new module 'system-quote'

[Bruno Haible]

This is the module 'system-quote'.

It turns out that on native Windows, when going through cmd.exe, it is
not possible to pass arguments that contains a newline ('\n') or a CR ('\r')
character: the command gets truncated at such a character. Compared to
this problem, the handling of the '%' character is easy.


2012-05-08  Bruno Haible  <address@hidden>

        New module 'system-quote'.
        * lib/system-quote.h: New file.
        * lib/system-quote.c: New file.
        * modules/system-quote: New file.

============================= lib/system-quote.h =============================
/* Quoting for a system command.
   Copyright (C) 2001-2012 Free Software Foundation, Inc.
   Written by Bruno Haible <address@hidden>, 2012.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#ifndef _SYSTEM_QUOTE_H
#define _SYSTEM_QUOTE_H

/* When passing a command the system's command interpreter, we must quote the
   program name and arguments, since
     - Unix shells interpret characters like " ", "'", "<", ">", "$" etc. in a
       special way,
     - Windows CreateProcess() interprets characters like ' ', '\t', '\\', '"'
       etc. (but not '<' and '>') in a special way,
     - Windows cmd.exe also interprets characters like '<', '>', '&', '%', etc.
       in a special way.  Note that it is impossible to pass arguments that
       contain newlines or carriage return characters to programs through
       cmd.exe.  */

#include <stddef.h>

#ifdef __cplusplus
extern "C" {
#endif

/* Identifier for the kind of interpreter of the command.  */
enum system_command_interpreter
{
  /* The interpreter used by the system() and popen() functions.
     This is equivalent to SCI_POSIX_SH on Unix platforms and
     SCI_WINDOWS_CMD on native Windows platforms.  */
  SCI_SYSTEM                    = 0
  /* The POSIX /bin/sh.  */
  , SCI_POSIX_SH                = 1
#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
  /* The native Windows CreateProcess() function.  */
  , SCI_WINDOWS_CREATEPROCESS   = 2
  /* The native Windows cmd.exe interpreter.  */
  , SCI_WINDOWS_CMD             = 3
#endif
};

/* Returns the number of bytes needed for the quoted string.  */
extern size_t
       system_quote_length (enum system_command_interpreter interpreter,
                            const char *string);

/* Copies the quoted string to p and returns the incremented p.
   There must be room for shell_quote_length (string) + 1 bytes at p.  */
extern char *
       system_quote_copy (char *p,
                          enum system_command_interpreter interpreter,
                          const char *string);

/* Returns the freshly allocated quoted string.  */
extern char *
       system_quote (enum system_command_interpreter interpreter,
                     const char *string);

/* Returns a freshly allocated string containing all argument strings, quoted,
   separated through spaces.  */
extern char *
       system_quote_argv (enum system_command_interpreter interpreter,
                          char * const *argv);

#ifdef __cplusplus
}
#endif

#endif /* _SYSTEM_QUOTE_H */
============================= lib/system-quote.c =============================
/* Quoting for a system command.
   Copyright (C) 2012 Free Software Foundation, Inc.
   Written by Bruno Haible <address@hidden>, 2012.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */
#include "system-quote.h"

#include <stdbool.h>
#include <stdlib.h>
#include <string.h>

#include "sh-quote.h"
#include "xalloc.h"

#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
/* The native Windows CreateProcess() function interprets characters like
   ' ', '\t', '\\', '"' (but not '<' and '>') in a special way:
   - Space and tab are interpreted as delimiters. They are not treated as
     delimiters if they are surrounded by double quotes: "...".
   - Unescaped double quotes are removed from the input. Their only effect is
     that within double quotes, space and tab are treated like normal
     characters.
   - Backslashes not followed by double quotes are not special.
   - But 2*n+1 backslashes followed by a double quote become
     n backslashes followed by a double quote (n >= 0):
       \" -> "
       \\\" -> \"
       \\\\\" -> \\"
   - '*' characters may get expanded or lead to a failure with error code
     ERROR_PATH_NOT_FOUND.
 */
# define SHELL_SPECIAL_CHARS "\"\\ 
\001\002\003\004\005\006\007\010\011\012\013\014\015\016\017\020\021\022\023\024\025\026\027\030\031\032\033\034\035\036\037*"
# define SHELL_SPACE_CHARS " 
\001\002\003\004\005\006\007\010\011\012\013\014\015\016\017\020\021\022\023\024\025\026\027\030\031\032\033\034\035\036\037"
/* The native Windows cmd.exe command interpreter also interprets:
   - '\n', '\r' as a command terminator - no way to escape it,
   - '<', '>' as redirections,
   - '|' as pipe operator,
   - '%var%' as a reference to the environment variable VAR (uppercase),
     even inside quoted strings,
   - '&' '[' ']' '{' '}' '^' '=' ';' '!' '\'' '+' ',' '`' '~' for other
     purposes, according to
     
<http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/cmd.mspx?mfr=true>
   We quote a string like '%var%' by putting the '%' characters outside of
   double-quotes and the rest of the string inside double-quotes: %"var"%.
   This is guaranteed to not be a reference to an environment variable.
 */
# define CMD_SPECIAL_CHARS "\"\\ 
\001\002\003\004\005\006\007\010\011\012\013\014\015\016\017\020\021\022\023\024\025\026\027\030\031\032\033\034\035\036\037!%&'*+,;<=>[]^`{|}~"
# define CMD_FORBIDDEN_CHARS "\n\r"
#endif

size_t
system_quote_length (enum system_command_interpreter interpreter,
                     const char *string)
{
  switch (interpreter)
    {
#if !((defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__)
    case SCI_SYSTEM:
#endif
    case SCI_POSIX_SH:
      return shell_quote_length (string);

