Resumable Uploads for HTTP
draft-ietf-httpbis-resumable-upload-05
| Document | Type | Active Internet-Draft (httpbis WG) | |
|---|---|---|---|
| Authors | Marius Kleidl , Guoye Zhang , Lucas Pardue | ||
| Last updated | 2024-10-21 | ||
| Replaces | draft-tus-httpbis-resumable-uploads-protocol | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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draft-ietf-httpbis-resumable-upload-05
HTTP M. Kleidl, Ed.
Internet-Draft Transloadit
Intended status: Standards Track G. Zhang, Ed.
Expires: 24 April 2025 Apple Inc.
L. Pardue, Ed.
Cloudflare
21 October 2024
Resumable Uploads for HTTP
draft-ietf-httpbis-resumable-upload-05
Abstract
HTTP clients often encounter interrupted data transfers as a result
of canceled requests or dropped connections. Prior to interruption,
part of a representation may have been exchanged. To complete the
data transfer of the entire representation, it is often desirable to
issue subsequent requests that transfer only the remainder of the
representation. HTTP range requests support this concept of
resumable downloads from server to client. This document describes a
mechanism that supports resumable uploads from client to server using
HTTP.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-httpbis-resumable-
upload/.
Discussion of this document takes place on the HTTP Working Group
mailing list (mailto:ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/. Working Group
information can be found at https://httpwg.org/.
Source for this draft and an issue tracker can be found at
https://github.com/httpwg/http-extensions/labels/resumable-upload.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 24 April 2025.
Copyright Notice
Copyright (c) 2024 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
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Example 1: Complete upload of file with known size . . . 5
3.2. Example 2: Upload as a series of parts . . . . . . . . . 7
4. Upload Creation . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Feature Detection . . . . . . . . . . . . . . . . . . . . 11
4.2. Draft Version Identification . . . . . . . . . . . . . . 12
5. Offset Retrieval . . . . . . . . . . . . . . . . . . . . . . 12
6. Upload Append . . . . . . . . . . . . . . . . . . . . . . . . 14
7. Upload Cancellation . . . . . . . . . . . . . . . . . . . . . 17
8. Header Fields . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Upload-Offset . . . . . . . . . . . . . . . . . . . . . . 18
8.2. Upload-Limit . . . . . . . . . . . . . . . . . . . . . . 18
8.3. Upload-Complete . . . . . . . . . . . . . . . . . . . . . 19
8.4. Upload-Length . . . . . . . . . . . . . . . . . . . . . . 19
9. Media Type application/partial-upload . . . . . . . . . . . . 19
10. Problem Types . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1. Mismatching Offset . . . . . . . . . . . . . . . . . . . 20
10.2. Completed Upload . . . . . . . . . . . . . . . . . . . . 20
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11. Offset values . . . . . . . . . . . . . . . . . . . . . . . . 21
12. Redirection . . . . . . . . . . . . . . . . . . . . . . . . . 21
13. Content Codings . . . . . . . . . . . . . . . . . . . . . . . 21
14. Transfer Codings . . . . . . . . . . . . . . . . . . . . . . 22
15. Integrity Digests . . . . . . . . . . . . . . . . . . . . . . 22
15.1. Representation Digests . . . . . . . . . . . . . . . . . 22
15.2. Content Digests . . . . . . . . . . . . . . . . . . . . 23
16. Subsequent Resources . . . . . . . . . . . . . . . . . . . . 23
17. Upload Strategies . . . . . . . . . . . . . . . . . . . . . . 24
17.1. Optimistic Upload Creation . . . . . . . . . . . . . . . 24
17.1.1. Upgrading To Resumable Uploads . . . . . . . . . . . 24
17.2. Careful Upload Creation . . . . . . . . . . . . . . . . 25
18. Security Considerations . . . . . . . . . . . . . . . . . . . 26
19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
20. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
20.1. Normative References . . . . . . . . . . . . . . . . . . 29
20.2. Informative References . . . . . . . . . . . . . . . . . 30
Appendix A. Informational Response . . . . . . . . . . . . . . . 30
Appendix B. Feature Detection . . . . . . . . . . . . . . . . . 30
Appendix C. Upload Metadata . . . . . . . . . . . . . . . . . . 32
Appendix D. FAQ . . . . . . . . . . . . . . . . . . . . . . . . 33
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 33
Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Since draft-ietf-httpbis-resumable-upload-04 . . . . . . . . . 33
Since draft-ietf-httpbis-resumable-upload-03 . . . . . . . . . 33
Since draft-ietf-httpbis-resumable-upload-02 . . . . . . . . . 34
Since draft-ietf-httpbis-resumable-upload-01 . . . . . . . . . 34
Since draft-ietf-httpbis-resumable-upload-00 . . . . . . . . . 34
Since draft-tus-httpbis-resumable-uploads-protocol-02 . . . . . 35
Since draft-tus-httpbis-resumable-uploads-protocol-01 . . . . . 35
Since draft-tus-httpbis-resumable-uploads-protocol-00 . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction
HTTP clients often encounter interrupted data transfers as a result
of canceled requests or dropped connections. Prior to interruption,
part of a representation (see Section 3.2 of [HTTP]) might have been
exchanged. To complete the data transfer of the entire
representation, it is often desirable to issue subsequent requests
that transfer only the remainder of the representation. HTTP range
requests (see Section 14 of [HTTP]) support this concept of resumable
downloads from server to client.
HTTP methods such as POST or PUT can be used by clients to request
processing of representation data enclosed in the request message.
The transfer of representation data from client to server is often
referred to as an upload. Uploads are just as likely as downloads to
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suffer from the effects of data transfer interruption. Humans can
play a role in upload interruptions through manual actions such as
pausing an upload. Regardless of the cause of an interruption,
servers may have received part of the representation before its
occurrence and it is desirable if clients can complete the data
transfer by sending only the remainder of the representation. The
process of sending additional parts of a representation using
subsequent HTTP requests from client to server is herein referred to
as a resumable upload.
Connection interruptions are common and the absence of a standard
mechanism for resumable uploads has lead to a proliferation of custom
solutions. Some of those use HTTP, while others rely on other
transfer mechanisms entirely. An HTTP-based standard solution is
desirable for such a common class of problem.
This document defines an optional mechanism for HTTP that enables
resumable uploads in a way that is backwards-compatible with
conventional HTTP uploads. When an upload is interrupted, clients
can send subsequent requests to query the server state and use this
information to send the remaining data. Alternatively, they can
cancel the upload entirely. Different from ranged downloads, this
protocol does not support transferring different parts of the same
representation in parallel.
2. Conventions and Definitions
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.
The terms Byte Sequence, Item, String, Token, Integer, and Boolean
are imported from [STRUCTURED-FIELDS].
