golongpoll

Golang long polling library. Makes web pub-sub easy via HTTP long-poll servers and clients.

Resources

• go docs
• examples - shows how to use the longpoll server and go/js clients.
• go client
• javascript client
• longpoll http api - in case you want to create your own client.
• longpoll with gin apps

QuickStart

To create a longpoll server:

import (
  "github.com/jcuga/golongpoll"
)

// This uses the default/empty options. See section on customizing, and Options go docs.
manager, err := golongpoll.StartLongpoll(golongpoll.Options{})

// Expose pub-sub. You could omit the publish handler if you don't want
// to allow clients to publish. For example, if clients only subscribe to data.
if err == nil {
  http.HandleFunc("/events", manager.SubscriptionHandler)
  http.HandleFunc("/publish", manager.PublishHandler)
  http.ListenAndServe("127.0.0.1:8101", nil)
} else {
  // handle error creating longpoll manager--typically this means a bad option.
}

The above snippet will create a LongpollManager which has a SubscriptionHandler and a PublishHandler that can served via http (or using https). When created, the manager spins up a separate goroutine that handles the plumbing for pub-sub.

LongpollManager also has a Publish function that can be used to publish events. You can call manager.Publish("some-category", "some data here") and/or expose the manager.PublishHandler and allow publishing of events via the longpoll http api. For publishing within the same program as the manager/server, calling manager.Publish() does not use networking--under the hood it uses the go channels that are part of the pub-sub plumbing. You could also wrap the manager in an http handler closure that calls publish as desired.

See the Examples on how to use the golang and javascript clients as well as how to wrap the manager.PublishHandler or call manager.Publish() directly.

How it Works

You can think of the longpoll manager as a goroutine that uses channels to service pub-sub requests. The manager has a map[string]eventBuffer (actually a map[string]*expiringBuffer) that holds events per category as well as a data structure (another sort of map) for the subscription request book-keeping. The PublishHandler and SubscribeHandler interact with the manager goroutine via channels.

The events are stored using in-memory buffers that have a configured max number of events per category. Optionally, the events can be automatically removed based on a time-to-live setting. Since this is all in-memory, there is an optional add-on for auto-persisting and repopulating data from disk. This allows events to persist across program restarts (not the default option/behavior!) One can also create their own custom add-on as well. See the Customizing section.

One important limitation/design-decision to be aware of: the SubscriptionHandler supports subscribing to a single cateogry. If you want to subscribe to more than one category, you must make more than one call to the subscription handler--or create multiple clients each with a different category. Note however that clients are free to publish to more than one categor--to any category really, unless the manager's publish handler is not being served or there is wrapping handler logic that forbids this. Whether or not this limitation is a big deal depends on how you are using categories. This decision reduces the internal complexity and is likely not to change any time soon.

Customizing

See golongpoll.Options on how to configure the longpoll manager. This includes:

• MaxEventBufferSize - for the max number of events per category, after which oldest-first is truncated. Defaults to 250.
• EventTimeToLiveSeconds - how long events exist in the buffer, defaults to forever (as long as MaxEventBufferSize isn't reached).
• AddOn - optional way to provide custom behavior. The only add-on at the moment is FilePersistorAddOn (Usage example). See AddOn interface for creating your own custom add-on.

Remember, you don't have to expose LongpollManager.SubscriptionHandler and PublishHandler directly (or at all). You can wrap them with your own http handler that adds additional logic or validation before invoking the inner handler. See the authentication example for how to require auth via header data before those handlers get called. For publishing, you can also call manager.Publish() directly, or wrap the manager via a closure to create a custom http handler that publishes data.

long polling and gin

Need to add long polling to a Gin HTTP Framework app? Simply wrap golongpoll's manager pub/sub functions with a gin.Context and pass to router.POST and router.GET:

package main

import (
	"net/http"

	"github.com/gin-gonic/gin"

	"github.com/jcuga/golongpoll"
)

func main() {
	// Create longpoll manger with default opts
	manager, err := golongpoll.StartLongpoll(golongpoll.Options{})
	if err != nil {
		panic(err)
	}

	router := gin.Default()
	router.POST("/pub", wrapWithContext(manager.PublishHandler))
	router.GET("/sub", wrapWithContext(manager.SubscriptionHandler))
	router.Run(":8001")
}

func wrapWithContext(lpHandler func(http.ResponseWriter, *http.Request)) func(*gin.Context) {
	return func(c *gin.Context) {
		lpHandler(c.Writer, c.Request)
	}
}