a2a

package
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 Go to latest Published: Feb 15, 2026 License: Apache-2.0 Imports: 15 Imported by: 0

Documentation

Overview

Package a2a provides types for the Agent-to-Agent (A2A) protocol.

Types are derived from the A2A protocol specification (a2a.proto) and use camelCase JSON tags matching the JSON-RPC binding convention.

Index

Constants

View Source 
const (
	MethodSendMessage          = "message/send"
	MethodSendStreamingMessage = "message/stream"
	MethodGetTask              = "tasks/get"
	MethodCancelTask           = "tasks/cancel"
	MethodListTasks            = "tasks/list"
	MethodTaskSubscribe        = "tasks/subscribe"
)

A2A JSON-RPC method names.

Variables

This section is empty.

Functions

func ExtractResponseText 

func ExtractResponseText(task *Task) string

ExtractResponseText extracts text from a completed A2A task. It checks the status message first, then artifacts.

func InferContentType 

func InferContentType(mediaType string) string

InferContentType maps a MIME type to a PromptKit content type string.

func MessageToMessage 

func MessageToMessage(msg *Message) (*types.Message, error)

MessageToMessage converts an A2A Message to a PromptKit Message.

func PartToContentPart 

func PartToContentPart(part *Part) (types.ContentPart, error)

PartToContentPart converts an A2A Part to a PromptKit ContentPart.

func ReadSSE 

func ReadSSE(ctx context.Context, r io.Reader, ch chan<- StreamEvent)

ReadSSE reads SSE events from r and sends parsed StreamEvents to ch.

Types

type AgentCapabilities 

type AgentCapabilities struct {
	Streaming         bool             `json:"streaming,omitempty"`
	PushNotifications bool             `json:"pushNotifications,omitempty"`
	ExtendedAgentCard bool             `json:"extendedAgentCard,omitempty"`
	Extensions        []AgentExtension `json:"extensions,omitempty"`
}

AgentCapabilities describes what the agent supports.

type AgentCard 

type AgentCard struct {
	Name                string            `json:"name"`
	Description         string            `json:"description,omitempty"`
	Version             string            `json:"version,omitempty"`
	Provider            *AgentProvider    `json:"provider,omitempty"`
	Capabilities        AgentCapabilities `json:"capabilities,omitzero"`
	Skills              []AgentSkill      `json:"skills,omitempty"`
	DefaultInputModes   []string          `json:"defaultInputModes,omitempty"`
	DefaultOutputModes  []string          `json:"defaultOutputModes,omitempty"`
	SupportedInterfaces []AgentInterface  `json:"supportedInterfaces,omitempty"`
	IconURL             string            `json:"iconUrl,omitempty"`
	DocumentationURL    string            `json:"documentationUrl,omitempty"`
}

AgentCard describes an agent's capabilities and endpoints.

type AgentExtension 

type AgentExtension struct {
	URI         string `json:"uri"`
	Description string `json:"description,omitempty"`
	Required    bool   `json:"required,omitempty"`
}

AgentExtension describes an optional protocol extension.

type AgentInterface 

type AgentInterface struct {
	URL             string `json:"url"`
	ProtocolBinding string `json:"protocolBinding,omitempty"`
	ProtocolVersion string `json:"protocolVersion,omitempty"`
}

AgentInterface describes a protocol endpoint.

type AgentProvider 

type AgentProvider struct {
	Organization string `json:"organization"`
	URL          string `json:"url,omitempty"`
}

AgentProvider identifies the organization behind an agent.

type AgentSkill 

type AgentSkill struct {
	ID          string   `json:"id"`
	Name        string   `json:"name"`
	Description string   `json:"description,omitempty"`
	Tags        []string `json:"tags,omitempty"`
	Examples    []string `json:"examples,omitempty"`
	InputModes  []string `json:"inputModes,omitempty"`
	OutputModes []string `json:"outputModes,omitempty"`
}

AgentSkill describes a specific skill an agent can perform.

type Artifact 

type Artifact struct {
	ArtifactID  string         `json:"artifactId"`
	Name        string         `json:"name,omitempty"`
	Description string         `json:"description,omitempty"`
	Parts       []Part         `json:"parts"`
	Extensions  []string       `json:"extensions,omitempty"`
	Metadata    map[string]any `json:"metadata,omitempty"`
}

Artifact is a named output generated by an agent.

func ContentPartsToArtifacts 

func ContentPartsToArtifacts(parts []types.ContentPart) ([]Artifact, error)

ContentPartsToArtifacts converts PromptKit ContentParts into A2A Artifacts. It creates a single Artifact containing all non-empty parts. Returns nil if parts is empty or all parts fail to convert.

type CancelTaskRequest 

type CancelTaskRequest struct {
	ID string `json:"id"`
}

CancelTaskRequest is the params for tasks/cancel.

type Client 

type Client struct {
	// contains filtered or unexported fields
}

Client is an HTTP client for discovering and calling external A2A agents.

func NewClient 

func NewClient(baseURL string, opts ...ClientOption) *Client

NewClient creates a Client targeting baseURL.