#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
    case SCI_WINDOWS_CREATEPROCESS:
      {
        size_t len = strlen (string);
        bool quote_around =
          (len == 0 || strpbrk (string, SHELL_SPECIAL_CHARS) != NULL);
        size_t backslashes = 0;
        size_t length = len;

        if (quote_around)
          length++;
        for (; len > 0; string++, len--)
          {
            char c = *string;

            if (c == '"')
              length += backslashes + 1;
            if (c == '\\')
              backslashes++;
            else
              backslashes = 0;
          }
        if (quote_around)
          length += backslashes + 1;
        return length;
      }

    case SCI_SYSTEM:
    case SCI_WINDOWS_CMD:
      {
        size_t len = strlen (string);
        bool quote_around =
          (len == 0 || strpbrk (string, CMD_SPECIAL_CHARS) != NULL);
        size_t backslashes = 0;
        size_t length = len;

        if (quote_around)
          length++;
        for (; len > 0; string++, len--)
          {
            char c = *string;

            if (c == '"')
              length += backslashes + 1;
            if (c == '%')
              length += backslashes + 2;
            if (c == '\\')
              backslashes++;
            else
              backslashes = 0;
          }
        if (quote_around)
          length += backslashes + 1;
        return length;
      }
#endif

    default:
      /* Invalid interpreter.  */
      abort ();
    }
}

char *
system_quote_copy (char *p,
                   enum system_command_interpreter interpreter,
                   const char *string)
{
  switch (interpreter)
    {
#if !((defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__)
    case SCI_SYSTEM:
#endif
    case SCI_POSIX_SH:
      return shell_quote_copy (p, string);

#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
    case SCI_WINDOWS_CREATEPROCESS:
      {
        size_t len = strlen (string);
        bool quote_around =
          (len == 0 || strpbrk (string, SHELL_SPECIAL_CHARS) != NULL);
        size_t backslashes = 0;

        if (quote_around)
          *p++ = '"';
        for (; len > 0; string++, len--)
          {
            char c = *string;

            if (c == '"')
              {
                size_t j;

                for (j = backslashes + 1; j > 0; j--)
                  *p++ = '\\';
              }
            *p++ = c;
            if (c == '\\')
              backslashes++;
            else
              backslashes = 0;
          }
        if (quote_around)
          {
            size_t j;

            for (j = backslashes; j > 0; j--)
              *p++ = '\\';
            *p++ = '"';
          }
        *p = '\0';
        return p;
      }

    case SCI_SYSTEM:
    case SCI_WINDOWS_CMD:
      {
        size_t len = strlen (string);
        bool quote_around =
          (len == 0 || strpbrk (string, CMD_SPECIAL_CHARS) != NULL);
        size_t backslashes = 0;

        if (quote_around)
          *p++ = '"';
        for (; len > 0; string++, len--)
          {
            char c = *string;

            if (c == '"')
              {
                size_t j;

                for (j = backslashes + 1; j > 0; j--)
                  *p++ = '\\';
              }
            if (c == '%')
              {
                size_t j;

                for (j = backslashes; j > 0; j--)
                  *p++ = '\\';
                *p++ = '"';
              }
            *p++ = c;
            if (c == '%')
              *p++ = '"';
            if (c == '\\')
              backslashes++;
            else
              backslashes = 0;
          }
        if (quote_around)
          {
            size_t j;

            for (j = backslashes; j > 0; j--)
              *p++ = '\\';
            *p++ = '"';
          }
        *p = '\0';
        return p;
      }
#endif

    default:
      /* Invalid interpreter.  */
      abort ();
    }
}

char *
system_quote (enum system_command_interpreter interpreter,
              const char *string)
{
  switch (interpreter)
    {
#if !((defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__)
    case SCI_SYSTEM:
#endif
    case SCI_POSIX_SH:
      return shell_quote (string);

#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
    case SCI_WINDOWS_CREATEPROCESS:
    case SCI_SYSTEM:
    case SCI_WINDOWS_CMD:
      {
        size_t length = system_quote_length (interpreter, string);
        char *quoted = XNMALLOC (length, char);
        system_quote_copy (quoted, interpreter, string);
        return quoted;
      }
#endif

    default:
      /* Invalid interpreter.  */
      abort ();
    }
}

char *
system_quote_argv (enum system_command_interpreter interpreter,
                   char * const *argv)
{
  if (*argv != NULL)
    {
      char * const *argp;
      size_t length;
      char *command;
      char *p;

      length = 0;
      for (argp = argv; ; )
        {
          length += system_quote_length (interpreter, *argp) + 1;
          argp++;
          if (*argp == NULL)
            break;
        }

      command = XNMALLOC (length, char);

      p = command;
      for (argp = argv; ; )
        {
          p = system_quote_copy (p, interpreter, *argp);
          argp++;
          if (*argp == NULL)
            break;
          *p++ = ' ';
        }
      *p = '\0';

      return command;
    }
  else
    return xstrdup ("");
}
============================ modules/system-quote ============================
Description:
Quoting for a system command.

Files:
lib/system-quote.h
lib/system-quote.c

Depends-on:
sh-quote
xalloc

configure.ac:

Makefile.am:
lib_SOURCES += system-quote.h system-quote.c

Include:
"system-quote.h"

License:
GPL

Maintainer:
Bruno Haible
==============================================================================