@interop/was-client

Wallet Attached Storage Client (@interop/was-client)

A developer-friendly client for Wallet Attached Storage (WAS) servers, with a database-driver-inspired navigational API over zcap-authorized HTTP.

Table of Contents

• Background
• Install
• Usage
  • Creating a client (signer + zcapClient)
  • The handle model
  • Spaces
  • Collections
  • Resources: JSON and binary
  • Delegation and sharing
  • Public sharing and access-control policies
  • Resource metadata
  • Conditional writes (optimistic concurrency)
  • Storage introspection: backends and quotas
  • Registering a Bring-Your-Own-Storage backend
  • Encrypted collections (EDV-over-WAS): pass-through encryption via the WAS client (recommended)
  • Export and import
  • The manual-request escape hatch
• Errors and the 404/null caveat
• Contribute
• License

Background

The WAS protocol exposes a general purpose database-like container model -- SpacesRepository > Space > Collection > Resource -- over HTTP, authorized with Authorization Capabilities (zcaps).

@interop/was-client wraps that ZcapClient and exposes the containment model through cheap, lazy navigational handles modeled on a document store's DX (client > db > collection), using WAS-specific verbs (add/get/put/list/delete) rather than insertOne/findOne (WAS has no query-by-filter yet).

Document db driver	WAS client
new Client(url)	new WasClient({ serverUrl, zcapClient })
client.db('app')	was.space(spaceId)
db.collection('users')	space.collection(collectionId)
collection.insertOne(doc)	collection.add(doc)
collection.findOne({ _id })	collection.get(resourceId)
collection.replaceOne({ _id }, d)	collection.put(resourceId, data)
collection.find().toArray()	collection.list()
collection.deleteOne({ _id })	collection.resource(resourceId).delete()

Install

• Node.js 24+ is recommended.

pnpm install @interop/was-client

Usage

Creating a client (signer + zcapClient)

A WasClient signs every request with a key you control. The key is held by an ezcap ZcapClient, which you build from a did:key identity. You will need two companion packages alongside this one (this library already depends on @interop/ed25519-signature):

pnpm install @interop/ezcap @interop/did-method-key @interop/ed25519-verification-key

The primary form wraps a ZcapClient you build yourself. The did:key driver generates a key pair and a matching DID document, wiring the signer's id/controller correctly:

import { ZcapClient } from '@interop/ezcap'
import * as didKey from '@interop/did-method-key'
import { Ed25519Signature2020 } from '@interop/ed25519-signature'
import { Ed25519VerificationKey } from '@interop/ed25519-verification-key'
import { WasClient } from '@interop/was-client'

// 1. Generate a did:key identity (didDocument + keyPairs).
const didKeyDriver = didKey.driver()
didKeyDriver.use({ keyPairClass: Ed25519VerificationKey })
const { didDocument, keyPairs } = await didKeyDriver.generate()

// 2. Build the ezcap ZcapClient (it holds the signer and signs every request).
const zcapClient = new ZcapClient({
  didDocument,
  keyPairs,
  SuiteClass: Ed25519Signature2020
})

// 3. Wrap it.
const was = new WasClient({ serverUrl: 'https://was.example', zcapClient })

If you already have a single signer, WasClient.fromSigner() builds the ZcapClient internally (using the Ed25519Signature2020 suite). A signer is any object with { id, sign() }; here we get one from a generated key. The signer's id must be a did:key so the server can resolve and verify it:

import { Ed25519VerificationKey } from '@interop/ed25519-verification-key'
import { WasClient } from '@interop/was-client'

// Pass a 32-byte `seed` for a deterministic key, or omit it for a random one.
const keyPair = await Ed25519VerificationKey.generate({ seed })
keyPair.controller = `did:key:${keyPair.fingerprint()}`
keyPair.id = `${keyPair.controller}#${keyPair.fingerprint()}`

const was = WasClient.fromSigner({
  serverUrl: 'https://was.example',
  signer: keyPair.signer()
})

The seed is where a passphrase-, stored-secret-, or KMS-derived key plugs in: deriving the same 32-byte seed yields the same DID, and therefore access to the same spaces. (Apps with user accounts often derive the signer from a passphrase via CapabilityAgent.fromSecret() from @digitalbazaar/webkms-client -- not required, just a common alternative.)

serverUrl is the base for both URL building and zcap invocationTargets, so the "server URL must equal the invocation target host:port" constraint holds by construction.

