webtty: switch upward protocol to JSON

Switch the client-to-server messages from the HTML forms format to
JSON (for the webtty app).  Message numbers are sent but not yet used.

webtty.js

@@ -144,22 +144,14 @@ function urlDec(encstr) {
 
 /* Returns the contents of a form */
 function getFormValues(formtext) {
-  var pairstrs = formtext.split("&");
-  var data = {};
-  for (var i = 0; i < pairstrs.length; i++)
-  {
-    var eqsign = pairstrs[i].indexOf("=");
-    if (eqsign > 0) {
-      rawname = pairstrs[i].slice(0, eqsign);
-      rawval = pairstrs[i].slice(eqsign + 1);
-      name = urlDec(rawname);
-      val = urlDec(rawval);
-      if (!(name in data))
-        data[name] = [];
-      data[name].push(val);
-    }
+  var jsonobj;
+  try {
+    jsonobj = JSON.parse(formtext);
+  } catch (e) {
+    if (e instanceof SyntaxError)
+      return null;
   }
-  return data;
+  return jsonobj;
 }
 
 function login(req, res, formdata) {
@@ -298,14 +290,14 @@ function handler(req, res) {
           sendError(res, 1);
           return;
         }
-        if (formdata["quit"] == "quit") {
+        if (formdata["t"] == "q") {
           /* The client wants to quit. */
           // FIXME need to send a message back to the client
           cterm.close();
         }
-        else if (formdata["keys"]) {
+        else if (formdata["t"] == "d" && typeof(formdata["d"]) == "string") {
           /* process the keys */
-          hexstr = formdata["keys"][0].replace(/[^0-9a-f]/gi, "");
+          hexstr = formdata["d"].replace(/[^0-9a-f]/gi, "");
           if (hexstr.length % 2 != 0) {
             sendError(res, 2);
             return;