filter: add basic pattern matching for label keys

Following PR adds basic pattern matching to filter by labels for `keys`.
Adds support for use-cases like `--filter label=some.prefix.com/key/*`
where end-users want to match a pattern for keys as compared to exact
value.

Signed-off-by: Aditya Rajan <arajan@redhat.com>

pkg/util/filters.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+	"regexp"
 	"strings"
 	"time"
 
@@ -94,6 +95,28 @@ func PrepareFilters(r *http.Request) (*map[string][]string, error) {
 	return &filterMap, nil
 }
 
+func wildCardToRegexp(pattern string) string {
+	var result strings.Builder
+	for i, literal := range strings.Split(pattern, "*") {
+		// Replace * with .*
+		if i > 0 {
+			result.WriteString(".*")
+		}
+		// Quote any regular expression meta characters in the
+		// literal text.
+		result.WriteString(regexp.QuoteMeta(literal))
+	}
+	return result.String()
+}
+
+func matchPattern(pattern string, value string) bool {
+	if strings.Contains(pattern, "*") {
+		result, _ := regexp.MatchString(wildCardToRegexp(pattern), value)
+		return result
+	}
+	return false
+}
+
 // MatchLabelFilters matches labels and returns true if they are valid
 func MatchLabelFilters(filterValues []string, labels map[string]string) bool {
 outer:
@@ -106,7 +129,7 @@ outer:
 			filterValue = ""
 		}
 		for labelKey, labelValue := range labels {
-			if labelKey == filterKey && (filterValue == "" || labelValue == filterValue) {
+			if ((labelKey == filterKey) || matchPattern(filterKey, labelKey)) && (filterValue == "" || labelValue == filterValue) {
 				continue outer
 			}
 		}

test/e2e/volume_ls_test.go

@@ -45,6 +45,17 @@ var _ = Describe("Podman volume ls", func() {
 		Expect(len(session.OutputToStringArray())).To(Equal(2))
 	})
 
+	It("podman ls volume filter with a key pattern", func() {
+		session := podmanTest.Podman([]string{"volume", "create", "--label", "helloworld=world", "myvol2"})
+		session.WaitWithDefaultTimeout()
+		Expect(session).Should(Exit(0))
+
+		session = podmanTest.Podman([]string{"volume", "ls", "--filter", "label=hello*"})
+		session.WaitWithDefaultTimeout()
+		Expect(session).Should(Exit(0))
+		Expect(len(session.OutputToStringArray())).To(Equal(2))
+	})
+
 	It("podman ls volume with JSON format", func() {
 		session := podmanTest.Podman([]string{"volume", "create", "myvol"})
 		session.WaitWithDefaultTimeout()