refactor(docker): Adding a safer way to retrieve the next link

Signed-off-by: Vincent Boutour <[email protected]>

pkg/docker/docker.go

@@ -19,6 +19,7 @@ import (
 const (
 	registryURL = "https://index.docker.io"
 	authURL     = "https://auth.docker.io/token"
+	nextLink    = `rel="next"`
 )
 
 type authResponse struct {
@@ -108,7 +109,7 @@ func (a app) LatestVersions(repository string, patterns []string) (map[string]se
 
 		<-done
 
-		url = getNextURL(resp, registry)
+		url = getNextURL(resp.Header, registry)
 	}
 
 	return versions, nil
@@ -132,16 +133,27 @@ func (a app) getImageDetails(ctx context.Context, repository string) (string, st
 	return registryURL, repository, token, nil
 }
 
-func getNextURL(resp *http.Response, registry string) string {
-	link := resp.Header.Get("link")
-	if len(link) == 0 {
+func getNextURL(headers http.Header, registry string) string {
+	links := headers.Values("link")
+	if len(links) == 0 {
 		return ""
 	}
 
-	parts := strings.Split(link, ";")
-	path := strings.Trim(strings.Trim(parts[0], "<"), ">")
+	for _, link := range links {
+		if !strings.Contains(link, nextLink) {
+			continue
+		}
+
+		for _, part := range strings.Split(link, ";") {
+			if strings.Contains(part, nextLink) {
+				continue
+			}
+
+			return fmt.Sprintf("%s%s", registry, strings.TrimSpace(strings.Trim(strings.Trim(part, "<"), ">")))
+		}
+	}
 
-	return fmt.Sprintf("%s%s", registry, path)
+	return ""
 }
 
 func (a app) login(ctx context.Context, repository string) (string, error) {

pkg/docker/docker_test.go

@@ -0,0 +1,59 @@
+package docker
+
+import (
+	"net/http"
+	"testing"
+)
+
+func TestGetNextURL(t *testing.T) {
+	type args struct {
+		headers  http.Header
+		registry string
+	}
+
+	upperCaseHeader := http.Header{}
+	upperCaseHeader.Add("Link", `rel="next"; /v2/test`)
+
+	lowerCaseHeader := http.Header{}
+	lowerCaseHeader.Add("link", `rel="prev"; /v2/prev`)
+	lowerCaseHeader.Add("link", `rel="next"; /v2/next`)
+
+	var cases = []struct {
+		intention string
+		args      args
+		want      string
+	}{
+		{
+			"empty",
+			args{
+				headers:  http.Header{},
+				registry: "http://localhost",
+			},
+			"",
+		},
+		{
+			"uppercase link with next",
+			args{
+				headers:  upperCaseHeader,
+				registry: "http://localhost",
+			},
+			"http://localhost/v2/test",
+		},
+		{
+			"lowercase link with previous and next inverted",
+			args{
+				headers:  lowerCaseHeader,
+				registry: "http://localhost",
+			},
+			"http://localhost/v2/next",
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.intention, func(t *testing.T) {
+			if got := getNextURL(tc.args.headers, tc.args.registry); got != tc.want {
+				t.Errorf("getNextURL() =`%s`, want`%s`", got, tc.want)
+			}
+		})
+	}
+}