Enum A2aError 

#[non_exhaustive]
pub enum A2aError {
    MethodNotFound(String),
    InvalidParams(String),
    Json(Error),
    Bus(BusError),
    TaskNotFound(String),
    Server(String),
    OwnershipUnavailable,
    Unauthorized(String),
    Misconfigured(String),
    ResumeBufferExpired {
        since_id: u64,
    },
    Internal {
        source: Box<dyn Error + Send + Sync>,
    },
    Rpc {
        code: i32,
        message: String,
    },
    Timeout(Duration),
    LeaderDied {
        stream_id: String,
    },
}

Errors returned by the A2A server / handler.

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.

MethodNotFound(String)

JSON-RPC method name not recognised. Maps to JSON-RPC -32601.

InvalidParams(String)

Params payload could not be decoded into the method’s param type. Maps to JSON-RPC -32602.

Json(Error)

JSON parse failure. Maps to JSON-RPC -32700.

Bus(BusError)

Bus-layer failure (subscribe / publish / KV).

TaskNotFound(String)

Task id not present in the store.

Server(String)

Catch-all server-side failure. Maps to JSON-RPC -32000.

OwnershipUnavailable

The tenant-ownership store was unreachable, or returned an inconclusive verdict, while gating a request under strict tenant binding — the request is denied fail-closed rather than served unprotected. Maps to JSON-RPC -32000; Display is redaction-safe (carries no caller/principal/task detail on the wire — that lives in the server-side log emitted before this is returned).

Unauthorized(String)

Authentication or authorisation failure. Maps to A2A-specific -32001.

Misconfigured(String)

The server was started with an invalid or dangerous configuration (e.g. non-loopback bind with an anonymous authenticator without the explicit allow_public_bind opt-in). Maps to JSON-RPC -32000.

ResumeBufferExpired

Resume requested with a cursor older than the oldest retained event in the buffer. Maps to JSON-RPC application code crate::envelope::codes::RESUME_BUFFER_EXPIRED (-32010).

Fields

since_id: u64

Cursor the caller supplied.

Internal

Server-side internal failure that preserves the underlying typed cause via Error::source. Distinct from A2aError::Server (bare string) because the source chain matters for tracing.

Maps to JSON-RPC SERVER_ERROR (-32000). Display is the stable, redaction-safe string "internal error" — the inner cause is reachable only via Error::source() so callers that log server-side see the chain while wire envelopes carry no internal detail. Use for server-internal serialization, encode, or IPC failures that should NOT be mis-classified as client-input parse errors.

Fields

source: Box<dyn Error + Send + Sync>

Underlying typed cause, preserved for Error::source().

Rpc

The remote A2A peer answered with a JSON-RPC error envelope. Raised client-side by crate::client::A2aClient when a reply carries error instead of result; the code/message are the peer’s verbatim JSON-RPC error payload so the caller can branch on the wire code (e.g. -32601 method-not-found, -32000 server error).

Fields

code: i32

The peer’s verbatim JSON-RPC error code — branch on it for the wire-level cause (e.g. -32601 method-not-found, -32000 server).

message: String

The peer’s verbatim error message; treat as untrusted display text (it originated on the remote side).

Timeout(Duration)

No reply arrived on the client’s inbox before the per-call deadline elapsed. Raised client-side by crate::client::A2aClient; the bus accepted the publish but the peer never answered (crashed, slow, or wrong agent id).

LeaderDied

Multi-replica orphan: the streaming leader for this task died (TTL-expired KV claim) or never claimed leadership. Maps to JSON-RPC application code crate::envelope::codes::LEADER_DIED (-32099). The dispatcher writes a terminal frame to the resume buffer before raising so future resume clients see clean termination + can retry. ADR-020.

Fields

stream_id: String

Leader-registry stream id (e.g. a2a.t-1) so the client can correlate with bus telemetry.

Implementations

impl A2aError

pub fn to_json_rpc_error(&self, request_id: Value) -> JsonRpcResponse

Map this error onto a JsonRpcResponse carrying the matching JSON-RPC error code.

Trait Implementations

impl Debug for A2aError

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

Formats the value using the given formatter.

impl Display for A2aError

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

Formats the value using the given formatter.

impl Error for A2aError

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<BusError> for A2aError

fn from(source: BusError) -> Self

Converts to this type from the input type.

impl From<Error> for A2aError

fn from(source: Error) -> Self

Converts to this type from the input type.