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parser.js
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parser.js
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import * as UCAN from "./ucan.js"
import * as UTF8 from "./utf8.js"
import { base64urlpad } from "multiformats/bases/base64"
import * as json from "@ipld/dag-json"
import { CID } from "multiformats"
import { identity } from "multiformats/hashes/identity"
import * as raw from "multiformats/codecs/raw"
/**
* Parse JWT formatted UCAN. Note than no validation takes place here.
*
* @template {UCAN.Capability} C
* @param {UCAN.JWT<UCAN.Data<C>>} input
* @returns {UCAN.Data<C>}
*/
export const parse = input => {
const segments = input.split(".")
const [header, body, signature] =
segments.length === 3
? segments
: ParseError.throw(
`Can't parse UCAN: ${input}: Expected JWT format: 3 dot-separated base64url-encoded values.`
)
return {
header: parseHeader(header),
body: parseBody(body),
signature: base64urlpad.baseDecode(signature),
}
}
/**
* @param {string} header
* @returns {UCAN.Header}
*/
export const parseHeader = header => {
const { ucv, alg, typ } = json.decode(base64urlpad.baseDecode(header))
const _type = parseJWT(typ)
return {
version: parseUCV(ucv),
algorithm: parseAlgorithm(alg),
}
}
/**
* @template {UCAN.Capability} C
* @param {string} input
* @returns {UCAN.Body<C>}
*/
export const parseBody = input => {
const body = json.decode(base64urlpad.baseDecode(input))
return {
issuer: parseDID(body.iss),
audience: parseDID(body.aud),
expiration: parseInt(body.exp, 10),
nonce: parseOptionalString(body.nnc, "nnc"),
notBefore: parseMaybeInt(body.nbf, "nbf"),
facts: parseOptionalArray(body.fct, parseFact, "fct") || [],
proofs: parseProofs(body.prf),
capabilities: /** @type {C[]} */ (
parseArray(body.att, parseCapability, "att")
),
}
}
/**
* @param {unknown} input
*/
const parseCapability = input => parseStruct(input, asCapability, "att")
/**
* @template {UCAN.Capability} C
* @param {object & {can?:unknown, with?:unknown}|C} input
* @returns {C}
*/
export const asCapability = input => {
const capability = /** @type {C} */ ({
...input,
can: parseAbility(input.can),
with: parseResource(input.with),
})
const resource = capability.with
// @see https://github.com/ucan-wg/spec/#422-action
if (
resource.endsWith("*") &&
capability.can !== "*" &&
(resource.startsWith("my:") || resource.startsWith("as:did:"))
) {
return ParseError.throw(
`Capability has invalid 'can: ${JSON.stringify(
input.can
)}', for all 'my:*' or 'as:<did>:*' it must be '*'.`
)
}
return capability
}
/**
* @param {unknown} input
*/
const parseAbility = input =>
typeof input !== "string"
? ParseError.throw(
`Capability has invalid 'can: ${JSON.stringify(
input
)}', value must be a string`
)
: input.slice(1, -1).includes("/")
? /** @type {UCAN.Ability} */ (input.toLocaleLowerCase())
: input === "*"
? input
: ParseError.throw(
`Capability has invalid 'can: "${input}"', value must have at least one path segment`
)
/**
* @param {unknown} input
*/
const parseResource = input =>
typeof input !== "string"
? ParseError.throw(
`Capability has invalid 'with: ${JSON.stringify(
input
)}', value must be a string`
)
: parseURL(input) ||
ParseError.throw(
`Capability has invalid 'with: "${input}"', value must be a valid URI string`
)
/**
* @param {string} input
*/
const parseURL = input => {
try {
new URL(input)
return input
} catch (_) {
return null
}
}
/**
* @template T
* @param {unknown} input
* @param {(input:unknown) => T} parser
* @param {string} context
* @returns {T[]}
*/
const parseArray = (input, parser, context) =>
Array.isArray(input)
? input.map(parser)
: ParseError.throw(`${context} must be an array`)
/**
* @template T
* @param {unknown} input
* @param {(input:unknown) => T} parser
* @param {string} context
* @returns {T[]|undefined}
*/
const parseOptionalArray = (input, parser, context) =>
input === undefined ? input : parseArray(input, parser, context)
/**
* @template T
* @param {unknown} input
* @param {(input:object) => T} parser
* @param {string} context
* @returns {T}
*/
const parseStruct = (input, parser, context) =>
input != null && typeof input === "object"
? parser(input)
: ParseError.throw(`${context} must be of type object`)
/**
* @param {unknown} input
* @returns {UCAN.Fact}
*/
const parseFact = input => parseStruct(input, Object, "fct elements")
/**
* @param {unknown} input
*/
const parseProofs = input =>
Array.isArray(input)
? parseArray(input, parseProof, "prf")
: [parseProof(input)]
/**
* @param {unknown} input
* @returns {UCAN.Proof}
*/
const parseProof = input => {
const proof =
typeof input === "string"
? input
: ParseError.throw(
`prf has invalid value ${JSON.stringify(input)}, must be a string`
)
try {
return /** @type {UCAN.Proof} */ (CID.parse(proof))
} catch (error) {
return /** @type {UCAN.Proof} */ (
CID.create(1, raw.code, identity.digest(UTF8.encode(proof)))
)
}
}
/**
* @param {unknown} input
* @returns {UCAN.DID}
*/
const parseDID = input =>
typeof input === "string" && input.startsWith("did:")
? /** @type {UCAN.DID} */ (input)
: ParseError.throw(`DID has invalid representation '${input}'`)
/**
* @param {unknown} input
* @param {string} [context]
*/
const parseOptionalString = (input, context = "Field") => {
switch (typeof input) {
case "string":
case "undefined":
return input
default:
return ParseError.throw(`${context} has invalid value ${input}`)
}
}
/**
* @param {unknown} input
* @param {string} [context]
*/
const parseMaybeInt = (input, context = "Field") => {
switch (typeof input) {
case "undefined":
return undefined
case "number":
return parseInt(/** @type {any} */ (input), 10)
default:
return ParseError.throw(
`${context} has invalid value ${JSON.stringify(input)}`
)
}
}
/**
* @param {unknown} input
* @returns {UCAN.Version}
*/
const parseUCV = input =>
/\d+\.\d+\.\d+/.test(/** @type {string} */ (input))
? /** @type {UCAN.Version} */ (input)
: ParseError.throw(`Header has invalid version 'ucv: "${input}"'`)
/**
* @param {unknown} input
* @returns {"JWT"}
*/
const parseJWT = input =>
input === "JWT"
? input
: ParseError.throw(`Header has invalid type 'typ: "${input}"'`)
/**
* @param {unknown} input
*/
const parseAlgorithm = input => {
switch (input) {
case "EdDSA":
return 0xed
case "RS256":
return 0x1205
default:
return ParseError.throw(
`Header has invalid algorithm 'alg: ${JSON.stringify(input)}'`
)
}
}
class ParseError extends TypeError {
/**
* @param {string} message
* @returns {never}
*/
static throw(message) {
throw new this(message)
}
}