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Up to [Public] / 2006 / webapi / FileAPI|
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1.1 arangana 1:
2:
3:
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12:
13:
14:
15:
16:
17: File API
1.14 ! arangana 18:
1.1 arangana 19:
20:
21:
22:
30:
31:
32:
33:
37:
38:
39: Arun Ranganathan
40: Mozilla Corporation
41:
42:
43: ED
44:
45:
46:
47:
48:
49:
50:
51: Abstract
52:
53: This specification provides an API
54: for representing file objects in web applications, as well as programmatically selecting them and accessing their data. This includes:
55:
56:
57:
58: - A FileList sequence, which represents an array of individually selected files from the underlying system.
59: The user interface for selection can be invoked via
<input type="file">, i.e. when the
1.14 ! arangana 60: input element is in the File Upload state [HTML5] .
1.1 arangana 61: - A Blob interface, which represents raw binary data, and allows access to ranges of bytes within the Blob object.
62: - A File interface, which includes readonly informational attributes about a file
63: such as its name, its mediatype, and a URL to access its data.
64: - A FileReader interface, which provides methods to read a
65: File, and an event model to obtain the results of these reads.
1.12 arangana 66: - A FileError interface and a FileException exception
1.1 arangana 67: which define error conditions used by this specification.
68:
69:
70:
1.4 arangana 71: Additionally, this specification defines objects to be used within threaded web applications for the synchronous reading of files.
1.1 arangana 72:
73: The section on Requirements and Use Cases [REQ] covers the motivation behind this specification.
74:
75: This API is designed to be used in conjunction with other APIs and elements on the web platform,
76: notably: XMLHttpRequest (e.g. with an overloaded send()
77: method for File objects), postMessage, DataTransfer (part
78: of the drag and drop API defined in [HTML5,]) and
1.12 arangana 79: Web Workers. Additionally, it should be possible to programmatically obtain a list of files from the
1.14 ! arangana 80: input element when it is
! 81: in the File Upload state[HTML5].
1.1 arangana 82: These kinds of behaviors are defined in the appropriate affiliated specifications.
83:
84:
85:
86:
87:
88:
89: Status of this Document
90: public-webapps@w3.org http://lists.w3.org/Archives/Public/public-webapps/?>
91:
92: Previous discussion of this specification has taken place on two other
93: mailing lists: public-webapps@w3.org">public-webapps@w3.org
94: (http://lists.w3.org/Archives/Public/public-webapps/">archive)
95: and public-webapi@w3.org">public-webapi@w3.org
96: (http://lists.w3.org/Archives/Public/public-webapi/">archive). Ongoing
97: discussion will be on the public-webapps@w3.org">public-webapps@w3.org
98: mailing list.
99:
100:
101:
102: This section describes the status of this document at the time of its publication.
103: Other documents may supersede this document, since it is only an editor's draft.
104: A list of current W3C
105: publications and the latest revision of this technical report can be found in the
106: http://www.w3.org/TR/">W3C
107: technical reports index at http://www.w3.org/TR/.
108:
109:
110:
111: This document is produced by the http://www.w3.org/2008/webapps">Web Applications
112: WG in the W3C
113: http://www.w3.org/Interaction/">Interaction Domain.
114:
115:
116: Web content and browser developers are encouraged to review this draft. Please send comments to
117: public-webapps@w3.org">public-webapps@w3.org, the W3C's
118: public email list for issues related to Web APIs.
119: http://lists.w3.org/Archives/Public/public-webapps/">Archives of the
120: list are available.
121:
122:
123: This document is produced by the Web Applications Working Group,
124: part of the Rich Web Clients Activity
125: in the W3C Interaction Domain.
126: Changes made to this document can be found in the
127: W3C public CVS server.
128:
129: http://www.w3.org/2004/01/pp-impl/42538/status?>
130:
131:
132:
133: Table of Contents
134:
135:
136:
137:
138:
139: Introduction
140:
141: This section is informative.
142:
143:
1.4 arangana 144: Web applications should have the ability to manipulate as wide
1.1 arangana 145: as possible a range of user input, including files that a user may wish to upload
146: to a remote server or manipulate inside a rich web application. This specification
147: defines the basic representations for files, lists of files, errors raised by access to files,
148: and programmatic ways to read files. The interfaces and API defined in this
1.4 arangana 149: specification can be used with other interfaces and APIs exposed to the web platform.
150:
1.1 arangana 151:
1.4 arangana 152:
153: File reads should happen asynchronously on the main thread, with an optional synchronous API used
154: within threaded web applications. An asynchronous API for reading files prevents blocking and UI "freezing" on a user
155: agent's main thread. This specification defines an asynchronous API based on an event model to read and access a file's
156: data. Moreover,
157: this specification defines separate interfaces for files and the objects used to read a file's data.
158: While a File object provides a reference to a single
159: file that a user has selected from a file picker (typically spawned by the HTML input element), a FileReader
160: object provides asynchronous read methods to
161: access that file's data through event handler attributes and the firing of events. The use of events and event handlers allows separate code blocks the ability
162: to monitor the progress of the read (which is useful for remote drives that appear to be local, but behave slower than local drives), error conditions that may arise,
163: and successful reading of a file. An example will be illustrative.
164:
165: In the example below, different code blocks handle progress, error, and success conditions.
