Add Job.mkTree extension method (#504)

It can be useful to print a hierarchy of coroutines for debug purposes.

src/commonMain/kotlin/fr/acinq/lightning/utils/coroutines.kt

@@ -0,0 +1,32 @@
+package fr.acinq.lightning.utils
+
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.job
+
+private fun Job.print(buffer: StringBuilder, prefix: String, childrenPrefix: String) {
+    buffer.append(prefix)
+    buffer.append(job.toString())
+    buffer.append('\n')
+    val it = job.children.iterator()
+    while (it.hasNext()) {
+        val child = it.next()
+        if (it.hasNext()) {
+            child.print(buffer, "$childrenPrefix├── ", "$childrenPrefix│   ")
+        } else {
+            child.print(buffer, "$childrenPrefix└── ", "$childrenPrefix    ")
+        }
+    }
+}
+
+/**
+ * Extension method to print a hierarchy of coroutines for debug purposes.
+ * Usage:
+ * ```
+ *    println(scope.coroutineContext.job.mkTree())
+ * ```
+ */
+fun Job.mkTree(): String {
+    val sb = StringBuilder()
+    job.print(sb, "", "")
+    return sb.toString()
+}

src/jvmMain/kotlin/fr/acinq/lightning/io/JvmTcpSocket.kt

@@ -31,8 +31,8 @@ class JvmTcpSocket(val socket: Socket, val loggerFactory: LoggerFactory) : TcpSo
 
     override suspend fun send(bytes: ByteArray?, offset: Int, length: Int, flush: Boolean) =
         withContext(Dispatchers.IO) {
+            ensureActive()
             try {
-                ensureActive()
                 if (bytes != null) connection.output.writeFully(bytes, offset, length)
                 if (flush) connection.output.flush()
             } catch (ex: ClosedSendChannelException) {