docs/decisions.md

@@ -761,16 +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.canCarry()` reads it rather than `closed`. The bind itself cannot wait for what it
+  `OutgoingRequests.canCarry()` reads it rather than `closed`. The gate is told what happened and
-  creates, so `pastDrain()` lets the three bind commands past the gate and the window, the same door
+  never reads back into the session: a collaborator that has to ask does not own its decision, which
-  `unbind()` takes through `now()`. The gate is told what happened and never reads back into the
+  is how the first cut ended up answering the same question two different ways at admit and at
-  session: a collaborator that has to ask does not own its decision, which is how the first cut ended
+  release. The retry in `carry()` asks `gate.awaitsNextLink()` rather than `canCarry()`, which also
-  up answering the same question two different ways at admit and at release. For the same reason the
+  reads the socket: a loop condition the gate does not gate on spins against a gate that admits it
-  retry in `pastDrain()` asks `gate.isUp()` rather than `canCarry()`, which also reads the socket — a
+  straight back.
-  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
-  `end()` are the only callers of `stop()`. A third caller has to shut the gate itself.
 
 
 ## Internals and tests

src/link-gate.ts

@@ -42,6 +42,11 @@ export class LinkGate {
 		return this.up;
 	}
 
+	/** Shut, with another link on its way to reopen it. */
+	awaitsNextLink(): boolean {
+		return !this.up && this.returning;
+	}
+
 	/** Why the gate will never admit a request, or undefined while one may still get through. */
 	refusal(): Error | undefined {
 		return this.up || this.returning ? undefined : over();

src/outgoing-requests.ts

@@ -93,11 +93,11 @@ export class OutgoingRequests {
 			return Promise.resolve({ err: new Error('Session is shutting down') });
 		}
 
-		return this.pastDrain(input, options);
+		return this.carry(input, options);
 	}
 
-	/** The same path without that refusal, which a receipt for a held message has to take. */
+	/** The same path without the drain's refusal, which a receipt for a held message has to take. */
-	async pastDrain(
+	async carry(
 		input: PduObjectInput,
 		options: SendOptions,
 	): Promise<Result<{ pduObj: PduObject }>> {
@@ -125,8 +125,7 @@ export class OutgoingRequests {
 
 			const attempt = await this.attempt(input, options).finally(() => { this.window.release(); });
 
-			// Nothing reached the socket, so the next link carries it instead of the caller resending.
+			if (!this.retriesOnNextLink(attempt)) return attempt.result;
-			if (!attempt.retryOnNextLink || this.gate.isUp() || this.gate.refusal()) return attempt.result;
 		}
 	}
 
@@ -151,6 +150,12 @@ export class OutgoingRequests {
 		return { err: new Error(`Shut down with ${String(unfinished)} request(s) unfinished`) };
 	}
 
+	/** Nothing reached the socket, so the next link carries it instead of the caller resending. */
+	private retriesOnNextLink(attempt: Attempt): boolean {
+		// Until the gate is shut it admits the retry straight back onto the dead socket, and the loop spins.
+		return attempt.retryOnNextLink && this.gate.awaitsNextLink();
+	}
+
 	/** Why a request cannot go out at all, as opposed to not yet. */
 	private refuse(input: PduObjectInput, options: SendOptions): Error | undefined {
 		// Before the gate and the window, or an aborted call waits for what it will never use.

src/session.ts

@@ -261,7 +261,7 @@ export class Session extends EventEmitter<SessionEvents> {
 			reportError: err => { this.emit('sessionError', err); },
 			reportMessageDlr: merged => { this.emit('messageDlr', merged); },
 			send: input => this.send(input),
-			sendPastDrain: input => this.outgoing.pastDrain(input, {}),
+			sendPastDrain: input => this.outgoing.carry(input, {}),
 			smsListeners: () => this.listenerCount('sms'),
 		};
 	}
@@ -395,6 +395,7 @@ export class Session extends EventEmitter<SessionEvents> {
 		else this.emitClose();
 	}
 
+	// Copied into the gate at teardown, so stopping the loop anywhere but drain() and end() has to shut the gate too.
 	private retrying(): boolean {
 		return this.reconnectLoop !== undefined && !this.reconnectLoop.isStopped();
 	}

test/session-extras.test.ts

@@ -1448,6 +1448,18 @@ describe('LinkGate', () => {
 
 		assert.match(held.err?.message ?? '', /Aborted while waiting for a link/);
 	});
+
+	test('awaits the next link only while shut with one on its way', () => {
+		const gate = new LinkGate({ log: silentLog, timeout: 100 });
+
+		assert.equal(gate.awaitsNextLink(), false, 'up');
+		gate.shut(true);
+		assert.equal(gate.awaitsNextLink(), true, 'shut, returning');
+		gate.open();
+		assert.equal(gate.awaitsNextLink(), false, 'reopened');
+		gate.shut(false);
+		assert.equal(gate.awaitsNextLink(), false, 'shut for good');
+	});
 });
 
 describe('SendWindow', () => {

todo.md

@@ -199,11 +199,6 @@ next work ([decision](docs/decisions.md#internals-and-tests)).
 
 ### Locality — next, ahead of everything below; 5–6 today, and the gate is 7
 
-- [ ] **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
-      `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
       helpers all named some abstraction of "body". Return a named source — `'short_message' |
@@ -326,7 +321,8 @@ next work ([decision](docs/decisions.md#internals-and-tests)).
 
 - [ ] **Make `LinkGate.isUp()`'s doc true or its state match it.** It says a link attached but not
       yet bound cannot carry a request, while `up` starts `true`, so the first link and a server
-      session are up before any bind. From the comprehension panel of #25.
+      session are up before any bind. The gate decision in `docs/decisions.md` makes the same claim
+      in its title, and carries the same fix. From the comprehension panel of #25.
 
 - [ ] **Move `checkSessionOptions()`'s doc comment to what it describes.** It explains why a count
       below 1 is refused, which is `checkLimits`' job, and says nothing of the function it heads.