166:
167: function startRead() {
168: // obtain input element through DOM
169:
170: var file = document.getElementById('file').files[0];
171: if(file){
172: getAsText(file);
173: }
174: }
175:
176: function getAsText(readFile) {
177:
178: var reader = new FileReader();
179:
180: // Read file into memory as UTF-16
181: reader.readAsText(readFile, "UTF-16");
182:
183: // Handle progress, success, and errors
184: reader.onprogress = updateProgress;
185: reader.onload = loaded;
186: reader.onerror = errorHandler;
187: }
188:
189: function updateProgress(evt) {
190: if (evt.lengthComputable) {
191: // evt.loaded and evt.total are ProgressEvent properties
192: var loaded = (evt.loaded / evt.total);
193: if (loaded < 1) {
194: // Increase the prog bar length
1.11 arangana 195: // style.width = (loaded * 200) + "px";
1.4 arangana 196: }
197: }
198: }
199:
200: function loaded(evt) {
201: // Obtain the read file data
1.8 arangana 202: var fileString = evt.target.result;
1.4 arangana 203: // Handle UTF-16 file dump
204: if(utils.regexp.isChinese(fileString)) {
205: //Chinese Characters + Name validation
206: }
207: else {
208: // run other charset test
209: }
210: // xhr.send(fileString)
211: }
212:
213: function errorHandler(evt) {
214: if(evt.target.error.code == evt.target.error.NOT_READABLE_ERR) {
215: // The file could not be read
216: }
217: }
218:
219:
220:
1.1 arangana 221:
222:
223: Conformance
224:
225:
226: Everything in this specification is normative except for
227: examples and sections marked as being informative.
228:
229:
230: The keywords “MUST”,
231: “MUST NOT”,
232: “REQUIRED”,
233: “SHALL”,
234: “SHALL NOT”,
235: “RECOMMENDED”,
236: “MAY” and
237: “OPTIONAL” in this document are to be
238: interpreted as described in
239: Key words for use in RFCs to
240: Indicate Requirement Levels
1.12 arangana 241: [RFC2119].
1.1 arangana 242:
243:
244: The following conformance classes are defined by this specification:
245:
246:
247: - conforming implementation
248: -
249:
250: A user agent is considered to be a
251: conforming implementation
252: if it satisfies all of the MUST-,
253: REQUIRED- and SHALL-level
254: criteria in this specification that apply to implementations.
255:
256:
257:
258:
1.2 arangana 259:
1.1 arangana 260: Terminology and Algorithms
261: The terms and algorithms <fragment>, <scheme>, document base URL,
262: event handler attributes, event handler event type,
263: Function,
264: origin, resolve a URL, same origin,
265: task, task source, URL, URL character encoding, the
266: "already started" flag for script processing, and
267: queue a task are defined by the HTML 5 specification [HTML5].
268: This specification includes algorithms (steps) as part of the definition of methods. Conforming implementations (referred to as "user agents" from here on) MAY use other algorithms in the
269: implementation of these methods, provided
270: the end result is the same.
271:
272:
1.12 arangana 273:
1.1 arangana 274: The FileList Sequence
275:
276:
277: This sequence parameterized type exposes the list of files that have been selected.
278:
279:
1.12 arangana 280: typedef sequence<File> FileList;
1.1 arangana 281:
282:
283:
1.4 arangana 284: Sample usage typically involves DOM access to the <input type="file"> element within a form, and then accessing selected files.
1.1 arangana 285:
286:
287: // uploadData is a form element
288: // fileChooser is input element of type 'file'
289: var file = document.forms['uploadData']['fileChooser'].files[0];
290:
291: if(file)
292: {
293: // Perform file ops
294: }
295:
296:
297:
298: The HTMLInputElement interface [HTML5] has a readonly FileList attribute, which is what is
299: being accessed in the above example. Some conforming user agents support multiple file selections within HTML forms, in which case the
1.4 arangana 300: FileList object MUST make available all selected files.
1.1 arangana 301:
302:
1.2 arangana 303:
1.1 arangana 304: The Blob Interface
305:
306: This interface represents raw data. It provides a method to slice data objects between ranges of bytes into
307: further chunks of raw data.
308: It also provides an attribute representing the size of the chunk of data.
309: The File interface inherits from this interface.
310:
311:
312: interface Blob {
313:
314: readonly attribute unsigned long long size;
1.14 ! arangana 315: readonly attribute ArrayBuffer blobBuffer;
! 316: readonly attribute DOMString type;
! 317: readonly attribute DOMString url;
1.1 arangana 318: //slice Blob into byte-ranged chunks
319:
320: Blob slice(in long long start,
1.14 ! arangana 321: in long long length,
! 322: optional DOMString contentType);
1.1 arangana 323:
1.7 arangana 324: };
1.1 arangana 325:
1.2 arangana 326:
1.1 arangana 327: Attributes
1.14 ! arangana 328: sizeRepresents the size of the Blob object in bytes.
! 329: blobBufferThe ArrayBuffer representation of the Blob object, which can be used with multiple different views of the binary data. [Typed Arrays]
typeThe ASCII-encoded string in lower case representing the media type of the file, expressed as an RFC2046 MIME type [RFC2046]. User agents SHOULD return the MIME type of the file,
media-type
! 333: token defined in section 3.7 "Media Types" of RFC 2616 [HTTP].
! 334: urlMethods and Parameters
1.8 arangana 342: - The
slice method
1.12 arangana 343: Returns a new Blob object between the ranges of bytes specified.
344: The start parameter is a value for the start point of a slice call.
345: The length parameter is a value for the end point of a
346: slice call as byte offsets from start.
1.14 ! arangana 347: The contentType parameter is optional, and can be used to set a content type on a
! 348: Blob.
1.12 arangana 349: The slice method MUST clamp on values of size if index arithmetic exceeds the bounds of size.
