WACZ is a media type that allows web archive collections to be
packaged and shared on the web as a discrete file. A WACZ file includes
all the data that is needed for the rendering archived content as well as
contextual information required for users to interpret it. Rendering
software can obtain this data on demand using HTTP Range requests,
without requiring the entire file to be fully retrieved, or for it to be
otherwise mediated by specialized server side software.
## Status of This Document
This is a stable version of the WACZ standard and is in active use by
the Webrecorder project. Please open [GitHub issues](https://github.com/webrecorder/specs/issues/)
for questions and suggestions.
## Terminology
This section defines the terms used in this specification and throughout web
archives infrastructure. A link to these terms is included whenever they appear
in this specification.
- Collection
- An arbitrary set of related archived web pages and metadata based on some topic, website domain(s), time period, or other conceptual grouping.
- Context
- Descriptive information about a web archive that helps a person using that web archive understand and interpret what the archive contains. This information can include why the content was selected for the archive, when it was created, who created it, and what tools or applications were used to create it.
- IIPC
- The International Internet Preservation Consortium. An organization of libraries, archives and other organizations established in 2003 to coordinate efforts to preserve web content.
- Media Type
- A two-part identifier for file formats that are transferred on the World Wide Web and the underlying Internet. [[IANA-MEDIA-TYPES]].
- Package
- A file format that allows distinct files or bitstreams to be represented within it. Popular examples of packaging formats include ZIP, PDF, MP4, tar and Open Office XML.
- Page
- A web document as viewed in a web browser that is viewing a specific URL. Sometimes referred to as a web page.
- WACZ
- Web Archive Collection Zipped. A file that conforms to this specification which is used to package up WARC data and metadata into a ZIP file for distribution and replay on the web
- WARC
- A file containing concatenated representations of web resources conforming to the [[WARC]] specification.
- Wayback Machine
- A well known web application for replaying archived web pages that was initially developed at the Internet Archive and has been forked as an open soruce application by the IIPC.
- Web Archive
- A collection of files that preserve representations of web resources in the WARC format. A web archive may also include derivative files such as CDX indexes for accessing records within the archive.
- ZIP file
- A file conforming to the [[ZIP]] specification which is used to aggregate, compress, and encrypt files into a single interoperable container. WACZ allows for both ZIP and ZIP64 encodings for larger archives.
## Introduction
This specification defines a directory structure and ZIP format
specification for sharing and distributing web archives. ZIP files
using this format can be referred to as WACZ (Web Archive Collection
Zipped).
### Motivation
The goal of this specification is to provide a portable format for
web archives in order to achieve two broad goals for web archives:
1. *Social*: to provide an interoperable way of sharing web archive
collections that includes the contextual information needed
for users to interpret and meaningfully interact with them.
2. *Technical*: to provide an efficient way to dynamically load
*small amounts of data* from a remotely hosted file
on static storage, without requiring the entire file
to be downloaded, or for the intervention of specialized
server side applications.
To use and make sense of a web archive collection, it is necessary to have the
archived web content as well as contextual information that describes what the
collection contains as well as when and how it was created. The collection also
requires a set of entry points or pages to use for browsing the collection.
All of this data needs to be packaged together so that the various pieces can be
easily copied and transferred without accidentally separating them. This data
package needs to to be easily transported from one storage system to another,
sent as an attachment in an email, placed on a thumb drive, and hosted by simply
serving it up at a given URL as a static document, possibly from cloud object
storage, or a CDN.
Hosting web archives currently requires complex server infrastructure (e.g. a
Wayback Machine) to serve WARC data in such a way that can be
viewed in the browser. The WACZ format provides a storage approach
optimized for efficient random-access to packaged up WARC data that allows
the browser to render a page by fetching only what is needed for that
particular page. This is done by leveraging the ZIP format's built-in
index to locate the contents of the web archive and its constituent metadata.
WACZ is not designed to replace other web archiving formats. Rather it
establishes a file packaging convention for all the data needed by a browser for
efficient rendering of a web archive collection, and its contextualization.
### Existing Tools
The [py-wacz](https://github.com/webrecorder/py-wacz) repository contains a
reference implementation for creating WACZ files from existing WARC files, and
validating them. Parts of the specification are also implemented and in use by
[wabac.js](https://github.com/webrecorder/wabac.js) and
[ReplayWeb.page](https://replayweb.page).
## WACZ Object
A WACZ object consists of the following:
1. A `datapackage.json` file for recording technical and descriptive metadata
specified in [[FRICTIONLESS-DATA-PACKAGE]].
