mrw-cxx/mrw/exec.hpp

#ifndef __MRW_EXEC_HPP__
#define __MRW_EXEC_HPP__

#include <string>
#include <list>
#include <mrw/exception.hpp>

namespace mrw {

  /** @defgroup CmdExec Execute UNIX Commands

      There is no easy way to safely execute UNIX commands and to
      return the output of the callee to the caller. @c system ist
      first of all known to be unsafe, because it opens a shell, and
      second there is no way to transfer the output back to the
      caller. On the other hand, starting a new process with @c fork
      and @c exec and passing the output of the callee to the caller
      using pipes is quite complex and needs much more than one simple
      line of code. This is the gap that is filled with this command
      execution classes. There's a class for the command to be
      executed and a class for the execution of the command.

      Forking a subprocess and evaluating the result becomes so easy:

      @code
      try {
        // execute the command: /bin/ls -l /tmp
        mrw::Exec ls =
          (mrw::Cmd("/bin/ls"), "-l", "/tmp").execute(false);
        // evaluate the result
        if (ls.success())
          std::cout<<"Execution successful, result was:"<<std::endl;
        else
          std::cerr<<"Error in execution, error was:"<<std::endl;
        std::cout<<ls.result()<<std::endl;
        std::cerr<<ls.error()<<std::endl;
      } catch (ExecutionFailedExc& x) {
        // a fatal execution error occurred
        // you can trace x.what() and x.stacktrace()
      }
      @endcode
  */
  //@{
  
  class Cmd;
  
  /** @brief Exception: Execution of command failed.

      This exception is thrown, if the exection of a command in
      mrw::Exec is failed. That means, it was not possible to fork or
      to create the necessary pipes, or the command executing process
      terminated with an error. In the last case, you can access the
      error stream from @c stderr respectively @c cerr with method
      mrw::Exec::error().
  */
  class ExecutionFailedExc: public mrw::exception {
  public:
    ExecutionFailedExc(const std::string&, const std::string&)
      throw(std::bad_exception);
    virtual ~ExecutionFailedExc() throw() {}
    virtual const char* what() const throw() {return _what.c_str();}
  private:
    std::string _what;
  };

  /** @brief Execute a command in a new process.

      This class handles the execution of a command in a new process
      and returns the two streams @c cout and @cerr, also known as @c
      stderr and @stdout.

      There are different ways of usage for this class. A simple way,
      one line of code, to get only the resulting stream (no error)
      is:

      @code
      string stdout =
        (mrw::Cmd("/bin/ls"), "-l", "/tmp").execute(false).result();
      @endcode

      If you need not only the resulting @c stdout stream, but also
      the error stream @c stderr, then you need to store the result:

      @code
      mrw::Exec ls =
        (mrw::Cmd("/bin/ls"), "-l", "/tmp").execute(false);
      if (!ls) ...; // command termianted with error
      // ls.result() contains stdout
      // ls.error() contains stderr
      @endcode

      @note Please note that the command execution may throw an exception.
  */
  class Exec {
  public:
    
    /** @brief Create an executor given a command.
        Construction without passing a command is not possible. */
    Exec(const mrw::Cmd&) throw(std::bad_exception);
    
    Exec(const mrw::Exec&) throw(std::bad_exception);
    ~Exec() throw();
    Exec& operator=(const mrw::Exec&) throw(std::bad_exception);
    
    /** @brief Execute the command.
        
        @param bool
         - @c true throw an exception if return status is not zero
         - @c false throw only an exception in case of a fatal error
         
        @throw ExecutionFailedExc is thrown if
         - fork fails
         - creation or setup of pipes failed
         - if given parameter is @c true (the default) also if the
           executed program terminates with an error
    */
    Exec& execute(bool=true) throw(mrw::exception);
    
    /** @brief Executes the command if not done, streams @c stdout into a string

        If the command has not yet been executed successfully, it is
        first executed, then the @c stdout output of the called
        program is appended to the string.

