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bundle

README.md

go/bundle

This directory contains a reference implementation of the Web Bundles spec.

Overview

We currently provide three command-line tools: gen-bundle, sign-bundle and dump-bundle.

gen-bundle command is a bundle generator tool. gen-bundle consumes a set of http exchanges (currently in the form of HAR format, URL list file, or static files in a local directory), and emits a web bundle.

sign-bundle command attaches a signature to a bundle. There are two supported ways to sign: using signatures section or integrity block. sign-bundle takes an existing bundle file, a private key and possibly a certificate, and emits a new bundle file with cryptographic signature added.

dump-bundle command is a bundle inspector tool. dump-bundle dumps the enclosed http exchanges of a given web bundle file in a human readable form.

You are also welcome to use the code as golang lib (e.g. import "github.com/WICG/webpackage/go/bundle"), but please be aware that the API is not yet stable and is subject to change any time.

Getting Started

Prerequisite

golang environment needs to be set up in prior to using the tool. We are testing the tool on latest golang. Please refer to Go Getting Started documentation for the details.

Installation

We recommend using go install (Golang 1.18+) to install the command-line tool.

go install github.com/WICG/webpackage/go/bundle/cmd/...@latest

Usage

gen-bundle

gen-bundle generates a web bundle. There are three ways to provide a set of exchanges to bundle; by a HAR file, by a URL list, and by a local directory.

These command-line flags are common to all the three options:

  • -version specifies WebBundle format version. Possible values are: b2 (default) and b1.
  • -primaryURL specifies the bundle's main resource URL. This URL is also used as the fallback destination when browser cannot process the bundle. If bundle format is b1, this option is required.
  • -manifestURL specifies the bundle's manifest URL. This option can be specified only for bundle version b1.
  • -o specifies name of the output bundle file. Default file name if unspecified is out.wbn.
  • -headerOverride adds additional response header to all bundled responses. Existing values of the header are overwritten.

From a HAR file

One convenient way to generate HAR file is via Chrome Devtools:

  1. Open DevTools, navigate to Network panel.
  2. Make sure that "Disable cache" box is checked.
  3. Reload the page.
  4. Right click on any resource and select "Save as HAR with content".

generating har with devtools

Once you have the har file, generate the web bundle via:

gen-bundle -har foo.har -o foo.wbn -primaryURL https://example.com/

From a URL list

gen-bundle also accepts -URLList FILE flag. FILE is a plain text file with one URL on each line. gen-bundle fetches these URLs and put the responses into the bundle. For example, you could create urls.txt with:

# A line starting with '#' is a comment.
https://example.com/
https://example.com/style.css
https://example.com/script.js

then run:

gen-bundle -URLList urls.txt \
           -primaryURL https://example.com/ \
           -o example_com.wbn

Note that gen-bundle does not automatically discover subresources; you have to enumerate all the necessary subresources in the URL list file.

From a local directory

You can also create a bundle from a local directory. For example, if you have the necessary files for the site https://www.example.com/ in static/ directory, run:

gen-bundle -dir static -baseURL https://example.com/ -o foo.wbn -primaryURL https://example.com/

If -baseURL flag is not specified, resources will have relative URLs in the generated bundle file.

sign-bundle

sign-bundle is split into the following sub-commands:

  • signatures-section
  • integrity-block
  • dump-id

Using signatures-section sub-command

sign-bundle signatures-section takes an existing bundle file, a certificate and a private key, and emits a new bundle file with cryptographic signature for the bundled resources added.

It updates a bundle attaching a cryptographic signature of its exchanges. To use this tool, you need a pair of a private key and a certificate in the application/cert-chain+cbor format. See signatures-section extension and go/signedexchange for more information on how to create a key and certificate pair.

Assuming you have a key and certificate pair for example.org, this command will sign all exchanges in unsigned.wbn whose URL's hostname is example.org, and writes a new bundle to signed.wbn.

sign-bundle signatures-section \
  -i unsigned.wbn \
  -certificate cert.cbor \
  -privateKey priv.key \
  -validityUrl https://example.org/resource.validity.msg \
  -o signed.wbn

Using integrity-block sub-command

sign-bundle integrity-block takes an existing bundle file and an ed25519 private key, and emits a new bundle file with cryptographic signature added to the integrity block.

It updates a bundle prepending the web bundle with an integrity block containing a stack of signatures over the hash of the web bundle. To use this tool, you need an ed25519 private key in .pem format.

An unencrypted ed25519 private key can be generated with:

openssl genpkey -algorithm Ed25519 -out ed25519key.pem

For better security, one should prefer using passphrase-encrypted ed25519 private keys. To encrypt an unencrypted private key, run:

# encrypt the key (will ask for a passphrase, make sure to use a strong one)
openssl pkcs8 -in ed25519key.pem -topk8 -out encrypted_ed25519key.pem
# delete the unencrypted key
rm ed25519key.pem

sign-bundle integrity-block \
  -i unsigned.wbn \
  -privateKey encrypted_ed25519key.pem \
  -o signed.swbn

In case you chose to use an encrypted private key, it will be prompted during the signing process. If one wants to use the tool programmatically (e.g. as part of their DevOps pipeline), they can bypass the prompt by setting the password into an environment variable named WEB_BUNDLE_SIGNING_PASSPHRASE.

See integrityblock-explainer for more information about what an integrity block is.

Using dump-id sub-command

sign-bundle dump-id is a helper tool to print out the Web Bundle ID which is corresponding to the given ed25519 key. The ID is base32-encoded lowercase representation of the ed25519 public key with a predefined suffix.

Web Bundle ID can be used for example as the origin of an Isolated Web App.

sign-bundle dump-id -privateKey privkey.pem

or

sign-bundle dump-id -publicKey pubkey.pem

dump-bundle

dump-bundle dumps the content of a web bundle in a human readable form. To display content of a bundle file, invoke:

dump-bundle -i foo.wbn

dump-bundle doesn't support web bundles signed with integrity block.

Using Bundles

Bundles generated with gen-bundle can be opened with web browsers supporting web bundles.

Chrome (79+) experimentally supports Web Bundles with some limitations. See this document for more details.