Information and documentation — WARC file format

ISO 28500:2009 specifies the WARC file format: to store both the payload content and control information from mainstream Internet application layer protocols, such as the Hypertext Transfer Protocol (HTTP), Domain Name System (DNS), and File Transfer Protocol (FTP); to store arbitrary metadata linked to other stored data (e.g. subject classifier, discovered language, encoding); to support data compression and maintain data record integrity; to store all control information from the harvesting protocol (e.g. request headers), not just response information; to store the results of data transformations linked to other stored data; to store a duplicate detection event linked to other stored data (to reduce storage in the presence of identical or substantially similar resources); to be extended without disruption to existing functionality; to support handling of overly long records by truncation or segmentation, where desired.

Information et documentation — Format de fichier WARC

Informatika in dokumentacija - Datotečna oblika zapisa WARC

General Information

Status
Withdrawn
Publication Date
12-May-2009
Withdrawal Date
12-May-2009
Current Stage
9599 - Withdrawal of International Standard
Completion Date
14-Aug-2017

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INTERNATIONAL ISO
STANDARD 28500
First edition
2009-05-15

Information and documentation — WARC
file format
Information et documentation — Format de fichier WARC




Reference number
ISO 28500:2009(E)
©
ISO 2009

---------------------- Page: 1 ----------------------
ISO 28500:2009(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.


COPYRIGHT PROTECTED DOCUMENT


©  ISO 2009
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland

ii © ISO 2009 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 28500:2009(E)
Contents Page
Foreword. v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 2
3.1 Terms and definitions. 2
3.2 Abbreviated terms . 2
4 File and record model. 3
5 Named fields. 5
5.1 General. 5
5.2 WARC-Record-ID (mandatory) . 6
5.3 Content-Length (mandatory) . 6
5.4 WARC-Date (mandatory). 6
5.5 WARC-Type (mandatory) . 6
5.6 Content-Type. 7
5.7 WARC-Concurrent-To. 7
5.8 WARC-Block-Digest. 8
5.9 WARC-Payload-Digest. 8
5.10 WARC-IP-Address. 8
5.11 WARC-Refers-To. 9
5.12 WARC-Target-URI . 9
5.13 WARC-Truncated . 9
5.14 WARC-Warcinfo-ID . 10
5.15 WARC-Filename . 10
5.16 WARC-Profile . 10
5.17 WARC-Identified-Payload-Type. 10
5.18 WARC-Segment-Number. 10
5.19 WARC-Segment-Origin-ID. 11
5.20 WARC-Segment-Total-Length . 11
6 WARC record types . 11
6.1 General. 11
6.2 'warcinfo'. 11
6.3 'response' . 12
6.4 'resource' . 13
6.5 'request' . 13
6.6 'metadata'. 14
6.7 'revisit'. 15
6.8 'conversion' . 16
6.9 'continuation'. 16
7 Record segmentation . 16
8 Registration of MIME media types application/warc and application/warc-fields . 17
8.1 General. 17
8.2 application/warc. 17
8.3 application/warc-fields . 18
9 WARC file name, size and compression . 18
Annex A (informative) Use cases for writing WARC records . 19
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ISO 28500:2009(E)
Annex B (informative) Examples of WARC records. 22
Annex C (informative) WARC file size and name recommendations . 26
Annex D (informative) Compression recommendations . 27
Bibliography . 28

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ISO 28500:2009(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 28500 was prepared by Technical Committee ISO/TC 46, Information and documentation, Subcommittee
SC 4, Technical interoperability.
© ISO 2009 – All rights reserved v

