Ionic File plugin creates blank file

Ionic Native
1

Hi folks,

I have to download pdf file based on data coming from API, thus for this I am using ionic native file plugin for creating the file and saving it in the device storage.
Following is the process

  1. Receives data as octect-stream from API
  2. Create blobs
  3. By using writeFile() of file plugin I store it in the device storage.

The pdf file gets created successfully, with correct size and format, but when I open it, file is empty as in no data is displayed.

Can anyone shed some light on this.
Following is the code

import { File } from '@ionic-native/file/ngx';

downloadPDF() {
    if (this.platform.is('android')) {
      this.androidPermissions.checkPermission(this.androidPermissions.PERMISSION.WRITE_EXTERNAL_STORAGE)
        .then(status => {
          if (status.hasPermission) {
            this.downloadFile();
          }
          else {
            this.androidPermissions.requestPermission(this.androidPermissions.PERMISSION.WRITE_EXTERNAL_STORAGE)
              .then(status => {
                if (status.hasPermission) {
                  this.downloadFile();
                }
              })
          }
        })
    } else {
      this.downloadFile();
    }
  }

downloadFile() {
    
    this.apiService.postRequest(URL, "").subscribe(resp => {
      let blobData = new Blob([resp._body], { type: "application/pdf" });
      console.log("blobData", blobData);
      let fileName ="myPdf.pdf";
      this.writeImageFile(blobData, 'Download', fileName, true);
    })
  }

writeImageFile(imageData, newdirectory, fileName, isBlob?) {
    console.log("inside write file fucntion");
    let rootdirectory = this.file.externalApplicationStorageDirectory;
    console.log("rootdirectory", rootdirectory)
    console.log("new directory", rootdirectory + newdirectory)//imageobj["entityGuid"]
    let imagetowrite: any;
    if (isBlob)
      imagetowrite = imageData;

    console.log("imagetowrite", imagetowrite);
    return this.file.createDir(rootdirectory, newdirectory, false).then(newdir => {
      console.log(newdir)
      console.log(fileName)
      return this.file.writeFile(rootdirectory + newdirectory, fileName, imagetowrite, { replace: true }).then(filedata => {
        console.log(filedata)
        console.log(rootdirectory + newdirectory + "/" + fileName)

        return filedata
        // this.readFile()
      }).catch(err1 => {
        console.log("directory does not exist - error")
        console.log(err1)
      })
    }).catch(err => {
      console.log(err)
      console.log(fileName)
      return this.file.writeFile(rootdirectory + newdirectory, fileName, imagetowrite, { replace: true }).then(filedata => {
        console.log(filedata)
        return filedata
      }).catch(err1 => {
        console.log("directory exist - error")
        console.log(err1)
      })
    })
  }