INTERNET-DRAFT J. Salsman Filename: <draft-salsman-www-device-upload-07.txt> Cisco Systems to be submitted to the W3C, HTML activity for forms 1 June 1999 Form-based Device Input in HTML Status of this Memo This draft extends an experimental protocol for the Internet community. This draft does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited. This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html 1. Abstract Currently, HTML forms allow the producer of the form to request information -- including files of data -- from the operator reading the form. However, this capability is limited because HTML forms don't provide a way to ask the operator to submit input from arbitrary sources such as audio devices like microphones. Since input and upload from various devices is a feature that will benefit many applications, this draft proposes an extension to the HTML INPUT TYPE=FILE form element specified in [RFC 1867] to allow information providers to express requests for uploads from audio and other devices uniformly. A discussion of MIME audio data types to facilitate useful audio upload responses follows. Also security discussions are included, as are audio usability and quality discussions, and a description of a backward compatibility strategy allowing new user agents to utilize HTML written with earlier proposals for audio input in mind. Motivations, including language instruction assistance, voice transcription, and high-quality transmission under low-bandwidth conditions, conclude. 2. Introduction The following protocol extensions are defined by this memo: - a DEVICE attribute to be used in HTML with the INPUT element along with the TYPE=FILE attribute-value, which identifies the peripheral device from which the input file is to be taken. The following nine device names are suggested in this memo: microphone, mic, filesystem, files, camera, keyboard, scanner, serial, any. - an HTTP request header named Client-File-Maxlength, specifying a decimal integer of bytes, which specifies the input buffer length available to the client for storage of input data for file upload. - two parameters for the MIME Content-Disposition header: - 'device' -- the lowercase value of the DEVICE attribute, or 'unavailable' if the requested device is supported but unavailable, or 'unsupported' if the device is not supported or the MIME type(s) requested in the ACCEPT attribute are not supported. - 'alternates' -- a space-separated list of MIME types which indicates the types available from the requested device when the requested type(s) are unsupported. - and the TYPE=AUDIO HTML Input element extension, first published in 1993 by Dave Raggett within the HTML+ Discussion Document, and implemented before the introduction of [RFC 1867]. 3. Extensions Section 3.1 of [RFC 1867] provides for the presentation of an arbitrary "widget" to specify input for file uploads. When an INPUT tag of type FILE is encountered with a DEVICE attribute, the associated value (such as MICROPHONE, or MIC) should select the use of a widget capable of buffering and editing real-time input (such as speech) from the specified device, instead of selecting a file. If an ACCEPT attribute also has a value in a device file input element, the browser may constrain the MIME type of uploaded data to match those with the list of types specified as the value of the ACCEPT attribute. If the value of the DEVICE attribute is FILESYSTEM (or FILES) then the INPUT element may be treated as usual according to [RFC 1867] except that the subset of files presented to the operator to choose from may be constrained by the specified list of MIME types instead of a pattern of file names or extensions. Please note that without DEVICE=FILES the ACCEPT attribute will probably be treated as a filename pattern. If the value of the DEVICE parameter is ANY, the operator may be offered a choice of all available supported devices and files, restricted to the choices compatible with the MIME types specified in the ACCEPT attribute, if present. File-upload forms are submitted with ENCTYPE="multipart/form-data" -- an alternate FORM tag specification for sending MIME content. Each "part" of such a submission, representing the value of each input element in the submitted form, is given a Content-Disposition header, which in the case of 'content-disposition: file' -- may also have a Content-Type header representing the MIME type of the data being uploaded. Files uploaded using the extensions in this memo SHOULD [RFC 2119] include a Content-Type header when the file type is known or can be accurately determined by the client browser. Since no original filename as specified in section 3.3 of [RFC 1867] will be available for arbitrary peripheral input, parameters of the 'content-disposition: form-data' submission headers SHOULD include a 'device' parameter with the lowercase value of the DEVICE attribute of the associated form input element, unless the device or MIME type(s) specified are unsupported in which case the value of the 