Fix GitbookIO/plugin-youtube#2: hash remote image for local path

lib/utils/images.js

@@ -22,7 +22,11 @@ var convertSVG = function(source, dest, options) {
         	if (error.code == 127) error = new Error("Need to install 'svgexport' using 'npm install svgexport -g'");
         	return d.reject(error);
         }
-        d.resolve();
+        if (fs.existsSync(dest)) {
+            d.resolve();
+        } else {
+            d.reject(new Error("Error converting "+source));
+        }
     });
 
 	return d.promise;

lib/utils/page.js

@@ -4,6 +4,7 @@ var path = require('path');
 var cheerio = require('cheerio');
 var domSerializer = require('dom-serializer');
 var request = require('request');
+var crc = require("crc");
 
 var links = require('./links');
 var imgUtils = require('./images');
@@ -123,7 +124,7 @@ function normalizeHtml(src, options) {
             // If image is external and ebook, then downlaod the images
             if (isExternal) {
                 origin = src;
-                src = "/"+fs.getUniqueFilename(outputRoot,  path.basename(src));
+                src = "/"+crc.crc32(origin).toString(16)+path.extname(origin);
                 src = links.toAbsolute(src, options.base, options.output);
                 isExternal = false;
             }
@@ -226,6 +227,7 @@ function normalizeHtml(src, options) {
 function convertImages(images, options) {
     if (!options.convertImages) return Q();
 
+    var downloaded = [];
     options.book.log.debug.ln("convert ", images.length, "images to png");
 
     return _.reduce(images, function(prev, image) {
@@ -235,8 +237,9 @@ function convertImages(images, options) {
 
         // Write image if need to be download
         .then(function() {
-            if (!image.origin) return;
+            if (!image.origin && !_.contains(downloaded, image.origin)) return;
             options.book.log.debug("download image", image.origin, "...");
+            downloaded.push(image.origin);
             return options.book.log.debug.promise(fs.writeStream(imgin, request(image.origin)));
         })
 
@@ -247,7 +250,7 @@ function convertImages(images, options) {
         })
 
         // Convert
-        .then(function(){
+        .then(function() {
             if (!image.dest) return;
             var imgout = path.resolve(options.book.options.output, image.dest);
             options.book.log.debug("convert image", image.source, "to", image.dest, "...");