Adding 5s sleep between retry and fixing retry logic.

src/sidebar.js

@@ -1,4 +1,9 @@
 var concurrency = 5
+var retry_delay = 15/* seconds */
+
+function sleep(delay) {
+    return new Promise((resolve) => setTimeout(resolve, delay*1000));
+}
 
 function getCurrentTab() {
     console.debug("Querying active tab.");
@@ -65,7 +70,8 @@ class Book{
             .catch((error)=>{
                 if (!retry){
                     console.warn(`Failed ${url} - ${error.message}`)
-                    return this.downloadResource(url, true)
+                    return sleep(retry_delay)
+                            .then(()=>{return this.downloadResource(url, true)})
                 } else {
                     console.error(`Giving up on ${url} - ${error.message}`)
                     throw `Failed second try on ${url} - ${error.message}`
@@ -76,7 +82,8 @@ class Book{
                     return res
                 } else if (!retry){
                     console.warn(`Failed ${url} - ${res.status} - ${res.statusText}`)
-                    return this.downloadResource(url, true)
+                    return sleep(retry_delay)
+                            .then(()=>{return this.downloadResource(url, true)})
                 } else {
                     console.error(`Giving up on ${url} - ${res.status} - ${res.statusText}`)
                     throw `Failed second try on ${url} - ${res.status} - ${res.statusText}`
@@ -174,6 +181,11 @@ class Book{
 
     downloadContent(){
         return Promise.map(Object.keys(this.book_files), (url) => {
+                return this.downloadContentFile(url)
+            },{concurrency: concurrency})
+    }
+
+    downloadContentFile(url){
         return this.downloadAndReport(url, this.book_files[url].filename)
         .then((res) => {
             if (res.ok){
@@ -187,7 +199,6 @@ class Book{
         .catch((error)=>{
             throw `Failed to download book content: "${error}"`
         })
-            },{concurrency: concurrency})
     }
 
     insertBookFile(url, filename){