'device' header parameter may be 'unsupported', or unless the device is unavailable in which case the value SHOULD be 'unavailable'. If the MIME types requested are unsupported, an additional parameter 'alternates' may be included with a space-separated list of MIME types of the same content-type which may be supported as alternatives for the specified device. The 'alternates' parameter is not intended as a content negotiation feature; merely a way for a server to log upload failures which were constrained by the lack of type conversion facilities. The content-disposition header parameter syntax is described in [RFC 2183], which along with [RFC 1867], contain examples of the protocols extended by this memo. There may be significant limitations on the client browser's ability to buffer input for upload. Browsers may provide an estimate of the default MAXLENGTH available for device input and upload through the HTTP header 'Client-file-maxlength:' followed immediately with the decimal representation of the number of bytes representing the content-length available to the browser for buffering (reference: section 14 of RFC 2068.) A server may also provide information about the largest file size it can accept for upload, by using the MAXLENGTH attribute with a value representing the decimal integer of bytes in the HTML form's INPUT elements. Furthermore, the VALUE attribute may be used to provide a numeric disambiguation between multiple similar devices when present. Under most conditions the operator SHOULD be allowed to select the device from ambiguous sources of input, or re-select it if specified with a VALUE parameter. The VALUE attribute may also be used to specify alternative methods of input when the value of VALUE is nonnumeric. If real time events, such as those described and proposed by Gregory S. Aist in "A General Architecture for a Real-Time Discourse Agent and a Case Study in Computerized Oral Reading Tutoring" (Carnegie Mellon University Computational Linguistics Program, 6 December 1996), are required, then the Real-time Transport Protocol (RTP, currently RFC 1889) may be used instead. Because of security concerns discussed in section 9 below, HTML scripts MUST NOT be able to invoke a form submission when the form involves any kind of file upload without explicit instructions from the session operator to the contrary. 3.1. Examples In this short form, the HTML author has requested the upload of sampled microphone input from the operator upon form submission: <FORM ENCTYPE="multipart/form-data" METHOD=POST ACTION="_URL_"> Say something: <INPUT NAME=SPEECH1 TYPE=FILE DEVICE=MIC> <INPUT TYPE=SUBMIT VALUE="Send Speech"> </FORM> Below MIC is not used as an abbreviation. The author of the HTML has requested that the data input from the microphone be encoded as either the MIME type Audio/L16 -- sixteen bit signed linear audio samples (most-significant byte first) -- as specified in [RFC 1890] section 4.4.8, with a single (monaural) channel and a sample rate of 11,025 samples per second, or an unspecified extended MIME Audio type named 'x-cepstral-voc'. Please note that MIME types are here separated by spaces except when the following character is a semicolon, in which case the following non-space string should be of the form ";parameter=value" which modifies the preceding MIME type, but space before such parameters is optional. <INPUT NAME=SPEECH2 TYPE=FILE DEVICE=MICROPHONE ACCEPT="audio/L16;rate=11025 ;channels=1 audio/x-cepstral-voc"> <INPUT NAME=FILE1 TYPE=FILE DEVICE=FILES ACCEPT="text/*"> Below the form element may be used to upload a file as usual, except that the files to select from may be constrained to text files, without explicit regard of their filename or extensions. Please note that "/*" after "text" is optional. <INPUT NAME=FILE1 TYPE=FILE DEVICE=FILE ACCEPT="text/*"> The next two examples show how these extensions may be used to request input from other kinds of devices, such as the second of two or more cameras connected to the system running the browser. Please note that the VALUE is only a suggestion, and the browser operator should still be offered to select from multiple devices, with the only difference being the default selection. <INPUT NAME=PICTURE1 TYPE=FILE DEVICE=CAMERA VALUE=2> For this next example only, if there is only one keyboard, the operator's preferred editor may be invoked, but the filename should be unique and not influenced in any way by the string "EMACS". If that value influences the selection of an editor, it should do so with a pre-specified table (such as a "mailcap" file) and should not be used as any part of the command string of the editor executed. <INPUT NAME=ESSAY1 TYPE=FILE DEVICE=KEYBOARD VALUE=EMACS> The example below requests the operator to select images from any device, including the filesystem, for upload to the server, as long as they are less than 100 KB (and any values specified in the Server-file-maxlength and Client-file-maxlength HTTP headers; the minimum of all three values should take precedence.) <INPUT NAME=PICTURE2 TYPE=FILE DEVICE=ANY ACCEPT="image" MAXLENGTH=100000> 4. Compatibility with earlier forms of audio input Audio microphone input was proposed in late 1993 and implemented (with url-encoded submission data) in experimental versions of X-Mosaic in Germany no later than 1995. To accommodate the syntax of these earlier extensions, a browser might interpret an HTML statement such as <INPUT TYPE=AUDIO ...> as the device input form <INPUT TYPE=FILE DEVICE=MICROPHONE ...> with all other attribute/value pairs of the original INPUT element kept the same as specified. This would retain compatibility for all implementations of which the author of this draft is aware. 5. User interface usability and quality concerns for audio An audio sample is customarily recorded on computer equipment with a dialog routine capable of allowing the user to record, pause, play back, erase, or otherwise edit the recording. Browsers may provide the operator with the same kind of dialog routine for audio device input. And if a MAXLENGTH has been specified or is in force because of limited buffer size, a display of the buffer size used and remaining may be displayed as a dynamic bar graph (or as a percentage if graphics are unavailable.) A display of time in seconds used and remaining in the buffer may also be provided. Most MIME types defined for audio do not provide high-quality audio encodings. The 'audio/basic' and other types which use a sample rate of 8,000 samples per second truncate the audio spectrum at 4,000 Hz according to the Nyquist theorem, discarding information important for discerning consonants. Also, audio/basic and other MIME Audio types use a sample size of eight bits, which does not usually provide enough dynamic range for accurate automatic speech recognition unless published automatic gain control algorithms are reliably used. If sixteen-bit unsigned audio encodings are used according to section 4.4.8 of [RFC 1890], the sample rate -- specified as the 'rate' parameter of the MIME type 'audio/l16' -- may be at least 11,025 or 16,000 to adequately provide sufficient information for automatic speech recognition. Otherwise, the audio feature extraction encoding of the speech recognition algorithm may be used to provide a more compact representation to shorten the upload. 6. HTML Document Type Description changes Along with the extension to the HTML InputType entity described in the previous section, this proposal makes an addition to the HTML DTD for the INPUT element ATTLIST of an #IMPLIED attribute DEVICE of type CDATA, and reserves an #IMPLIED attribute CONNEG, also of type CDATA. Contemporary revisions of HTML are being defined as modules within XML, which involves a different DTD structure. The preceding paragraph was written with the HTML 3.2 DTD in mind, and is no longer up to date. It still serves to disambiguate the syntax of the proposal. It is worth noting that all attribute values must be quoted in XML, and "empty" tags (unitary elements which are not used to bracket text, e.g., input but not form) must end with space followed by a forward-slash before the trailing angle bracket. For example: <input type="file" device="camera" accept="video/mpeg" /> Registration of new DEVICE names not suggested in this draft will be administered by the W3C HTML activity or delegated to IANA as described in BCP 26 (RFC 2434) at the option of the W3C HTML activity. The official definition of the assigned DEVICE values may be reflected in the comments of the DTD when approved and published by the W3C or other authority, immediately following the definition of the DEVICE attribute. 7. Motivations The primary motivation for these extensions is to add the capability of speech input to Web-based educational systems. [MR 1, 2] Other motivations include the development of "dictation servers" [MR 3] capable of transforming spoken audio uploaded though an HTTP session to the corresponding text suitable for sending in email or including in another document, for example. Natural language continuous speech recognition software conforming to standard APIs for automatic dictation is as of this writing available for free in small quantity so there is ample reason to believe that transcription servers might soon become commonplace on the Web with these extensions. These extensions could also be a help to hearing-impaired people who could use a "phonology server" to practice improving pronunciation. Larry Masinter, author of [RFC 1867], and member of the IETF Content Negotiation Working Group has indicated that graphical paper scanners might be used for applications such as OCR and bar-code upload. "DEVICE=SCANNER" and "DEVICE=SERIAL" are suggested. Finally, it is important to note that the addition of this proposal will allow web-enabled devices, such as radio telephones, to transmit high-quality asynchronous content, such as voicemail, under conditions of very low bandwidth. 