Handle protocol relative URLs correctly when downloading episodes and images

fixes #568

app/src/androidTest/java/de/test/antennapod/util/URLCheckerTest.java

@@ -73,4 +73,32 @@ public class URLCheckerTest extends AndroidTestCase {
         final String out = URLChecker.prepareURL(in);
         assertEquals("https://example.com", out);
     }
+
+    public void testProtocolRelativeUrlIsAbsolute() throws Exception {
+        final String in = "https://example.com";
+        final String inBase = "http://examplebase.com";
+        final String out = URLChecker.prepareURL(in, inBase);
+        assertEquals(in, out);
+    }
+
+    public void testProtocolRelativeUrlIsRelativeHttps() throws Exception {
+        final String in = "//example.com";
+        final String inBase = "https://examplebase.com";
+        final String out = URLChecker.prepareURL(in, inBase);
+        assertEquals("https://example.com", out);
+
+    }
+
+    public void testProtocolRelativeUrlIsHttpsWithAPSubscribeProtocol() throws Exception {
+        final String in = "//example.com";
+        final String inBase = "antennapod-subscribe://https://examplebase.com";
+        final String out = URLChecker.prepareURL(in, inBase);
+        assertEquals("https://example.com", out);
+    }
+
+    public void testProtocolRelativeUrlBaseUrlNull() throws Exception {
+        final String in = "example.com";
+        final String out = URLChecker.prepareURL(in, null);
+        assertEquals("http://example.com", out);
+    }
 }

core/src/main/java/de/danoeh/antennapod/core/storage/DownloadRequester.java

@@ -90,7 +90,7 @@ public class DownloadRequester {
         return true;
     }
 
-    private void download(Context context, FeedFile item, File dest,
+    private void download(Context context, FeedFile item, FeedFile container, File dest,
                           boolean overwriteIfExists, String username, String password, boolean deleteOnFailure, Bundle arguments) {
         if (!isDownloadingFile(item)) {
             if (!isFilenameAvailable(dest.toString()) || (deleteOnFailure && dest.exists())) {
@@ -129,7 +129,8 @@ public class DownloadRequester {
             if (BuildConfig.DEBUG)
                 Log.d(TAG,
                         "Requesting download of url " + item.getDownload_url());
-            item.setDownload_url(URLChecker.prepareURL(item.getDownload_url()));
+            String baseUrl = (container != null) ? container.getDownload_url() : null;
+            item.setDownload_url(URLChecker.prepareURL(item.getDownload_url(), baseUrl));
 
             DownloadRequest request = new DownloadRequest(dest.toString(),
                     URLChecker.prepareURL(item.getDownload_url()), item.getHumanReadableIdentifier(),
@@ -171,7 +172,7 @@ public class DownloadRequester {
             args.putInt(REQUEST_ARG_PAGE_NR, feed.getPageNr());
             args.putBoolean(REQUEST_ARG_LOAD_ALL_PAGES, loadAllPages);
 
-            download(context, feed, new File(getFeedfilePath(context),
+            download(context, feed, null, new File(getFeedfilePath(context),
                     getFeedfileName(feed)), true, username, password, true, args);
         }
     }
@@ -183,7 +184,8 @@ public class DownloadRequester {
     public synchronized void downloadImage(Context context, FeedImage image)
             throws DownloadRequestException {
         if (feedFileValid(image)) {
-            download(context, image, new File(getImagefilePath(context),
+            FeedFile container = (image.getOwner() instanceof FeedFile) ? (FeedFile) image.getOwner() : null;
+            download(context, image, container, new File(getImagefilePath(context),
                     getImagefileName(image)), false, null, null, false, null);
         }
     }
@@ -209,7 +211,7 @@ public class DownloadRequester {
                 dest = new File(getMediafilePath(context, feedmedia),
                         getMediafilename(feedmedia));
             }
-            download(context, feedmedia,
+            download(context, feedmedia, feed,
                     dest, false, username, password, false, null);
         }
     }

core/src/main/java/de/danoeh/antennapod/core/util/URLChecker.java

@@ -1,5 +1,6 @@
 package de.danoeh.antennapod.core.util;
 
+import android.net.Uri;
 import android.util.Log;
 
 import org.apache.commons.lang3.StringUtils;
@@ -51,4 +52,28 @@ public final class URLChecker {
             return url;
         }
     }
+
+    /**
+     * Checks if URL is valid and modifies it if necessary.
+     * This method also handles protocol relative URLs.
+     *
+     * @param url  The url which is going to be prepared
+     * @param base The url against which the (possibly relative) url is applied. If this is null,
+     *             the result of prepareURL(url) is returned instead.
+     * @return The prepared url
+     */
+    public static String prepareURL(String url, String base) {
+        if (base == null) {
+            return prepareURL(url);
+        }
+        url = StringUtils.trim(url);
+        base = prepareURL(base);
+        Uri urlUri = Uri.parse(url);
+        Uri baseUri = Uri.parse(base);
+        if (urlUri.isRelative() && baseUri.isAbsolute()) {
+            return urlUri.buildUpon().scheme(baseUri.getScheme()).build().toString();
+        } else {
+            return prepareURL(url);
+        }
+    }
 }