如何在onNext调用中从上下文/范围中获取变量?(java/grpc)

问题描述

我正在使用上下文="https://github.com/grpc/grpc-java" rel ="nofollow noreferrer"> grpc/java .

I am working with contexts within grpc/java.

我最终要尝试

1)从每个传入请求中获取作为标头附加的元数据(cred元数据)

1) grab metadata attached as a header from each incoming request (cred metadata)

2)将其附加到grpc范围/上下文，以便在服务器端出现请求时可以访问它.

2) attach this to the grpc scope/context, so that I have access to it when the request comes in, server side.

这是一种无法解决API的变通方法.尽管如此，我已经定义了一个拦截器，该拦截器将剥离元数据的每个传入请求.

It's kind of a work around for not being able to change the API as much as I would like to. Nonetheless, I have defined an Interceptor that will strip each incoming request of the metadata.

public class OnBehalfOfInterceptor implements ServerInterceptor {

    @Override
    public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(
       final ServerCall<ReqT, RespT> call,
       final Metadata headers,
       final ServerCallHandler<ReqT, RespT> next
    ) {

        Context ctx = Context.current();

        String mayDelegate = headers.get(
            Metadata.Key.of("may-delegate", Metadata.ASCII_STRING_MARSHALLER)
        );
        String onBehalfOf;

        if (mayDelegate != null && str2bool(mayDelegate)) {
            onBehalfOf = headers.get(
                Metadata.Key.of("on-behalf-of", Metadata.ASCII_STRING_MARSHALLER)
            );
            ctx = ctx.withValue(
                    Context.key("on-behalf-of"),
                    onBehalfOf
            );
        }

        return Contexts.interceptCall(ctx, call, headers, next);
    }

}

此代码尝试查找字符串"on-behalf-of"，如果找到它，则将其附加到当前上下文.

This code attempts to find a string "on-behalf-of" and if it finds it, attaches it to the current context.

现在，当我调试当前的Context时，我可以看到以下输出

Now, when I go to debug the current Context, I am able to see the following output

Context.current().keyValueEntries.root.values[1]

result
    key "on-behalf-of"
    value "my id"

这是.onNext()调用中的调试输出，我能够看到上下文变量，正如我认为的那样.但是，当我不在调试运行时环境中时，我无法获取"keyValueEntries".我猜想这是调试器提供的，不一定是Context类的成员.

This was the debug output inside a .onNext() call, I was able to see the context variables as I figured I should be able to. However, I am not able to grab "keyValueEntries" while I am not in the debug run time environment. I'm guessing that it is something that the debugger provides, not necessarily a member of the Context class.

所以...如何正确访问附加到当前上下文的变量?我尝试了一些不同的示例，并调试了它们的方式.

So... How do I properly get access to the variables that I had attached to the current context? I've tried a few different examples and debugged my way through them.

Context.current().get(Context.key("on-behalf-of"))

// this ^ returns null

我只是在想这个错误吗?有没有更简单的方法可以从传入请求中获取元数据?

Am I just thinking about this wrong? Is there an easier way to grab metadata off of the incoming request?

推荐答案

Context.Key 使用引用相等.您应该在两个位置使用相同的 Key 实例.传递的字符串只是调试字符串.如该文档:

Context.Key uses reference equality. You should use the same Key instance in both locations. The String passed is just a debug string. As written in the documentation:

使用引用相等性意味着您可以使用Java可见性限制，以与 ThreadLocal 相同的方式来限制哪些代码可以访问上下文状态.

Using reference equality means you can use Java visibility restrictions to limit what code has access to the context state, in the same way that's possible with ThreadLocal.

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