The handle model

The client exposes the WAS containment model (SpacesRepository > Space > Collection > Resource) as navigational handles. Handles are lazy and synchronous to obtain -- only the verb methods hit the network. Lazy chains never throw: was.space(x).collection(y) does no I/O and just accumulates URL context. Existence is checked on the first network verb.

const space = await was.createSpace({ name: 'Home' })

const collection = await space.createCollection({
  name: 'Verifiable Credentials'
})

await collection.put('vc-1', {
  type: ['VerifiableCredential'],
  name: 'Diploma'
})
const vc = await collection.get('vc-1') // parsed JSON object, or null on a miss

await collection.resource('vc-1').delete() // delete one resource by id
await space.delete() // delete the whole space (idempotent)

delete() is uniform at every level, takes no argument, and always deletes the thing the handle points at -- so there is no "delete the collection" vs "delete one item" footgun. The next sections cover each level in turn.

Spaces

A Space is the top-level container, created from the spaces repository. The server requires a name; controller defaults to the client's own DID, and the server generates the id unless you pass one.

const space = await was.createSpace({ name: 'Home' }) // POST /spaces/

// Lazy handle to an existing space by id -- no I/O until a verb runs.
const same = was.space(space.id)

// Read the Space Description (null if missing or not visible to you).
const desc = await space.describe() // { id, type: ['Space'], name, controller } | null

// Upsert: merges the given fields over the current description.
await space.configure({ name: 'Home (renamed)' })

await space.delete() // idempotent

List the spaces in the repository visible to your signer with was.listSpaces(). It returns a { url, totalItems, items } listing holding only the spaces whose controller your invocation is authorized for; an unauthorized caller gets an empty list rather than an error. To enumerate what is inside a space, use space.collections() (below).

const { totalItems, items } = await was.listSpaces()
// items: [{ id, url, name? }, ...]

Collections

A Collection lives inside a Space and holds resources. WAS does not auto-create parents, so createCollection throws NotFoundError if the space does not exist. The server generates the id unless you pass one (a handful of reserved ids are rejected).

// Create.
const collection = await space.createCollection({
  name: 'Verifiable Credentials'
})

// Lazy handle to an existing collection by id.
const same = space.collection(collection.id)

// Read the Collection Description (null if missing or not visible).
const desc = await collection.describe() // { id, type: ['Collection'], name } | null

// Update (upsert; merges over the current description).
await collection.configure({ name: 'Credentials' })

// List the collections in a space.
const collections = await space.collections()
// { url, totalItems, items: [{ id, name, url }, ...] } | null

// List the resources inside this collection. Transparently follows the
// server's `next` pagination links, buffering every page into one listing.
const resources = await collection.list()
// { id, url, totalItems, items: [{ id, url, contentType }, ...], ... } | null

// For a large collection, stream one page (or item) at a time instead of
// buffering the whole thing -- follows `next` on demand, stops early on `break`.
for await (const item of collection.listItems()) {
  // item: { id, url, contentType, name? }
}
// `collection.listPages()` yields whole pages if you'd rather page yourself.

await collection.delete() // deletes the whole collection; idempotent

To delete a single resource instead of the whole collection, use collection.resource(id).delete().

Resources: JSON and binary

A Resource is a JSON object or binary blob keyed by id within a Collection. Use add() for a server-generated id or put(id, ...) to create-or-replace at a known id (both throw NotFoundError if the parent collection is missing):

// Server-generated id; returns { id, url, contentType? }.
const added = await collection.add({
  type: ['VerifiableCredential'],
  name: 'Diploma'
})

// Create or replace at a known id (upsert).
await collection.put('vc-1', {
  type: ['VerifiableCredential'],
  name: 'Diploma'
})

const vc = await collection.get('vc-1') // parsed JSON object, or null on a miss
await collection.resource('vc-1').delete() // idempotent

Writes detect the payload: a plain object/array is sent as JSON; a Blob/Uint8Array/Buffer is sent as binary, with the content-type taken from options.contentType, the Blob.type, or application/octet-stream.

