WIP #64: using 3 gateways and returning first successful result

plugins/gateway-ipns.js

@@ -22,18 +22,58 @@ var gateways = [
     'https://ipfs.best-practice.se/ipns/'   // Sweden
 ]
 
+
+/*
+ * to do this right we need a Promise.any() polyfill
+ * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/any
+ */
+Promise.any = async (promises) => {
+    // Promise.all() is the polar opposite of Promise.any()
+    // in that it returns as soon as there is a first rejection
+    // but without it, it returns an array of resolved results
+    return Promise.all(
+        promises.map(p => {
+            return new Promise((resolve, reject) =>
+                // swap reject and resolve, so that we can use Promise.all()
+                // and get the result we need
+                Promise.resolve(p).then(reject, resolve)
+            );
+        })
+    // now, swap errors and values back
+    ).then(
+        err => Promise.reject(err),
+        val => Promise.resolve(val)
+    );
+};
+
+
 /**
  * getting content using regular HTTP(S) fetch()
  */
 let fetchContentFromGatewayIPNS = (url) => {
     
+        
     // we're going to try a random gateway and building an URL of the form:
     // https://<gateway_address>/<ipnsPubkey>/<rest_of_URL>
-    var ipnsUrl = gateways[Math.floor(Math.random() * gateways.length)] + ipnsPubKey + url.replace(/https?:\/\/[^/]+/, '')
+    var ipnsUrl = ipnsPubKey + url.replace(/https?:\/\/[^/]+/, '')
+    
+    // pick 3 gateways, at random
+    var useGateways = new Array()
+    while (useGateways.length < 3) {
+        // put in the address while we're at it
+        useGateways.push(
+            gateways
+                .splice(Math.floor(Math.random() * gateways.length), 1)[0] + ipnsUrl
+        )
+    }
     
-    console.log(`Samizdat: gateway IPNS:\n+-- fetching: ${ipnsUrl}`)
+    // debug log
+    console.log(`Samizdat: gateway IPNS fetching:\n  ${useGateways.join('\n  ')}`)
     
-    return fetch(ipnsUrl, {cache: "reload"})
+    return Promise.any(
+        useGateways.map(
+            u=>fetch(u, {cache: "reload"})
+        ))
         .then((response) => {
             // 4xx? 5xx? that's a paddlin'
             if (response.status >= 400) {