350: In particular, this means that for a given slice call:
1.1 arangana 351:
1.9 arangana 352: - If
start + length > size then a user agent MUST return a Blob object as if
1.8 arangana 353: slice(start, size-start) was called.
1.9 arangana 354: - If
start > size then a user agent MUST return a Blob object of size 0
1.8 arangana 355:
1.1 arangana 356:
1.12 arangana 357:
358:
1.14 ! arangana 359: Now that developers can use slice to specify the content type, should the use of RFC2046 formalism be relaxed?
1.1 arangana 360:
1.2 arangana 361:
1.1 arangana 362: The File Interface
363:
1.14 ! arangana 364: This interface describes a single file in a FileList and exposes its name. It inherits from Blob.
1.1 arangana 365:
366:
367: interface File : Blob {
368:
369: readonly attribute DOMString name;
1.14 ! arangana 370:
1.1 arangana 371: };
372:
1.2 arangana 373:
382:
1.2 arangana 383:
1.1 arangana 384: The FileReader Interface
385:
1.2 arangana 386: This interface provides methods to read files in memory, and to access the data from those files using progress events and
387: event handler attributes [DOM3Events]. It is desirable to read
388: data from file systems asynchronously in the main thread of user agents. This interface provides such an asynchronous API, and is specified to be used
1.12 arangana 389: within the context of the global object (Window [HTML5]) as well as Web Workers (WorkerUtils [WebWorkers]).
1.1 arangana 390:
391:
392:
393: [Constructor]
394: interface FileReader {
395:
396: // async read methods
397: void readAsBinaryString(in Blob fileBlob);
398: void readAsText(in Blob fileBlob, [Optional] in DOMString encoding);
399: void readAsDataURL(in File file);
400:
401: void abort();
402:
403: // states
1.11 arangana 404: const unsigned short EMPTY = 0;
1.12 arangana 405: const unsigned short LOADING = 1;
1.1 arangana 406: const unsigned short DONE = 2;
407:
408:
409: readonly attribute unsigned short readyState;
410:
411: // file data
1.8 arangana 412: readonly attribute DOMString result;
1.1 arangana 413:
414: readonly attribute FileError error;
415:
416: // event handler attributes
417: attribute Function onloadstart;
418: attribute Function onprogress;
419: attribute Function onload;
420: attribute Function onabort;
421: attribute Function onerror;
422: attribute Function onloadend;
423:
424: };
425: FileReader implements EventTarget;
426:
1.2 arangana 427:
1.1 arangana 428: The FileReader Task Source
429: The FileReader interface enables asynchronous reads on individual files by dispatching events to event handler methods.
430: Unless stated otherwise, the
431: task source that is used in this specification is the
1.12 arangana 432: FileReader. This task source is used for events tasks that are asynchronously dispatched, or for
1.1 arangana 433: event tasks that are queued for dispatching.
434:
1.2 arangana 435:
1.1 arangana 436: Constructors
437: When the FileReader() constructor is invoked, the user agent MUST return a new FileReader object.
438:
1.12 arangana 439:
1.1 arangana 440: Event Handler Attributes
441:
442: The following are the event
443: handler attributes (and their corresponding event
444: handler event types) that user agents MUST support on
445: FileReader as
446: DOM attributes:
447:
448:
449:
450:
451:
1.12 arangana 452: 1.1 arangana 453: attributes">event handler attribute
454:
1.12 arangana 455: event handler event type
1.1 arangana 456:
457:
458:
459:
1.12 arangana 460: onloadstart
1.1 arangana 461:
462: loadstart
463:
464:
1.12 arangana 465: onprogress
1.1 arangana 466:
467: progress
468:
469:
1.12 arangana 470: onabort
1.1 arangana 471:
472: abort
473:
474:
1.12 arangana 475: onerror
1.1 arangana 476:
477: error
478:
479:
1.12 arangana 480: onload
1.1 arangana 481:
482: load
483:
484:
1.12 arangana 485: onloadend
1.1 arangana 486:
487: loadend
488:
489:
490:
491:
1.2 arangana 492:
1.1 arangana 493: FileReader States
494: The FileReader object can be in one of 3 states. The
495: readyState attribute, on getting,
496: MUST return the current state, which MUST be one of the following values:
497:
1.11 arangana 498: EMPTY (numeric value 0)The object has been constructed, and there are no pending reads.
LOADING (numeric value 1)A file is being read. One of the read methods is being processed.
DONE (numeric value 2)The entire file has been read into memory, or a file error occurred during read, or the read was
504: aborted using abort().
505: The FileReader
506: is no longer reading a file.
508:
1.2 arangana 509:
1.1 arangana 510: Reading a File
1.2 arangana 511:
1.1 arangana 512: Multiple Reads
513:
514: The FileReader interface makes available three asynchronous read methods --
1.12 arangana 515: readAsBinaryString,
1.2 arangana 516: readAsText, and readAsDataURL, which
517: read files into memory. If
518: multiple read methods are called on the same FileReader object, user agents
519: MUST only process the last call
1.1 arangana 520: to a read method, which is the call that occurs last in a script block that has the "already started" flag set
521: [HTML5].
1.12 arangana 522:
1.1 arangana 523:
524:
1.2 arangana 525:
1.8 arangana 526: The result attribute
527: On getting, the result attribute returns a file's data in string format, or null,
1.12 arangana 528: depending on the read method that has been called on the FileReader object, and
1.1 arangana 529: any errors that may have occurred.
530: It can also return partial file data.
