flagext: Add new type URLEscaped

Sometimes we need to store just escaped URL in the config like S3 URL that contains credentials which can include characters like
`:` and `/`. Currently we cannot use normal `flagext.URLValue` as it just uses unescaped URL.

Please check issue
grafana/loki#1607

flagext/urlescaped.go

@@ -0,0 +1,63 @@
+package flagext
+
+import "net/url"
+
+// URLEscaped is a url.URL that can be used as a flag.
+// URL value it contains will always be URL escaped and safe.
+type URLEscaped struct {
+	*url.URL
+}
+
+// String implements flag.Value
+func (v URLEscaped) String() string {
+	if v.URL == nil {
+		return ""
+	}
+	return v.URL.String()
+}
+
+// Set implements flag.Value
+// Set make sure given URL string is escaped.
+func (v *URLEscaped) Set(s string) error {
+	s = url.QueryEscape(s)
+
+	u, err := url.Parse(s)
+	if err != nil {
+		return err
+	}
+	v.URL = u
+	return nil
+}
+
+// UnmarshalYAML implements yaml.Unmarshaler.
+func (v *URLEscaped) UnmarshalYAML(unmarshal func(interface{}) error) error {
+	var s string
+	if err := unmarshal(&s); err != nil {
+		return err
+	}
+
+	// An empty string means no URL has been configured.
+	if s == "" {
+		v.URL = nil
+		return nil
+	}
+
+	return v.Set(s)
+}
+
+// Marshalyaml Implements yaml.Marshaler.
+func (v URLEscaped) MarshalYAML() (interface{}, error) {
+	if v.URL == nil {
+		return "", nil
+	}
+
+	// Mask out passwords when marshalling URLs back to YAML.
+	u := *v.URL
+	if u.User != nil {
+		if _, set := u.User.Password(); set {
+			u.User = url.UserPassword(u.User.Username(), "********")
+		}
+	}
+
+	return u.String(), nil
+}

flagext/urlescaped_test.go

@@ -0,0 +1,38 @@
+package flagext
+
+import (
+	"flag"
+	"fmt"
+	"net/url"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gopkg.in/yaml.v2"
+)
+
+const (
+	testS3URL = "s3://ASDFGHJIQWETTYUI:Jkasduahdkjh213kj1h31+lkjaflkjzvKASDOasofhjafaKFAF/GoQd@region/bucket_name"
+)
+
+func TestURLEscaped(t *testing.T) {
+	expected, err := url.Parse(url.QueryEscape(testS3URL))
+	require.NoError(t, err)
+
+	// flag
+	var v URLEscaped
+	flags := flag.NewFlagSet("test", flag.ExitOnError)
+	flags.Var(&v, "v", "some secret credentials")
+	err = flags.Parse([]string{"-v", testS3URL})
+
+	assert.Equal(t, v.String(), expected.String())
+
+	// yaml
+	yv := struct {
+		S3 URLEscaped `yaml:"s3"`
+	}{}
+	err = yaml.Unmarshal([]byte(fmt.Sprintf("s3: %s", testS3URL)), &yv)
+	assert.NoError(t, err)
+	assert.Equal(t, yv.S3.String(), expected.String())
+
+}