Real-time JS object synchronisation over SSE and WebSockets in Go and JavaScript (Node.js and browser)

• Simple API
• Synchronise any JSON marshallable struct in Go
• Synchronise any JSON stringifiable struct in Node
• Delta updates using JSONPatch (RFC6902)
• Supports Server-Sent Events (EventSource) and WebSockets
• SSE client-side poly-fill to fallback to long-polling in older browsers (IE8+).
• Implement delta queries (return all results, then incrementally return changes)

Server (Go)

//syncable struct
type Foo struct {
	velox.State
	A, B int
}
foo := &Foo{}
//serve velox.js client library (assets/dist/velox.min.js)
http.Handle("/velox.js", velox.JS)
//serve velox sync endpoint for foo
http.Handle("/sync", velox.SyncHandler(foo))
//make changes
foo.A = 42
foo.B = 21
//push to client
foo.Push()

Server (Node)

//syncable object
let foo = {
  a: 1,
  b: 2
};
//express server
let app = express();
//serve velox.js client library (assets/dist/velox.min.js)
app.get("/velox.js", velox.JS);
//serve velox sync endpoint for foo (adds $push method)
app.get("/sync", velox.handle(foo));
//make changes
foo.a = 42;
foo.b = 21;
//push to client
foo.$push();

Client (Node and Browser)

// load script /velox.js
var foo = {};
var v = velox("/sync", foo);
v.onupdate = function() {
  //foo.A === 42 and foo.B === 21
};

Server API (Go)

Server API (Node)

• velox.handle(object) function returns v - Creates a new route handler for use with express
• velox.state(object) function returns state - Creates or restores a velox state from a given object
• state.handle(req, res) function returns Promise - Handle the provided express request/response. Resolves on connection close. Rejects on any error.

Client API (Node and Browser)

• velox(url, object) function returns v - Creates a new SSE velox connection
• velox.sse(url, object) function returns v - Creates a new SSE velox connection
• velox.ws(url, object) function returns v - Creates a new WS velox connection
• v.onupdate(object) function - Called when a server push is received
• v.onerror(err) function - Called when a connection error occurs
• v.onconnect() function - Called when the connection is opened
• v.ondisconnect() function - Called when the connection is closed
• v.onchange(bool) function - Called when the connection is opened or closed
• v.connected bool - Denotes whether the connection is currently open
• v.ws bool - Denotes whether the connection is in web sockets mode
• v.sse bool - Denotes whether the connection is in server-sent events mode

See this simple example/ and view it live here: https://velox.jpillora.com

Here is a screenshot from this example page, showing the messages arriving as either a full replacement of the object or just a delta. The server will send which ever is smaller.

• JS object properties beginning with $ will be ignored to play nice with Angular.

• JS object with an $apply function will automatically be called on each update to play nice with Angular.

• velox.SyncHandler is just a small wrapper around velox.Sync:

  	```go
  	func SyncHandler(gostruct interface{}) http.Handler {
  		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
  			if conn, err := Sync(gostruct, w, r); err == nil {
  				conn.Wait()
  			}
  		})
  	}
  	```
  

• Object synchronization is currently one way (server to client) only.
• Object diff has not been optimized. It is a simple property-by-property comparison.

• WebRTC support
• Plain http server support in Node
• WebSockets support in Node

Copyright © 2018 Jaime Pillora <dev@jpillora.com>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.