use server sent events for live poll updates without page refresh

also just use the material theme directly because holy moly
themeswitcher is having a bad time

1 files changed, 130 insertions, 0 deletions

diff --git a/sse/broker.go b/sse/broker.go
new file mode 100644
index 0000000..464b333
--- /dev/null
+++ b/sse/broker.go
@@ -0,0 +1,130 @@
+/*
+The MIT License (MIT)
+
+Copyright (c) 2017-2021 Ismael Celis and contributors
+
+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.
+*/
+
+package sse
+
+import (
+	"io"
+	"log"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+const patience time.Duration = time.Second * 1
+
+type (
+	NotificationEvent struct {
+		EventName string
+		Payload   interface{}
+	}
+
+	NotifierChan chan NotificationEvent
+
+	Broker struct {
+
+		// Events are pushed to this channel by the main events-gathering routine
+		Notifier NotifierChan
+
+		// New client connections
+		newClients chan NotifierChan
+
+		// Closed client connections
+		closingClients chan NotifierChan
+
+		// Client connections registry
+		clients map[NotifierChan]struct{}
+	}
+)
+
+func NewBroker() (broker *Broker) {
+	// Instantiate a broker
+	return &Broker{
+		Notifier:       make(NotifierChan, 1),
+		newClients:     make(chan NotifierChan),
+		closingClients: make(chan NotifierChan),
+		clients:        make(map[NotifierChan]struct{}),
+	}
+}
+
+func (broker *Broker) ServeHTTP(c *gin.Context) {
+	eventName := c.Param("topic")
+
+	// Each connection registers its own message channel with the Broker's connections registry
+	messageChan := make(NotifierChan)
+
+	// Signal the broker that we have a new connection
+	broker.newClients <- messageChan
+
+	// Remove this client from the map of connected clients
+	// when this handler exits.
+	defer func() {
+		broker.closingClients <- messageChan
+	}()
+
+	c.Stream(func(w io.Writer) bool {
+		// Emit Server Sent Events compatible
+		event := <-messageChan
+
+		switch eventName {
+		case event.EventName:
+			c.SSEvent(event.EventName, event.Payload)
+		}
+
+		// Flush the data immediately instead of buffering it for later.
+		c.Writer.Flush()
+
+		return true
+	})
+}
+
+// Listen for new notifications and redistribute them to clients
+func (broker *Broker) Listen() {
+	for {
+		select {
+		case s := <-broker.newClients:
+
+			// A new client has connected.
+			// Register their message channel
+			broker.clients[s] = struct{}{}
+			log.Printf("Client added. %d registered clients", len(broker.clients))
+		case s := <-broker.closingClients:
+
+			// A client has dettached and we want to
+			// stop sending them messages.
+			delete(broker.clients, s)
+			log.Printf("Removed client. %d registered clients", len(broker.clients))
+		case event := <-broker.Notifier:
+
+			// We got a new event from the outside!
+			// Send event to all connected clients
+			for clientMessageChan := range broker.clients {
+				select {
+				case clientMessageChan <- event:
+				case <-time.After(patience):
+					log.Print("Skipping client.")
+				}
+			}
+		}
+	}
+}