Embedded gRPC Web Proxy for Ktor

An embedded gRPC Web proxy for Java/Kotlin gRPC servers using Ktor as HTTP server.

GRPC is a versatile RPC protocol with good support for many programming languages. Javascript applications running in a browser, however, cannot use the binary gRPC protocol directly, instead the gRPC Web protocol can be used, which offers some features of binary gRPC and uses regular HTTP/1 as transport.

To access a regular gRPC server via the gRPC Web protocol, a proxy is needed to convert protocols. There are only a few such gRPC Web proxies available, a common one is envoy.

In small setups, a dedicated gRPC Web proxy can be avoided with an embedded proxy such as this. This project provides a handler that integrates into the HTTP server Ktor that proxies between gRPC Web calls and an internal or external binary gRPC server.

Features

• Both gRPC Web and gRPC Web Text protocols are supported
• CORS support, server responds to CORS preflight OPTION calls and sets headers to allow CORS calls
• Proxied gRPC server can be in-process or external
• HTTPS provided by Ktor

Not supported:

• Routing to multiple gRPC servers

Usage

val channel = InProcessChannelBuilder.forName("my-server").build()
val webServer = embeddedServer(Netty, 40927) {
    routing {
        route("grpcweb") {
            handleGrpcWebCalls(channel)
        }
    }
}
webServer.start()