return the download URL of a file uploaded to firebase

问题

Is there a simple way to get the download URL of a file uploaded to Firebase?

(I've tried playing around with the snapshot returned by my upload function and couldn't find anything...)

     fileref.put(file).then(function(snapshot){
     self.addEntry(snapshot);   
     ///  return snapshot.url???
     });

回答1:

To get the Url created by default from the snapshot you can use downloadURL, meaning snapshot.downloadURL.

Remember to always keep tracking the progress of the upload by using .on('state_changed'), Documentation here.

回答2:

The documentation referenced by Yamil - Firebase javascript SDK file upload - recommends using the snapshot's ref property to invoke the getDownloadURL method, which returns a promise containing the download link:

Using your code as a starting point:

fileref.put(file)
   .then(snapshot => {
       return snapshot.ref.getDownloadURL();   // Will return a promise with the download link
   })

   .then(downloadURL => {
      console.log(`Successfully uploaded file and got download link - ${downloadURL}`);
      return downloadURL;
   })

   .catch(error => {
      // Use to signal error if something goes wrong.
      console.log(`Failed to upload file and get link - ${error}`);
   });

I know it seems like unnecessary effort and that you should be able to get the link via a property of the snapshot, but this is what the Firebase team recommends - they probably have a good reason for doing it this way.

回答3:

When using user based security rules as given in official docs

// Only an individual user can write to "their" images

  match /{userId}/{imageId} {
    allow write: if request.auth.uid == userId;
  }

url retrieved by snapshot.downloadURL is exposing userId. How to overcome this security risk.

来源：https://stackoverflow.com/questions/43911080/return-the-download-url-of-a-file-uploaded-to-firebase