Docker Registry 重定向的问题

func shouldCopyHeaderOnRedirect(headerKey string, initial, dest *url.URL) bool {
  	switch CanonicalHeaderKey(headerKey) {
  	case "Authorization", "Www-Authenticate", "Cookie", "Cookie2":
  		// Permit sending auth/cookie headers from "foo.com"
  		// to "sub.foo.com".
  
  		// Note that we don't send all cookies to subdomains
  		// automatically. This function is only used for
  		// Cookies set explicitly on the initial outgoing
  		// client request. Cookies automatically added via the
  		// CookieJar mechanism continue to follow each
  		// cookie's scope as set by Set-Cookie. But for
  		// outgoing requests with the Cookie header set
  		// directly, we don't know their scope, so we assume
  		// it's for *.domain.com.
  
  		// TODO(bradfitz): once issue 16142 is fixed, make
  		// this code use those URL accessors, and consider
  		// "http://foo.com" and "http://foo.com:80" as
  		// equivalent?
  
  		// TODO(bradfitz): better hostname canonicalization,
  		// at least once we figure out IDNA/Punycode (issue
  		// 13835).
  		ihost := strings.ToLower(initial.Host)
  		dhost := strings.ToLower(dest.Host)
  		return isDomainOrSubdomain(dhost, ihost)
  	}
  	// All other headers are copied:
  	return true
  }
  
  // isDomainOrSubdomain reports whether sub is a subdomain (or exact
  // match) of the parent domain.
  //
  // Both domains must already be in canonical form.
  func isDomainOrSubdomain(sub, parent string) bool {
  	if sub == parent {
  		return true
  	}
  	// If sub is "foo.example.com" and parent is "example.com",
  	// that means sub must end in "."+parent.
  	// Do it without allocating.
  	if !strings.HasSuffix(sub, parent) {
  		return false
  	}
  	return sub[len(sub)-len(parent)-1] == '.'
  }