Rust Slow Time Server¶

Overview¶

The slow-time-server is a Rust MCP test fixture for timeout, retry, circuit-breaker, session-pool, and load-testing scenarios. It replaces the previous Go slow-time-server implementation.

This server is intentionally a test utility. Do not expose it outside a trusted test network.

Transport¶

The Rust server exposes MCP JSON-RPC over Streamable HTTP:

POST /mcp - canonical MCP endpoint
POST / - compatibility alias for MCP JSON-RPC requests

SSE and the old Go HTTP endpoint are not available in the Rust implementation. Use /mcp instead of the old /http endpoint.

Tools¶

Tool	Description
`get_slow_time`	Returns current time after configured or requested delay.
`convert_slow_time`	Converts a timestamp between timezones after a delay.
`get_instant_time`	Returns current time without artificial delay.
`get_timeout_time`	Sleeps for the maximum delay to exercise timeout handling.
`get_flaky_time`	Returns a simulated failure according to `FAILURE_RATE`.

get_slow_time and convert_slow_time accept both delay_ms and delay_seconds. delay_ms takes precedence when both are provided. Delays are capped at 10 minutes.

HTTP Endpoints¶

Endpoint	Description
`POST /mcp`	MCP JSON-RPC endpoint.
`POST /`	MCP JSON-RPC alias.
`GET /health`	Instant health check.
`GET /version`	Version metadata.
`GET /api/v1/time?timezone=UTC&delay=250ms`	REST time helper with delay.
`GET /api/v1/config`	Current latency configuration.
`GET /api/v1/stats`	Request and failure counters.
`GET /api/v1/test/echo?message=hello`	Echo helper for connectivity tests.

Configuration¶

Variable	Default	Description
`BIND_ADDRESS`	`0.0.0.0:8081`	Bind address.
`DEFAULT_LATENCY`	`5s`	Default delay for slow tools. Supports `ms`, `s`, and `m`.
`FAILURE_RATE`	`0.0`	Failure probability for `get_flaky_time`, from `0.0` to `1.0`.
`RUST_LOG`	`info`	Logging level.

Run¶

cd mcp-servers/rust/slow-time-server
make run

The repository resilience profile exposes the server on port 8889:

make resilience-up
curl -s http://localhost:8889/health

MCP Examples¶

List tools:

curl -s http://localhost:8081/mcp \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'

Call the slow time tool with millisecond delay:

curl -s http://localhost:8081/mcp \
  -H 'Content-Type: application/json' \
  -d '{
    "jsonrpc": "2.0",
    "id": 2,
    "method": "tools/call",
    "params": {
      "name": "get_slow_time",
      "arguments": {"timezone": "UTC", "delay_ms": 100}
    }
  }'

Call the slow time tool with second delay:

curl -s http://localhost:8081/mcp \
  -H 'Content-Type: application/json' \
  -d '{
    "jsonrpc": "2.0",
    "id": 3,
    "method": "tools/call",
    "params": {
      "name": "get_slow_time",
      "arguments": {"timezone": "UTC", "delay_seconds": 0.25}
    }
  }'

Migration From Go¶

This is a full replacement for the Go slow-time-server.

Removed Go endpoints and modes:

/sse
/messages
/http
/api/v1/docs
/api/v1/openapi.json
stdio, SSE, dual, and REST-only transport modes

Current Rust replacements:

Use POST /mcp for MCP JSON-RPC.
Use /health for container and compose health checks.
Use /api/v1/time, /api/v1/config, and /api/v1/stats for REST test helpers.
Build containers with mcp-servers/rust/slow-time-server/Containerfile.

The old Go binary health-check flags are removed. Container health checks now call curl -sf http://localhost:8081/health, so the runtime image includes curl.

Validation¶

cargo fmt --check -p slow-time-server
cargo test -p slow-time-server
cargo clippy -p slow-time-server -- -D warnings