docker/docker_image_src.go
func simplifyContentType(contentType string) string {
	if contentType == "" {
		return contentType
	}
	mimeType, _, err := mime.ParseMediaType(contentType)
	if err != nil {
		return ""
	}
	return mimeType
}
func simplifyContentType(contentType string) string {
	if contentType == "" {
		return contentType
	}
	mimeType, _, err := mime.ParseMediaType(contentType)
	if err != nil {
		return ""
	}
	return mimeType
}
// simplifyContentType drops parameters from a HTTP media type (see https://tools.ietf.org/html/rfc7231#section-3.1.1.1)
// Alternatively, an empty string is returned unchanged, and invalid values are "simplified" to an empty string.