src: fix external memory usage going negative

src/node_crypto.h

@@ -198,7 +198,9 @@ class SecureContext : public BaseObject {
   }
 
   inline void Reset() {
-    env()->isolate()->AdjustAmountOfExternalAllocatedMemory(-kExternalSize);
+    if (ctx_.get() != nullptr) {
+      env()->isolate()->AdjustAmountOfExternalAllocatedMemory(-kExternalSize);
+    }
     ctx_.reset();
     cert_.reset();
     issuer_.reset();

test/parallel/test-gc-tls-external-memory.js

@@ -0,0 +1,35 @@
+'use strict';
+// Flags: --expose-gc
+
+// Tests that memoryUsage().external doesn't go negative
+// when a lot tls connections are opened and closed
+
+const common = require('../common');
+if (!common.hasCrypto)
+  common.skip('missing crypto');
+
+const assert = require('assert');
+const net = require('net');
+const tls = require('tls');
+
+// Payload doesn't matter. We just need to have the tls
+// connection try and connect somewhere.
+const yolo = Buffer.alloc(10000).fill('yolo');
+const server = net.createServer(function(socket) {
+  socket.write(yolo);
+});
+
+server.listen(0, function() {
+  const { port } = server.address();
+  let runs = 0;
+  connect();
+
+  function connect() {
+    global.gc();
+    assert(process.memoryUsage().external >= 0);
+    if (runs++ < 512)
+      tls.connect(port).on('error', connect);
+    else
+      server.close();
+  }
+});