admincmd

Linux deamons/servers often need a back door for administration purposes. This project provides a solution that help build a command line server that can be easily be incorporated into an existing program written in c++, and users can use tools such as telnet or nc to communicate with the server.

The main work user need to do is to include one header file AdminCMDServer.h, create an object of AdminCMDServer, provide it with server ip and port to listen on, and implement 3 callback functions in a CRTP-ish style to handle events:

// A client established a connection to the server
void onAdminConnect(AdminCMDServer::Connection& conn);

// A client disconnected from the server
void onAdminDisconnect(AdminCMDServer::Connection& conn, const std::string& error);

// A client sent a command
void onAdminCMD(AdminCMDServer::Connection& conn, int argc, const char** argv);

And for each admin connection, user can access user defined structure via user_data, get remote network address via getPeername(), write response msg via write() and close the connection via close():

class Connection {
public:
  // data member with user defined type
  ConnUserData user_data;
  
  // get remote network address
  // return true on success
  bool getPeername(struct sockaddr_in& addr);
  
  // more = true: MSG_MORE flag is set on this write
  // return true on success
  bool write(const char* data, uint32_t size, bool more = false);
  
  // close this connection with a reason
  void close(const char* reason = "user close");
};

Thread Model

AdminCMDServer does not create threads itself, thus it needs user to drive it by calling poll() repetitively(poll() is non-blocking), it's up to the user to use existing threads or create an new thread to poll and it's user's responsibility to ensure thread safety.

Server Output

AdminCMDServer does not write errors to stdout or log files. User should use getLastError() to get error msg when init() failed.

Connection Timeout

By default admin connection won't timeout, but it can be enabled by setting AdminCMDServer's template parameter uint64_t ConnTimeout, the value is measured by a difference of user provided timestamps, and the timestamps are passed in as the optional parameter of poll: void poll(uint64_t now = 0).

Command Format

Shell style command is supported, that is, when you build a c program and run it by ./a.out args..., the arguments will be parsed into int argc, const char** argv in the program. To be specific, when not in quotes, all characters will be escaped by backslash(\), spaces will delimite arguments and line feed(\n) will end the command; When in single quotes('), none character will be escaped; When in double quotes("), only backslash(\) and double quote(") will be escaped.

References

https://github.com/MengRao/pollnet