pstream.h

// PStreams - POSIX Process I/O for C++

//        Copyright (C) 2001 - 2024 Jonathan Wakely
// Distributed under the Boost Software License, Version 1.0.
//    (See accompanying file LICENSE_1_0.txt or copy at
//          http://www.boost.org/LICENSE_1_0.txt)
//
// SPDX-License-Identifier: BSL-1.0

/**
 * @file pstream.h
 * @brief Declares all PStreams classes.
 * @author Jonathan Wakely
 *
 * Defines classes redi::ipstream, redi::opstream, redi::pstream
 * and redi::rpstream.
 */

#ifndef REDI_PSTREAM_H_SEEN
#define REDI_PSTREAM_H_SEEN

#include <ios>
#include <streambuf>
#include <istream>
#include <ostream>
#include <string>
#include <vector>
#include <algorithm>    // for min()
#include <cerrno>       // for errno
#include <cstddef>      // for size_t, NULL
#include <cstdlib>      // for exit()
#include <sys/types.h>  // for pid_t
#include <sys/wait.h>   // for waitpid()
#include <sys/ioctl.h>  // for ioctl() and FIONREAD
#if defined(__sun)
# include <sys/filio.h> // for FIONREAD on Solaris 2.5
#endif
#include <unistd.h>     // for pipe() fork() exec() and filedes functions
#include <signal.h>     // for kill()
#include <fcntl.h>      // for fcntl()
#if REDI_EVISCERATE_PSTREAMS
# include <stdio.h>     // for FILE, fdopen()
#endif


/// The library version.
#define PSTREAMS_VERSION 0x0104   // 1.0.4

/**
 *  @namespace redi
 *  @brief  All PStreams classes are declared in namespace redi.
 *
 *  Like the standard iostreams, PStreams is a set of class templates,
 *  taking a character type and traits type. As with the standard streams
 *  they are most likely to be used with @c char and the default
 *  traits type, so typedefs for this most common case are provided.
 *
 *  The @c pstream_common class template is not intended to be used directly,
 *  it is used internally to provide the common functionality for the
 *  other stream classes.
 */
namespace redi
{
  /// Common base class providing constants and typenames.
  struct pstreams
  {
    /// Type used to specify how to connect to the process.
    typedef std::ios_base::openmode           pmode;

    /// Type used to hold the arguments for a command.
    typedef std::vector<std::string>          argv_type;

    /// Type used for file descriptors.
    typedef int                               fd_type;

    static const pmode pstdin  = std::ios_base::out; ///< Write to stdin
    static const pmode pstdout = std::ios_base::in;  ///< Read from stdout
    static const pmode pstderr = std::ios_base::app; ///< Read from stderr

    /// Create a new process group for the child process.
    static const pmode newpg   = std::ios_base::trunc;

  protected:
    enum {
      bufsz = 32, ///< Size of pstreambuf buffers.
      pbsz  = 2   ///< Number of putback characters kept.
    };

#if __cplusplus >= 201103L
    template<typename T>
      using stringable = decltype((void)std::string(std::declval<const T&>()));
#endif
  };

  /// Class template for stream buffer.
  template <typename CharT, typename Traits = std::char_traits<CharT> >
    class basic_pstreambuf
    : public std::basic_streambuf<CharT, Traits>
    , public pstreams
    {
    public:
      // Type definitions for dependent types
      typedef CharT                             char_type;
      typedef Traits                            traits_type;
      typedef typename traits_type::int_type    int_type;
      typedef typename traits_type::off_type    off_type;
      typedef typename traits_type::pos_type    pos_type;
      /** @deprecated use pstreams::fd_type instead. */
      typedef fd_type                           fd_t;

      /// Default constructor.
      basic_pstreambuf();

      /// Constructor that initialises the buffer with @a cmd.
      basic_pstreambuf(const std::string& cmd, pmode mode);

      /// Constructor that initialises the buffer with @a file and @a argv.
      basic_pstreambuf( const std::string& file,
                        const argv_type& argv,
                        pmode mode );

#if __cplusplus >= 201103L
      basic_pstreambuf(basic_pstreambuf&&) noexcept;
      basic_pstreambuf& operator=(basic_pstreambuf&&) noexcept;
      void swap(basic_pstreambuf&) noexcept;
#endif

      /// Destructor.
      ~basic_pstreambuf();

      /// Initialise the stream buffer with @a cmd.
      basic_pstreambuf*
      open(const std::string& cmd, pmode mode);

      /// Initialise the stream buffer with @a file and @a argv.
      basic_pstreambuf*
      open(const std::string& file, const argv_type& argv, pmode mode);

      /// Close the stream buffer and wait for the process to exit.
      basic_pstreambuf*
      close();

      /// Send a signal to the process.
      basic_pstreambuf*
      kill(int signal = SIGTERM);

      /// Send a signal to the process' process group.
      basic_pstreambuf*
      killpg(int signal = SIGTERM);

      /// Close the pipe connected to the process' stdin.
      void
      peof();

      /// Change active input source.
      bool
      read_err(bool readerr = true);

      /// Report whether the stream buffer has been initialised.
      bool
      is_open() const;

      /// Report whether the process has exited.
      bool
      exited();

#if REDI_EVISCERATE_PSTREAMS
      /// Obtain FILE pointers for each of the process' standard streams.
      std::size_t
      fopen(FILE*& in, FILE*& out, FILE*& err);
#endif

      /// Return the exit status of the process.
      int
      status() const;

      /// Return the error number (errno) for the most recent failed operation.
      int
      error() const;

    protected:
      /// Transfer characters to the pipe when character buffer overflows.
      int_type
      overflow(int_type c);

      /// Transfer characters from the pipe when the character buffer is empty.
      int_type
      underflow();

      /// Make a character available to be returned by the next extraction.
      int_type
      pbackfail(int_type c = traits_type::eof());

      /// Write any buffered characters to the stream.
      int
      sync();

      /// Insert multiple characters into the pipe.
      std::streamsize
      xsputn(const char_type* s, std::streamsize n);

      /// Insert a sequence of characters into the pipe.
      std::streamsize
      write(const char_type* s, std::streamsize n);

      /// Extract a sequence of characters from the pipe.
      std::streamsize
      read(char_type* s, std::streamsize n);

      /// Report how many characters can be read from active input without blocking.
      std::streamsize
      showmanyc();

    protected:
      /// Enumerated type to indicate whether stdout or stderr is to be read.
      enum buf_read_src { rsrc_out = 0, rsrc_err = 1 };

      /// Initialise pipes and fork process.
      pid_t
      fork(pmode mode);

      /// Wait for the child process to exit.
      int
      wait(bool nohang = false);

      /// Return the file descriptor for the output pipe.
      fd_type&
      wpipe();

      /// Return the file descriptor for the active input pipe.
      fd_type&
      rpipe();

      /// Return the file descriptor for the specified input pipe.
      fd_type&
      rpipe(buf_read_src which);

      void
      create_buffers(pmode mode);

      void
      destroy_buffers(pmode mode);

      /// Writes buffered characters to the process' stdin pipe.
      bool
      empty_buffer();

      bool
      fill_buffer(bool non_blocking = false);

      /// Return the active input buffer.
      char_type*
      rbuffer();

      buf_read_src
      switch_read_buffer(buf_read_src);

    private:
#if __cplusplus >= 201103L
      using basic_streambuf = std::basic_streambuf<char_type, traits_type>;
#else
      basic_pstreambuf(const basic_pstreambuf&);
      basic_pstreambuf& operator=(const basic_pstreambuf&);
#endif

      void
      init_rbuffers();

      pid_t         ppid_;        // pid of process
      fd_type       wpipe_;       // pipe used to write to process' stdin
      fd_type       rpipe_[2];    // two pipes to read from, stdout and stderr
      char_type*    wbuffer_;
      char_type*    rbuffer_[2];
      char_type*    rbufstate_[3];
      /// Index into rpipe_[] to indicate active source for read operations.
      buf_read_src  rsrc_;
      int           status_;      // hold exit status of child process
      int           error_;       // hold errno if fork() or exec() fails
    };

  /// Class template for common base class.
  template <typename CharT, typename Traits = std::char_traits<CharT> >
    class pstream_common
    : virtual public std::basic_ios<CharT, Traits>
    , virtual public pstreams
    {
    protected:
      typedef basic_pstreambuf<CharT, Traits>       streambuf_type;
      typedef std::basic_ios<CharT, Traits>         ios_type;

      typedef pstreams::pmode                       pmode;
      typedef pstreams::argv_type                   argv_type;

      /// Default constructor.
      pstream_common();

      /// Constructor that initialises the stream by starting a process.
      pstream_common(const std::string& cmd, pmode mode);

      /// Constructor that initialises the stream by starting a process.
      pstream_common(const std::string& file, const argv_type& argv, pmode mode);

