Fetch image from azure-blob and send it to client without saving locally using node server

Question

Fetch image from azure-blob and send it to client without saving locally using node server

2.6k views Asked by Niraj Gawande At 20 November 2024 at 03:14

I want to fetch image from azure blob storage and send it over to client without saving it locally. I am able to get image from blob storage and save it to local file but struggling to send it to client without saving locally. Please find code below

    const containerClient = blobServiceClient.getContainerClient(containerName);
    const blockBlobClient = containerClient.getBlobClient(blobName);

    const downloadBlockBlobResponse = await blockBlobClient.download(0);
    console.log('\nDownloaded blob content...');
    let f = await streamToString(downloadBlockBlobResponse.readableStreamBody)
    
    reply.type('image/jpg').send(f)

streamToString function is as follows

     async function streamToString(readableStream) {
        return new Promise((resolve, reject) => {
        const chunks = [];
        readableStream.on("data", (data) => {
            chunks.push(data.toString());
        });
        readableStream.on("end", () => {
            resolve(chunks.join(""));
        });
        readableStream.on("error", reject);
     });
}

I get blank screen in browser when I run this code

Original Q&A

There are 1 answers

**Stanley Gong** · Accepted Answer · 2020-10-23 03:04:55

If you want to fetch an image from azure blob storage and send it over to the client without saving it locally, the Node server sending a SAS token to the client and the client get this image from Azure storage directly would be a better solution I think. It also eases the pressure of the Node server: generate a SAS token and send it to the client is ok, no need to read data from Storage.

Try the code below to generate a SAS token:

var azure = require('azure-storage');
    var connString = "your storage connection string";
    var container ="your container name";
    var blobName = "your image name"
    var blobService = azure.createBlobService(connString);

    // Create a SAS token that expires in an hour
    // Set start time to five minutes ago to avoid clock skew.
    var startDate = new Date();
    startDate.setMinutes(startDate.getMinutes() - 5);
    var expiryDate = new Date(startDate);
    expiryDate.setMinutes(startDate.getMinutes() + 60);
    


    var sharedAccessPolicy = {
        AccessPolicy: {
            Permissions: [azure.BlobUtilities.SharedAccessPermissions.READ],  //grent read permission only
            Start: startDate,
            Expiry: expiryDate
        }
    };
    
    var sasToken = blobService.generateSharedAccessSignature(container, blobName, sharedAccessPolicy);
    
    var response = {};

    response.image = blobService.getUrl(container,blobName,sasToken);
    
    res.send(response);

Result:

Client-side could use this image URL to access this image directly from storage:

Try this to convert imageURL to base64 image content so that you can save/show images directly based on their content:

<html>

<body>
    <img id="displayImg">
</body>


<script>

var nodeResult = {"image":"https://stantest1016.blob.core.windows.net/stantest/test.jpeg?st=2020-10-26T04%3A53%3A51Z&se=2020-10-26T05%3A53%3A51Z&sp=r&sv=2018-03-28&sr=b&sig=ZjY3LYbgvMn%2BSr4dAEUoqidVRT4YyH1FcW1DeKlpjYo%3D"}


function getImageData(nodeResult){


var xhr = new XMLHttpRequest();
  xhr.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
        var reader = new FileReader();
        reader.readAsDataURL(this.response);
        reader.onload = function() {
            document.getElementById('displayImg').src = reader.result;
        }
  };
    
   
    
  };
  xhr.open('GET', nodeResult.image);
  xhr.responseType = 'blob';
  xhr.send();

}


getImageData(nodeResult);
</script>

</html>

Result:

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TechQA.

Fetch image from azure-blob and send it to client without saving locally using node server

There are 1 answers

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