New string functions

* libmailutils/string/strcount.c (mu_str_count): Take an array of
(ASCII) characters to count occurrences of.  Optionally store individual
counts in an array passed as the 3rd argument.
* include/mailutils/cstr.h (mu_str_count): Change proto.
(mu_c_str_escape, mu_c_str_escape_trans)
(mu_c_str_unescape_inplace, mu_c_str_unescape)
(mu_c_str_unescape_trans): New protos.
* libmailutils/string/cstrescape.c: New file.
* libmailutils/string/cstrunescape.c: New file.
* libmailutils/string/Makefile.am: Add new files.

@@ -32,7 +32,7 @@ main (int argc, char **argv)
     }
 
   if (!mu_file_name_is_safe (argv[0])
-      || (argv[0][0] == '/' && mu_str_count (argv[0], '/') < 2))
+      || (argv[0][0] == '/' && mu_str_count (argv[0], "/", NULL) < 2))
     {
       mu_error ("unsafe file name");
       return 1;

@@ -36,13 +36,13 @@ main (int argc, char **argv)
     }
 
   if (!mu_file_name_is_safe (argv[0])
-      || (argv[0][0] == '/' && mu_str_count (argv[0], '/') < 2))
+      || (argv[0][0] == '/' && mu_str_count (argv[0], "/", NULL) < 2))
     {
       mu_error ("%s: unsafe file name", argv[0]);
       return 1;
     }
   if (!mu_file_name_is_safe (argv[1])
-      || (argv[1][0] == '/' && mu_str_count (argv[1], '/') < 2))
+      || (argv[1][0] == '/' && mu_str_count (argv[1], "/", NULL) < 2))
     {
       mu_error ("%sunsafe file name", argv[0]);
       return 1;

@@ -46,7 +46,18 @@ char *mu_str_stripws (char *string);
 
 int mu_string_split (const char *string, char *delim, mu_list_t list);
 
-size_t mu_str_count (char const *str, int chr);
+size_t mu_str_count (char const *str, char const *chr, size_t *cnt);
+
+int mu_c_str_escape (char const *str, char const *chr, char const *xtab,
+		     char **ret_str);
+int mu_c_str_escape_trans (char const *str, char const *trans, char **ret_str);
+
+int mu_c_str_unescape_inplace (char *str, char const *chr, char const *xtab);
+int mu_c_str_unescape (char const *str, char const *chr, char const *xtab,
+		       char **ret_str);
+int mu_c_str_unescape_trans (char const *str, char const *trans,
+			     char **ret_str);
+
   
 #ifdef __cplusplus
 }

@@ -21,6 +21,8 @@ libstring_la_SOURCES = \
  cpystr.c\
  cstrcasecmp.c\
  cstrcasestr.c\
+ cstrescape.c\
+ cstrunescape.c\
  cstrlower.c\
  cstrupper.c\
  hexstr.c\

