dacite

Chapter 5: Sharing

Chapter 4 gave us authorization — authenticated stores where access is proven structurally from roots. Each user has a scoped tree. How does Alice give Bob read access to a subtree without her full root?

No new primitives. Just a shares map convention in every root, plus a claim protocol. Users share with users; server shares with users — uniform mechanism.

5.1 Root Structure Convention

root = {
  \"value\": <app data>,
  \"shares\": {name: {target: #H, authorized: Set}, ...},
  \"groups\": {name: Set, ...}
}

Managed via PUTs.

5.2 Claim Protocol

1. Alice PUTs shares[\"photos\"] = {#T, #{bob}}
2. Alice → Bob OOB: "claim photos from me"
3. Bob → Server: CLAIM \"photos\" alice
4. Server: Alice root → shares["photos"] → bob ∈ auth? → #T to Bob roots
5. Bob GET/PUT from #T (read-only on Alice’s tree)

sequenceDiagram
    participant A as Alice
    participant B as Bob
    participant S as Server

    Note over A: shares["photos"]:<br/>{target: #T, authorized: #{bob}}

    A->>B: out-of-band: "claim 'photos' from me"
    B->>S: CLAIM "photos" from Alice
    Note over S: look up Alice's root<br/>find shares["photos"]<br/>check bob ∈ authorized ✓<br/>extract #T
    S-->>B: added #T to valid roots
    B->>S: GET/PUT using #T as proof root

5.3 Server Uses Shares

server-root.shares = {
  \"alice\": {#RA, #{alice}},
  \"team\": {#TP, #{alice,bob}}
}

Auth = claim server share. No special server state.

graph TD
    SR["Server Root"] --> SV["value: config"]
    SR --> SS["shares"]
    SS --> SA["'alice': {#RA, #{alice}}"]
    SS --> SB["'bob': {#RB, #{bob}}"]
    SS --> ST["'team': {#TP, #{alice,bob,carol}}"]
    SA --> RA["Alice's tree"]
    SB --> RB["Bob's tree"]
    ST --> TP["Team tree"]
    style SR fill:#4a9,stroke:#333,color:#fff

5.4 Read-Only + Edit Flow

Claim → read/incorporate → your share back. Bidirectional, no write-back.

5.5 Named Groups

authorized: \"team\" → root.groups["team"] = #{alice,bob}

Update once → everywhere.

\"public\": #{neg} — cofinite (Ch2).

5.6 Share Types

Type	Auth Set
Private	#{me}
Direct	#{me,bob}
Shared	#{team}
Public	#{neg}

5.7 Named Refs

Alice updates target → Bob reclaims latest. Revoke: dissoc/auth change.

5.8 Patterns

Photos: update target. Edits: re-share modified. Team: multi-auth share.

5.9 Cross-User Sharing

graph TD
    AE["Alice's tree"] --> SM["Shared subtree #SM"]
    BE["Bob's tree"] --> SM
    SM --> N1["shared nodes"]
    SM --> N2["shared nodes"]
    style SM fill:#aa4,stroke:#333,color:#fff

Deduplication natural.

5.10 Audit

Proof chains = trail.

5.11 Eliminated Concepts

Old	New
Grants/lifecycle	Shares in data
Gift queues	Claim-time lookup
Service root	Server shares

5.12 API Surface

Primitives

Fn	Sig
claim	(Server, id, sharer, name) → #H
authorized?	(Root, name, id) → bool

Derived

share, unshare, add-group — hamt ops.

Zero new primitives — conventions atop Ch4.

5.13 What This Provides

1. Subtree sharing — scoped by construction
2. Uniform — server/users same root/protocol
3. Mutable refs — via normal PUTs (no protocol mutability)
4. Composability — re-share received data

Top of stack: hash → values → stores → auth → sharing.

This site is open source. Improve this page.