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ISO 28500:2009(E)
Introduction
Websites and web pages emerge and disappear from the World Wide Web every day. For the past ten years,
memory storage organizations have tried to find the most appropriate ways to collect and keep track of this
vast quantity of important material using web-scale tools such as web crawlers. A web crawler is a program
that browses the web in an automated manner according to a set of policies; starting with a list of URLs, it
saves each page identified by a URL, finds all the hyperlinks in the page (e.g. links to other pages, images,
videos, scripting or style instructions, etc.), and adds them to the list of URLs to visit recursively. Storing and
managing the billions of saved web page objects itself presents a challenge.
At the same time, those same organizations have a rising need to archive large numbers of digital files not
necessarily captured from the web (e.g. entire series of electronic journals, or data generated by
environmental sensing equipment). A general requirement that appears to be emerging is for a container
format that permits one file simply and safely to carry a very large number of constituent data objects for the
purpose of storage, management, and exchange. Those data objects (or resources) need to be of unrestricted
type (including many binary types for audio, CAD, compressed files, etc.), but fortunately the container needs
only minimal knowledge of the nature of the objects.
The WARC (Web ARChive) file format offers a convention for concatenating multiple resource records (data
objects), each consisting of a set of simple text headers and an arbitrary data block into one long file. The
WARC format is an extension of the ARC file format (ARC) that has traditionally been used to store "web
crawls" as sequences of content blocks harvested from the World Wide Web. Each capture in an ARC file is
preceded by a one-line header that very briefly describes the harvested content and its length. This is directly
followed by the retrieval protocol response messages and content. The original ARC format file has been used
by the Internet Archive (IA) since 1996 for managing billions of objects, and by several national libraries.
The motivation to extend the ARC format arose from the discussion and experiences of the International
Internet Preservation Consortium (IIPC), whose members include the national libraries of Australia, Canada,
Denmark, Finland, France, Iceland, Italy, Norway, Sweden, The British Library (UK), The Library of Congress
(USA), and the Internet Archive (IA). The California Digital Library and the Los Alamos National Laboratory
also provided input on extending and generalizing the format.
The WARC format is expected to be a standard way to structure, manage and store billions of resources
collected from the web and elsewhere. It will be used to build applications for harvesting (such as the open
source Heritrix web crawler), managing, accessing, and exchanging content. The way WARC files will be
created and resources stored and rendered will depend on software and applications implementations.
Besides the primary content recorded in ARCs, the extended WARC format accommodates related secondary
content, such as assigned metadata, abbreviated duplicate detection events, later-date transformations, and
segmentation of large resources. The extension may also be useful for more general applications than web
archiving. To aid the development of tools that are backwards compatible, WARC content is clearly
distinguishable from pre-revision ARC content.
The WARC file format is made sufficiently different from the legacy ARC format files so that software tools can
unambiguously detect and correctly process both WARC and ARC records; given the large amount of existing
archival data in the previous ARC format, it is important that access and use of this legacy not be interrupted
when transitioning to the WARC format.
After the Internet Engineering Steering Group (IESG: http://www.ietf.org/iesg.html) approval, IANA (Internet
Assigned Numbers Authority: http://www.iana.org/) is expected to register the WARC type "application/warc"
using the application provided in this International Standard and following procedures defined in [RFC2048].

vi © ISO 2009 – All rights reserved

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INTERNATIONAL STANDARD ISO 28500:2009(E)

Information and documentation — WARC file format
1 Scope
This International Standard specifies the WARC file format:
⎯ to store both the payload content and control information from mainstream Internet application layer
protocols, such as the HTTP, DNS, and FTP;
⎯ to store arbitrary metadata linked to other stored data (e.g. subject classifier, discovered language,
encoding);
⎯ to support data compression and maintain data record integrity;
⎯ to store all control information from the harvesting protocol (e.g. request headers), not just response
information;
⎯ to store the results of data transformations linked to other stored data;
⎯ to store a duplicate detection event linked to other stored data (to reduce storage in the presence of
identical or substantially similar resources);
⎯ to be extended without disruption to existing functionality;
⎯ to support handling of overly long records by truncation or segmentation, where desired.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 8601, Data elements and interchange formats — Information interchange — Representation of dates and
times
[RFC1035] Mockapetris, P. Domain names — Implementation and specification. STD 13, November 1987.
Available at: http://www.faqs.org/rfcs/rfc1035.html
[RFC1884] Hinden, R. and Deering, S. IP Version 6 Addressing Architecture. December 1995. Available at:
http://www.faqs.org/rfcs/rfc1884.html
[RFC2045] Freed, N. and Borenstein, N. Multipurpose Internet Mail Extensions (MIME) Part One: Format of
Internet Message Bodies. November 1996. Available at: http://www.faqs.org/rfcs/rfc2045
[RFC2540] Eastlake, D. Detached Domain Name System (DNS) Information. March 1999. Available at:
http://www.faqs.org/rfcs/rfc2540.html
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P. and Berners-Lee, T.
Hypertext Transfer Protocol — HTTP/1.1. June 1999 (TXT, PS, PDF, HTML, XML). Available at:
http://www.faqs.org/rfcs/rfc2616.html
© ISO 2009 – All rights reserved 1