// JSON
await collection.put('doc', { hello: 'world' })

// Binary
const bytes = new TextEncoder().encode('plain text body')
await collection.put('note.txt', bytes, { contentType: 'text/plain' })

const resource = collection.resource('note.txt')
await resource.get() // a Blob (whose .type carries the content-type)
await resource.getText() // 'plain text body'
await resource.getBytes() // Uint8Array

Reads auto-parse: get() returns a parsed object for a JSON content-type and a Blob otherwise; getText() / getBytes() are explicit escape hatches.

A write value is a JSON object/array or binary (Blob/Uint8Array) -- the ResourceData type. A top-level JSON primitive (a bare string, number, boolean, or null) is not accepted; it is a compile-time error. To store one, either wrap it in an object (put('greeting', { value: 'hello' })) or write it as binary via a Blob:

await collection.put('greeting', new Blob(['hello'], { type: 'text/plain' }))

Delegation and sharing

was.grant(...) is the general delegation primitive; space.grant(...) and collection.grant(...) are sugar that prefill the grant target with the handle's URL. The recipient rebuilds access from the received zcap with fromCapability().

// Alice grants Bob read access to a resource.
const added = await collection.add({ secret: 'value' })
const zcap = await was.grant({
  to: bobDid,
  actions: ['GET'], // HTTP verbs: 'GET' | 'PUT' | 'POST' | 'DELETE'
  target: added.url
})

// Bob, holding the zcap, rebuilds a handle at the right depth.
const handle = bobWas.fromCapability(zcap) // a Resource here
await handle.get() // succeeds; a write would be denied by the GET-only grant

Actions are HTTP verbs (GET / PUT / POST / DELETE). The WAS server authorizes on these case-sensitively (uppercase), but grant() also accepts the lowercase forms and normalizes them to uppercase in the signed zcap -- so actions: ['get'] still validates server-side.

Public sharing and access-control policies

A Space, Collection, or Resource can carry an access-control policy that grants read access beyond capabilities -- most commonly making it world-readable ("share via public link"). The policy methods live on all three handles:

// Make a whole collection world-readable (the "create public link" case).
await collection.setPublic() // sugar for setPolicy({ type: 'PublicCanRead' })

// Anyone (even unauthenticated) can now read its resources.
const link = added.url // hand this URL out; a plain GET resolves it

// Inspect or revoke.
const policy = await collection.getPolicy() // { type: 'PublicCanRead' } | null
const isPublic = await collection.isPublic() // true if its own policy is PublicCanRead
await collection.clearPolicy() // revert to capability-only access (idempotent)

// setPolicy() is the generic, forward-compatible primitive; setPublic() is sugar.
await space.setPolicy({ type: 'PublicCanRead' }) // inherited by all contents
await resource.setPublic() // a single public resource

Policies are resolved most-specific-first (Resource over Collection over Space) and are permissive-only -- they broaden access, never restrict a valid capability holder. Managing a policy is a controller-level operation. Discover a policy via space.linkset() / collection.linkset() (RFC9264) or the linkset property on a description.

isPublic() is a read-only convenience that returns true when the Space, Collection, or Resource has a { type: 'PublicCanRead' } policy -- that is, when it has been made public via setPublic() (or an equivalent setPolicy() call). It's meant to drive data-browser style UI, to show a "This space(/collection/resource) has been shared publicly" type of icon.

Consuming public links (unauthenticated reads)

The flip side of setPublic(): reading a PublicCanRead resource or collection with no authorization, by its URL. These use an unsigned plain fetch (no capability invocation), so they work for a consumer who only holds the link.