      /// Pure virtual destructor.
      virtual
      ~pstream_common() = 0;

#if __cplusplus >= 201103L
      pstream_common(pstream_common&& rhs) noexcept
      : command_(std::move(rhs.command_))
      , buf_(std::move(rhs.buf_))
      {
        /* derived class is responsible for ios_type::move(rhs) happening */
      }

      pstream_common&
      operator=(pstream_common&& rhs) noexcept
      {
        command_ = std::move(rhs.command_);
        buf_ = std::move(rhs.buf_);
        return *this;
      }

      void
      swap(pstream_common& rhs) noexcept
      {
        /* derived class is responsible for ios_type::swap(rhs) happening */
        command_.swap(rhs.command_);
        buf_.swap(rhs.buf_);
      }
#endif // C++11

      /// Start a process.
      void
      do_open(const std::string& cmd, pmode mode);

      /// Start a process.
      void
      do_open(const std::string& file, const argv_type& argv, pmode mode);

    public:
      /// Close the pipe, returning the program's exit status, as
      /// pclose(3) does.
      int
      close();

      /// Report whether the stream's buffer has been initialised.
      bool
      is_open() const;

      /// Return the command used to initialise the stream.
      const std::string&
      command() const;

      /// Return a pointer to the stream buffer.
      streambuf_type*
      rdbuf() const;

#if REDI_EVISCERATE_PSTREAMS
      /// Obtain FILE pointers for each of the process' standard streams.
      std::size_t
      fopen(FILE*& in, FILE*& out, FILE*& err);
#endif

    protected:
      std::string       command_; ///< The command used to start the process.
      streambuf_type    buf_;     ///< The stream buffer.
    };


  /**
   * @class basic_ipstream
   * @brief Class template for Input PStreams.
   *
   * Reading from an ipstream reads the command's standard output and/or
   * standard error (depending on how the ipstream is opened)
   * and the command's standard input is the same as that of the process
   * that created the object, unless altered by the command itself.
   */

  template <typename CharT, typename Traits = std::char_traits<CharT> >
    class basic_ipstream
    : public std::basic_istream<CharT, Traits>
    , public pstream_common<CharT, Traits>
    , virtual public pstreams
    {
      typedef std::basic_istream<CharT, Traits>     istream_type;
      typedef pstream_common<CharT, Traits>         pbase_type;

      using pbase_type::buf_;  // declare name in this scope

      // Ensure a basic_ipstream will read from at least one pipe
      pmode readable(pmode mode)
      {
        if (!(mode & (pstdout|pstderr)))
          mode |= pstdout;
        return mode;
      }

    public:
      /// Type used to specify how to connect to the process.
      typedef typename pbase_type::pmode            pmode;

      /// Type used to hold the arguments for a command.
      typedef typename pbase_type::argv_type        argv_type;

      /// Default constructor, creates an uninitialised stream.
      basic_ipstream()
      : istream_type(NULL), pbase_type()
      { }

      /**
       * @brief Constructor that initialises the stream by starting a process.
       *
       * Initialises the stream buffer by calling do_open() with the supplied
       * arguments.
       *
       * @param cmd   a string containing a shell command.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, pmode)
       */
      explicit
      basic_ipstream(const std::string& cmd, pmode mode = pstdout)
      : istream_type(NULL), pbase_type(cmd, readable(mode))
      { }

      /**
       * @brief Constructor that initialises the stream by starting a process.
       *
       * Initialises the stream buffer by calling do_open() with the supplied
       * arguments.
       *
       * @param file  a string containing the pathname of a program to execute.
       * @param argv  a vector of argument strings passed to the new program.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      basic_ipstream( const std::string& file,
                      const argv_type& argv,
                      pmode mode = pstdout )
      : istream_type(NULL), pbase_type(file, argv, readable(mode))
      { }

      /**
       * @brief Constructor that initialises the stream by starting a process.
       *
       * Initialises the stream buffer by calling
       * @c do_open(argv[0],argv,mode|pstdout)
       *
       * @param argv  a vector of argument strings passed to the new program.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      explicit
      basic_ipstream(const argv_type& argv, pmode mode = pstdout)
      : istream_type(NULL), pbase_type(argv.at(0), argv, readable(mode))
      { }

#if __cplusplus >= 201103L
      template<typename T, typename = stringable<T>>
        explicit
        basic_ipstream(std::initializer_list<T> args, pmode mode = pstdout)
        : basic_ipstream(argv_type(args.begin(), args.end()), mode)
        { }

      basic_ipstream(basic_ipstream&& rhs)
      : istream_type(std::move(rhs))
      , pbase_type(std::move(rhs))
      { istream_type::set_rdbuf(std::addressof(pbase_type::buf_)); }

      basic_ipstream&
      operator=(basic_ipstream&& rhs)
      {
        istream_type::operator=(std::move(rhs));
        pbase_type::operator=(std::move(rhs));
        return *this;
      }

      void
      swap(basic_ipstream& rhs)
      {
        istream_type::swap(rhs);
        pbase_type::swap(rhs);
      }
#endif // C++11

      /**
       * @brief Destructor.
       *
       * Closes the stream and waits for the child to exit.
       */
      ~basic_ipstream()
      { }

      /**
       * @brief Start a process.
       *
       * Calls do_open( @a cmd , @a mode|pstdout ).
       *
       * @param cmd   a string containing a shell command.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, pmode)
       */
      void
      open(const std::string& cmd, pmode mode = pstdout)
      {
        this->do_open(cmd, readable(mode));
      }

      /**
       * @brief Start a process.
       *
       * Calls do_open( @a file , @a argv , @a mode|pstdout ).
       *
       * @param file  a string containing the pathname of a program to execute.
       * @param argv  a vector of argument strings passed to the new program.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      void
      open( const std::string& file,
            const argv_type& argv,
            pmode mode = pstdout )
      {
        this->do_open(file, argv, readable(mode));
      }

      /**
       * @brief Set streambuf to read from process' @c stdout.
       * @return  @c *this
       */
      basic_ipstream&
      out()
      {
        this->buf_.read_err(false);
        return *this;
      }

      /**
       * @brief Set streambuf to read from process' @c stderr.
       * @return  @c *this
       */
      basic_ipstream&
      err()
      {
        this->buf_.read_err(true);
        return *this;
      }
    };


  /**
   * @class basic_opstream
   * @brief Class template for Output PStreams.
   *
   * Writing to an open opstream writes to the standard input of the command;
   * the command's standard output is the same as that of the process that
   * created the pstream object, unless altered by the command itself.
   */

  template <typename CharT, typename Traits = std::char_traits<CharT> >
    class basic_opstream
    : public std::basic_ostream<CharT, Traits>
    , public pstream_common<CharT, Traits>
    , virtual public pstreams
    {
      typedef std::basic_ostream<CharT, Traits>     ostream_type;
      typedef pstream_common<CharT, Traits>         pbase_type;

      using pbase_type::buf_;  // declare name in this scope

    public:
      /// Type used to specify how to connect to the process.
      typedef typename pbase_type::pmode            pmode;

      /// Type used to hold the arguments for a command.
      typedef typename pbase_type::argv_type        argv_type;

      /// Default constructor, creates an uninitialised stream.
      basic_opstream()
      : ostream_type(NULL), pbase_type()
      { }

      /**
       * @brief Constructor that initialises the stream by starting a process.
       *
       * Initialises the stream buffer by calling do_open() with the supplied
       * arguments.
       *
       * @param cmd   a string containing a shell command.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, pmode)
       */
      explicit
      basic_opstream(const std::string& cmd, pmode mode = pstdin)
      : ostream_type(NULL), pbase_type(cmd, mode|pstdin)
      { }

      /**
       * @brief Constructor that initialises the stream by starting a process.
       *
       * Initialises the stream buffer by calling do_open() with the supplied
       * arguments.
       *
       * @param file  a string containing the pathname of a program to execute.
       * @param argv  a vector of argument strings passed to the new program.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      basic_opstream( const std::string& file,
                      const argv_type& argv,
                      pmode mode = pstdin )
      : ostream_type(NULL), pbase_type(file, argv, mode|pstdin)
      { }

      /**
       * @brief Constructor that initialises the stream by starting a process.
       *
       * Initialises the stream buffer by calling
       * @c do_open(argv[0],argv,mode|pstdin)
       *
       * @param argv  a vector of argument strings passed to the new program.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      explicit
      basic_opstream(const argv_type& argv, pmode mode = pstdin)
      : ostream_type(NULL), pbase_type(argv.at(0), argv, mode|pstdin)
      { }

