Enum RmcpServerKitError 

#[non_exhaustive]
pub enum RmcpServerKitError {
    Config(String),
    Auth(String),
    Rbac(String),
    RateLimited(String),
    RateLimitedFor {
        message: String,
        retry_after: Duration,
    },
    Io(Error),
    Json(Error),
    Toml(Error),
    Tls(String),
    Startup(String),
    Internal(String),
    Metrics(String),
}

Generic MCP server error type.

Application crates should define their own error types and convert from/into RmcpServerKitError where needed.

Client-facing message invariant

The String payloads of Auth, Rbac, RateLimited, and the message field of RateLimitedFor are rendered verbatim to the HTTP client by IntoResponse. Construction sites MUST keep these client-safe: no internal error text, source-error chains, file paths, IPs, SQL, or dependency details. Internal-only variants (Config, Io, Json, Toml, Tls, Startup, Internal, Metrics) are collapsed to a generic "internal server error" body and their detail is logged server-side only. Use client_message to obtain the exact body that will be sent to the client for any variant.

The recurring mistake is interpolating an upstream error into one of these variants - map_err(|e| Auth(format!("... {e}"))). That publishes a dependency’s error chain to unauthenticated callers, and usually attaches the wrong status besides (a crypto or I/O fault is a 500, not a 401). Route such failures to Internal instead. A heuristic regression test in this module’s test suite scans src/ for that specific shape; it is a tripwire, not a proof, so the invariant still rests on review.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Config(String)

Configuration parsing or validation failed.

Auth(String)

Authentication failed (bad/missing credential).

Rbac(String)

Authorization (RBAC) denied the request.

RateLimited(String)

Request was rejected by a rate limiter.

RateLimitedFor

Request was rejected by a rate limiter that knows the wait time.

Renders as HTTP 429 with a Retry-After header (RFC 9110 delta-seconds: the duration is rounded up to whole seconds, minimum 1) and the message as a plain-text body. The legacy RateLimited variant remains headerless.

Fields

message: String

Plain-text client-facing message (response body).

retry_after: Duration

Best-effort wait until the next request could be admitted.

Io(Error)

Underlying I/O error.

Json(Error)

JSON (de)serialization error.

Toml(Error)

TOML parse error (configuration loading).

Tls(String)

TLS configuration failure (certificate load, key parse, rustls config).

Startup(String)

Server startup failure (binding, listener, runtime initialization).

Internal(String)

Internal failure with no client-actionable cause.

Detail is logged server-side and collapsed to "internal server error" on the wire. Use this for runtime faults that are neither configuration nor startup problems – e.g. a cryptographic primitive failing – rather than reaching for a client-facing variant.

Metrics(String)

Metrics registration failure (e.g. Prometheus duplicate or invalid metric).

Implementations

impl RmcpServerKitError

pub fn client_message(&self) -> Cow<'_, str>

The exact body this error sends to the HTTP client.

Client-facing variants (Auth, Rbac, RateLimited, RateLimitedFor) return their message verbatim; all internal variants return the generic "internal server error" so implementation detail never leaks on the wire. This is the single source of truth for the client body - the IntoResponse impl uses it - so callers can assert or reuse the client-safe text without duplicating the mapping.

See the type-level “Client-facing message invariant” for the contract construction sites must uphold.

Trait Implementations

impl Debug for RmcpServerKitError

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for RmcpServerKitError

fn fmt(&self, __formatter: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Error for RmcpServerKitError

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0:

use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.

impl From<Error> for RmcpServerKitError

fn from(source: Error) -> Self

Converts to this type from the input type.

impl From<Error> for RmcpServerKitError

fn from(source: Error) -> Self

Converts to this type from the input type.

impl From<Error> for RmcpServerKitError

fn from(source: Error) -> Self

Converts to this type from the input type.

impl IntoResponse for RmcpServerKitError

fn into_response(self) -> Response

Create a response.