// Fetch a single public resource (auto-parses JSON, returns binary as a Blob).
const doc = await was.publicRead({
  resourceUrl: 'https://was.example/space/s/c/r'
}) // Json | Blob | null

// List a public collection -- e.g. a blog published as a public-read collection.
const listing = await was.publicListCollection({
  collectionUrl: 'https://was.example/space/s/c'
}) // ResourceListing | null

// Or stream a large public collection one item/page at a time:
for await (const item of was.publicListCollectionItems({
  collectionUrl: 'https://was.example/space/s/c'
})) {
  // item: { id, url, contentType, name? }
}
// (`was.publicListCollectionPages(...)` yields whole pages.)

Both follow the read-method 404/null caveat: a missing or non-public target resolves to null.

Resource metadata

Each Resource has a metadata object at its reserved /meta path: server-managed properties (contentType, size, optional createdAt / updatedAt) plus a user-writable custom object (name and tags).

const resource = collection.resource('vc-1')

const meta = await resource.meta() // ResourceMetadata | null (null on a miss)

// setMeta() is a full replacement of `custom`; omitted properties are cleared.
await resource.setMeta({ custom: { name: 'Diploma', tags: { year: '2026' } } })

// setName() / setTags() are read-modify-write sugar that preserve the other.
await resource.setName('Renamed diploma') // keeps existing tags
await resource.setTags({ status: 'verified' }) // keeps existing name

The custom.name is the same value surfaced as a resource's name in collection listings; updating one updates the other.

Conditional writes (optimistic concurrency)

Against a backend that advertises the conditional-writes feature (see below), a Resource carries a strong ETag validator that changes on every write. Use it to prevent the lost-update problem -- two clients that both read version N and each write N+1, the second silently clobbering the first.

const { etag } = await collection.put('doc', { v: 1 }) // writes return the ETag
const meta = await collection.resource('doc').meta() // meta().etag also carries it

// Update-if-unchanged: succeeds only if `doc` is still at `etag`, else throws
// PreconditionFailedError (HTTP 412).
await collection.put('doc', { v: 2 }, { ifMatch: etag })

// Create-if-absent: succeeds only if `doc` does not yet exist (else 412).
await collection.put('new-doc', { v: 1 }, { ifNoneMatch: true })

// Delete-if-unchanged.
await collection.resource('doc').delete({ ifMatch: someEtag })

Recover from a PreconditionFailedError by re-reading the current etag, re-applying your change on top of the new version, and retrying.

On an encrypted collection this is automatic: the EDV codec advances the document sequence and pins each write to the current ETag for you, so a stale write surfaces as a PreconditionFailedError (the EDV sequence becomes enforced rather than advisory). The explicit ifMatch / ifNoneMatch options above are for plaintext collections.

Storage introspection: backends and quotas

A Space can report the storage backends available to it and a per-backend usage report. Both are optional server features (a server without them surfaces a NotImplementedError); both follow the read-method 404/null caveat.

const backends = await space.backends() // BackendDescriptor[] | null
const report = await space.quotas() // SpaceQuotaReport | null
// report.backends[i]: { id, state, usageBytes, limit, restrictedActions, ... }

A Collection can likewise report the backend it is stored on and its own usage, scoped to that backend (same optional-feature and 404/null caveats).

const backend = await collection.backend() // BackendDescriptor | null
const usage = await collection.quota() // BackendUsage | null
// usage: { id, state, usageBytes, limit, restrictedActions, measuredAt, ... }

A BackendDescriptor's optional features array advertises optional server affordances -- things the backend actively does beyond the baseline read/write API (e.g. conditional-writes, blinded-index-query, chunked-streams). An absent token means the backend makes no claim to it, so treat it as unsupported rather than assuming a default. (Client-side encryption is not a backend feature -- see below.)

const backend = await collection.backend()
if (backend?.features?.includes('conditional-writes')) {
  // backend enforces If-Match / If-None-Match write preconditions
}