+/* GNU Mailutils -- a suite of utilities for electronic mail
+   Copyright (C) 2016 Free Software Foundation, Inc.
+
+   GNU Mailutils 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, or (at your option)
+   any later version.
+
+   GNU Mailutils 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 GNU Mailutils.  If not, see <http://www.gnu.org/licenses/>. */
+
+#include <config.h>
+#include <stdlib.h>
+#include <string.h>
+#include <mailutils/cstr.h>
+#include <mailutils/errno.h>
+
+/* Examines STR for occurrences of characters from CHR.  Returns in RET_STR
+   a malloc'ed string where each occurrence of CHR[i] is replaced by a
+   backslash, followed by XTAB[i].
+
+   If CHR is NULL, RET_STR contains a malloc'ed copy of STR (XTAB is
+   ignored).
+
+   If XTAB is NULL, XTAB = CHR is assumed.
+
+   Callers are advised to include backslash into both CHR and XTAB.
+
+   Returns 0 on success, error code if an error occurred.
+   
+   Example:
+
+   Escape each occurrence of backslash and double quote:
+   
+     mu_c_str_escape (str, "\\\"", NULL, &ret_str)
+*/
+int
+mu_c_str_escape (char const *str, char const *chr, char const *xtab,
+		 char **ret_str)
+{
+  char *newstr;
+  size_t n;
+  int c;
+  
+  if (!ret_str)
+    return MU_ERR_OUT_PTR_NULL;
+  
+  if (!str)
+    {
+      *ret_str = NULL;
+      return 0;
+    }
+
+  if (!chr)
+    {
+      newstr = strdup (str);
+      if (!newstr)
+	return errno;
+      *ret_str = newstr;
+      return 0;
+    }
+
+  n = strlen (chr);
+
+  if (xtab)
+    {
+      if (strlen (xtab) != n)
+	return EINVAL;
+    }
+  else
+    xtab = chr;
+  
+  n = mu_str_count (str, chr, NULL);
+  
+  newstr = malloc (strlen (str) + n + 1);
+  if (!newstr)
+    return errno;
+  *ret_str = newstr;
+  
+  if (n == 0)
+    {
+      strcpy (newstr, str);
+      return 0;
+    }
+
+  while ((c = *str++) != 0)
+    {
+      char *p = strchr (chr, c);
+
+      if (p)
+	{
+	  *newstr++ = '\\';
+          *newstr++ = xtab[p - chr];
+	}
+      else
+	*newstr++ = c;
+    }
+  *newstr = 0;
+
+  return 0;
+}
+
+/* Escape certain characters in STR.  Return allocated string in RET_STR.
+
+   Escapable characters are defined by the array TRANS, which consists of an
+   even number of elements.  Each pair of characters in this array contains:
+
+     TRANS[i+1]  - character to be escaped
+     TRANS[i]    - character to use in escape sequence for TRANS[i+1].
+
+   Each TRANS[i+1] is replaced by backslash + TRANS[i].
+
+   Returns 0 on success, or error code if an error occurred.
+
+   E.g., to escape control characters, backslash and double-quote using
+   C convention:
+
+      mu_c_str_escape_trans (str, "\\\\\"\"a\ab\bf\fn\nr\rt\tv\v", &ret)
+
+   See also mu_wordsplit_c_escape_tab in wordsplit.c
+*/
+int
+mu_c_str_escape_trans (char const *str, char const *trans, char **ret_str)
+{
+  char *chr, *xtab;
+  size_t n, i;
+  int rc;
+  
+  if (trans)
+    {
+      n = strlen (trans);
+      if (n % 2)
+	return EINVAL;
+      chr = malloc (n + 2);
+      if (!chr)
+	return errno;
+      xtab = chr + n / 2 + 1;
+      for (i = 0; i < n; i += 2)
+	{
+	  chr[i / 2] = trans[i + 1];
+	  xtab[i / 2] = trans[i];
+	}
+      chr[i / 2] = xtab[i / 2] = 0;
+    }
+  else
+    {
+      chr = xtab = NULL;
+    }
+
+  rc = mu_c_str_escape (str, chr, xtab, ret_str);
+
+  free (chr);
+
+  return rc;
+}
+	
+    

