Internet Engineering Task Force T. Harding, Ed.
Internet-Draft Axway
Intended status: Informational October 10, 2012
Expires: April 13, 2013
AS2 Restart for Very Large Messages
draft-harding-as2-restart-04
Abstract
AS2 Restart provides a method for AS2 clients and servers to restart
payload transfers from the point of failure without requiring the
entire document to be resent.
Keywords
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
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
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This Internet-Draft will expire on April 13, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Transfer ID . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. HEAD Query . . . . . . . . . . . . . . . . . . . . . . . . 3
3.3. POST . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Important Considerations . . . . . . . . . . . . . . . . . . . 5
5. Example Messages . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Inital Send . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Restart . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
8. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
AS2 [RFC4130] has experienced widespread adoption and is continually
being asked to send or receive larger files by the business
community. As the size of the file transfers increase it has become
evident that a mechanism is required that will allow trading partners
to restart failed transfers from the point of failure. This document
will outline a method of implementing a failed transfer restart
mechamism using existing HTTP headers so backwards compatibilty will
exist with AS2 servers not wishing to support AS2 Restart.
2. Overview
Clients wishing to utilize the AS2 Restart mechanism for a particular
file transfer will include the HTTP ETAG header which contains an
unique transfer-id. The message will contain an HTTP Content-Range
header indicating the start and end byte range of the message. The
receiving HTTP server will utilize the ETAG and Content-Range headers
to perform a temporary cache of the received file. In the event of a
transfer failure a restart from the point of failure can occur. A
client can query a server using the HTTP HEAD request to determine
the number of bytes of data already received by the server. The HTTP
Head request will contain an ETAG header with a transfer-id of a
previous transfer so the server can respond with a Content-length
header value equalling the number of bytes already received from a
previous transfer.
3. Protocol
3.1. Transfer ID
The transfer id is a unique value that references a previous file
transfer. The uniqueness of the transfer id is guaranteed by the
sending client and will reference only one instantiation of a
particular file transfer. The transfer id will follow the
definitions of an entity tag as per [RFC2616] section 3.11 minus the
weak indicator.
3.2. HEAD Query
The HEAD query will be used by the sending client to query a server
as to the status of a previous file transfer. The server will
respond to the HEAD query with the number of bytes already received
for a particular transfer-id value. The returned Content-Length byte
count is the number of bytes of the received content which does not
include the http headers. If the returned Content-Length value from
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the HEAD query equals the total instance value the sending system
will send at least one byte of data in the next POST. The value of
the single byte that is transferred MUST equal the value of the last
byte of data of the transferred message. This will allow the client
to restablish a network connection to the server while it waits for
the appropriate response from the server. The HEAD query MUST
include the AS2-To and AS2-From headers from [RFC4130] to accommodate
firewalls and proxies looking for the presence of these headers.
HEAD Query
+-------------+ +-------------------+ +-------------+
| HTTP Client |--->| Etag: transfer id |--->| HTTP Server |
| | | AS2-To: receiverid| | |
| | | AS2-From: senderid| | |
|_____________| |___________________| |_____________|
| |
| |
| +---------------------------+ |
-----| Response: 200 OK |<---------
| Content-Length: file size |
|___________________________|
Figure 1
AS2 servers that do not understand the HEAD query or do not support
AS2 Restart may return a non 200 ok response or return a Content-
Length of zero. In either case the client will (re)send the complete
AS2 message to the server.
3.3. POST
A posted message will contain the ETAG header with an unique transfer
id and a Content-Range header indicating the range of bytes contained
within the message. The Content-Range header value will be the range
within the body of the message and does not include the http headers
of the message. A Content-Range header is not required if the
sending client is sending a file for the first time or wishes to
overwrite all existing data on the server. However, if chunked
transfer encoding is utilized a Content-Range header is recommended
as some receiving systems implement a minimum file caching size and
will not cache the inbound message if the message size cannot be
determined from the inbound http headers. If a server determines
that the supplied Content-Range header field value is not valid the
server MUST return an http response code of 416. The returned 416
http response will indicate the valid starting byte position for the
requested resource, See [RFC2616] section 14.16. Example: Content-
Range: bytes */233333 The instance-length specifies the current
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length of the selected resource.
POST
+-------------+ +----------------------+ +-------------+
| HTTP Client |--->| POST | | HTTP Server |
| | | Etag: transfer id |--->| |
| | | Content-Range: | | |
| | | bytes 0-1000/1001 | | |
|_____________| |______________________| |_____________|
+ |
| |
| +---------------------------+ |
-----| Response: 200 OK |<-----------
|___________________________|
Figure 2
4. Important Considerations
The HTTP restart server will be concerned with temp files bogging
down the system disk space and should develop a routine to garbage
collect any old (aged) files in the restart directory. If a client
queries the server about a existing file that was partially sent and
the file was deleted due to aging from the system, the server will
return a 200 ok response with a content-length of zero bytes.
Therefore the client will be required to resend the complete message.
The unique id mentioned earlier in this document must be unique so no
two systems create the same id.
It is strongly recommended that the Content-Range header be included
in all POSTed messages as some systems use the values present in the
header to determine inbound file size and whether this exceeds a
minimum file size restriction for caching files.
5. Example Messages
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5.1. Inital Send
HEAD Command
HEAD /exchange/axway1 HTTP/1.1\n
Etag: "ci1257348820455.829541_tharding_2k_te"
AS2-To: sender_id
AS2-From: receiver_id
AS2-Version: 1.2
Connection: close
Host: yourhost.com
The HEAD request is used to query the server to determine if a
partially transfered file exists on the server. The HEAD request
MUST contain the AS2-To and AS2-From header fields with the
identifiers associated with the cached file. The AS2-Version value
MUST be 1.2. The format of the included AS2 header fields are
defined in [RFC4130] Section 6.1. The HEAD request query is OPTIONAL
before the initial send of a document, however some systems may use
the HEAD request as a way to determine if the ETAG value is already
in use.
Response
HTTP/1.1 200 OK
Connection: close
Content-Length: 0
The returned Content-Length value indicates the number of bytes
associated with a specific transfer that resides on the server. A
returned Content-Length value of 0 indicates that the server does not
have a partially saved file or the server does not support AS2
restart. In either case the sending system will send all bytes
associated with a message. Non 2xx http return codes will indicate
that the receiving server does not support AS2 restart.
POST Command
POST /exchange/axway1 HTTP/1/1
<existing AS2 HTTP header fields>
Etag: "ci1257348820455.829541_tharding_2k_te"
Content-Length: 307502443
<Message body>
The initial POST of a message SHOULD include a method to determine
the overall size of the incoming message. This can be a Content-
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Length header field or a Content-Range header field or both. Systems
that support a min file size for restart will required at least one
of the these headers.
5.2. Restart
HEAD Command
HEAD /exchange/axway1 HTTP/1.1\n
Etag: "ci1257348820455.829541_tharding_2k_te"
AS2-To: sender_id
AS2-From: receiver_id
AS2-Version: 1.2
Connection: close
Host: yourhost.com
Response
HTTP/1.1 200 OK
Connection: close
Content-Length: 65982464
The returned Content-Length value indicates the number of bytes of
data already received from a previous send. This value does not
include the HTTP headers of the message but only the Content data.
POST Command
POST /exchange/axway1 HTTP/1/1
<existing AS2 HTTP header fields>
Etag: "ci1257348820455.829541_tharding_2k_te"
Content-Range: bytes 65982464-307502442/307502443
Content-Length: 241519979
<Message body>
A message that is resent will indicate the starting byte of the
content data by using the Content-Range header. The Content-Range
header value will indicate the first byte and the last byte of the
message.
6. IANA Considerations
This memo includes no request to IANA.
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7. Security Considerations
Refer to the Security Considerations section of AS2 [RFC4130].
8. Normative References
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC4130] Moberg, D. and R. Drummond, "MIME-Based Secure Peer-to-
Peer Business Data Interchange Using HTTP, Applicability
Statement 2 (AS2)", RFC 4130, July 2005.
Author's Address
Terry Harding (editor)
Axway
Phoenix, Arizona
US
Phone:
Email: tharding@us.axway.com
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