Registering a Bring-Your-Own-Storage backend

Beyond the server's built-in default backend, the Space controller can register an external ("Bring Your Own Storage") backend -- e.g. a wallet connecting a user's own Google Drive. Registration is a controller-authorized write: the body carries the secret-bearing connection material (an OAuth authorization code or refresh token), and the server stores it and returns the sanitized descriptor (never the secrets).

const descriptor = await space.registerBackend({
  id: 'gdrive-personal', // unique within the Space
  name: 'My Google Drive',
  provider: 'google-drive', // selects the server-side adapter
  storageMode: ['document', 'blob'],
  connection: {
    kind: 'oauth2-google',
    authorizationCode: '4/0Ab...', // one-time PKCE code (or a refreshToken)
    redirectUri: 'https://wallet.example/oauth/callback'
  }
})
// descriptor.connection: { kind, status: 'registered', account?, scope?, ... }

Once registered, select it on a Collection by id; reads of the backend reflect its connection status (registered | connected | expired | revoked | unreachable), which a storage-management UI uses to prompt re-consent:

await space.createCollection({
  id: 'photos',
  backend: { id: 'gdrive-personal' }
})

const [, gdrive] = (await space.backends()) ?? []
if (gdrive?.connection?.status === 'expired') {
  // re-consent: swap in fresh connection material (create-or-replace by id)
  await space.updateBackend({
    id: 'gdrive-personal',
    provider: 'google-drive',
    connection: { kind: 'oauth2-google', authorizationCode: '4/0Cd...' }
  })
}

// Deregister (idempotent): forgets the record and its stored connection.
await space.deregisterBackend('gdrive-personal')

registerBackend() throws a ConflictError if the id already exists or the server does not permit the provider; updateBackend() returns the descriptor when it created a record and null when it replaced one in place (the server sends no body on an in-place replace).

A registered backend's record exists immediately, but whether its connection can actually serve bytes depends on the server having a live provider adapter for it. Until then it is registered but inert (status: 'registered').

Encrypted collections (EDV-over-WAS): pass-through encryption via the WAS client (recommended)

This is the recommended way to use encrypted collections. For the low-level alternative -- driving an EdvClientCore directly via WasTransport -- see docs/edv-client-core-usage.md.

Client-side end-to-end encryption is a per-collection concern -- not a backend feature (an encrypted document is opaque JSON any document backend stores faithfully). Two things drive it, kept separate:

• Policy (is this collection encrypted?) is declared on the collection itself: createCollection({ encryption: { scheme: 'edv' } }) writes a non-secret encryption marker to the Collection Description. Any authorized reader -- including a delegated consumer that did not create the collection -- discovers it by reading the Description, so it knows to decrypt.
• Keys come from an encryption provider you pass to WasClient (built from the opt-in @interop/was-client/edv subpath, so plaintext consumers never pull the crypto graph). It is a pure keystore: resolveKeys returns the collection's keys, which live in your wallet. The server only ever stores opaque JWE envelopes.

The ordinary Collection/Resource handles then transparently encrypt on write and decrypt on read for any collection the marker (or an override) declares encrypted.

import { WasClient } from '@interop/was-client'
import { createEdvEncryption } from '@interop/was-client/edv'

const encryption = createEdvEncryption({
  // The keystore: return the collection's keys (from your wallet).
  async resolveKeys({ spaceId, collectionId }) {
    return { keyAgreementKey, keyResolver }
  }
})
const was = WasClient.fromSigner({ serverUrl, signer, encryption })

// Declare the collection encrypted (writes the marker). The returned handle is
// pre-seeded, so the first write encrypts with no extra round-trip.
const vault = await was
  .space(spaceId)
  .createCollection({ id: 'vault', encryption: { scheme: 'edv' } })
const { id } = await vault.add({ secret: 'hello' }) // encrypted; id is an EDV id
const back = await vault.get(id) // { secret: 'hello' } -- decrypted

// A consumer that did not create it discovers the marker and decrypts with its
// own keys -- no override needed; one cached read of the Description:
const same = was.space(spaceId).collection('vault')
await same.get(id) // reads the marker, then decrypts

The switch is the marker: a handle encrypts a collection when its Description declares encryption (resolution reads the Description once, then caches -- no round-trip for plaintext-only clients or when an override is set). Keys are then required: if the collection is declared encrypted but your keystore returns no keys, reads/writes throw EncryptionError (fail-closed) -- they never silently fall back to plaintext.

