repl: add an internal "paused" mode

PR-URL: https://github.com/nodejs/node/pull/15566
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

lib/repl.js

@@ -169,6 +169,34 @@ function REPLServer(prompt,
 
   eval_ = eval_ || defaultEval;
 
+  // Pause taking in new input, and store the keys in a buffer.
+  const pausedBuffer = [];
+  let paused = false;
+  function pause() {
+    paused = true;
+  }
+  function unpause() {
+    if (!paused) return;
+    paused = false;
+    let entry;
+    while (entry = pausedBuffer.shift()) {
+      const [type, payload] = entry;
+      switch (type) {
+        case 'key': {
+          const [d, key] = payload;
+          self._ttyWrite(d, key);
+          break;
+        }
+        case 'close':
+          self.emit('exit');
+          break;
+      }
+      if (paused) {
+        break;
+      }
+    }
+  }
+
   function defaultEval(code, context, file, cb) {
     var err, result, script, wrappedErr;
     var wrappedCmd = false;
@@ -420,6 +448,10 @@ function REPLServer(prompt,
     'DEP0075');
 
   self.on('close', function emitExit() {
+    if (paused) {
+      pausedBuffer.push(['close']);
+      return;
+    }
     self.emit('exit');
   });
 
@@ -557,10 +589,14 @@ function REPLServer(prompt,
     }
   });
 
-  // Wrap readline tty to enable editor mode
+  // Wrap readline tty to enable editor mode and pausing.
   const ttyWrite = self._ttyWrite.bind(self);
   self._ttyWrite = (d, key) => {
     key = key || {};
+    if (paused && !(self.breakEvalOnSigint && key.ctrl && key.name === 'c')) {
+      pausedBuffer.push(['key', [d, key]]);
+      return;
+    }
     if (!self.editorMode || !self.terminal) {
       ttyWrite(d, key);
       return;