531: Partial file data is the part of the file that has been read into memory currently
1.12 arangana 532: during processing one of the two read methods,
533: readAsBinaryString and
1.8 arangana 534: readAsText. The list below is normative for the result attribute:
1.1 arangana 535:
536:
1.11 arangana 537: On getting, if the readyState is EMPTY (no read method has been called)
1.8 arangana 538: then the result attribute MUST return null.
On getting, if an error in reading the file has occurred (using any read method),
1.8 arangana 540: then the result attribute MUST return the null.
On getting, if the readAsDataURL read method is
1.8 arangana 542: used, the result attribute MUST return a Data URL [DataURL] encoding of the file's data.
On getting, if the readAsBinaryString read method is called
1.8 arangana 544: (and no error in reading the file has occurred), then the result attribute MUST return a string representing the file's data as a binary string, in which
545: every byte is represented by an integer in the range [0..255]. On getting, while processing the
1.13 arangana 546: readAsBinaryString read method, the result
1.1 arangana 547: attribute SHOULD return partial file data in binary string format.
On getting, if the readAsText read method is called
1.1 arangana 549: (and no error in reading the file has occurred),
1.8 arangana 550: then the result attribute MUST return a string representing the file's data as a text string, and SHOULD decode the string in memory in the format specified
551: by the encoding determination. On getting, while processing the
1.12 arangana 552: readAsText read method, this attibute SHOULD return
1.1 arangana 553: partial file data in the format specified by
1.8 arangana 554: the encoding determination.
1.1 arangana 555:
557:
1.2 arangana 558:
1.1 arangana 559: The readAsBinaryString() method
560:
1.12 arangana 561: When the readAsBinaryString(fileBlob) method is called, the user agent MUST run the steps below (unless otherwise indicated).
1.1 arangana 562:
563:
1.11 arangana 564: Set readyState to EMPTY
1.1 arangana 565: and set
1.8 arangana 566: result to null.
If an error occurs during file read, set readyState to
1.8 arangana 568: DONE and set result to null. Proceed to the error steps below.
1.1 arangana 569:
1.2 arangana 570: Dispatch a progress event called
1.13 arangana 571: loadend.
Dispatch a progress event called
1.1 arangana 573: error. Set the error attribute; on getting, the
574: error attribute MUST be a
1.12 arangana 575: a FileError object with a valid error code that indicates the kind of
1.1 arangana 576: file error that has occurred.
577: Terminate this overall set of steps.
580: If no error has occurred, set readyState to LOADING
Queue a task to dispatch a progress event called loadstart.
Make progress notifications. As the bytes from the fileBlob argument are read,
584: user agents SHOULD ensure that on getting,
1.8 arangana 585: the result attribute returns partial file data representing the number of bytes currently loaded
1.12 arangana 586: (as a fraction of the total) [ProgressEvents], as a binary string.
1.1 arangana 587:
When the file has been read into memory fully, set readyState to DONE
Set the result attribute to be fileBlob's data content
1.1 arangana 590: represented as a binary string;
1.8 arangana 591: on getting, the result attribute returns the (complete) data of fileBlob
1.1 arangana 592: as a binary string.
Terminate this overall set of steps.
595:
1.2 arangana 596:
1.1 arangana 597: The readAsDataURL() method
598: When the readAsDataURL(file) method is called, the user agent MUST run the steps below (unless otherwise indicated).
599:
1.11 arangana 600: Set readyState to EMPTY and set
1.8 arangana 601: result to null.
If an error occurs during file read, OR if a user agent's URL length limitations prevent returning data as a Data URL
1.2 arangana 603: [DataURL],
1.1 arangana 604: set readyState to
1.8 arangana 605: DONE and set result to null. Proceed to the error steps below.
1.1 arangana 606:
1.2 arangana 607: Dispatch a progress event called
1.13 arangana 608: loadend.
Dispatch a progress event called
1.1 arangana 610: error. Set the error attribute; on getting, the
611: error attribute MUST be a
1.12 arangana 612: a FileError object with a valid error code that indicates the kind of
1.1 arangana 613: file error that has occurred.
Terminate this overall set of steps.
616: If no error has occurred, set readyState to LOADING
Queue a task to dispatch a progress event called loadstart.
When the file has been read into memory fully, set readyState to DONE
Set the result attribute to be file's data content
1.1 arangana 623: represented as a Data URL [DataURL];
1.8 arangana 624: on getting, the result attribute returns the (complete) data of file as a
1.1 arangana 625: Data URL [DataURL]
Terminate this overall set of steps.
628:
1.3 arangana 629:
1.1 arangana 630: The readAsText() method
631:
632: When the readAsText(fileBlob, encoding) method is called (the encoding argument is optional),
633: the user agent MUST run the steps below (unless otherwise indicated).
634:
635:
1.11 arangana 636: Set readyState to EMPTY
1.1 arangana 637: and set
1.8 arangana 638: result to null.
If an error occurs during file read,
640: set readyState to
1.8 arangana 641: DONE and set result to null. Proceed to the error steps below.
1.1 arangana 642:
1.2 arangana 643: Dispatch a progress event called
1.13 arangana 644: loadend.
Dispatch a progress event called
1.1 arangana 646: error. Set the error attribute; on getting, the
647: error attribute MUST be a
1.12 arangana 648: a FileError object with a valid error code that indicates the kind of
1.1 arangana 649: file error that has occurred.
650: Terminate this overall set of steps.
653: If no error has occurred, set readyState to LOADING
Queue a task to dispatch a progress event called loadstart.
