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index.js
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index.js
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'use strict'
const crypto = require('crypto')
const Transform = require('stream').Transform
const SPEC_ALGORITHMS = ['sha256', 'sha384', 'sha512']
const BASE64_REGEX = /[a-z0-9+/]+(?:=?=?)/i
const SRI_REGEX = /^([^-]+)-([^?]+)([?\S*]*)$/
const STRICT_SRI_REGEX = /^([^-]+)-([A-Za-z0-9+/]+(?:=?=?))([?\x21-\x7E]*)$/
const VCHAR_REGEX = /[\x21-\x7E]+/
class IntegrityMetadata {
constructor (metadata, opts) {
const strict = !!(opts && opts.strict)
this.source = metadata.trim()
// 3.1. Integrity metadata
// https://w3c.github.io/webappsec-subresource-integrity/#integrity-metadata-description
const match = this.source.match(
strict
? STRICT_SRI_REGEX
: SRI_REGEX
)
if (!match) { return }
if (strict && !SPEC_ALGORITHMS.some(a => a === match[1])) { return }
this.algorithm = match[1]
this.digest = match[2]
const rawOpts = match[3]
this.options = rawOpts ? rawOpts.slice(1).split('?') : []
}
toString (opts) {
if (opts && opts.strict) {
// Strict mode enforces the standard as close to the foot of the
// letter as it can.
if (!(
// The spec has very restricted productions for algorithms.
// https://www.w3.org/TR/CSP2/#source-list-syntax
SPEC_ALGORITHMS.some(x => x === this.algorithm) &&
// Usually, if someone insists on using a "different" base64, we
// leave it as-is, since there's multiple standards, and the
// specified is not a URL-safe variant.
// https://www.w3.org/TR/CSP2/#base64_value
this.digest.match(BASE64_REGEX) &&
// Option syntax is strictly visual chars.
// https://w3c.github.io/webappsec-subresource-integrity/#grammardef-option-expression
// https://tools.ietf.org/html/rfc5234#appendix-B.1
(this.options || []).every(opt => opt.match(VCHAR_REGEX))
)) {
return ''
}
}
const options = this.options && this.options.length
? `?${this.options.join('?')}`
: ''
return `${this.algorithm}-${this.digest}${options}`
}
}
class Integrity {
toString (opts) {
opts = opts || {}
let sep = opts.sep || ' '
if (opts.strict) {
// Entries must be separated by whitespace, according to spec.
sep = sep.replace(/\S+/g, ' ')
}
return Object.keys(this).map(k => {
return this[k].map(meta => {
return IntegrityMetadata.prototype.toString.call(meta, opts)
}).filter(x => x.length).join(sep)
}).filter(x => x.length).join(sep)
}
concat (integrity, opts) {
const other = typeof integrity === 'string'
? integrity
: serialize(integrity)
return parse(`${this.toString()} ${other}`, opts)
}
}
module.exports.parse = parse
function parse (sri, opts) {
opts = opts || {}
if (typeof sri === 'string') {
return _parse(sri, opts)
} else if (sri.algorithm && sri.digest) {
const fullSri = new Integrity()
fullSri[sri.algorithm] = [sri]
return _parse(serialize(fullSri, opts), opts)
} else {
return _parse(serialize(sri, opts), opts)
}
}
function _parse (integrity, opts) {
// 3.4.3. Parse metadata
// https://w3c.github.io/webappsec-subresource-integrity/#parse-metadata
return integrity.trim().split(/\s+/).reduce((acc, string) => {
const metadata = new IntegrityMetadata(string, opts)
if (metadata.algorithm && metadata.digest) {
const algo = metadata.algorithm
if (!acc[algo]) { acc[algo] = [] }
acc[algo].push(metadata)
}
return acc
}, new Integrity())
}
module.exports.serialize = serialize
module.exports.unparse = serialize
function serialize (obj, opts) {
if (obj.algorithm && obj.digest) {
return IntegrityMetadata.prototype.toString.call(obj, opts)
} else {
return Integrity.prototype.toString.call(obj, opts)
}
}
module.exports.fromData = fromData
function fromData (data, opts) {
opts = opts || {}
const algorithms = opts.algorithms || ['sha512']
const optString = opts.options && opts.options.length
? `?${opts.options.join('?')}`
: ''
return algorithms.reduce((acc, algo) => {
const digest = crypto.createHash(algo).update(data).digest('base64')
const meta = new IntegrityMetadata(
`${algo}-${digest}${optString}`,
opts
)
if (meta.algorithm && meta.digest) {
const algo = meta.algorithm
if (!acc[algo]) { acc[algo] = [] }
acc[algo].push(meta)
}
return acc
}, new Integrity())
}
module.exports.fromStream = fromStream
function fromStream (stream, opts) {
opts = opts || {}
const algorithms = opts.algorithms || ['sha512']
const optString = opts.options && opts.options.length
? `?${opts.options.join('?')}`
: ''
const P = opts.promise || Promise
return new P((resolve, reject) => {
const hashes = algorithms.map(algo => crypto.createHash(algo))
stream.on('data', d => hashes.forEach(hash => hash.update(d)))
stream.on('error', reject)
stream.on('end', () => {
resolve(algorithms.reduce((acc, algo, i) => {
const hash = hashes[i]
const digest = hash.digest('base64')
const meta = new IntegrityMetadata(
`${algo}-${digest}${optString}`,
opts
)
if (meta.algorithm && meta.digest) {
const algo = meta.algorithm
if (!acc[algo]) { acc[algo] = [] }
acc[algo].push(meta)
}
return acc
}, new Integrity()))
})
})
}
module.exports.checkData = checkData
function checkData (data, sri, opts) {
opts = opts || {}
sri = parse(sri, opts)
const pickAlgorithm = opts.pickAlgorithm || getPrioritizedHash
const algorithm = Object.keys(sri).reduce((acc, algo) => {
return pickAlgorithm(acc, algo) || acc
})
const digests = sri[algorithm].map(m => m.digest)
const digest = crypto.createHash(algorithm).update(data).digest('base64')
return digests.some(d => d === digest) && algorithm
}
module.exports.checkStream = checkStream
function checkStream (stream, sri, opts) {
opts = opts || {}
const P = opts.Promise || Promise
const checker = createCheckerStream(sri, opts)
return new P((resolve, reject) => {
stream.pipe(checker)
stream.on('error', reject)
checker.on('error', reject)
checker.on('verified', algo => {
resolve(algo)
})
})
}
module.exports.createCheckerStream = createCheckerStream
function createCheckerStream (sri, opts) {
opts = opts || {}
sri = parse(sri, opts)
const pickAlgorithm = opts.pickAlgorithm || getPrioritizedHash
const algorithm = Object.keys(sri).reduce((acc, algo) => {
return pickAlgorithm(acc, algo) || acc
})
const digests = sri[algorithm].map(m => m.digest)
const hash = crypto.createHash(algorithm)
const stream = new Transform({
transform: function (chunk, enc, cb) {
hash.update(chunk, enc)
cb(null, chunk, enc)
},
flush: function (cb) {
const digest = hash.digest('base64')
if (digests.some(d => d === digest)) {
stream.emit('verified', algorithm)
return cb()
} else {
const err = new Error(`${algorithm} integrity checksum failed`)
err.code = 'EBADCHECKSUM'
err.found = digest
err.expected = digests
err.algorithm = algorithm
return cb(err)
}
}
})
return stream
}
function getPrioritizedHash (algo1, algo2) {
return algo1
}