builder: Fix URL build for base URL with subpath

When building the upstream URL, if the b.UpstreamURL was set do a url
with a subpath included, the subpath was being discarded by
URL.ResolveReference(). In order to preserve the subpath in the base,
the provided subpath must be manually added to the base URL object.

Signed-off-by: Rodrigo Chiossi <rodrigo.chiossi@intel.com>

builder/builder.go

@@ -27,6 +27,7 @@ import (
 	"net/url"
 	"os"
 	"os/exec"
+	"path"
 	"path/filepath"
 	"runtime"
 	"sort"
@@ -171,17 +172,16 @@ func (b *Builder) getLatestUpstreamVersion() (string, error) {
 // buildUpstreamURL builds the full upstream URL based on a b.UpstreamURL and a
 // supplied subpath
 func (b *Builder) buildUpstreamURL(subpath string) (string, error) {
-	// Build the URL
-	end, err := url.Parse(subpath)
-	if err != nil {
-		return "", err
-	}
 	base, err := url.Parse(b.UpstreamURL)
 	if err != nil {
 		return "", err
 	}
 
-	return base.ResolveReference(end).String(), nil
+	for _, token := range strings.Split(subpath, "/") {
+		base.Path = path.Join(base.Path, token)
+	}
+
+	return base.String(), nil
 }
 
 // DownloadFileFromUpstreamAsString will download a file from the Upstream URL