Client-Side Streaming in gRPC

Client-side streaming in gRPC enables you to send a sequence of messages from the client to the server using a single established connection. In this pattern, the client writes multiple messages to the stream, and the server processes the stream and responds with a single message once the client has finished sending data.

How Client-Side Streaming Works

• The client initiates a request to the server, opening a stream;
• The client sends multiple messages over the stream, one after another;
• The server receives the messages as they arrive but does not respond until the client signals that it has finished sending data;
• Once the client completes its message stream, the server processes the received data and returns a single response message.

This approach is different from unary RPCs, where only one request and one response are exchanged, and from server-side streaming, where the server sends a stream of responses for a single client request.

Typical Use Cases

• Uploading large files or data sets in chunks, such as media uploads or logs;
• Sending a series of sensor readings or telemetry data for aggregation;
• Collecting user input or events over time before processing them as a batch.

Trade-Offs and Considerations

• Reduced network overhead: Sending multiple messages over a single connection minimizes connection setup and teardown costs;
• Increased client responsibility: The client must manage the timing and order of message transmission, handling errors and retries as needed;
• Server-side latency: The server only responds after all client messages are received, which may introduce a delay before the client receives feedback;
• Flow control: Both client and server must handle flow control to avoid overwhelming the network or the server's processing capacity.

Practical Relevance

Client-side streaming is valuable when you need to send a sequence of related data points or large payloads that do not fit into a single message. It is especially useful for scenarios where batching or aggregating data on the client side improves efficiency, such as uploading logs, telemetry, or large files. By leveraging client-side streaming, you can create scalable, efficient, and robust communication patterns between distributed systems in modern applications.