Make progress notifications. As the bytes from the fileBlob argument are read,
657: user agents SHOULD ensure that on getting,
1.8 arangana 658: the result attribute returns partial file data representing the number of bytes currently loaded
1.12 arangana 659: (as a fraction of the total) [ProgressEvents], decoded in memory according to the encoding determination.
1.1 arangana 660:
When the file has been read into memory fully, set readyState to DONE
Set the result attribute to be fileBlob's data content
1.3 arangana 663: represented as a string in a format determined by the encoding determination;
1.8 arangana 664: on getting, the result attribute returns the (complete) data of fileBlob
1.2 arangana 665: as a string, decoded in memory according to the encoding determination.
Terminate this overall set of steps.
1.12 arangana 667:
669:
672:
1.2 arangana 673:
674: The abort() method
675:
1.12 arangana 676: When the abort() method is called, the user agent MUST run the steps below:
1.2 arangana 677:
1.8 arangana 678: Set readyState to DONE and result
1.6 arangana 679: to null.
Terminate any steps while processing a read method.
Dispatch a progress event called error. Set the
682: error attribute to a FileError object with the appropriate code(in this case, ABORT_ERR;
683: see error conditions).
Dispatch a progress event called abort
Dispatch a progress event called loadend
Stop dispatching any further progress events.
688:
689:
690:
1.1 arangana 691: Blob and File Parameters
1.12 arangana 692: Each of the read methods take mandatory File or
1.1 arangana 693: Blob parameters.
694:
695:
696: - file
697: This is a File object used to invoke the readAsDataURL() method. It will typically be a reference to a single file in a
698: FileList
- fileBlob
700: This is a Blob object used to invoke the readAsText() and readAsBinaryString() methods.
701: For the purposes of this specification, it will typically be a reference to a single file in a
702: FileList
704:
1.2 arangana 705:
1.1 arangana 706: Determining Encoding
1.12 arangana 707: When reading files using the readAsText() read method, the optional
1.1 arangana 708: encoding string parameter MUST be a name or an alias of a character set
709: used on the Internet [IANACHARSET], or else is considered invalid. If the encoding argument supplied is valid, user agents SHOULD
1.2 arangana 710: decode the fileBlob using that encoding. If the encoding argument is invalid,
711: or the optional encoding argument is not supplied,
1.1 arangana 712: or the user agent cannot decode the fileBlob using encoding, the following
1.2 arangana 713: encoding determination algorithm MUST be
1.1 arangana 714: followed:
715:
1.3 arangana 716: - User agents SHOULD decode
fileBlob data using encoding, if it is provided.
1.2 arangana 717: If the encoding argument is invalid, or the optional encoding argument is not supplied,
1.1 arangana 718: or the user agent cannot decode the fileBlob using encoding, then let charset be null.
719: -
720:
721:
For each of the rows in the
722: following table, starting with the first one and going down, if the
723: first bytes of fileBlob match the bytes given in the first
724: column, then let charset be the encoding given in the cell in
725: the second column of that row. If there is no match charset
726: remains null.
727:
728:
729:
730:
731: Bytes in Hexadecimal
732:
733: Description
734:
735:
742:
743:
744: FE FF
745:
746: UTF-16BE BOM
747:
748:
749:
750: FF FE
751:
752: UTF-16LE BOM
753:
754:
755: EF BB BF
756:
757: UTF-8 BOM
762:
763:
764:
765: -
766:
If charset is null let charset be UTF-8.
767:
768:
-
769:
770:
Return the result of decoding the fileBlob using
1.8 arangana 771: charset; on getting, the result attribute of the FileReader
1.3 arangana 772: object returns a string in charset format. The synchronous
1.2 arangana 773: readAsText method of the FileReaderSync object returns a string in charset format.
774: Replace bytes or sequences of bytes that are not
775: valid according to the charset with a single U+FFFD character [Unicode].
1.1 arangana 776:
777:
778:
1.2 arangana 779:
780: Events
1.12 arangana 781: When this specification says to make progress notifications for a read method,
782: the following steps MUST be followed:
1.2 arangana 783:
784:
785: While the read method is processing, queue a task to
1.12 arangana 786: dispatch a progress event called progress about every 50ms or for every byte
1.2 arangana 787: read into memory, whichever is least frequent.
When the data from the file or fileBlob
789: has been completely read into memory, queue a task to dispatch a progress event called
790: load
When the data from the file or fileBlob
792: has been completely read into memory, queue a task to dispatch a progress event called
793: loadend
795:
796: When this specification says to dispatch a progress event called e (for some
1.3 arangana 797: ProgressEvent e [DOM3Events] dispatched on a FileReader reader),
1.12 arangana 798: the following list MUST be followed:
1.2 arangana 799:
800: The progress event e does not bubble. e.bubbles MUST be false [DOM3Events]
The progress event e is NOT cancelable. e.cancelable MUST be false [DOM3Events]
The progress event e is dispatched on the FileReader object
1.2 arangana 803: (which is the task source in this specification, and the EventTarget). User agents MUST call
1.3 arangana 804: reader.dispatchEvent(e) [DOM3Events]
806:
807: Event Summary
808: The following are the events that are dispatched on FileReader objects.
809:
810:
811:
812:
813: Event name
814:
815: Interface
816:
817: Dispatched when…
818:
819:
820:
821: loadstart
822:
823: ProgressEvent
824:
825: When the read starts.
