bearer j2YnGtXjzzzHNjkd1CJxoQubA1o= 656 Content-Type: application/json; charset=UTF-8 657 Referer: https://drinks-unhosted.5apps.com/ 658 If-Match: "1382694045000" 660 {"name":"test", "updated":true, "@context":"http://remotestorag\ 661 e.io/spec/modules/myfavoritedrinks/drink"} 663 And the server may respond with a 412 Conflict or a 200 OK status: 665 HTTP/1.1 200 OK 666 Access-Control-Allow-Origin: https://drinks-unhosted.5apps.com 667 ETag: "1382694048000" 669 12.7. GET 671 A GET request would also include the bearer token, and optionally 672 an If-None-Match header: 674 GET /storage/michiel/myfavoritedrinks/test HTTP/1.1 675 Host: 3pp.io:4439 676 Origin: https://drinks-unhosted.5apps.com 677 Authorization: Bearer j2YnGtXjzzzHNjkd1CJxoQubA1o= 678 Referer: https://drinks-unhosted.5apps.com/ 679 If-None-Match: "1382694045000", "1382694048000" 681 And the server may respond with a 304 Not Modified status: 683 HTTP/1.1 304 Not Modified 684 Access-Control-Allow-Origin: https://drinks-unhosted.5apps.com 685 ETag: "1382694048000" 687 Or a 200 OK status, plus a response body: 689 HTTP/1.1 200 OK 690 Access-Control-Allow-Origin: https://drinks-unhosted.5apps.com 691 Content-Type: application/json; charset=UTF-8 692 Content-Length: 106 693 ETag: "1382694048000" 694 Cache-Control: no-cache 696 {"name":"test", "updated":true, "@context":"http://remotestora\ 697 ge.io/spec/modules/myfavoritedrinks/drink"} 699 If the GET URL would have been "/storage/michiel/myfavoritedrinks/", 700 a 200 OK response would have a folder description as the response 701 body: 703 HTTP/1.1 200 OK 704 Access-Control-Allow-Origin: https://drinks-unhosted.5apps.com 705 Content-Type: application/ld+json 706 Content-Length: 171 707 ETag: "1382694048000" 708 Cache-Control: no-cache 710 {"@context":"http://remotestorage.io/spec/folder-version","ite\ 711 ms":{"test":{"ETag":"1382694048000","Content-Type":"application/json; \ 712 charset=UTF-8","Content-Length":106}}} 714 If the GET URL would have been a non-existing document like 715 "/storage/michiel/myfavoritedrinks/x", the response would have a 404 716 Not Found status, and no ETag header: 718 HTTP/1.1 404 Not Found 719 Access-Control-Allow-Origin: https://drinks-unhosted.5apps.com 721 12.8. DELETE 723 A DELETE request may look like this: 725 DELETE /storage/michiel/myfavoritedrinks/test HTTP/1.1 726 Host: 3pp.io:4439 727 Origin: https://drinks-unhosted.5apps.com 728 Authorization: Bearer j2YnGtXjzzzHNjkd1CJxoQubA1o= 729 Content-Type: application/json; charset=UTF-8 730 Referer: https://drinks-unhosted.5apps.com/ 731 If-Match: "1382694045000" 733 And the server may respond with a 412 Conflict or a 200 OK status: 735 HTTP/1.1 412 Conflict 736 Access-Control-Allow-Origin: https://drinks-unhosted.5apps.com 737 ETag: "1382694048000" 739 13. Distributed versioning 741 This section is non-normative, and is intended to explain some of 742 the design choices concerning ETags and folder listings. At the 743 same time it will hopefully help readers who intend to develop an 744 application that uses remoteStorage as its per-user data storage. 745 When multiple clients have read/write access to the same document, 746 versioning conflicts may occur. For instance, client A may make 747 a PUT request that changes the document from version 1 to version 748 2, after which client B may make a PUT request attempting to change 749 the same document from version 1 to version 3. 751 In this case, client B can add an 'If-Match: "1"' header, which 752 would trigger a 412 Conflict response code, since the current 753 version ("2") does not match the version required as a condition by 754 the header If-Match header ("1"). 