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ISO 28500:2009(E)
[RFC2822] Resnick, P. (ed.) Internet Message Format. April 2001. Available at:
http://www.faqs.org/rfcs/rfc2822
[RFC3629] Yergeau, F. UTF-8, a transformation format of ISO 10646. STD 63, November 2003. Available at:
http://www.faqs.org/rfcs/rfc3629.html
[RFC3986] Berners-Lee, T., Fielding, R., Masinter, L. Uniform Resource Identifier (URI): Generic Syntax. STD
66, January 2005 (TXT, HTML, XML). Available at: http://www.faqs.org/rfcs/rfc3986.html
[RFC4027] Josefsson, S. Domain Name System Media Types. April 2005. Available at:
http://www.faqs.org/rfcs/rfc4027.html
[W3CDTF] Date and Time Formats: note submitted to the W3C. 15 September 1997 (W3C profile of
ISO 8601). Available at: http://www.w3.org/TR/NOTE-datetime
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
WARC record
basic constituent of a WARC file, consisting of a sequence of WARC records
3.1.2
WARC record content block
part (zero or more octets) of a WARC record that follows the header and that forms the main body of a WARC
record
3.1.3
WARC record payload
data object referred to, or contained by a WARC record as a meaningful subset of the content block
3.1.4
WARC record header
beginning of a WARC record, consisting of one first line declaring the record to be in the WARC format with a
given version number, followed by lines of named fields up to a blank line
3.1.5
WARC named fields
set of elements consisting of a name, a colon, and a value, with long values continued on indented lines
3.1.6
WARC logical record
in the context of segmentation, a logical record may be composed of multiple segments, each represented by
a WARC record
3.2 Abbreviated terms
ABNF augmented Backus-Naur form
ARC archive
CRLF carriage return line feed
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ISO 28500:2009(E)
DNS domain name system
FTP file transfer protocol
HTTP hypertext transport protocol
IANA Internet Assigned Numbers Authority
IESG Internet Engineering Steering Group
RFC request for comments
UR (I/L/N) uniform resource (identifier/locator/name)
WARC web archive
4 File and record model
A WARC format file is the simple concatenation of one or more WARC records. The first record usually
describes the records to follow. In general, record content is either the direct result of a retrieval attempt (web
pages, inline images, URL redirection information, DNS hostname lookup results, stand-alone files, etc.) or is
synthesized material (e.g. metadata, transformed content) that provides additional information about archived
content.
A WARC record shall consist of a record header followed by a record content block and two new lines. The
WARC record header shall consist of one first line declaring the record to be in the WARC format with a given
version number, then a variable number of line-oriented named fields terminated by a blank line. The WARC
record header format shall follow the general rules of HTTP/1.1 [RFC2616] and [RFC2822] headers with one
major exception: it shall also allow UTF-8 characters, as specified in [RFC3629].
The top-level view of a WARC file can be expressed in an ABNF grammar, reusing the augmented constructs
defined in section 2.1 of HTTP/1.1 [RFC2616]. (In particular, note that to avoid the risk of confusion, where
any WARC rule has the same name as an [RFC2616] rule, the definition here has been made the same,
except in the case of the CHAR rule, which in WARC includes multibyte UTF-8 characters.)
warc-file  = 1*warc-record
warc-record = header CRLF
        block CRLF CRLF
header    = version warc-fields
version   = "WARC/1.0" CRLF
warc-fields = *named-field CRLF
block    = *OCTET
The record version shall appear first in every record and hence shall also begin the WARC file itself.
The WARC record relies heavily on named fields. Each named field consists of a name followed by a colon
(":") and the field value. Field names are not case-sensitive. The field value may be preceded by any amount
of linear white space (LWS), though a single space is preferred. Header fields can be extended over multiple
lines by preceding each extra line with at least one space or tab character.
Named fields may appear in any order and field values may contain any UTF-8 character. Both defined-fields
and extension-fields follow the generic named-field format. Extension-fields may be used in extensions of the
core format.
© ISO 2009 – All rights reserved 3

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ISO 28500:2009(E)
named-field   = field-name ":" [ field-value ]
field-name   = token
field-value   = *( field-content | LWS )   ; further qualified
                        ; by field
                        ; definitions
field-content  =          and consisting of either *TEXT or combinations
         of token, separators, and quoted-string>
OCTET      =
token      = 1*
         except CTLs or separators>
separators   = "(" | ")" | "<" | ">" | "@"
           | "," | ";" | ":" | "\" | <">
           | "/" | "[" | "]" | "?" | "="
           | "{" | "}" | SP | HT
TEXT      =          but including LWS>
CHAR      =  ; (0-191, 194-244)
DIGIT      =
CTL       =          (octets 0 - 31) and DEL (127)>
CR       =  ; (13)
LF       =      ; (10)
SP       =       ; (32)
HT       =   ; (9)
CRLF      = CR LF
LWS       = [CRLF] 1*( SP | HT )     ; semantics same as
                        ; single SP
quoted-string  = ( <"> *(qdtext | quoted-pair ) <"> )
qdtext     = >
quoted-pair   = "\" CHAR           ; single-character quoting
uri       = "<" <'URI' per RFC3986> ">"