2. An extensible directory and naming convention for web archive data.
3. A method for bundling the directory layout in a ZIP file.
### Directory Layout
A WACZ contains a directory structure, that contains web archive
collection data which MUST conform to the [[FRICTIONLESS-DATA-PACKAGE]]
specification. This directory structure looks like:
├── archive
│ └── data.warc.gz
├── datapackage.json
├── datapackage-digest.json
├── indexes
│ └── index.cdx.gz
└── pages
└── pages.jsonl
### Directories and Files
#### archive
The `archive` directory MUST contain one or more files in the [[WARC]] format.
The files SHOULD use the `.warc` file extension unless they are GZIP encoded in
which case they MUST use the `.warc.gz` file extension.
archive
└── data.warc
#### indexes
The `indexes` directory MUST include one or more indexes for the WARC data stored
in `archive`. These index files allow clients to efficiently look up a URL to
see if it is contained in the WACZ. Index files MUST contain CDXJ data
and MAY be gzip compressed [[PYWB-CDXJ]].
indexes
└── index.cdx.gz
#### pages.jsonl
The `pages/pages.jsonl` MUST be present and include a list of 'Page' objects as
[[JSON-Lines]] where each line MUST contain at least the following properties:
- `url` - a URL for the page
- `ts` - a [[RFC3339]] datetime string
Each entry in the [[JSONL]] file MAY contain the following properties to aid in
navigating a web archive collection:
- `title` - a string describing the resource
- `id` - an arbitrary identifier for the resource
- `text` - text extracted from the snapshot
- `size` - an integer that represents the number of bytes for the page and all its resources
{"format": "json-pages-1.0", "id": "pages", "title": "All Pages"}
{"id": "1db0ef709a", "url": "https://www.example.com/page", "size": 1256, "ts": "2020-10-07T21:22:36Z", "title": "Example Domain", "text": "Example Domain This domain is for use in illustrative examples in documents. You may use this domain in literature without prior coordination or asking for permission. More information..."}
{"id": "12304e6ba9", "url": "https://www.example.com/another", "size": 1256, "ts": "2020-10-07T21:23:36Z", "title": "Another Page", "text": "Example Domain This domain is for use in illustrative examples in documents. You may use this domain in literature without prior coordination or asking for permission. More information..."}
Each entry in the [[JSONL]] file MAY contain additional properties as long as
they do not interfere with the required properties.
Other [[JSONL]] files MAY be added on using the same format in the `pages/`
directory. A common use case is to include only the main pages in the
`pages.jsonl`, while including additional pages, such as those discovered
automatically via a crawl in an another file e.g. `extraPages.jsonl`.
#### datapackage.json
The `datapackage.json` file MUST be present at the root of the WACZ which
serves as the manifest for the web archive and is compliant with the
[[FRICTIONLESS-DATA-PACKAGE]] specification. It MUST contain the following
properties:
- `profile`: the string `data-package`
- `resources`: a list of file names, paths, sizes and fixity for all files
contained in the WACZ.
- `wacz_version`: the version of WACZ used, for example `1.1.1`
{
"profile": "data-package",
"wacz_version": "1.1.1",
"resources": [
{
"name": "pages.jsonl",
"path": "pages/pages.jsonl",
"hash": "sha256:8a7fc0d302700bed02294404a627ddbbf0e35487565b1c6181c729dff8d2fff6",
"bytes": 75
},
{
"name": "data.warc",
"path": "archive/data.warc",
"hash": "sha256:0e7101316ba5d4b66f86a371ee615fbd20f9d3f32d32563ed2c829db062f7714",
"bytes": 11469796
}
]
}
The `datapackage.json` SHOULD include properties that allow rendering
applications to present the user with contextual information about the
web archive:
- `title`: a string or one sentence description for the collection
- `description`: a longer description of the archive's contents
which MUST be Markdown formatted (plain text is valid Markdown)
- `created`: a [[RFC3339]] datetime for when the WACZ file was created
- `modified`: a [[RFC3339]] datetime for when the WACZ file was last modified
- `software`: A description of what software was used to create the WACZ file
- `mainPageUrl`: An optional URL of the main or starting page in the collection
to be used for initial replay
- `mainPageDate`: An optional ISO-formatted date of the main or startng page in
the collection to be used for initial replay
Other properties from the [[FRICTIONLESS-DATA-PACKAGE]] specification such as
`licenses`, `version`, `organization`, `contributors`, `email` MAY be used.
Custom properties that do not interfere with pre-existing properties MAY also
be used.