#if __cplusplus >= 201103L
      /**
       * @brief Constructor that initialises the stream by starting a process.
       *
       * @param args  a list of argument strings passed to the new program.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      template<typename T, typename = stringable<T>>
        explicit
        basic_opstream(std::initializer_list<T> args, pmode mode = pstdin)
        : basic_opstream(argv_type(args.begin(), args.end()), mode)
        { }

      basic_opstream(basic_opstream&& rhs)
      : ostream_type(std::move(rhs))
      , pbase_type(std::move(rhs))
      { ostream_type::set_rdbuf(std::addressof(pbase_type::buf_)); }

      basic_opstream&
      operator=(basic_opstream&& rhs)
      {
        ostream_type::operator=(std::move(rhs));
        pbase_type::operator=(std::move(rhs));
        return *this;
      }

      void
      swap(basic_opstream& rhs)
      {
        ostream_type::swap(rhs);
        pbase_type::swap(rhs);
      }
#endif // C++11

      /**
       * @brief Destructor
       *
       * Closes the stream and waits for the child to exit.
       */
      ~basic_opstream() { }

      /**
       * @brief Start a process.
       *
       * Calls do_open( @a cmd , @a mode|pstdin ).
       *
       * @param cmd   a string containing a shell command.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, pmode)
       */
      void
      open(const std::string& cmd, pmode mode = pstdin)
      {
        this->do_open(cmd, mode|pstdin);
      }

      /**
       * @brief Start a process.
       *
       * Calls do_open( @a file , @a argv , @a mode|pstdin ).
       *
       * @param file  a string containing the pathname of a program to execute.
       * @param argv  a vector of argument strings passed to the new program.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      void
      open( const std::string& file,
            const argv_type& argv,
            pmode mode = pstdin)
      {
        this->do_open(file, argv, mode|pstdin);
      }
    };


  /**
   * @class basic_pstream
   * @brief Class template for Bidirectional PStreams.
   *
   * Writing to a pstream opened with @c pmode @c pstdin writes to the
   * standard input of the command.
   * Reading from a pstream opened with @c pmode @c pstdout and/or @c pstderr
   * reads the command's standard output and/or standard error.
   * Any of the process' @c stdin, @c stdout or @c stderr that is not
   * connected to the pstream (as specified by the @c pmode)
   * will be the same as the process that created the pstream object,
   * unless altered by the command itself.
   */
  template <typename CharT, typename Traits = std::char_traits<CharT> >
    class basic_pstream
    : public std::basic_iostream<CharT, Traits>
    , public pstream_common<CharT, Traits>
    , virtual public pstreams
    {
      typedef std::basic_iostream<CharT, Traits>    iostream_type;
      typedef pstream_common<CharT, Traits>         pbase_type;

      using pbase_type::buf_;  // declare name in this scope

    public:
      /// Type used to specify how to connect to the process.
      typedef typename pbase_type::pmode            pmode;

      /// Type used to hold the arguments for a command.
      typedef typename pbase_type::argv_type        argv_type;

      /// Default constructor, creates an uninitialised stream.
      basic_pstream()
      : iostream_type(NULL), pbase_type()
      { }

      /**
       * @brief Constructor that initialises the stream by starting a process.
       *
       * Initialises the stream buffer by calling do_open() with the supplied
       * arguments.
       *
       * @param cmd   a string containing a shell command.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, pmode)
       */
      explicit
      basic_pstream(const std::string& cmd, pmode mode = pstdout|pstdin)
      : iostream_type(NULL), pbase_type(cmd, mode)
      { }

      /**
       * @brief Constructor that initialises the stream by starting a process.
       *
       * Initialises the stream buffer by calling do_open() with the supplied
       * arguments.
       *
       * @param file  a string containing the pathname of a program to execute.
       * @param argv  a vector of argument strings passed to the new program.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      basic_pstream( const std::string& file,
                     const argv_type& argv,
                     pmode mode = pstdout|pstdin )
      : iostream_type(NULL), pbase_type(file, argv, mode)
      { }

      /**
       * @brief Constructor that initialises the stream by starting a process.
       *
       * Initialises the stream buffer by calling
       * @c do_open(argv[0],argv,mode)
       *
       * @param argv  a vector of argument strings passed to the new program.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      explicit
      basic_pstream(const argv_type& argv, pmode mode = pstdout|pstdin)
      : iostream_type(NULL), pbase_type(argv.at(0), argv, mode)
      { }

#if __cplusplus >= 201103L
      /**
       * @brief Constructor that initialises the stream by starting a process.
       *
       * @param l     a list of argument strings passed to the new program.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      template<typename T, typename = stringable<T>>
        explicit
        basic_pstream(std::initializer_list<T> l, pmode mode = pstdout|pstdin)
        : basic_pstream(argv_type(l.begin(), l.end()), mode)
        { }

      basic_pstream(basic_pstream&& rhs)
      : iostream_type(std::move(rhs))
      , pbase_type(std::move(rhs))
      { iostream_type::set_rdbuf(std::addressof(pbase_type::buf_)); }

      basic_pstream&
      operator=(basic_pstream&& rhs)
      {
        iostream_type::operator=(std::move(rhs));
        pbase_type::operator=(std::move(rhs));
        return *this;
      }

      void
      swap(basic_pstream& rhs)
      {
        iostream_type::swap(rhs);
        pbase_type::swap(rhs);
      }
#endif // C++11

      /**
       * @brief Destructor
       *
       * Closes the stream and waits for the child to exit.
       */
      ~basic_pstream() { }

      /**
       * @brief Start a process.
       *
       * Calls do_open( @a cnd , @a mode ).
       *
       * @param cmd   a string containing a shell command.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, pmode)
       */
      void
      open(const std::string& cmd, pmode mode = pstdout|pstdin)
      {
        this->do_open(cmd, mode);
      }

      /**
       * @brief Start a process.
       *
       * Calls do_open( @a file , @a argv , @a mode ).
       *
       * @param file  a string containing the pathname of a program to execute.
       * @param argv  a vector of argument strings passed to the new program.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      void
      open( const std::string& file,
            const argv_type& argv,
            pmode mode = pstdout|pstdin )
      {
        this->do_open(file, argv, mode);
      }

      /**
       * @brief Set streambuf to read from process' @c stdout.
       * @return  @c *this
       */
      basic_pstream&
      out()
      {
        this->buf_.read_err(false);
        return *this;
      }

      /**
       * @brief Set streambuf to read from process' @c stderr.
       * @return  @c *this
       */
      basic_pstream&
      err()
      {
        this->buf_.read_err(true);
        return *this;
      }
    };


  /**
   * @class basic_rpstream
   * @brief Class template for Restricted PStreams.
   *
   * Writing to an rpstream opened with @c pmode @c pstdin writes to the
   * standard input of the command.
   * It is not possible to read directly from an rpstream object, to use
   * an rpstream as in istream you must call either basic_rpstream::out()
   * or basic_rpstream::err(). This is to prevent accidental reads from
   * the wrong input source. If the rpstream was not opened with @c pmode
   * @c pstderr then the class cannot read the process' @c stderr, and
   * basic_rpstream::err() will return an istream that reads from the
   * process' @c stdout, and vice versa.
   * Reading from an rpstream opened with @c pmode @c pstdout and/or
   * @c pstderr reads the command's standard output and/or standard error.
   * Any of the process' @c stdin, @c stdout or @c stderr that is not
   * connected to the pstream (as specified by the @c pmode)
   * will be the same as the process that created the pstream object,
   * unless altered by the command itself.
   */

  template <typename CharT, typename Traits = std::char_traits<CharT> >
    class basic_rpstream
    : public std::basic_ostream<CharT, Traits>
    , private std::basic_istream<CharT, Traits>
    , private pstream_common<CharT, Traits>
    , virtual public pstreams
    {
      typedef std::basic_ostream<CharT, Traits>     ostream_type;
      typedef std::basic_istream<CharT, Traits>     istream_type;
      typedef pstream_common<CharT, Traits>         pbase_type;

      using pbase_type::buf_;  // declare name in this scope

    public:
      /// Type used to specify how to connect to the process.
      typedef typename pbase_type::pmode            pmode;

      /// Type used to hold the arguments for a command.
      typedef typename pbase_type::argv_type        argv_type;

      /// Default constructor, creates an uninitialised stream.
      basic_rpstream()
      : ostream_type(NULL), istream_type(NULL), pbase_type()
      { }

      /**
       * @brief  Constructor that initialises the stream by starting a process.
       *
       * Initialises the stream buffer by calling do_open() with the supplied
       * arguments.
       *
       * @param cmd   a string containing a shell command.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, pmode)
       */
      explicit
      basic_rpstream(const std::string& cmd, pmode mode = pstdout|pstdin)
      : ostream_type(NULL) , istream_type(NULL) , pbase_type(cmd, mode)
      { }

      /**
       * @brief  Constructor that initialises the stream by starting a process.
       *
       * Initialises the stream buffer by calling do_open() with the supplied
       * arguments.
       *
       * @param file a string containing the pathname of a program to execute.
       * @param argv a vector of argument strings passed to the new program.
       * @param mode the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      basic_rpstream( const std::string& file,
                      const argv_type& argv,
                      pmode mode = pstdout|pstdin )
      : ostream_type(NULL), istream_type(NULL), pbase_type(file, argv, mode)
      { }