826:
827:
828:
1.3 arangana 829: progress
1.2 arangana 830:
831: ProgressEvent
832:
1.12 arangana 833: While reading (and decoding) file or fileBlob data, and reporting partial file data (progess.loaded/progress.total)
1.2 arangana 834:
835:
1.13 arangana 836: abort
1.2 arangana 837:
838: ProgressEvent
839:
840: When the read has been aborted. For instance, by invoking the
841: abort() method.
842:
843:
1.3 arangana 844: error
1.1 arangana 845:
1.2 arangana 846: ProgressEvent
1.1 arangana 847:
1.2 arangana 848: When the read has failed (see errors).
849:
850:
851:
1.3 arangana 852: load
1.2 arangana 853:
854: ProgressEvent
855:
856: When the read has successfully completed.
857:
858:
1.3 arangana 859: loadend
1.2 arangana 860:
861: ProgressEvent
862:
1.8 arangana 863: When the request has completed (either in success or failure).
1.2 arangana 864:
1.8 arangana 865:
1.2 arangana 866:
867:
868:
869:
870:
871: Reading on Threads
872: Web Workers allow for the use of synchronous file read APIs, since the effect of such read mechanisms on the main thread is mitigated.
1.12 arangana 873: This section defines a synchronous API, which can be used within Workers [Web Workers]. Workers can avail of both the asynchronous API (the
1.2 arangana 874: FileReader
875: object) and the synchronous API (the FileReaderSync object).
876:
877: The FileReaderSync Interface
878: This interface provides methods to read files in memory, and to access the data from those files as strings.
879:
880:
881: [Constructor]
882: interface FileReaderSync {
883:
884: // Synchronously return strings
885: // All three methods raise FileException
886:
887: DOMString readAsBinaryString(in Blob fileBlob);
888: DOMString readAsText(in Blob fileBlob, [Optional] in DOMString encoding);
889: DOMString readAsDataURL(in File file);
890: };
891:
892:
893: The FileReaderSync object's read methods -- namely
1.12 arangana 894: readAsBinaryString, readAsText, and
1.2 arangana 895: readAsDataURL -- have the same method signatures as the read methods of the
896: FileReader object, and read files into memory. The difference is that these are specified to behave synchronously, with string return values.
897: These methods raise FileException.
898:
1.3 arangana 899:
1.12 arangana 900:
1.2 arangana 901: The readAsBinaryString method
1.12 arangana 902: When the readAsBinaryString(fileBlob) method is called, the following steps MUST be followed:
1.2 arangana 903:
904: If an error occurs during file read, throw a
905: FileException with the appropriate error code. Terminate these overall steps.
If no error has occurred, read fileBlob into memory. Return the data contents of
907: fileBlob as a binary string.
909:
910:
911: The readAsText method
912: When the readAsText(fileBlob, encoding) method is called (the
913: encoding argument is optional), the following steps MUST be followed:
914:
915: If an error occurs during file read, throw a
916: FileException with the appropriate error code. Terminate these overall steps.
If no error has occurred, read fileBlob into memory. Return the data contents of fileBlob
918: using the encoding determination algorithm.
920:
1.12 arangana 921:
1.2 arangana 922: The readAsDataURL method
923:
1.12 arangana 924: When the readAsDataURL(file) method is called, the following steps MUST be followed:
1.2 arangana 925:
926: If an error occurs during file read, throw a
927: FileException with the appropriate error code. Terminate these overall steps.
If no error has occurred, read fileBlob into memory. Return the data contents of fileBlob
929: as a Data URL [DataURL]
930: URL length limitiations for Data URLs limit the usefulness of this call. A user agent may throw an ENCODING_ERR
931: for file
932: arguments which, when encoded as Data URLs, exceed URL length limitations for that user agent.[DataURL]
933:
935:
1.1 arangana 936:
1.2 arangana 937: TODO: Land sample code here
938:
939:
940: Errors and Exceptions
941:
1.3 arangana 942: Error conditions can occur when reading files from the underlying filesystem. The list below of potential error conditions is informative,
1.12 arangana 943: with links to normative descriptions of error codes:
1.3 arangana 944:
945: The file being accessed may not exist at the time one of the asynchronous read methods or synchronous
1.12 arangana 946: read methods
1.3 arangana 947: are called. This may be due to it having been moved or deleted after a reference to it was acquired (e.g. concurrent modification with another application). See
948: NOT_FOUND_ERR
A file may be unreadable. This may be due to permission problems that occur after a reference to a file has been acquired
950: (e.g. concurrent lock with another application). See NOT_READABLE_ERR
User agents MAY determine that some files are unsafe for use within Web applications. A file may change on disk since the original file selection,
952: thus resulting in an invalid read. Additionally, some file and directory structures may be considered restricted
953: by the underlying filesystem; attempts to read from them may be considered a security violation. See the security considerations.
954: See SECURITY_ERR
Files may be too large to return to the data structures of a Web application. An example might be that URL length limitations imposed by user agents on Data URLs may
956: make obtaining large files encoded as Data URLs impossible to return [DataURL]. See ENCODING_ERR
During the reading of a file, the Web application may itself wish to abort (see abort()) the call to an asynchronous read method. See
958: ABORT_ERR
1.8 arangana 959:
962:
963: The FileError Interface
964:
965: This interface is used to report errors asynchronously. The FileReader object's error attribute is a
1.13 arangana 966: FileError object, and is accessed asynchronously through the onerror event handler when
1.3 arangana 967: error events are generated.
