rpcperms: enable rich gRPC status errors in middleware API

[hxrshxz]

Change Description

Enable the RPC middleware API to return "rich" gRPC errors with full error details including gRPC error codes (fixes #6729).

Previously, errors intercepted by the RPC middleware were always serialized as plain error strings. This meant middleware could only see

Steps to Test

1. Run the rpcperms package tests:

go test -v ./rpcperms/...

2. Build the project to verify no regressions:

go build ./...

Pull Request Checklist

Testing

• Your PR passes all CI checks.
• Tests covering the positive and negative (error paths) are included.

Code Style and Documentation

• The change is not insubstantial.
• The change obeys the Code Documentation and Commenting guidelines, and lines wrap at 80.
• Commits follow the Ideal Git Commit Structure.
• No new logging statements (change only affects internal error handling).
• No new lncli commands (RPC middleware API enhancement only).
• This is a small enhancement; marked with [skip ci] not needed as tests are included.

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[gemini-code-assist]

Summary of Changes

Hello @hxrshxz, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly upgrades the RPC middleware API by enabling it to process and return "rich" gRPC status errors. Previously, the middleware could only handle errors as simple strings, losing valuable context like gRPC error codes. With this enhancement, the system can now serialize and deserialize full google.rpc.Status protobuf messages, providing a more robust and detailed error handling mechanism for intercepted RPC calls.

Highlights

• Rich gRPC Error Support: The RPC middleware API now supports "rich" gRPC errors, including full error details and gRPC error codes, addressing issue rpc: enable the RPC middleware API to return "rich" errors  #6729.
• Enhanced Error Serialization: Errors intercepted by the middleware are no longer limited to plain error strings; they can now be serialized as google.rpc.Status protos, preserving detailed error information.
• Improved Error Handling: This change allows middleware to inspect and modify complete error information, providing a more robust and flexible error handling mechanism within the RPC system.

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[gemini-code-assist]

Code Review

This pull request enhances the RPC middleware API to support rich gRPC status errors, allowing middleware to inspect and modify errors with full details, including gRPC error codes. Previously, errors were just plain strings. The changes involve differentiating between plain errors and gRPC status errors during serialization for interception, and then correctly parsing them back when a replacement is provided by the middleware. New tests have been added to cover this new functionality. The implementation is solid, but there's a critical issue with a missing import alias that will prevent the code from compiling.

[Copilot]

Pull request overview

This PR enhances the RPC middleware API to support rich gRPC status errors with full error details including gRPC error codes, addressing issue #6729. Previously, errors intercepted by middleware were always serialized as plain strings, losing important error code information.

Key changes:

• Added support for serializing and deserializing gRPC status errors as google.rpc.Status proto messages
• Introduced new constants to distinguish between plain error strings and rich gRPC status errors
• Updated error handling logic to preserve gRPC error codes throughout the middleware pipeline

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
rpcperms/middleware_handler.go	Implements the core functionality to serialize/deserialize gRPC status errors, adds constants for error type names, and introduces the parseErrorReplacement function to handle both plain and rich errors
rpcperms/middleware_handler_test.go	Adds comprehensive test coverage for the new error handling functionality, including tests for plain errors, gRPC status errors with different codes, and error parsing edge cases

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[hxrshxz]

@gemini-code-assist please reivew

[gemini-code-assist]

Thanks for the ping, @hxrshxz! I've completed my review of this pull request.

This is a well-implemented change that significantly improves the RPC middleware API by enabling it to handle rich gRPC status errors. The introduction of google.rpc.Status protobuf messages for error serialization and deserialization is a robust solution that preserves valuable error context, such as gRPC error codes.

Here's a summary of my findings:

• Correctness: The logic for detecting, serializing, and deserializing gRPC status errors is sound. The parseErrorReplacement function correctly distinguishes between plain error strings and rich gRPC status errors, and NewMessageInterceptionRequest handles both cases appropriately.
• Maintainability: The code is clean, readable, and follows good practices. The new constants (StatusTypeNameError, StatusTypeNameStatus) enhance clarity, and the dedicated parseErrorReplacement function improves modularity.
• Testing: The added unit tests (TestParseErrorReplacement, TestParseErrorReplacementWithStatus, TestNewMessageInterceptionRequestWithStatusError) provide excellent coverage for the new functionality, including edge cases like invalid proto serialization and verification of preserved error codes and messages. This gives high confidence in the correctness of the changes.

Overall, this is a great improvement to the error handling mechanism within the RPC system. The changes are well-thought-out and thoroughly tested. I'm happy with the current state of the PR.

[lightninglabs-deploy]

@hxrshxz, remember to re-request review from reviewers when ready

[hxrshxz]

@yyforyongyu Please have a look thank you

[saubyk]

!lightninglabs-deploy mute