756 Client B is now aware of the conflict, and may consult the user, 757 saying the update to version 3 failed. The user may then choose, 758 through the user interface of client B, whether version 2 or 759 version 3 should be kept, or maybe the document should be reverted 760 on the server to version 1, or a merged version 4 is needed. Client 761 B may then make a request that puts the document to the version the 762 user wishes; this time setting an 'If-Match: "2"' header instead. 764 Both client A and client B would periodically poll the root 765 folder of each scope they have access to, to see if the version 766 of the root folder changed. If it did, then one of the versions 767 listed in there will necessarily have changed, and the client can 768 make a GET request to that child folder or document, to obtain 769 its latest version. 771 Because an update in a document will result in a version change of 772 its containing folder, and that change will propagate all the way 773 to the root folder, it is not necessary to poll each document for 774 changes individually. 776 As an example, the root folder may contain 10 directories, 777 each of which contain 10 directories, which each contain 10 778 documents, so their paths would be for instance '/0/0/1', '/0/0/2', 779 etcetera. Then one GET request to the root folder '/' will be 780 enough to know if any of these 1000 documents has changed. 782 Say document '/7/9/2' has changed; then the GET request to '/' will 783 come back with a different ETag, and entry '7/' will have a 784 different value in its JSON content. The client could then request 785 '/7/', '/7/9/', and '/7/9/2' to narrow down the one document that 786 caused the root folder's ETag to change. 788 Note that the remoteStorage server does not get involved in the 789 conflict resolution. It keeps the canonical current version at all 790 times, and allows clients to make conditional GET and PUT requests, 791 but it is up to whichever client discovers a given version 792 conflict, to resolve it. 794 14. Security Considerations 796 To prevent man-in-the-middle attacks, the use of HTTPS instead of 797 http is important for both the interface itself and all end-points 798 involved in WebFinger, OAuth, and (if present) the storage-first 799 application launch dashboard. 801 A malicious party could link to an application, but specifying a 802 remoteStorage account address that it controls, thus tricking the 803 user into using a trusted application to send sensitive data to the 804 wrong remoteStorage server. To mitigate this, applications SHOULD 805 clearly display to which remoteStorage server they are sending the 806 user's data. 808 Applications could request scopes that the user did not intend to 809 give access to. The user SHOULD always be prompted to carefully 810 review which scopes an application is requesting. 812 An application may upload malicious HTML pages and then trick the 813 user into visiting them, or upload malicious client-side scripts, 814 that take advantage of being hosted on the user's domain name. The 815 origin on which the remoteStorage server has its interface SHOULD 816 therefore NOT be used for anything else, and the user SHOULD be 817 warned not to visit any web pages on that origin. In particular, the 818 OAuth dialog and launch dashboard or token revocation interface 819 SHOULD be on a different origin than the remoteStorage interface. 821 Where the use of bearer tokens is impractical, a user may choose to 822 store documents on hard-to-guess URLs [CAPABILITIES] whose path 823 after starts with '/public/', while sharing this URL 824 only with the intended audience. That way, only parties who know the 825 document's hard-to-guess URL, can access it. The server SHOULD 826 therefore make an effort to detect and stop brute-force attacks that 827 attempt to guess the location of such documents. 