Make sure the ID is not used when uploading a file

www/common/outer/upload.js

@@ -1,8 +1,9 @@
 define([
     '/file/file-crypto.js',
     '/common/common-hash.js',
+    '/bower_components/nthen/index.js',
     '/bower_components/tweetnacl/nacl-fast.min.js',
-], function (FileCrypto, Hash) {
+], function (FileCrypto, Hash, nThen) {
     var Nacl = window.nacl;
     var module = {};
 
@@ -14,13 +15,29 @@ define([
         var path = file.path;
 
         var password = file.password;
-        var hash = Hash.createRandomHash('file', password);
-        var secret = Hash.getSecrets('file', hash, password);
-        var key = secret.keys.cryptKey;
-        var id = secret.channel;
+        var hash, secret, key, id, href;
+
+        var getNewHash = function () {
+            hash = Hash.createRandomHash('file', password);
+            secret = Hash.getSecrets('file', hash, password);
+            key = secret.keys.cryptKey;
+            id = secret.channel;
+            href = '/file/#' + hash;
+        };
 
-        // XXX check id here (getFileSize)
+        var getValidHash = function (cb) {
+            getNewHash();
+            common.getFileSize(href, password, function (err, size) {
+                if (err || typeof(size) !== "number") {  throw new Error(err || "Invalid size!"); }
+                if (size === 0) { return void cb(); }
+                getValidHash();
+            });
+        };
 
+        nThen(function (waitFor) {
+            // Generate a hash and check if the resulting id is valid (not already used)
+            getValidHash(waitFor());
+        }).nThen(function () {
             var next = FileCrypto.encrypt(u8, metadata, key);
 
             var estimate = FileCrypto.computeEncryptedSize(u8.length, metadata);
@@ -56,7 +73,6 @@ define([
                     var uri = ['', 'blob', id.slice(0,2), id].join('/');
                     console.log("encrypted blob is now available as %s", uri);
 
-                var href = '/file/#' + hash;
 
                     var title = metadata.name;
 
@@ -97,6 +113,8 @@ define([
                 }
                 next(again);
             });
+        });
+
     };
     return module;
 });