fix application bug

vendor/github.com/go-acme/lego/acme/api/service.go

@@ -0,0 +1,45 @@
+package api
+
+import (
+	"net/http"
+	"regexp"
+)
+
+type service struct {
+	core *Core
+}
+
+// getLink get a rel into the Link header
+func getLink(header http.Header, rel string) string {
+	var linkExpr = regexp.MustCompile(`<(.+?)>;\s*rel="(.+?)"`)
+
+	for _, link := range header["Link"] {
+		for _, m := range linkExpr.FindAllStringSubmatch(link, -1) {
+			if len(m) != 3 {
+				continue
+			}
+			if m[2] == rel {
+				return m[1]
+			}
+		}
+	}
+	return ""
+}
+
+// getLocation get the value of the header Location
+func getLocation(resp *http.Response) string {
+	if resp == nil {
+		return ""
+	}
+
+	return resp.Header.Get("Location")
+}
+
+// getRetryAfter get the value of the header Retry-After
+func getRetryAfter(resp *http.Response) string {
+	if resp == nil {
+		return ""
+	}
+
+	return resp.Header.Get("Retry-After")
+}