Byte Range PATCH
draft-ietf-httpapi-patch-byterange-02
| Document | Type | Active Internet-Draft (httpapi WG) | |
|---|---|---|---|
| Author | Austin Wright | ||
| Last updated | 2024-07-08 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
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| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
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| Send notices to | (None) |
draft-ietf-httpapi-patch-byterange-02
Building Blocks for HTTP APIs A. Wright
Internet-Draft 8 July 2024
Intended status: Standards Track
Expires: 9 January 2025
Byte Range PATCH
draft-ietf-httpapi-patch-byterange-02
Abstract
This document specifies a media type for PATCH payloads that
overwrites a specific byte range, facilitating random access writes
and segmented uploads of resources.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on 9 January 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
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. Modifying a content range with PATCH . . . . . . . . . . . . 3
2.1. The Content-Range field . . . . . . . . . . . . . . . . . 4
2.2. The Content-Length field . . . . . . . . . . . . . . . . 5
2.3. The Content-Offset field . . . . . . . . . . . . . . . . 5
2.4. The Content-Type field . . . . . . . . . . . . . . . . . 6
2.5. Other fields . . . . . . . . . . . . . . . . . . . . . . 6
2.6. Applying a patch . . . . . . . . . . . . . . . . . . . . 6
2.7. Range units . . . . . . . . . . . . . . . . . . . . . . . 6
3. Byterange Media Types . . . . . . . . . . . . . . . . . . . . 7
3.1. The multipart/byteranges media type . . . . . . . . . . . 7
3.2. The message/byterange media type . . . . . . . . . . . . 8
3.2.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. The application/byteranges media type . . . . . . . . . . 9
3.3.1. Syntax . . . . . . . . . . . . . . . . . . . . . . . 9
4. Preserving Incomplete Uploads with "Prefer: transaction" . . 11
5. Segmented document creation with PATCH . . . . . . . . . . . 11
5.1. Complete Length Example . . . . . . . . . . . . . . . . . 13
6. Registrations . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1. message/byterange . . . . . . . . . . . . . . . . . . . . 14
6.2. application/byteranges . . . . . . . . . . . . . . . . . 15
6.3. Content-Offset . . . . . . . . . . . . . . . . . . . . . 16
6.4. "transaction" preference . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7.1. Uninitialized ranges . . . . . . . . . . . . . . . . . . 16
7.2. Initializing large documents . . . . . . . . . . . . . . 16
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.1. Normative References . . . . . . . . . . . . . . . . . . 17
8.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. Discussion . . . . . . . . . . . . . . . . . . . . . 18
A.1. Sparse Documents . . . . . . . . . . . . . . . . . . . . 18
A.2. Recovering from interrupted PUT . . . . . . . . . . . . . 18
A.3. Splicing and Binary Diff . . . . . . . . . . . . . . . . 19
A.4. Ending Indeterminate Length Uploads . . . . . . . . . . . 19
A.5. Reading Content-Range and Content-Offset in the
headers . . . . . . . . . . . . . . . . . . . . . . . . . 19
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
Filesystem interfaces typically provide some way to write at a
specific position in a file. While HTTP supports reading byte range
offsets using the Range header (Section 14 of [RFC9110]), this
technique cannot generally be used in PUT, because the server may
ignore the Content-Range header while executing the write, causing
data corruption. However, by using a method and media type that the
server must understand, writes to byte ranges with Content-Range
semantics becomes possible even when server support is undetermined.
This media type is intended for use in a wide variety of applications
where overwriting specific parts of the file is desired. This
includes idempotently writing data to a stream, appending data to a
file, overwriting specific byte ranges, or writing to multiple
regions in a single operation (for example, appending audio to a
recording in progress while updating metadata at the beginning of the
file).
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 [RFC8941] and [RFC9112].
For brevity, example HTTP requests or responses may add newlines or
whitespace, or omit some headers necessary for message transfer.
The term "byte" is used in the [RFC9110] sense to mean "octet."
Ranges are zero-indexed and inclusive. For example, "bytes 0-0"
means the first byte of the document, and "bytes 1-2" is a range with
two bytes, starting one byte into the document. Ranges of zero bytes
are described by an address offset rather than a range. For example,
"at byte 5" would separate the byte ranges 0-4 and 5-9.
2. Modifying a content range with PATCH
Sending a Content-Range field in a PUT request (A "partial PUT",
[RFC9110], Section 14.5) requires server support to be processed
correctly. Without such support, the server's normal behavior would
be to ignore the header, replacing the entire resource with just the
part that changed, potentially causing corruption. To mitigate this,
Content-Range may be used in conjunction with the PATCH method
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[RFC5789] and a media type whose semantics are to write at the
specified byte offset. This document re-uses the "multipart/
byteranges" media type, and defines the "message/byterange" and
"application/byteranges" media types, to opportunistically carry this
field.
A byte range patch lists one or more _parts_. Each part specifies two
essential components:
1. Part fields: a list of HTTP fields that specify metadata,
including the range being written to, the length of the body, and
information about the target document that cannot be listed in
the PATCH headers, e.g. Content-Type (where it would describe
the patch itself, rather than the document being updated).
2. A part body: the actual data to write to the specified location.
Each part MUST indicate a single contiguous range to be written to.
Servers MUST reject byte range patches that don't contain a known
range with a 422 or 400 error. (This would mean the client may be
using a yet-undefined mechanism to specify the target range.)
The simplest form to represent a byte range patch is the "message/
byterange" media type, which is similar to an HTTP message:
Content-Range: bytes 2-5/12
cdef
This patch represents an instruction to write the four bytes "cdef"
at an offset of 2 bytes. A document listing the digits 0-9 on a
line, would look like this after applying the patch:
01cdef6789␍␊
Although this example is a text document with a line terminator, part
bodies are only interperted as binary data, and can potentially
overwrite individual bytes of multi-byte characters.
2.1. The Content-Range field
The Content-Range field (as seen inside a patch document) is used to
specify where in the target document the part body will be written.
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The client MAY indicate the anticipated final size of the document by
providing the complete-length form, for example the "12" in bytes
0-11/12. The complete-length does not affect the write by itself,
however the server MAY use it for other purposes, especially for
preallocating disk space, or deciding when an upload in multiple
parts has finished.
If the client does not know or care about the final length of the
document, it MAY use * in place of complete-length. For example,
bytes 0-11/*. Most random access writes will take this form.
The unsatisfied-range form (e.g. bytes */1000) sets the size of the
document, but without writing any data. It may be used to truncate a
document (to invert an append operation), to allocate space for a
document without specifying any of its contents, or to signal that an
upload has ended when the previous part or request did not specify a
complete-length. The part body MUST be empty.
If the "last-pos" is is unknown because the upload is indeterminate
length (the Content-Length of the request is not known from the
start, or the upload might continue indefinitely), then the Content-
Offset field must be used instead.
2.2. The Content-Length field
A "Content-Length" part field, if provided, describes the length of
the part body. (To describe the size of the entire target resource,
see the Content-Range field.)
If provided, it MUST exactly match the length of the range specified
in the Content-Range field, and servers MUST error when the Content-
Length mismatches the length of the range.
2.3. The Content-Offset field
The Content-Range field specifies an offset to write the content at,
when the end of the write is not known. It is used instead of
Content-Range when the Content-Length is not known.
Its syntax is specified as a Structured Field [RFC8941]:
Content-Offset = sf-item
The value indicates how much of the target document is to be skipped
over, typically the number of bytes. It MUST be an sf-integer.
It accepts two parameters:
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The "unit" parameter indicates the unit associated with the value. A
missing "unit" parameter is equivelant to providing unit=bytes.
The "complete-length" parameter is equivelant to the complete-length
value in Content-Range. When provided, it MUST be an sf-integer
specifying the intended final length of the document. A missing
"complete-length" is equivelant to providing * in Content-Range.
2.4. The Content-Type field
A "Content-Type" part field MUST have the same effect as if provided
in a PUT request uploading the entire resource (patch applied). Its
use is typically limited to resource creation.
2.5. Other fields
Other part fields in the patch document SHOULD have the same meaning
as if it is a message-level header in a PUT request uploading the
entire resource (patch applied).
Use of such fields SHOULD be limited to cases where the meaning in
the HTTP request headers would be different, where they would
describe the entire patch, rather than the part body. For example,
the "Content-Type" or "Content-Location" fields.
2.6. Applying a patch
Servers SHOULD NOT accept requests that write beyond, and not
adjacent to, the end of the resource. This would create a sparse
file, where some bytes are undefined. For example, writing at byte
601 of a resource where bytes 0-599 are defined; this would leave
byte 600 undefined. Servers that accept sparse writes MUST NOT
disclose uninitialized content, and SHOULD fill in undefined regions
with zeros.
The expected length of the write can be computed from the part
fields. If the actual length of the part body mismatches the
expected length, this MUST be treated the same as a network
interruption at the shorter length, but anticipating the longer
length. Recovering from this interruption may involve rolling back
the entire request, or saving as many bytes as possible. The client
can then recover as it would recover from a network interruption.
2.7. Range units
Currently, the only defined range unit is "bytes", however this may
be other, yet-to-be-defined values.
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In the case of "bytes", the bytes that are read are exactly the same
as the bytes that are changed. However, other units may define write
semantics different from a read, if symmetric behavior would not make
sense. For example, if a Content-Range field adds an item in a JSON
array, this write may add a leading or trailing comma, not
technically part of the item itself, in order to keep the resulting
document well-formed.
Even though the length in alternate units isn't changed, the byte
length might. This might only be acceptable to servers storing these
values in a database or memory structure, rather than on a byte-based
filesystem.
3. Byterange Media Types
3.1. The multipart/byteranges media type
The following illustrates a request with a "multipart/byteranges"
body to write two ranges in a document:
PATCH /uploads/foo HTTP/1.1
Content-Type: multipart/byteranges; boundary=THIS_STRING_SEPARATES
Content-Length: 206
If-Match: "xyzzy"
If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
--THIS_STRING_SEPARATES
Content-Range: bytes 2-6/25
Content-Type: text/plain
23456
--THIS_STRING_SEPARATES
Content-Range: bytes 17-21/25
Content-Type: text/plain
78901
--THIS_STRING_SEPARATES--
The syntax for multipart messages is defined in [RFC2046],
Section 5.1.1. While the body cannot contain the boundary, servers
MAY use the Content-Length field to skip to the boundary (potentially
ignoring a boundary in the body, which would be an error by the
client). Content-Range MUST NOT be used in place of Content-Length
for this purpose.
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The multipart/byteranges type may be used for operations where
multiple regions must be updated at the same time; clients expect all
the changes to be recorded as a single operation, or that if there's
an interruption, all of the parts will be rolled back together.
However, the exact behavior is at the discretion of the server.
3.2. The message/byterange media type
When making a request with a single byte range, there is no need for
a multipart boundary marker. This document defines a new media type
"message/byterange" with the same semantics as a single byte range in
a multipart/byteranges message, but with a simplified syntax that
only needs to be parsed to the first empty line.
The "message/byterange" form may be used in a PATCH request as so:
PATCH /uploads/foo HTTP/1.1
Content-Type: message/byterange
Content-Length: 272
If-Match: "xyzzy"
If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
Content-Range: bytes 100-299/600
Content-Type: text/plain
[200 bytes...]
This represents a request to modify a 600-byte document, starting at
a 100-byte offset, overwriting 200 bytes of it.
3.2.1. Syntax
The syntax re-uses concepts from the "multipart/byteranges" media
type, except it omits the multipart separator, and so only allows a
single range to be specified. It is also similar to the "message/
http" media type, except the first line (the status line or request
line) is omitted; a message/byterange document can be fed into a
message/http parser by first prepending a line like "PATCH /
HTTP/1.1".
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.
The field-line and message-body productions are specified in
[RFC9112].
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byterange-document = *( field-line CRLF )
CRLF
[ message-body ]
This document has the same semantics as a single part in a
"multipart/byteranges" document (Section 5.1.1 of [RFC2046]) or any
response with a 206 (Partial Content) status code (Section 15.3.7 of
[RFC9110]). A "message/byterange" document may be trivially
transformed into a "multipart/byteranges" document by prepending a
dash-boundary and CRLF, and appending a close-delimiter (a CRLF,
dash-boundary, terminating "--", and optional CRLF).
3.3. The application/byteranges media type
The "application/byteranges" has the same semantics as "multipart/
byteranges" but follows a binary format similar to "message/bhttp"
[RFC9292], which may be more suitable for some clients and servers,
as all variable length strings are tagged with their length.
3.3.1. Syntax
Parsing starts by looking for a "Known-Length Message" or an
"Indeterminate-Length Message". One or the other is distinguished by
the different Framing Indicator.
The remainder of the message is parsed by reading fields, then the
content, by a method depending on if the message is known-length or
indeterminate-length. If there are additional parts, they begin
immediately after the end of a Content.
The "Known-Length Field Section", "Known-Length Content",
"Indeterminate-Length Field Section", "Indeterminate-Length Content",
"Indeterminate-Length Content Chunk", "Field Line" definitions are
identical to their definition in message/bhttp. They are used in one
or more Known-Length Message and/or Indeterminate-Length Message
productions, concatenated together.
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Patch {
Message (..) ...
}
Known-Length Message {
Framing Indicator (i) = 8,
Known-Length Field Section (..),
Known-Length Content (..),
}
Indeterminate-Length Message {
Framing Indicator (i) = 10,
Indeterminate-Length Field Section (..),
Indeterminate-Length Content (..),
}
Known-Length Field Section {
Length (i),
Field Line (..) ...,
}
Known-Length Content {
Content Length (i),
Content (..),
}
Indeterminate-Length Field Section {
Field Line (..) ...,
Content Terminator (i) = 0,
}
Indeterminate-Length Content {
Indeterminate-Length Content Chunk (..) ...,
Content Terminator (i) = 0,
}
Indeterminate-Length Content Chunk {
Chunk Length (i) = 1..,
Chunk (..),
}
Field Line {
Name Length (i) = 1..,
Name (..),
Value Length (i),
Value (..),
}
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4. Preserving Incomplete Uploads with "Prefer: transaction"
The stateless design of HTTP generally implies that a request is
atomic (otherwise parties would need to keep track of the state of a
request while it's in progress). Clients need not need be concerned
with the side-effects of error halfway through an upload.
However, some clients may desire partial state changes, particularly
when remaking the upload is more expensive than recovering from an
interruption. In these cases, clients will prefer the incomplete
upload to be preserved as much as possible, so they may resume from
where the incomplete request was terminated.
The client's preference for atomic or upload-preserving behavior may
be signaled by a Prefer header:
Prefer: transaction=atomic
Prefer: transaction=persist
The transaction=atomic preference indicates that the request SHOULD
commit only when a successful response is returned, and not any time
before the end of the upload.
The transaction=persist preference indicates that uploaded data
SHOULD be continuously committed, so that if the upload is
interrupted, it is possible to resume the upload from where it left
off.
This preference is generally applicable to any HTTP request (and not
merely for PATCH or byte range patches). Servers SHOULD indicate
when this preference was honored, using a "Preference-Applied"
response header. For example:
Preference-Applied: transaction=persist
Servers might consider signaling this in a 103 (Early Hints) response
[RFC8297], since once the final response is written, this may no
longer be useful information.
5. Segmented document creation with PATCH
As an alternative to using PUT to create a new resource, the contents
of a resource may be uploaded in segments, written across several
PATCH requests.
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A user-agent may also use PATCH to recover from an interrupted PUT
request, if it was expected to create a new resource. The server
will store the data sent to it by the user agent, but will not
finalize the upload until the complete length of the document is
known and received.
1. The client makes a PUT or PATCH request to a URL, a portion of
which is randomized, to be unpredictable to other clients. This
first request creates the resource, and should include Prefer:
transaction=persist (to continuously commit the upload) and If-
None-Match: * (to verify the target does not exist). If a PUT
request, the server reads the Content-Length header and stores
the intended complete length of the document. If a PATCH
request, the "Content-Range" field in the "message/byterange"
patch is read for the complete length. The complete length may
also be undefined, and defined in a later request.
2. If any request is interrupted, the client may make a HEAD request
to determine how much, if any, of the previous response was
stored, and resumes uploading from that point. The server will
return 200 (OK), but this may only indicate the write has been
saved; the server is not obligated to begin acting on the upload
until it is complete.
3. If the client sees from the HEAD response that additional data
remains to be uploaded, it may make a PATCH request to resume
uploading. Even if no data was uploaded or the resource was not
created, the client should attempt creating the resource with
PATCH to mitigate the possibility of another interrupted
connection with a server that does not save incomplete transfers.
However if in response to PATCH, the server reports 405 (Method
Not Allowed), 415 (Unsupported Media Type), or 501 (Not
Implemented), then the client must resort to retrying the PUT
request.
4. The server detects the completion of the final request when the
current received data matches the indicated complete length. For
example, a Content-Range: 500-599/600 field is a write at the end
of the resource. The server processes the upload and returns a
response for it.
If the client does not know the complete length of its upload (for
example, an upload of live audio), it may use the indeterminate
length form "*" to append data to the document. The end of the
upload is then signaled with an "unsatisfied-range" form (e.g.
Content-Range: */1000), which instructs the server that the upload is
complete if it has received all 1000 bytes.
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For building POST endpoints that support large uploads, clients can
first upload the data to a scratch file as described above, and then
submit a link to the file in a POST request.
For updating an existing large file, the client can upload to a
scratch file, then execute a MOVE (Section 9.9 of [RFC4918]) over the
intended target.
5.1. Complete Length Example
A single PUT request that creates a new resource may 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 200, indicating that the
complete upload was stored.
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 200 (OK).
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...]
The server responds with 200 (OK). Since this completely writes out
the 600-byte document, the server may also perform final processing,
for example, checking that the document is well formed. The server
MAY return an error code if there is a syntax or other error, or in
an earlier response as soon as it it able to detect an error, however
the exact behavior is left undefined.
6. Registrations
6.1. message/byterange
Type name: message
Subtype name: byterange
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: binary
Security considerations: See Section 7
Interoperability considerations: See Section 3.2 of this document
Published specification: This document
Applications that use this media type: HTTP applications that
process filesystem-like writes to locations within a resource.
Fragment identifier considerations: N/A
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
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Person and email address to contact for further information: See Aut
hors' Addresses section.
Intended usage: COMMON
Restrictions on usage: None.
Author: See Authors' Addresses section.
Change controller: IESG
6.2. application/byteranges
Type name: application
Subtype name: byteranges
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: binary
Security considerations: See Section 7
Interoperability considerations: See Section 3.3 of this document
Published specification: This document
Applications that use this media type: HTTP applications that
process filesystem-like writes to locations within a resource.
Fragment identifier considerations: N/A
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
Person and email address to contact for further information: See Aut
hors' Addresses section.
Intended usage: COMMON
Restrictions on usage: None.
Author: See Authors' Addresses section.
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Change controller: IESG
6.3. Content-Offset
Field name: Content-Offset
Status: permanent
Specification document: This document.
6.4. "transaction" preference
Preference: transaction
Value: either "atomic" or "persist"
Description: Specify if the client would prefer incomplete uploads
to be saved, or committed only on success.
Reference: Section 4
7. Security Considerations
7.1. Uninitialized ranges
A byterange patch may permit writes to offsets beyond the end of the
resource. This may have non-obvious behavior.
Servers supporting sparse files MUST NOT return uninitialized memory
or storage contents. Uninitialized regions may be initialized prior
to executing the write, or this may be left to the filesystem if it
can guarantee that unallocated space will be read as a constant
value.
7.2. Initializing large documents
A byte range patch typically only requires server resources
proportional to the patch size. One exception is pre-initializing
space when growing a file. This occurs when a complete-length is
specified in the Content-Range field, which hints at the final upload
size, or when writing to an offset far after the end of the file, and
the server initializes the space in between. This initialization
could be a very expensive operation compared to the actual size of
the patch.
In general, servers SHOULD treat an initialization towards resource
limits, and issue a 400 (Client Error) as appropriate. Note that 413
(Payload Too Large) would be misleading in this situation, as it
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would indicate the patch itself is too large, and the client should
break up the patches into smaller chunks, rather than the intended
signal that the final upload size isd too large.
8. References
8.1. 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/rfc/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/rfc/rfc5234>.
[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>.
[RFC8941] 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>.
[RFC9110] 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>.
[RFC9112] 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>.
8.2. Informative References
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<https://www.rfc-editor.org/rfc/rfc2046>.
[RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed
Authoring and Versioning (WebDAV)", RFC 4918,
DOI 10.17487/RFC4918, June 2007,
<https://www.rfc-editor.org/rfc/rfc4918>.
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[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>.
[RFC8297] Oku, K., "An HTTP Status Code for Indicating Hints",
RFC 8297, DOI 10.17487/RFC8297, December 2017,
<https://www.rfc-editor.org/rfc/rfc8297>.
[RFC9292] Thomson, M. and C. A. Wood, "Binary Representation of HTTP
Messages", RFC 9292, DOI 10.17487/RFC9292, August 2022,
<https://www.rfc-editor.org/rfc/rfc9292>.
Appendix A. Discussion
// This section to be removed before final publication.
A.1. Sparse Documents
This pattern can enable multiple, parallel uploads to a document at
the same time. For example, uploading a large log file from multiple
devices. However, this document does not define any ways for clients
to track the unwritten regions in sparse documents, and the existing
conditional request headers are designed to cause conflicts.
Parallel uploads may require a byte-level locking scheme or conflict-
free operators. This may be addressed in a later document.
A.2. Recovering from interrupted PUT
Servers do not necessarily save the results of an incomplete upload;
since most clients prefer atomic writes, many servers will discard an
incomplete upload. A mechanism to indicate a preference for atomic
vs. non-atomic writes may be defined at a later time.
Byte range PATCH cannot by itself provide recovery from an
interrupted PUT to an existing document, as it is not generally
possible to distinguish what was received by the server from what
already existed.
One technique would be to use a 1xx interim response to indicate a
location where the partial upload is being stored. If PUT request is
interrupted, the client can make PATCH requests to this temporary,
non-atomic location to complete the upload. When the last part is
uploaded, the original interrupted PUT request will finish.
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Another technique would be to send a 1xx interim response to indicate
how much of the upload has been committed. When a client receives
this, it can skip that many bytes from the next attempt in a PATCH
request.
A.3. Splicing and Binary Diff
Operations more complicated than standard filesystem operations are
out of scope for this media type. A feature of byte range patch is
an upper limit on the complexity of applying the patch. In contrast,
prepending, splicing, replace, or other complicated file operations
could potentially require the entire file on disk be rewritten.
Consider registering a media type for VCDIFF in this document, under
the topic of "Media type registrations for byte-level patching".
A.4. Ending Indeterminate Length Uploads
When uploading a patch with indeterminate-length form, Since the
server doesn't know the complete-length, it might not be able to
assume that the end of the request is also the end of the whole
document, even if the request ended cleanly (the client may have
reasons to split apart the upload). This needs to be signaled by a
subsequent request with an unsatisfied-range specifying the final
length of the document.
A.5. Reading Content-Range and Content-Offset in the headers
Some parties may prefer that the message body need not be parsed at
all, but instead leverage existing HTTP mechanisms to carry the part
field data. Similar to how a 206 status code indicates that the
response body is partial, a reserved value of Content-Type (in a
PATCH request) could signal the server to read the Content-Range from
the request headers, and the whole request body is the part body.
Author's Address
Austin Wright
Email: aaa@bzfx.net
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