+/* GNU Mailutils -- a suite of utilities for electronic mail
+   Copyright (C) 2016 Free Software Foundation, Inc.
+
+   GNU Mailutils 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, or (at your option)
+   any later version.
+
+   GNU Mailutils 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 GNU Mailutils.  If not, see <http://www.gnu.org/licenses/>. */
+
+#include <config.h>
+#include <stdlib.h>
+#include <string.h>
+#include <mailutils/cstr.h>
+#include <mailutils/errno.h>
+
+/* Copy characters from IN to OUT.  Replace each occurrences of backslash
+   followed by a character XTAB[i] with CHR[i].
+
+   OUT should be large enough to accomodate the translated string (same length
+   as IN, in the worst case).  It is OK if IN==OUT.
+
+   Both XTAB and CHR must not be NULL and must contain the same number of
+   elements. 
+ */
+static void
+c_str_unescape (char const *in, char *out, char const *chr, char const *xtab)
+{
+  size_t i, j;
+  
+  for (i = j = 0; in[i]; i++, j++)
+    {
+      if (in[i] == '\\')
+	break;
+      out[j] = in[i];
+    }
+
+  if (in[i])
+    {
+      for (; in[i]; i++, j++)
+	{
+	  if (in[i] == '\\')
+	    {
+	      char *p;
+	      if (in[i+1] && (p = strchr (xtab, in[i+1])) != NULL)
+		{
+		  out[j] = chr[p - xtab];
+		  i++;
+		  continue;
+		}
+	    }
+	  out[j] = in[i];
+	}
+    }
+  out[j] = 0;
+}
+
+/* Modifies STR, by replacing each occurrence of \ followed by a charater
+   XTAB[i] with CHR[i].
+
+   Either XTAB or CHR can be NULL, in which case XTAB=CHR is assumed.
+
+   If both XTAB and CHR are NULL, STR is unchanged.
+   
+   STR == NULL is OK.
+
+   Returns 0 success, and EINVAL if lengths of CHR and XTAB differ.
+*/
+int
+mu_c_str_unescape_inplace (char *str, char const *chr, char const *xtab)
+{
+  if (!str)
+    return 0;
+  if (!xtab)
+    {
+      if (chr)
+	xtab = chr;
+      else
+	return 0;
+    }
+  else if (!chr)
+    chr = xtab;
+  else if (strlen (chr) != strlen (xtab))
+    return EINVAL;
+  c_str_unescape (str, str, chr, xtab);
+  return 0;
+}
+
+/* A counterpart of mu_c_str_escape.  Creates an allocated (using malloc(3))
+   copy of STR, where each occurrence of \ followed by a charater XTAB[i]
+   is replaced with single character CHR[i].
+
+   Either XTAB or CHR can be NULL, in which case XTAB=CHR is assumed.
+
+   If both XTAB and CHR are NULL, the result is *RET_STR will contain exact
+   malloc'ed copy of STR.
+   
+   STR == NULL is OK: in that case *RET_STR will also be NULL.
+
+   Returns 0 success, EINVAL if lengths of CHR and XTAB differ,
+   MU_ERR_OUT_PTR_NULL if RET_STR is NULL, and ENOMEM if memory allocation
+   failed.
+ */
+int
+mu_c_str_unescape (char const *str, char const *chr, char const *xtab,
+		   char **ret_str)
+{
+  char *newstr;
+  size_t i, size;
+  
+  if (!ret_str)
+    return MU_ERR_OUT_PTR_NULL;
+  
+  if (!str)
+    {
+      *ret_str = NULL;
+      return 0;
+    }
+
+  if (!xtab)
+    {
+      if (chr)
+	xtab = chr;
+      else
+	{
+	  char *p = strdup (str);
+	  if (!p)
+	    return errno;
+	  *ret_str = p;
+	}
+    }
+  else if (!chr)
+    chr = xtab;
+  else if (strlen (chr) != strlen (xtab))
+    return EINVAL;
+
+  size = 0;
+  for (i = 0; str[i]; i++)
+    {
+      if (str[i] == '\\' && str[i + 1] && strchr (xtab, str[i + 1]))
+	i++;
+      size++;
+    }
+
+  newstr = malloc (size + 1);
+  if (!newstr)
+    return errno;
+  *ret_str = newstr;
+  
+  c_str_unescape (str, newstr, chr, xtab);
+
+  return 0;
+}
+
+/* A counterpart of mu_c_str_escape_trans.
+
+   Creates an allocated (using malloc(3)) copy of STR, where each occurrence 
+   of \ followed by TRANS[i] is replaced by TRANS[i+1].
+
+   Returns 0 on success, or error code if an error occurred.
+   
+   See also mu_wordsplit_c_escape_tab in wordsplit.c
+ */
+int
+mu_c_str_unescape_trans (char const *str, char const *trans, char **ret_str)
+{
+  char *chr, *xtab;
+  size_t n, i;
+  int rc;
+  
+  if (trans)
+    {
+      n = strlen (trans);
+      if (n % 2)
+	return EINVAL;
+      chr = malloc (n + 2);
+      if (!chr)
+	return errno;
+      xtab = chr + n / 2 + 1;
+      for (i = 0; i < n; i += 2)
+	{
+	  chr[i / 2] = trans[i + 1];
+	  xtab[i / 2] = trans[i];
+	}
+      chr[i / 2] = xtab[i / 2] = 0;
+    }
+  else
+    {
+      chr = xtab = NULL;
+    }
+
+  rc = mu_c_str_unescape (str, chr, xtab, ret_str);
+
+  free (chr);
+
+  return rc;
+}
+  

@@ -16,29 +16,45 @@
 
 #include <config.h>
 #include <limits.h>
+#include <string.h>
 #include <mailutils/util.h>
 
-/* Return the number of occurrences of the ASCII character CHR in the
-   UTF-8 string STR. */
+/* Count number of occurrences of each ASCII character from CHR in the
+   UTF-8 string STR.  Unless CNT is NULL, fill it with the counts for
+   each character (so that CNT[i] contains number of occurrences of
+   CHR[i]).  Return total number of occurrences. */
 size_t
-mu_str_count (char const *str, int chr)
+mu_str_count (char const *str, char const *chr, size_t *cnt)
 {
   unsigned char c;
-  size_t count = 0;
   int consume = 0;
+  size_t count = 0;
 
-  if (!str || chr < 0 || chr > UCHAR_MAX)
+  if (!str || !chr)
     return 0;
   
+  if (cnt)
+    {
+      int i;
+      
+      for (i = 0; chr[i]; i++)
+	cnt[i] = 0;
+    }
+  
   while ((c = *str++) != 0)
     {
       if (consume)
 	consume--;
       else if (c < 0xc0)
 	{
-	  if (c == chr)
+	  char *p = strchr (chr, c);
+	  if (p)
+	    {
+	      if (cnt)
+		cnt[p - chr]++;
 	      count++;
 	    }
+	}
       else if (c & 0xc0)
 	consume = 1;
       else if (c & 0xe0)