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Metadata and headers

The request and response of Unary services can include metadata. Metadata is treated as HTTP headers, and can be set and read by both clients and servers. Metadata is represented by the Metadata class in gRPC.

This is useful when you need to add additional information to requests and responses, such as header authentication mechanisms or version information.

Client​

Adding metadata to a request​

To add metadata to a request, use the WithHeaders method of MagicOnionClient. The following example uses the Metadata class to add an Authorization header to the request.

var client = MagicOnionClient.Create<IGreeterService>(channel).WithHeaders(new Metadata
    { "authorization", "Bearer {token}" }
});

You can also set CallOptions by passing the MagicOnionClientOptions class when creating a client, or using the MagicOnionClient.WithOptions method. Additionally, you can set metadata at the time of the request using client filters.

Reading metadata from a response​

You can read metadata using the ResponseHeadersAsync property of the UnaryResult struct. ResponseHeadersAsync waits for the server to respond.

The following is an example of reading metadata from a response.

var client = MagicOnionClient.Create<IGreeterService>(channel);
var result = client.SayHelloAsync("Alice", 18);

var headers = await result.ResponseHeadersAsync;

Server​

You can also read the metadata of requests received from clients on the server, and add metadata to responses.

Reading metadata from a request​

You can read the metadata of a request using the CallContext.RequestHeaders property of the ServiceContext class.

if (Context.CallContext.RequestHeaders.GetValue("authorization") is {} authorizationHeader)
{
    ...
}

Adding metadata to a response​

You can add metadata to a response using the CallContext.WriteResponseHeadersAsync method of the ServiceContext class.

Context.CallContext.WriteResponseHeadersAsync(new Metadata
{
    { "x-server-version", "1.0.0" }
});

In addition, it is also possible to set values as HTTP headers from HttpContext, which is a standard method in ASP.NET Core.

Context.CallContext.GetHttpContext().Response.Headers.TryAdd("x-server-version", "1.0.0");