vcs-test/vcweb: fix various extraction issues for serving modules with authentication

• The /auth subdirectory wasn't downloading content from GCS.

• The zip extraction logic was failing for zip files that do not
  contain explicit directory entries.

• The invocation of http.FileServer wasn't trimming the /auth prefix,
  so rejections would work correctly but successful authentication
  would return 404s instead of serving the file.

Updates golang/go#26232

Change-Id: I3a72d7dfca62435c53f4bc7efaebae3900f2c175
Reviewed-on: https://go-review.googlesource.com/c/build/+/170880
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

vcs-test/vcweb/auth.go

@@ -113,5 +113,5 @@ func (h *authHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	http.FileServer(h.dir).ServeHTTP(w, r)
+	http.StripPrefix("/auth/", http.FileServer(h.dir)).ServeHTTP(w, r)
 }

vcs-test/vcweb/load.go

@@ -16,7 +16,6 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"strings"
 	"sync"
 	"time"
 
@@ -119,10 +118,11 @@ func loadFS(dir1, dir2 string, force bool) {
 	check(os.MkdirAll(tmp, 0777))
 
 	for _, f := range zr.File {
-		if strings.HasSuffix(f.Name, "/") {
+		if f.FileInfo().IsDir() {
 			check(os.MkdirAll(filepath.Join(tmp, f.Name), 0777))
 			continue
 		}
+		check(os.MkdirAll(filepath.Join(tmp, filepath.Dir(f.Name)), 0777))
 		w, err := os.Create(filepath.Join(tmp, f.Name))
 		check(err)
 		r, err := f.Open()

vcs-test/vcweb/main.go

@@ -42,6 +42,7 @@ func usage() {
 }
 
 var isLoadDir = map[string]bool{
+	"auth":   true,
 	"go":     true,
 	"git":    true,
 	"hg":     true,