      /**
       * @brief Constructor that initialises the stream by starting a process.
       *
       * Initialises the stream buffer by calling
       * @c do_open(argv[0],argv,mode)
       *
       * @param argv  a vector of argument strings passed to the new program.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      explicit
      basic_rpstream(const argv_type& argv, pmode mode = pstdout|pstdin)
      : ostream_type(NULL), istream_type(NULL)
      , pbase_type(argv.at(0), argv, mode)
      { }

#if __cplusplus >= 201103L
      /**
       * @brief Constructor that initialises the stream by starting a process.
       *
       * @param l     a list of argument strings passed to the new program.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      template<typename T, typename = stringable<T>>
        explicit
        basic_rpstream(std::initializer_list<T> l, pmode mode = pstdout|pstdin)
        : basic_rpstream(argv_type(l.begin(), l.end()), mode)
        { }

      basic_rpstream(basic_rpstream&& rhs)
      : ostream_type(NULL), istream_type(std::move(rhs))
      , pbase_type(std::move(rhs))
      { istream_type::set_rdbuf(std::addressof(pbase_type::buf_)); }

      basic_rpstream&
      operator=(basic_rpstream&& rhs)
      {
        swap(rhs);
        return *this;
      }

      void
      swap(basic_rpstream& rhs)
      {
        istream_type::swap(rhs);
        pbase_type::swap(rhs);
      }
#endif // C++11

      /// Destructor
      ~basic_rpstream() { }

      /**
       * @brief  Start a process.
       *
       * Calls do_open( @a cmd , @a mode ).
       *
       * @param cmd   a string containing a shell command.
       * @param mode  the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, pmode)
       */
      void
      open(const std::string& cmd, pmode mode = pstdout|pstdin)
      {
        this->do_open(cmd, mode);
      }

      /**
       * @brief  Start a process.
       *
       * Calls do_open( @a file , @a argv , @a mode ).
       *
       * @param file a string containing the pathname of a program to execute.
       * @param argv a vector of argument strings passed to the new program.
       * @param mode the I/O mode to use when opening the pipe.
       * @see   do_open(const std::string&, const argv_type&, pmode)
       */
      void
      open( const std::string& file,
            const argv_type& argv,
            pmode mode = pstdout|pstdin )
      {
        this->do_open(file, argv, mode);
      }

      /**
       * @brief  Obtain a reference to the istream that reads
       *         the process' @c stdout.
       * @return @c *this
       */
      istream_type&
      out()
      {
        this->buf_.read_err(false);
        return *this;
      }

      /**
       * @brief  Obtain a reference to the istream that reads
       *         the process' @c stderr.
       * @return @c *this
       */
      istream_type&
      err()
      {
        this->buf_.read_err(true);
        return *this;
      }
    };


  /// Type definition for common template specialisation.
  typedef basic_pstreambuf<char> pstreambuf;
  /// Type definition for common template specialisation.
  typedef basic_ipstream<char> ipstream;
  /// Type definition for common template specialisation.
  typedef basic_opstream<char> opstream;
  /// Type definition for common template specialisation.
  typedef basic_pstream<char> pstream;
  /// Type definition for common template specialisation.
  typedef basic_rpstream<char> rpstream;


  /**
   * When inserted into an output pstream the manipulator calls
   * basic_pstreambuf<C,T>::peof() to close the output pipe,
   * causing the child process to receive the end-of-file indicator
   * on subsequent reads from its @c stdin stream.
   *
   * @brief   Manipulator to close the pipe connected to the process' stdin.
   * @param   s  An output PStream class.
   * @return  The stream object the manipulator was invoked on.
   * @see     basic_pstreambuf<C,T>::peof()
   * @relates basic_opstream basic_pstream basic_rpstream
   */
  template <typename C, typename T>
    inline std::basic_ostream<C,T>&
    peof(std::basic_ostream<C,T>& s)
    {
      typedef basic_pstreambuf<C,T> pstreambuf_type;
      if (pstreambuf_type* p = dynamic_cast<pstreambuf_type*>(s.rdbuf()))
        p->peof();
      return s;
    }


  /*
   * member definitions for pstreambuf
   */


  /**
   * @class basic_pstreambuf
   * Provides underlying streambuf functionality for the PStreams classes.
   */

  /** Creates an uninitialised stream buffer. */
  template <typename C, typename T>
    inline
    basic_pstreambuf<C,T>::basic_pstreambuf()
    : ppid_(-1)   // initialise to -1 to indicate no process run yet.
    , wpipe_(-1)
    , wbuffer_()
    , rbuffer_()
    , rbufstate_()
    , rsrc_(rsrc_out)
    , status_(-1)
    , error_(0)
    {
      rpipe_[rsrc_out] = rpipe_[rsrc_err] = -1;
    }

  /**
   * Initialises the stream buffer by calling open() with the supplied
   * arguments.
   *
   * @param cmd   a string containing a shell command.
   * @param mode  the I/O mode to use when opening the pipe.
   * @see   open()
   */
  template <typename C, typename T>
    inline
    basic_pstreambuf<C,T>::basic_pstreambuf(const std::string& cmd, pmode mode)
    : ppid_(-1)   // initialise to -1 to indicate no process run yet.
    , wpipe_(-1)
    , wbuffer_()
    , rbuffer_()
    , rbufstate_()
    , rsrc_(rsrc_out)
    , status_(-1)
    , error_(0)
    {
      rpipe_[rsrc_out] = rpipe_[rsrc_err] = -1;
      open(cmd, mode);
    }

  /**
   * Initialises the stream buffer by calling open() with the supplied
   * arguments.
   *
   * @param file  a string containing the name of a program to execute.
   * @param argv  a vector of argument strings passsed to the new program.
   * @param mode  the I/O mode to use when opening the pipe.
   * @see   open()
   */
  template <typename C, typename T>
    inline
    basic_pstreambuf<C,T>::basic_pstreambuf( const std::string& file,
                                             const argv_type& argv,
                                             pmode mode )
    : ppid_(-1)   // initialise to -1 to indicate no process run yet.
    , wpipe_(-1)
    , wbuffer_()
    , rbuffer_()
    , rbufstate_()
    , rsrc_(rsrc_out)
    , status_(-1)
    , error_(0)
    {
      rpipe_[rsrc_out] = rpipe_[rsrc_err] = -1;
      open(file, argv, mode);
    }

  /**
   * Closes the stream by calling close().
   * @see close()
   */
  template <typename C, typename T>
    inline
    basic_pstreambuf<C,T>::~basic_pstreambuf()
    {
      close();
    }

#if __cplusplus >= 201103L
  /**
   * Move constructor.
   */
  template <typename C, typename T>
    inline
    basic_pstreambuf<C,T>::basic_pstreambuf( basic_pstreambuf&& rhs ) noexcept
    : basic_streambuf(static_cast<const basic_streambuf&>(rhs))
    , ppid_(rhs.ppid_)
    , wpipe_(rhs.wpipe_)
    , rpipe_{rhs.rpipe_[0], rhs.rpipe_[1]}
    , wbuffer_(rhs.wbuffer_)
    , rbuffer_{rhs.rbuffer_[0], rhs.rbuffer_[1]}
    , rbufstate_{rhs.rbufstate_[0], rhs.rbufstate_[1], rhs.rbufstate_[2]}
    , rsrc_(rhs.rsrc_)
    , status_(rhs.status_)
    , error_(rhs.error_)
    {
      rhs.ppid_ = -1;
      rhs.wpipe_ = -1;
      rhs.rpipe_[0] = rhs.rpipe_[1] = -1;
      rhs.wbuffer_ = nullptr;
      rhs.rbuffer_[0] = rhs.rbuffer_[1] = nullptr;
      rhs.rbufstate_[0] = rhs.rbufstate_[1] = rhs.rbufstate_[2] = nullptr;
      rhs.rsrc_ = rsrc_out;
      rhs.status_ = -1;
      rhs.error_ = 0;
      rhs.setg(nullptr, nullptr, nullptr);
      rhs.setp(nullptr, nullptr);
    }

  template <typename C, typename T>
    inline basic_pstreambuf<C,T>&
    basic_pstreambuf<C,T>::operator=( basic_pstreambuf&& rhs ) noexcept
    {
      close();
      basic_streambuf::operator=(static_cast<const basic_streambuf&>(rhs));
      swap(rhs);
      return *this;
    }

  template <typename C, typename T>
    inline void
    basic_pstreambuf<C,T>::swap( basic_pstreambuf& rhs ) noexcept
    {
      basic_streambuf::swap(static_cast<basic_streambuf&>(rhs));
      std::swap(ppid_, rhs.ppid_);
      std::swap(wpipe_, rhs.wpipe_);
      std::swap(rpipe_, rhs.rpipe_);
      std::swap(wbuffer_, rhs.wbuffer_);
      std::swap(rbuffer_, rhs.rbuffer_);
      std::swap(rbufstate_, rhs.rbufstate_);
      std::swap(rsrc_, rhs.rsrc_);
      std::swap(status_, rhs.status_);
      std::swap(error_, rhs.error_);
    }
#endif // C++11

