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

Former-commit-id: ed635ee95de7160cde11eaabc0c1dcb0e460a620

_examples/database/mysql/api/httperror.go

@@ -0,0 +1,60 @@
+package api
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/kataras/iris/v12"
+)
+
+// Error holds the error sent by server to clients (JSON).
+type Error struct {
+	StatusCode int    `json:"code"`
+	Method     string `json:"-"`
+	Path       string `json:"-"`
+	Message    string `json:"message"`
+	Timestamp  int64  `json:"timestamp"`
+}
+
+func newError(statusCode int, method, path, format string, args ...interface{}) Error {
+	msg := format
+	if len(args) > 0 {
+		// why we check for that? If the original error message came from our database
+		// and it contains fmt-reserved words
+		// like %s or %d we will get MISSING(=...) in our error message and we don't want that.
+		msg = fmt.Sprintf(msg, args...)
+	}
+
+	if msg == "" {
+		msg = iris.StatusText(statusCode)
+	}
+
+	return Error{
+		StatusCode: statusCode,
+		Method:     method,
+		Path:       path,
+		Message:    msg,
+		Timestamp:  time.Now().Unix(),
+	}
+}
+
+// Error implements the internal Go error interface.
+func (e Error) Error() string {
+	return fmt.Sprintf("[%d] %s: %s: %s", e.StatusCode, e.Method, e.Path, e.Message)
+}
+
+// Is implements the standard `errors.Is` internal interface.
+// Usage: errors.Is(e, target)
+func (e Error) Is(target error) bool {
+	if target == nil {
+		return false
+	}
+
+	err, ok := target.(Error)
+	if !ok {
+		return false
+	}
+
+	return (err.StatusCode == e.StatusCode || e.StatusCode == 0) &&
+		(err.Message == e.Message || e.Message == "")
+}