Added support for resuming downloads

src/main/java/com/rarchives/ripme/ripper/AbstractRipper.java

@@ -616,4 +616,6 @@ public abstract class AbstractRipper
 
     // If true ripme uses a byte progress bar
     protected boolean useByteProgessBar() { return false;}
+    // If true ripme will try to resume a broken download for this ripper
+    protected boolean tryResumeDownload() { return false;}
 }

src/main/java/com/rarchives/ripme/ripper/DownloadFileThread.java

@@ -59,28 +59,25 @@ class DownloadFileThread extends Thread {
         this.cookies = cookies;
     }
 
-    private int getTotalBytes(URL url) throws IOException {
-        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
-        conn.setRequestMethod("HEAD");
-        conn.setRequestProperty("accept",  "*/*");
-        conn.setRequestProperty("Referer", this.url.toExternalForm()); // Sic
-        conn.setRequestProperty("User-agent", AbstractRipper.USER_AGENT);
-        return conn.getContentLength();
-    }
-
 
     /**
      * Attempts to download the file. Retries as needed.
      * Notifies observers upon completion/error/warn.
      */
     public void run() {
+        long fileSize = 0;
+        int bytesTotal = 0;
+        int bytesDownloaded = 0;
+        if (saveAs.exists() && observer.tryResumeDownload()) {
+            fileSize = saveAs.length();
+        }
         try {
             observer.stopCheck();
         } catch (IOException e) {
             observer.downloadErrored(url, "Download interrupted");
             return;
         }
-        if (saveAs.exists()) {
+        if (saveAs.exists() && !observer.tryResumeDownload()) {
             if (Utils.getConfigBoolean("file.overwrite", false)) {
                 logger.info("[!] Deleting existing file" + prettySaveAs);
                 saveAs.delete();
@@ -90,22 +87,6 @@ class DownloadFileThread extends Thread {
                 return;
             }
         }
-
-        int bytesTotal, bytesDownloaded = 0;
-        if (observer.useByteProgessBar()) {
-            try {
-                bytesTotal = getTotalBytes(this.url);
-            } catch (IOException e) {
-                logger.error("Failed to get file size at " + this.url, e);
-                observer.downloadErrored(this.url, "Failed to get file size of " + this.url);
-                return;
-            }
-
-            observer.setBytesTotal(bytesTotal);
-            observer.sendUpdate(STATUS.TOTAL_BYTES, bytesTotal);
-            logger.debug("Size of file at " + this.url + " = " + bytesTotal + "b");
-        }
-
         URL urlToDownload = this.url;
         boolean redirected = false;
         int tries = 0; // Number of attempts to download
@@ -139,11 +120,20 @@ class DownloadFileThread extends Thread {
                     cookie += key + "=" + cookies.get(key);
                 }
                 huc.setRequestProperty("Cookie", cookie);
+                if (observer.tryResumeDownload()) {
+                    if (fileSize != 0) {
+                        huc.setRequestProperty("Range", "bytes=" + fileSize + "-");
+                    }
+                }
                 logger.debug("Request properties: " + huc.getRequestProperties());
                 huc.connect();
 
                 int statusCode = huc.getResponseCode();
                 logger.debug("Status code: " + statusCode);
+                if (statusCode != 206 && observer.tryResumeDownload()) {
+                    // TODO find a better way to handle servers that don't support resuming downloads then just erroring out
+                    throw new IOException("Server doesn't support resuming downloads");
+                }
                 if (statusCode  / 100 == 3) { // 3xx Redirect
                     if (!redirected) {
                         // Don't increment retries on the first redirect
@@ -171,6 +161,15 @@ class DownloadFileThread extends Thread {
                     observer.downloadErrored(url, "Imgur image is 404: " + url.toExternalForm());
                     return;
                 }
+
+                // If the ripper is using the bytes progress bar set bytesTotal to huc.getContentLength()
+                if (observer.useByteProgessBar()) {
+                    bytesTotal = huc.getContentLength();
+                    observer.setBytesTotal(bytesTotal);
+                    observer.sendUpdate(STATUS.TOTAL_BYTES, bytesTotal);
+                    logger.debug("Size of file at " + this.url + " = " + bytesTotal + "b");
+                }
+
                 // Save file
                 bis = new BufferedInputStream(huc.getInputStream());
 
@@ -179,8 +178,12 @@ class DownloadFileThread extends Thread {
                     String fileExt = URLConnection.guessContentTypeFromStream(bis).replaceAll("image/", "");
                     saveAs = new File(saveAs.toString() + "." + fileExt);
                 }
-
+                // If we're resuming a download we append data to the existing file
+                if (statusCode == 206) {
+                    fos = new FileOutputStream(saveAs, true);
+                } else {
                     fos = new FileOutputStream(saveAs);
+                }
                 byte[] data = new byte[1024 * 256]; int bytesRead;
                 while ( (bytesRead = bis.read(data)) != -1) {
                     try {