Question

如何为用户通过BlobStore API提交的Google云端存储对象生成公共链接？

Answer 1

有几种方法可以提供公共GCS对象。一个是签名的URL。另一个是getServingUrl() App Engine方法。

但是，如果每个人都可以看到该对象，那么您可以做一些更简单的事情。设置对象的权限以向“AllUsers”授予READ权限，允许在没有任何身份验证的情况下读取对象，然后只需将用户引用到此路径：

https://storage.googleapis.com/BUCKET_NAME/OBJECT_NAME

就是这样！

您可以通过API或使用此gsutil命令将对象设置为可公开读取：gsutil acl ch -g AllUsers:R gs://BUCKET_NAME/OBJECT_NAME

Answer 2

如何为Google云端存储对象生成公开链接？

通过console手动创建服务帐户，并生成.p12密钥文件。
用户将文件上传到使用以下内容生成的网址后

blobstoreService.createUploadUrl("/fileUploadingHandler", 
        UploadOptions.Builder.withMaxUploadSizeBytes(1024*1024*10) // 10 MB max
                             .googleStorageBucketName(BUCKET_NAME));

servlet（处理/fileUploadingHandler）可以检索GCS对象的文件名并生成临时签名的公共链接，如下所示：

Map<String, List<FileInfo>> fileInfoMap = blobstoreService.getFileInfos(request);
List<FileInfo> fileInfos = fileInfoMap.get("fileName");
FileInfo fileInfo = fileInfos.get(0);
String[] parts = fileInfo.getGsObjectName().split("/"); // get rid of /gs/buck_name/
String fileName = parts[parts.length - 1];
String signedUrl = GcsUrlSigner.generateSignedUrl(fileName);
// send the temporary public link (signedUrl) back to the user

import com.google.api.client.util.Base64;

import java.io.InputStream;
import java.net.URLEncoder;
import java.security.KeyStore;
import java.security.PrivateKey;
import java.security.Signature;

/**
 * Created by Fouad on 22-Dec-15.
 */
public class GcsUrlSigner
{
    private static final String DEFAULT_BUCKET_NAME = "XXXXXXXX.appspot.com";
    private static final String PUBLIC_URL_SERVICE_ACCOUNT_EMAIL = "XXXXXXXX@XXXXXX.iam.gserviceaccount.com";
    private static final String PUBLIC_URL_SERVICE_ACCOUNT_PKCS12_FILE_PATH = "XXXXXX.p12"; // located in the same folder as GcsUrlSigner.java
    private static final String PUBLIC_URL_SERVICE_ACCOUNT_PKCS12_FILE_PASSWORD = "notasecret";
    private static final long PUBLIC_URL_EXPIRATION_SECONDS = System.currentTimeMillis() / 1000 + 60; // 60 seconds

    public static String generateSignedUrl(String objectName) throws Exception
    {
        return generateSignedUrl(DEFAULT_BUCKET_NAME, objectName);
    }

    public static String generateSignedUrl(String bucketName, String objectName) throws Exception
    {
        PrivateKey key = loadKeyFromPkcs12(PUBLIC_URL_SERVICE_ACCOUNT_PKCS12_FILE_PATH, PUBLIC_URL_SERVICE_ACCOUNT_PKCS12_FILE_PASSWORD.toCharArray());
        return getSigningURL(key, "GET", PUBLIC_URL_EXPIRATION_SECONDS, bucketName, objectName);
    }

    private static String getSigningURL(PrivateKey key, String verb, long expirationSeconds, String bucketName, String objectName) throws Exception
    {
        String url_signature = signString(key, verb + "\n\n\n" + expirationSeconds + "\n" + "/" + bucketName + "/" + objectName);
        String signed_url = "https://storage.googleapis.com/" + bucketName + "/" + objectName +
                "?GoogleAccessId=" + PUBLIC_URL_SERVICE_ACCOUNT_EMAIL +
                "&Expires=" + expirationMillis +
                "&Signature=" + URLEncoder.encode(url_signature, "UTF-8");
        return signed_url;
    }

    private static PrivateKey loadKeyFromPkcs12(String filename, char[] password) throws Exception
    {
        InputStream is = GcsUrlSigner.class.getResourceAsStream(PUBLIC_URL_SERVICE_ACCOUNT_PKCS12_FILE_PATH);
        KeyStore ks = KeyStore.getInstance("PKCS12");
        ks.load(is, password);
        return (PrivateKey) ks.getKey("privatekey", password);
    }

    private static String signString(PrivateKey key, String stringToSign) throws Exception
    {
        if(key == null) throw new Exception("Private Key not initalized");

        Signature signer = Signature.getInstance("SHA256withRSA");
        signer.initSign(key);
        signer.update(stringToSign.getBytes("UTF-8"));

        byte[] rawSignature = signer.sign();

        return new String(Base64.encodeBase64(rawSignature), "UTF-8");
    }
}

生成Google云端存储对象的公共链接

2 个答案: