Internet DRAFT - draft-wright-http-partial-upload
draft-wright-http-partial-upload
HTTP A. Wright
Internet-Draft December 05, 2019
Intended status: Experimental
Expires: June 7, 2020
Partial Uploads in HTTP
draft-wright-http-partial-upload-01
Abstract
This document specifies a new media type intended for use in PATCH
payloads that allows a resource to be uploaded in several segments,
instead of a single large request.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 7, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 2
2. Modifying a content range with PATCH . . . . . . . . . . . . 3
3. Segmented upload with PATCH . . . . . . . . . . . . . . . . . 3
3.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Registrations . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. 2__ (Sparse Resource) status code . . . . . . . . . . . . 5
4.2. message/byterange media type . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5.1. Unallocated ranges . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
This introduces a mechanism that allows user agents to upload a
document over several requests. Similar solutions have been known as
partial uploads, segmented uploading, or resumable uploads.
HTTP is a stateless protocol, which implies that if a request is
interrupted, there can be no way to resume it. This is not normally
an issue if there is an alternate way of arriving to the desired
state from an incomplete state transition. For example, if a
download is interrupted, the user-agent may request just the missing
parts in a Range request. However, if an upload is interrupted, no
method exists for the client to synchronize its state with the server
and only upload the remaining data; the entire request must be
canceled and retried. This document standardizes a media type for
PATCH and a new status code for uploading new resources over several
segmented requests.
1.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document uses ABNF as defined in [RFC5234] and imports grammar
rules from [RFC7230].
For brevity, example HTTP requests or responses may add newlines or
whitespace, or omit some headers necessary for message transfer.
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2. Modifying a content range with PATCH
The PATCH method [RFC5789] allows a client to modify a resource in a
specific way, as specified by the request payload. This document
formalizes the concept of using "multipart/byteranges" [RFC7233] as a
patch file, allowing usage in PATCH; and introduces a simplified form
"message/byterange" that only patches a single range.
The "message/byterange" form may be used in a request as so:
PATCH /uploads/foo HTTP/1.1
Content-Type: message/byterange
Content-Length: 283
If-Match: "xyzzy"
If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
Content-Range: bytes 100-299/600
Content-Type: text/plain
Content-Length: 200
[200 bytes...]
This request asks to modify a 600-byte document, overwriting 200
bytes of it, starting at a 100-byte offset.
3. Segmented upload with PATCH
As an alternative to using PUT to create a new resource, the contents
of a resource may be uploaded in segments, each written across
several PATCH requests.
The first PATCH request creates the resource and uploads the first
segment. To ensure the resource does not exist, the request SHOULD
include "If-None-Match: *". The request payload is a "message/
byterange" document containing the first segment of the resource to
be uploaded, and the total length of the resource to be uploaded.
Upon processing, the server returns "2__ Sparse Resource" indicating
the document is error-free up to this point, but that more writes are
necessary before the resource will be considered fully written.
Additional segments are uploaded with the same format.
When the final segment is uploaded, the server detects the resource
is completely uploaded, and returns the final status code.
If the client loses the state of the upload, or the connection is
terminated, the user agent can re-synchronize by issuing a "HEAD"
request for the resource to get the current uploaded length. The
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response will typically be 200 (OK) or 2__ (Sparse Resource). If
2__, the user agent may resume uploading the document from that
offset.
3.1. Example
A single PUT request that creates a new file can be split apart into
multiple PATCH requests. Here is an example that uploads a 600-byte
document across three 200-byte segments.
The first PATCH request creates the resource:
PATCH /uploads/foo HTTP/1.1
Content-Type: message/byterange
Content-Length: 281
If-None-Match: *
Content-Range: bytes 0-199/600
Content-Type: text/plain
Content-Length: 200
[200 bytes...]
This request allocates a 600 byte document, and uploading the first
200 bytes of it. The server responds with 2__ (Sparse Resource),
indicating that the resource has been allocated and all uploaded data
is saved, but acknowledging the more data must still be uploaded by
the client.
Additional requests upload the remainder of the document:
PATCH /uploads/foo HTTP/1.1
Content-Type: message/byterange
Content-Length: 283
If-None-Match: *
Content-Range: bytes 200-399/600
Content-Type: text/plain
Content-Length: 200
[200 bytes...]
This second request also returns 2__ (Sparse Resource), since there
are still 200 bytes that are not written to.
A third request uploads the final portion of the document:
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PATCH /uploads/foo HTTP/1.1
Content-Type: message/byterange
Content-Length: 283
If-None-Match: *
Content-Range: bytes 200-399/600
Content-Type: text/plain
Content-Length: 200
[200 bytes...]
Since the document is fully written to, the server responds with 200
(OK), the same response as if the entire 600 bytes were written in a
PUT request.
4. Registrations
4.1. 2__ (Sparse Resource) status code
The 2__ (Sparse Resource) status code indicates that while the
request succeeded, the request target is not ready for use, and the
server is awaiting more data to be written.
In response to a GET request, representations returned with this
status code might not be valid according to their media type, but
could become valid once more data is appended.
In response to a PATCH request, it means the operation succeeded, but
more uploads are necessary before the server can do anything else
with the resource.
This is a 2xx class status because it indicates the request was
filled as requested, and may safely be handled the same as a 200 (OK)
response. However, it is only expected to be seen by clients making
partial uploads; clients not expecting this status MAY treat it as an
error.
Responses to a HEAD request MUST return the same end-to-end headers
as a GET request. Normally, HTTP allows HEAD responses to omit
certain header fields related to the payload; however Content-Length
and Content-Range are essential fields for synchronizing the state of
partial uploads. Hop-by-hop headers may still be omitted.
Several alternate names for this status code can be considered,
including: Incomplete Content, Partial Resource, or Incomplete
Upload.
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4.2. message/byterange media type
The "message/byterange" media type patches the defined byte range to
some specified contents. It is similar to the "multipart/byteranges"
media type, except it omits the multipart separator, and so only
allows a single range to be specified.
It follows the syntax of HTTP message headers and body. It MUST
include the Content-Range header field. If the message length is
known by the sender, it SHOULD contain the Content-Length header
field. Unknown or nonapplicable header fields MUST be ignored.
"header-field" and "message-body" are specified in [RFC7230].
byterange-document = *( header-field CRLF )
CRLF
[ message-body ]
A patch is applied to a document by changing the range of bytes to
the contents of the patch message payload. Servers MAY treat an
invalid or nonexistent range as an error.
5. Security Considerations
5.1. Unallocated ranges
Servers must consider what happens when clients make writes to a
sparse file.
Servers will normally only allow patch ranges to start inside or
immediately after the end of the representation. Servers supporting
sparse writes MUST NOT disclose the contents of memory. This may be
done at file creation time, or left to the filesystem if it can
guarantee this behavior.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
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[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC7233] Fielding, R., Ed., Lafon, Y., Ed., and J. Reschke, Ed.,
"Hypertext Transfer Protocol (HTTP/1.1): Range Requests",
RFC 7233, DOI 10.17487/RFC7233, June 2014,
<https://www.rfc-editor.org/info/rfc7233>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
6.2. Informative References
[RFC5789] Dusseault, L. and J. Snell, "PATCH Method for HTTP",
RFC 5789, DOI 10.17487/RFC5789, March 2010,
<https://www.rfc-editor.org/info/rfc5789>.
Author's Address
Austin Wright
Email: aaa@bzfx.net
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