Per-handle override (escape hatch). Pass encryption in the handle options to force the decision and skip the Description read -- { scheme: 'edv' } (keys from the keystore), { scheme: 'edv', keys } (keys inline), or 'plaintext':

const vault = was.space(spaceId).collection('vault', {
  encryption: { scheme: 'edv' }
})

Migrating a pre-marker vault (created before the marker existed, keys-only): re-declare it once with collection.configure({ encryption: { scheme: 'edv' } }) (the marker is set-once: declaring it on a collection that lacks one is allowed, changing or clearing an existing one is rejected). Until then, a per-handle override reads it correctly.

Encrypted collections are a stricter contract, not a drop-in (documents-only scope for now):

• Ids. add() mints an EDV id (a z-prefixed multibase value used verbatim as the WAS resource id). put(id, ...) accepts only an EDV-format id; a human-readable id is rejected (it would leak onto the URL) -- carry a human-readable label inside the encrypted content instead. By default the minted id is random (the classic mutable-document model); pass createEdvEncryption({ idDerivation: 'content' }) to derive it from the envelope's JWE ciphertext instead, making documents content-addressed -- the id is then stable across replicas (no mapping table), at the cost of immutability (an "update" is delete-old + add-new).
• Metadata. resource.setName() / setTags() / setMeta() work on an encrypted collection: the user-writable custom (name / tags) is encrypted into an envelope before it is sent, so the server never sees the plaintext, and meta() decrypts it back for a keyed reader. The /meta endpoint has its own ETag (metaVersion), independent of the content ETag.
• Binary. A small Blob/Uint8Array is encrypted as a single document; larger binaries are rejected until chunked encrypted blobs land.
• Raw reads. get() decrypts; the getText() / getBytes() escape hatches do not (they return the stored representation).

Export and import

const archive = await space.export() // Uint8Array (application/x-tar)
const stats = await otherSpace.import(archive)
// { collectionsCreated, collectionsSkipped, resourcesCreated, resourcesSkipped,
//   policiesCreated, policiesSkipped }

The manual-request escape hatch

was.request(...) mirrors ezcap's generic request() for hand-built calls. As a deliberate escape hatch it returns the raw HttpResponse and throws raw ezcap/ky errors -- it does not apply the null-on-404 or typed-error conveniences.

const response = await was.request({ path: `/space/${spaceId}`, method: 'GET' })

Errors and the 404/null caveat

Read methods (describe/get/list) return null on a 404, following MongoDB's findOne semantics. WAS returns 404 for both not-found and unauthorized, so null means "not visible to you" rather than strictly "does not exist". Write/delete methods throw a typed error instead.

Status	Read methods	Write / delete methods
404	null	NotFoundError
400	ValidationError	ValidationError
401	AuthRequiredError	AuthRequiredError
409	ConflictError	ConflictError
413	PayloadTooLargeError	PayloadTooLargeError
501	NotImplementedError	NotImplementedError
507	QuotaExceededError	QuotaExceededError
5xx	WasServerError	WasServerError

All error classes extend WasError (carrying status, the problem-kind type URI, title, details, and requestUrl). When the server sends a problem+json type (the spec's Error Type Registry), mapError() dispatches on that kind first and falls back to the HTTP status -- so, for example, a 409 id-conflict from createSpace({ id }) is catchable as a ConflictError, and a 507 quota-exceeded (a client-actionable storage-full condition, not a server fault) as a QuotaExceededError. delete() additionally treats a 404 as success, so it is idempotent.

Spec endpoints a given server has not yet implemented surface as NotImplementedError (the server's 501).

Contribute

PRs accepted. See CONTRIBUTING.md for editor setup (Prettier, ESLint, and EditorConfig) and how it maps to CI.

License

MIT License 2026 Interop Alliance.