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

Former-commit-id: ed635ee95de7160cde11eaabc0c1dcb0e460a620

_examples/url-shortener/factory.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+	"net/url"
+
+	"github.com/google/uuid"
+)
+
+// Generator the type to generate keys(short urls)
+type Generator func() string
+
+// DefaultGenerator is the defautl url generator
+var DefaultGenerator = func() string {
+	id, _ := uuid.NewRandom()
+	return id.String()
+}
+
+// Factory is responsible to generate keys(short urls)
+type Factory struct {
+	store     Store
+	generator Generator
+}
+
+// NewFactory receives a generator and a store and returns a new url Factory.
+func NewFactory(generator Generator, store Store) *Factory {
+	return &Factory{
+		store:     store,
+		generator: generator,
+	}
+}
+
+// Gen generates the key.
+func (f *Factory) Gen(uri string) (key string, err error) {
+	// we don't return the parsed url because #hash are converted to uri-compatible
+	// and we don't want to encode/decode all the time, there is no need for that,
+	// we save the url as the user expects if the uri validation passed.
+	_, err = url.ParseRequestURI(uri)
+	if err != nil {
+		return "", err
+	}
+
+	key = f.generator()
+	// Make sure that the key is unique
+	for {
+		if v := f.store.Get(key); v == "" {
+			break
+		}
+		key = f.generator()
+	}
+
+	return key, nil
+}