The terms "representation", "representation data", "representation
metadata", "content", "client" and "server" are from [HTTP].
3. Overview
Resumable uploads are supported in HTTP through use of a temporary
resource, an _upload resource_, that is separate from the resource
being uploaded to (hereafter, the _target resource_) and specific to
that upload. By interacting with the upload resource, a client can
retrieve the current offset of the upload (Section 5), append to the
upload (Section 6), and cancel the upload (Section 7).
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The remainder of this section uses an example of a file upload to
illustrate different interactions with the upload resource. Note,
however, that HTTP message exchanges use representation data (see
Section 8.1 of [HTTP]), which means that resumable uploads can be
used with many forms of content -- not just static files.
3.1. Example 1: Complete upload of file with known size
In this example, the client first attempts to upload a file with a
known size in a single HTTP request to the target resource. An
interruption occurs and the client then attempts to resume the upload
using subsequent HTTP requests to the upload resource.
1) The client notifies the server that it wants to begin an upload
(Section 4). The server reserves the required resources to accept
the upload from the client, and the client begins transferring the
entire file in the request content.
An informational response can be sent to the client, which signals
the server's support of resumable upload as well as the upload
resource URL via the Location header field (Section 10.2.2 of
[HTTP]).
Client Server
| |
| POST |
|------------------------------------------->|
| |
| | Reserve resources
| | for upload
| |-----------------.
| | |
| |<----------------'
| |
| 104 Upload Resumption Supported |
| with upload resource URL |
|<-------------------------------------------|
| |
| Flow Interrupted |
|------------------------------------------->|
| |
Figure 1: Upload Creation
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2) If the connection to the server is interrupted, the client might
want to resume the upload. However, before this is possible the
client needs to know the amount of data that the server received
before the interruption. It does so by retrieving the offset
(Section 5) from the upload resource.
Client Server
| |
| HEAD to upload resource URL |
|------------------------------------------------>|
| |
| 204 No Content with Upload-Offset |
|<------------------------------------------------|
| |
Figure 2: Offset Retrieval
3) The client can resume the upload by sending the remaining file
content to the upload resource (Section 6), appending to the already
stored data in the upload. The Upload-Offset value is included to
ensure that the client and server agree on the offset that the upload
resumes from.
Client Server
| |
| PATCH to upload resource URL with Upload-Offset |
|------------------------------------------------>|
| |
| 201 Created on completion |
|<------------------------------------------------|
| |
Figure 3: Upload Append
4) If the client is not interested in completing the upload, it can
instruct the upload resource to delete the upload and free all
related resources (Section 7).
Client Server
| |
| DELETE to upload resource URL |
|------------------------------------------------>|
| |
| 204 No Content on completion |
|<------------------------------------------------|
| |
Figure 4: Upload Cancellation
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3.2. Example 2: Upload as a series of parts
In some cases, clients might prefer to upload a file as a series of
parts sent serially across multiple HTTP messages. One use case is
to overcome server limits on HTTP message content size. Another use
case is where the client does not know the final size, such as when
file data originates from a streaming source.
This example shows how the client, with prior knowledge about the
server's resumable upload support, can upload parts of a file
incrementally.
1) If the client is aware that the server supports resumable upload,
it can start an upload with the Upload-Complete field value set to
false and the first part of the file.
Client Server
| |
| POST with Upload-Complete: ?0 |
|------------------------------------------------>|
| |
| 201 Created with Upload-Complete: ?0 |
| and Location on completion |
|<------------------------------------------------|
| |
Figure 5: Incomplete Upload Creation
2) Subsequently, parts are appended (Section 6). The last part of
the upload has a Upload-Complete field value set to true to indicate
the complete transfer.
Client Server
| |
| PATCH to upload resource URL with |
| Upload-Offset and Upload-Complete: ?1 |
|------------------------------------------------>|
| |
| 201 Created on completion |
|<------------------------------------------------|
| |
Figure 6: Upload Append Last Chunk
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4. Upload Creation
When a resource supports resumable uploads, the first step is
creating the upload resource. To be compatible with the widest range
of resources, this is accomplished by including the Upload-Complete
header field in the request that initiates the upload.
As a consequence, resumable uploads support all HTTP request methods
that can carry content, such as POST, PUT, and PATCH. Similarly, the
response to the upload request can have any status code. Both the
method(s) and status code(s) supported are determined by the
resource.
Upload-Complete MUST be set to false if the end of the request
content is not the end of the upload. Otherwise, it MUST be set to
true. This header field can be used for request identification by a
server. The request MUST NOT include the Upload-Offset header field.
If the request is valid, the server SHOULD create an upload resource.
Then, the server MUST include the Location header field in the
response and set its value to the URL of the upload resource. The
client MAY use this URL for offset retrieval (Section 5), upload
append (Section 6), and upload cancellation (Section 7).
Once the upload resource is available and while the request content
is being uploaded, the target resource MAY send one or more
informational responses with a 104 (Upload Resumption Supported)
status code to the client. In the first informational response, the
Location header field MUST be set to the URL pointing to the upload
resource. In subsequent informational responses, the Location header
field MUST NOT be set. An informational response MAY contain the
Upload-Offset header field with the current upload offset as the
value to inform the client about the upload progress.
The server MUST send the Upload-Offset header field in the response
if it considers the upload active, either when the response is a
success (e.g. 201 (Created)), or when the response is a failure (e.g.
409 (Conflict)). The Upload-Offset field value MUST be equal to the
end offset of the entire upload, or the begin offset of the next
chunk if the upload is still incomplete. The client SHOULD consider
the upload failed if the response has a status code that indicates a
success but the offset indicated in the Upload-Offset field value
does not equal the total of begin offset plus the number of bytes
uploaded in the request.
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If the request completes successfully and the entire upload is
complete, the server MUST acknowledge it by responding with a 2xx
(Successful) status code. Servers are RECOMMENDED to use 201
(Created) unless otherwise specified. The response MUST NOT include
the Upload-Complete header field with the value of false.
If the request completes successfully but the entire upload is not
yet complete, as indicated by an Upload-Complete field value of false
in the request, the server MUST acknowledge it by responding with the
201 (Created) status code and an Upload-Complete header value set to
false.
The request can indicate the upload's final size in two different
ways. Both indicators may be present in the same request as long as
they convey the same size. If the sizes are inconsistent, the server
MUST reject the request by responding with a 400 (Bad Request) status
code.
* If the request includes an Upload-Complete field value set to true
and a valid Content-Length header field, the client attempts to
upload a fixed-length resource in one request. In this case, the
upload's final size is the Content-Length field value and the
server MUST record it to ensure its consistency. The value can
therefore not be used if the upload is split across multiple
requests.
* If the request includes the Upload-Length header field, the server
MUST record its value as the upload's final size. A client SHOULD
provide this header field if the upload length is known at the
time of upload creation.
The upload is not automatically completed if the offset reaches the
upload's final size. Instead, a client MUST indicate the completion
of an upload through the Upload-Complete header field. Indicating an
upload's final size can help the server allocate necessary resources
for the upload and provide early feedback if the size does not match
the server's limits (Section 8.2).
The server MAY enforce a maximum size of an upload resource. This
limit MAY be equal to the upload's final size, if available, or an
arbitrary value. The limit's value or its existence MUST NOT change
throughout the lifetime of the upload resource. The server MAY
indicate such a limit to the client by including the Upload-Limit
header field in the informational or final response to upload
creation. If the client receives an Upload-Limit header field
indicating that the maximum size is less than the amount of bytes it
intends to upload to a resource, it SHOULD stop the current upload
transfer immediately and cancel the upload (Section 7).
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The request content MAY be empty. If the Upload-Complete header
field is then set to true, the client intends to upload an empty
resource representation. An Upload-Complete header field is set to
false is also valid. This can be used to create an upload resource
URL before transferring data, which can save client or server
resources. Since informational responses are optional, this
technique provides another mechanism to learn the URL, at the cost of
an additional round-trip before data upload can commence.
If the server does not receive the entire request content, for
example because of canceled requests or dropped connections, it
SHOULD append as much of the request content starting at its
beginning and without discontinuities as possible. If the server did
not append the entire request content, the upload MUST NOT be
considered complete.
POST /upload HTTP/1.1
Host: example.com
Upload-Draft-Interop-Version: 6
Upload-Complete: ?1
Content-Length: 100
Upload-Length: 100
[content (100 bytes)]
HTTP/1.1 104 Upload Resumption Supported
Upload-Draft-Interop-Version: 6
Location: https://example.com/upload/b530ce8ff
HTTP/1.1 104 Upload Resumption Supported
Upload-Draft-Interop-Version: 6
Upload-Offset: 50
Upload-Limit: max-size=1000000000
HTTP/1.1 201 Created
Location: https://example.com/upload/b530ce8ff
Upload-Offset: 100
Upload-Limit: max-size=1000000000
The next example shows an upload creation, where only the first 25
bytes of a 100 bytes upload are transferred. The server acknowledges
the received data and that the upload is not complete yet:
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POST /upload HTTP/1.1
Host: example.com
Upload-Draft-Interop-Version: 6
Upload-Complete: ?0
Content-Length: 25
Upload-Length: 100
[partial content (25 bytes)]
HTTP/1.1 201 Created
Location: https://example.com/upload/b530ce8ff
Upload-Complete: ?0
Upload-Offset: 25
Upload-Limit: max-size=1000000000
If the client received an informational response with the upload URL
in the Location field value, it MAY automatically attempt upload
resumption when the connection is terminated unexpectedly, or if a
5xx status is received. The client SHOULD NOT automatically retry if
it receives a 4xx status code.
File metadata can affect how servers might act on the uploaded file.
Clients can send representation metadata (see Section 8.3 of [HTTP])
in the request that starts an upload. Servers MAY interpret this
metadata or MAY ignore it. The Content-Type header field
(Section 8.3 of [HTTP]) can be used to indicate the media type of the
file. The applied content codings are specified using the Content-
Encoding header field and are retained throughout the entire upload.
When resuming an interrupted upload, the same content codings are
used for appending to the upload, producing a representation of the
upload resource. The Content-Disposition header field ([RFC6266])
can be used to transmit a filename; if included, the parameters
SHOULD be either filename, filename* or boundary.
4.1. Feature Detection
If the client has no knowledge of whether the resource supports
resumable uploads, a resumable request can be used with some
additional constraints. In particular, the Upload-Complete field
value (Section 8.3) MUST NOT be false if the server support is
unclear. This allows the upload to function as if it is a regular
upload.
Servers SHOULD use the 104 (Upload Resumption Supported)
informational response to indicate their support for a resumable
upload request.
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Clients MUST NOT attempt to resume an upload unless they receive 104
(Upload Resumption Supported) informational response, or have other
out-of-band methods to determine server support for resumable
uploads.
4.2. Draft Version Identification
*RFC Editor's Note:* Please remove this section and Upload-Draft-
Interop-Version from all examples prior to publication of a final
version of this document.
The current interop version is 6.
Client implementations of draft versions of the protocol MUST send a
header field Upload-Draft-Interop-Version with the interop version as
its value to its requests. The Upload-Draft-Interop-Version field
value is an Integer.
Server implementations of draft versions of the protocol MUST NOT
send a 104 (Upload Resumption Supported) informational response when
the interop version indicated by the Upload-Draft-Interop-Version
header field in the request is missing or mismatching.
Server implementations of draft versions of the protocol MUST also
send a header field Upload-Draft-Interop-Version with the interop
version as its value to the 104 (Upload Resumption Supported)
informational response.
Client implementations of draft versions of the protocol MUST ignore
a 104 (Upload Resumption Supported) informational response with
missing or mismatching interop version indicated by the Upload-Draft-
Interop-Version header field.
The reason both the client and the server are sending and checking
the draft version is to ensure that implementations of the final RFC
will not accidentally interop with draft implementations, as they
will not check the existence of the Upload-Draft-Interop-Version
header field.
5. Offset Retrieval
If an upload is interrupted, the client MAY attempt to fetch the
offset of the incomplete upload by sending a HEAD request to the
upload resource.
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The request MUST NOT include an Upload-Offset, Upload-Complete, or
Upload-Length header field. The server MUST reject requests with
either of these fields by responding with a 400 (Bad Request) status
code.
If the server considers the upload resource to be active, it MUST
respond with a 204 (No Content) or 200 (OK) status code. The
response MUST include the Upload-Offset header field, with the value
set to the current resumption offset for the target resource. The
response MUST include the Upload-Complete header field; the value is
set to true only if the upload is complete. The response MUST
include the Upload-Length header field set to the upload's final size
if one was recorded during the upload creation (Section 4). The
response MAY include the Upload-Limit header field if corresponding
limits on the upload resource exist.
An upload is considered complete only if the server completely and
successfully received a corresponding creation request (Section 4) or
append request (Section 6) with the Upload-Complete header value set
to true.
The client MUST NOT perform offset retrieval while creation
(Section 4) or append (Section 6) is in progress.
The offset MUST be accepted by a subsequent append (Section 6). Due
to network delay and reordering, the server might still be receiving
data from an ongoing transfer for the same upload resource, which in
the client's perspective has failed. The server MAY terminate any
transfers for the same upload resource before sending the response by
abruptly terminating the HTTP connection or stream. Alternatively,
the server MAY keep the ongoing transfer alive but ignore further
bytes received past the offset.
The client MUST NOT start more than one append (Section 6) based on
the resumption offset from a single offset retrieving request.
In order to prevent HTTP caching ([CACHING]), the response SHOULD
include a Cache-Control header field with the value no-store.
If the server does not consider the upload resource to be active, it
MUST respond with a 404 (Not Found) status code.
The resumption offset can be less than or equal to the number of
bytes the client has already sent. The client MAY reject an offset
which is greater than the number of bytes it has already sent during
this upload. The client is expected to handle backtracking of a
reasonable length. If the offset is invalid for this upload, or if
the client cannot backtrack to the offset and reproduce the same
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content it has already sent, the upload MUST be considered a failure.
The client MAY cancel the upload (Section 7) after rejecting the
offset.
The following example shows an offset retrieval request. The server
indicates the new offset and that the upload is not complete yet:
HEAD /upload/b530ce8ff HTTP/1.1
Host: example.com
Upload-Draft-Interop-Version: 6
HTTP/1.1 204 No Content
Upload-Offset: 100
Upload-Complete: ?0
Cache-Control: no-store
The client SHOULD NOT automatically retry if a 4xx (Client Error)
status code is received.
6. Upload Append
Upload appending is used for resuming an existing upload.
The request MUST use the PATCH method with the application/partial-
upload media type and MUST be sent to the upload resource. The
Upload-Offset field value (Section 8.1) MUST be set to the resumption
offset.
If the end of the request content is not the end of the upload, the
Upload-Complete field value (Section 8.3) MUST be set to false.
The server SHOULD respect representation metadata received during
creation (Section 4). An upload append request continues uploading
the same representation as used in the upload creation (Section 4)
and thus uses the same content codings, if they were applied. For
example, if the initial upload creation included the Content-
Encoding: gzip header field, the upload append request resumes the
transfer of the gzipped data without indicating again that the gzip
coding is applied.
If the server does not consider the upload associated with the upload
resource active, it MUST respond with a 404 (Not Found) status code.
The client MUST NOT perform multiple upload transfers for the same
upload resource in parallel. This helps avoid race conditions, and
data loss or corruption. The server is RECOMMENDED to take measures
to avoid parallel upload transfers: The server MAY terminate any
creation (Section 4) or append for the same upload URL. Since the
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client is not allowed to perform multiple transfers in parallel, the
server can assume that the previous attempt has already failed.
Therefore, the server MAY abruptly terminate the previous HTTP
connection or stream.
If the offset indicated by the Upload-Offset field value does not
match the offset provided by the immediate previous offset retrieval
(Section 5), or the end offset of the immediate previous incomplete
successful transfer, the server MUST respond with a 409 (Conflict)
status code. The server MAY use the problem type [PROBLEM] of
"https://iana.org/assignments/http-problem-types#mismatching-upload-
offset" in the response; see Section 10.1.
The server applies the patch document of the application/partial-
upload media type by appending the request content to the targeted
upload resource. If the server does not receive the entire patch
document, for example because of canceled requests or dropped
connections, it SHOULD append as much of the patch document starting
at its beginning and without discontinuities as possible. Appending
a continuous section starting at the patch document's beginning
constitutes a successful PATCH as defined in Section 2 of [RFC5789].
If the server did not receive and apply the entire patch document,
the upload MUST NOT be considered complete.
While the request content is being uploaded, the target resource MAY
send one or more informational responses with a 104 (Upload
Resumption Supported) status code to the client. These informational
responses MUST NOT contain the Location header field. They MAY
include the Upload-Offset header field with the current upload offset
as the value to inform the client about the upload progress.
The server MUST send the Upload-Offset header field in the response
if it considers the upload active, either when the response is a
success (e.g. 201 (Created)), or when the response is a failure (e.g.
409 (Conflict)). The value MUST be equal to the end offset of the
entire upload, or the begin offset of the next chunk if the upload is
still incomplete. The client SHOULD consider the upload failed if
the status code indicates a success but the offset indicated by the
Upload-Offset field value does not equal the total of begin offset
plus the number of bytes uploaded in the request.
If the upload is already complete, the server MUST NOT modify the
upload resource and MUST respond with a 400 (Bad Request) status
code. The server MAY use the problem type [PROBLEM] of
"https://iana.org/assignments/http-problem-types#completed-upload" in
the response; see Section 10.2.
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If the request completes successfully and the entire upload is
complete, the server MUST acknowledge it by responding with a 2xx
(Successful) status code. Servers are RECOMMENDED to use a 201
(Created) response if not otherwise specified. The response MUST NOT
include the Upload-Complete header field with the value set to false.
If the request completes successfully but the entire upload is not
yet complete indicated by the Upload-Complete field value set to
false, the server MUST acknowledge it by responding with a 201
(Created) status code and the Upload-Complete field value set to
true.
If the request includes the Upload-Complete field value set to true
and a valid Content-Length header field, the client attempts to
upload the remaining resource in one request. In this case, the
upload's final size is the sum of the upload's offset and the
Content-Length header field. If the server does not have a record of
the upload's final size from creation or the previous append, the
server MUST record the upload's final size to ensure its consistency.
If the server does have a previous record, that value MUST match the
upload's final size. If they do not match, the server MUST reject
the request with a 400 (Bad Request) status code.
The server MUST prevent that the offset exceeds the upload's final
size when appending. If a final size has been recorded and the
upload append request exceeds this value, the server MUST stop
appending bytes to the upload once the offset reaches the final size
and reject the request with a 400 (Bad Request) status code. It is
not sufficient to rely on the Content-Length header field for
enforcement because the header field might not be present.
The request content MAY be empty. If the Upload-Complete field is
then set to true, the client wants to complete the upload without
appending additional data.
The following example shows an upload append. The client transfers
the next 100 bytes at an offset of 100 and does not indicate that the
upload is then completed. The server acknowledges the new offset:
PATCH /upload/b530ce8ff HTTP/1.1
Host: example.com
Upload-Offset: 100
Upload-Draft-Interop-Version: 6
Content-Length: 100
Content-Type: application/partial-upload
[content (100 bytes)]
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HTTP/1.1 201 Created
Upload-Offset: 200
The client MAY automatically attempt upload resumption when the
connection is terminated unexpectedly, or if a 5xx (Server Error)
status code is received. The client SHOULD NOT automatically retry
if a 4xx (Client Error) status code is received.
7. Upload Cancellation
If the client wants to terminate the transfer without the ability to
resume, it can send a DELETE request to the upload resource. Doing
so is an indication that the client is no longer interested in
continuing the upload, and that the server can release any resources
associated with it.
The client MUST NOT initiate cancellation without the knowledge of
server support.
The request MUST use the DELETE method. The request MUST NOT include
an Upload-Offset or Upload-Complete header field. The server MUST
reject the request with a Upload-Offset or Upload-Complete header
field with a 400 (Bad Request) status code.
If the server successfully deactivates the upload resource, it MUST
respond with a 204 (No Content) status code.
The server MAY terminate any in-flight requests to the upload
resource before sending the response by abruptly terminating their
HTTP connection(s) or stream(s).
If the server does not consider the upload resource to be active, it
MUST respond with a 404 (Not Found) status code.
If the server does not support cancellation, it MUST respond with a
405 (Method Not Allowed) status code.
The following example shows an upload cancellation:
DELETE /upload/b530ce8ff HTTP/1.1
Host: example.com
Upload-Draft-Interop-Version: 6
HTTP/1.1 204 No Content
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8. Header Fields
8.1. Upload-Offset
The Upload-Offset request and response header field indicates the
resumption offset of corresponding upload, counted in bytes. The
Upload-Offset field value is an Integer.
8.2. Upload-Limit
The Upload-Limit response header field indicates limits applying the
upload resource. The Upload-Limit field value is a Dictionary. The
following limits are defined:
* The max-size key specifies a maximum size that an upload resource
is allowed to reach, counted in bytes. The value is an Integer.
* The min-size key specifies a minimum size for a resumable upload,
counted in bytes. The server MAY NOT create an upload resource if
the client indicates that the uploaded data is smaller than the
minimum size by including the Content-Length and Upload-Complete:
?1 fields, but the server MAY still accept the uploaded data. The
value is an Integer.
* The max-append-size key specifies a maximum size counted in bytes
for the request content in a single upload append request
(Section 6). The server MAY reject requests exceeding this limit
and a client SHOULD NOT send larger upload append requests. The
value is an Integer.
* The min-append-size key specifies a minimum size counted in bytes
for the request content in a single upload append request
(Section 6) that does not complete the upload by setting the
Upload-Complete: ?1 field. The server MAY reject non-completing
requests below this limit and a client SHOULD NOT send smaller
non-completing upload append requests. A server MUST NOT reject
an upload append request due to smaller size if the request
includes the Upload-Complete: ?1 field. The value is an Integer.
* The expires key specifies the remaining lifetime of the upload
resource in seconds counted from the generation of the response by
the server. After the resource's lifetime is reached, the server
MAY make the upload resource inaccessible and a client SHOULD NOT
attempt to access the upload resource. The lifetime MAY be
extended but SHOULD NOT be reduced once the upload resource is
created. The value is an Integer.
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When parsing this header field, unrecognized keys MUST be ignored and
MUST NOT fail the parsing to facilitate the addition of new limits in
the future.
A server that supports the creation of a resumable upload resource
(Section 4) under a target URI MUST include the Upload-Limit header
field with the corresponding limits in a response to an OPTIONS
request sent to this target URI. If a server supports the creation
of upload resources for any target URI, it MUST include the Upload-
Limit header field with the corresponding limits in a response to an
OPTIONS request with the * target. The limits announced in an
OPTIONS response SHOULD NOT be less restrictive than the limits
applied to an upload once the upload resource has been created. If
the server does not apply any limits, it MUST use min-size=0 instead
of an empty header value. A client can use an OPTIONS request to
discover support for resumable uploads and potential limits before
creating an upload resource.
8.3. Upload-Complete
The Upload-Complete request and response header field indicates
whether the corresponding upload is considered complete. The Upload-
Complete field value is a Boolean.
The Upload-Complete header field MUST only be used if support by the
resource is known to the client (Section 4.1).
8.4. Upload-Length
The Upload-Length request and response header field indicates the
number of bytes to be uploaded for the corresponding upload resource,
counted in bytes. The Upload-Length field value is an Integer.
9. Media Type application/partial-upload
The application/partial-upload media type describes a contiguous
block of data that should be uploaded to a resource. There is no
minimum block size and the block might be empty. The start and end
of the block might align with the start and end of the file that
should be uploaded, but they are not required to be aligned.
10. Problem Types
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10.1. Mismatching Offset
This section defines the "https://iana.org/assignments/http-problem-
types#mismatching-upload-offset" problem type [PROBLEM]. A server
MAY use this problem type when responding to an upload append request
(Section 6) to indicate that the Upload-Offset header field in the
request does not match the upload resource's offset.
Two problem type extension members are defined: the expected-offset
and provided-offset members. A response using this problem type
SHOULD populate both members, with the value of expected-offset taken
from the upload resource and the value of provided-offset taken from
the upload append request.
The following example shows an example response, where the resource's
offset was 100, but the client attempted to append at offset 200:
HTTP/1.1 409 Conflict
Content-Type: application/problem+json
{
"type":"https://iana.org/assignments/http-problem-types#mismatching-upload-offset",
"title": "offset from request does not match offset of resource",
"expected-offset": 100,
"provided-offset": 200
}
10.2. Completed Upload
This section defines the "https://iana.org/assignments/http-problem-
types#completed-upload" problem type [PROBLEM]. A server MAY use
this problem type when responding to an upload append request
(Section 6) to indicate that the upload has already been completed
and cannot be modified.
The following example shows an example response:
HTTP/1.1 400 Bad Request
Content-Type: application/problem+json
{
"type":"https://iana.org/assignments/http-problem-types#completed-upload",
"title": "upload is already completed"
}
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11. Offset values
The offset of an upload resource is the number of bytes that have
been appended to the upload resource. Appended data cannot be
removed from an upload and, therefore, the upload offset MUST NOT
decrease. A server MUST NOT generate responses containing an Upload-
Offset header field with a value that is smaller than was included in
previous responses for the same upload resource. This includes
informational and final responses for upload creation (Section 4),
upload appending (Section 6), and offset retrieval (Section 5).
If a server loses data that has been appended to an upload, it MUST
consider the upload resource invalid and reject further use of the
upload resource. The Upload-Offset header field in responses serves
as an acknowledgement of the append operation and as a guarantee that
no retransmission of the data will be necessary. Client can use this
guarantee to free resources associated to already uploaded data while
the upload is still ongoing.
12. Redirection
The 301 (Moved Permanently) and 302 (Found) status codes MUST NOT be
used in offset retrieval (Section 5) and upload cancellation
(Section 7) responses. For other responses, the upload resource MAY
return a 308 (Permanent Redirect) status code and clients SHOULD use
the new permanent URI for subsequent requests. If the client
receives a 307 (Temporary Redirect) response to an offset retrieval
(Section 5) request, it MAY apply the redirection directly in an
immediate subsequent upload append (Section 6).
13. Content Codings
Since the codings listed in Content-Encoding are a characteristic of
the representation (see Section 8.4 of [HTTP]), both the client and
the server always compute the values for Upload-Offset and optionally
Upload-Length on the content coded data (that is, the representation
data). Moreover, the content codings are retained throughout the
entire upload, meaning that the server is not required to decode the
representation data to support resumable uploads. See Appendix A of
[DIGEST-FIELDS] for more information.
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14. Transfer Codings
Unlike Content-Encoding (see Section 8.4.1 of [HTTP]), Transfer-
Encoding (see Section 6.1 of [HTTP/1.1]) is a property of the
message, not of the representation. Moreover, transfer codings can
be applied in transit (e.g., by proxies). This means that a client
does not have to consider the transfer codings to compute the upload
offset, while a server is responsible for transfer decoding the
message before computing the upload offset. The same applies to the
value of Upload-Length. Please note that the Content-Length header
field cannot be used in conjunction with the Transfer-Encoding header
field.
15. Integrity Digests
The integrity of an entire upload or individual upload requests can
be verifying using digests from [DIGEST-FIELDS].
15.1. Representation Digests
Representation digests help verify the integrity of the entire data
that has been uploaded so far, which might strech across multiple
requests.
If the client knows the integrity digest of the entire data before
creating an upload resource, it MAY include the Repr-Digest header
field when creating an upload (Section 4). Once the upload is
completed, the server can compute the integrity digest of the
received upload representation and compare it to the provided digest.
If the digests don't match the server SHOULD consider the transfer
failed and not process the uploaded data further. This way, the
integrity of the entire uploaded data can be protected.
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Alternatively, when creating an upload (Section 4), the client MAY
ask the server to compute and return the integrity digests using a
Want-Repr-Digest field conveying the preferred algorithms. The
response SHOULD include at least one of the requested digests, but
MAY not include it. The server SHOULD compute the representation
digests using the preferred algorithms once the upload is complete
and include the corresponding Repr-Digest header field in the
response. Alternatively, the server MAY compute the digest
continuously during the upload and include the Repr-Digest header
field in responses to upload creation (Section 4) and upload
appending requests (Section 6) even when the upload is not completed
yet. This allows the client to simultaneously compute the digest of
the transmitted upload data, compare its digest to the server's
digest, and spot data integrity issues. If an upload is spread
across multiple requests, data integrity issues can be found even
before the upload is fully completed.
15.2. Content Digests
Content digests help verify the integrity of the content in an
individual request.
If the client knows the integrity digest of the content from an
upload creation (Section 4) or upload appending (Section 6) request,
it MAY include the Content-Digest header field in the request. Once
the content has been received, the server can compute the integrity
digest of the received content and compare it to the provided digest.
If the digests don't match the server SHOULD consider the transfer
failed and not append the content to the upload resource. This way,
the integrity of an individual request can be protected.
16. Subsequent Resources
The server might process the uploaded data and make its results
available in another resource during or after the upload. This
subsequent resource is different from the upload resource created by
the upload creation request (Section 4). The subsequent resource
does not handle the upload process itself, but instead facilitates
further interaction with the uploaded data. The server MAY indicate
the location of this subsequent resource by including the Content-
Location header field in the informational or final responses
generated while creating (Section 4), appending to (Section 6), or
retrieving the offset (Section 5) of an upload. For example, a
subsequent resource could allow the client to fetch information
extracted from the uploaded data.
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17. Upload Strategies
The definition of the upload creation request (Section 4) provides
the client with flexibility to choose whether the file is fully or
partially transferred in the first request, or if no file data is
included at all. Which behavior is best largely depends on the
client's capabilities, its intention to avoid data re-transmission,
and its knowledge about the server's support for resumable uploads.
The following subsections describe two typical upload strategies that
are suited for common environments. Note that these modes are never
explicitly communicated to the server and clients are not required to
stick to one strategy, but can mix and adapt them to their needs.
17.1. Optimistic Upload Creation
An "optimistic upload creation" can be used independent of the
client's knowledge about the server's support for resumable uploads.
However, the client must be capable of handling and processing
interim responses. An upload creation request then includes the full
file because the client anticipates that the file will be transferred
without interruptions or resumed if an interruption occurs.
The benefit of this method is that if the upload creation request
succeeds, the file was transferred in a single request without
additional round trips.
A possible drawback is that the client might be unable to resume an
upload. If an upload is interrupted before the client received a 104
(Upload Resumption Supported) intermediate response with the upload
URL, the client cannot resume that upload due to the missing upload
URL. The intermediate response might not be received if the
interruption happens too early in the message exchange, the server
does not support resumable uploads at all, the server does not
support sending the 104 (Upload Resumption Supported) intermediate
response, or an intermediary dropped the intermediate response.
Without a 104 response, the client needs to either treat the upload
as failed or retry the entire upload creation request if this is
allowed by the application.
17.1.1. Upgrading To Resumable Uploads
Optimistic upload creation allows clients and servers to
automatically upgrade non-resumable uploads to resumable ones. In a
non-resumable upload, the file is transferred in a single request,
usually POST or PUT, without any ability to resume from
interruptions. The client can offer the server to upgrade such a
request to a resumable upload (see Section 4.1) by adding the Upload-
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Complete: ?1 header field to the original request. The Upload-Length
header field SHOULD be added if the upload's final size is known
upfront. The request is not changed otherwise.
A server that supports resumable uploads at the target URI can create
a resumable upload resource and send its upload URL in a 104 (Upload
Resumption Supported) intermediate response for the client to resume
the upload after interruptions. A server that does not support
resumable uploads or does not want to upgrade to a resumable upload
for this request ignores the Upload-Complete: ?1 header. The
transfer then falls back to a non-resumable upload without additional
cost.
This upgrade can also be performed transparently by the client
without the user taking an active role. When a user asks the client
to send a non-resumable request, the client can perform the upgrade
and handle potential interruptions and resumptions under the hood
without involving the user. The last response received by the client
is considered the response for the entire file upload and should be
presented to the user.
17.2. Careful Upload Creation
For a "careful upload creation" the client knows that the server
supports resumable uploads and sends an empty upload creation request
without including any file data. Upon successful response reception,
the client can use the included upload URL to transmit the file data
(Section 6) and resume the upload at any stage if an interruption
occurs. The client should inspect the response for the Upload-Limit
header field, which would indicate limits applying to the remaining
upload procedure.
The retransmission of file data or the ultimate upload failure that
can happen with an "optimistic upload creation" is therefore avoided
at the expense of an additional request that does not carry file
data.
This approach best suited if the client cannot receive intermediate
responses, e.g. due to a limitation in the provided HTTP interface,
or if large files are transferred where the cost of the additional
request is miniscule compared to the effort of transferring the large
file itself.
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18. Security Considerations
The upload resource URL is the identifier used for modifying the
upload. Without further protection of this URL, an attacker may
obtain information about an upload, append data to it, or cancel it.
To prevent this, the server SHOULD ensure that only authorized
clients can access the upload resource. In addition, the upload
resource URL SHOULD be generated in such a way that makes it hard to
be guessed by unauthorized clients.
Some servers or intermediaries provide scanning of content uploaded
by clients. Any scanning mechanism that relies on receiving a
complete file in a single request message can be defeated by
resumable uploads because content can be split across multiple
messages. Servers or intermediaries wishing to perform content
scanning SHOULD consider how resumable uploads can circumvent
scanning and take appropriate measures. Possible strategies include
waiting for the upload to complete before scanning a full file, or
disabling resumable uploads.
Resumable uploads are vulnerable to Slowloris-style attacks
[SLOWLORIS]. A malicious client may create upload resources and keep
them alive by regularly sending PATCH requests with no or small
content to the upload resources. This could be abused to exhaust
server resources by creating and holding open uploads indefinitely
with minimal work.
Servers SHOULD provide mitigations for Slowloris attacks, such as
increasing the maximum number of clients the server will allow,
limiting the number of uploads a single client is allowed to make,
imposing restrictions on the minimum transfer speed an upload is
allowed to have, and restricting the length of time an upload
resource can exist.
19. IANA Considerations
IANA is asked to register the following entries in the "Hypertext
Transfer Protocol (HTTP) Field Name Registry":
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+=================+===========+==============================+
| Field Name | Status | Reference |
+=================+===========+==============================+
| Upload-Complete | permanent | Section 8.3 of this document |
+-----------------+-----------+------------------------------+
| Upload-Offset | permanent | Section 8.1 of this document |
+-----------------+-----------+------------------------------+
| Upload-Limit | permanent | Section 8.2 of this document |
+-----------------+-----------+------------------------------+
| Upload-Length | permanent | Section 8.4 of this document |
+-----------------+-----------+------------------------------+
Table 1
IANA is asked to register the following entry in the "HTTP Status
Codes" registry:
Value: 104 (suggested value)
Description: Upload Resumption Supported
Specification: This document
IANA is asked to register the following entry in the "Media Types"
registry:
Type name: application
Subtype name: partial-upload
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: binary
Security considerations: see Section 18 of this document
Interoperability considerations: N/A
Published specification: This document
Applications that use this media type: Applications that transfer
files over unreliable networks or want pause- and resumable
uploads.
Fragment identifier considerations: N/A
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Additional information:
* Deprecated alias names for this type: N/A
* Magic number(s): N/A
* File extension(s): N/A
* Macintosh file type code(s): N/A
* Windows Clipboard Name: N/A
Person and email address to contact for further information: See the
Authors' Addresses section of this document.
Intended usage: COMMON
Restrictions on usage: N/A
Author: See the Authors' Addresses section of this document.
Change controller: IETF
IANA is asked to register the following entry in the "HTTP Problem
Types" registry:
Type URI: https://iana.org/assignments/http-problem-
types#mismatching-upload-offset Title:
Mismatching Upload Offset Recommended HTTP status code:
409 Reference:
This document
IANA is asked to register the following entry in the "HTTP Problem
Types" registry:
Type URI: https://iana.org/assignments/http-problem-types#completed-
upload Title:
Upload Is Completed Recommended HTTP status code:
400 Reference:
This document
20. References
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20.1. Normative References
[CACHING] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Caching", STD 98, RFC 9111,
DOI 10.17487/RFC9111, June 2022,
<https://www.rfc-editor.org/rfc/rfc9111>.
[DIGEST-FIELDS]
Polli, R. and L. Pardue, "Digest Fields", RFC 9530,
DOI 10.17487/RFC9530, February 2024,
<https://www.rfc-editor.org/rfc/rfc9530>.
[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
[HTTP/1.1] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP/1.1", STD 99, RFC 9112, DOI 10.17487/RFC9112,
June 2022, <https://www.rfc-editor.org/rfc/rfc9112>.
[PROBLEM] Nottingham, M., Wilde, E., and S. Dalal, "Problem Details
for HTTP APIs", RFC 9457, DOI 10.17487/RFC9457, July 2023,
<https://www.rfc-editor.org/rfc/rfc9457>.
[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/rfc/rfc2119>.
[RFC5789] Dusseault, L. and J. Snell, "PATCH Method for HTTP",
RFC 5789, DOI 10.17487/RFC5789, March 2010,
<https://www.rfc-editor.org/rfc/rfc5789>.
[RFC6266] Reschke, J., "Use of the Content-Disposition Header Field
in the Hypertext Transfer Protocol (HTTP)", RFC 6266,
DOI 10.17487/RFC6266, June 2011,
<https://www.rfc-editor.org/rfc/rfc6266>.
[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/rfc/rfc8174>.
[STRUCTURED-FIELDS]
Nottingham, M. and P. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.
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20.2. Informative References
[SLOWLORIS]
"RSnake" Hansen, R., "Welcome to Slowloris - the low
bandwidth, yet greedy and poisonous HTTP client!", June
2009, <https://web.archive.org/web/20150315054838/
http://ha.ckers.org/slowloris/>.
Appendix A. Informational Response
The server is allowed to respond to upload creation (Section 4)
requests with a 104 (Upload Resumption Supported) intermediate
response as soon as the server has validated the request. This way,
the client knows that the server supports resumable uploads before
the complete response is received. The benefit is the clients can
defer starting the actual data transfer until the server indicates
full support (i.e. resumable are supported, the provided upload URL
is active etc).
On the contrary, support for intermediate responses (the 1XX range)
in existing software is limited or not at all present. Such software
includes proxies, firewalls, browsers, and HTTP libraries for clients
and server. Therefore, the 104 (Upload Resumption Supported) status
code is optional and not mandatory for the successful completion of
an upload. Otherwise, it might be impossible in some cases to
implement resumable upload servers using existing software packages.
Furthermore, as parts of the current internet infrastructure
currently have limited support for intermediate responses, a
successful delivery of a 104 (Upload Resumption Supported) from the
server to the client should be assumed.
We hope that support for intermediate responses increases in the near
future, to allow a wider usage of 104 (Upload Resumption Supported).
Appendix B. Feature Detection
This specification includes a section about feature detection (it was
called service discovery in earlier discussions, but this name is
probably ill-suited). The idea is to allow resumable uploads to be
transparently implemented by HTTP clients. This means that
application developers just keep using the same API of their HTTP
library as they have done in the past with traditional, non-resumable
uploads. Once the HTTP library gets updated (e.g. because mobile OS
or browsers start implementing resumable uploads), the HTTP library
can transparently decide to use resumable uploads without explicit
configuration by the application developer. Of course, in order to
use resumable uploads, the HTTP library needs to know whether the
server supports resumable uploads. If no support is detected, the
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HTTP library should use the traditional, non-resumable upload
technique. We call this process feature detection.
Ideally, the technique used for feature detection meets following
*criteria* (there might not be one approach which fits all
requirements, so we have to prioritize them):
1. Avoid additional roundtrips by the client, if possible (i.e. an
additional HTTP request by the client should be avoided).
2. Be backwards compatible to HTTP/1.1 and existing network
infrastructure: This means to avoid using new features in HTTP/2,
or features which might require changes to existing network
infrastructure (e.g. nginx or HTTP libraries)
3. Conserve the user's privacy (i.e. the feature detection should
not leak information to other third-parties about which URLs have
been connected to)
Following *approaches* have already been considered in the past. All
except the last approaches have not been deemed acceptable and are
therefore not included in the specification. This follow list is a
reference for the advantages and disadvantages of some approaches:
*Include a support statement in the SETTINGS frame.* The SETTINGS
frame is a HTTP/2 feature and is sent by the server to the client to
exchange information about the current connection. The idea was to
include an additional statement in this frame, so the client can
detect support for resumable uploads without an additional roundtrip.
The problem is that this is not compatible with HTTP/1.1.
Furthermore, the SETTINGS frame is intended for information about the
current connection (not bound to a request/response) and might not be
persisted when transmitted through a proxy.
*Include a support statement in the DNS record.* The client can
detect support when resolving a domain name. Of course, DNS is not
semantically the correct layer. Also, DNS might not be involved if
the record is cached or retrieved from a hosts files.
*Send a HTTP request to ask for support.* This is the easiest
approach where the client sends an OPTIONS request and uses the
response to determine if the server indicates support for resumable
uploads. An alternative is that the client sends the request to a
well-known URL to obtain this response, e.g. /.well-known/resumable-
uploads. Of course, while being fully backwards-compatible, it
requires an additional roundtrip.
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*Include a support statement in previous responses.* In many cases,
the file upload is not the first time that the client connects to the
server. Often additional requests are sent beforehand for
authentication, data retrieval etc. The responses for those requests
can also include a header field which indicates support for resumable
uploads. There are two options: - Use the standardized Alt-Svc
response header field. However, it has been indicated to us that
this header field might be reworked in the future and could also be
semantically different from our intended usage. - Use a new response
header field Resumable-Uploads: https://example.org/files/* to
indicate under which endpoints support for resumable uploads is
available.
*Send a 104 intermediate response to indicate support.* The clients
normally starts a traditional upload and includes a header field
indicate that it supports resumable uploads (e.g. Upload-Offset: 0).
If the server also supports resumable uploads, it will immediately
respond with a 104 intermediate response to indicate its support,
before further processing the request. This way the client is
informed during the upload whether it can resume from possible
connection errors or not. While an additional roundtrip is avoided,
the problem with that solution is that many HTTP server libraries do
not support sending custom 1XX responses and that some proxies may
not be able to handle new 1XX status codes correctly.
*Send a 103 Early Hint response to indicate support.* This approach
is the similar to the above one, with one exception: Instead of a new
104 (Upload Resumption Supported) status code, the existing 103
(Early Hint) status code is used in the intermediate response. The
103 code would then be accompanied by a header field indicating
support for resumable uploads (e.g. Resumable-Uploads: 1). It is
unclear whether the Early Hints code is appropriate for that, as it
is currently only used to indicate resources for prefetching them.
Appendix C. Upload Metadata
When an upload is created (Section 4), the Content-Type and Content-
Disposition header fields are allowed to be included. They are
intended to be a standardized way of communicating the file name and
file type, if available. However, this is not without controversy.
Some argue that since these header fields are already defined in
other specifications, it is not necessary to include them here again.
Furthermore, the Content-Disposition header field's format is not
clearly enough defined. For example, it is left open which
disposition value should be used in the header field. There needs to
be more discussion whether this approach is suited or not.
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However, from experience with the tus project, users are often asking
for a way to communicate the file name and file type. Therefore, we
believe it is help to explicitly include an approach for doing so.
Appendix D. FAQ
* *Are multipart requests supported?* Yes, requests whose content is
encoded using the multipart/form-data are implicitly supported.
The entire encoded content can be considered as a single file,
which is then uploaded using the resumable protocol. The server,
of course, must store the delimiter ("boundary") separating each
part and must be able to parse the multipart format once the
upload is completed.
Acknowledgments
This document is based on an Internet-Draft specification written by
Jiten Mehta, Stefan Matsson, and the authors of this document.
The tus v1 protocol (https://tus.io/) is a specification for a
resumable file upload protocol over HTTP. It inspired the early
design of this protocol. Members of the tus community helped
significantly in the process of bringing this work to the IETF.
The authors would like to thank Mark Nottingham for substantive
contributions to the text.
Changes
This section is to be removed before publishing as an RFC.
Since draft-ietf-httpbis-resumable-upload-04
* Clarify implications of Upload-Limit header.
* Allow client to fetch upload limits upfront via OPTIONS.
* Add guidance on upload creation strategy.
* Add Upload-Length header to indicate length during creation.
* Describe possible usage of Want-Repr-Digest.
Since draft-ietf-httpbis-resumable-upload-03
* Add note about Content-Location for referring to subsequent
resources.
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* Require application/partial-upload for appending to uploads.
* Explain handling of content and transfer codings.
* Add problem types for mismatching offsets and completed uploads.
* Clarify that completed uploads must not be appended to.
* Describe interaction with Digest Fields from RFC9530.
* Require that upload offset does not decrease over time.
* Add Upload-Limit header field.
* Increase the draft interop version.
Since draft-ietf-httpbis-resumable-upload-02
* Add upload progress notifications via informational responses.
* Add security consideration regarding request filtering.
* Explain the use of empty requests for creation uploads and
appending.
* Extend security consideration to include resource exhaustion
attacks.
* Allow 200 status codes for offset retrieval.
* Increase the draft interop version.
Since draft-ietf-httpbis-resumable-upload-01
* Replace Upload-Incomplete header with Upload-Complete.
* Replace terminology about procedures with HTTP resources.
* Increase the draft interop version.
Since draft-ietf-httpbis-resumable-upload-00
* Remove Upload-Token and instead use Server-generated upload URL
for upload identification.
* Require the Upload-Incomplete header field in Upload Creation
Procedure.
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* Increase the draft interop version.
Since draft-tus-httpbis-resumable-uploads-protocol-02
None
Since draft-tus-httpbis-resumable-uploads-protocol-01
* Clarifying backtracking and preventing skipping ahead during the
Offset Receiving Procedure.
* Clients auto-retry 404 is no longer allowed.
Since draft-tus-httpbis-resumable-uploads-protocol-00
* Split the Upload Transfer Procedure into the Upload Creation
Procedure and the Upload Appending Procedure.
Authors' Addresses
Marius Kleidl (editor)
Transloadit
Email: marius@transloadit.com
Guoye Zhang (editor)
Apple Inc.
Email: guoye_zhang@apple.com
Lucas Pardue (editor)
Cloudflare
Email: lucas@lucaspardue.com
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