packer: Properly handle ? in URLs in cache keys

/cc @sit - Found another edge case

packer/cache.go

@@ -73,14 +73,14 @@ func (f *FileCache) RUnlock(key string) {
 
 func (f *FileCache) cachePath(key string, hashKey string) string {
 	suffix := ""
-	dotIndex := strings.LastIndex(key, ".")
+	endIndex := strings.Index(key, "?")
-	if dotIndex > -1 {
+	if endIndex == -1 {
-		suffix = key[dotIndex:len(key)]
+		endIndex = len(key)
+	}
 
-		idx := strings.Index(suffix, "?")
+	dotIndex := strings.LastIndex(key[0:endIndex], ".")
-		if idx != -1 {
+	if dotIndex > -1 {
-			suffix = suffix[0:idx]
+		suffix = key[dotIndex:endIndex]
-		}
 	}
 
 	return filepath.Join(f.CacheDir, hashKey+suffix)

packer/cache_test.go

@@ -37,8 +37,8 @@ func TestFileCache(t *testing.T) {
 	defer os.RemoveAll(cacheDir)
 
 	cache := &FileCache{CacheDir: cacheDir}
-	path := cache.Lock("foo.ext?foo=bar")
+	path := cache.Lock("foo.ext?foo=bar.foo")
-	defer cache.Unlock("foo.ext?foo=bar")
+	defer cache.Unlock("foo.ext?foo=bar.foo")
 	if !strings.HasSuffix(path, ".ext") {
 		t.Fatalf("bad extension with question mark: %s", path)
 	}