blob: introduce conditional write option for storage

[ocampeau]

This commit introduces support for conditional writes for major cloud providers: aws, gcp, azure.

It does so by adding a new write options: IfNotExist.

When set to true, conditions are set for each cloud storage driver to enable the desired behavior.

Addresses #3518

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[vangent]

Can you add a drivertest that exercises this new feature?

It'll be tricky for you to verify on GCP/Azure/AWS, but you should be able to get it working with memblob and fileblob. Once you've done that, you can comment it out, we can get this merged, and then I can generate the goldens for the GCP/Azure/AWS packages.

[ocampeau]

Thanks @vangent for the quick feedback. I have provided the implementation for the fileblob and memblob driver. I also added a test in the drivertest package.

Following your suggestion, I ran the tests for the memblob and fileblob package, and they all passed. I haven't been able to test for the cloud providers though. I have commented out the test so you can run them in your CI as mentioned.

Let me know if there is anything else that needs to be fixed.

[codecov]

Codecov Report

Attention: Patch coverage is 26.47059% with 25 lines in your changes missing coverage. Please review.

Project coverage is 70.47%. Comparing base (7caced7) to head (2b8057c).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
blob/fileblob/fileblob.go	36.84%	10 Missing and 2 partials ⚠️
blob/azureblob/azureblob.go	0.00%	6 Missing ⚠️
blob/memblob/memblob.go	25.00%	2 Missing and 1 partial ⚠️
blob/gcsblob/gcsblob.go	0.00%	1 Missing and 1 partial ⚠️
blob/s3blob/s3blob.go	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3533      +/-   ##
==========================================
- Coverage   70.55%   70.47%   -0.09%     
==========================================
  Files         113      113              
  Lines       14347    14382      +35     
==========================================
+ Hits        10123    10135      +12     
- Misses       3497     3515      +18     
- Partials      727      732       +5     

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[vangent]

For future reference, please don't rebase/force-push. It makes it so I have to review the whole PR again every time rather than just the commits/changes since my last review.

[vangent]

Thanks for the contribution!