Although UTF-8 characters are allowed, the 'encoded-word' mechanism of [RFC2047] may also be used when
writing WARC fields and shall also be understood by WARC reading software.
The rest of the WARC record grammar concerns defined-field parameters such as record identifier, record
type, creation time, content length, and content type.
defined-field = WARC-Type
        | WARC-Record-ID
        | WARC-Date
        | Content-Length
        | Content-Type
        | WARC-Concurrent-To
        | WARC-Block-Digest
        | WARC-Payload-Digest
        | WARC-IP-Address
        | WARC-Refers-To
        | WARC-Target-URI
        | WARC-Truncated
        | WARC-Warcinfo-ID
        | WARC-Filename        ; warcinfo only
        | WARC-Profile         ; revisit only
        | WARC-Identified-Payload-Type
        | WARC-Segment-Origin-ID    ; continuation only
        | WARC-Segment-Number
        | WARC-Segment-Total-Length  ; continuation only

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ISO 28500:2009(E)
Every WARC record shall have a type, reported in the WARC-Type field. Eight WARC record types are
defined in this International Standard as follows:
⎯ 'warcinfo',
⎯ 'response',
⎯ 'resource',
⎯ 'request',
⎯ 'metadata',
⎯ 'revisit',
⎯ 'conversion',
⎯ 'continuation'.
Other types of WARC records may be defined in extensions of the core format. The relevant fields for each
record type are described in detail in Clause 6. Each field's meaning and legal value format are described in
Clause 5.
The record block shall contain octet content, interpreted based on the record type and other header values. All
records shall include a Content-Length field to specify the length of the block.
Some record types (and possibly future record types) also define a payload, such as a meaningful subset of
the block or content from a predecessor record. Some headers pertain to the payload of a record rather than
the block directly.
For example, in a 'response' record with a content block consisting of HTTP headers and a data object, the
payload would be the data object. All 'response', 'resource', 'request', 'conversion' and 'continuation' records
may have a payload. All 'warcinfo', 'metadata' and 'revisit' records shall not have a payload.
Content matching the warc-file rule shall have the MIME content-type "application/warc", as specified in 8.2.
Content matching only the warc-fields rule is useful as a simple descriptive format, and has MIME content-
type "application/warc-fields", as specified in 8.3.
5 Named fields
5.1 General
Named fields within a WARC record provide information about the current record. WARC both reuses
appropriate headers from other standards and defines new headers, all beginning "WARC-", for WARC-
specific purposes.
WARC named fields of the same type shall not be repeated in the same WARC record (for example, a WARC
record shall not have several WARC-Date or several WARC-Target-URI), except as noted (e.g.
WARC-Concurrent-To).
Because new fields may be defined in extensions to the core WARC format, WARC processing software shall
ignore fields with unrecognized names.
© ISO 2009 – All rights reserved 5

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ISO 28500:2009(E)
5.2 WARC-Record-ID (mandatory)
A WARC-Record-ID is an identifier assigned to the current record that is globally unique for its period of
intended use. No identifier scheme is mandated by this specification, but each WARC-Record-ID shall be a
legal URI and clearly indicate a documented and registered scheme to which it conforms (e.g. via a URI
scheme prefix such as "http:" or "urn:"). Care should be taken to ensure that this value is written with no
internal white space.
WARC-Record-ID  = "WARC-Record-ID" ":" uri

All records shall have a WARC-Record-ID field.
5.3 Content-Length (mandatory)
The Content-Length is the number of octets in the block, similar to [RFC2616]. If no block is present, a value
of "0" (zero) shall be used.
Content-Length  = "Content-Length" ":" 1*DIGIT

All records shall have a Content-Length field.
5.4 WARC-Date (mandatory)
The WARC-Date is a 14-digit UTC time-stamp formatted as YYYY-MM-DDThh:mm:ssZ, and shall conform to
the W3C profile of ISO 8601, i.e. [W3CDTF]. The time-stamp shall represent the instant that data capture for
record creation began. Multiple records written as part of a single capture event (see 5.7) shall use the same
WARC-Date, even though the times of their writing will not be exactly synchronized.
WARC-Date  = "WARC-Date" ":" w3c-iso8601
w3c-iso8601 =

