Overriding http host header of gRPC client in golang

It is a common requirement to override the http host header of gRPC client in golang. gRPC is a high-performance, cross-language remote procedure call framework. When using gRPC to communicate, it is sometimes necessary to customize the host header of the http request. PHP editor Xigua will introduce you how to implement this function in golang to better meet your business needs.

Question content

I sent the request over the connection through the gRPC client

conn, err := grpc.Dial("hostname:port",opts...)

From the server side, I see that the host in http.request is the exact hostname:port. Then, my nginx server settings are as follows

server {
    listen port http2;
    server_name hostname;
    # ...
}
server {
    listen port http2;
    server_name another_hostname;
    # ...
}

This is a common virtual hosting technology. No matter which hostname I use in grpc.Dial(xxx:port) it works fine. However, when I put

md := metadata.New(map[string]string{"host":"another_hostname:port"})

In the grpc context (will be populated in the header of the http2 request). This request will be blocked by nginx and I get

rpc error: code = Internal desc = unexpected HTTP status code received from server: 400 (Bad Request); transport: received unexpected content-type "text/html"

The reason why you need to enter the host name manually is because the host name in grpc.Dial is fixed. And I can't use a different location to do the reverse proxy because port is followed by the routing path of the restful api.

If the hostname is fixed and the route is also fixed, are there any other ways to reverse proxy?

(23/09) Update: It turns out that the host header in http2 has been replaced by the :Authority pseudo header.

Workaround

gRPC uses HTTP/2 and does not use the :host header, but instead uses the :authority pseudo-header. The value of this header is determined here: https://github .com/grpc/grpc-go/blob/aa6ce35c792863305e0f42acc27f2c7153275f89/clientconn.go#L1942

TL;PhD

By default, the value used for the :authority header is the endpoint portion of the user dial target, in the format url://authority/endpoint.

gRPC-Go also supports a dialup option to override this authority. See: https://pkg.go.dev/google.golang.org/ grpc#WithAuthority. But also note that this dialing option overrides the ServerName value used during the TLS handshake.

If you have further questions/concerns, please feel free to contact us via our GitHub repository. Your queries will get better response time there.

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