8. Scaling considerations The protocol proposed in this draft has been proven to scale for very large files, but is not intended for open-ended uploads of content of indeterminate length. RTP (RFC 1889) is much more appropriate for such open-ended transmission of device input. 9. Security considerations Browser operators may not want to send their files, recordings, pictures, video, or other device inputs to arbitrary sites without their explicit permission and direction. Therefore, browser authors are encouraged to disallow the submission of forms which include any kind of file upload by any means other than the standard HTML operator-controlled buttons for form submission without explicit instruction from the session operator to the contrary. Accordingly, the SIZE parameter, document style sheets, and document layers may be prevented from obscuring any kind of file upload widget, especially those capable of accepting a default filename. Furthermore, just as the operator may take direct action to initiate, terminate, review and edit recording as described in the previous section, browser authors are encouraged to prevent HTML scripts from taking those and similar actions, unless for example the operator has specifically enabled such script actions with a security option. Even then, such preferences may be specified by the operator to reset after an interval or at the end of the session. Finally, explicit information may be needed to insure that the operator is informed when files are being uploaded. 10. Author's address and acknowledgments James Salsman W3C Representative Cisco Systems, San Jose, California Bovik Research Inst., a non-profit organization 1285 Montecito Ave Apt 57 Mountain View, CA 94043 Email: jps@bovik.org, jsalsman@cisco.com Phone: (650) 967-2737 Larry Masinter and Harald Alvestrand contributed excellent advice. Ed Tecot contributed the means of device and media independence. David McMillian contributed to the description of capabilities of the audio widget. Syracuse Language Systems, The Learning Co., and EduSoft, Ltd., contributed much of the inspiration; Jack Mostow et alli did much more work for younger grades. Dave Raggett helped integrate into the fast-paced development of HTML. Keith Moore provided invaluable comments and assistance. 11. Provisional copyright statement and permissions This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that this paragraph is included on all such copies and derivative works. However, this document itself may not be modified in any way, except as needed for the purpose of developing Internet and W3C standards or as required to translate it into languages other than English. Copyright (c) 1999. The limited permissions granted above are perpetual and will not be revoked by the author or his successors or assigns. Moreover, the author will not make any effort to restrict the use of the information contained in this document. This document and the information contained herein is provided on an "as is" basis and the author disclaims all warranties, express or implied, including but not limited to any warranty that the use of the information herein will not infringe on any rights or any implied warranties of merchantability or fitness for a particular purpose. In the opinion of the author, use of the information contained in this document does not infringe on any rights. References [RFC 1867] Form-based File Upload in HTML. E. Nebel & L. Masinter, November 1995. [RFC 1890] RTP Profile for Audio and Video Conferences with Minimal Control. H. Schulzrinne, January 1996. [RFC 2068] Hypertext Transfer Protocol -- HTTP/1.1. R. Fielding, J. Gettys, J. Mogul, H. Frystyk, & T. Berners-Lee, January 1997. [RFC 2119] Key words for use in RFCs to Indicate Requirement Levels. S. Bradner, March 1997. [RFC 2183] Communicating Presentation Information in Internet Messages: The Content-Disposition Header. R. Troost, S. Dorner, & K. Moore, August 1997. [MR 1] http://www.cs.cmu.edu/~listen Literacy instruction by a reading tutor that listens, from Carnegie Mellon's Project LISTEN. [MR 2] http://www.ordinate.com Over-the-phone automated testing of English fluency, listening, and vocabulary from Ordinate Corporation. [MR 3] http://www.cybertranscriber.com Automatic transcription from spoken dictation from Speech Machines Corporation. END OF DRAFT Filename: <draft-salsman-www-device-upload-07.txt> changes from -05 to -06: title shortened 'type' parameter --> Content-type header (doesn't break CGI.pm) itemized: HTML element attributes, HTTP request, content-disposition parameters (IANA parameter templates to be filed seperatly upon approval) removed server-file-maxlength due to redundancy with HTML MAXLENGTH removed CONNEG reservations and disclaimed content negotiation grammar adjusted with RFC 2119 in mind format changes and section renumbering for Application Area additional examples, incl. XML tag style references put in RFC style changes from -06 to -07: corrected historical notes to reference dsr@w3.org's HTML+ draft deleted reference to 'Content-disposition: file' which never occurs :jps