  /**
   * Starts a new process by passing @a command to the shell (/bin/sh)
   * and opens pipes to the process with the specified @a mode.
   *
   * If @a mode contains @c pstdout the initial read source will be
   * the child process' stdout, otherwise if @a mode  contains @c pstderr
   * the initial read source will be the child's stderr.
   *
   * Will duplicate the actions of  the  shell  in searching for an
   * executable file if the specified file name does not contain a slash (/)
   * character.
   *
   * @warning
   * There is no way to tell whether the shell command succeeded, this
   * function will always succeed unless resource limits (such as
   * memory usage, or number of processes or open files) are exceeded.
   * This means is_open() will return true even if @a command cannot
   * be executed.
   * Use pstreambuf::open(const std::string&, const argv_type&, pmode)
   * if you need to know whether the command failed to execute.
   *
   * @param   command  a string containing a shell command.
   * @param   mode     a bitwise OR of one or more of @c out, @c in, @c err.
   * @return  NULL if the shell could not be started or the
   *          pipes could not be opened, @c this otherwise.
   * @see     <b>execl</b>(3)
   */
  template <typename C, typename T>
    basic_pstreambuf<C,T>*
    basic_pstreambuf<C,T>::open(const std::string& command, pmode mode)
    {
      const char * shell_path = "/bin/sh";
#if 0
      const std::string argv[] = { "sh", "-c", command };
      return this->open(shell_path, argv_type(argv, argv+3), mode);
#else
      basic_pstreambuf<C,T>* ret = NULL;

      if (!is_open())
      {
        switch(fork(mode))
        {
        case 0 :
          // this is the new process, exec command
          ::execl(shell_path, "sh", "-c", command.c_str(), (char*)NULL);

          // can only reach this point if exec() failed

          // parent can get exit code from waitpid()
          ::_exit(errno);
          // using std::exit() would make static dtors run twice

        case -1 :
          // couldn't fork, error already handled in pstreambuf::fork()
          break;

        default :
          // this is the parent process
          // activate buffers
          create_buffers(mode);
          ret = this;
        }
      }
      return ret;
#endif
    }

  /**
   * @brief  Helper function to close a file descriptor.
   *
   * Inspects @a fd and calls <b>close</b>(3) if it has a non-negative value.
   *
   * @param   fd  a file descriptor.
   * @relates basic_pstreambuf
   */
  inline void
  close_fd(pstreams::fd_type& fd)
  {
    if (fd >= 0 && ::close(fd) == 0)
      fd = -1;
  }

  /**
   * @brief  Helper function to close an array of file descriptors.
   *
   * Calls @c close_fd() on each member of the array.
   * The length of the array is determined automatically by
   * template argument deduction to avoid errors.
   *
   * @param   fds  an array of file descriptors.
   * @relates basic_pstreambuf
   */
  template <int N>
    inline void
    close_fd_array(pstreams::fd_type (&fds)[N])
    {
      for (std::size_t i = 0; i < N; ++i)
        close_fd(fds[i]);
    }

  /**
   * Starts a new process by executing @a file with the arguments in
   * @a argv and opens pipes to the process with the specified @a mode.
   *
   * By convention @c argv[0] should be the file name of the file being
   * executed.
   *
   * If @a mode contains @c pstdout the initial read source will be
   * the child process' stdout, otherwise if @a mode  contains @c pstderr
   * the initial read source will be the child's stderr.
   *
   * Will duplicate the actions of  the  shell  in searching for an
   * executable file if the specified file name does not contain a slash (/)
   * character.
   *
   * Iff @a file is successfully executed then is_open() will return true.
   * Otherwise, pstreambuf::error() can be used to obtain the value of
   * @c errno that was set by <b>execvp</b>(3) in the child process.
   *
   * The exit status of the new process will be returned by
   * pstreambuf::status() after pstreambuf::exited() returns true.
   *
   * @param   file  a string containing the pathname of a program to execute.
   * @param   argv  a vector of argument strings passed to the new program.
   * @param   mode  a bitwise OR of one or more of @c out, @c in and @c err.
   * @return  NULL if a pipe could not be opened or if the program could
   *          not be executed, @c this otherwise.
   * @see     <b>execvp</b>(3)
   */
  template <typename C, typename T>
    basic_pstreambuf<C,T>*
    basic_pstreambuf<C,T>::open( const std::string& file,
                                 const argv_type& argv,
                                 pmode mode )
    {
      basic_pstreambuf<C,T>* ret = NULL;

      if (!is_open())
      {
        // constants for read/write ends of pipe
        enum { RD, WR };

        // open another pipe and set close-on-exec
        fd_type ck_exec[] = { -1, -1 };
        if (-1 == ::pipe(ck_exec)
            || -1 == ::fcntl(ck_exec[RD], F_SETFD, FD_CLOEXEC)
            || -1 == ::fcntl(ck_exec[WR], F_SETFD, FD_CLOEXEC))
        {
          error_ = errno;
          close_fd_array(ck_exec);
        }
        else
        {
          switch(fork(mode))
          {
          case 0 :
            // this is the new process, exec command
            {
              char** arg_v = new char*[argv.size()+1];
              for (std::size_t i = 0; i < argv.size(); ++i)
              {
                const std::string& src = argv[i];
                char*& dest = arg_v[i];
                dest = new char[src.size()+1];
                dest[ src.copy(dest, src.size()) ] = '\0';
              }
              arg_v[argv.size()] = NULL;

              ::execvp(file.c_str(), arg_v);

              // can only reach this point if exec() failed

              // parent can get error code from ck_exec pipe
              error_ = errno;

              while (::write(ck_exec[WR], &error_, sizeof(error_)) == -1
                  && errno == EINTR)
              { }

              ::close(ck_exec[WR]);
              ::close(ck_exec[RD]);

              ::_exit(error_);
              // using std::exit() would make static dtors run twice
            }

          case -1 :
            // couldn't fork, error already handled in pstreambuf::fork()
            close_fd_array(ck_exec);
            break;

          default :
            // this is the parent process

            // check child called exec() successfully
            ::close(ck_exec[WR]);
            switch (::read(ck_exec[RD], &error_, sizeof(error_)))
            {
            case 0:
              // activate buffers
              create_buffers(mode);
              ret = this;
              break;
            case -1:
              error_ = errno;
              break;
            default:
              // error_ contains error code from child
              // call wait() to clean up and set ppid_ to 0
              this->wait();
              break;
            }
            ::close(ck_exec[RD]);
          }
        }
      }
      return ret;
    }

  /**
   * Creates pipes as specified by @a mode and calls @c fork() to create
   * a new process. If the fork is successful the parent process stores
   * the child's PID and the opened pipes and the child process replaces
   * its standard streams with the opened pipes.
   *
   * If an error occurs the error code will be set to one of the possible
   * errors for @c pipe() or @c fork().
   * See your system's documentation for these error codes.
   *
   * @param   mode  an OR of pmodes specifying which of the child's
   *                standard streams to connect to.
   * @return  On success the PID of the child is returned in the parent's
   *          context and zero is returned in the child's context.
   *          On error -1 is returned and the error code is set appropriately.
   */
  template <typename C, typename T>
    pid_t
    basic_pstreambuf<C,T>::fork(pmode mode)
    {
      pid_t pid = -1;

      // Three pairs of file descriptors, for pipes connected to the
      // process' stdin, stdout and stderr
      // (stored in a single array so close_fd_array() can close all at once)
      fd_type fd[] = { -1, -1, -1, -1, -1, -1 };
      fd_type* const pin = fd;
      fd_type* const pout = fd+2;
      fd_type* const perr = fd+4;

      // constants for read/write ends of pipe
      enum { RD, WR };

      // N.B.
      // For the pstreambuf pin is an output stream and
      // pout and perr are input streams.

      if (!error_ && mode&pstdin && ::pipe(pin))
        error_ = errno;

      if (!error_ && mode&pstdout && ::pipe(pout))
        error_ = errno;

      if (!error_ && mode&pstderr && ::pipe(perr))
        error_ = errno;

      if (!error_)
      {
        pid = ::fork();
        switch (pid)
        {
          case 0 :
          {
            // this is the new process

