Merge pull request 'A provisioner is told what the mesh derived for each consumer (hq ADR 0201, issue 124)' (#10) from feat/a-provider-declares-what-it-derives into main

src/provisioner/index.ts

@@ -23,6 +23,16 @@ export interface Provision {
   readonly password: string;
   /** What the consumer contributed, per the interface's spec keys (e.g. `{ name: "umami" }`). */
   readonly values: Readonly<Record<string, unknown>>;
+  /** What this provider's own definition said it derives for this consumer, already derived by
+   *  the mesh (novox/hq ADR 0201).
+   *
+   *  **The rule is declared, not computed here.** A provider that names the resource it gives each
+   *  consumer — a bucket, a database, a vhost — writes that name in its `serves` block with
+   *  `${consumer:as}` or `${consumer:as:dns}` in it. The mesh fills it for this consumer and hands
+   *  the same filled value to the consumer's own configuration, so the two ends cannot disagree.
+   *  An adapter reads it from here; an adapter that recomputed it would be the second rule this
+   *  removed. Empty for a provider that derives nothing. */
+  readonly derived: Readonly<Record<string, unknown>>;
   /** Where the consumer is, for a provider that must reach back to it. Usually unused. */
   readonly at?: string;
   /** The consumer node, for logging and lifecycle events. */
@@ -34,7 +44,12 @@ export interface Provision {
  *  the credential is the mesh's, already delivered to the consumer. */
 export interface Adapter {
   create(p: Provision): Promise<void>;
-  remove(p: { readonly as: string }): Promise<void>;
+  /** Withdraw what `create` made for this consumer. `derived` is what the mesh last derived for
+   *  it, remembered by the harness: the mesh has already dropped the consumer from the
+   *  contributions file by the time this is called, so it cannot be read again, and a provider
+   *  that recomputed it would be keeping the second copy of a rule this removed
+   *  (novox/hq ADR 0201). */
+  remove(p: { readonly as: string; readonly derived: Readonly<Record<string, unknown>> }): Promise<void>;
   /** Optional: whether the backend still holds this consumer's credential exactly as `p` says.
    *  Asked of every consumer already applied, every `verifyEveryMs`. `false` makes the harness apply
    *  it again on the same pass, so a backend that lost what it was given (a server restarted
@@ -69,6 +84,7 @@ interface Contribution {
   readonly node?: string;
   readonly at?: string;
   readonly values?: Readonly<Record<string, unknown>>;
+  readonly derived?: Readonly<Record<string, unknown>>;
 }
 
 /**
@@ -88,7 +104,9 @@ export function runProvisioner(resource: string, adapter: Adapter, opts: Provisi
   // hour rather than one a minute, and it is said loudly rather than quietly repeated.
   const lost = new Map<string, { times: number; nextAt: number }>();
 
-  const applied = new Map<string, string>(); // login (`as`) -> hash of what was last applied
+  // login (`as`) -> what was last applied: the hash that says whether it changed, and the
+  // derivation to hand back on withdrawal, which by then is no longer in the file.
+  const applied = new Map<string, { hash: string; derived: Readonly<Record<string, unknown>> }>();
   let stopped = false;
 
   async function reconcile(): Promise<void> {
@@ -112,12 +130,14 @@ export function runProvisioner(resource: string, adapter: Adapter, opts: Provisi
         console.error(`[provisioner:${resource}] ${g.as}: secret not readable yet (${g.secret}): ${err}`);
         continue;
       }
-      const h = hash(g.as, password, g.values ?? {});
-      const p: Provision = { as: g.as, password, values: g.values ?? {}, at: g.at, consumer: g.node };
+      const h = hash(g.as, password, g.values ?? {}, g.derived ?? {});
+      const p: Provision = {
+        as: g.as, password, values: g.values ?? {}, derived: g.derived ?? {}, at: g.at, consumer: g.node,
+      };
       // Set when the backend reported this consumer lost: how many successful re-applies in a row
       // it has now needed, counting this one.
       let reapplying: number | undefined;
-      if (applied.get(g.as) === h) {
+      if (applied.get(g.as)?.hash === h) {
         if (!verifying) continue;
         const brake = lost.get(g.as);
         if (brake && Date.now() < brake.nextAt) continue;
@@ -148,7 +168,7 @@ export function runProvisioner(resource: string, adapter: Adapter, opts: Provisi
       }
       try {
         await adapter.create(p);
-        applied.set(g.as, h);
+        applied.set(g.as, { hash: h, derived: p.derived });
         if (reapplying === undefined) {
           // Applied for a new login, password or values: whatever was counted before does not carry over.
           lost.delete(g.as);
@@ -171,10 +191,10 @@ export function runProvisioner(resource: string, adapter: Adapter, opts: Provisi
     // Withdraw every login the provider made that the mesh no longer asks for. The mesh drops a
     // consumer from the file when it goes away; that is how a login is withdrawn rather than kept
     // working for ever. Only logins this harness created are touched.
-    for (const as of [...applied.keys()]) {
+    for (const [as, was] of [...applied.entries()]) {
       if (wantByAs.has(as)) continue;
       try {
-        await adapter.remove({ as });
+        await adapter.remove({ as, derived: was.derived });
         applied.delete(as);
         lost.delete(as);
       } catch (err) {
@@ -247,8 +267,16 @@ function scrub(err: unknown, password: string): string {
   return text;
 }
 
-function hash(as: string, password: string, values: Readonly<Record<string, unknown>>): string {
-  return JSON.stringify([as, password, values]);
+function hash(
+  as: string,
+  password: string,
+  values: Readonly<Record<string, unknown>>,
+  derived: Readonly<Record<string, unknown>>,
+): string {
+  // The derivation is in the hash because it can change without the login or the password
+  // changing: a provider that renames what it derives has given this consumer a different
+  // resource, and an adapter trusted from memory would never be told (novox/hq ADR 0201).
+  return JSON.stringify([as, password, values, derived]);
 }
 
 function envOrThrow(name: string): string {