PutObject incompatibility with RFC-7232 and difference to AWS

[steve-o]

Per RFC-7232 §6: precedence a PUT request should return 412 not 304.

 3.  When If-None-Match is present, evaluate the If-None-Match
       precondition:

       *  if true, continue to step 5

       *  if false for GET/HEAD, respond 304 (Not Modified)

       *  if false for other methods, respond 412 (Precondition Failed)

However AWS S3 documentation does not explicitly note support for conditional requests for PutObject, only on GetObject (and some others like CopyObject).

GET /Key+?partNumber=PartNumber&response-cache-control=ResponseCacheControl&response-content-disposition=ResponseContentDisposition&response-content-encoding=ResponseContentEncoding&response-content-language=ResponseContentLanguage&response-content-type=ResponseContentType&response-expires=ResponseExpires&versionId=VersionId HTTP/1.1
Host: Bucket.s3.amazonaws.com
If-Match: IfMatch
If-Modified-Since: IfModifiedSince
If-None-Match: IfNoneMatch
If-Unmodified-Since: IfUnmodifiedSince

Apparently AWS returns a not implemented response: https://stackoverflow.com/questions/12654828/amazon-s3-avoid-overwriting-objects-with-the-same-name (?)

Expected Behavior

Minio should either copy AWS S3, or correctly follow RFC-7232. Either way differences should be noted in the documentation.

Current Behavior

⚠️ Running behind Cloudflare tunnels
Minio returns 304:

PUT https://...
if-none-match: "afa3a23620d1c15e7081a5bdf6cd5f94"

HTTP 304 Not Modified

Steps to Reproduce (for bugs)

1. Upload a file
2. Re-upload the same file with a if-none-match header with matching ETag.

Context

Trying to prevent duplicate uploads of the same content.

Your Environment

• Version used (minio --version): RELEASE.2023-11-20T22-40-07Z
• Server setup and configuration: Docker

[harshavardhana]

We don't intend to change here and comply with AWS S3.

These headers are necessary for optimistic concurrency.

Will add the 412 instead of 304.