            // for each open pipe close one end and redirect the
            // respective standard stream to the other end

            if (*pin >= 0)
            {
              ::close(pin[WR]);
              ::dup2(pin[RD], STDIN_FILENO);
              ::close(pin[RD]);
            }
            if (*pout >= 0)
            {
              ::close(pout[RD]);
              ::dup2(pout[WR], STDOUT_FILENO);
              ::close(pout[WR]);
            }
            if (*perr >= 0)
            {
              ::close(perr[RD]);
              ::dup2(perr[WR], STDERR_FILENO);
              ::close(perr[WR]);
            }

#ifdef _POSIX_JOB_CONTROL
            if (mode&newpg)
              ::setpgid(0, 0); // Change to a new process group
#endif

            break;
          }
          case -1 :
          {
            // couldn't fork for some reason
            error_ = errno;
            // close any open pipes
            close_fd_array(fd);
            break;
          }
          default :
          {
            // this is the parent process, store process' pid
            ppid_ = pid;

            // store one end of open pipes and close other end
            if (*pin >= 0)
            {
              wpipe_ = pin[WR];
              ::close(pin[RD]);
            }
            if (*pout >= 0)
            {
              rpipe_[rsrc_out] = pout[RD];
              ::close(pout[WR]);
            }
            if (*perr >= 0)
            {
              rpipe_[rsrc_err] = perr[RD];
              ::close(perr[WR]);
            }
          }
        }
      }
      else
      {
        // close any pipes we opened before failure
        close_fd_array(fd);
      }
      return pid;
    }

  /**
   * Closes all pipes and calls wait() to wait for the process to finish.
   * If an error occurs the error code will be set to one of the possible
   * errors for @c waitpid().
   * See your system's documentation for these errors.
   *
   * @return  @c this on successful close or @c NULL if there is no
   *          process to close or if an error occurs.
   */
  template <typename C, typename T>
    basic_pstreambuf<C,T>*
    basic_pstreambuf<C,T>::close()
    {
      const bool running = is_open();

      basic_pstreambuf::sync(); // might call wait() and reap the child process

      // rather than trying to work out whether or not we need to clean up
      // just do it anyway, all cleanup functions are safe to call twice.

      destroy_buffers(pstdin|pstdout|pstderr);

      // close pipes before wait() so child gets EOF/SIGPIPE
      close_fd(wpipe_);
      close_fd_array(rpipe_);

      do
      {
        error_ = 0;
      } while (wait() == -1 && error() == EINTR);

      return running ? this : NULL;
    }

  /**
   *  Used to be called on construction to initialise the arrays for reading.
   *  No longer used.
   */
  template <typename C, typename T>
#if __cplusplus >= 201402L && __has_cpp_attribute(deprecated)
    [[deprecated]]
#elif __GNUC__
    __attribute__((deprecated))
#endif
    inline void
    basic_pstreambuf<C,T>::init_rbuffers()
    {
      rpipe_[rsrc_out] = rpipe_[rsrc_err] = -1;
      rbuffer_[rsrc_out] = rbuffer_[rsrc_err] = NULL;
      rbufstate_[0] = rbufstate_[1] = rbufstate_[2] = NULL;
    }

  template <typename C, typename T>
    void
    basic_pstreambuf<C,T>::create_buffers(pmode mode)
    {
      if (mode & pstdin)
      {
        delete[] wbuffer_;
        wbuffer_ = new char_type[bufsz];
        this->setp(wbuffer_, wbuffer_ + bufsz);
      }
      if (mode & pstdout)
      {
        delete[] rbuffer_[rsrc_out];
        rbuffer_[rsrc_out] = new char_type[bufsz];
        rsrc_ = rsrc_out;
        this->setg(rbuffer_[rsrc_out] + pbsz, rbuffer_[rsrc_out] + pbsz,
            rbuffer_[rsrc_out] + pbsz);
      }
      if (mode & pstderr)
      {
        delete[] rbuffer_[rsrc_err];
        rbuffer_[rsrc_err] = new char_type[bufsz];
        if (!(mode & pstdout))
        {
          rsrc_ = rsrc_err;
          this->setg(rbuffer_[rsrc_err] + pbsz, rbuffer_[rsrc_err] + pbsz,
              rbuffer_[rsrc_err] + pbsz);
        }
      }
    }

  template <typename C, typename T>
    void
    basic_pstreambuf<C,T>::destroy_buffers(pmode mode)
    {
      if (mode & pstdin)
      {
        this->setp(NULL, NULL);
        delete[] wbuffer_;
        wbuffer_ = NULL;
      }
      if (mode & pstdout)
      {
        if (rsrc_ == rsrc_out)
          this->setg(NULL, NULL, NULL);
        delete[] rbuffer_[rsrc_out];
        rbuffer_[rsrc_out] = NULL;
      }
      if (mode & pstderr)
      {
        if (rsrc_ == rsrc_err)
          this->setg(NULL, NULL, NULL);
        delete[] rbuffer_[rsrc_err];
        rbuffer_[rsrc_err] = NULL;
      }
    }

  template <typename C, typename T>
    typename basic_pstreambuf<C,T>::buf_read_src
    basic_pstreambuf<C,T>::switch_read_buffer(buf_read_src src)
    {
      if (rsrc_ != src)
      {
        char_type* tmpbufstate[] = {this->eback(), this->gptr(), this->egptr()};
        this->setg(rbufstate_[0], rbufstate_[1], rbufstate_[2]);
        for (std::size_t i = 0; i < 3; ++i)
          rbufstate_[i] = tmpbufstate[i];
        rsrc_ = src;
      }
      return rsrc_;
    }

  /**
   * Suspends execution and waits for the associated process to exit, or
   * until a signal is delivered whose action is to terminate the current
   * process or to call a signal handling function. If the process has
   * already exited (i.e. it is a "zombie" process) then wait() returns
   * immediately.  Waiting for the child process causes all its system
   * resources to be freed.
   *
   * error() will return EINTR if wait() is interrupted by a signal.
   *
   * @param   nohang  true to return immediately if the process has not exited.
   * @return  1 if the process has exited and wait() has not yet been called.
   *          0 if @a nohang is true and the process has not exited yet.
   *          -1 if no process has been started or if an error occurs,
   *          in which case the error can be found using error().
   */
  template <typename C, typename T>
    int
    basic_pstreambuf<C,T>::wait(bool nohang)
    {
      int child_exited = -1;
      if (is_open())
      {
        int exit_status;
        switch(::waitpid(ppid_, &exit_status, nohang ? WNOHANG : 0))
        {
          case 0 :
            // nohang was true and process has not exited
            child_exited = 0;
            break;
          case -1 :
            error_ = errno;
            break;
          default :
            // process has exited
            ppid_ = 0;
            status_ = exit_status;
            child_exited = 1;
            // Close wpipe, would get SIGPIPE if we used it.
            destroy_buffers(pstdin);
            close_fd(wpipe_);
            // Must free read buffers and pipes on destruction
            // or next call to open()/close()
            break;
        }
      }
      return child_exited;
    }

  /**
   * Sends the specified signal to the process.  A signal can be used to
   * terminate a child process that would not exit otherwise.
   *
   * If an error occurs the error code will be set to one of the possible
   * errors for @c kill().  See your system's documentation for these errors.
   *
   * @param   signal  A signal to send to the child process.
   * @return  @c this or @c NULL if @c kill() fails.
   */
  template <typename C, typename T>
    inline basic_pstreambuf<C,T>*
    basic_pstreambuf<C,T>::kill(int signal)
    {
      basic_pstreambuf<C,T>* ret = NULL;
      if (is_open())
      {
        if (::kill(ppid_, signal))
          error_ = errno;
        else
        {
#if 0
          // TODO call exited() to check for exit and clean up? leave to user?
          if (signal==SIGTERM || signal==SIGKILL)
            this->exited();
#endif
          ret = this;
        }
      }
      return ret;
    }

  /**
   * Sends the specified signal to the process group of the child process.
   * A signal can be used to terminate a child process that would not exit
   * otherwise, or to kill the process and its own children.
   *
   * If an error occurs the error code will be set to one of the possible
   * errors for @c getpgid() or @c kill().  See your system's documentation
   * for these errors. If the child is in the current process group then
   * NULL will be returned and the error code set to EPERM.
   *
   * @param   signal  A signal to send to the child process.
   * @return  @c this on success or @c NULL on failure.
   */
  template <typename C, typename T>
    inline basic_pstreambuf<C,T>*
    basic_pstreambuf<C,T>::killpg(int signal)
    {
      basic_pstreambuf<C,T>* ret = NULL;
#ifdef _POSIX_JOB_CONTROL
      if (is_open())
      {
        pid_t pgid = ::getpgid(ppid_);
        if (pgid == -1)
          error_ = errno;
        else if (pgid == ::getpgrp())
          error_ = EPERM;  // Don't commit suicide
        else if (::killpg(pgid, signal))
          error_ = errno;
        else
          ret = this;
      }
#else
      error_ = ENOTSUP;
#endif
      return ret;
    }

