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* Sheafify a set of providers into an authority manager.
*
* `sheafify({ name, providers })` returns a `Sheaf` — an immutable object
* that produces dispatch sections over a fixed set of providers.
*
* Each dispatch through a granted section:
* 1. Filters to providers whose guard covers the point (getMatchingProviders)
* 2. Collapses equivalent candidates (same metadata → one representative)
* 3. Decomposes metadata into constraints + options
* 4. Invokes the policy on the distinguished options
* 5. Dispatches to some element of the chosen candidate
*/
import { makeExo } from '@endo/exo';
import { M } from '@endo/patterns';
import type { InterfaceGuard } from '@endo/patterns';
import type { MethodSchema } from '@metamask/kernel-utils';
import { makeDiscoverableExo } from '@metamask/kernel-utils';
import { stringify } from '@metamask/kernel-utils';
import { asyncifyMethodGuards } from './guard.ts';
import { getMatchingProviders } from './match.ts';
import { evaluateMetadata } from './metadata.ts';
import type {
Candidate,
MetadataSpec,
Section,
Policy,
PolicyContext,
Provider,
Sheaf,
} from './types.ts';
type EncodedEntry = [key: string, type: string, value: unknown];
const encodeMetadataEntry = (key: string, value: unknown): EncodedEntry => {
if (value === undefined) {
return [key, 'undefined', null];
}
if (typeof value === 'bigint') {
return [key, 'bigint', String(value)];
}
if (typeof value === 'number') {
if (Number.isNaN(value)) {
return [key, 'NaN', null];
}
if (value === Infinity) {
return [key, '+Infinity', null];
}
if (value === -Infinity) {
return [key, '-Infinity', null];
}
if (Object.is(value, -0)) {
return [key, '-0', null];
}
}
return [key, typeof value, value];
};
/**
* Serialize metadata for equivalence-class keying (collapse step).
*
* Uses type-tagged encoding so that values JSON.stringify conflates
* (undefined, null, NaN, Infinity, -Infinity) produce distinct keys.
*
* @param metadata - The metadata value to serialize.
* @returns A string key for equivalence comparison.
*/
const metadataKey = (metadata: Record<string, unknown>): string => {
const keys = Object.keys(metadata);
if (keys.length === 0) {
return 'null';
}
const entries = Object.entries(metadata)
.sort(([a], [b]) => a.localeCompare(b))
.map(([key, val]) => encodeMetadataEntry(key, val));
return JSON.stringify(entries);
};
/**
* Collapse candidates into equivalence classes by metadata identity.
* Returns one representative per class; the choice within a class is arbitrary.
*
* @param candidates - The candidates to collapse.
* @returns One representative per equivalence class.
*/
const collapseEquivalent = <MetaData extends Record<string, unknown>>(
candidates: Candidate<MetaData>[],
): Candidate<MetaData>[] => {
const seen = new Set<string>();
const representatives: Candidate<MetaData>[] = [];
for (const entry of candidates) {
const key = metadataKey(entry.metadata);
if (!seen.has(key)) {
seen.add(key);
representatives.push(entry);
}
}
return representatives;
};
/**
* Decompose candidate metadata into constraints (shared by all) and
* stripped candidates (carrying only distinguishing keys).
*
* @param candidates - The collapsed candidates.
* @returns Constraints and stripped candidates.
*/
const decomposeMetadata = <MetaData extends Record<string, unknown>>(
candidates: Candidate<MetaData>[],
): {
constraints: Partial<MetaData>;
stripped: Candidate<Partial<MetaData>>[];
} => {
const constraints: Record<string, unknown> = {};
const head = candidates[0];
Iif (head === undefined) {
return { constraints: {} as Partial<MetaData>, stripped: [] };
}
const first = head.metadata;
for (const key of Object.keys(first)) {
const val = first[key];
const shared = candidates.every((entry) => {
const meta = entry.metadata;
return Object.hasOwn(meta, key) && Object.is(meta[key], val);
});
if (shared) {
constraints[key] = val;
}
}
const stripped = candidates.map((entry) => {
const remaining: Record<string, unknown> = {};
for (const [key, val] of Object.entries(entry.metadata)) {
if (!Object.hasOwn(constraints, key)) {
remaining[key] = val;
}
}
return { exo: entry.exo, metadata: remaining as Partial<MetaData> };
});
return { constraints: constraints as Partial<MetaData>, stripped };
};
/**
* Invoke a method on a section exo, throwing if the handler is missing.
*
* @param exo - The section exo to invoke.
* @param method - The method name to call.
