Make sure that markdown is always rendered

- If a server was running, forward the stdin stream.
- If a new tab is opened, re-use the last rendered markdown.

Author: Rob--W

instant-markdown-d

@@ -15,10 +15,10 @@ var server = require('http').createServer(httpHandler),
 // directory of the open file!
 if (process.env.INSTANT_MARKDOWN_OPEN_TO_THE_WORLD) {
   // Listen on any interface.
-  server.listen(8090, onListening);
+  server.listen(8090, onListening).once('error', onServerError);
 } else {
   // Listen locally.
-  server.listen(8090, '127.0.0.1', onListening);
+  server.listen(8090, '127.0.0.1', onListening).once('error', onServerError);
 }
 
 var md = new MarkdownIt({
@@ -37,7 +37,13 @@ var md = new MarkdownIt({
   }
 });
 
-function writeMarkdown(input) {
+var lastWrittenMarkdown = '';
+function writeMarkdown(body) {
+  lastWrittenMarkdown = md.render(body);
+  io.sockets.emit('newContent', lastWrittenMarkdown);
+}
+
+function readAllInput(input, callback) {
   var body = '';
   input.on('data', function(data) {
     body += data;
@@ -46,7 +52,7 @@ function writeMarkdown(input) {
     }
   });
   input.on('end', function() {
-    io.sockets.emit('newContent', md.render(body));
+    callback(body);
   });
 }
 
@@ -103,7 +109,7 @@ function httpHandler(req, res) {
       break;
 
     case 'PUT':
-      writeMarkdown(req);
+      readAllInput(req, writeMarkdown);
       res.writeHead(200);
       res.end();
       break;
@@ -114,8 +120,9 @@ function httpHandler(req, res) {
 
 io.sockets.on('connection', function(sock){
   process.stdout.write('connection established!');
-  writeMarkdown(process.stdin);
-  process.stdin.resume();
+  if (lastWrittenMarkdown) {
+    sock.emit('newContent', lastWrittenMarkdown);
+  }
 });
 
 
@@ -126,4 +133,27 @@ function onListening() {
   else {  // assume unix/linux
     exec('xdg-open http://localhost:8090');
   }
+  readAllInput(process.stdin, function(body) {
+    writeMarkdown(body);
+  });
+  process.stdin.resume();
+}
+
+function onServerError(e) {
+  if (e.code === 'EADDRINUSE') {
+    readAllInput(process.stdin, function(body) {
+      // Forward to existing instant-markdown-d server.
+      require('http').request({
+        hostname: 'localhost',
+        port: 8090,
+        path: '/',
+        method: 'PUT',
+      }).end(body);
+    });
+    process.stdin.resume();
+    return;
+  }
+
+  // Another unexpected error. Raise it again.
+  throw e;
 }