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<pre class="metadata">
Indent: 2
Title: File API
Shortname: FileAPI
Level: none
Group: webapps
Editor: Marijn Kruisselbrink, Google, mek@chromium.org, w3cid 72440
Former Editor: Arun Ranganathan, Mozilla Corporation, http://arunranga.com/, arun@mozilla.com, w3cid 37240
Prepare For TR: true
Status: ED
ED: https://w3c.github.io/FileAPI/
TR: https://www.w3.org/TR/FileAPI/
Repository: w3c/FileAPI
!Tests: <a href=https://github.com/web-platform-tests/wpt/tree/master/FileAPI>web-platform-tests FileAPI/</a> (<a href=https://github.com/web-platform-tests/wpt/labels/FileAPI>ongoing work</a>)
Abstract: This specification provides an API for representing file objects in web applications,
as well as programmatically selecting them and accessing their data. This includes:
* A {{FileList}} interface, which represents an array of individually selected files from the underlying system. The user interface for selection can be invoked via <code><input type="file"></code>, i.e. when the input element is in the <code>File Upload</code> state [[HTML]].
* A {{Blob}} interface, which represents immutable raw binary data, and allows access to ranges of bytes within the {{Blob}} object as a separate {{Blob}}.
* A {{File}} interface, which includes readonly informational attributes about a file such as its name and the date of the last modification (on disk) of the file.
* A {{FileReader}} interface, which provides methods to read a {{File}} or a {{Blob}}, and an event model to obtain the results of these reads.
* A <a section href="#url">URL scheme</a> for use with binary data such as files, so that they can be referenced within web applications.
Additionally, this specification defines objects to be used within threaded web applications for the synchronous reading of files.
[[#requirements]] covers the motivation behind this specification.
This API is designed to be used in conjunction with other APIs and elements on the web platform, notably:
{{XMLHttpRequest}} (e.g. with an overloaded {{XMLHttpRequest/send()}} method for {{File}} or {{Blob}} arguments),
{{Worker/postMessage(message, options)|postMessage()}},
{{DataTransfer}} (part of the drag and drop API defined in [[HTML]])
and Web Workers.
Additionally, it should be possible to programmatically obtain a list of files from the <{input}> element
when it is in the <code>File Upload</code> state [[HTML]].
These kinds of behaviors are defined in the appropriate affiliated specifications.
Status Text: Previous discussion of this specification has taken place on two other mailing lists: <a href="mailto:public-webapps@w3.org">public-webapps@w3.org</a> (<a href="http://lists.w3.org/Archives/Public/public-webapps/">archive</a>) and <a href="mailto:public-webapi@w3.org">public-webapi@w3.org</a> (<a href="http://lists.w3.org/Archives/Public/public-webapi/">archive</a>). Ongoing discussion will be on the <a href="mailto:public-webapps@w3.org">public-webapps@w3.org</a> mailing list.
This draft consists of changes made to the previous Last Call Working Draft. Please send comments to the <a href="mailto:public-webapi@w3.org">public-webapi@w3.org</a> as described above. You can see Last Call Feedback on the W3C Wiki: <a href="http://www.w3.org/wiki/Webapps/LCWD-FileAPI-20130912">http://www.w3.org/wiki/Webapps/LCWD-FileAPI-20130912</a>
An [implementation report](https://wpt.fyi/results/FileAPI) is automatically generated from the test suite.
Translate Ids: dictdef-blobpropertybag dfn-BlobPropertyBag, dictdef-filepropertybag dfn-FilePropertyBag, filereadersync dfn-FileReaderSync, filelist dfn-filelist, filereader dfn-filereader, file dfn-file, blob dfn-Blob, blob-section blob, file-section file
Markup Shorthands: css no, markdown yes
</pre>
<pre class="link-defaults">
spec: dom
type:interface
text:Document
spec: html
type: element
text: a
text: iframe
type: element-attr
text: download; for: a
spec: infra
type: dfn
text: list
text: string
text: code point
spec: streams
type: dfn
text: chunk
spec: url
type: dfn
text: url; for:/
type: interface
text: URL
</pre>
<pre class="anchors">
spec: mimesniff; urlPrefix: https://mimesniff.spec.whatwg.org/
type: dfn
text: parsable mime type
spec: ecma-262; urlPrefix: http://tc39.github.io/ecma262/
type: interface
text: Array; url: sec-array-constructor
text: Date; url: sec-date-constructor
spec: media-source; urlPrefix: http://w3c.github.io/media-source/
type: interface
text: MediaSource; url: #mediasource
</pre>
# Introduction # {#intro}
*This section is informative.*
Web applications should have the ability to manipulate as wide as possible a range of user input,
including files that a user may wish to upload to a remote server or manipulate inside a rich web application.
This specification defines the basic representations for files,
lists of files,
errors raised by access to files,
and programmatic ways to read files.
Additionally, this specification also defines an interface that represents "raw data"
which can be asynchronously processed on the main thread of conforming user agents.
The interfaces and API defined in this specification can be used with other interfaces and APIs exposed to the web platform.