968:
969:
970: interface FileError {
971: // File error codes
972: // Found in DOMException
973: const unsigned short NOT_FOUND_ERR = 8;
974: const unsigned short SECURITY_ERR = 18;
975: const unsigned short ABORT_ERR = 20;
976:
977: // Added by this specification
978: const unsigned short NOT_READABLE_ERR = 24;
979: const unsigned short ENCODING_ERR = 26;
980:
981: readonly attribute unsigned short code;
982: };
983:
984: The code attribute MUST return one of the constants of the FileError error, which MUST be
985: the most appropriate code from the table below.
986:
987:
988: The FileException exception
989:
1.12 arangana 990: Errors in the synchronous read methods for Web Workers [WebWorkers] are reported using the
1.3 arangana 991: FileException exception.
992:
993:
994: exception FileException {
995:
996: const unsigned short NOT_FOUND_ERR = 8;
997: const unsigned short SECURITY_ERR = 18;
998: const unsigned short ABORT_ERR = 20;
999:
1000: const unsigned short NOT_READABLE_ERR = 24;
1001: const unsigned short ENCODING_ERR = 26;
1002:
1.7 arangana 1003: unsigned short code;
1.3 arangana 1004: };
1005:
1006: The code attribute MUST return one of the constants of the FileException
1007: exception, which MUST be
1008: the most appropriate code from the table below.
1009:
1010:
1011: Error Code Descriptions
1012: Constant
1.12 arangana 1013: Code
1.3 arangana 1014: Situation
1015: NOT_FOUND_ERR
1016: 8
1017: User agents MUST use this code if the file resource could not be found at the time the read was processed
1018:
1019: SECURITY_ERR
1020: 18
1.11 arangana 1021: User agents MAY use this code if:
1.3 arangana 1022: - it is determined that certain files are unsafe for access within a Web application
1023: - it is determined that too many read calls are being made on file resources
1.11 arangana 1024: - it is determined that the file has changed on disk since the user selected it
1.3 arangana 1025:
1026: This is a security error code to be used in situations not covered by any other error codes.
1027:
1028: ABORT_ERR
1029:
1030: 20
1031: User agents MUST use this code if the read operation was aborted, typically with a call to abort()
1032:
1033: NOT_READABLE_ERR
1034: 24
1035: User agents MUST use this code if the file cannot be read, typically due due to permission problems that occur after a
1036: reference to a file has been acquired (e.g. concurrent lock with another application).
1037:
1038:
1039: ENCODING_ERR
1040: 26
1041:
1042: User agents MAY use this code if URL length limitations for Data URLs in their implementations place limits on the file data that can be
1043: represented as a Data URL [DataURL]. User agents MUST NOT use this code for the asynchronous readAsText() call
1044: and MUST NOT use this code for the synchronous readAsText() call, since encoding is determined by the
1045: encoding determination algorithm.
1.2 arangana 1046:
1.3 arangana 1047:
1048:
1.2 arangana 1049:
1.14 ! arangana 1050:
! 1051: A URL for Blob and File reference
1.4 arangana 1052:
1.12 arangana 1053: This section does not enjoy the full consensus of the WG.
1.14 ! arangana 1054:
! 1055: The proposed URL scheme is filedata: . Mozilla already ships with moz-filedata:
! 1056: Will reusing the url with uuid scheme described in RFC4122 [RFC4122] face origin-determination issues?
! 1057: Are there further security caveats?
! 1058: Is using a subset of HTTP response codes acceptable practice, or should we forgo response codes in this specification?
! 1059: Lifetime issues with respect to threads needs to be considered.
! 1060:
1.4 arangana 1061:
1062:
1.11 arangana 1063:
1064: Security Considerations
1065:
1066: This section is informative.
1067:
1068:
1069: This specification allows web content to read files from the underlying file system, as well as provides a means for files to be accessed by unique identifiers,
1070: and as such is subject to some security considerations. This specification also assumes that the
1071: primary user interaction is with the <input type="file"/> element of HTML forms [HTML5], and that all files that are being read by
1072: FileReader objects have first been selected by the user. Important security considerations include preventing malicious file
1073: selection attacks (selection looping), preventing access to system-sensitive files, and guarding against modifications of files on disk after a selection has taken place.
1074:
1075: Preventing selection looping. During file selection, a user may be bombarded with the file picker associated with <input
1076: type="file"/> (in a "must choose" loop that forces selection before the file picker is dismissed) and a user agent may prevent file
1077: access to any selections by making the FileList object returned be of size 0.
System-sensitive files (e.g. files in /usr/bin, password files, other native operating system executables) typically should not
1.14 ! arangana 1079: be exposed to web content, and should not be accessed via URNs. User agents MAY raise a SECURITY_ERR
1.11 arangana 1080: if such files are accessed or a read method
1081: is called on them.
Post-selection file modifications occur when a file changes on disk after it has been selected. In such cases, if a
1083: read method is called on a file, user agents MAY raise a SECURITY_ERR
1085: This section is provisional; more security data may supplement this in subsequent drafts.
1086:
1.1 arangana 1087:
1088: Requirements and Use Cases
1089: This section covers what the requirements are for this API, as well as illustrates some use cases. This version of the API does not satisfy all use cases;
1090: subsequent versions may elect to address these.
1091:
1092: Once a user has given permission, user agents should provide the ability to read and parse data directly from a local file programmatically.
1093:
1094: - Example: A lyrics viewer. User wants to read song lyrics from songs in his plist file. User browses for plist file. File is opened,
1095: read, parsed, and presented to the user as a sortable, actionable list within a web application. User can select songs to fetch lyrics. User uses the
1096: "browse for file" dialog.
1097:
1098: Data should be able to be stored locally so that it is available for later use, which is useful for offline data access for web applications.
