imago-azure-storage/common.js

An opinionated async wrapper for azure-storage for working with Azure Storage such as tables and queues.

const { Readable } = require('stream');

/**
 * Converts a stream into a string.
 * @param {Writable} stream - Any stream, e.g. a MemoryStream.
 */
function readStreamAsString(stream) {
  const bufferParts = [];

  // TODO FIXME - it may happen that the promise never resolves?
  // Should we have a timeout?
  return new Promise((resolve, reject) => {
    stream.on('data', (buffer) => {
      bufferParts.push(buffer);
    });

    stream.on('end', () => {
      resolve(Buffer.concat(bufferParts));
    });

    stream.on('error', (error) => {
      reject(error);
    });
  });
}

/**
 * Converts a buffer or string into a readable stream.
 * @param {string|Buffer} contentStringOrBuffer
 */
function stringToStream(contentStringOrBuffer) {
  const dataStream = new Readable();

  // For some reason, if content is a string, then content.length
  // will be incorrect and Azure will create an incomplete file. So convert
  // the string into the buffer.
  const contentBuffer = Buffer.from(contentStringOrBuffer);

  dataStream.push(contentBuffer);
  dataStream.push(null); // end the stream

  return [dataStream, contentBuffer.length];
}

/**
 * Converts the array of objects, each of which is in Azure Table's internal
 * format, into an array of normal JavaScript objects where each key is a
 * column name.
 * @param {object[]} data
 */
async function azureTablesArrayToObject(data) {
  const result = [];
  for (const row of data) {
    result.push(azureTablesRowToObject(row));
  }
  return result;
}

function azureTablesRowToObject(row) {
  const data = {};
  Object.keys(row).forEach((column) => {
    if (column !== '.metadata') {
      data[column] = row[column]._;
    }
  });
  return data;
}

module.exports = {
  azureTablesArrayToObject,
  azureTablesRowToObject,
  readStreamAsString,
  stringToStream,
};