The {{File}} interface represents file data typically obtained from the underlying file system,
and the {{Blob}} interface
("Binary Large Object" - a name originally introduced to web APIs in <a href="https://developers.google.com/gears/?csw=1">Google Gears</a>)
represents immutable raw data.
{{File}} or {{Blob}} reads should happen asynchronously on the main thread,
with an optional synchronous API used within threaded web applications.
An asynchronous API for reading files prevents blocking and UI "freezing" on a user agent's main thread.
This specification defines an asynchronous API based on an *event model*
to read and access a {{File}} or {{Blob}}’s data.
A {{FileReader}} object provides asynchronous read methods to access that file's data
through event handler content attributes and the firing of events.
The use of events and event handlers allows separate code blocks the ability
to monitor the *progress of the read*
(which is particularly useful for remote drives or mounted drives,
where file access performance may vary from local drives)
and error conditions that may arise during reading of a file.
An example will be illustrative.
<div class="example">
In the example below, different code blocks handle progress, error, and success conditions.
<pre highlight="js">
function startRead() {
// obtain input element through DOM
var file = document.getElementById('file').files[0];
if(file){
getAsText(file);
}
}
function getAsText(readFile) {
var reader = new FileReader();
// Read file into memory as UTF-16
reader.readAsText(readFile, "UTF-16");
// Handle progress, success, and errors
reader.onprogress = updateProgress;
reader.onload = loaded;
reader.onerror = errorHandler;
}
function updateProgress(evt) {
if (evt.lengthComputable) {
// evt.loaded and evt.total are ProgressEvent properties
var loaded = (evt.loaded / evt.total);
if (loaded < 1) {
// Increase the prog bar length
// style.width = (loaded * 200) + "px";
}
}
}
function loaded(evt) {
// Obtain the read file data
var fileString = evt.target.result;
// Handle UTF-16 file dump
if(utils.regexp.isChinese(fileString)) {
//Chinese Characters + Name validation
}
else {
// run other charset test
}
// xhr.send(fileString)
}
function errorHandler(evt) {
if(evt.target.error.name == "NotReadableError") {
// The file could not be read
}
}
</pre>
</div>
# Terminology and Algorithms # {#terminology}
When this specification says to <dfn id="terminate-an-algorithm" lt="terminate an algorithm|terminate this algorithm">terminate an algorithm</dfn>
the user agent must terminate the algorithm after finishing the step it is on.
Asynchronous <a>read methods</a> defined in this specification may return before the algorithm in question is terminated,
and can be terminated by an {{FileReader/abort()}} call.
The algorithms and steps in this specification use the following mathematical operations:
* max(a,b) returns the maximum of a and b,
and is always performed on integers as they are defined in WebIDL [[WebIDL]];
in the case of max(6,4) the result is 6.
This operation is also defined in ECMAScript [[!ECMA-262]].
* min(a,b) returns the minimum of a and b,
and is always performed on integers as they are defined in WebIDL [[WebIDL]];
in the case of min(6,4) the result is 4.
This operation is also defined in ECMAScript [[ECMA-262]].
* Mathematical comparisons such as < (less than), ≤ (less than or equal to), and > (greater than) are as in ECMAScript [[ECMA-262]].
The term <dfn id="UnixEpoch">Unix Epoch</dfn> is used in this specification to refer to the time 00:00:00 UTC on January 1 1970
(or 1970-01-01T00:00:00Z ISO 8601);
this is the same time that is conceptually "<code>0</code>" in ECMA-262 [[ECMA-262]].
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# The Blob Interface and Binary Data # {#blob-section}
A {{Blob}} object refers to a <a>byte</a> sequence,
and has a {{Blob/size}} attribute which is the total number of bytes in the byte sequence,
and a {{Blob/type}} attribute,
which is an ASCII-encoded string in lower case representing the media type of the <a>byte</a> sequence.
Each {{Blob}} must have an internal <dfn id="snapshot-state" for=Blob>snapshot state</dfn>,
which must be initially set to the state of the underlying storage,
if any such underlying storage exists.
Further normative definition of <a>snapshot state</a> can be found for {{File}}s.
<xmp class="idl">
[Exposed=(Window,Worker), Serializable]
interface Blob {
constructor(optional sequence<BlobPart> blobParts,
optional BlobPropertyBag options = {});
readonly attribute unsigned long long size;
readonly attribute DOMString type;
// slice Blob into byte-ranged chunks
Blob slice(optional [Clamp] long long start,
optional [Clamp] long long end,
optional DOMString contentType);
// read from the Blob.
[NewObject] ReadableStream stream();
[NewObject] Promise<USVString> text();
[NewObject] Promise<ArrayBuffer> arrayBuffer();
};
enum EndingType { "transparent", "native" };
dictionary BlobPropertyBag {
DOMString type = "";
EndingType endings = "transparent";
};
typedef (BufferSource or Blob or USVString) BlobPart;
</xmp>
{{Blob}} objects are [=serializable objects=]. Their [=serialization steps=],
given |value| and |serialized|, are:
1. Set |serialized|.\[[SnapshotState]] to |value|'s [=snapshot state=].
2. Set |serialized|.\[[ByteSequence]] to |value|'s underlying byte sequence.
Their [=deserialization step=], given |serialized| and |value|, are:
1. Set |value|'s [=snapshot state=] to |serialized|.\[[SnapshotState]].
2. Set |value|'s underlying byte sequence to |serialized|.\[[ByteSequence]].
<div algorithm="get stream">
A {{Blob}} |blob| has an associated <dfn for=Blob>get stream</dfn> algorithm,
which runs these steps:
1. Let |stream| be a [=new=] {{ReadableStream}} created in |blob|'s [=relevant Realm=].
1. [=ReadableStream/Set up=] |stream|.
