diff --git a/rpc.js b/rpc.js
index b48df570a..c27c15f92 100644
--- a/rpc.js
+++ b/rpc.js
@@ -29,7 +29,7 @@ var WARN = function (e, output) {
 };
 
 var isValidId = function (chan) {
-    return chan && chan.length && /^[a-fA-F0-9]/.test(chan) &&
+    return chan && chan.length && /^[a-zA-Z0-9=+-]*$/.test(chan) &&
         [32, 48].indexOf(chan.length) > -1;
 };
 
@@ -1006,6 +1006,7 @@ var isUnauthenticatedCall = function (call) {
         'GET_MULTIPLE_FILE_SIZE',
         'IS_CHANNEL_PINNED',
         'IS_NEW_CHANNEL',
+        'GET_HISTORY_OFFSET'
     ].indexOf(call) !== -1;
 };
 
@@ -1049,8 +1050,21 @@ const mkEvent = function (once) {
     };
 };
 
-/*::const ConfigType = require('./config.example.js');*/
-RPC.create = function (config /*:typeof(ConfigType)*/, cb /*:(?Error, ?Function)=>void*/) {
+/*::
+const flow_Config = require('./config.example.js');
+type Config_t = typeof(flow_Config);
+import type { ChainPadServer_Storage_t } from './storage/file.js'
+type NetfluxWebsocketSrvContext_t = {
+    store: ChainPadServer_Storage_t,
+    getHistoryOffset: (
+        ctx: NetfluxWebsocketSrvContext_t,
+        channelName: string,
+        lastKnownHash: ?string,
+        cb: (err: ?Error, offset: ?number)=>void
+    )=>void
+};
+*/
+RPC.create = function (config /*:Config_t*/, cb /*:(?Error, ?Function)=>void*/) {
     // load pin-store...
     console.log('loading rpc module...');
 
@@ -1081,8 +1095,24 @@ RPC.create = function (config /*:typeof(ConfigType)*/, cb /*:(?Error, ?Function)
         return msg && msg.length === 2 && isUnauthenticatedCall(msg[0]);
     };
 
-    var handleUnauthenticatedMessage = function (msg, respond) {
+    var handleUnauthenticatedMessage = function (msg, respond, nfwssCtx) {
         switch (msg[0]) {
+            case 'GET_HISTORY_OFFSET': {
+                if (typeof(msg[1]) !== 'object' || typeof(msg[1].channelName) !== 'string') {
+                    return respond('INVALID_ARG_FORMAT', msg);
+                }
+                const msgHash = typeof(msg[1].msgHash) === 'string' ? msg[1].msgHash : undefined;
+                nfwssCtx.getHistoryOffset(nfwssCtx, msg[1].channelName, msgHash, (e, ret) => {
+                    if (e) {
+                        if (e.code !== 'ENOENT') {
+                            WARN(e.stack, msg);
+                        }
+                        return respond(e.message);
+                    }
+                    respond(e, [null, ret, null]);
+                });
+                break;
+            }
             case 'GET_FILE_SIZE':
                 return void getFileSize(Env, msg[1], function (e, size) {
                     if (e) {
@@ -1133,7 +1163,7 @@ RPC.create = function (config /*:typeof(ConfigType)*/, cb /*:(?Error, ?Function)
         }
 
         if (isUnauthenticateMessage(msg)) {
-            return handleUnauthenticatedMessage(msg, respond);
+            return handleUnauthenticatedMessage(msg, respond, ctx);
         }
 
         var signature = msg.shift();
@@ -1334,7 +1364,7 @@ RPC.create = function (config /*:typeof(ConfigType)*/, cb /*:(?Error, ?Function)
     };
 
     var rpc = function (
-        ctx /*:{ store: Object }*/,
+        ctx /*:NetfluxWebsocketSrvContext_t*/,
         data /*:Array<Array<any>>*/,
         respond /*:(?string, ?Array<any>)=>void*/)
     {
diff --git a/storage/file.js b/storage/file.js
index ce6c3ae13..62ed4fa39 100644
--- a/storage/file.js
+++ b/storage/file.js
@@ -7,6 +7,12 @@ var nThen = require("nthen");
 const ToPull = require('stream-to-pull-stream');
 const Pull = require('pull-stream');
 
+const isValidChannelId = function (id) {
+    return typeof(id) === 'string' &&
+        [32, 48].indexOf(id.length) > -1 &&
+        /^[a-zA-Z0-9=+-]*$/.test(id);
+};
+
 var mkPath = function (env, channelId) {
     return Path.join(env.root, channelId.slice(0, 2), channelId) + '.ndjson';
 };
@@ -161,7 +167,9 @@ const readMessagesBin = (env, id, start, msgHandler, cb) => {
         mkBufferSplit(),
         mkOffsetCounter(),
         Pull.asyncMap((data, moreCb) => { msgHandler(data, moreCb, ()=>{ keepReading = false; moreCb(); }); }),
-        Pull.drain(()=>(keepReading), cb)
+        Pull.drain(() => (keepReading), (err) => {
+            cb((keepReading) ? err : undefined);
+        })
     );
 };
 
@@ -414,35 +422,44 @@ module.exports.create = function (
         }
         cb({
             readMessagesBin: (channelName, start, asyncMsgHandler, cb) => {
+                if (!isValidChannelId(channelName)) { return void cb(new Error('EINVAL')); }
                 readMessagesBin(env, channelName, start, asyncMsgHandler, cb);
             },
             message: function (channelName, content, cb) {
+                if (!isValidChannelId(channelName)) { return void cb(new Error('EINVAL')); }
                 message(env, channelName, content, cb);
             },
             messageBin: (channelName, content, cb) => {
+                if (!isValidChannelId(channelName)) { return void cb(new Error('EINVAL')); }
                 messageBin(env, channelName, content, cb);
             },
             getMessages: function (channelName, msgHandler, cb) {
+                if (!isValidChannelId(channelName)) { return void cb(new Error('EINVAL')); }
                 getMessages(env, channelName, msgHandler, cb);
             },
             removeChannel: function (channelName, cb) {
+                if (!isValidChannelId(channelName)) { return void cb(new Error('EINVAL')); }
                 removeChannel(env, channelName, function (err) {
                     cb(err);
                 });
             },
             closeChannel: function (channelName, cb) {
+                if (!isValidChannelId(channelName)) { return void cb(new Error('EINVAL')); }
                 closeChannel(env, channelName, cb);
             },
             flushUnusedChannels: function (cb) {
                 flushUnusedChannels(env, cb);
             },
-            getChannelSize: function (chanName, cb) {
-                channelBytes(env, chanName, cb);
+            getChannelSize: function (channelName, cb) {
+                if (!isValidChannelId(channelName)) { return void cb(new Error('EINVAL')); }
+                channelBytes(env, channelName, cb);
             },
             getChannelMetadata: function (channelName, cb) {
+                if (!isValidChannelId(channelName)) { return void cb(new Error('EINVAL')); }
                 getChannelMetadata(env, channelName, cb);
             },
             clearChannel: function (channelName, cb) {
+                if (!isValidChannelId(channelName)) { return void cb(new Error('EINVAL')); }
                 clearChannel(env, channelName, cb);
             },
         });
diff --git a/www/common/outer/async-store.js b/www/common/outer/async-store.js
index 68c217108..e00500472 100644
--- a/www/common/outer/async-store.js
+++ b/www/common/outer/async-store.js
@@ -24,7 +24,7 @@ define([
 
     var storeHash;
 
-    var store = {};
+    var store = window.CryptPad_AsyncStore = {};
 
 
     var onSync = function (cb) {