Tier 1: pool curl resources, RDMA RAII + decline-fallback, fix RemoveObjectsResult UB

[harshavardhana]

Summary

Tier 1 of the C++-native modernization audit, plus two latent bug fixes uncovered while running the full test suite against AIStor + RDMA. End-to-end validated on coe09 (client) against a single-node coe08 RDMA MinIO build of latest eos.

Changes

Performance (HTTP transport)

• http.cc: move curl_global_init to a one-time function-local static (was per-request via curlpp::Cleanup; non-thread-safe, expensive — OpenSSL init etc.)
• http.cc: attach a process-wide CURLSH to each curlpp::Easy so the connection cache, DNS cache, and TLS session cache survive the Easy handle's lifetime. One mutex per CURL_LOCK_DATA_* slot — a single mutex covering all slots self-deadlocks because libcurl can hold one slot's lock while acquiring another on the same thread.
• http.cc: enable CURLOPT_TCP_KEEPALIVE so pooled sockets survive idle gaps.

Thread safety

• baseclient.{h,cc}: guard region_map_ with std::shared_mutex. Read sites now use find() rather than operator[], so they no longer silently insert empty entries on every miss and can take a shared lock; erase + write sites take a unique lock.
• baseclient.cc: UploadPart propagates args.headers into the wrapped PutObjectApiArgs so caller-supplied per-part headers reach the signer.

GPU-direct friendliness

• request.cc: BuildHeaders honors a caller-supplied x-amz-content-sha256. When the caller pre-sets it (e.g. UNSIGNED-PAYLOAD for a device-resident body) the signer uses that value and skips Sha256Hash(body) — avoids dragging GPU memory through OpenSSL just to compute a signing hash that TLS already authenticates.
• client.cc: the GPU-buffer HTTP fallback in PutObject sets UNSIGNED-PAYLOAD, and the multipart loop propagates it into every UploadPart.

RDMA path robustness

• client.cc: wrap the page-aligned part buffer and cuMemObj registration in AlignedBuffer + ScopedRDMARegistration RAII guards so deregister-before-free ordering is enforced structurally, not by careful early-return ordering.
• client.cc: when cuMemObjGetDescriptor declines to register (peermem not loaded, IB unhealthy, GPUDirect misconfigured), silently skip the RDMA path and fall through to HTTP multipart instead of failing the whole call.

Bug fixes uncovered during validation

• client.cc: fix UB in RemoveObjectsResult::Populate — when the caller's func returned false on the first call (empty batch), done_ flipped to true but itr_ stayed uninitialized. operator bool() then compared an uninit iterator → SIGSEGV the first time a caller copied/dereferenced the result. Confirmed pre-existing in main (reproduces with Tier 1 reverted). Pin itr_ to errors.end() on empty batches.
• tests/tests.cc: SelectObjectContent now detects MethodNotAllowed (AIStor doesn't implement S3 Select) and prints skipped: instead of failing the suite.

Validation

Built with MINIO_CPP_ENABLE_RDMA=ON against vendored cuObj + libcufile, on coe09 (mlx5_0 IB NIC, 400 Gbps). Server: single-node AIStor at 15.15.15.59:9200 from latest miniohq/eos with make install-cgo TAGS=rdma.

MakeBucket()                ✅
RemoveBucket()              ✅
BucketExists()              ✅
ListBuckets()               ✅
StatObject()                ✅
RemoveObject()              ✅
DownloadObject()            ✅
GetObject()                 ✅
ListObjects()               ✅
ListObjects() 1010 objects  ✅
PutObject()                 ✅
CopyObject()                ✅
UploadObject()              ✅
RemoveObjects()             ✅
SelectObjectContent()       ⏭ skipped (server returned MethodNotAllowed — S3 Select not implemented in AIStor)
ListenBucketNotification()  ✅

RDMA round-trip (./GetPutRDMA 15.15.15.59:9200 minioadmin minioadmin 10485760) also passes: PUT + GET of a 10 MiB host-allocated, page-aligned, cuObj-registered buffer succeed against the AIStor RDMA endpoint.

Test plan

• MINIO_CPP_ENABLE_RDMA=ON build (release)
• Full tests binary exit 0 against AIStor
• GetPutRDMA round-trip against AIStor RDMA endpoint
• Build matrix: MINIO_CPP_ENABLE_RDMA=OFF (non-RDMA consumers)
• Larger object multipart with the UNSIGNED-PAYLOAD path