1. Run the following steps [=in parallel=]:
1. While not all bytes of |blob| have been read:
1. Let |bytes| be the [=byte sequence=] that results from reading a [=chunk=] from |blob|, or
failure if a chunk cannot be read.
1. [=Queue a global task=] on the [=file reading task source=] given |blob|'s
[=relevant global object=] to perform the following steps:
1. If |bytes| is failure, then [=ReadableStream/error=] |stream| with a [=failure reason=] and
abort these steps.
1. Let |chunk| be a new {{Uint8Array}} wrapping an {{ArrayBuffer}} containing |bytes|. If
creating the {{ArrayBuffer}} throws an exception, then [=ReadableStream/error=] |stream|
with that exception and abort these steps.
1. [=ReadableStream/Enqueue=] |chunk| in |stream|.
Issue: We need to specify more concretely what reading from a Blob actually does,
what possible errors can happen, perhaps something about chunk sizes, etc.
1. Return |stream|.
</div>
## Constructors ## {#constructorBlob}
<div algorithm="blob-constructor">
The {{Blob()}} constructor can be invoked with zero or more parameters.
When the {{Blob()}} constructor is invoked,
user agents must run the following steps:
1. If invoked with zero parameters,
return a new {{Blob}} object consisting of 0 bytes,
with {{Blob/size}} set to 0,
and with {{Blob/type}} set to the empty string.
1. Let |bytes| be the result of [=processing blob parts=] given {{blobParts}} and {{Blob/Blob(blobParts, options)/options}}.
1. If the {{BlobPropertyBag/type}} member of the {{Blob/Blob(blobParts, options)/options}} argument is not the empty string,
run the following sub-steps:
1. Let |t| be the {{BlobPropertyBag/type}} dictionary member.
If |t| contains any characters outside the range U+0020 to U+007E,
then set |t| to the empty string and return from these substeps.
1. Convert every character in |t| to [=ASCII lowercase=].
1. Return a {{Blob}} object referring to |bytes| as its associated <a>byte</a> sequence,
with its {{Blob/size}} set to the length of |bytes|,
and its {{Blob/type}} set to the value of |t| from the substeps above.
</div>
### Constructor Parameters ### {#constructorParams}
The {{Blob()}} constructor can be invoked with the parameters below:
<dl>
<dt>A <dfn id="dfn-blobParts" argument for="Blob/Blob(blobParts, options)"><code>blobParts</code></dfn> <code>sequence</code>
<dd>which takes any number of the following types of elements, and in any order:
* {{BufferSource}} elements.
* {{Blob}} elements.
* {{USVString}} elements.
<dt id="dfn-BlobPropertyBagMembers">An *optional* {{BlobPropertyBag}}
<dd>which takes these optional members:
* <dfn id="dfn-BPtype" dict-member for="BlobPropertyBag">type</dfn>,
the ASCII-encoded string in lower case representing the media type of the {{Blob}}.
Normative conditions for this member are provided in the [[#constructorBlob]].
* <dfn dict-member for="BlobPropertyBag">endings</dfn>,
an enum which can take the values {{"transparent"}} or {{"native"}}.
By default this is set to {{"transparent"}}. If set to {{"native"}},
[=convert line endings to native|line endings will be converted to native=]
in any {{USVString}} elements in {{blobParts}}.
</dl>
<div algorithm="process-blob-parts">
To <dfn lt="process blob parts|processing blob parts">process blob parts</dfn> given a sequence of {{BlobPart}}'s |parts|
and {{BlobPropertyBag}} |options|,
run the following steps:
1. Let |bytes| be an empty sequence of bytes.
1. For each |element| in |parts|:
1. If |element| is a {{USVString}}, run the following substeps:
1. Let |s| be |element|.
1. If the {{BlobPropertyBag/endings}} member of |options| is {{"native"}},
set |s| to the result of [=converting line endings to native=] of |element|.
1. Append the result of [=UTF-8 encoding=] |s| to |bytes|.
Note: The algorithm from WebIDL [[WebIDL]] replaces unmatched surrogates in an invalid utf-16 string
with U+FFFD replacement characters.
Scenarios exist when the {{Blob}} constructor may result in some data loss
due to lost or scrambled character sequences.
1. If |element| is a {{BufferSource}}, <a lt="get a copy of the buffer source">get
a copy of the bytes held by the buffer source</a>, and append those bytes to |bytes|.
1. If |element| is a {{Blob}},
append the bytes it represents to |bytes|.
Note: The {{Blob/type}} of the {{Blob}} array element is ignored and will not affect {{Blob/type}} of returned
{{Blob}} object.