1100:
1101: - Example: A Calendar App. User's company has a calendar. User wants to sync local events to company calendar, marked
1102: as "busy" slots (without leaking personal info). User browses for file and selects it. The text/calendar file is parsed
1103: in the browser, allowing the user to merge the files to one calendar view.
1104: The user wants to then save the file back to his local calendar file. (using "Save As" ?). The user can also send the
1105: integrated calendar file back to the server calendar store asynchronously.
1106:
1107:
1108: User agents should provide the ability to save a local file programmatically given an amount of data and a file name.
1110:
1111: - Example: A Spreadsheet App. User interacts with a form, and generates some input. The form then generates a
1112: CSV (Comma Separated Variables) output for the user to import into a spreadsheet, and uses "Save...". The generated
1113: output can also be directly integrated into a web-based spreadsheet, and
1114: uploaded asynchronously.
1115:
1116: User agents should provide a streamlined programmatic ability to send data from a file to a remote server that works more
1118: efficiently than form-based uploads today
1119:
1120: - Example: A Video/Photo Upload App. User is able to select large files for upload, which can then be "chunk-transfered" to the server.
1121:
1122: User agents should provide an API exposed to script that exposes the features above. The user is notified by UI anytime interaction with the file
1124: system takes place, giving the user full ability to cancel or abort the transaction. The user is notified of any file selections, and can cancel these.
1125: No invocations to these APIs occur silently without user intervention.
1126:
1129:
1.13 arangana 1130:
1.5 arangana 1131: Acknowledgements
1132:
1133:
1134: This specification was originally developed by the SVG Working Group. Many thanks to Mark Baker and Anne van Kesteren for their feedback.
1135: Thanks to Robin Berjon for editing the original specification.
1136: Special thanks to Jonas Sicking, Olli Pettay, Nikunj Mehta, Garrett Smith, Michael Nordman, Ian Hickson, Sam Weinig, Aaron Boodman, Julian Reschke
1137: Thanks to the W3C WebApps WG, and to participants on the public-webapps@w3.org listserv
1138:
1.1 arangana 1139:
1140: References
1.5 arangana 1141: ToDo: Add author names
1.1 arangana 1142:
1143: Normative references
1144:
1145: - RFC2119
1146: - http://www.ietf.org/rfc/rfc2119.txt">Key words for use in RFCs to Indicate Requirement Levels
1147: - XMLHttpRequest
1148: - http://www.w3.org/TR/XMLHttpRequest2/">XMLHttpRequest Level 2
1149: - HTML5
1150: - http://dev.w3.org/html5/spec/Overview.html">HTML 5: A vocabulary and associated APIs for HTML and XHTML
1151: - ProgressEvents 1.0
1152: - http://www.w3.org/TR/progress-events">Progress Events 1.0
1153: - RFC2397
1154: - http://www.ietf.org/rfc/rfc2397.txt">The "data" URL Scheme
1155: - Web Workers
1156: - http://dev.w3.org/html5/workers/">Web Workers
1157: - DOM 3 Core
1158: - http://www.w3.org/TR/DOM-Level-3-Core/core.html">DOM 3 Core
1159: - DOM 3 Events
1160: - http://www.w3.org/TR/DOM-Level-3-Events/">DOM 3 Events
1161: - DOMException Extensions Defined in HTML5
1162: - http://dev.w3.org/html5/spec/Overview.html#exceptions">DOM 3 Core DOMException Extensions Defined in HTML5
1163: - Unicode
1.12 arangana 1164: - http://www.unicode.org/versions/Unicode5.2.0/">The Unicode Standard, Version 5.2.0.
1.1 arangana 1165: - RFC4122
1.5 arangana 1166: - http://www.ietf.org/rfc/rfc4122.txt">A Universally Unique IDentifier (UUID) URN Namespace
1.1 arangana 1167: - RFC2616
1168: - http://www.w3.org/Protocols/rfc2616/rfc2616.html">Hypertext Transfer Protocol -- HTTP/1.1
1169: - RFC2046
1170: - http://www.ietf.org/rfc/rfc2046.txt">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Extensions
1171: - RFC3986
1172: - http://www.ietf.org/rfc/rfc3986.txt">Uniform Resource Identifier (URI): Generic Syntax
1173: - RFC1738
1174: - http://tools.ietf.org/html/rfc1738">Uniform Resource Locators (URL)
1.14 ! arangana 1175: - Typed Arrays
! 1176: - https://cvs.khronos.org/svn/repos/registry/trunk/public/webgl/doc/spec/TypedArray-spec.html">Typed Arrays
1.1 arangana 1177:
1178:
1.5 arangana 1179:
1180: Informative References
1181:
1182: - IANA Charsets
1183: - http://www.iana.org/assignments/character-sets">Official Names for Character Sets on the Internet
1184: - File Upload State of the input element
1185: - http://dev.w3.org/html5/spec/Overview.html#file-upload-state">File Upload State of the HTML5
input Element
1186: - RFC5234
1187: - http://www.ietf.org/rfc/rfc5234.txt">Augmented BNF for Syntax Specifications: ABNF
1188: - RFC4648
1189: - http://tools.ietf.org/html/rfc4648">The Base16, Base32, and Base64 Data Encodings
1.12 arangana 1190: - Google Gears Blob API
1.5 arangana 1191: - http://code.google.com/apis/gears/api_blob.html">Google Gears Blob API
1192:
1.1 arangana 1193:
1194:
1.5 arangana 1195:
1196:
1.14 ! arangana 1197:
1.1 arangana 1198:
1199: