Storage: Expose preconditions via the google-cloud-storage API

[brennie]

It would be very useful if google-cloud-storage exposed a way to set preconditions on upload. I am currently hacking around this by replacing google.cloud.storage.blob. _MULTIPART_URL_TEMPLATE and google.cloud.storage.blob._RESUMABLE_URL_TEMPLATE with versions that have the precondition I require, e.g.

from google.cloud import storage as gcs

gcs.blob._MULTIPART_URL_TEMPLATE = (
    f'{gcs.blob._MULTIPART_URL_TEMPLATE}&ifGenerationMatch=0'
)
gcs.blob._RESUMABLE_URL_TEMPLATE = (
    f'{gcs.blob._RESUMABLE_URL_TEMPLATE}&ifGenerationMatch=0'
)

Luckily I am only uploading blobs that I do not want to exist beforehand. It would be great if there were a way to programmatically do this, but I could not find anything after pouring over the documentation and source code.

I hope you'll implement this in a future version.

Thanks for your time!

[dhermes]

Thanks for the request @brennie this is definitely something worth adding!

[bits01]

Thanks for posting the hack, very useful until the feature is implemented.

[tseaver]

For uploads, there are three cases:

• Do not pass the ifGenerationMatch query string parameter (this would need to be the default for backward-compatibility)
• Pass &ifGenerationMatch=0 if there is no generation set on the blob resource.
• Pass &ifGenerationMatch=<current-generation> if there is a generation set.

After a chat with @frankyn, I'm closing this issue: he will be working with the GCS team to prioritize more complete precondition support in our feature backlog.

[amygdala]

Is there an ETA for this?