1. Return |bytes|.
</div>
<div algorithm="convert-line-endings-to-native">
To <dfn lt="convert line endings to native|converting line endings to native">
convert line endings to native</dfn> in a [=string=] |s|,
run the following steps:
1. Let |native line ending| be be the [=code point=] U+000A LF.
1. If the underlying platform's conventions are
to represent newlines as a carriage return and line feed sequence,
set |native line ending| to the [=code point=] U+000D CR
followed by the [=code point=] U+000A LF.
1. Set |result| to the empty [=string=].
1. Let |position| be a [=position variable=] for |s|,
initially pointing at the start of |s|.
1. Let |token| be the result of [=collecting a sequence of code points=]
that are not equal to U+000A LF or U+000D CR
from |s| given |position|.
1. Append |token| to |result|.
1. While |position| is not past the end of |s|:
1. If the [=code point=] at |position| within |s| equals U+000D CR:
1. Append |native line ending| to |result|.
1. Advance |position| by 1.
1. If |position| is not past the end of |s|
and the [=code point=] at |position| within |s| equals U+000A LF
advance |position| by 1.
1. Otherwise if the [=code point=] at |position| within |s| equals U+000A LF,
advance |position| by 1 and append |native line ending| to |result|.
1. Let |token| be the result of [=collecting a sequence of code points=]
that are not equal to U+000A LF or U+000D CR
from |s| given |position|.
1. Append |token| to |result|.
1. Return |result|.
</div>
<div class="example">
Examples of constructor usage follow.
<pre class="lang-javascript">
// Create a new Blob object
var a = new Blob();
// Create a 1024-byte ArrayBuffer
// buffer could also come from reading a File
var buffer = new ArrayBuffer(1024);
// Create ArrayBufferView objects based on buffer
var shorts = new Uint16Array(buffer, 512, 128);
var bytes = new Uint8Array(buffer, shorts.byteOffset + shorts.byteLength);
var b = new Blob(["foobarbazetcetc" + "birdiebirdieboo"], {type: "text/plain;charset=utf-8"});
var c = new Blob([b, shorts]);
var a = new Blob([b, c, bytes]);
var d = new Blob([buffer, b, c, bytes]);
</pre>
</div>
## Attributes ## {#attributes-blob}
<dl dfn-type="attribute" dfn-for="Blob">
<dt><dfn id="dfn-size">size</dfn>
<dd>Returns the size of the <a>byte</a> sequence in number of bytes.
On getting, conforming user agents must return the total number of bytes that can be read by a {{FileReader}} or {{FileReaderSync}} object,
or 0 if the {{Blob}} has no bytes to be read.
<dt><dfn id="dfn-type">type</dfn>
<dd>The ASCII-encoded string in lower case representing the media type of the {{Blob}}.
On getting, user agents must return the type of a {{Blob}}
as an ASCII-encoded string in lower case,
such that when it is converted to a <a>byte</a> sequence,
it is a <a>parsable MIME type</a>,
or the empty string – 0 bytes – if the type cannot be determined.
The {{Blob/type}} attribute can be set by the web application itself through constructor invocation
and through the {{Blob/slice()}} call;
in these cases, further normative conditions for this attribute are in [[#constructorBlob]],
[[#file-constructor]],
and [[#slice-method-algo]] respectively.
User agents can also determine the {{Blob/type}} of a {{Blob}},
especially if the <a>byte</a> sequence is from an on-disk file;
in this case, further normative conditions are in the <a>file type guidelines</a>.
Note: The type <var ignore>t</var> of a {{Blob}} is considered a <a>parsable MIME type</a>,
if performing the <a>parse a MIME type</a> algorithm to a byte sequence converted from
the ASCII-encoded string representing the Blob object's type does not return failure.
Note: Use of the {{Blob/type}} attribute informs the [=package data=] algorithm
and determines the `Content-Type` header when [=/fetching=] [=blob URLs=].
</dl>
## Methods and Parameters ## {#methodsandparams-blob}
### The {{Blob/slice()}} method ### {#slice-method-algo}
The <dfn id="dfn-slice" method for=Blob lt="slice(start, end, contentType), slice(start, end), slice(start), slice()">slice()</dfn> method
returns a new {{Blob}} object with bytes ranging from
the optional {{start}} parameter
up to but not including the optional {{end}} parameter,
and with a {{Blob/type}} attribute that is the value of the optional {{contentType!!argument}} parameter.
It must act as follows:
1. The optional <dfn argument for="Blob/slice(start, end, contentType)" id="dfn-start">start</dfn> parameter
is a value for the start point of a {{slice()}} call,
and must be treated as a byte-order position,
with the zeroth position representing the first byte.
User agents must process {{Blob/slice()}} with {{start}} normalized according to the following:
<ol type="a">
<li>If the optional {{start}} parameter is not used as a parameter when making this call, let |relativeStart| be 0.
<li>If {{start}} is negative, let |relativeStart| be <code>max(({{Blob/size}} + {{start}}), 0)</code>.
<li>Else, let |relativeStart| be <code>min(start, size)</code>.
</ol>
1. The optional <dfn argument for="Blob/slice(start, end, contentType)" id="dfn-end">end</dfn> parameter
is a value for the end point of a {{slice()}} call.
