Using a Presigned URL to Upload Data to OBS

Solution Architecture

Each request initiated by an app client applies for a presigned URL from the app server. The validity period of the presigned URL is determined by the app server. Figure 1 describes the process.

Figure 1 Process for a mobile app to access data in OBS

Role Analysis

• App client: End user's mobile app. It requests a presigned URL from the app server, and uploads data to or downloads data from OBS.
• App server: A backend provided by developers of Android or iOS apps. It manages the credential information and issues presigned URLs.
• OBS: Huawei Cloud's object storage service. It processes requests from mobile apps.

Prerequisites

• A bucket has been created.

  Create a bucket on OBS Console. Configure the bucket permissions, and allow it to be read/written privately, read publicly, or written privately.

  For details, see Creating a Bucket and Configuring a Custom Bucket Policy.

• Access keys (AK and SK) have been obtained.

  The presigned URL is generated using the access keys. For details about how to obtain access keys, see Access Keys (AK/SK). The user who uses the access keys (AK/SK) needs to have the minimum required permissions. For details about how to authorize the permissions, see Creating a User and Granting OBS Permissions.

Resource and Cost Planning

The table below describes the resources that you need in this practice.

Procedure

1. Configure an app server.
   1. Obtain the SDK.
   2. Generate the code for issuing a presigned URL.

      For details, see Authentication of Signature in a URL.

      The following example describes how to use Java for development on the app server.

      

      The application server needs to identify the common request header and user-defined request header based on the operation type initiated by the app, and add the headers to the presigned URL for computing the signature.

      • For details about common request headers, see Constructing a Request.
      • For details about user-defined request headers, see the corresponding operation in the API Reference. For example, for PUT uploads, see Uploading Objects - PUT.

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      // Endpoint of the requested bucket String endPoint = "http://your-endpoint"; // Hard-coded or plaintext AK and SK are risky. For security purposes, encrypt your AK and SK and store them in the configuration file or environment variables. In this example, the AK and SK are stored in environment variables for identity authentication. Before running the code in this example, configure environment variables ACCESS_KEY_ID and SECRET_ACCESS_KEY_ID. // Obtain an AK and SK pair on the management console. For details, see https://support.huaweicloud.com/eu/usermanual-ca/ca_01_0003.html. String ak = System.getenv("ACCESS_KEY_ID"); String sk = System.getenv("SECRET_ACCESS_KEY_ID"); //Create an ObsClient. ObsClient obsClient = new ObsClient(ak, sk, endPoint); //Define the expiration time, in seconds. long expireSeconds = 3600L; //Specify the requested operation. TemporarySignatureRequest request = new TemporarySignatureRequest(HttpMethodEnum.PUT, expireSeconds); //Specify the bucket name and object name involved in this operation. request.setBucketName("bucketname"); request.setObjectKey("objectname"); TemporarySignatureResponse response = obsClient.createTemporarySignature(request); //If the following message is returned, the presigned URL is successfully issued, and you can print the URL information. System.out.println(response.getSignedUrl());

2. Use the presigned URL to initiate an OBS access request.

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   public class Demo extends Activity { private static String bucketName = "my-obs-bucket-demo"; private static String objectKey = "my-obs-object-key-demo"; private static OkHttpClient httpClient; private static StringBuffer sb; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); sb = new StringBuffer(); /* * Constructs a client instance with your account for accessing OBS */ httpClient = new OkHttpClient.Builder().followRedirects(false).retryOnConnectionFailure(false) .cache(null).build(); final TextView tv = (TextView)findViewById(R.id.tv); tv.setText("Click to start test"); tv.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { tv.setClickable(false); AsyncTask<Void, Void, String> task = new DownloadTask(); task.execute(); } }); } class DownloadTask extends AsyncTask<Void, Void, String> { @Override protected String doInBackground(Void... params) { try { /* * You need to construct an object upload request and send it to the application server to generate a presigned URL for accessing OBS. * If the response result is stored in response, obtain the URL using the getSignedUrl() method. */ sb.append("Uploading a new object to OBS from a file\n\n"); Request.Builder builder = new Request.Builder(); //Make a PUT request to upload an object. Request httpRequest = builder.url(response.getSignedUrl()).put(RequestBody.create(MediaType.parse(contentType), "Hello OBS".getBytes("UTF-8"))).build(); Call c = httpClient.newCall(httpRequest); Response res = c.execute(); sb.append("\tStatus:" + res.code()); if (res.body() != null) { sb.append("\tContent:" + res.body().string() + "\n"); } res.close(); /* * You need to construct an object download request and send it to the application server to generate a presigned URL for accessing OBS. * If the response result is stored in response, obtain the URL using the getSignedUrl() method. */ sb.append("Downloading an object\n\n"); Request.Builder builder = new Request.Builder(); //Make a GET request to download an object. Request httpRequest = builder.url(response.getSignedUrl()).get().build(); OkHttpClient httpClient = new OkHttpClient.Builder().followRedirects(false).retryOnConnectionFailure(false).cache(null).build(); Call c = httpClient.newCall(httpRequest); Response res = c.execute(); System.out.println("\tStatus:" + res.code()); if (res.body() != null) { sb.append("\tContent:" + res.body().string() + "\n"); } res.close(); return sb.toString(); } catch (Exception e) { sb.append("\n\n"); sb.append(e.getMessage()); return sb.toString(); } finally { if (httpClient != null) { try { /* * Close obs client */ httpClient.close(); } catch (IOException e) { } } } } @Override protected void onPostExecute(String result) { TextView tv = (TextView)findViewById(R.id.tv); tv.setText(result); tv.setOnClickListener(null); tv.setMovementMethod(ScrollingMovementMethod.getInstance()); } } }