feat(websocket): add websocket cpb for a2a-rs

Cargo.toml

@@ -6,6 +6,7 @@ members = [
     "a2a-pb",
     "a2a-grpc",
     "a2a-slimrpc",
+    "a2a-websocket",
     "a2acli",
     "examples",
 ]
@@ -37,6 +38,7 @@ a2a-server = { package = "a2a-server-lf", path = "a2a-server", version = "0.2.7"
 a2a-pb = { package = "a2a-pb", path = "a2a-pb", version = "0.1.7" }
 a2a-grpc = { package = "a2a-grpc", path = "a2a-grpc", version = "0.2.1" }
 a2a-slimrpc = { package = "a2a-slimrpc", path = "a2a-slimrpc", version = "0.1.10" }
+a2a-websocket = { package = "a2a-websocket", path = "a2a-websocket", version = "0.1.0" }
 
 # Serialization
 serde = { version = "1", features = ["derive"] }
@@ -74,12 +76,19 @@ pbjson-build = "0.9"
 protoc-bin-vendored = "3"
 slim_bindings = { package = "agntcy-slim-bindings", version = "1.3.0" }
 
+# WebSocket
+fastwebsockets = { version = "0.10", features = ["upgrade", "with_axum"] }
+http-body-util = "0.1"
+hyper-util = { version = "0.1", features = ["tokio"] }
+bytes = "1"
+
 # Utilities
 rcgen = { version = "0.14", default-features = false, features = ["crypto", "pem", "aws_lc_rs"] }
 rustls-pemfile = "2"
 chrono = { version = "0.4", features = ["serde"] }
 base64 = "0.22"
 thiserror = "2"
+parking_lot = "0.12"
 uuid = { version = "1", features = ["v7"] }
 semver = "1"
 tracing = "0.1"

README.md

@@ -16,6 +16,7 @@ The workspace supports:
 - REST / HTTP+JSON
 - gRPC via `tonic`
 - SLIMRPC via `slim_bindings`
+- WebSocket custom protocol binding via `fastwebsockets`
 - Server-Sent Events for streaming responses
 - Protobuf-based interop with other SDKs and runtimes
 
@@ -29,6 +30,7 @@ The workspace supports:
 | `a2a-pb` | Protobuf schema, generated types, ProtoJSON-capable generated types, and native <-> protobuf conversion helpers |
 | `a2a-grpc` | gRPC client and server bindings built on `tonic` |
 | `a2a-slimrpc` | SLIMRPC client and server bindings built on `slim_bindings` |
+| `a2a-websocket` | WebSocket custom protocol binding (client and server) built on `fastwebsockets` and `axum` |
 | `a2acli` | Standalone A2A client CLI, published as `a2a-cli`, for inspecting agent cards, sending messages, managing tasks, and handling push configs |
 | `examples/helloworld` | Minimal runnable example agent |
 
@@ -40,6 +42,7 @@ The workspace supports:
 | HTTP+JSON / REST | `a2a-client` | `a2a-server` |
 | gRPC | `a2a-grpc` | `a2a-grpc` |
 | SLIMRPC | `a2a-slimrpc` | `a2a-slimrpc` |
+| WebSocket | `a2a-websocket` | `a2a-websocket` |
 
 The gRPC support uses the schema in `a2a-pb/proto/a2a.proto`. The REST and
 JSON-RPC bindings are intended to stay wire-compatible with other A2A SDKs,
@@ -138,6 +141,7 @@ a2a-server = { package = "a2a-server-lf", git = "https://github.com/a2aproject/a
 a2a-pb = { package = "a2a-pb", git = "https://github.com/a2aproject/a2a-rs.git" }
 a2a-grpc = { package = "a2a-grpc", git = "https://github.com/a2aproject/a2a-rs.git" }
 a2a-slimrpc = { package = "a2a-slimrpc", git = "https://github.com/a2aproject/a2a-rs.git" }
+a2a-websocket = { package = "a2a-websocket", git = "https://github.com/a2aproject/a2a-rs.git" }
 ```
 
 Typical usage is:
@@ -147,6 +151,7 @@ Typical usage is:
 - `a2a-server` for agent implementations on `axum`
 - `a2a-grpc` when you need gRPC transport support
 - `a2a-slimrpc` when you need SLIMRPC transport support
+- `a2a-websocket` when you need the WebSocket custom protocol binding
 - `a2a-pb` when you need direct access to protobuf messages or conversion helpers
 
 ## Repository Layout
@@ -157,6 +162,7 @@ Typical usage is:
 - `a2a-pb/`: protobuf schema and conversion layer
 - `a2a-grpc/`: tonic-based bindings
 - `a2a-slimrpc/`: SLIMRPC bindings
+- `a2a-websocket/`: WebSocket custom protocol bindings
 - `a2acli/`: standalone A2A client CLI and published binary package
 - `examples/helloworld/`: runnable sample agent
 

a2a-pb/proto/a2a.proto

@@ -339,7 +339,7 @@ message AgentInterface {
   string url = 1 [(google.api.field_behavior) = REQUIRED];
   // The protocol binding supported at this URL. This is an open form string, to be
   // easily extended for other protocol bindings. The core ones officially
-  // supported are `JSONRPC`, `GRPC` and `HTTP+JSON`.
+  // supported are `JSONRPC`, `GRPC`, `HTTP+JSON`, `SLIMRPC`, and `WEBSOCKET`.
   string protocol_binding = 2 [(google.api.field_behavior) = REQUIRED];
   // Tenant ID to be used in the request when calling the agent.
   string tenant = 3;

a2a-pb/src/gen/lf.a2a.v1.rs

@@ -221,7 +221,7 @@ pub struct AgentInterface {
     pub url: ::prost::alloc::string::String,
     /// The protocol binding supported at this URL. This is an open form string, to be
     /// easily extended for other protocol bindings. The core ones officially
-    /// supported are `JSONRPC`, `GRPC` and `HTTP+JSON`.
+    /// supported are `JSONRPC`, `GRPC`, `HTTP+JSON`, `SLIMRPC`, and `WEBSOCKET`.
     #[prost(string, tag = "2")]
     pub protocol_binding: ::prost::alloc::string::String,
     /// Tenant ID to be used in the request when calling the agent.

a2a-websocket/CHANGELOG.md

@@ -0,0 +1,28 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+## [0.1.0] - 2026-05-06
+
+### Added
+
+- Add WebSocket custom protocol binding for A2A v1, including:
+  - `WebSocketTransport` and `WebSocketTransportFactory` implementing the
+    `a2a_client::transport::Transport` and `TransportFactory` traits.
+  - `websocket_router` adapting an `a2a_server::RequestHandler` to an
+    `axum::Router` that serves the binding over a persistent WebSocket
+    connection with full bidirectional streaming and multiplexing.
+  - JSON envelope types (`WsRequestEnvelope`, `WsResponseEnvelope`,
+    `WsErrorObject`) implementing the wire format defined in the
+    A2A WebSocket binding specification.
+  - Mapping helpers between `A2AError` and the canonical WebSocket
+    error type strings, plus close-code selection for fatal failures.
+  - Service parameter handling that combines connection-scoped headers
+    with per-request `serviceParams` (per-request takes precedence).
+- Re-export `TRANSPORT_PROTOCOL_WEBSOCKET` from the `a2a` core crate so
+  application code can register the factory using the shared constant.