Upgrade fasta2a to A2A v0.2.3 and Enable Dependency Injection #2103
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Enable pydantic-ai agents that use dependency injection to work with the A2A protocol by adding a deps_factory parameter to to_a2a(). Changes: - Add deps_factory parameter to Agent.to_a2a() method - Update AgentWorker to use deps_factory when creating dependencies - Add comprehensive tests for the feature - Add bank_support_a2a example showing real-world usage - Update documentation with examples The deps_factory receives the A2A Task object and returns dependencies matching the agent's deps_type. This enables agents to get context from task metadata (e.g., user authentication, database connections).
- Change Part types to use 'kind' field instead of 'type' - Add new fields to Message type: message_id, context_id, task_id, kind - Add MessageSendConfiguration and MessageSendParams types - Replace tasks/send with message/send and message/stream methods - Update JSON-RPC request/response types for new protocol - Remove deprecated File-related types This is a breaking change that updates fasta2a to comply with the current A2A protocol specification, focusing on clean implementation without backward compatibility.
- Replace tasks/send with message/send in routing - Add send_message method to TaskManager - Remove deprecated send_task method - Add TODO for message/stream implementation - Update imports for new message types Minimal changes to support the new protocol while maintaining the existing code style and architecture.
- Add TaskSendParams back as internal framework type - Update AgentWorker to use 'kind' field instead of 'type' - Update file part handling for new schema structure - Maintain type safety in worker interface - Preserve deps_factory functionality TaskSendParams is now explicitly marked as an internal type for broker/worker communication, separate from the A2A protocol.
- Replace send_task with send_message method - Update to use MessageSendParams and MessageSendConfiguration - Return Task < /dev/null | Message union type from send_message - Remove client-generated task IDs (now server-generated) - Update imports for new protocol types The client now uses message/send instead of tasks/send and properly handles the response which can be either a Task or Message.
- Add type guards (is_task/is_message) for handling Task < /dev/null | Message union types - Update all tests to use new send_message API that returns SendMessageResponse - Fix all test assertions to check for both 'error' and 'result' fields - Update Part type access to check 'kind' field before accessing type-specific fields - Fix GetTaskResponse handling where 'result' is NotRequired - Clean up unused imports after protocol migration - Update event docstrings to reference message/stream instead of legacy methods - Add proper imports and type annotations for streaming support - Fix task_manager to use properly typed TaskSendParams for broker calls - Handle AgentWorker deps with conditional logic based on deps_factory presence - Fix bank_support_a2a.py example with proper Task type import
- Add required context_id field to Task (spec line 89) - Add required kind: 'task' field to Task (spec line 94) - Update streaming events to use taskId instead of id (spec lines 175-176) - Add contextId field to streaming events - Add kind field to TaskArtifactUpdateEvent for event type identification - Add InvalidAgentResponseError (-32006) error code - Remove session_id throughout codebase (not in v0.2.3 spec) - Replace all session_id usage with context_id - Update type guard to check for new required Task fields - Update all tests to expect new Task structure
- Message structure updates: - Made kind: 'message' field required (was NotRequired) - Added reference_task_ids array field - Added extensions array field - Update all Message creation to include required kind field - Artifact structure updates: - Added required artifact_id field (spec line 123) - Removed index field (not in spec, was implementation detail) - Added extensions array field - Generate unique artifact_id using uuid - FilePart structure updates: - Changed from flat structure to nested file: FileWithBytes < /dev/null | FileWithUri - Created FileWithBytes and FileWithUri types matching spec - Updated all FilePart usage to use nested structure - Updated _map_request_parts to handle nested file content - Updated tests: - All Message instances now include kind: 'message' - All artifacts include artifact_id and no longer have index - All FilePart usage converted to nested structure - Fixed message history entries to include kind field
- Add append and last_chunk fields to TaskArtifactUpdateEvent for chunk-based streaming - Implement StreamEvent union type with proper discriminator for broker communication - Enhance broker with streaming capabilities and proper event routing - Add streaming support to task manager with chunk handling - Update storage layer to handle appending artifacts - Extend application layer with streaming functionality - Add comprehensive tests for streaming scenarios
- Add proper exception logging in Worker._handle_task_operation to aid debugging
- Fix pyright type errors in _a2a.py:
- Properly extract text content from ModelRequest parts
- Add type annotation for metadata dict
- Fix current_message type inference
- Rename Worker.build_message_history parameter from 'task_history' to 'history' for clarity
- Remove exception re-raise in worker to allow graceful task failure without crashing the worker
PR Change SummaryUpgraded A2A support to version 0.2.3 and introduced dependency injection capabilities for enhanced usability in real-world applications.
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Summary
The goal of this PR is to bring pydantic-ai's A2A support up to the current protocol specification and makes it practically usable for real-world applications.
Key improvements:
deps_factorysupport toAgent.to_a2a(), allowing agents that use pydantic-ai's core dependency injection feature to work with A2ABackground
The initial A2A support in pydantic-ai implemented v0.1 of the protocol, which was superseded by the non-backwards-compatible v0.2 just days after the implementation landed. This unfortunate timing meant that pydantic-ai's A2A support was incompatible with the rest of the ecosystem from the start.
Additionally, the initial implementation only worked with agents that didn't use dependency injection - a significant limitation given that dependency injection is a core pydantic-ai feature used in most real-world applications.
What Changed
1. A2A Protocol v0.2.3 Upgrade
Before:
tasks/sendAfter:
message/sendandmessage/stream)Key protocol changes:
tasks/send→message/sendtype→kindin all message parts2. Dependency Injection Support
Before:
to_a2a()only worked with agents that had no dependenciesAfter:
deps_factoryparameter enables full dependency injection support3. Streaming and Structured Output Support
New capabilities:
agent.iter()to stream partial responses as they're generatedImplementation Details
Protocol Upgrade
Dependency Injection
deps_factoryparameter toAgent.to_a2a()Testing
bank_support_a2aexample demonstrating real-world usage with authenticationUsage Example
See the
bank_support_a2aexample for a complete demonstration of usingdeps_factorywith A2A. This example shows how to:Migration Guide
For the few early adopters who may have tried the v0.1 implementation:
message/sendinstead oftasks/sendkindfield instead oftypeRelated Issues
Fixes #1795 - Implements the core A2A v0.2.3 protocol methods
message/sendandmessage/streamto replace the deprecatedtasks/sendmethod from v0.1.Related Links