Internode Transport Capabilities

Status: design note for backend-neutral capability reporting. This document does not add a backend or transport crate.

Open-source Scope

The OSS scope is:

define honest capability reporting for the InternodeDataTransport adapter;
keep tcp-http as the default backend;
keep existing TCP/HTTP behavior unchanged;
document the capability fields needed for maintainable transport code;
avoid adding dependencies or backend implementations.

The OSS scope is not:

adding another transport backend;
replacing the current TCP/HTTP path;
adding benchmark plans for another transport;
changing object correctness semantics.

Purpose

InternodeDataTransportCapabilities describes what a backend can honestly do for RustFS internode data-plane transfers. The fields describe observable adapter behavior without naming a specific transport implementation.

The capability report is descriptive. It does not select a backend, negotiate with peers, or weaken object correctness semantics.

Capability Fields

Field	Meaning
`streaming_read`	The backend can open a remote disk reader for `read_file_stream`.
`streaming_write`	The backend can open a remote disk writer for `create_file` or `append_file`.
`streaming_walk_dir`	The backend can stream `walk_dir` responses.
`ordered_delivery`	Bytes for each opened transfer are delivered in order.
`max_transfer_size`	Optional RustFS-level cap for a single transfer. `None` means no additional cap beyond the backend/protocol/runtime limits.
`fallback_supported`	The backend can participate in the behavior-preserving TCP fallback path.

TCP/HTTP Backend

The default TCP/HTTP backend reports only capabilities it actually provides:

Field	TCP/HTTP value	Reason
`streaming_read`	`true`	`HttpReader` streams `/rustfs/rpc/read_file_stream` responses.
`streaming_write`	`true`	`HttpWriter` streams `/rustfs/rpc/put_file_stream` request bodies.
`streaming_walk_dir`	`true`	`HttpReader` streams `/rustfs/rpc/walk_dir` responses.
`ordered_delivery`	`true`	Each HTTP request body or response body is consumed as an ordered byte stream.
`max_transfer_size`	`None`	RustFS does not impose an extra per-transfer cap at the capability layer.
`fallback_supported`	`true`	TCP/HTTP is the behavior-preserving default and fallback path.

Capability Compatibility

Any new capability field should describe observable RustFS behavior without assuming a specific transport implementation:

Capability shape	Interpretation
`max_transfer_size=Some(n)`	The backend has a RustFS-visible transfer size ceiling and callers must split larger transfers or use fallback behavior.
`ordered_delivery=false`	The backend cannot be used behind the current stream API without an ordering or reassembly layer.

Unsupported or mismatched capabilities must not silently change quorum, integrity verification, retry, or timeout semantics.