How to build a readable stream in Node.js and TypeScript?

Question

I connected the typescript function to Azure Blobstorage through Rest-API and this works fine for me. Now I want to get each blob contents and read the contents of each blobs.

I try this with this code here, but it returns an error:

const blobServiceClient = new BlobServiceClient(`https://${accountName}.blob.core.windows.net?${sasToken}`,
      pipeline)
    const containerClient = blobServiceClient.getContainerClient(containerName)
    console.log(containerClient)
    if (!containerClient.exists()) {
      console.log("the container does not exit")
      await containerClient.create()

    }
    const client = containerClient.getBlockBlobClient(this.currentFile.name)

    //name of uploded blob
    console.log(this.currentFile.name)
    //metaata from the blob
    console.log(client)

    //List each blobs in the container
    for await (const blob of containerClient.listBlobsFlat()) {
      console.log('\t', blob.name);
      const blockBlobClient = containerClient.getBlockBlobClient(blob.name);
      const downloadBlockBlobResponse = await blockBlobClient.download(0);
      console.log('\nDownloaded blob content...');
      console.log('\t', await streamToString(downloadBlockBlobResponse.readableStreamBody));
      //end of loop
  }



  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);
    });
  }

The error is:

ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'on' of undefined TypeError: Cannot read property 'on' of undefined

So how to solve the problem? Thanks

Answer 1

Download the official sample code .

It runs normally on my side. Check if your local lack of dependencies, or the permissions in the storage need to be set.

// Copyright (c) Microsoft Corporation.
// Licensed under the MIT license.

/*
 Setup: Enter your storage account name and shared key in main()
*/

import {
 BlobServiceClient,
  StorageSharedKeyCredential,
  BlobDownloadResponseModel
} from "@azure/storage-blob";

// Load the .env file if it exists
import * as dotenv from "dotenv";
dotenv.config();

export async function main() {
  // Enter your storage account name and shared key
  const account = process.env.ACCOUNT_NAME || "pans*****age";
  const accountKey = process.env.ACCOUNT_KEY || "IHa48xxo+0anyKQ2GzQ2K*******ZBxgJ0VotCpGs/PMftkebb9UFqyg==";

  // Use StorageSharedKeyCredential with storage account and account key
  // StorageSharedKeyCredential is only available in Node.js runtime, not in browsers
  const sharedKeyCredential = new StorageSharedKeyCredential(account, accountKey);

  // ONLY AVAILABLE IN NODE.JS RUNTIME
  // DefaultAzureCredential will first look for Azure Active Directory (AAD)
  // client secret credentials in the following environment variables:
  //
  // - AZURE_TENANT_ID: The ID of your AAD tenant
  // - AZURE_CLIENT_ID: The ID of your AAD app registration (client)
  // - AZURE_CLIENT_SECRET: The client secret for your AAD app registration
  //
  // If those environment variables aren't found and your application is deployed
  // to an Azure VM or App Service instance, the managed service identity endpoint
  // will be used as a fallback authentication source.
  // const defaultAzureCredential = new DefaultAzureCredential();

  // You can find more TokenCredential implementations in the [@azure/identity](https://www.npmjs.com/package/@azure/identity) library
  // to use client secrets, certificates, or managed identities for authentication.

  // Use AnonymousCredential when url already includes a SAS signature
  // const anonymousCredential = new AnonymousCredential();

  // List containers
  const blobServiceClient = new BlobServiceClient(
    // When using AnonymousCredential, following url should include a valid SAS or support public access
    `https://${account}.blob.core.windows.net`,
    sharedKeyCredential
  );

  let i = 1;
  for await (const container of blobServiceClient.listContainers()) {
    console.log(`Container ${i++}: ${container.name}`);
  }

  // Create a container
  const containerName = `newcontainer${new Date().getTime()}`;
  const containerClient = blobServiceClient.getContainerClient(containerName);

  const createContainerResponse = await containerClient.create();
  console.log(`Create container ${containerName} successfully`, createContainerResponse.requestId);

  // Create a blob
  const content = "hello, 你好";
  const blobName = "newblob" + new Date().getTime();
  const blockBlobClient = containerClient.getBlockBlobClient(blobName);
  const uploadBlobResponse = await blockBlobClient.upload(content, Buffer.byteLength(content));
  console.log(`Upload block blob ${blobName} successfully`, uploadBlobResponse.requestId);

  // List blobs
  i = 1;
  for await (const blob of containerClient.listBlobsFlat()) {
    console.log(`Blob ${i++}: ${blob.name}`);
  }

  // Get blob content from position 0 to the end
  // In Node.js, get downloaded data by accessing downloadBlockBlobResponse.readableStreamBody
  // In browsers, get downloaded data by accessing downloadBlockBlobResponse.blobBody
  const downloadBlockBlobResponse: BlobDownloadResponseModel = await blockBlobClient.download(0);
  console.log(
    "Downloaded blob content",
    await streamToString(downloadBlockBlobResponse.readableStreamBody!)
  );

  // Delete container
  await containerClient.delete();

  console.log("deleted container");
}

// A helper method used to read a Node.js readable stream into string
async function streamToString(readableStream: NodeJS.ReadableStream) {
  return new Promise((resolve, reject) => {
    const chunks: string[] = [];
    readableStream.on("data", (data) => {
      chunks.push(data.toString());
    });
    readableStream.on("end", () => {
      resolve(chunks.join(""));
    });
    readableStream.on("error", reject);
  });
}

main().catch((err) => {
  console.error("Error running sample:", err.message);
});