* @param args - The positional arguments.
* @returns The synchronous return value of the method (typically a Promise).
*/
const invokeExo = (exo: Section, method: string, args: unknown[]): unknown => {
const obj = exo as Record<string, (...a: unknown[]) => unknown>;
const fn = obj[method];
if (fn === undefined) {
throw new Error(`Section has guard for '${method}' but no handler`);
}
return fn.call(obj, ...args);
};
type ResolvedProvider<M extends Record<string, unknown>> = {
exo: Section;
spec: MetadataSpec<M> | undefined;
};
const drivePolicy = async <M extends Record<string, unknown>>(
policy: Policy<M>,
candidates: Candidate<Partial<M>>[],
context: PolicyContext<M>,
invoke: (candidate: Candidate<Partial<M>>) => Promise<unknown>,
): Promise<unknown> => {
const errors: unknown[] = [];
const gen = policy(candidates, context);
let next = await gen.next([...errors]);
while (!next.done) {
try {
const result = await invoke(next.value);
await gen.return(undefined);
return result;
} catch (error) {
errors.push(error);
next = await gen.next([...errors]);
}
}
throw new Error(`No viable section for ${context.method}`, {
cause: errors,
});
};
export const sheafify = <
MetaData extends Record<string, unknown> = Record<string, unknown>,
>({
name,
providers,
}: {
name: string;
providers: Provider<MetaData>[];
}): Sheaf<MetaData> => {
const frozenProviders: readonly ResolvedProvider<MetaData>[] = harden(
providers.map((provider) => ({
exo: provider.exo,
spec: provider.metadata,
})),
);
const buildSection = ({
guard,
policy,
schema,
}: {
guard: InterfaceGuard;
policy: Policy<MetaData>;
schema?: Record<string, MethodSchema>;
}): object => {
const asyncMethodGuards = asyncifyMethodGuards(guard);
const asyncGuard =
schema === undefined
? M.interface(`${name}:section`, asyncMethodGuards)
: M.interface(`${name}:section`, asyncMethodGuards, {
defaultGuards: 'passable',
});
const dispatch = async (
method: string,
args: unknown[],
): Promise<unknown> => {
const candidates = getMatchingProviders(frozenProviders, method, args);
const evaluatedCandidates: Candidate<MetaData>[] = candidates.map(
(provider) => ({
exo: provider.exo,
metadata: evaluateMetadata(provider.spec, args),
}),
);
switch (evaluatedCandidates.length) {
case 0:
throw new Error(`No section covers ${method}(${stringify(args, 0)})`);
case 1:
return invokeExo(
(evaluatedCandidates[0] as Candidate<MetaData>).exo,
method,
args,
);
default: {
const collapsed = collapseEquivalent(evaluatedCandidates);
if (collapsed.length === 1) {
return invokeExo(
(collapsed[0] as Candidate<MetaData>).exo,
method,
args,
);
}
const { constraints, stripped } = decomposeMetadata(collapsed);
const strippedToCollapsed = new Map(
stripped.map((strippedCandidate, i) => [
strippedCandidate,
collapsed[i] as Candidate<MetaData>,
]),
);
return drivePolicy(
policy,
stripped,
{ method, args, constraints },
async (candidate) => {
const resolved = strippedToCollapsed.get(candidate);
if (resolved === undefined) {
throw new Error(
`Policy yielded an unrecognized candidate for '${method}'. ` +
`The yielded value must be one of the Candidate objects ` +
`passed into the policy (object identity, not structural equality). ` +
`Did the policy construct a new object instead of yielding from the candidates array?`,
);
}
return invokeExo(resolved.exo, method, args);
},
);
}
}
};
const handlers: Record<string, (...args: unknown[]) => Promise<unknown>> =
{};
for (const method of Object.keys(asyncMethodGuards)) {
handlers[method] = async (...args: unknown[]) => dispatch(method, args);
}
const exo = (schema === undefined
? makeExo(`${name}:section`, asyncGuard, handlers)
: makeDiscoverableExo(
`${name}:section`,
handlers,
schema,
asyncGuard,
)) as unknown as Section;
return exo;
};
const getSection = ({
guard,
policy,
}: {
guard: InterfaceGuard;
policy: Policy<MetaData>;
}): object => buildSection({ guard, policy });
const getDiscoverableSection = ({
guard,
policy,
schema,
}: {
guard: InterfaceGuard;
policy: Policy<MetaData>;
schema: Record<string, MethodSchema>;
}): object => buildSection({ guard, policy, schema });
return harden({
getSection,
getDiscoverableSection,
});
};
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