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package registry
import (
"encoding/json"
"errors"
"net/http"
"regexp"
)
var (
ErrNoMorePages = errors.New("no more pages")
)
// getPaginatedJSON accepts a string and a pointer, and returns the
// next page URL while updating pointed-to variable with a parsed JSON
// value. When there are no more pages it returns `ErrNoMorePages`.
func (registry *Registry) getPaginatedJSON(url string, response interface{}) (string, error) {
resp, err := registry.Client.Get(url)
if err != nil {
return "", err
}
defer resp.Body.Close()
decoder := json.NewDecoder(resp.Body)
err = decoder.Decode(response)
if err != nil {
return "", err
}
return getNextLink(resp)
}
// Matches an RFC 5988 (https://tools.ietf.org/html/rfc5988#section-5)
// Link header. For example,
//
// <http://registry.example.com/v2/_catalog?n=5&last=tag5>; type="application/json"; rel="next"
//
// The URL is _supposed_ to be wrapped by angle brackets `< ... >`,
// but e.g., quay.io does not include them. Similarly, params like
// `rel="next"` may not have quoted values in the wild.
var nextLinkRE = regexp.MustCompile(`^ *<?([^;>]+)>? *(?:;[^;]*)*; *rel="?next"?(?:;.*)?`)
func getNextLink(resp *http.Response) (string, error) {
for _, link := range resp.Header[http.CanonicalHeaderKey("Link")] {
parts := nextLinkRE.FindStringSubmatch(link)
if parts != nil {
return parts[1], nil
}
}
return "", ErrNoMorePages
}
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