grpc-http1: A gRPC via HTTP/1 Enabling Library for Go

This library enables using all the functionality of a gRPC server even if it is exposed behind a reverse proxy which does not support HTTP/2, or only supports it for clients (such as Amazon's ALB). This is accomplished via either adaptive downgrading to the gRPC-Web response format or utilizing WebSockets.

For a high-level overview, see this Medium post about the gRPC-Web downgrade option and this Medium post about the gRPC-WebSocket option.

Connection Compatibility Overview

The following table shows what can be expected when a client/server instrumented with the capability offered by this library compared to an unmodified gRPC client/server, both when accessing it directly and when accessing it via a reverse proxy not supporting HTTP/2.

	Plain Old gRPC Server		HTTP/1 Downgrading gRPC Server
	direct	behind reverse proxy	direct	behind reverse proxy
Plain Old gRPC Client	✅	❌	✅	❌
gRPC-Web downgrade client mode	✅	❌	✅	(:white_check_mark:)
gRPC-WebSocket client mode	❌	❌	✅	✅

The (:white_check_mark:) for the gRPC-Web downgrading client indicates a subset of gRPC calls will be possible, but not all. These include all calls that do not rely on client-side streaming (i.e., all unary and server-streaming calls).

As you can see, when using the client in gRPC-Web downgrade mode, it is possible to instrument the client or the server without any (functional) regressions - there may be a small but fairly negligible performance penalty. This means rolling this feature out to your clients and servers does not need to happen in a strictly synchronous fashion. However, you will only be able to work with a server behind an HTTP/2-incompatible reverse proxy if both the client and the server have been instrumented via this library. To use the client in gRPC-WebSocket mode, both the client and server must be instrumented via this library.

Usage

This library has the canonical import path golang.stackrox.io/grpc-http1. It fully supports Go modules and requires Go version 1.13+ to be built and used. To add it as a dependency in your current project, run go get golang.stackrox.io/grpc-http1.

Server-side

For using this library on the server-side, you'll need to bypass the regular (*grpc.Server).Serve method and instead use the ServeHTTP method of the *grpc.Server object -- it is experimental, but we found it to be fairly stable and reliable.

The only exported function in the golang.grpc.io/grpc-http1/server package is CreateDowngradingHandler, which returns a http.Handler that can be served by a Go HTTP server. It is crucial this server is configured to support HTTP/2; otherwise, your clients using the vanilla gRPC client will no longer be able to talk to it. You can find an example of how to do so in the _integration-tests/ directory.

Client-Side

For connecting to a gRPC server via a client-side proxy, use the ConnectViaProxy function exported from the golang.grpc.io/grpc-http1/client package. This function has the following signature:

func ConnectViaProxy(ctx context.Context, endpoint string, tlsClientConf *tls.Config, opts ...ConnectOption) (*grpc.ClientConn, error)

The first two arguments are the same as for grpc.DialContext. The third argument specifies the TLS client config to be used for connecting to the target address. Note that this is different from the usual gRPC API, which specifies client TLS config via the grpc.WithTransportCredentials. For a plaintext (unencrypted) connection to the server, pass a nil TLS config; however, this does not free you from passing the grpc.WithInsecure() (nor grpc.WithTransportCredentials(insecure.NewCredentials())) gRPC dial option.

The last (variadic) parameter specifies options that modify the dialing behavior. You can pass any gRPC dial options via client.DialOpts(...); however, the grpc.WithTransportCredentials option will not be needed. By default, adaptive gRPC-Web downgrading is used. To use WebSockets, pass true to the client.UseWebSocket option.

Another important option is client.ForceHTTP2(), which needs to be used for a plaintext connection to a server that is not HTTP/1.1 capable (e.g., the vanilla gRPC server). This option is ignored when WebSockets are used. Again, check out the code in the _integration-tests directory.