Overriding files in GCS bucket

Google Cloud Compute Infrastructure
4

Hi again @amlanroy1980 ,

In Google Cloud Storage (GCS), conditional uploads allow you to upload files to the bucket only if certain conditions are met. These conditions can be based on the metadata of an existing file in the bucket, such as the etag (entity tag) or update time. By using conditional headers, you can control whether an upload should proceed based on the current state of the file in GCS.

Conditional Headers in GCS →

https://cloud.google.com/storage/docs/request-preconditions

GCS supports two conditional headers for uploads: If-Match:

    • This header allows you to specify the etag of the existing file in the bucket.
    • The upload will proceed only if the existing file’s etag matches the etag provided in the header.
    • This is useful for ensuring that you only update a file if it has not been modified since you last checked its etag.

  2. If-None-Match:

    • This header allows you to specify the etag of the existing file in the bucket.
    • The upload will proceed only if the existing file’s etag does not match the etag provided in the header.
    • This is useful for ensuring that you only upload a new file if the file does not currently exist in the bucket.

Here’s an example of how you might use the If-Match header in Python using the Google Cloud Storage client library:

from google.cloud import storage

Initialize the GCS client

client = storage.Client()

Define the bucket and file name

bucket_name = ‘your-bucket-name’
file_name = ‘your-file-name.json’

Get the bucket

bucket = client.bucket(bucket_name)

Get the existing file blob

blob = bucket.blob(file_name)

Retrieve the metadata of the existing file

if blob.exists():
existing_metadata = blob.metadata
existing_etag = blob.etag

Compare update time (assuming it’s stored as a custom metadata field)

incoming_update_time = ‘2024-04-01T12:00:00Z’ # Replace with the incoming update time

Perform the conditional upload only if the incoming update time is more recent

if incoming_update_time > existing_metadata.get(‘update_time’, ‘’):

Set the If-Match header with the existing etag

blob.upload_from_filename(‘path/to/new/file.json’, if_match=existing_etag)
print(‘File updated successfully.’)
else:
print(‘No update needed; incoming data is not more recent.’)
else:

If the file does not exist, upload the new file without conditions

blob.upload_from_filename(‘path/to/new/file.json’)
print(‘File uploaded successfully.’)

In this example, you first retrieve the metadata of the existing file and compare the update time with the incoming data. If the incoming data is more recent, you proceed with the conditional upload using the If-Match header. Otherwise, the upload is skipped.

5 Likes