Do not cache dnslink lookup when API is offline

Author: lidel

lib/api.js

@@ -57,7 +57,7 @@ function isDnslinkPresent (fqdn) {
   try {
     xhr.send(null)
   } catch (e) {
-    return false
+    return null
   }
   if (xhr.status === 200) {
     let json = JSON.parse(xhr.responseText)
@@ -71,9 +71,11 @@ function isDnslinkPresentCached (fqdn) {
   let ipfsSupport = dnsCache.get(fqdn)
   if (typeof ipfsSupport === 'undefined') {
     ipfsSupport = isDnslinkPresent(fqdn)
-    dnsCache.put(fqdn, ipfsSupport)
+    if (ipfsSupport !== null) { // dont cache is API was down
+      dnsCache.put(fqdn, ipfsSupport)
+    }
   }
-  return ipfsSupport
+  return !!ipfsSupport
 }
 
 exports.apiUrl = apiUrl