spendbook

import "gno.land/p/g1qp5pt8cdq2f6kfdamn3yuxwg6quqnfpyewzz39/spendbook"

import "gno.land/p/g1ut6uspuh73e02yauxpmyt8g3wwddaq8utagvm3/spendbook"

book = spendbook.MustNew(MaxLiveGrants)

curl -sS 'https://gno.land/p/g1qp5pt8cdq2f6kfdamn3yuxwg6quqnfpyewzz39/spendbook$download&file=spendbook.gno' | shasum -a 256

curl -sS 'https://onyx.testnets.gno.land/p/g1ut6uspuh73e02yauxpmyt8g3wwddaq8utagvm3/spendbook$download&file=spendbook.gno' | shasum -a 256

Overview

Package spendbook is a pure allowance primitive for realms that need to let one party spend another party's funds, up to a bounded amount, over many transactions. It is to *delegated spending* what duebook is to *time*: it holds no coins, performs no effects, imports no chain APIs, and owns no package-level state. The importing realm owns a *Book, supplies the clock, and performs its own effects.

Why this package exists

The ecosystem's existing allowance primitive, gno.land/p/jaekwon/allowancesender/v0, is scoped to a single call and says so in its own documentation:

"Allowance survives across N txs but not N+1 txs." Use a session counter pattern in the granter realm; this package's Close is binary, not deadline-based.

It then declines block-height expiry on the grounds that it "would require runtime cooperation". That is true only for a package that reads the clock itself. spendbook does not: every operation takes `now` as an argument, which makes the window arithmetic a pure function and the whole package unit-testable without a chain. Three application realms in the searched sources each hand-rolled this mechanism internally rather than importing one; see DISCOVERY.md.

The one idea

An allowance is not a balance. It is a *permission with a ceiling that refills*. The owner says "this spender may draw at most PerPeriod per window, at most Total ever, until ExpiresAt, and I can revoke it now":

if err := book.Spend(id, spenderKey, now, amount); err != nil { panic(err) // revoked, expired, over the window cap, over the total } // ... the realm moves the coins here, under its own authority

Spend checks every bound and CONSUMES the allowance in the same call, before returning. The realm then acts. Because the realm performs the effect itself, no closure, callback, or capability ever crosses a realm boundary. spendbook cannot be handed code to run, so it cannot be tricked into running the wrong code.

Windows are anchored, not sliding

A window is derived from a fixed origin — the Anchor set at Open — by integer division:

index(now) = (now - Anchor) / PeriodLength

so the boundaries are the same for everyone and a spender cannot reset a window by choosing when to call. A sliding "PerPeriod per trailing N blocks" window would let a spender draw the full cap at the end of one trailing span and again at the start of the next; anchoring removes the choice. The refill is a RESET, not a carry: an unused allowance does not accumulate into the next window, because the point of the cap is to bound worst-case loss per window, and a carry would unbound it.

PeriodLength == 0 means one window that never rolls: a pure lifetime allowance, where PerPeriod is the only cap that matters.

Amendments cannot enlarge the live window

An owner who could raise PerPeriod mid-window would be able to undo the bound a spender is relying on, and — worse in the other direction — an owner who drains a relationship and then lowers terms retroactively could strand a spender mid-settlement. The rule here is one-sided and enforced in Amend:

• TIGHTER-OR-EQUAL terms apply IMMEDIATELY. Lowering a ceiling can never authorize a draw that was not already authorized, so there is no reason to delay it, and delaying it would make the owner's only fast remedy Revoke.
• LOOSER terms are PENDING and take effect at the next window boundary, never inside the current one.

This is the same adversarial problem that r/samcrew/agent_registry_v2 solves by locking its price while any credit entry exists; the shape here is a deferral rather than a lock, so terms can still move.

With PeriodLength == 0 there is no next boundary, so a loosening amendment is refused with ErrNoBoundary rather than silently queued forever. PeriodLength itself is IMMUTABLE: changing it would move every future boundary, which is an enlargement vector wearing a different hat.

State growth

Revoked allowances are removed, not archived. IDs are allocated monotonically and never reused, so a revoked ID can never be resurrected and there is nothing to keep. Live allowances are capped per Book at construction, so storage is bounded by maxLive regardless of how many allowances have ever existed. Audit history belongs in the consuming realm's events.

An EXPIRED allowance is not self-removing, and bounded storage is not the same as a usable Book: Spend refuses it forever while it still holds a slot. Reap exists for exactly that and is permissionless, because an expired allowance can authorize nothing and so removing it takes nothing from anyone.

What this package does NOT bound is how many of a Book's slots ONE owner may hold — maxLive is a single global figure, so any owner permitted to Open can exhaust it and lock out the rest. That is a policy question with no answer a primitive can pick (per-owner quota? first-come? owner whitelist?), so it is left where the authentication already lives: the consuming realm decides who may Open, and a Book shared across mutually untrusting owners needs its own per-owner cap on top of this one. Named here rather than implied, because "bounded" reads like "safe to share".

Consumer contract (the parts the package cannot enforce)

1. SUPPLY A REAL CLOCK. spendbook cannot verify that `now` came from runtime.ChainHeight() or time.Now().Unix(). A realm that lets a caller choose `now` has handed the spender the power to roll the window at will, which defeats every cap in this package. Pass the chain's own clock, and use the same units for the life of the Book.
2. AUTHENTICATE THE SPENDER KEY. spendbook compares the key string it is given against the one recorded at Open. It cannot tell whether that string is the real caller. Derive it from cur.Previous().Address(), never from an argument the caller supplies.
3. SPEND BEFORE SENDING. Spend consumes the allowance and returns; the realm then moves coins. Doing it in the other order means a failed send leaves the allowance consumed, or a successful send leaves it unconsumed — both are real losses. State first, effect second.
4. AN ALLOWANCE IS NOT CUSTODY. spendbook authorizing 100 does not mean 100 exists. The realm must check its own held balance separately; this package bounds permission, not solvency.

Imports

• errors
• gno.land/p/nt/avl/v0
• strconv

Constants and variables

MaxKeyLen bounds an owner or spender key. A bech32 gno address is 40 characters; the headroom exists so a realm may namespace its keys.

const MaxKeyLen = 128

MaxLiveLimit is the largest maxLive a Book may be constructed with. It bounds the worst-case cost of Iterate, which scans the live set.

const MaxLiveLimit = 10000

Errors returned by Book operations.

var (
	ErrInvalidConfig  = errors.New("spendbook: invalid book configuration")
	ErrEmptyOwner     = errors.New("spendbook: empty owner key")
	ErrEmptySpender   = errors.New("spendbook: empty spender key")
	ErrKeyTooLong     = errors.New("spendbook: key exceeds MaxKeyLen")
	ErrInvalidNow     = errors.New("spendbook: now must be non-negative")
	ErrInvalidTerms   = errors.New("spendbook: invalid terms")
	ErrInvalidAmount  = errors.New("spendbook: amount must be positive")
	ErrBookFull       = errors.New("spendbook: live allowance cap reached")
	ErrNotFound       = errors.New("spendbook: no such live allowance")
	ErrNotExpired     = errors.New("spendbook: allowance has not expired")
	ErrNotOwner       = errors.New("spendbook: caller does not own this allowance")
	ErrNotSpender     = errors.New("spendbook: caller is not this allowance's spender")
	ErrExpired        = errors.New("spendbook: allowance has expired")
	ErrNotStarted     = errors.New("spendbook: allowance has not started")
	ErrPeriodExceeded = errors.New("spendbook: amount exceeds the window cap")
	ErrTotalExceeded  = errors.New("spendbook: amount exceeds the lifetime cap")
	ErrNoBoundary     = errors.New("spendbook: no reachable next window boundary")
	ErrOverflow       = errors.New("spendbook: int64 overflow")
	ErrIDExhausted    = errors.New("spendbook: identifier space exhausted")
)

Types

type Allowance

type Allowance struct {
	ID        uint64
	Owner     string
	Spender   string
	Terms     Terms
	Anchor    int64 // window origin; also the earliest spendable instant
	CreatedAt int64

	SpentTotal  int64 // over the allowance's whole life
	SpentWindow int64 // within WindowIndex
	WindowIndex int64

	// Pending terms, applied at the next window boundary. Meaningful only
	// when HasPending is true.
	Pending    Terms
	HasPending bool
}

Allowance is one owner's grant to one spender. It is returned BY VALUE: holders cannot reach into a Book through it.

Exported field	Type	Doc
ID	uint64
Owner	string
Spender	string
Terms	Terms
Anchor	int64	window origin; also the earliest spendable instant
CreatedAt	int64
SpentTotal	int64	over the allowance's whole life
SpentWindow	int64	within WindowIndex
WindowIndex	int64
Pending	Terms	Pending terms, applied at the next window boundary. Meaningful only when HasPending is true.
HasPending	bool

Allowance.IsExpired

func (a Allowance) IsExpired(now int64) bool

IsExpired reports whether the allowance is past its expiry at now. An allowance with no expiry is never expired.

Allowance.Remaining

func (a Allowance) Remaining(now int64) int64

Remaining reports how much the spender may draw right now: the lesser of what the current window leaves and what the lifetime cap leaves. It is 0 for an allowance that is expired, not yet started, or fully drawn.

It is a projection, not a reservation. Nothing is held, and the figure can change in the same block if someone else's call advances the clock past a boundary.

type Book

type Book struct {
	maxLive int
	nextID  uint64    // never decreases; IDs are never reused
	live    *avl.Tree // padded id -> Allowance
}

Book holds the live allowances of one consuming realm. The zero value is not usable; construct with New.

Book.Amend

func (b *Book) Amend(id uint64, owner string, now int64, terms Terms) (bool, error)

Amend changes an allowance's terms. Only its owner may amend.

PeriodLength is immutable and must be passed unchanged. Terms that are weakly tighter in every dimension apply immediately; anything looser becomes pending and takes effect at the next window boundary. A lifetime allowance has no next boundary, so a loosening amendment on one is refused with ErrNoBoundary.

The returned bool reports whether the amendment applied immediately (true) or was queued (false). A caller that ignores it cannot tell whether the new ceiling is in force, which is exactly the thing worth knowing.

Book.Count

func (b *Book) Count() int

Count returns the number of live allowances.

Book.Get

func (b *Book) Get(id uint64) (Allowance, error)

Get returns a copy of a live allowance.

Book.Iterate

func (b *Book) Iterate(fn func(Allowance) bool)

Iterate calls fn for every live allowance in id order, stopping early if fn returns true. The allowance is passed by value, so fn cannot mutate the book through it.

Book.MaxLive

func (b *Book) MaxLive() int

MaxLive returns the Book's cap on simultaneously live allowances.

Book.Open

func (b *Book) Open(owner, spender string, now int64, terms Terms) (uint64, error)

Open records a new allowance and returns its id. now becomes the window anchor and the earliest instant the spender may draw.

An owner may open several allowances for the same spender; they are independent, and the ids are what tell them apart. spendbook does not merge or deduplicate them, because "one allowance per pair" is a policy some consuming realms want and others do not, and a primitive that decided it here could not be talked out of it.

Book.Reap

func (b *Book) Reap(id uint64, now int64) error

Reap removes an allowance that has expired at now, and may be called by anyone. It returns ErrNotFound for an unknown id and ErrNotExpired for one that is still alive.

Permissionless on purpose, and the reasoning is the whole justification: an expired allowance can never authorize another draw, so removing it takes nothing from the owner and grants nothing to the caller. Without it an expiry is a slow leak against maxLive -- Spend refuses the dead allowance forever while it holds a slot, so a Book shared between owners could fill with corpses and refuse new Opens, and the only remedy would be the owner of each corpse noticing and calling Revoke.

This relies on `now` exactly as much as Spend does. A realm that lets a caller choose `now` has already broken consumer contract item 1, and such a realm would let a caller reap a LIVE allowance by naming a future instant.

Book.Remaining

func (b *Book) Remaining(id uint64, now int64) int64

Remaining reports what the spender of id may draw at now, or 0 if there is no such live allowance. A caller that must distinguish "nothing left" from "no such allowance" should use Get.

Book.Revoke

func (b *Book) Revoke(id uint64, owner string) error

Revoke removes an allowance. Only its owner may revoke, and it takes effect immediately -- there is no window to wait for, because revocation is the owner's remedy and a delayed remedy is not one.

The id is not reused, so a revoked allowance cannot be resurrected: a later Spend on it returns ErrNotFound forever.

Book.Spend

func (b *Book) Spend(id uint64, spender string, now int64, amount int64) error

Spend consumes amount from allowance id on behalf of spender and returns nil if every bound permits it. The caller then performs its own effect.

On any error NOTHING is consumed. The write happens once, after the last check, so a refused Spend leaves the book exactly as it was.

type Terms

type Terms struct {
	PerPeriod    int64
	PeriodLength int64
	Total        int64
	ExpiresAt    int64
}

Terms are the ceilings on an allowance. Zero has a distinct meaning in three of the four fields and it is never "zero allowed":

PerPeriod > 0 required. The cap per window. PeriodLength 0 means ONE window that never rolls (lifetime). Total 0 means no lifetime cap. ExpiresAt 0 means no expiry.

Functions

MustNew

func MustNew(maxLive int) *Book

MustNew is New but panics on error.

New

func New(maxLive int) (*Book, error)

New returns an empty Book. maxLive caps simultaneously live allowances and must be in [1, MaxLiveLimit].

---

Doc text is reproduced as vm/qdoc returns it. The node markdown-escapes doc comments, so a bracket or angle bracket may carry a backslash the committed source does not have. The source itself is at source and in this repository.