use Request().Context().Done() channel instead of the ResponseWriter().CloseNotify() one

Former-commit-id: e380a3624c03faada74c9efc24266679c3ff5e2b

_examples/response-writer/stream-writer/main.go

@@ -1,13 +1,15 @@
 package main
 
 import (
-	"fmt" // just an optional helper
+	"errors"
 	"io"
 	"time" // showcase the delay
 
 	"github.com/kataras/iris/v12"
 )
 
+var errDone = errors.New("done")
+
 func main() {
 	app := iris.New()
 
@@ -17,15 +19,21 @@ func main() {
 		i := 0
 		ints := []int{1, 2, 3, 5, 7, 9, 11, 13, 15, 17, 23, 29}
 		// Send the response in chunks and wait for half a second between each chunk.
-		ctx.StreamWriter(func(w io.Writer) bool {
-			fmt.Fprintf(w, "Message number %d<br>", ints[i])
+		err := ctx.StreamWriter(func(w io.Writer) error {
+			ctx.Writef("Message number %d<br>", ints[i])
 			time.Sleep(500 * time.Millisecond) // simulate delay.
 			if i == len(ints)-1 {
-				return false // close and flush
+				return errDone // ends the loop.
 			}
 			i++
-			return true // continue write
+			return nil // continue write
 		})
+
+		if err != errDone {
+			// Test it by canceling the request before the stream ends:
+			// [ERRO] $DATETIME stream: context canceled.
+			ctx.Application().Logger().Errorf("stream: %v", err)
+		}
 	})
 
 	type messageNumber struct {
@@ -33,7 +41,6 @@ func main() {
 	}
 
 	app.Get("/alternative", func(ctx iris.Context) {
-		ctx.ContentType("application/json")
 		ctx.Header("Transfer-Encoding", "chunked")
 		i := 0
 		ints := []int{1, 2, 3, 5, 7, 9, 11, 13, 15, 17, 23, 29}
@@ -52,3 +59,10 @@ func main() {
 
 	app.Listen(":8080")
 }
+
+/*
+Look the following methods too:
+- Context.OnClose(callback)
+- Context.OnConnectionClose(callback) and
+- Context.Request().Context().Done()/.Err() too
+*/