extract readTextFromUri into FileHelper

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/util/FileHelper.java

@@ -41,7 +41,11 @@ import org.sufficientlysecure.keychain.R;
 import org.sufficientlysecure.keychain.compatibility.DialogFragmentWorkaround;
 import org.sufficientlysecure.keychain.ui.dialog.FileDialogFragment;
 
+import java.io.ByteArrayOutputStream;
 import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.UnsupportedEncodingException;
 import java.text.DecimalFormat;
 
 public class FileHelper {
@@ -234,6 +238,39 @@ public class FileHelper {
         return new DecimalFormat("#,##0.#").format(size / Math.pow(1024, digitGroups)) + " " + units[digitGroups];
     }
 
+    public static String readTextFromUri(Context context, Uri outputUri, String charset)
+        throws IOException {
+
+        byte[] decryptedMessage;
+        {
+            InputStream in = context.getContentResolver().openInputStream(outputUri);
+            ByteArrayOutputStream out = new ByteArrayOutputStream();
+            byte[] buf = new byte[256];
+            int read;
+            while ( (read = in.read(buf)) > 0) {
+                out.write(buf, 0, read);
+            }
+            in.close();
+            out.close();
+            decryptedMessage = out.toByteArray();
+        }
+
+        String plaintext;
+        if (charset != null) {
+            try {
+                plaintext = new String(decryptedMessage, charset);
+            } catch (UnsupportedEncodingException e) {
+                // if we can't decode properly, just fall back to utf-8
+                plaintext = new String(decryptedMessage);
+            }
+        } else {
+            plaintext = new String(decryptedMessage);
+        }
+
+        return plaintext;
+
+    }
+
     public static interface FileDialogCallback {
         public void onFileSelected(File file, boolean checked);
     }