        @throw ExecutionFailedExc in case of any failure or if the
        executed program does not return a zero exit status.
    */
    Exec& operator>>(std::string&) throw(mrw::exception);
    
    /** @brief Executes the command if not done, returns @c stdout as string

        If the command has not yet been executed successfully, it is
        first executed, then the @c stdout output of the called
        program is returned.

        @return @c stdout of the called program

        @throw ExecutionFailedExc in case of any failure or if the
        executed program does not return a zero exit status.
    */
    operator std::string&() throw(mrw::exception);

    /** @return
         - @c true if the last execution was successful
         - @c false if the last execution failed or the command was
           never executed
    */
    operator bool() throw(std::bad_exception);

    /** @brief Executes the command if not done, returns @c stdout as string

        If the command has not yet been executed successfully, it is
        first executed, then the @c stdout output of the called
        program is returned.

        @return @c stdout of the called program

        @throw ExecutionFailedExc in case of any failure or if the
        executed program does not return a zero exit status.
    */
    std::string& result() throw(mrw::exception);

    /** @brief Executes the command if not done, returns @c stderr as string

        If the command has not yet been executed successfully, it is
        first executed, then the @c stderr error output of the called
        program is returned.

        @return @c stderr of the called program

        @throw ExecutionFailedExc in case of any failure or if the
        executed program does not return a zero exit status.
    */
    std::string& error() throw(mrw::exception);
    
    /** @return
         - @c true if the last execution was successful
         - @c false if the last execution failed or the command was
           never executed
    */
    bool success() throw(std::bad_exception);
    
  private:
    Exec(); // no default constructor
    mrw::Cmd* _cmd;
    std::string _res, _err;
    bool _success;
  };

  /** @brief A system command to be executed

      This class is used in conjunction with mrw::Exec. It mus be
      initialized with the command name, then the command parameters
      are appended either with commas, or by streaming them into the
      command, whatever you like.

      You can stream the data into the class:

      @code
      mrw::Cmd ls("/bin/ls"); // the command to execute is: /bin/ls
      ls<<"-l"<<"/tmp"; // the command is now: /bin/ls -l /tmp
      @endcode

      Or you can setup your command with commas:

      @code
      mrw::Cmd ls = (mrw::Cmd(/bin/ls), "-l", "/tmp");
      @endcode
  */
  class Cmd {
  public:
    /** @brief Create a command given the name of the executable
        @param std::string the name of the program to execute (no parameter)
        @note There is no default constructor. */
    Cmd(const std::string&) throw(std::bad_exception);

    /** @brief Append a parameter to a command
        @param std::string a parameter&nbsp;/ commandline argument
        to append to the command */
    Cmd& operator,(const std::string&) throw(std::bad_exception);
    
    /** @brief Append a parameter to a command
        @param std::string a parameter&nbsp;/ commandline argument
        to append to the command */
    Cmd& operator<<(const std::string&) throw(std::bad_exception);

    /** @return the command including parameter */
    operator std::string() const throw(std::bad_exception);

    /** @return a mrw::Exec that's constructed with this class */
    operator Exec() const throw(std::bad_exception);

    /** @brief Create a mrw::Exec and execute the command

        Creates a mrw::Exec, executes the command, passes the flag to
        mrw::Exec::execute() and returns the created mrw::Exec. The
        result of the execution can be retrieved through the returned
        mrw::Exec object: The methods mrw::Exec::success(),
        mrw::Exec::result() and mrw::Exec::error() provide the
        necessary information.
        
        @param bool
         - @c true throw an exception if return status is not zero
         - @c false throw only an exception in case of a fatal error

        @return the mrw::Exec that has executed the command
         
        @throw ExecutionFailedExc is thrown if
         - fork fails
         - creation or setup of pipes failed
         - if given parameter is @c true (the default) also if the
           executed program terminates with an error
    */
    Exec execute(bool=true) const throw(mrw::exception);
    
  private:
    friend class Exec; // is allowed to call path() and args()
    Cmd(); // no default constructor
    const char* path() const throw(std::bad_exception);
    char** args() const throw(std::bad_exception);
    typedef std::list<std::string> ArgList;
    ArgList _cmd;
  };
  //@}
}
#endif