From e8f40d68c3b986362b8d6420adedb34c69c224e5 Mon Sep 17 00:00:00 2001
From: BrianHotopp <brihoto@gmail.com>
Date: Mon, 17 Aug 2026 14:08:21 -0400
Subject: [PATCH] [2.x] fix: sbtn to log connection errors

onClose now logs sbt server disconnected when the close wasn't initiated by the client.

Generated-by: Oh My Pi (kimi-code/k3)
---
 .../sbt/internal/client/NetworkClient.scala   |  26 ++++-
 .../NetworkClientSilentDisconnectTest.scala   | 102 ++++++++++++++++++
 notes/2.0.0/silent-reconnect.md               |   3 +
 3 files changed, 126 insertions(+), 5 deletions(-)
 create mode 100644 main-command/src/test/scala/sbt/internal/client/NetworkClientSilentDisconnectTest.scala
 create mode 100644 notes/2.0.0/silent-reconnect.md

diff --git a/main-command/src/main/scala/sbt/internal/client/NetworkClient.scala b/main-command/src/main/scala/sbt/internal/client/NetworkClient.scala
index ed0bd78f8..7b98c82bc 100644
--- a/main-command/src/main/scala/sbt/internal/client/NetworkClient.scala
+++ b/main-command/src/main/scala/sbt/internal/client/NetworkClient.scala
@@ -156,6 +156,11 @@ class NetworkClient(
 
   private def mkSocket(file: File): (Socket, Option[String]) = ClientSocket.socket(file, useJNI)
 
+  private[sbt] def logFailure(e: Exception): Unit = {
+    errorStream.println(s"sbt client failed: $e")
+    e.printStackTrace(errorStream)
+  }
+
   private def portfile = arguments.baseDirectory / "project" / "target" / "active.json"
 
   def connection: ServerSession = connectionHolder.synchronized {
@@ -311,7 +316,12 @@ class NetworkClient(
       override protected def onRequest(msg: JsonRpcRequestMessage): Unit = self.onRequest(msg)
       override protected def onResponse(msg: JsonRpcResponseMessage): Unit = self.onResponse(msg)
       override protected def onClose(): Unit = if (!rebooting.get) {
-        if (exitClean.get != false) exitClean.set(!running.get)
+        if (exitClean.get != false) {
+          val serverDropped = running.get
+          exitClean.set(!serverDropped)
+          if (serverDropped && !shutdownOnly)
+            console.appendLog(Level.Error, "sbt server disconnected")
+        }
         running.set(false)
         Option(interactiveThread.get).foreach(_.interrupt())
       }
@@ -1473,8 +1483,11 @@ object NetworkClient {
     try {
       if (client.connect(promptCompleteUsers = false)) client.run()
       else 1
-    } catch { case _: Exception => 1 }
-    finally client.close()
+    } catch {
+      case e: Exception =>
+        client.logFailure(e)
+        1
+    } finally client.close()
   }
   def client(
       baseDirectory: File,
@@ -1505,8 +1518,11 @@ object NetworkClient {
         if (client.connect(promptCompleteUsers = false)) client.run()
         else 1
       }
-    } catch { case _: Exception => 1 }
-    finally client.close()
+    } catch {
+      case e: Exception =>
+        client.logFailure(e)
+        1
+    } finally client.close()
   }
   def client(
       baseDirectory: File,
diff --git a/main-command/src/test/scala/sbt/internal/client/NetworkClientSilentDisconnectTest.scala b/main-command/src/test/scala/sbt/internal/client/NetworkClientSilentDisconnectTest.scala
new file mode 100644
index 000000000..d0416d8e1
--- /dev/null
+++ b/main-command/src/test/scala/sbt/internal/client/NetworkClientSilentDisconnectTest.scala
@@ -0,0 +1,102 @@
+/*
+ * sbt
+ * Copyright 2023, Scala center
+ * Copyright 2011 - 2022, Lightbend, Inc.
+ * Copyright 2008 - 2010, Mark Harrah
+ * Licensed under Apache License 2.0 (see LICENSE)
+ */
+
+package sbt.internal.client
+
+import java.io.{ ByteArrayOutputStream, File, InputStream, PrintStream }
+import java.net.{ ServerSocket, Socket }
+import java.nio.file.Files
+import java.util.concurrent.CountDownLatch
+import verify.BasicTestSuite
+
+/**
+ * Regression test for the silent half of #9484: the server is up (its portfile
+ * exists and accepts connections) but drops the client's connection during a
+ * batch run. The client must say why it failed instead of exiting 1 silently.
+ */
+object NetworkClientSilentDisconnectTest extends BasicTestSuite:
+
+  /** A server that accepts one connection, reads nothing, then closes it. */
+  class DropServer:
+    val serverSocket = new ServerSocket(0, 50, java.net.InetAddress.getLoopbackAddress)
+    val accepted = new CountDownLatch(1)
+    val thread = new Thread(() =>
+      try
+        val s: Socket = serverSocket.accept()
+        accepted.countDown()
+        Thread.sleep(200) // let the client write its handshake into the kernel buffer
+        s.close()
+      catch case _: Exception => ()
+    )
+    thread.setDaemon(true)
+    thread.start()
+    def port: Int = serverSocket.getLocalPort
+    def close(): Unit =
+      try serverSocket.close()
+      catch case _: Exception => ()
+
+  def withDropServer[A](f: DropServer => A): A =
+    val server = new DropServer
+    try f(server)
+    finally server.close()
+
+  def projectWithPortfile(port: Int): File =
+    val base = Files.createTempDirectory("silent-disconnect-project").toFile
+    Files.writeString(
+      base.toPath.resolve("build.sbt"),
+      "lazy val root = (project in file(\".\"))\n"
+    )
+    val target = base.toPath.resolve("project").resolve("target")
+    Files.createDirectories(target)
+    Files.writeString(
+      target.resolve("active.json"),
+      s"""{"uri":"tcp://127.0.0.1:$port","tokenfilePath":null,"tokenfileUri":null}"""
+    )
+    base
+
+  test("a dropped connection during a batch run must not exit silently"):
+    withDropServer: server =>
+      val base = projectWithPortfile(server.port)
+      val (code, explained) = runBatchClient(base)
+      assert(code == 1, s"expected exit 1, got $code")
+      assert(
+        explained.contains("disconnected"),
+        s"client exited 1 without explaining the disconnect: '$explained'"
+      )
+
+  test("a corrupt portfile must not fail silently"):
+    val base = Files.createTempDirectory("corrupt-portfile-project").toFile
+    Files.writeString(
+      base.toPath.resolve("build.sbt"),
+      "lazy val root = (project in file(\".\"))\n"
+    )
+    val target = base.toPath.resolve("project").resolve("target")
+    Files.createDirectories(target)
+    Files.writeString(target.resolve("active.json"), "not json")
+    val (code, explained) = runBatchClient(base)
+    assert(code == 1, s"expected exit 1, got $code")
+    assert(
+      explained.contains("sbt client failed"),
+      s"client exited 1 without explaining the failure: '$explained'"
+    )
+
+  private def runBatchClient(base: File): (Int, String) =
+    val errBytes = new ByteArrayOutputStream
+    val outBytes = new ByteArrayOutputStream
+    val err = new PrintStream(errBytes, true)
+    val out = new PrintStream(outBytes, true)
+    val code = NetworkClient.client(
+      base,
+      Array("compile"),
+      new InputStream { override def read(): Int = -1 },
+      out,
+      err,
+      false,
+    )
+    (code, errBytes.toString("UTF-8") + outBytes.toString("UTF-8"))
+end NetworkClientSilentDisconnectTest
diff --git a/notes/2.0.0/silent-reconnect.md b/notes/2.0.0/silent-reconnect.md
new file mode 100644
index 000000000..0d7ab56e1
--- /dev/null
+++ b/notes/2.0.0/silent-reconnect.md
@@ -0,0 +1,3 @@
+### Fixes
+
+- Don't exit silently when the thin client loses its connection to the server mid-run or hits an exception during connect. The client now logs `sbt server disconnected` when the server drops the connection, and prints the exception with a stack trace when the connect or run phase throws. Previously these paths returned exit code 1 with no output, which made CI failures undebuggable. Addresses [#9484](https://github.com/sbt/sbt/issues/9484).