feat(gateway): support If-None-Match wildcard

[ilcm96]

Summary

Add S3 conditional-write support for If-None-Match: * to JuiceFS Gateway.

• enforce create-only semantics for PutObject, CopyObject, and multipart completion
• publish new directory markers through a fully prepared temporary inode and RenameNoReplace
• preserve the target state when a conditional directory-marker request fails
• atomically create markers on implicit directories with --head-dir=false; return 412 Precondition Failed for existing explicit markers or directories exposed by --head-dir=true
• clean up temporary directory-marker inodes on every failed publish path
• add unit, race, and S3 integration coverage, including repeated If-None-Match header fields

Fixes #6460.

MinIO dependency

This PR depends on juicedata/minio#84.

The current go.mod replacement intentionally points to the pushed feature commit in my MinIO fork so this PR and its CI can be tested before the MinIO PR is merged. After #84 is merged, I will update the replacement to the corresponding github.com/juicedata/minio commit before this PR is merged.

Verification

All verification was run in Docker:

go test ./pkg/gateway -count=1
go test ./cmd -run IfNoneMatch -count=1  # in the MinIO repository
bash -n integration/s3gateway_test.sh

The live JuiceFS Gateway checks also verified:

• conditional zero-byte PUT and CopyObject against an implicit directory return 200 with --head-dir=false, preserving the directory inode and child data; with --head-dir=true, they return 412
• a new directory marker is created successfully and a duplicate conditional write returns 412
• repeated raw If-None-Match fields are combined correctly: an empty field followed by * returns 412, while * followed by an ETag returns 400
• the existing object content remains unchanged after failed conditional requests

[CLAassistant]

All committers have signed the CLA.

[myangitzh]

Hi,Could we add destination If-Match: support alongside If-None-Match: *? AWS supports it for PutObject, CopyObject, and CompleteMultipartUpload.
If this is too large for the current PR, could we open a follow-up PR and track it?

S3 User Guide: https://docs.aws.amazon.com/AmazonS3/latest/userguide/conditional-requests.html

[ilcm96]

@myangitzh

Could we add destination If-Match: support alongside If-None-Match: *?

Thanks for the suggestion. I'd prefer to keep this PR focused on If-None-Match: * and track destination If-Match: <ETag> support separately.

The current implementation atomically checks that the destination does not exist. If-Match would also need to compare the destination's ETag and commit the replacement atomically, so a concurrent write cannot invalidate the comparison. That needs additional gateway and metadata work, along with tests for PUT, CopyObject, and multipart completion. I think a separate follow-up would make that easier to review and validate.

[ilcm96]

MinIO PR juicedata/minio#84 has been merged. I rebased this PR onto the latest main and updated the MinIO pin from my temporary fork to the merged upstream commit (f2266df40f17).

[codecov]

Codecov Report

❌ Patch coverage is 39.66480% with 108 lines in your changes missing coverage. Please review.
✅ Project coverage is 22.22%. Comparing base (4e99198) to head (8164c6c).

Files with missing lines	Patch %	Lines
pkg/meta/sql.go	0.00%	46 Missing ⚠️
pkg/meta/redis.go	0.00%	41 Missing ⚠️
pkg/meta/base.go	73.68%	10 Missing and 5 partials ⚠️
pkg/meta/tkv.go	82.85%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #7479       +/-   ##
===========================================
- Coverage   57.18%   22.22%   -34.96%     
===========================================
  Files         181       31      -150     
  Lines       60100    25143    -34957     
===========================================
- Hits        34370     5589    -28781     
+ Misses      22111    18950     -3161     
+ Partials     3619      604     -3015     

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