Crate mock_nexus 

Mock Nexus raw-storage server with a failure-scenario table.

Implements just enough HTTP/1.1 (std only) to exercise the nexus-raw transport contract. GET/HEAD/PUT with Content-Length or chunked bodies, DELETE with 204/404. Percent-encoded paths stored verbatim. One request per connection, Connection: close on every response. GET honors resumable downloads: a single open Range: bytes=N- is answered with 206 and Content-Range, out-of-range starts get 416. Any other Range form is ignored. A Scenario selects a failure mode: truncated PUT and GET bodies, connection resets, held uploads, missing Content-Length, slow links, drifted documents, flaky 503s, 503s with a Retry-After pause, rate-limit 429s with Retry-After, redirects, and Basic-auth gating.

Rust conformance tests use the library API directly. The mock-nexus binary exposes the same scenarios to shell- and Python-driven tests:

let server = mock_nexus::MockNexus::start(mock_nexus::Scenario::Atomic)?;
let url = format!("{}1.14.0/version.json", server.base_url());

Presets are named points in a behavior space; a Spec composes the space itself: layers stack (Spec::atomic().with_auth(..).with_flaky(3)), and MockNexus::start_spec runs a composed instance. A composed instance never enters the contract tables: presets and their drift guards are the contract, specs are code-level composition.

A group repository is a separate deployment kind, not a scenario: MockNexus::start_group aggregates two or more running members, forwarding reads in member order and refusing writes. On a group handle the store mutators (MockNexus::insert, MockNexus::enable_drift) are no-ops: a group stores nothing.

The client-facing contract page docs/reference/invariants.md is rendered from SCENARIO_DOCS. A drift test in the invariants module fails when a scenario change does not regenerate it.

Structs

Drip

Slow-drip parameters simulating a low-bandwidth link.

MockNexus

Handle to a running mock server. Dropping it stops the accept loop and releases the port. In-flight connection threads finish on their own.

ReqLog

One served request, in arrival order.

ScenarioDoc

One scenario’s row on the wire-invariants page: the id, the human name, the wire behavior and the invariant it pins.

Spec

The composable behavior of one hosted instance.

Enums

Outcome

Outcome of one request recorded in the request log.

Scenario

Failure scenario a MockNexus server simulates.

Constants

SCENARIOS

SCENARIO_DOCS

One row per SCENARIOS entry, in the same order. A unit test in this module pins the alignment.

Functions

render_invariants_markdown

Render docs/reference/invariants.md from SCENARIO_DOCS. The drift test fails when the file and this rendering diverge.