[Audit Logging] Logger and factory APIs in C-Core and C++.

[rockspore]

Audit logging APIs for both built-in loggers and third-party logger implementations.

C-Core and C++ have independent base classes of loggers and factories for users to implement.

[rockspore]

@ctiller @markdroth PTAL. Is this what you had in your mind yesterday?

[ctiller]

class AuditContext { -- no need for a typedef

[ctiller]

I'd make this a reference

[ctiller]

I don't think we need inheritance here: this should be its own type.

[ctiller]

No inheritance here.

[ctiller]

This should just be Log(...), and we'll have an instance that has a unique_ptr<grpc::AuditLogger> log_ that we call log_->Log(...) on.

[rockspore]

So it means this class defined in C-Core can have a dependence on the C++ class, right? I initially was about to do this but wasn't sure if it's fine to have such a reversed dependency.

[rockspore]

Oh. is the following flow correct?

// C-Core
class AuditLogger {
 public:
  virtual void Log() = 0;
};

// C++
class AuditLogger {
 public:
  virtual void Log() = 0;
};

class AuditLoggerFactory {
 public:
  virtual std::unique_ptr<AuditLogger> CreateAuditLogger() = 0;
  std::unique_ptr<CoreLogger> CreateCoreLogger() {
    return std::make_unique<CoreLogger>(CreateAuditLogger());
  }
};

// non-public API
class CoreLogger : public grpc_core::AuditLogger {
 public:
  CoreLogger(std::unique_ptr<AuditLogger> logger) : logger_(logger) {}
  void Log() { logger_->Log(); }
 private:
  std::unique_ptr<AuditLogger> logger_;
};

[markdroth]

This looks great!