How to check file format before uploading a file in container using loopback-component-storage?

Question

I have tried this way sample code. I can successfully upload the file, but before that I have to validate file type and allow only *.csv files.

Answer 1

You can use mime node module for that. https://www.npmjs.com/package/mime

Answer 2

You must complement sample code as follows:

1. Edit server/datasources.json, add to storage datasources the allowedContentTypes field, an array of mime types that you want support

   ...
    "storage": {
        "name": "storage",
        "connector": "loopback-component-storage",
        "provider": "filesystem", 
        "root": "/var/www/storage",
        "maxFileSize": "52428800",
        "allowedContentTypes":["text/csv", "application/vnd.ms-excel"]
    }
   ...
   

2. This step is optional but is a good practice. The error can be handled in callback, also can add a remote hook in the container model file common/models/container.js

    module.exports = function (container) {
      container.afterRemoteError('upload', function (ctx, next) {
       //do any with ctx.error
     });
    }