神奇的504 Bad Gateway Timeout

今天遇到一个神奇的BUG，一个终端去下载一张图片，出现了504 Bad Gateway Timeout错误，把同样的url放到PC浏览器上又能正常打开，最后问题是解决了，但是具体原因还没搞清楚。

望有高人看到指点一下

出现问题的代码如下：

HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();
connection.setRequestMethod("GET");
if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {
InputStream is = connection.getInputStream();
BufferedInputStream bis = new BufferedInputStream(is);

bis.mark(1024);
byte[] buffer = new byte[1024];
bis.read(buffer);
String orientation = parseOrientation(buffer);

// decode bitmap size
bis.reset();
bis.mark(bis.available());
Options options = new Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeStream(bis, null, options);

// decode scaled bitmap
bis.reset();
options.inSampleSize = calculateScaleSize(options.outWidth, options.outHeight);
options.inJustDecodeBounds = false;
Bitmap scaleBitmap = BitmapFactory.decodeStream(bis, null, options);
bis.close();
is.close();
}

经过多次尝试后，下面代码可以正常下载到图片：

HttpURLConnection connection = (HttpURLConnection) new URL(url).openConnection();
connection.setRequestMethod("GET");
if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {
InputStream is = connection.getInputStream();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] buffer = new byte[10240];
int length;
while ((length = is.read(buffer)) > -1) {
baos.write(buffer, 0, length);
}
baos.flush();
Log.d(TAG, "download finish: " + baos.size());

ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
baos.close();
is.close();
bais.mark(1024);

buffer = new byte[1024];
bais.read(buffer);
String orientation = parseOrientation(buffer);

// decode bitmap size
bais.reset();
bais.mark(bais.available());
Options options = new Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeStream(bais, null, options);

// decode scaled bitmap
bais.reset();
options.inSampleSize = calculateScaleSize(options.outWidth, options.outHeight);
options.inJustDecodeBounds = false;
Bitmap scaleBitmap = BitmapFactory.decodeStream(bais, null, options);
bais.close();
is.close();
}