Read buffer helper

app/src/main/java/eu/faircode/email/ActivitySetup.java

@@ -717,10 +717,8 @@ public class ActivitySetup extends ActivityBase implements FragmentManager.OnBac
                     else {
                         byte[] salt = new byte[16];
                         byte[] prefix = new byte[16];
-                        if (raw.read(salt) != salt.length)
-                            throw new IOException("Invalid file size");
-                        if (raw.read(prefix) != prefix.length)
-                            throw new IOException("Invalid file size");
+                        Helper.readBuffer(raw, salt);
+                        Helper.readBuffer(raw, prefix);
 
                         SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
                         KeySpec keySpec = new PBEKeySpec(password.toCharArray(), salt, KEY_ITERATIONS, KEY_LENGTH);

app/src/main/java/eu/faircode/email/Helper.java

@@ -1124,6 +1124,16 @@ public class Helper {
         }
     }
 
+    public static void readBuffer(InputStream is, byte[] buffer) throws IOException {
+        int left = buffer.length;
+        while (left > 0) {
+            int count = is.read(buffer, buffer.length - left, left);
+            if (count < 0)
+                throw new IOException("EOF");
+            left -= count;
+        }
+    }
+
     static void copy(File src, File dst) throws IOException {
         try (InputStream in = new FileInputStream(src)) {
             try (FileOutputStream out = new FileOutputStream(dst)) {