  /**
   *  This function can call pstreambuf::wait() and so may change the
   *  object's state if the child process has already exited.
   *
   *  @return  True if the associated process has exited, false otherwise.
   *  @see     basic_pstreambuf<C,T>::wait()
   */
  template <typename C, typename T>
    inline bool
    basic_pstreambuf<C,T>::exited()
    {
      return ppid_ == 0 || wait(true) == 1;
    }


  /**
   *  @return  The exit status of the child process, or -1 if wait()
   *           has not yet been called to wait for the child to exit.
   *  @see     basic_pstreambuf<C,T>::wait()
   */
  template <typename C, typename T>
    inline int
    basic_pstreambuf<C,T>::status() const
    {
      return status_;
    }

  /**
   *  @return  The error code of the most recently failed operation, or zero.
   */
  template <typename C, typename T>
    inline int
    basic_pstreambuf<C,T>::error() const
    {
      return error_;
    }

  /**
   *  Closes the output pipe, causing the child process to receive the
   *  end-of-file indicator on subsequent reads from its @c stdin stream.
   */
  template <typename C, typename T>
    inline void
    basic_pstreambuf<C,T>::peof()
    {
      sync();
      destroy_buffers(pstdin);
      close_fd(wpipe_);
    }

  /**
   * Unlike pstreambuf::exited(), this function will not call wait() and
   * so will not change the object's state.  This means that once a child
   * process is executed successfully this function will continue to
   * return true even after the process exits (until wait() is called.)
   *
   * @return  true if a previous call to open() succeeded and wait() has
   *          not been called and determined that the process has exited,
   *          false otherwise.
   */
  template <typename C, typename T>
    inline bool
    basic_pstreambuf<C,T>::is_open() const
    {
      return ppid_ > 0;
    }

  /**
   * Toggle the stream used for reading. If @a readerr is @c true then the
   * process' @c stderr output will be used for subsequent extractions, if
   * @a readerr is false the the process' stdout will be used.
   * @param   readerr  @c true to read @c stderr, @c false to read @c stdout.
   * @return  @c true if the requested stream is open and will be used for
   *          subsequent extractions, @c false otherwise.
   */
  template <typename C, typename T>
    inline bool
    basic_pstreambuf<C,T>::read_err(bool readerr)
    {
      buf_read_src src = readerr ? rsrc_err : rsrc_out;
      if (rpipe_[src]>=0)
      {
        switch_read_buffer(src);
        return true;
      }
      return false;
    }

  /**
   * Called when the internal character buffer is not present or is full,
   * to transfer the buffer contents to the pipe.
   *
   * @param   c  a character to be written to the pipe.
   * @return  @c traits_type::eof() if an error occurs, otherwise if @a c
   *          is not equal to @c traits_type::eof() it will be buffered and
   *          a value other than @c traits_type::eof() returned to indicate
   *          success.
   */
  template <typename C, typename T>
    typename basic_pstreambuf<C,T>::int_type
    basic_pstreambuf<C,T>::overflow(int_type c)
    {
      if (!empty_buffer())
        return traits_type::eof();
      else if (!traits_type::eq_int_type(c, traits_type::eof()))
        return this->sputc(c);
      else
        return traits_type::not_eof(c);
    }


  template <typename C, typename T>
    int
    basic_pstreambuf<C,T>::sync()
    {
      return !exited() && empty_buffer() ? 0 : -1;
    }

  /**
   * @param   s  character buffer.
   * @param   n  buffer length.
   * @return  the number of characters written.
   */
  template <typename C, typename T>
    std::streamsize
    basic_pstreambuf<C,T>::xsputn(const char_type* s, std::streamsize n)
    {
      std::streamsize done = 0;
      while (done < n)
      {
        if (std::streamsize nbuf = this->epptr() - this->pptr())
        {
          nbuf = std::min(nbuf, n - done);
          traits_type::copy(this->pptr(), s + done, nbuf);
          this->pbump(nbuf);
          done += nbuf;
        }
        else if (!empty_buffer())
          break;
      }
      return done;
    }

  /**
   * @return  true if the buffer was emptied, false otherwise.
   */
  template <typename C, typename T>
    bool
    basic_pstreambuf<C,T>::empty_buffer()
    {
      const std::streamsize count = this->pptr() - this->pbase();
      if (count > 0)
      {
        const std::streamsize written = this->write(this->wbuffer_, count);
        if (written > 0)
        {
          if (const std::streamsize unwritten = count - written)
            traits_type::move(this->pbase(), this->pbase()+written, unwritten);
          this->pbump(-written);
          return true;
        }
      }
      return false;
    }

  /**
   * Called when the internal character buffer is is empty, to re-fill it
   * from the pipe.
   *
   * @return The first available character in the buffer,
   * or @c traits_type::eof() in case of failure.
   */
  template <typename C, typename T>
    typename basic_pstreambuf<C,T>::int_type
    basic_pstreambuf<C,T>::underflow()
    {
      if (this->gptr() < this->egptr() || fill_buffer())
        return traits_type::to_int_type(*this->gptr());
      else
        return traits_type::eof();
    }

  /**
   * Attempts to make @a c available as the next character to be read by
   * @c sgetc().
   *
   * @param   c   a character to make available for extraction.
   * @return  @a c if the character can be made available,
   *          @c traits_type::eof() otherwise.
   */
  template <typename C, typename T>
    typename basic_pstreambuf<C,T>::int_type
    basic_pstreambuf<C,T>::pbackfail(int_type c)
    {
      if (this->gptr() != this->eback())
      {
        this->gbump(-1);
        if (!traits_type::eq_int_type(c, traits_type::eof()))
          *this->gptr() = traits_type::to_char_type(c);
        return traits_type::not_eof(c);
      }
      else
         return traits_type::eof();
    }

  template <typename C, typename T>
    std::streamsize
    basic_pstreambuf<C,T>::showmanyc()
    {
      int avail = 0;
      if (sizeof(char_type) == 1)
        avail = fill_buffer(true) ? this->egptr() - this->gptr() : -1;
#ifdef FIONREAD
      else
      {
        if (::ioctl(rpipe(), FIONREAD, &avail) == -1)
          avail = -1;
        else if (avail)
          avail /= sizeof(char_type);
      }
#endif
      return std::streamsize(avail);
    }

  /**
   * @return  true if the buffer was filled, false otherwise.
   */
  template <typename C, typename T>
    bool
    basic_pstreambuf<C,T>::fill_buffer(bool non_blocking)
    {
      const std::streamsize pb1 = this->gptr() - this->eback();
      const std::streamsize pb2 = pbsz;
      const std::streamsize npb = std::min(pb1, pb2);

      char_type* const rbuf = rbuffer();

      if (npb)
        traits_type::move(rbuf + pbsz - npb, this->gptr() - npb, npb);

      std::streamsize rc = -1;

      if (non_blocking)
      {
        const int flags = ::fcntl(rpipe(), F_GETFL);
        if (flags != -1)
        {
          const bool blocking = !(flags & O_NONBLOCK);
          if (blocking)
            ::fcntl(rpipe(), F_SETFL, flags | O_NONBLOCK);  // set non-blocking

          error_ = 0;
          rc = read(rbuf + pbsz, bufsz - pbsz);

          if (rc == -1 && error_ == EAGAIN)  // nothing available
            rc = 0;
          else if (rc == 0)  // EOF
            rc = -1;

          if (blocking)
            ::fcntl(rpipe(), F_SETFL, flags); // restore
        }
      }
      else
        rc = read(rbuf + pbsz, bufsz - pbsz);

      if (rc > 0 || (rc == 0 && non_blocking))
      {
        this->setg( rbuf + pbsz - npb,
                    rbuf + pbsz,
                    rbuf + pbsz + rc );
        return true;
      }
      else
      {
        this->setg(NULL, NULL, NULL);
        return false;
      }
    }

  /**
   * Writes up to @a n characters to the pipe from the buffer @a s.
   *
   * @param   s  character buffer.
   * @param   n  buffer length.
   * @return  the number of characters written.
   */
  template <typename C, typename T>
    inline std::streamsize
    basic_pstreambuf<C,T>::write(const char_type* s, std::streamsize n)
    {
      std::streamsize nwritten = 0;
      if (wpipe() >= 0)
      {
        nwritten = ::write(wpipe(), s, n * sizeof(char_type));
        if (nwritten == -1)
          error_ = errno;
        else
          nwritten /= sizeof(char_type);
      }
      return nwritten;
    }

  /**
   * Reads up to @a n characters from the pipe to the buffer @a s.
   *
   * @param   s  character buffer.
   * @param   n  buffer length.
   * @return  the number of characters read.
   */
  template <typename C, typename T>
    inline std::streamsize
    basic_pstreambuf<C,T>::read(char_type* s, std::streamsize n)
    {
      std::streamsize nread = 0;
      if (rpipe() >= 0)
      {
        nread = ::read(rpipe(), s, n * sizeof(char_type));
        if (nread == -1)
          error_ = errno;
        else
          nread /= sizeof(char_type);
      }
      return nread;
    }