All records shall have a WARC-Date field.
See Annex A for examples on usage of WARC-Date fields.
5.5 WARC-Type (mandatory)
WARC-Type is the type of WARC record. Record types defined in this International Standard are:
⎯ 'warcinfo',
⎯ 'response',
⎯ 'resource',
⎯ 'request',
⎯ 'metadata',
⎯ 'revisit',
⎯ 'conversion', and
⎯ 'continuation'.
6 © ISO 2009 – All rights reserved

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ISO 28500:2009(E)
Other types of WARC records may be defined in extensions of the core format. Types are further described in
Clause 6.
A WARC file need not contain any particular record types, though starting all WARC files with a 'warcinfo'
record is recommended.
WARC-Type  = "WARC-Type" ":" record-type
record-type = "warcinfo" | "response" | "resource"
      | "request"
...

SLOVENSKI STANDARD
SIST ISO 28500:2009
01-december-2009
,QIRUPDWLNDLQGRNXPHQWDFLMD'DWRWHþQDREOLND]DSLVD:$5&
Information and documentation - WARC file format
Information et documentation - Format de fichier WARC
Ta slovenski standard je istoveten z: ISO 28500:2009
ICS:
35.240.30 Uporabniške rešitve IT v IT applications in information,
informatiki, dokumentiranju in documentation and
založništvu publishing
SIST ISO 28500:2009 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ISO 28500:2009

---------------------- Page: 2 ----------------------

SIST ISO 28500:2009

INTERNATIONAL ISO
STANDARD 28500
First edition
2009-05-15

Information and documentation — WARC
file format
Information et documentation — Format de fichier WARC




Reference number
ISO 28500:2009(E)
©
ISO 2009

---------------------- Page: 3 ----------------------

SIST ISO 28500:2009
ISO 28500:2009(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.


COPYRIGHT PROTECTED DOCUMENT


©  ISO 2009
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland

ii © ISO 2009 – All rights reserved

---------------------- Page: 4 ----------------------

SIST ISO 28500:2009
ISO 28500:2009(E)
Contents Page
Foreword. v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 2
3.1 Terms and definitions. 2
3.2 Abbreviated terms . 2
4 File and record model. 3
5 Named fields. 5
5.1 General. 5
5.2 WARC-Record-ID (mandatory) . 6
5.3 Content-Length (mandatory) . 6
5.4 WARC-Date (mandatory). 6
5.5 WARC-Type (mandatory) . 6
5.6 Content-Type. 7
5.7 WARC-Concurrent-To. 7
5.8 WARC-Block-Digest. 8
5.9 WARC-Payload-Digest. 8
5.10 WARC-IP-Address. 8
5.11 WARC-Refers-To. 9
5.12 WARC-Target-URI . 9
5.13 WARC-Truncated . 9
5.14 WARC-Warcinfo-ID . 10
5.15 WARC-Filename . 10
5.16 WARC-Profile . 10
5.17 WARC-Identified-Payload-Type. 10
5.18 WARC-Segment-Number. 10
5.19 WARC-Segment-Origin-ID. 11
5.20 WARC-Segment-Total-Length . 11
6 WARC record types . 11
6.1 General. 11
6.2 'warcinfo'. 11
6.3 'response' . 12
6.4 'resource' . 13
6.5 'request' . 13
6.6 'metadata'. 14
6.7 'revisit'. 15
6.8 'conversion' . 16
6.9 'continuation'. 16
7 Record segmentation . 16
8 Registration of MIME media types application/warc and application/warc-fields . 17
8.1 General. 17
8.2 application/warc. 17
8.3 application/warc-fields . 18
9 WARC file name, size and compression . 18
Annex A (informative) Use cases for writing WARC records . 19
© ISO 2009 – All rights reserved iii

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SIST ISO 28500:2009
ISO 28500:2009(E)
Annex B (informative) Examples of WARC records. 22
Annex C (informative) WARC file size and name recommendations . 26
Annex D (informative) Compression recommendations . 27
Bibliography . 28

iv © ISO 2009 – All rights reserved

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SIST ISO 28500:2009
ISO 28500:2009(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 28500 was prepared by Technical Committee ISO/TC 46, Information and documentation, Subcommittee
SC 4, Technical interoperability.
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Introduction
Websites and web pages emerge and disappear from the World Wide Web every day. For the past ten years,
memory storage organizations have tried to find the most appropriate ways to collect and keep track of this
vast quantity of important material using web-scale tools such as web crawlers. A web crawler is a program
that browses the web in an automated manner according to a set of policies; starting with a list of URLs, it
saves each page identified by a URL, finds all the hyperlinks in the page (e.g. links to other pages, images,
videos, scripting or style instructions, etc.), and adds them to the list of URLs to visit recursively. Storing and
managing the billions of saved web page objects itself presents a challenge.
At the same time, those same organizations have a rising need to archive large numbers of digital files not
necessarily captured from the web (e.g. entire series of electronic journals, or data generated by
environmental sensing equipment). A general requirement that appears to be emerging is for a container
format that permits one file simply and safely to carry a very large number of constituent data objects for the
purpose of storage, management, and exchange. Those data objects (or resources) need to be of unrestricted
type (including many binary types for audio, CAD, compressed files, etc.), but fortunately the container needs
only minimal knowledge of the nature of the objects.
The WARC (Web ARChive) file format offers a convention for concatenating multiple resource records (data
objects), each consisting of a set of simple text headers and an arbitrary data block into one long file. The
WARC format is an extension of the ARC file format (ARC) that has traditionally been used to store "web
crawls" as sequences of content blocks harvested from the World Wide Web. Each capture in an ARC file is
preceded by a one-line header that very briefly describes the harvested content and its length. This is directly
followed by the retrieval protocol response messages and content. The original ARC format file has been used
by the Internet Archive (IA) since 1996 for managing billions of objects, and by several national libraries.
The motivation to extend the ARC format arose from the discussion and experiences of the International
Internet Preservation Consortium (IIPC), whose members include the national libraries of Australia, Canada,
Denmark, Finland, France, Iceland, Italy, Norway, Sweden, The British Library (UK), The Library of Congress
(USA), and the Internet Archive (IA). The California Digital Library and the Los Alamos National Laboratory
also provided input on extending and generalizing the format.
The WARC format is expected to be a standard way to structure, manage and store billions of resources
collected from the web and elsewhere. It will be used to build applications for harvesting (such as the open
source Heritrix web crawler), managing, accessing, and exchanging content. The way WARC files will be
created and resources stored and rendered will depend on software and applications implementations.
Besides the primary content recorded in ARCs, the extended WARC format accommodates related secondary
content, such as assigned metadata, abbreviated duplicate detection events, later-date transformations, and
segmentation of large resources. The extension may also be useful for more general applications than web
archiving. To aid the development of tools that are backwards compatible, WARC content is clearly
distinguishable from pre-revision ARC content.
The WARC file format is made sufficiently different from the legacy ARC format files so that software tools can
unambiguously detect and correctly process both WARC and ARC records; given the large amount of existing
archival data in the previous ARC format, it is important that access and use of this legacy not be interrupted
when transitioning to the WARC format.
After the Internet Engineering Steering Group (IESG: http://www.ietf.org/iesg.html) approval, IANA (Internet
Assigned Numbers Authority: http://www.iana.org/) is expected to register the WARC type "application/warc"
using the application provided in this International Standard and following procedures defined in [RFC2048].

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Information and documentation — WARC file format
1 Scope
This International Standard specifies the WARC file format:
⎯ to store both the payload content and control information from mainstream Internet application layer
protocols, such as the HTTP, DNS, and FTP;
⎯ to store arbitrary metadata linked to other stored data (e.g. subject classifier, discovered language,
encoding);
⎯ to support data compression and maintain data record integrity;
⎯ to store all control information from the harvesting protocol (e.g. request headers), not just response
information;
⎯ to store the results of data transformations linked to other stored data;
⎯ to store a duplicate detection event linked to other stored data (to reduce storage in the presence of
identical or substantially similar resources);
⎯ to be extended without disruption to existing functionality;
⎯ to support handling of overly long records by truncation or segmentation, where desired.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 8601, Data elements and interchange formats — Information interchange — Representation of dates and
times
[RFC1035] Mockapetris, P. Domain names — Implementation and specification. STD 13, November 1987.
Available at: http://www.faqs.org/rfcs/rfc1035.html
[RFC1884] Hinden, R. and Deering, S. IP Version 6 Addressing Architecture. December 1995. Available at:
http://www.faqs.org/rfcs/rfc1884.html
[RFC2045] Freed, N. and Borenstein, N. Multipurpose Internet Mail Extensions (MIME) Part One: Format of
Internet Message Bodies. November 1996. Available at: http://www.faqs.org/rfcs/rfc2045
[RFC2540] Eastlake, D. Detached Domain Name System (DNS) Information. March 1999. Available at:
http://www.faqs.org/rfcs/rfc2540.html
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P. and Berners-Lee, T.
Hypertext Transfer Protocol — HTTP/1.1. June 1999 (TXT, PS, PDF, HTML, XML). Available at:
http://www.faqs.org/rfcs/rfc2616.html
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[RFC2822] Resnick, P. (ed.) Internet Message Format. April 2001. Available at:
http://www.faqs.org/rfcs/rfc2822
[RFC3629] Yergeau, F. UTF-8, a transformation format of ISO 10646. STD 63, November 2003. Available at:
http://www.faqs.org/rfcs/rfc3629.html
[RFC3986] Berners-Lee, T., Fielding, R., Masinter, L. Uniform Resource Identifier (URI): Generic Syntax. STD
66, January 2005 (TXT, HTML, XML). Available at: http://www.faqs.org/rfcs/rfc3986.html
[RFC4027] Josefsson, S. Domain Name System Media Types. April 2005. Available at:
http://www.faqs.org/rfcs/rfc4027.html
[W3CDTF] Date and Time Formats: note submitted to the W3C. 15 September 1997 (W3C profile of
ISO 8601). Available at: http://www.w3.org/TR/NOTE-datetime
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
WARC record
basic constituent of a WARC file, consisting of a sequence of WARC records
3.1.2
WARC record content block
part (zero or more octets) of a WARC record that follows the header and that forms the main body of a WARC
record
3.1.3
WARC record payload
data object referred to, or contained by a WARC record as a meaningful subset of the content block
3.1.4
WARC record header
beginning of a WARC record, consisting of one first line declaring the record to be in the WARC format with a
given version number, followed by lines of named fields up to a blank line
3.1.5
WARC named fields
set of elements consisting of a name, a colon, and a value, with long values continued on indented lines
3.1.6
WARC logical record
in the context of segmentation, a logical record may be composed of multiple segments, each represented by
a WARC record
3.2 Abbreviated terms
ABNF augmented Backus-Naur form
ARC archive
CRLF carriage return line feed
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DNS domain name system
FTP file transfer protocol
HTTP hypertext transport protocol
IANA Internet Assigned Numbers Authority
IESG Internet Engineering Steering Group
RFC request for comments
UR (I/L/N) uniform resource (identifier/locator/name)
WARC web archive
4 File and record model
A WARC format file is the simple concatenation of one or more WARC records. The first record usually
describes the records to follow. In general, record content is either the direct result of a retrieval attempt (web
pages, inline images, URL redirection information, DNS hostname lookup results, stand-alone files, etc.) or is
synthesized material (e.g. metadata, transformed content) that provides additional information about archived
content.
A WARC record shall consist of a record header followed by a record content block and two new lines. The
WARC record header shall consist of one first line declaring the record to be in the WARC format with a given
version number, then a variable number of line-oriented named fields terminated by a blank line. The WARC
record header format shall follow the general rules of HTTP/1.1 [RFC2616] and [RFC2822] headers with one
major exception: it shall also allow UTF-8 characters, as specified in [RFC3629].
The top-level view of a WARC file can be expressed in an ABNF grammar, reusing the augmented constructs
defined in section 2.1 of HTTP/1.1 [RFC2616]. (In particular, note that to avoid the risk of confusion, where
any WARC rule has the same name as an [RFC2616] rule, the definition here has been made the same,
except in the case of the CHAR rule, which in WARC includes multibyte UTF-8 characters.)
warc-file  = 1*warc-record
warc-record = header CRLF
        block CRLF CRLF
header    = version warc-fields
version   = "WARC/1.0" CRLF
warc-fields = *named-field CRLF
block    = *OCTET
The record version shall appear first in every record and hence shall also begin the WARC file itself.
The WARC record relies heavily on named fields. Each named field consists of a name followed by a colon
(":") and the field value. Field names are not case-sensitive. The field value may be preceded by any amount
of linear white space (LWS), though a single space is preferred. Header fields can be extended over multiple
lines by preceding each extra line with at least one space or tab character.
Named fields may appear in any order and field values may contain any UTF-8 character. Both defined-fields
and extension-fields follow the generic named-field format. Extension-fields may be used in extensions of the
core format.
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named-field   = field-name ":" [ field-value ]
field-name   = token
field-value   = *( field-content | LWS )   ; further qualified
                        ; by field
                        ; definitions
field-content  =          and consisting of either *TEXT or combinations
         of token, separators, and quoted-string>
OCTET      =
token      = 1*
         except CTLs or separators>
separators   = "(" | ")" | "<" | ">" | "@"
           | "," | ";" | ":" | "\" | <">
           | "/" | "[" | "]" | "?" | "="
           | "{" | "}" | SP | HT
TEXT      =          but including LWS>
CHAR      =  ; (0-191, 194-244)
DIGIT      =
CTL       =          (octets 0 - 31) and DEL (127)>
CR       =  ; (13)
LF       =      ; (10)
SP       =       ; (32)
HT       =   ; (9)
CRLF      = CR LF
LWS       = [CRLF] 1*( SP | HT )     ; semantics same as
                        ; single SP
quoted-string  = ( <"> *(qdtext | quoted-pair ) <"> )
qdtext     = >
quoted-pair   = "\" CHAR           ; single-character quoting
uri       = "<" <'URI' per RFC3986> ">"

