Fix streaming RPC frame validation

[wasphin]

What problem does this PR solve?

Issue Number: resolve

Problem Summary:

Streaming RPC frames are consumed directly by the streaming parser and do not pass through InputMessenger's authentication hook. A stream could also accept a frame carrying its ID from a socket other than the socket that created the stream.

What is changed and the side effects?

Changed:

• Reject streaming frames on server sockets when configured authentication has not completed successfully.
• Expose the socket authentication state needed by the streaming parser.
• Keep server-accepted streams bound to the socket of their creating RPC and reject frames arriving from another socket.
• Add separate unit tests for direct unauthenticated frame rejection and the complete client/server authentication and streaming service path.
• Use an OS-assigned port in the service-path test to avoid test-environment port conflicts.

Side effects:

• Performance effects: One authentication-state check per server-side streaming frame when server authentication is configured, plus a socket identity check before dispatching a frame to a stream.

• Breaking backward compatibility: No. Authenticated streaming RPC behavior and the wire format are unchanged.

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Check List:

• Please make sure your changes are compilable.
• When providing us with a new feature, it is best to add related tests.
• Please follow Contributor Covenant Code of Conduct.

[Copilot]

Pull request overview

This PR strengthens the server-side streaming RPC protocol handling in bRPC by ensuring streaming frames are subject to authentication state and by preventing streams from accepting frames over a different socket than the one that established/bound the stream via the creating RPC.

Changes:

• Enforce server-side rejection of streaming frames when server authentication is configured but the socket has not successfully authenticated.
• Bind server-accepted streams to the creating RPC’s socket and drop frames delivered on “foreign” sockets.
• Add unit tests covering unauthenticated streaming-frame rejection and end-to-end authenticated RPC + streaming behavior (including using an OS-assigned port to avoid conflicts).

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/brpc_streaming_rpc_unittest.cpp	Adds unit tests for unauthenticated-frame rejection and authenticated service-path streaming.
src/brpc/stream.cpp	Tightens socket binding behavior for streams; rejects frames from mismatched sockets.
src/brpc/stream_impl.h	Tracks whether a stream is server-accepted to enforce socket-binding rules.
src/brpc/socket.h	Exposes a new Socket::IsAuthenticated() API for protocol-layer checks.
src/brpc/socket.cpp	Implements Socket::IsAuthenticated() using the existing auth flag/error state.
src/brpc/policy/streaming_rpc_protocol.cpp	Adds an authentication-state gate for server-side streaming frame parsing (when invoked with server context).

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[wasphin]

Updated all existing SetHostSocket callers to handle binding failures. The server response paths now fail the affected streams instead of marking them connected, and the client extra-stream path fails the request streams and returns.

[wasphin]

Updated the test to configure authentication through public ServerOptions and Start(0, ...). It continues to use an OS-assigned port.