#### datapackage-digest.json
A `datapackage-digest.json` file SHOULD be included in the root of the WACZ to
verify the `datapackage.json` manifest with a hash and thus for the entire
contents of the WACZ. If present the following properties MUST be included:
* `path`: the string "datapackage.json"
* `hash`: a cryptographic hash for the `datapackage.json` file
{
"path": "datapackage.json",
"hash": "sha256:ec1f44ab13e2c94b0ddf66e9673d585ba4a77e6f8c9cc30d8665da434557e885"
}
For an approach to recording a cryptographic signature in the
`datapackage-digest.json` in order to assert and prove the authorship of a WACZ
please see [WACZ Signing and Verification](/wacz-auth/latest/).
### Other files and directories
Other files and directories MAY be present in a WACZ as long as they do
not interfere with specified files and directories that are used by WACZ.
Specifically, custom files and directories MUST NOT be added to the existing WACZ directories, `archive`, `indexes` and `pages`. Additional files MUST be listed in the resources section of `datapackage.json` to ensure conformance with [[FRICTIONLESS-DATA-PACKAGE]]
### Zip Format
The entire directory structure MUST be stored in a standard [[ZIP]] file.
#### Zip Compression
Already compressed files MUST NOT be compressed again to allow for random access.
- All `archive/` files should be stored in ZIP with 'STORE' mode.
- All `index/*.cdx.gz` files should be stored in ZIP with 'STORE' mode.
- All files (`*.jsonl`, `*.json`, `*.idx`, `*.cdx`, `*.cdxj`) can be stored in
the ZIP with either 'DEFLATE' or 'STORE' mode.
#### Zip Format File Extension
A ZIP file that follows this Web Archive Collection format spec MUST use the extension `.wacz`.
Such a file can be referred to as a WACZ file or a WACZ.
## Processing Model
The [[ZIP]] file format provides efficient random access, which means archived
web pages can be retrieved efficiently even from large web archive collections
without requiring the entire WACZ to be transferred. To achieve this WACZ
clients can read portions of the ZIP file on-demand using HTTP RANGE requests
[[RFC7233]].
The processing model works as follows. Given a ZIP file, a client can quickly:
1. Read all entries to determine the contents of the ZIP file
2. Load collection metadata from the `datapackage.json`
3. Load a list of pages from `pages.jsonl`, if any
To lookup a given URL the client needs to:
1. Read the full CDX from ZIP
2. Binary search index looking for the URL
3. If a match found, get offset/length/location in WARC
4. Read compressed WARC chunk in ZIP
This approach is being used by [ReplayWeb.page](https://replayweb.page)
## Publishing
Because they are ZIP files WACZ can be hosted on the web as static files. This
allows web archives to be easily maintained over time without relying on complex
server side software, apart from widely available, open source, and well tested
web server applications. If desirable WACZ files can be managed and made
accessibile using HTTP object stores available from cloud hosting providers, and
content deliver networks that geographically position web-archives closer to
their users. However there are certain considerations to make when publishing
WACZ files.
### Content-Length
WACZ clients need to know how large an entire WACZ file is in order to
download it prior to rendering, or to read it dynamically. To support this HTTP
responses for WACZ files MUST use the `Content-Length` HTTP header.
### Partial Requests
Clients that render WACZ files typically need to be able to fetch content from
the WACZ file on demand. For example when displaying archived content for a
given URL that URL needs to be looked up in the CDXJ index, and the byte offsets
from the index entry are then used to retrieve a portion of a given WARC file
that is enclosed in the WACZ.
In order for clients to be able to perform this dynamic retrieval web servers
that publish WACZ files MUST support HTTP range requests [[RFC7233]]. HTTP
responses for WACZ HTTP requests SHOULD server WACZ files using the
`Accept-Ranges` HTTP header.
### CORS
WACZ files and the their clients MAY be served from the same host name. However
it can be useful to view the web archive from a host name that is distinct from
the host name that is publishing the WACZ file. For example this is the
case when publishing WACZ files using a cloud provider's HTTP object storage
(e.g. `s3.amazonaws.com`) and making it viewable at another domain (`e.g.
example.org`). It also is the case when WACZ publishers want to allow their web
archives to circulate on the web, and be viewable in multiple locations.
For security reasons browsers restrict access to files hosted on a
different domain than the websites that is trying to load them. In order to
support loading from different domains WACZ files SHOULD be made available using
the `access-control-allow-origin` [[CORS]] HTTP header.
### Media Type
WACZ HTTP responses for WACZ files SHOULD be published with the
`application/wacz` media type.
### Example Response
Given these requirements a minimal HTTP response for a WACZ could look
like:
HTTP/2 200
Content-Type: application/wacz
Content-Length: 20961755
Accept-Ranges: bytes
Access-Control-Allow-Origin: *