reorganization of _examples and add some new examples such as iris+groupcache+mysql+docker

Former-commit-id: ed635ee95de7160cde11eaabc0c1dcb0e460a620

_examples/response-writer/transactions/main.go

@@ -0,0 +1,54 @@
+package main
+
+import (
+	"github.com/kataras/iris/v12"
+	"github.com/kataras/iris/v12/context"
+)
+
+func main() {
+	app := iris.New()
+
+	// subdomains works with all available routers, like other features too.
+
+	app.Get("/", func(ctx iris.Context) {
+		ctx.BeginTransaction(func(t *context.Transaction) {
+			// OPTIONAl STEP: , if true then the next transictions will not be executed if this transiction fails
+			// t.SetScope(context.RequestTransactionScope)
+
+			// OPTIONAL STEP:
+			// create a new custom type of error here to keep track of the status code and reason message
+			err := context.NewTransactionErrResult()
+
+			// we should use t.Context if we want to rollback on any errors lives inside this function clojure.
+			t.Context().Text("Blablabla this should not be sent to the client because we will fill the err with a message and status")
+
+			// virtualize a fake error here, for the sake of the example
+			fail := true
+			if fail {
+				err.StatusCode = iris.StatusInternalServerError
+				// NOTE: if empty reason then the default or the custom http error will be fired (like ctx.FireStatusCode)
+				err.Reason = "Error: Virtual failure!!"
+			}
+
+			// OPTIONAl STEP:
+			// but useful if we want to post back an error message to the client if the transaction failed.
+			// if the reason is empty then the transaction completed successfully,
+			// otherwise we rollback the whole response writer's body,
+			// headers and cookies, status code and everything lives inside this transaction
+			t.Complete(err)
+		})
+
+		ctx.BeginTransaction(func(t *context.Transaction) {
+			t.Context().HTML("<h1>This will sent at all cases because it lives on different transaction and it doesn't fails</h1>")
+			// * if we don't have any 'throw error' logic then no need of scope.Complete()
+		})
+
+		// OPTIONALLY, depends on the usage:
+		// at any case, what ever happens inside the context's transactions send this to the client
+		ctx.HTML("<h1>Let's add a second html message to the response, " +
+			"if the transaction was failed and it was request scoped then this message would " +
+			"not been shown. But it has a transient scope(default) so, it is visible as expected!</h1>")
+	})
+
+	app.Listen(":8080")
+}