Method computeEtag

httpheaders/conditionalheaders/request.go:95–125

computeEtag determines whether the If-None-Match header should be sent to the source image server. It returns etag value to be set and boolean indicating whether the conditional headers should be sent at all.

()

// source image server. It returns etag value to be set and boolean indicating
// whether the conditional headers should be sent at all.
func (c *Request) computeEtag() (string, bool) {
	// If the feature is disabled or no header is present,
	// we shouldn't send the header at all, but it should not affect other headers
	if !c.config.ETagEnabled || len(c.ifNoneMatch) == 0 {
		return "", false
	}

	// If etag buster is not set, we should send the header as is if present
	if len(c.config.ETagBuster) == 0 {
		return c.ifNoneMatch, false
	}

	// Unquote and remove /W
	ifNoneMatch := httpheaders.UnquoteEtag(c.ifNoneMatch)

	// We expect that incoming ETag header has the buster
	rest, busterFound := strings.CutPrefix(ifNoneMatch, c.config.ETagBuster+"/")
	if !busterFound {
		return "", true // do not send any conditional headers otherwise (???)
	}

	// Parse the rest of the header as base64-encoded string, if it fails,
	// we should not send any conditional headers (invalid etag)
	etag, err := base64.RawURLEncoding.DecodeString(rest)
	if err != nil {
		return "", true // do not send any conditional headers otherwise
	}

	// Quotes will be encoded into etag
	return string(etag), false
}

// injectLastModifiedHeader injects the Last-Modified header into the user response
func (c *Request) injectLastModifiedHeader(rw http.ResponseWriter) {