Backblaze B2's S3-compatible endpoint does not implement the S3 POST
Object operation. It returns HTTP 501 to every POST regardless of URL
style — both path-style (https://s3.<region>.backblazeb2.com/<bucket>/)
and virtual-hosted-style (https://<bucket>.s3.<region>.backblazeb2.com/).
Yesterday's BucketLookupDNS fix produced virtual-hosted URLs, which is
correct for AWS but doesn't help here — B2 rejects POST on either form.
Verified with `curl -X POST https://...backblazeb2.com/honeyDueProd/`
returning 501 directly, with no signature involved.
Replace minio-go's PresignedPostPolicy with PresignHeader + http.MethodPut.
The signed URL now points at a single PUT endpoint, with Content-Type
and Content-Length signed via headers — B2/S3/MinIO all accept it. Drop
the min/max content-length range (we sign exactly one length now);
post-upload size verification still happens in VerifyAndClaim via HEAD.
Response shape:
- URL (was: signed POST endpoint) → now: signed PUT URL
- Fields → renamed to Headers; client sends them as request headers,
not multipart form parts
- Method (new): always "PUT", emitted explicitly so clients don't
have to hardcode
Companion KMP/iOS commits switch the client paths from multipart POST
to single PUT. Existing builds in the field will need to be rebuilt.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Trey t
7cc5448a7c