Generate Presigned Url for Azure Blob throws Null pointer exception

Question

I want to generate a Presigned URL /SAS so that anyone with that url can access my file.

SDK Version : 12.8.0

I wrote the foll code :

BlockBlobClient blockBlobClient = objectStoreService.getBlobContainerClient().getBlobClient(fileName).getBlockBlobClient();

        String blobUrl = Utility.urlDecode(blockBlobClient.getBlobUrl());
        BlobSasPermission blobPermission = new BlobSasPermission()
                .setReadPermission(true);

        BlobServiceSasSignatureValues blobServiceSasSignatureValues = new BlobServiceSasSignatureValues(
                OffsetDateTime.now(ZoneOffset.UTC).plusSeconds(1000 * 60 * 60),
                blobPermission
        );
  
        blobUrl = blobUrl + "?" + blockBlobClient.generateSas(blobServiceSasSignatureValues);

But the code throws error as

java.lang.NullPointerException: The argument must not be null or an empty string. Argument name: storageSharedKeyCredentials.

Edit 1 : Tried with :

UserDelegationKey userDelegationKey = blobServiceClient.getUserDelegationKey(keyStart,keyExpiry);

String blobUrl = Utility.urlDecode(blobClient.getBlobUrl());

blobUrl = blobUrl + "?" + blobClient.generateUserDelegationSas(blobServiceSasSignatureValues,userDelegationKey);

But now getting :

"Status code 403, "AuthenticationFailedServer failed to authenticate the request. Make sure the value of Authorization header is formed correctly including the signature.\nRequestId:7b0f0d75-d01e-00a8-4d84-7c9aa3000000\nTime:2021-07-19T09:54:31.1312999ZThe specified signed resource is not allowed for the this resource level"",

Error is pretty straightforward - You will need to create storageSharedKeyCredentials to sign your SAS. — Gaurav Mantri
@GauravMantri , I dont have the account key to create the credentials. In my organization, we get access to blob store via service which only provides a sasToken, container name and container uri — Atharva Karanje
To generate a SAS token you will need either the account key or use Azure AD access token. You cannot generate a SAS token using another SAS token. — Gaurav Mantri
Oh ok. @GauravMantri, is there any other way wherein I can generate a presigned url for my file using these credentials ( Sas Token, Account name, Container URI, Container Name) ? — Atharva Karanje
Sure you can. I thought you wanted to create a new SAS token. Do you want to create a SAS URL for a blob given all these parameters. Correct? — Gaurav Mantri

Gaurav Mantri Gaurav Mantri · Accepted Answer · 2021-07-19T10:14:59

Assuming you have a SAS token with valid permissions, blob container URL and the name of the blob, you can generate the SAS URL for the blob using this simple logic:

{blob-container-url}/{blob-name}?{sas-token}

If you want to use the SDK, first you will create a BlobContainerClient using your blob container URL and SAS token and then create a BlockBlobClient using that blob container client:

BlobContainerClient blobContainerClient = new BlobContainerClientBuilder()
    .endpoint("{blob-container-url}?{sas-token}")
    .buildClient();

BlockBlobClient blockBlobClient = blobContainerClient.getBlobClient("{blob-name}").getBlockBlobClient();

You can then use this blockBlobClient to perform operations on your blob. You can use getUrl() method to get the URL of the blob.

Generate Presigned Url for Azure Blob throws Null pointer exception

1 Answers