From ab362397ba54f357459c0d0ba996939e475489f4 Mon Sep 17 00:00:00 2001
From: Ethan Atkins <contact@ethanatkins.com>
Date: Wed, 24 Jun 2020 19:20:54 -0700
Subject: [PATCH] Add remote cancellation support

This commit makes it possible for a remote client to cancel a running
task initiated by a different client by typing `cancel` into the shell.
It can be useful if the remote client has run something blocking like
console.

The console task can't safely be interrupted, so instead we write some
newlines filed by ctrl+d to exit the console.
---
 .../sbt/internal/util/ConsoleAppender.scala   |  1 +
 .../scala/sbt/internal/CommandExchange.scala  |  9 +++++
 .../sbt/internal/server/NetworkChannel.scala  | 34 +++++++++++++++++++
 3 files changed, 44 insertions(+)

diff --git a/internal/util-logging/src/main/scala/sbt/internal/util/ConsoleAppender.scala b/internal/util-logging/src/main/scala/sbt/internal/util/ConsoleAppender.scala
index 7b533ef61..fb7d6be16 100644
--- a/internal/util-logging/src/main/scala/sbt/internal/util/ConsoleAppender.scala
+++ b/internal/util-logging/src/main/scala/sbt/internal/util/ConsoleAppender.scala
@@ -658,6 +658,7 @@ private[sbt] object ProgressState {
             }
           } else {
             pe.command.toSeq.flatMap { cmd =>
+              val tail = if (isWatch) Nil else "enter 'cancel' to stop evaluation" :: Nil
               s"sbt server is running '$cmd'" :: tail
             }
           }
diff --git a/main/src/main/scala/sbt/internal/CommandExchange.scala b/main/src/main/scala/sbt/internal/CommandExchange.scala
index cbabbb6a5..3d47351be 100644
--- a/main/src/main/scala/sbt/internal/CommandExchange.scala
+++ b/main/src/main/scala/sbt/internal/CommandExchange.scala
@@ -350,6 +350,15 @@ private[sbt] final class CommandExchange {
     commandQueue.add(exit)
     ()
   }
+  private[this] def cancel(e: Exec): Unit = {
+    if (e.commandLine.startsWith("console")) {
+      val terminal = Terminal.get
+      terminal.write(13, 13, 13, 4)
+      terminal.printStream.println("\nconsole session killed by remote sbt client")
+    } else {
+      Util.ignoreResult(NetworkChannel.cancel(e.execId, e.execId.getOrElse("0")))
+    }
+  }
 
   private[this] class MaintenanceThread
       extends Thread("sbt-command-exchange-maintenance")
diff --git a/main/src/main/scala/sbt/internal/server/NetworkChannel.scala b/main/src/main/scala/sbt/internal/server/NetworkChannel.scala
index 5a50b3016..ecf4e1caa 100644
--- a/main/src/main/scala/sbt/internal/server/NetworkChannel.scala
+++ b/main/src/main/scala/sbt/internal/server/NetworkChannel.scala
@@ -698,6 +698,40 @@ object NetworkChannel {
   case object SingleLine extends ChannelState
   case object InHeader extends ChannelState
   case object InBody extends ChannelState
+  private[sbt] def cancel(
+      execID: Option[String],
+      id: String
+  ): Either[String, String] = {
+
+    Option(EvaluateTask.currentlyRunningEngine.get) match {
+      case Some((state, runningEngine)) =>
+        val runningExecId = state.currentExecId.getOrElse("")
+
+        def checkId(): Boolean = {
+          if (runningExecId.startsWith("\u2668")) {
+            (
+              Try { id.toLong }.toOption,
+              Try { runningExecId.substring(1).toLong }.toOption
+            ) match {
+              case (Some(id), Some(eid)) => id == eid
+              case _                     => false
+            }
+          } else runningExecId == id
+        }
+
+        // direct comparison on strings and
+        // remove hotspring unicode added character for numbers
+        if (checkId) {
+          runningEngine.cancelAndShutdown()
+          Right(runningExecId)
+        } else {
+          Left("Task ID not matched")
+        }
+
+      case None =>
+        Left("No tasks under execution")
+    }
+  }
 
   private[sbt] val disconnect: Command =
     Command.arb { s =>