std.Io.net Conformance

This ledger classifies Marionette's simulated std.Io.net surface against Zig 0.16.0. It is the source of truth for supported operations and options.

• Exact: portable observable behavior is intended to match host std.Io.net.
• Abstracted: the application contract is preserved without modeling a particular kernel implementation.
• Unsupported: the operation or option fails explicitly.
• Divergent: intentional behavior differs from the host contract and is stated here.

IP Streams

Surface	Classification	Simulated contract
IPv4 and IPv6 literal lookup	Exact	Returns the parsed address without host DNS state.
localhost lookup	Abstracted	Deterministically returns IPv6 then IPv4 loopback.
Other hostname lookup	Unsupported	Returns error.UnknownHostName; DNS and host files are ambient host state.
listen mode .stream, protocol .tcp	Exact	Creates a process-scoped listener.
Listen address scope	Abstracted	An unspecified IPv4 or IPv6 listener matches same-family literal destinations and conflicts with active wildcard or exact binds on that port. Address identity is not tied to modeled host interfaces, and IPv4/IPv6 remain separate families.
Other listen modes or protocols	Unsupported	Returns the corresponding mode/protocol error.
listen.kernel_backlog	Abstracted	Bounds pending, unaccepted connections; excess connects are refused deterministically.
listen.reuse_address = true	Abstracted	Accepted, while active-bind exclusivity remains enforced. The simulator has no kernel TIME_WAIT state to bypass.
Listen port 0	Exact	Assigns a deterministic port from the IANA dynamic port range.
connect mode .stream, protocol .tcp	Abstracted	Queues establishment through the deterministic network, assigns a deterministic client port, observes latency, and rejects a down source, down destination, disabled link, or full backlog before publishing either endpoint.
connect.timeout duration or deadline	Exact	Bounds queued establishment in simulated time and returns error.Timeout; failure rolls back the probe and unpublished socket state.
Connect cancellation	Exact	Cancellation at entry or while establishment is queued returns error.Canceled and rolls back the attempt.
accept	Abstracted	Blocks cancelably and returns deterministic peer metadata. The port comes from a rotating simulated client ephemeral-port cursor and may be reused after the modeled range wraps; active peer-tuple uniqueness is not modeled. The family matches the connect destination. Nodes do not model source interfaces, so the peer IP is copied from the connect destination rather than representing a genuine client source address.
Stream read/write ordering	Abstracted	Writes are segmented into ordered frames. Readers receive only a contiguous prefix. Loss terminally fails that receive stream; later frames are discarded.
Partial write progress	Exact	Once a write prefix is accepted, a later cancellation, reset, or resource failure returns the accepted byte count.
Read/write cancellation	Exact	Armed cancellation is delivered at entry and at blocking waits.
shutdown(.recv)	Abstracted	Discards inbound bytes and makes later reads return EOF. The opposite direction remains usable.
shutdown(.send)	Abstracted	Makes local writes fail and makes the peer observe EOF after accepted bytes. The opposite direction remains usable.
shutdown(.both)	Abstracted	Applies both directional shutdowns without closing the socket handle.
close	Abstracted	Releases local state and queued capacity. A process reset discards that endpoint's delayed outbound frames and terminally surfaces error.ConnectionResetByPeer; graceful close preserves already accepted bytes before EOF.

Explicit Scope

UDP, Unix-domain sockets, non-literal DNS, broader socket-option parity, and kernel-specific readiness behavior are unsupported. They should be added only when a pinned system under test requires them.

The no-fault differential tests run the same portable bidirectional exchange, accepted-peer port/family observations, send-half-close/EOF scenario, and IPv4 wildcard-listener exchange against host std.Io.net and Marionette. They do not claim source-IP equivalence. Fault behavior remains an explicit simulator abstraction rather than an attempt to reproduce one host kernel.