streaming_client

streaming_client is a production-default streaming client example. It uses the SDK’s libcurl-backed default HTTP transports instead of a synthetic requester and supports both HTTP+JSON SSE and JSON-RPC-over-SSE.

Prerequisites

The SDK always requires gRPC and Protobuf. This example also requires libcurl for the default HTTP+JSON and JSON-RPC streaming transports.

• Debian/Ubuntu: run ./scripts/install_build_deps.sh.
• macOS: run brew install cmake ninja protobuf grpc re2 abseil curl simdjson.
• Windows: use Visual Studio 2022 with the Desktop development with C++ workload and Git for Windows. Run ./scripts/install_build_deps.sh from Git Bash.

Build the client and example server

Linux or macOS:

./scripts/run_examples.sh build-example streaming_server streaming_client

The runner builds both programs and invokes their --help modes as non-blocking smoke checks. It does not leave the server running.

Windows Git Bash:

./scripts/install_build_deps.sh
rm -rf build-example-streaming_server build-example-streaming_client
./scripts/run_examples.sh build-example streaming_server streaming_client

The dependency script bootstraps vcpkg under ${VCPKG_ROOT:-$HOME/vcpkg}, installs the root manifest’s gRPC, Protobuf, and curl dependencies, and defaults both triplets to x64-windows. The example runner uses the same defaults, passes the vcpkg CMake toolchain, builds RelWithDebInfo, and locates the Visual Studio multi-configuration output automatically.

Delete an example build directory before retrying if it was previously configured without CMAKE_TOOLCHAIN_FILE; CMake caches the toolchain during the first configure.

Run the paired examples

Terminal 1 — start the HTTP+JSON SSE server:

./build-example-streaming_server/a2a_example

Terminal 2 — send a streaming request:

./build-example-streaming_client/a2a_example \
  --transport http_json \
  --endpoint http://127.0.0.1:8080/a2a \
  --operation send \
  --timeout-ms 10000

On Windows Git Bash, use:

./build-example-streaming_server/RelWithDebInfo/a2a_example.exe

./build-example-streaming_client/RelWithDebInfo/a2a_example.exe \
  --transport http_json \
  --endpoint http://127.0.0.1:8080/a2a \
  --operation send \
  --timeout-ms 10000

Stop the server with Ctrl+C. See ../streaming_server/README.md for custom listen addresses and server details.

Usage

Linux and macOS:

./build-example-streaming_client/a2a_example \
  --transport http_json|jsonrpc \
  --endpoint <url> \
  --operation send|subscribe \
  [--task-id <id>] \
  [--timeout-ms <milliseconds>] \
  [--cancel-after-first-event]

Windows Git Bash:

./build-example-streaming_client/RelWithDebInfo/a2a_example.exe \
  --transport http_json|jsonrpc \
  --endpoint <url> \
  --operation send|subscribe \
  [--task-id <id>] \
  [--timeout-ms <milliseconds>] \
  [--cancel-after-first-event]

The target server must advertise capabilities.streaming: true and expose the selected transport endpoint. Use --task-id with --operation send only when updating an existing task. Use --task-id with --operation subscribe to identify the existing task subscription.

Send streaming message

HTTP+JSON:

./build-example-streaming_client/a2a_example \
  --transport http_json \
  --endpoint http://127.0.0.1:8080/a2a \
  --operation send \
  --timeout-ms 10000

JSON-RPC:

./build-example-streaming_client/a2a_example \
  --transport jsonrpc \
  --endpoint http://127.0.0.1:8080/rpc \
  --operation send \
  --timeout-ms 10000

The repository’s streaming_server example currently exposes HTTP+JSON SSE. Use a JSON-RPC-capable server for the JSON-RPC command.

Subscribe to an existing task

./build-example-streaming_client/a2a_example \
  --transport http_json \
  --endpoint http://127.0.0.1:8080/a2a \
  --operation subscribe \
  --task-id task-123 \
  --timeout-ms 10000

For JSON-RPC, use the JSON-RPC endpoint and --transport jsonrpc. On Windows, use the multi-configuration executable path shown above.

Cancellation

Add --cancel-after-first-event to demonstrate explicit cancellation after the first decoded event. Cancellation is requested by the main thread after the observer signals that the first event arrived; callbacks are not expected after cancellation settles.

Output and lifecycle notes

The example prints every supported stream variant: Task, TaskStatusUpdateEvent, and TaskArtifactUpdateEvent. Observer callbacks run on the transport worker thread, so the observer is kept alive until completion, error, cancellation, or timeout. The wait is bounded by --timeout-ms; a timeout cancels the stream and returns non-zero.