func (*Client) CancelTask 

func (c *Client) CancelTask(ctx context.Context, taskID string) error

CancelTask cancels a task by ID via tasks/cancel.

func (*Client) Discover 

func (c *Client) Discover(ctx context.Context) (*AgentCard, error)

Discover fetches the agent card from /.well-known/agent.json. The card is cached after the first successful call.

func (*Client) GetTask 

func (c *Client) GetTask(ctx context.Context, taskID string) (*Task, error)

GetTask retrieves a task by ID via tasks/get.

func (*Client) ListTasks 

func (c *Client) ListTasks(ctx context.Context, params *ListTasksRequest) ([]*Task, error)

ListTasks lists tasks via tasks/list.

func (*Client) SendMessage 

func (c *Client) SendMessage(ctx context.Context, params *SendMessageRequest) (*Task, error)

SendMessage sends a message/send JSON-RPC request.

func (*Client) SendMessageStream 

func (c *Client) SendMessageStream(ctx context.Context, params *SendMessageRequest) (<-chan StreamEvent, error)

SendMessageStream sends a message/stream request and returns a channel of streaming events. The channel is closed when the stream ends or the context is canceled.

type ClientOption 

type ClientOption func(*Client)

ClientOption configures a Client.

func WithAuth 

func WithAuth(scheme, token string) ClientOption

WithAuth sets the Authorization header on all requests.

func WithHTTPClient 

func WithHTTPClient(hc *http.Client) ClientOption

WithHTTPClient sets the underlying HTTP client.

type Executor 

type Executor struct {
	// contains filtered or unexported fields
}

Executor implements tools.Executor for A2A agent tools. It dispatches tool calls to remote A2A agents via the A2A client.

func NewExecutor 

func NewExecutor() *Executor

NewExecutor creates a new A2A executor.

func (*Executor) Execute 

func (e *Executor) Execute(descriptor *tools.ToolDescriptor, args json.RawMessage) (json.RawMessage, error)

Execute calls a remote A2A agent with the tool arguments and returns the response.

func (*Executor) Name 

func (e *Executor) Name() string

Name returns "a2a" to match the Mode on A2A tool descriptors.

type GetTaskRequest 

type GetTaskRequest struct {
	ID            string `json:"id"`
	HistoryLength *int   `json:"historyLength,omitempty"`
}

GetTaskRequest is the params for tasks/get.

type JSONRPCError 

type JSONRPCError struct {
	Code    int    `json:"code"`
	Message string `json:"message"`
	Data    any    `json:"data,omitempty"`
}

JSONRPCError is a JSON-RPC 2.0 error object.

type JSONRPCRequest 

type JSONRPCRequest struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      any             `json:"id"`
	Method  string          `json:"method"`
	Params  json.RawMessage `json:"params,omitempty"`
}

JSONRPCRequest is a JSON-RPC 2.0 request.

type JSONRPCResponse 

type JSONRPCResponse struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      any             `json:"id"`
	Result  json.RawMessage `json:"result,omitempty"`
	Error   *JSONRPCError   `json:"error,omitempty"`
}

JSONRPCResponse is a JSON-RPC 2.0 response.

type ListTasksRequest 

type ListTasksRequest struct {
	ContextID     string     `json:"contextId"`
	Status        *TaskState `json:"status,omitempty"`
	PageSize      int        `json:"pageSize,omitempty"`
	PageToken     string     `json:"pageToken,omitempty"`
	HistoryLength *int       `json:"historyLength,omitempty"`
}

ListTasksRequest is the params for tasks/list.

type ListTasksResponse 

type ListTasksResponse struct {
	Tasks         []Task `json:"tasks"`
	NextPageToken string `json:"nextPageToken,omitempty"`
	PageSize      int    `json:"pageSize,omitempty"`
	TotalSize     int    `json:"totalSize,omitempty"`
}

ListTasksResponse is the result for tasks/list.

type Message 

type Message struct {
	MessageID        string         `json:"messageId"`
	ContextID        string         `json:"contextId,omitempty"`
	TaskID           string         `json:"taskId,omitempty"`
	Role             Role           `json:"role"`
	Parts            []Part         `json:"parts"`
	ReferenceTaskIDs []string       `json:"referenceTaskIds,omitempty"`
	Extensions       []string       `json:"extensions,omitempty"`
	Metadata         map[string]any `json:"metadata,omitempty"`
}

Message is a communication unit in the A2A protocol.

type Part 

type Part struct {
	Text *string        `json:"text,omitempty"`
	Raw  []byte         `json:"raw,omitempty"`
	URL  *string        `json:"url,omitempty"`
	Data map[string]any `json:"data,omitempty"`

	Metadata  map[string]any `json:"metadata,omitempty"`
	Filename  string         `json:"filename,omitempty"`
	MediaType string         `json:"mediaType,omitempty"`
}

Part represents a piece of content within a message or artifact. Exactly one of Text, Raw, URL, or Data should be set.

func ContentPartToA2APart 

func ContentPartToA2APart(part types.ContentPart) (Part, error)

