Add an example on how to use third-party handlers that are not compatible to the "next pattern"

Former-commit-id: 39a57bd97542142cb61eac9b0ee9b40df2334019

_examples/convert-handlers/real-usecase-raven/writing-middleware/main.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"runtime/debug"
+
+	"github.com/kataras/iris"
+
+	"github.com/getsentry/raven-go"
+)
+
+// At this example you will see how to convert any net/http middleware
+// that has the form of `(HandlerFunc) HandlerFunc`.
+// If the `raven.RecoveryHandler` had the form of
+// `(http.HandlerFunc)` or `(http.HandlerFunc, next http.HandlerFunc)`
+// you could just use the `irisMiddleware := iris.FromStd(nativeHandler)`
+// but it doesn't, however as you already know Iris can work with net/http directly
+// because of the `ctx.ResponseWriter()` and `ctx.Request()` are the original
+// http.ResponseWriter and *http.Request.
+// (this one is a big advantage, as a result you can use Iris for ever :)).
+//
+// The source code of the native middleware does not change at all.
+// https://github.com/getsentry/raven-go/blob/379f8d0a68ca237cf8893a1cdfd4f574125e2c51/http.go#L70
+// The only addition is the Line 18 and Line 39 (instead of handler(w,r))
+// and you have a new iris middleware ready to use!
+func irisRavenMiddleware(ctx iris.Context) {
+	w, r := ctx.ResponseWriter(), ctx.Request()
+
+	defer func() {
+		if rval := recover(); rval != nil {
+			debug.PrintStack()
+			rvalStr := fmt.Sprint(rval)
+			packet := raven.NewPacket(rvalStr, raven.NewException(errors.New(rvalStr), raven.NewStacktrace(2, 3, nil)), raven.NewHttp(r))
+			raven.Capture(packet, nil)
+			w.WriteHeader(iris.StatusInternalServerError)
+		}
+	}()
+
+	ctx.Next()
+}
+
+// https://docs.sentry.io/clients/go/integrations/http/
+func init() {
+	raven.SetDSN("https://<key>:<secret>@sentry.io/<project>")
+}
+
+func main() {
+	app := iris.New()
+	app.Use(irisRavenMiddleware)
+
+	app.Get("/", func(ctx iris.Context) {
+		ctx.Writef("Hi")
+	})
+
+	app.Run(iris.Addr(":8080"))
+}