829 The server SHOULD also detect and stop denial-of-service attacks 830 that aim to overwhelm its interface with too much traffic. 832 15. IANA Considerations 834 This document registers the following WebFinger properties: 835 * "http://remotestorage.io/spec/version" 836 * "http://tools.ietf.org/html/rfc6749#section-4.2" 837 * "http://tools.ietf.org/html/rfc6750#section-2.3" 838 * "http://tools.ietf.org/html/rfc7233" 839 * "http://remotestorage.io/spec/web-authoring" 841 16. Acknowledgements 843 The authors would like to thank everybody who contributed to the 844 development of this protocol, including Kenny Bentley, Javier Diaz, 845 Daniel Groeber, Bjarni Runar, Jan Wildeboer, Charles Schultz, Peter 846 Svensson, Valer Mischenko, Michiel Leenaars, Jan-Christoph 847 Borchardt, Garret Alfert, Sebastian Kippe, Max Wiehle, Melvin 848 Carvalho, Martin Stadler, Geoffroy Couprie, Niklas Cathor, Marco 849 Stahl, James Coglan, Ken Eucker, Daniel Brolund, elf Pavlik, Nick 850 Jennings, Markus Sabadello, Steven te Brinke, Matthias Treydte, 851 Rick van Rein, Mark Nottingham, Julian Reschke, Markus Lanthaler, 852 and Markus Unterwaditzer, among many others. 854 17. References 856 17.1. Normative References 858 [WORDS] 859 Bradner, S., "Key words for use in RFCs to Indicate Requirement 860 Levels", BCP 14, RFC 2119, March 1997. 862 [IRI] 863 Duerst, M., "Internationalized Resource Identifiers (IRIs)", 864 RFC 3987, January 2005. 866 [URI] 867 Fielding, R., "Uniform Resource Identifier (URI): Generic 868 Syntax", RFC 3986, January 2005. 870 [WEBFINGER] 871 Jones, P., Salguerio, G., Jones, M, and Smarr, J., 872 "WebFinger", RFC7033, September 2013. 874 [OAUTH] 875 "Section 4.2: Implicit Grant", in: Hardt, D. (ed), "The OAuth 876 2.0 Authorization Framework", RFC6749, October 2012. 878 [ORIGIN] 879 "Section 4: Origin of a URI", in: Barth, A., "The Web Origin 880 Concept", RFC6454, December 2011. 882 17.2. Informative References 884 [HTTPS] 885 Rescorla, E., "HTTP Over TLS", RFC2818, May 2000. 887 [HTTP] 888 Fielding et al., "Hypertext Transfer Protocol (HTTP/1.1): 889 Semantics and Content", RFC7231, June 2014. 891 [COND] 892 Fielding et al., "Hypertext Transfer Protocol (HTTP/1.1): 893 Conditional Requests", RFC7232, June 2014. 895 [RANGE] 896 Fielding et al., "Hypertext Transfer Protocol (HTTP/1.1): 897 Conditional Requests", RFC7233, June 2014. 899 [HTTP/2] 900 M. Belshe, R. Peon, M. Thomson, Ed. "Hypertext Transfer Protocol 901 Version 2 (HTTP/2)", RFC7540, May 2015. 903 [JSON-LD] 904 M. Sporny, G. Kellogg, M. Lanthaler, "JSON-LD 1.0", W3C 905 Proposed Recommendation, 906 http://www.w3.org/TR/2014/REC-json-ld-20140116/, January 2014. 908 [CORS] 909 van Kesteren, Anne (ed), "Cross-Origin Resource Sharing -- 910 W3C Candidate Recommendation 29 January 2013", 911 http://www.w3.org/TR/cors/, January 2013. 913 [KERBEROS] 914 C. Neuman et al., "The Kerberos Network Authentication Service 915 (V5)", RFC4120, July 2005. 917 [BEARER] 918 M. Jones, D. Hardt, "The OAuth 2.0 Authorization Framework: 919 Bearer Token Usage", RFC6750, October 2012. 921 [AUTHORING] 922 "Using remoteStorage for web authoring", reSite wiki, retrieved 923 September 2014. https://github.com/michielbdejong/resite/wiki 924 /Using-remoteStorage-for-web-authoring 926 [CAPABILITIES] 927 J. Tennison (ed.), "Good Practices for Capability URLs", 928 http://www.w3.org/TR/capability-urls/, February 2014. 930 18. Authors' addresses 932 Michiel B. de Jong 933 (independent) 935 Email: michiel@unhosted.org 937 F. Kooman 938 (independent) 940 Email: fkooman@tuxed.net