respond with ENOENT instead of E_NO_OWNERS when archiving a file that does not exist

lib/commands/channel.js

@@ -54,14 +54,29 @@ Channel.clearOwnedChannel = function (Env, safeKey, channelId, cb, Server) {
     });
 };
 
-var archiveOwnedChannel = function (Env, safeKey, channelId, cb, Server) {
+var archiveOwnedChannel = function (Env, safeKey, channelId, _cb, Server) {
     var unsafeKey = Util.unescapeKeyCharacters(safeKey);
+    nThen(function (w) {
+        // confirm that the channel exists before worrying about whether
+        // we have permission to delete it.
+        var cb = _cb;
+        Env.msgStore.getChannelSize(channelId, w(function (err, bytes) {
+            if (!bytes) {
+                w.abort();
+                return cb(err || "ENOENT");
+            }
+        }));
+    }).nThen(function (w) {
+        var cb = Util.both(w.abort, _cb);
         Metadata.getMetadata(Env, channelId, function (err, metadata) {
             if (err) { return void cb(err); }
             if (!Core.hasOwners(metadata)) { return void cb('E_NO_OWNERS'); }
             if (!Core.isOwner(metadata, unsafeKey)) {
                 return void cb('INSUFFICIENT_PERMISSIONS');
             }
+        });
+    }).nThen(function () {
+        var cb = _cb;
         // temporarily archive the file
         return void Env.msgStore.archiveChannel(channelId, function (e) {
             Env.Log.info('ARCHIVAL_CHANNEL_BY_OWNER_RPC', {