Although UTF-8 characters are allowed, the 'encoded-word' mechanism of [RFC2047] may also be used when
writing WARC fields and shall also be understood by WARC reading software.
The rest of the WARC record grammar concerns defined-field parameters such as record identifier, record
type, creation time, content length, and content type.
defined-field = WARC-Type
        | WARC-Record-ID
        | WARC-Date
        | Content-Length
        | Content-Type
        | WARC-Concurrent-To
        | WARC-Block-Digest
        | WARC-Payload-Digest
        | WARC-IP-Address
        | WARC-Refers-To
        | WARC-Target-URI
        | WARC-Truncated
        | WARC-Warcinfo-ID
        | WARC-Filename        ; warcinfo only
        | WARC-Profile         ; revisit only
        | WARC-Identified-Payload-Type
        | WARC-Segment-Origin-ID    ; continuation only
        | WARC-Segment-Number
        | WARC-Segment-Total-Length  ; continuation only

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Every WARC record shall have a type, reported in the WARC-Type field. Eight WARC record types are
defined in this International Standard as follows:
⎯ 'warcinfo',
⎯ 'response',
⎯ 'resource',
⎯ 'request',
⎯ 'metadata',
⎯ 'revisit',
⎯ 'conversion',
⎯ 'continuation'.
Other types of WARC records may be defined in extensions of the core format. The relevant fields for each
record type are described in detail in Clause 6. Each field's meaning and legal value format are described in
Clause 5.
The record block shall contain octet content, interpreted based on the record type and other header values. All
records shall include a Content-Length field to specify the length of the block.
Some record types (and possibly future record types) also define a payload, such as a meaningful subset of
the block or content from a predecessor record. Some headers pertain to the payload of a record rather than
the block directly.
For example, in a 'response' record with a content block consisting of HTTP headers and a data object, the
payload would be the data object. All 'response', 'resource', 'request', 'conversion' and 'continuation' records
may have a payload. All 'warcinfo', 'metadata' and 'revisit' records shall not have a payload.
Content matching the warc-file rule shall have the MIME content-type "application/warc", as specified in 8.2.
Content matching only the warc-fields rule is useful as a simple descriptive format, and has MIME content-
type "application/warc-fields", as specified in 8.3.
5 Named fields
5.1 General
Named fields within a WARC record provide information about the current record. WARC both reuses
appropriate headers from other standards and defines new headers, all beginning "WARC-", for WARC-
specific purposes.
WARC named fields of the same type shall not be repeated in the same WARC record (for example, a WARC
record shall not have several WARC-Date or several WARC-Target-URI), except as noted (e.g.
WARC-Concurrent-To).
Because new fields may be defined in extensions to the core WARC format, WARC processing software shall
ignore fields with unrecognized names.
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5.2 WARC-Record-ID (mandatory)
A WARC-Record-ID is an identifier assigned to the current record that is globally unique for its period of
intended use. No identifier scheme is mandated by this specification, but each WARC-Record-ID shall be a
legal URI and clearly indicate a documented and registered scheme to which it conforms (e.g. via a URI
scheme prefix such as "http:" or "urn:"). Care should be taken to ensure that this value is written with no
internal white space.
WARC-Record-ID  = "WARC-Record-ID" ":" uri

All records shall have a WARC-Record-ID field.
5.3 Content-Length (mandatory)
The Content-Length is the number of octets in the block, similar to [RFC2616]. If no block is present, a value
of "0" (zero) shall be used.
Content-Length  = "Content-Length" ":" 1*DIGIT

All records shall have a Content-Length field.
5.4 WARC-Date (mandatory)
The WARC-Date is a 14-digit UTC time-stamp formatted as YYYY-MM-DDThh:mm:ssZ, and shall conform to
the W3C profile of ISO 8601, i.e. [W3CDTF]. The time-stamp shall represent the instant that data capture for
record creation began. Multiple records written as part of a single capture event (see 5.7) shall use the same
WARC-Date, even though the times of their writin
...

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