How to download an excel (xlsx) file using Angular 5 HttpClient get method with Node/Express backend?

Question

I have an excel file in a directory on my nodejs server - Path to the file is - ./api/uploads/appsecuritydesign/output/appsecdesign.xlsx

On click of a button in my Angular 5 component I am just trying to download the file using FileSaver.

Below is my Angular component.

Here the template code for the button in Angular that will call the saveFile() function once clicked.

<a class="btn btn-primary" (click) = "saveFile()">Download</a>

Here is the saveFile() function.

   saveFile(){

    console.log("In ToolInput Component: ", this.token); //Okta token
          console.log("In ToolInput Component: ", this.whatamidoing); //this variable has the server FilePath

this.fileService.getappsecdesignfile(this.token, this.whatamidoing).subscribe(res => {
            let blobtool5 = new Blob([res], { type: 'application/vnd.ms-excel;charset=utf-8' });
            FileSaver.saveAs(blobtool5, 'Application_Security_Design.xlsx');
          },
          (err: HttpErrorResponse) => {
            if (err.error instanceof Error) {

                  console.log('An error occurred:', err.error.message);
                  console.log('Status', err.status);
                } else {
                  console.log(`Backend returned code ${err.status}, body was: ${err.error}`);
                  console.log('Status', err.status);
                }
          });
    }

At this point I checked the console.log in the browser. They are exactly what they are supposed to be. So I am passing the correct filepath and token to getappsecdesignfile method in my fileService.

Now Lets take a look at the getappsecdesignfile method in my fileService.

getappsecdesignfile ( token, tool5filepath ) : Observable<any>{

       console.log("In Service tool5filepath: ", tool5filepath);
       console.log("In Service token", token);
       console.log("In Service GET url: ", this.getappsecdesignfileurl);

       //Since the tool5filepath has / (slashes etc) I am encoding it below.

       let encodedtool5filepath = encodeURIComponent(tool5filepath);
       console.log('Encoded File Path: ', encodedtool5filepath);

       let req = new HttpRequest('GET', this.getappsecdesignfileurl,{params: new HttpParams().set('path', encodedtool5filepath)},{headers: new HttpHeaders().set('Accept', 'application/vnd.ms-excel').set('Authorization', token)});
       console.log(req);
       return this.http.request(req);

   }

That's all there is to the fileService method. Lets look at the console.logs from this method from the browser to ensure all the correct values are being set.

Now Lets take a look at the request itself before we go to the server part.

As far as I am concerned the headers are set correctly, params are set correctly. Two issues I see is that Angular's interceptors probably sets the responseType: json and adds a param op:s to my request.

Node/Express Server code.

app.get('/getappsecdesignfile', function(req, res){
console.log("In get method app security design");
    accessTokenString = req.headers.authorization;
    console.log("Okta Auth Token:", accessTokenString);

    console.log("Tool5 File Path from received from Angular: ", req.query.path); //this is where the server console logs shows Tool5 File Path after decoding: ./undefined

    oktaJwtVerifier.verifyAccessToken(accessTokenString)
    .then(jwt => {
    // the token is valid
      console.log(jwt.claims);

      res.setHeader('Content-Disposition', 'attachment; filename= + Application_Security_Design.xlsx');
      res.setHeader('Content-Type', 'application/vnd.ms-excel');

      let tool5filepath = './' + decodeURIComponent(req.query.path);
      console.log("Tool5 File Path after decoding: ", tool5filepath);
      res.download(tool5filepath);

      }).catch(err => {
        // a validation failed, inspect the error
        res.json({success : false, message : 'Authorization error.'});
      });
    });

If I use Postman the api works fine. However somewhere between Angular to Node communication something happens that I don't understand.

Below is what the server logs. (Big question how does this become undefined)?

Tool5 File Path from received from Angular:  undefined
Tool5 File Path after decoding:  ./undefined
Error: ENOENT: no such file or directory, stat '<dirpath>/undefined'

Here is what I see in the browser log:

zone.js:2933 GET http://localhost:3000/getappsecdesignfile 404 (Not Found)
toolinput.component.ts:137 Backend returned code 404, body was: <!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Error</title>
</head>
<body>
<pre>Error: ENOENT: no such file or directory, stat &#39;<dirpath>/undefined&#39;</pre>
</body>
</html>

Then the browser downloads a xlsx file that is corrupt and cannot be opened.

I have checked the file resides in the directory and is ready to be downloaded.

Thanks for any tips that can help me resolve this issue.

Answer 1

Finally figured it out.

2 specific changes made this work.

Change # 1 - Setting responseType : 'blob' and defining the params and headers first and then using them in http.get. (http is nothing but an object of type HttpClient from angular/common/http that has been injected into the service class.

getappsecdesignfile ( token, tool5filepath ) : Observable<any>{

       console.log("In Service tool5filepath: ", tool5filepath);
       console.log("In Service token", token);
       console.log("In Service GET url: ", this.getappsecdesignfileurl);

       let encodedtool5filepath = encodeURIComponent(tool5filepath);
       console.log('Encoded File Path: ', encodedtool5filepath);

       let getfileparams = new HttpParams().set('filepath', encodedtool5filepath);
       let getfileheaders = new HttpHeaders().set('Accept', 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet').set('Authorization', token);

       return this.http.get(this.getappsecdesignfileurl, {responseType: 'blob', params: getfileparams, headers: getfileheaders});
   }

Change # 2 - Component code - FileSaver. For some reason type: 'application/vnd.ms-excel' did not work in FileSaver. Here the res is nothing but the response from the http.get call.

let blobtool5 = new Blob([res], { type: 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet' });
FileSaver.saveAs(blobtool5, 'Application_Security_Design.xlsx');