User agents must process {{Blob/slice()}} with {{end}} normalized according to the following:
<ol type="a">
<li>If the optional {{end}} parameter is not used as a parameter when making this call, let |relativeEnd| be {{Blob/size}}.
<li>If {{end}} is negative, let |relativeEnd| be <code>max((size + end), 0)</code>.
<li>Else, let |relativeEnd| be <code>min(end, size)</code>.
</ol>
1. The optional <dfn argument for="Blob/slice(start, end, contentType)" id="dfn-contentTypeBlob">contentType</dfn> parameter
is used to set the ASCII-encoded string in lower case representing the media type of the Blob.
User agents must process the {{Blob/slice()}} with {{contentType}} normalized according to the following:
<ol type="a">
<li>If the {{contentType}} parameter is not provided, let |relativeContentType| be set to the empty string.
<li>Else let |relativeContentType| be set to {{contentType}} and run the substeps below:
1. If |relativeContentType| contains any characters outside the range of U+0020 to U+007E,
then set |relativeContentType| to the empty string and return from these substeps.
2. Convert every character in |relativeContentType| to [=ASCII lowercase=].
</ol>
1. Let |span| be <code>max((relativeEnd - relativeStart), 0)</code>.
1. Return a new {{Blob}} object |S| with the following characteristics:
<ol type="a">
<li>|S| refers to |span| consecutive <a>byte</a>s from <a>this</a>,
beginning with the <a>byte</a> at byte-order position |relativeStart|.
<li>|S|.{{Blob/size}} = |span|.
<li>|S|.{{Blob/type}} = |relativeContentType|.
</ol>
<div class="example">
The examples below illustrate the different types of {{slice()}} calls possible. Since the
{{File}} interface inherits from the {{Blob}} interface, examples are based on the use of the {{File}} interface.
<pre class="lang-javascript">
// obtain input element through DOM
var file = document.getElementById('file').files[0];
if(file)
{
// create an identical copy of file
// the two calls below are equivalent
var fileClone = file.slice();
var fileClone2 = file.slice(0, file.size);
// slice file into 1/2 chunk starting at middle of file
// Note the use of negative number
var fileChunkFromEnd = file.slice(-(Math.round(file.size/2)));
// slice file into 1/2 chunk starting at beginning of file
var fileChunkFromStart = file.slice(0, Math.round(file.size/2));
// slice file from beginning till 150 bytes before end
var fileNoMetadata = file.slice(0, -150, "application/experimental");
}
</pre>
</div>
### The {{Blob/stream()}} method ### {#stream-method-algo}
The <dfn method for=Blob>stream()</dfn> method, when invoked, must return
the result of calling [=get stream=] on [=this=].
### The {{Blob/text()}} method ### {#text-method-algo}
The <dfn method for=Blob>text()</dfn> method, when invoked, must run these steps:
1. Let |stream| be the result of calling [=get stream=] on [=this=].
1. Let |reader| be the result of [=get a reader|getting a reader=] from |stream|.
If that threw an exception, return a new promise rejected with that exception.
1. Let |promise| be the result of [=read all bytes|reading all bytes=] from |stream| with |reader|.
1. Return the result of transforming |promise| by a fulfillment handler that returns the result of
running [=UTF-8 decode=] on its first argument.
Note: This is different from the behavior of {{FileReader/readAsText()}} to align better
with the behavior of {{Body/text()|Fetch's text()}}. Specifically this method will always
use UTF-8 as encoding, while {{FileReader}} can use a different encoding depending on
the blob's type and passed in encoding name.
### The {{Blob/arrayBuffer()}} method ### {#arraybuffer-method-algo}
The <dfn method for=Blob>arrayBuffer()</dfn> method, when invoked, must run these steps:
1. Let |stream| be the result of calling [=get stream=] on [=this=].
1. Let |reader| be the result of [=get a reader|getting a reader=] from |stream|.
If that threw an exception, return a new promise rejected with that exception.
1. Let |promise| be the result of [=read all bytes|reading all bytes=] from |stream| with |reader|.
1. Return the result of transforming |promise| by a fulfillment handler that returns
a new {{ArrayBuffer}} whose contents are its first argument.
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# The File Interface # {#file-section}
A {{File}} object is a {{Blob}} object with a {{File/name}} attribute, which is a string;
it can be created within the web application via a constructor,
or is a reference to a <a>byte</a> sequence from a file from the underlying (OS) file system.
If a {{File}} object is a reference to a <a>byte</a> sequence originating from a file on disk,
then its <a>snapshot state</a> should be set to the state of the file on disk at the time the {{File}} object is created.
Note: This is a non-trivial requirement to implement for user agents,
and is thus not a *must* but a *should* [[RFC2119]].
User agents should endeavor to have a {{File}} object's <a>snapshot state</a>
set to the state of the underlying storage on disk at the time the reference is taken.
If the file is modified on disk following the time a reference has been taken,
the {{File}}'s <a>snapshot state</a> will differ from the state of the underlying storage.
User agents may use modification time stamps and other mechanisms to maintain <a>snapshot state</a>,
but this is left as an implementation detail.
When a {{File}} object refers to a file on disk,
user agents must return the {{Blob/type}} of that file,
and must follow the <dfn export>file type guidelines</dfn> below:
* User agents must return the {{Blob/type}} as an ASCII-encoded string in lower case,
such that when it is converted to a corresponding byte sequence,
it is a <a>parsable MIME type</a>,
or the empty string – 0 bytes – if the type cannot be determined.
* When the file is of type <code>text/plain</code>
user agents must NOT append a charset parameter to the <i>dictionary of parameters</i> portion of the media type [[!MIMESNIFF]].
* User agents must not attempt heuristic determination of encoding,
including statistical methods.
<pre class="idl">
[Exposed=(Window,Worker), Serializable]
interface File : Blob {
constructor(sequence<BlobPart> fileBits,
USVString fileName,
optional FilePropertyBag options = {});
readonly attribute DOMString name;
readonly attribute long long lastModified;
};
dictionary FilePropertyBag : BlobPropertyBag {
long long lastModified;
};
</pre>
{{File}} objects are [=serializable objects=]. Their [=serialization steps=],
given |value| and |serialized|, are:
1. Set |serialized|.\[[SnapshotState]] to |value|'s [=snapshot state=].
2. Set |serialized|.\[[ByteSequence]] to |value|'s underlying byte sequence.
3. Set |serialized|.\[[Name]] to the value of |value|'s {{File/name}} attribute.
4. Set |serialized|.\[[LastModified]] to the value of |value|'s {{File/lastModified}} attribute.
Their [=deserialization steps=], given |value| and |serialized|, are:
1. Set |value|'s [=snapshot state=] to |serialized|.\[[SnapshotState]].
2. Set |value|'s underlying byte sequence to |serialized|.\[[ByteSequence]].
3. Initialize the value of |value|'s {{File/name}} attribute to |serialized|.\[[Name]].
4. Initialize the value of |value|'s {{File/lastModified}} attribute to
|serialized|.\[[LastModified]].
## Constructor ## {#file-constructor}
<div algorithm="file-constructor">
The {{File}} constructor is invoked with two or three parameters,
depending on whether the optional dictionary parameter is used.
When the {{File()}} constructor is invoked,
user agents must run the following steps:
1. Let |bytes| be the result of [=processing blob parts=] given {{fileBits}}
and {{File/File(fileBits, fileName, options)/options}}.
2. Let |n| be the {{fileName}} argument to the constructor.
Note: Underlying OS filesystems use differing conventions for file name;
with constructed files, mandating UTF-16 lessens ambiquity when file names are converted to <a>byte</a> sequences.
3. Process {{FilePropertyBag}} dictionary argument by running the following substeps:
1. If the {{BlobPropertyBag/type}} member is provided and is not the empty string,
let |t| be set to the {{BlobPropertyBag/type}} dictionary member.
If |t| contains any characters outside the range U+0020 to U+007E,
then set |t| to the empty string and return from these substeps.
2. Convert every character in |t| to [=ASCII lowercase=].
3. If the {{FilePropertyBag/lastModified}} member is provided,
let |d| be set to the {{FilePropertyBag/lastModified}} dictionary member.
If it is not provided,
set |d| to the current date and time
represented as the number of milliseconds since the <a>Unix Epoch</a>
(which is the equivalent of <code>Date.now()</code> [[ECMA-262]]).
Note: Since ECMA-262 {{Date}} objects convert to <code>long long</code> values
representing the number of milliseconds since the <a>Unix Epoch</a>,
the {{FilePropertyBag/lastModified}} member could be a {{Date}} object [[ECMA-262]].
4. Return a new {{File}} object |F| such that:
2. |F| refers to the |bytes| <a>byte</a> sequence.
3. |F|.{{Blob/size}} is set to the number of total bytes in |bytes|.
4. |F|.{{File/name}} is set to |n|.
5. |F|.{{Blob/type}} is set to |t|.
6. |F|.{{File/lastModified}} is set to |d|.
</div>
### Constructor Parameters ### {#file-constructor-params}
The {{File()}} constructor can be invoked with the parameters below:
<dl>
<dt>A <dfn id="dfn-fileBits" argument for="File/File(fileBits, fileName, options)"><code>fileBits</code></dfn> <code>sequence</code>
<dd>which takes any number of the following elements, and in any order:
* {{BufferSource}} elements.
* {{Blob}} elements, which includes {{File}} elements.
* {{USVString}} elements.
<dt>A <dfn id="dfn-fileName" argument for="File/File(fileBits, fileName, options)"><code>fileName</code></dfn> parameter
<dd>A {{USVString}} parameter representing the name of the file;
normative conditions for this constructor parameter can be found in [[#file-constructor]].
<dt id="def-Properties">An optional {{FilePropertyBag}} dictionary
<dd>which in addition to the <a href="#dfn-BlobPropertyBagMembers">members</a> of
{{BlobPropertyBag}} takes one member:
* An optional <dfn dict-member for=FilePropertyBag id="dfn-FPdate">lastModified</dfn> member,
which must be a <code>long long</code>;
normative conditions for this member are provided in [[#file-constructor]].
