Validate image's binary mimetype on Node.js

image-checker.js

const fs = require('fs');
const path = require('path');
const assert = require("assert");
const imageType = require('image-type');
const readChunk = require('read-chunk');
const isSvg = require('is-svg');

/**
 * Validate image binary
 * if it is ok, return undefined,
 * if it is not ok, return an error object
 * https://github.com/sindresorhus/image-type
 * @param {Buffer} buffer
 * @param {string[]} mimeTypes
 * @returns {Error|undefined}
 */
function validateBinaryMIMEType(buffer, mimeTypes) {
  assert.ok(Array.isArray(mimeTypes) && mimeTypes.every(mimeType => mimeType.includes("/")),
    `Should be set an array of mimeType. e.g.) ['image/jpeg']`);
  const result = imageType(buffer);
  if (!result) {
    return new Error("This buffer is not image");
  }
  const isAllowed = mimeTypes.includes(result.mime);
  if (!isAllowed) {
    return new Error(`This buffer is disallowed image: ${result.mime}`);
  }
}

/**
 * validae content of file path
 * Careful: do check SVG also
 * @param {string} filePath
 * @param {string[]} mimeTypes
 * @returns {Error|undefined}
 * @example
 *
 * ```
 * const validationResult = validateMIMEType("test.png", ['image/jpeg', 'image/gif', 'image/png', 'image/svg+xml']);
 * if(validationResult) {
 *   console.error(validationResult)
 * }
 * ```
 */
function validateMIMEType(filePath, mimeTypes) {
  // SVG is not binary, check at first
  // https://github.com/sindresorhus/is-svg
  const allowSVG = mimeTypes.includes("image/svg+xml");
  const fileExt = path.extname(filePath);
  if (allowSVG && fileExt === ".svg") {
    const content = fs.readFileSync(filePath, "utf-8");
    if (!isSvg(content)) {
      return new Error(`This file is not svg`);
    }
    return;
  }
  // pick header of a binary
  const buffer = readChunk.sync(filePath, 0, 12);
  return validateBinaryMIMEType(buffer, mimeTypes);
}


module.exports.validateMIMEType = validateMIMEType;
module.exports.validateBinaryMIMEType = validateBinaryMIMEType;