Split linkDown() into canCarry() and droppedWhileDraining()

docs/decisions.md

@@ -761,12 +761,12 @@ rule and an index of the titles below.
   round trip before the bind is answered, so gating on `closed` let a send arriving in that window go
   out unbound and come back `ESME_RINVBNDSTS`. `LinkGate` owns the answer instead — `shut(returning)`
   on every teardown, `open()` only once `comeBackUp()` has a bound link — and
-  `OutgoingRequests.linkDown()` reads it rather than `closed`. The bind itself cannot wait for what it
+  `OutgoingRequests.canCarry()` reads it rather than `closed`. The bind itself cannot wait for what it
   creates, so `pastDrain()` lets the three bind commands past the gate and the window, the same door
   `unbind()` takes through `now()`. The gate is told what happened and never reads back into the
   session: a collaborator that has to ask does not own its decision, which is how the first cut ended
   up answering the same question two different ways at admit and at release. For the same reason the
-  retry in `pastDrain()` asks `gate.isUp()` rather than `linkDown()`, which also reads the socket — a
+  retry in `pastDrain()` asks `gate.isUp()` rather than `canCarry()`, which also reads the socket — a
   condition that loops on something the gate does not gate on spins against a gate that admits it
   straight back. `LinkGate.returning` is a copy of `retrying()` taken at teardown, and stays true
   only because nothing stops the reconnect loop without `emitClose()` following it: `drain()` and

src/outgoing-requests.ts

@@ -51,9 +51,14 @@ export class OutgoingRequests {
 		this.window = new SendWindow({ limit: options.maxOutstanding, log: options.log });
 	}
 
-	/** Read through a method: a drop can land while a request is awaiting. */
+	/** Whether a request made now reaches the socket. Read through a method: a drop can land while one awaits. */
-	linkDown(): boolean {
+	canCarry(): boolean {
-		return !this.gate.isUp() || this.transport.sock.destroyed;
+		return this.gate.isUp() && !this.transport.sock.destroyed;
+	}
+
+	/** The link went while draining, so the teardown settled what the drain waited on, not the peer. */
+	droppedWhileDraining(): boolean {
+		return this.draining && !this.canCarry();
 	}
 
 	/** A link is up and bound, so everything held for one goes out on it. */
@@ -84,8 +89,8 @@ export class OutgoingRequests {
 
 		if (wrong) return Promise.resolve({ err: wrong });
 
-		// A drain on a live link. A link that is down is the gate's answer, which says closed instead.
+		// With no link, the gate answers instead, and says closed.
-		if (this.draining && !this.linkDown()) {
+		if (this.draining && this.canCarry()) {
 			return Promise.resolve({ err: new Error('Session is shutting down') });
 		}
 

src/session.ts

@@ -333,7 +333,8 @@ export class Session extends EventEmitter<SessionEvents> {
 		this.reconnectLoop?.stop();
 		this.outgoing.stopAccepting();
 
-		if (this.outgoing.linkDown()) return {};
+		// No link, so nothing is on the wire to wait out.
+		if (!this.outgoing.canCarry()) return {};
 
 		const timeout = this.options.shutdownTimeout ?? defaults.shutdownTimeout;
 		const deadline = timeout > 0 ? Date.now() + timeout : 0;
@@ -341,8 +342,7 @@ export class Session extends EventEmitter<SessionEvents> {
 		const messages = await this.incoming.drain(this.answering(timeout), signal);
 		const requests = await this.outgoing.drain(leftOf(deadline), signal);
 
-		// The window empties on a teardown too, which settles everything the link was carrying.
+		if (this.outgoing.droppedWhileDraining()) {
-		if (this.outgoing.linkDown()) {
 			return { err: new Error('The session closed before the drain finished') };
 		}
 

todo.md

@@ -199,15 +199,10 @@ next work ([decision](docs/decisions.md#internals-and-tests)).
 
 ### Locality — next, ahead of everything below; 5–6 today, and the gate is 7
 
-- [ ] **Split the two questions `OutgoingRequests.linkDown()` answers.** `Session.drain()` calls it
-      twice for opposite conclusions — "nothing to drain, success" and "the link died under us,
-      failure" — and `outgoing-requests.ts` reads it a third way. Two named predicates. Named by 7
-      of 9 readers, who each reconstructed the ordering by hand.
-
 - [ ] **Name `pastDrain()`'s retry condition and what makes the loop end.** The exit is a
       three-term disjunction over two collaborators, whose comment covers the first term only, and
       the method is named for what it bypasses. Do not change what it asks: `gate.isUp()` rather than
-      `linkDown()` is deliberate and recorded.
+      `canCarry()` is deliberate and recorded.
 
 - [ ] **Replace `resolveBody`'s `settles` boolean with the decision it stands for.** One boolean
       chooses both whether to overwrite `data_coding` and which params to read it from, across four