Frequently asked questions (Android SDK)

Does OSS SDK for Android support DNS pre-resolution and cache policies?

Yes. Use HTTPDNS SDK and OkHttp together to implement DNS pre-resolution and caching. For more information, see Best practices for using HTTPDNS and OkHttp on Android.

1. Implement the API for a custom DNS resolution service.

   public class OkHttpDns implements Dns {
       private static final Dns SYSTEM = Dns.SYSTEM;
       HttpDnsService httpdns;
       private static OkHttpDns instance = null;
       private OkHttpDns(Context context) {
           this.httpdns = HttpDns.getService(context, "account id");
       }
       public static OkHttpDns getInstance(Context context) {
           if(instance == null) {
               instance = new OkHttpDns(context);
           }
           return instance;
       }
       @Override
       public List<InetAddress> lookup(String hostname) throws UnknownHostException {
           // Use the asynchronous resolution API to get the IP address.
           String ip = httpdns.getIpByHostAsync(hostname);
           if(ip != null) {
               // IP address resolved — use it for the network request.
               List<InetAddress> inetAddresses = Arrays.asList(InetAddress.getAllByName(ip));
               Log.e("OkHttpDns", "inetAddresses:" + inetAddresses);
               return inetAddresses;
           }
           // No IP address resolved — fall back to the system DNS service.
           return Dns.SYSTEM.lookup(hostname);
       }
   }

2. Create an OkHttpClient instance and configure DNS pre-resolution and caching.

   String endpoint = "http://oss-cn-hangzhou.aliyuncs.com";
   ClientConfiguration conf = new ClientConfiguration();
   conf.setConnectionTimeout(15 * 1000); // Connection timeout. Default: 15 seconds.
   conf.setSocketTimeout(15 * 1000); // Socket timeout. Default: 15 seconds.
   conf.setMaxConcurrentRequest(5); // Maximum concurrent requests. Default: 5.
   conf.setMaxErrorRetry(2); // Maximum retries. Default: 2.
   OkHttpClient.Builder builder = new OkHttpClient.Builder()
           .dns(OkHttpDns.getInstance(getApplicationContext()));
   // If you set a custom OkHttpClient, it overrides some ClientConfiguration settings.
   // Set those settings directly on the builder.
   if (conf != null) {
       Dispatcher dispatcher = new Dispatcher();
       dispatcher.setMaxRequests(conf.getMaxConcurrentRequest());
       builder.connectTimeout(conf.getConnectionTimeout(), TimeUnit.MILLISECONDS)
               .readTimeout(conf.getSocketTimeout(), TimeUnit.MILLISECONDS)
               .writeTimeout(conf.getSocketTimeout(), TimeUnit.MILLISECONDS)
               .followRedirects(conf.isFollowRedirectsEnable())
               .followSslRedirects(conf.isFollowRedirectsEnable())
               .dispatcher(dispatcher);
       if (conf.getProxyHost() != null && conf.getProxyPort() != 0) {
           builder.proxy(new Proxy(Proxy.Type.HTTP, new InetSocketAddress(conf.getProxyHost(), conf.getProxyPort())));
       }
   }
   // Android SDK 2.9.12 and later support conf.setOkHttpClient().
   conf.setOkHttpClient(builder.build());
   OSS oss = new OSSClient(getApplicationContext(), endpoint, credentialProvider, conf);

Why does the progress callback return totalSize=-1 when downloading objects?

• Cause: When OkHttp downloads objects of certain content types (text/cache-manifest, text/xml, text/plain, text/css, application/javascript, application/x-javascript, application/rss+xml, application/json, text/json) that are 1 KB or larger, it automatically adds the Accept-Encoding: gzip header — even if you did not set it. OSS then returns the object in gzip format without a Content-Length header, which causes the progress callback to report totalSize=-1.

• Fix: Set a Range header on the request. This prevents OkHttp from adding Accept-Encoding: gzip, so OSS returns Content-Length and the progress callback reports the correct size.

  Map<String, String> header = new HashMap<>();
  header.put("x-oss-range-behavior", "standard");
  // Replace examplebucket with your bucket name and exampledir/exampleobject.txt with the full object path.
  GetObjectRequest get = new GetObjectRequest("examplebucket", "exampledir/exampleobject.txt");
  get.setRange(new Range(0, -1));
  get.setRequestHeaders(header);
  OSSAsyncTask task = oss.asyncGetObject(get, new OSSCompletedCallback<GetObjectRequest, GetObjectResult>() {
      @Override
      public void onSuccess(GetObjectRequest request, GetObjectResult result) {
          InputStream inputStream = result.getObjectContent();
          byte[] buffer = new byte[2048];
          int len;
          try {
              while ((len = inputStream.read(buffer)) != -1) {
                  // Process the downloaded data.
              }
          } catch (IOException e) {
              e.printStackTrace();
          }
      }
      @Override
      public void onFailure(GetObjectRequest request, ClientException clientExcepion, ServiceException serviceException) {
          if (clientExcepion != null) {
              // Handle a local exception, such as a network error.
              clientExcepion.printStackTrace();
          }
          if (serviceException != null) {
              // Handle a service exception.
              Log.e("ErrorCode", serviceException.getErrorCode());
              Log.e("RequestId", serviceException.getRequestId());
              Log.e("HostId", serviceException.getHostId());
              Log.e("RawMessage", serviceException.getRawMessage());
          }
      }
  });

onFailure callback not triggered in Kotlin

• Cause

This is a Kotlin nullability issue. The OSS Android SDK defines the onFailure callback using Java syntax, where parameters are non-nullable by default:

@Override
public void onFailure(GetObjectRequest request, ClientException clientException, ServiceException serviceException){
    if (clientException != null) {
        clientException.printStackTrace();
    }
    if (serviceException != null) {
        Log.e("ErrorCode", serviceException.getErrorCode());
        Log.e("RequestId", serviceException.getRequestId());
        Log.e("HostId", serviceException.getHostId());
        Log.e("RawMessage", serviceException.getRawMessage());
    }
}

Kotlin treats these parameters as non-nullable, so the callback may not trigger as expected. Explicitly declare the parameters as nullable in the function signature:

onFailure(request: ResumableUploadRequest, clientException: ClientException?, serviceException: ServiceException?)