From 572cfb3bc4fa5193990b4fb269fb6a43956b6b90 Mon Sep 17 00:00:00 2001
From: Adam Budde <abudde@apple.com>
Date: Mon, 22 Jun 2026 12:43:17 -0700
Subject: [PATCH] HTTPBodyOutputStream should handle multiple terminal events

---
 .../HTTPBodyOutputStreamBridge.swift          | 15 ++++++--
 .../HTTPBodyOutputStreamTests.swift           | 38 +++++++++++++++++++
 2 files changed, 49 insertions(+), 4 deletions(-)

diff --git a/Sources/OpenAPIURLSession/URLSessionBidirectionalStreaming/HTTPBodyOutputStreamBridge.swift b/Sources/OpenAPIURLSession/URLSessionBidirectionalStreaming/HTTPBodyOutputStreamBridge.swift
index f542958..6e24c0b 100644
--- a/Sources/OpenAPIURLSession/URLSessionBidirectionalStreaming/HTTPBodyOutputStreamBridge.swift
+++ b/Sources/OpenAPIURLSession/URLSessionBidirectionalStreaming/HTTPBodyOutputStreamBridge.swift
@@ -207,7 +207,9 @@ extension HTTPBodyOutputStreamBridge {
             case .needBytes(_, let producerContinuation):
                 self = .closed(error)
                 return .cancelProducerAndCloseStream(producerContinuation)
-            case .closed: preconditionFailure("\(#function) called in invalid state: \(self)")
+            case .closed:
+                debug("Ignoring \(#function) event in closed state")
+                return .none
             }
         }
 
@@ -216,8 +218,10 @@ extension HTTPBodyOutputStreamBridge {
             case .waitingForBytes(_):
                 self = .closed(nil)
                 return .closeStream
-            case .initial, .haveBytes, .needBytes, .closed:
-                preconditionFailure("\(#function) called in invalid state: \(self)")
+            case .closed:
+                debug("Ignoring \(#function) event in closed state")
+                return .none
+            case .initial, .haveBytes, .needBytes: preconditionFailure("\(#function) called in invalid state: \(self)")
             }
         }
 
@@ -232,7 +236,10 @@ extension HTTPBodyOutputStreamBridge {
             case .needBytes(_, let producerContinuation):
                 self = .closed(nil)
                 return .cancelProducerAndCloseStream(producerContinuation)
-            case .initial, .closed: preconditionFailure("\(#function) called in invalid state: \(self)")
+            case .closed:
+                debug("Ignoring \(#function) event in closed state")
+                return .none
+            case .initial: preconditionFailure("\(#function) called in invalid state: \(self)")
             }
         }
 
diff --git a/Tests/OpenAPIURLSessionTests/URLSessionBidirectionalStreamingTests/HTTPBodyOutputStreamTests.swift b/Tests/OpenAPIURLSessionTests/URLSessionBidirectionalStreamingTests/HTTPBodyOutputStreamTests.swift
index 631ee65..a2d5263 100644
--- a/Tests/OpenAPIURLSessionTests/URLSessionBidirectionalStreamingTests/HTTPBodyOutputStreamTests.swift
+++ b/Tests/OpenAPIURLSessionTests/URLSessionBidirectionalStreamingTests/HTTPBodyOutputStreamTests.swift
@@ -376,6 +376,44 @@ class HTTPBodyOutputStreamBridgeTests: XCTestCase {
 
     }
 
+    func testWroteFinalChunkIsNoOpWhenAlreadyClosed() {
+        var state = HTTPBodyOutputStreamBridge.State.closed(URLError(.cannotFindHost))
+        guard case .none = state.wroteFinalChunk() else {
+            XCTFail("Expected .none action from wroteFinalChunk() in .closed state")
+            return
+        }
+        guard case .closed = state else {
+            XCTFail("Expected state to remain .closed, got \(state)")
+            return
+        }
+    }
+
+    func testEndEncounteredIsNoOpWhenAlreadyClosed() {
+        var state = HTTPBodyOutputStreamBridge.State.closed(URLError(.cannotFindHost))
+        guard case .none = state.endEncountered() else {
+            XCTFail("Expected .none action from endEncountered() in .closed state")
+            return
+        }
+        guard case .closed = state else {
+            XCTFail("Expected state to remain .closed, got \(state)")
+            return
+        }
+    }
+
+    func testErrorOccurredIsNoOpWhenAlreadyClosed() {
+        let firstError = URLError(.cannotFindHost)
+        var state = HTTPBodyOutputStreamBridge.State.closed(firstError)
+        guard case .none = state.errorOccurred(URLError(.timedOut)) else {
+            XCTFail("Expected .none action from errorOccurred() in .closed state")
+            return
+        }
+        guard case .closed(let storedError) = state else {
+            XCTFail("Expected state to remain .closed, got \(state)")
+            return
+        }
+        XCTAssertEqual((storedError as? URLError)?.code, firstError.code, "First error should win")
+    }
+
     // Wait for given condition to be true within wait duration.
     private func waitForCondition(_ label: String, within waitDuration: TimeInterval = 1.0, condition: () -> Bool)
         async throws