[node.js] Nodejs send file in response

You need use Stream to send file (archive) in a response, what is more you have to use appropriate Content-type in your response header.

There is an example function that do it:

const fs = require('fs');

// Where fileName is name of the file and response is Node.js Reponse. 
responseFile = (fileName, response) => {
  const filePath =  "/path/to/archive.rar" // or any file format

  // Check if file specified by the filePath exists 
  fs.exists(filePath, function(exists){
      if (exists) {     
        // Content-type is very interesting part that guarantee that
        // Web browser will handle response in an appropriate manner.
        response.writeHead(200, {
          "Content-Type": "application/octet-stream",
          "Content-Disposition": "attachment; filename=" + fileName
        });
        fs.createReadStream(filePath).pipe(response);
      } else {
        response.writeHead(400, {"Content-Type": "text/plain"});
        response.end("ERROR File does not exist");
      }
    });
  }
}

The purpose of the Content-Type field is to describe the data contained in the body fully enough that the receiving user agent can pick an appropriate agent or mechanism to present the data to the user, or otherwise deal with the data in an appropriate manner.

"application/octet-stream" is defined as "arbitrary binary data" in RFC 2046, purpose of this content-type is to be saved to disk - it is what you really need.

"filename=[name of file]" specifies name of file which will be downloaded.

For more information please see this stackoverflow topic.