</dl>
## Attributes ## {#file-attrs}
<dl dfn-type=attribute dfn-for=File>
<dt><dfn id="dfn-name">name</dfn>
<dd>The name of the file.
On getting, this must return the name of the file as a string.
There are numerous file name variations and conventions used by different underlying OS file systems;
this is merely the name of the file, without path information.
On getting, if user agents cannot make this information available,
they must return the empty string.
If a {{File}} object is created using a constructor,
further normative conditions for this attribute are found in [[#file-constructor]].
<dt><dfn id="dfn-lastModified">lastModified</dfn>
<dd>The last modified date of the file.
On getting, if user agents can make this information available,
this must return a <code>long long</code> set to the time the file was last modified
as the number of milliseconds since the <a>Unix Epoch</a>.
If the last modification date and time are not known,
the attribute must return the current date and time
as a <code>long long</code> representing the number of milliseconds since the <a>Unix Epoch</a>;
this is equivalent to <code class="lang-javascript">Date.now()</code> [[ECMA-262]].
If a {{File}} object is created using a constructor,
further normative conditions for this attribute are found in [[#file-constructor]].
</dl>
The {{File}} interface is available on objects that expose an attribute of type {{FileList}};
these objects are defined in HTML [[HTML]].
The {{File}} interface, which inherits from {{Blob}}, is immutable,
and thus represents file data that can be read into memory at the time a <a>read operation</a> is initiated.
User agents must process reads on files that no longer exist at the time of read as <a lt="file read error">errors</a>,
throwing a {{NotFoundError}} exception
if using a {{FileReaderSync}} on a Web Worker [[Workers]]
or firing an {{error!!event}} event
with the {{error!!attribute}} attribute returning a {{NotFoundError}}.
<div class="example">
In the examples below, metadata from a file object is displayed meaningfully, and a file object is created with a name and a last modified date.
<pre class="lang-javascript">
var file = document.getElementById("filePicker").files[0];
var date = new Date(file.lastModified);
println("You selected the file " + file.name + " which was modified on " + date.toDateString() + ".");
...
// Generate a file with a specific last modified date
var d = new Date(2013, 12, 5, 16, 23, 45, 600);
var generatedFile = new File(["Rough Draft ...."], "Draft1.txt", {type: "text/plain", lastModified: d})
...
</pre>
</div>
# The FileList Interface # {#filelist-section}
Note: The {{FileList}} interface should be considered "at risk"
since the general trend on the Web Platform is to replace such interfaces
with the {{Array}} platform object in ECMAScript [[ECMA-262]].
In particular, this means syntax of the sort <code class="lang-javascript">filelist.item(0)</code> is at risk;
most other programmatic use of {{FileList}} is unlikely to be affected by the eventual migration to an {{Array}} type.
This interface is a list of {{File}} objects.
<pre class="idl">
[Exposed=(Window,Worker), Serializable]
interface FileList {
getter File? item(unsigned long index);
readonly attribute unsigned long length;
};
</pre>
{{FileList}} objects are [=serializable objects=]. Their [=serialization steps=],
given |value| and |serialized|, are:
1. Set |serialized|.\[[Files]] to an empty [=list=].
2. For each |file| in |value|, append the [=sub-serialization=] of |file| to
|serialized|.\[[Files]].
Their [=deserialization step=], given |serialized| and |value|, are:
1. [=list/For each=] |file| of |serialized|.\[[Files]], add the [=sub-deserialization=] of |file| to |value|.
<div class="example">
Sample usage typically involves DOM access to the <code><input type="file"></code> element within a form,
and then accessing selected files.
<pre class="lang-javascript">
// uploadData is a form element
// fileChooser is input element of type 'file'
var file = document.forms['uploadData']['fileChooser'].files[0];
// alternative syntax can be
// var file = document.forms['uploadData']['fileChooser'].files.item(0);
if(file)
{
// Perform file ops
}
</pre>
</div>
## Attributes ## {#attributes-filelist}
<dl>
<dt><dfn attribute for=FileList id="dfn-length">length</dfn>
<dd>must return the number of files in the {{FileList}} object.
If there are no files, this attribute must return 0.
</dl>
## Methods and Parameters ## {#filelist-methods-params}
<dl>
<dt><dfn method for=FileList id="dfn-item">item(index)</dfn>
<dd>must return the |index|th {{File}} object in the {{FileList}}.
If there is no |index|th {{File}} object in the {{FileList}},
then this method must return <code>null</code>.
<dfn argument for="FileList/item(index)" id="dfn-index">index</dfn> must be treated by user agents
as value for the position of a {{File}} object in the {{FileList}},
with 0 representing the first file.
<a>Supported property indices</a> are the numbers in the range zero
to one less than the number of {{File}} objects represented by the {{FileList}} object.
If there are no such {{File}} objects,
then there are no supported property indices.
</dl>
Note: The {{HTMLInputElement}} interface has a readonly attribute of type {{FileList}},
which is what is being accessed in the above example.
Other interfaces with a readonly attribute of type {{FileList}} include the {{DataTransfer}} interface.
