What is difference between grpc and websocket? Which one is more suitable for bidirectional streaming connection?

Solution 1:

gRPC is not really the relevant part for comparison, it's that gRPC uses HTTP/2 which can certainly be compared to WebSockets.

https://www.infoq.com/articles/websocket-and-http2-coexist

This article outlines them quite well. Essentially, HTTP/2 is Client/Server with Server Push on the background, so you can make your request and simply stay on that connection listening for updates without the need for polling, for example.

Whilst WebSockets are not going away because of HTTP/2, they might not be considered necessary for use cases that center around "let me know when updates happen related to the thing I just did".

Solution 2:

gRPC is an API/Protocol on top of HTTP/2, so it is more relevant to compare HTTP/2 and Websockets.

Note: HTTP/2 Server Push is not relevant here either. That is a website optimization technique for cacheable (GET) resources.

Websocket and HTTP/2 support binary data frames with low overhead (a few bytes), however frames (whole payload) in Websocket is masked at sender and then unmasked at receiver. See What is the mask in a WebSocket frame?.

With HTTP/2 you can have multiple streams multiplexed over the same connection. This need to be handled by application developer or a library when using Websocket - if desired.

If your client is a browser, the answer to HTTP/2 or Websockets for low latency client to server messages may be relevant.