Enum TaskState 

#[non_exhaustive]
pub enum TaskState {
    Unspecified,
    Submitted,
    Working,
    InputRequired,
    AuthRequired,
    Completed,
    Failed,
    Canceled,
    Rejected,
}

The lifecycle state of a Task.

Per v1.0 spec (Section 5.5), enum values use ProtoJSON SCREAMING_SNAKE_CASE: "TASK_STATE_COMPLETED", "TASK_STATE_INPUT_REQUIRED", etc. Legacy lowercase/kebab-case values are accepted on deserialization.

This enum is closed to the v1.0 states. A future protocol revision that adds a state would be a wire-breaking change for the gRPC binding: an unknown TASK_STATE_* number from a newer peer is rejected by the protobuf conversion layer (with a field-scoped error) rather than silently discarded, so no task is ever reported in a bogus state.

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.

Unspecified

Proto default (0-value); should not appear in normal usage.

Submitted

Task received, not yet started.

Working

Task is actively being processed.

InputRequired

Agent requires additional input from the client to proceed.

AuthRequired

Agent requires the client to complete an authentication step.

Completed

Task finished successfully.

Failed

Task finished with an error.

Canceled

Task was canceled by the client.

Rejected

Task was rejected by the agent before execution.

Implementations

impl TaskState

pub const fn is_terminal(self) -> bool

Returns true if this state is a terminal (final) state.

Terminal states: Completed, Failed, Canceled, Rejected.

pub const fn is_interrupted(self) -> bool

Returns true if this state is an interrupted state.

Interrupted states: InputRequired, AuthRequired. Per Section 3.2.2, blocking SendMessage MUST return when the task reaches a terminal OR interrupted state.

pub const fn can_transition_to(self, next: TaskState) -> bool

Returns true if transitioning from self to next is a valid state transition per the A2A protocol.

The specification (§4.1.3) enumerates the task states and classifies them as terminal or interrupted, but it deliberately does not define a transition matrix — it never requires a task to pass through any intermediate state. Two rules follow from what it does say, and they are the only two enforced here:

1. Terminal states are final. Completed, Failed, Canceled, and Rejected transition nowhere, including to themselves.
2. Submitted is an entry state. Nothing transitions into it, and nothing transitions into the proto-default Unspecified. Unspecified as a source still transitions anywhere, since a task decoded with no state set must be able to take its real one.

Everything else is permitted. In particular Submitted → Completed is valid: an agent that answers a trivial request in one step never enters Working, and the reference SDKs emit exactly that sequence (the official a2a-tck SUT contract completes straight from Submitted). A stricter table here rejected conformant agents — including this SDK’s own users — with a spurious InvalidParams.

Trait Implementations

impl Clone for TaskState

fn clone(&self) -> TaskState

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for TaskState

impl Debug for TaskState

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for TaskState

fn deserialize<__D>( __deserializer: __D, ) -> Result<TaskState, <__D as Deserializer<'de>>::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Display for TaskState

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

Formats the value using the given formatter.

impl Eq for TaskState

impl From<TaskState> for TaskState

fn from(value: TaskState) -> TaskState

Converts to this type from the input type.

impl Hash for TaskState

fn hash<__H>(&self, state: &mut __H)

where __H: Hasher,

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for TaskState

fn eq(&self, other: &TaskState) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl Serialize for TaskState

fn serialize<__S>( &self, __serializer: __S, ) -> Result<<__S as Serializer>::Ok, <__S as Serializer>::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for TaskState

impl TryFrom<TaskState> for TaskState

type Error = ConvertError

The type returned in the event of a conversion error.

fn try_from( value: TaskState, ) -> Result<TaskState, <TaskState as TryFrom<TaskState>>::Error>

Performs the conversion.