How do I create a Google Cloud Storage resumable upload URL with Google Client Library for Java on App Engine?

Question

I found the follow note, which describes exactly what I'd like to do:

Note: If your users are only uploading resources (writing) to an access-controlled bucket, you can use the resumable uploads functionality of Google Cloud Storage, and avoid signing URLs or requiring a Google account. In a resumable upload scenario, your (server-side) code authenticates and initiates an upload to Google Cloud Storage without actually uploading any data. The initiation request returns an upload ID, which can then be used in a client request to upload the data. The client request does not need to be signed because the upload ID, in effect, acts as an authentication token. If you choose this path, be sure to transmit the upload ID over HTTPS.

https://cloud.google.com/storage/docs/access-control#Signed-URLs

However, I cannot figure out how to do this with the Google Cloud Storage Library for Java.

https://developers.google.com/resources/api-libraries/documentation/storage/v1/java/latest/

I can't find any reference to resumable files, or getting the URL for a file anywhere in this API. How can I do this?

Answer 1

That library does not expose the URLs that it creates to its caller, which means you can't use it to accomplish this. If you want to use either signed URLs or the trick you mention above, you'll need to implement it manually.

I would advise going with the signed URL solution over the solution where the server initializes the resumable upload, if possible. It's more flexible and easier to get right, and there are some odd edge cases with the latter method that you could run into.

Someone wrote a up a quick example of signing a URL from App Engine a while back in another question: Cloud storage and secure download strategy on app engine. GCS acl or blobstore

Answer 2

You can build the url yourself. Here is an example :

OkHttpClient client = new OkHttpClient();
AppIdentityService appIdentityService = credential.getAppIdentityService();
Collection<String> scopes = credential.getScopes();
String accessToken = appIdentityService.getAccessToken(scopes).getAccessToken();
Request request = new Request.Builder()
        .url("https://www.googleapis.com/upload/storage/v1/b/" + bucket + "/o?name=" + fileName + "&uploadType=resumable")
        .post(RequestBody.create(MediaType.parse(mimeType), new byte[0]))
        .addHeader("X-Upload-Content-Type", mimeType)
        .addHeader("X-Upload-Content-Length", "" + length)
        .addHeader("Origin", "http://localhost:8080")
        .addHeader("Origin", "*")
        .addHeader("authorization", "Bearer "+accessToken)
        .build();
Response response = client.newCall(request).execute();
return response.header("location");