ContentPartToA2APart converts a PromptKit ContentPart to an A2A Part.

type RPCError 

type RPCError struct {
	Code    int
	Message string
}

RPCError represents a JSON-RPC error returned by an A2A agent.

func (*RPCError) Error 

func (e *RPCError) Error() string

type Role 

type Role string

Role identifies the sender of a message. 

const (
	RoleUser  Role = "user"
	RoleAgent Role = "agent"
)

Role constants for message senders.

type SendMessageConfiguration 

type SendMessageConfiguration struct {
	AcceptedOutputModes []string `json:"acceptedOutputModes,omitempty"`
	HistoryLength       *int     `json:"historyLength,omitempty"`
	Blocking            bool     `json:"blocking,omitempty"`
}

SendMessageConfiguration controls message handling.

type SendMessageRequest 

type SendMessageRequest struct {
	Message       Message                   `json:"message"`
	Configuration *SendMessageConfiguration `json:"configuration,omitempty"`
	Metadata      map[string]any            `json:"metadata,omitempty"`
}

SendMessageRequest is the params for message/send and message/stream.

type StreamEvent 

type StreamEvent struct {
	StatusUpdate   *TaskStatusUpdateEvent
	ArtifactUpdate *TaskArtifactUpdateEvent
}

StreamEvent represents a single event received during message streaming. Exactly one field will be non-nil.

type SubscribeTaskRequest 

type SubscribeTaskRequest struct {
	ID string `json:"id"`
}

SubscribeTaskRequest is the params for tasks/subscribe.

type Task 

type Task struct {
	ID        string         `json:"id"`
	ContextID string         `json:"contextId"`
	Status    TaskStatus     `json:"status"`
	Artifacts []Artifact     `json:"artifacts,omitempty"`
	History   []Message      `json:"history,omitempty"`
	Metadata  map[string]any `json:"metadata,omitempty"`
}

Task is the top-level unit of work in the A2A protocol.

type TaskArtifactUpdateEvent 

type TaskArtifactUpdateEvent struct {
	TaskID    string         `json:"taskId"`
	ContextID string         `json:"contextId"`
	Artifact  Artifact       `json:"artifact"`
	Append    bool           `json:"append,omitempty"`
	LastChunk bool           `json:"lastChunk,omitempty"`
	Metadata  map[string]any `json:"metadata,omitempty"`
}

TaskArtifactUpdateEvent is sent during streaming when an artifact is produced.

type TaskState 

type TaskState string

TaskState represents the state of an A2A task. 

const (
	TaskStateSubmitted     TaskState = "submitted"
	TaskStateWorking       TaskState = "working"
	TaskStateCompleted     TaskState = "completed"
	TaskStateFailed        TaskState = "failed"
	TaskStateCanceled      TaskState = "canceled"
	TaskStateInputRequired TaskState = "input_required"
	TaskStateRejected      TaskState = "rejected"
	TaskStateAuthRequired  TaskState = "auth_required"
)

TaskState constants for the A2A protocol.

func (TaskState) MarshalJSON 

func (s TaskState) MarshalJSON() ([]byte, error)

MarshalJSON implements json.Marshaler.

func (*TaskState) UnmarshalJSON 

func (s *TaskState) UnmarshalJSON(data []byte) error

UnmarshalJSON implements json.Unmarshaler.

type TaskStatus 

type TaskStatus struct {
	State     TaskState  `json:"state"`
	Message   *Message   `json:"message,omitempty"`
	Timestamp *time.Time `json:"timestamp,omitempty"`
}

TaskStatus describes the current status of a task.

type TaskStatusUpdateEvent 

type TaskStatusUpdateEvent struct {
	TaskID    string         `json:"taskId"`
	ContextID string         `json:"contextId"`
	Status    TaskStatus     `json:"status"`
	Metadata  map[string]any `json:"metadata,omitempty"`
}

TaskStatusUpdateEvent is sent during streaming when a task's status changes.

type ToolBridge 

type ToolBridge struct {
	// contains filtered or unexported fields
}

ToolBridge discovers an A2A agent and creates ToolDescriptor entries for each of the agent's skills so they can be invoked through the standard tool registry.

func NewToolBridge 

func NewToolBridge(client *Client) *ToolBridge

NewToolBridge creates a ToolBridge backed by the given A2A client.

func (*ToolBridge) GetToolDescriptors 

func (b *ToolBridge) GetToolDescriptors() []*tools.ToolDescriptor

GetToolDescriptors returns all tool descriptors accumulated via RegisterAgent calls.

func (*ToolBridge) RegisterAgent 

func (b *ToolBridge) RegisterAgent(ctx context.Context) ([]*tools.ToolDescriptor, error)

RegisterAgent discovers the agent card and creates a ToolDescriptor for each skill. The descriptors are appended to the bridge's internal list (supporting multi-agent composition via GetToolDescriptors).

Source Files

View all Source files

Directories

Path Synopsis
Package mock provides a configurable mock A2A server for use in tests.
 Package mock provides a configurable mock A2A server for use in tests.

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