Escape URLs before adding them to bazel rules

Currently we produce the final URL by performing string
concatenation, which works fine in most cases.

The URL, however, might contain special characters that bazel
is later unable to process correctly. One such example:

  Error downloading passt-0^20221110.g4129764-1.el9.x86_64.rpm: Illegal character in path at index 78:
  https://mirror.stream.centos.org/9-stream/AppStream/x86_64/os/Packages/passt-0^20221110.g4129764-1.el9.x86_64.rpm

This issue made it necessary to manually tweak the WORKSPACE
file generated by bazeldnf:

  kubevirt/kubevirt@8052a7f

To solve this entire class of issues, use the functionality
offered by the net/url package to manipulare URLs. This will
automatically take care of performing all the necessary
escaping, as well as avoiding unnecessary slashes.

Signed-off-by: Andrea Bolognani <[email protected]>

pkg/bazel/bazel.go

@@ -3,6 +3,7 @@ package bazel
 import (
 	"fmt"
 	"io/ioutil"
+	"net/url"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -236,11 +237,15 @@ func (r *RPMRule) URLs() []string {
 	return nil
 }
 
-func (r *RPMRule) SetURLs(urls []string, href string) error {
+func (r *RPMRule) SetURLs(mirrors []string, href string) error {
 	urlsAttr := []build.Expr{}
-	for _, url := range urls {
-		u := strings.TrimSuffix(url, "/") + "/" + strings.TrimSuffix(href, "/")
-		urlsAttr = append(urlsAttr, &build.StringExpr{Value: u})
+	for _, mirror := range mirrors {
+		u, err := url.Parse(mirror)
+		if err != nil {
+			return err
+		}
+		u = u.JoinPath(href)
+		urlsAttr = append(urlsAttr, &build.StringExpr{Value: u.String()})
 	}
 	r.Rule.SetAttr("urls", &build.ListExpr{List: urlsAttr})
 	return nil