  /** @return a reference to the output file descriptor */
  template <typename C, typename T>
    inline pstreams::fd_type&
    basic_pstreambuf<C,T>::wpipe()
    {
      return wpipe_;
    }

  /** @return a reference to the active input file descriptor */
  template <typename C, typename T>
    inline pstreams::fd_type&
    basic_pstreambuf<C,T>::rpipe()
    {
      return rpipe_[rsrc_];
    }

  /** @return a reference to the specified input file descriptor */
  template <typename C, typename T>
    inline pstreams::fd_type&
    basic_pstreambuf<C,T>::rpipe(buf_read_src which)
    {
      return rpipe_[which];
    }

  /** @return a pointer to the start of the active input buffer area. */
  template <typename C, typename T>
    inline typename basic_pstreambuf<C,T>::char_type*
    basic_pstreambuf<C,T>::rbuffer()
    {
      return rbuffer_[rsrc_];
    }


  /*
   * member definitions for pstream_common
   */

  /**
   * @class pstream_common
   * Abstract Base Class providing common functionality for basic_ipstream,
   * basic_opstream and basic_pstream.
   * pstream_common manages the basic_pstreambuf stream buffer that is used
   * by the derived classes to initialise an iostream class.
   */

  /** Creates an uninitialised stream. */
  template <typename C, typename T>
    inline
    pstream_common<C,T>::pstream_common()
    : std::basic_ios<C,T>(NULL)
    , command_()
    , buf_()
    {
      this->std::basic_ios<C,T>::rdbuf(&buf_);
    }

  /**
   * Initialises the stream buffer by calling
   * do_open( @a command , @a mode )
   *
   * @param cmd   a string containing a shell command.
   * @param mode  the I/O mode to use when opening the pipe.
   * @see   do_open(const std::string&, pmode)
   */
  template <typename C, typename T>
    inline
    pstream_common<C,T>::pstream_common(const std::string& cmd, pmode mode)
    : std::basic_ios<C,T>(NULL)
    , command_(cmd)
    , buf_()
    {
      this->std::basic_ios<C,T>::rdbuf(&buf_);
      do_open(cmd, mode);
    }

  /**
   * Initialises the stream buffer by calling
   * do_open( @a file , @a argv , @a mode )
   *
   * @param file  a string containing the pathname of a program to execute.
   * @param argv  a vector of argument strings passed to the new program.
   * @param mode  the I/O mode to use when opening the pipe.
   * @see do_open(const std::string&, const argv_type&, pmode)
   */
  template <typename C, typename T>
    inline
    pstream_common<C,T>::pstream_common( const std::string& file,
                                         const argv_type& argv,
                                         pmode mode )
    : std::basic_ios<C,T>(NULL)
    , command_(file)
    , buf_()
    {
      this->std::basic_ios<C,T>::rdbuf(&buf_);
      do_open(file, argv, mode);
    }

  /**
   * This is a pure virtual function to make @c pstream_common abstract.
   * Because it is the destructor it will be called by derived classes
   * and so must be defined.  It is also protected, to discourage use of
   * the PStreams classes through pointers or references to the base class.
   *
   * @sa If defining a pure virtual seems odd you should read
   * http://www.gotw.ca/gotw/031.htm (and the rest of the site as well!)
   */
  template <typename C, typename T>
    inline
    pstream_common<C,T>::~pstream_common()
    {
    }

  /**
   * Calls rdbuf()->open( @a command , @a mode )
   * and sets @c failbit on error.
   *
   * @param cmd   a string containing a shell command.
   * @param mode  the I/O mode to use when opening the pipe.
   * @see   basic_pstreambuf::open(const std::string&, pmode)
   */
  template <typename C, typename T>
    inline void
    pstream_common<C,T>::do_open(const std::string& cmd, pmode mode)
    {
      if (!buf_.open((command_=cmd), mode))
        this->setstate(std::ios_base::failbit);
    }

  /**
   * Calls rdbuf()->open( @a file, @a  argv, @a mode )
   * and sets @c failbit on error.
   *
   * @param file  a string containing the pathname of a program to execute.
   * @param argv  a vector of argument strings passed to the new program.
   * @param mode  the I/O mode to use when opening the pipe.
   * @see   basic_pstreambuf::open(const std::string&, const argv_type&, pmode)
   */
  template <typename C, typename T>
    inline void
    pstream_common<C,T>::do_open( const std::string& file,
                                  const argv_type& argv,
                                  pmode mode )
    {
      if (!buf_.open((command_=file), argv, mode))
        this->setstate(std::ios_base::failbit);
    }

  /** Calls rdbuf->close() and sets @c failbit on error.  Returns
   *  process's exit status, as pclose(3) does. */
  template <typename C, typename T>
    inline int
    pstream_common<C,T>::close()
    {
      if (!buf_.close())
        this->setstate(std::ios_base::failbit);
      return buf_.status();
    }

  /**
   * @return  rdbuf()->is_open().
   * @see     basic_pstreambuf::is_open()
   */
  template <typename C, typename T>
    inline bool
    pstream_common<C,T>::is_open() const
    {
      return buf_.is_open();
    }

  /** @return a string containing the command used to initialise the stream. */
  template <typename C, typename T>
    inline const std::string&
    pstream_common<C,T>::command() const
    {
      return command_;
    }

  /** @return a pointer to the private stream buffer member. */
  // TODO  document behaviour if buffer replaced.
  template <typename C, typename T>
    inline typename pstream_common<C,T>::streambuf_type*
    pstream_common<C,T>::rdbuf() const
    {
      return const_cast<streambuf_type*>(&buf_);
    }


#if REDI_EVISCERATE_PSTREAMS
  /**
   * @def REDI_EVISCERATE_PSTREAMS
   * If this macro has a non-zero value then certain internals of the
   * @c basic_pstreambuf template class are exposed. In general this is
   * a Bad Thing, as the internal implementation is largely undocumented
   * and may be subject to change at any time, so this feature is only
   * provided because it might make PStreams useful in situations where
   * it is necessary to do Bad Things.
   */

  /**
   * @warning  This function exposes the internals of the stream buffer and
   *           should be used with caution. It is the caller's responsibility
   *           to flush streams etc. in order to clear any buffered data.
   *           The POSIX.1 function <b>fdopen</b>(3) is used to obtain the
   *           @c FILE pointers from the streambuf's private file descriptor
   *           members so consult your system's documentation for
   *           <b>fdopen</b>(3).
   *
   * @param   in    A FILE* that will refer to the process' stdin.
   * @param   out   A FILE* that will refer to the process' stdout.
   * @param   err   A FILE* that will refer to the process' stderr.
   * @return  An OR of zero or more of @c pstdin, @c pstdout, @c pstderr.
   *
   * For each open stream shared with the child process a @c FILE* is
   * obtained and assigned to the corresponding parameter. For closed
   * streams @c NULL is assigned to the parameter.
   * The return value can be tested to see which parameters should be
   * @c !NULL by masking with the corresponding @c pmode value.
   *
   * @see <b>fdopen</b>(3)
   */
  template <typename C, typename T>
    std::size_t
    basic_pstreambuf<C,T>::fopen(FILE*& in, FILE*& out, FILE*& err)
    {
      in = out = err = NULL;
      std::size_t open_files = 0;
      if (wpipe() > -1)
      {
        if ((in = ::fdopen(wpipe(), "w")))
        {
            open_files |= pstdin;
        }
      }
      if (rpipe(rsrc_out) > -1)
      {
        if ((out = ::fdopen(rpipe(rsrc_out), "r")))
        {
            open_files |= pstdout;
        }
      }
      if (rpipe(rsrc_err) > -1)
      {
        if ((err = ::fdopen(rpipe(rsrc_err), "r")))
        {
            open_files |= pstderr;
        }
      }
      return open_files;
    }

  /**
   *  @warning This function exposes the internals of the stream buffer and
   *  should be used with caution.
   *
   *  @param  in   A FILE* that will refer to the process' stdin.
   *  @param  out  A FILE* that will refer to the process' stdout.
   *  @param  err  A FILE* that will refer to the process' stderr.
   *  @return A bitwise-or of zero or more of @c pstdin, @c pstdout, @c pstderr.
   *  @see    basic_pstreambuf::fopen()
   */
  template <typename C, typename T>
    inline std::size_t
    pstream_common<C,T>::fopen(FILE*& fin, FILE*& fout, FILE*& ferr)
    {
      return buf_.fopen(fin, fout, ferr);
    }

#endif // REDI_EVISCERATE_PSTREAMS


} // namespace redi

/**
 * @mainpage PStreams Reference
 * @htmlinclude mainpage.html
 */

#endif  // REDI_PSTREAM_H_SEEN

// vim: ts=2 sw=2 expandtab