# Reading Data # {#reading-data-section}
## The File Reading Task Source ## {#blobreader-task-source}
This specification defines a new generic [=task source=] called the
<dfn id="fileReadingTaskSource">file reading task source</dfn>,
which is used for all [=queue a task|tasks that are queued=] in this specification
to read byte sequences associated with {{Blob}} and {{File}} objects.
It is to be used for features that trigger in response to asynchronously reading binary data.
## The {{FileReader}} API ## {#APIASynch}
<pre class="idl">
[Exposed=(Window,Worker)]
interface FileReader: EventTarget {
constructor();
// async read methods
undefined readAsArrayBuffer(Blob blob);
undefined readAsBinaryString(Blob blob);
undefined readAsText(Blob blob, optional DOMString encoding);
undefined readAsDataURL(Blob blob);
undefined abort();
// states
const unsigned short EMPTY = 0;
const unsigned short LOADING = 1;
const unsigned short DONE = 2;
readonly attribute unsigned short readyState;
// File or Blob data
readonly attribute (DOMString or ArrayBuffer)? result;
readonly attribute DOMException? error;
// event handler content attributes
attribute EventHandler onloadstart;
attribute EventHandler onprogress;
attribute EventHandler onload;
attribute EventHandler onabort;
attribute EventHandler onerror;
attribute EventHandler onloadend;
};
</pre>
A {{FileReader}} has an associated <dfn for=FileReader>state</dfn>,
that is `"empty"`, `"loading"`, or `"done"`. It is initially `"empty"`.
A {{FileReader}} has an associated <dfn for=FileReader>result</dfn>
(`null`, a {{DOMString}} or an {{ArrayBuffer}}). It is initially `null`.
A {{FileReader}} has an associated <dfn for=FileReader>error</dfn>
(`null` or a {{DOMException}}). It is initially `null`.
The <dfn constructor for=FileReader id=filereaderConstrctr>FileReader()</dfn> constructor,
when invoked, must return a new {{FileReader}} object.
The <dfn attribute for=FileReader>readyState</dfn> attribute's getter,
when invoked, switches on [=this=]'s [=FileReader/state=]
and runs the associated step:
: `"empty"`
:: Return {{EMPTY}}
: `"loading"`
:: Return {{LOADING}}
: `"done"`
:: Return {{DONE}}
The <dfn attribute for=FileReader>result</dfn> attribute's getter,
when invoked, must return [=this=]'s [=FileReader/result=].
The <dfn attribute for=FileReader>error</dfn> attribute's getter,
when invoked, must return [=this=]'s [=FileReader/error=].
<div algorithm="read operation">
A {{FileReader}} |fr| has an associated <dfn id=readOperation>read operation</dfn> algorithm,
which given |blob|, a |type| and an optional |encodingName|,
runs the following steps:
1. If |fr|'s [=FileReader/state=] is `"loading"`,
throw an {{InvalidStateError}} {{DOMException}}.
1. Set |fr|'s [=FileReader/state=] to `"loading"`.
1. Set |fr|'s [=FileReader/result=] to `null`.
1. Set |fr|'s [=FileReader/error=] to `null`.
1. Let |stream| be the result of calling [=get stream=] on |blob|.
1. Let |reader| be the result of [=get a reader|getting a reader=] from |stream|.
1. Let |bytes| be an empty [=byte sequence=].
1. Let |chunkPromise| be the result of [=read a chunk|reading a chunk=] from |stream| with |reader|.
1. Let |isFirstChunk| be true.
1. [=In parallel=], while true:
1. Wait for |chunkPromise| to be fulfilled or rejected.
1. If |chunkPromise| is fulfilled, and |isFirstChunk| is true,
[=queue a task=] to [=fire a progress event=] called {{loadstart}} at |fr|.
Issue(119): We might change {{loadstart}} to be dispatched synchronously,
to align with XMLHttpRequest behavior.
1. Set |isFirstChunk| to false.
1. If |chunkPromise| is fulfilled with an object whose `done` property is false and whose `value`
property is a `Uint8Array` object, run these steps:
1. Let |bs| be the [=byte sequence=] represented by the `Uint8Array` object.
1. Append |bs| to |bytes|.
1. If roughly 50ms have passed since these steps were last invoked,
[=queue a task=] to [=fire a progress event=] called {{progress}} at |fr|.
1. Set |chunkPromise| to the result of [=read a chunk|reading a chunk=] from |stream| with |reader|.
1. Otherwise, if |chunkPromise| is fulfilled with an object whose `done` property is true,
[=queue a task=] to run the following steps and abort this algorithm:
1. Set |fr|'s [=FileReader/state=] to `"done"`.
1. Let |result| be the result of
[=package data=] given |bytes|, |type|, |blob|'s {{Blob/type}}, and |encodingName|.
1. If [=package data=] threw an exception |error|:
1. Set |fr|'s [=FileReader/error=] to |error|.
1. [=Fire a progress event=] called {{error!!event}} at |fr|.
1. Else:
1. Set |fr|'s [=FileReader/result=] to |result|.
1. [=Fire a progress event=] called {{load}} at the |fr|.
1. If |fr|'s [=FileReader/state=] is not `"loading"`,