charset.c

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#include "config.h"
#include <ctype.h>
#include <errno.h>
#include <iconv.h>
#include <langinfo.h>
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
#include "config/lib.h"
#include "core/lib.h"
#include "charset.h"
#include "lib.h"
#include "memory.h"
#include "queue.h"
#include "regex3.h"
#include "string2.h"
#ifdef ENABLE_NLS
#include <libintl.h>
#endif
 
#ifndef EILSEQ
#define EILSEQ EINVAL
#endif
 
wchar_t ReplacementChar = '?';
 
bool CharsetIsUtf8 = false;
 
struct Lookup
{
  enum LookupType type;        
  struct Regex regex;          
  char *replacement;           
  TAILQ_ENTRY(Lookup) entries; 
};
TAILQ_HEAD(LookupList, Lookup);
 
static struct LookupList Lookups = TAILQ_HEAD_INITIALIZER(Lookups);
 
struct MimeNames
{
  const char *key;
  const char *pref;
};
 
const struct MimeNames PreferredMimeNames[] = {
  // clang-format off
  { "ansi_x3.4-1968",        "us-ascii"      },
  { "iso-ir-6",              "us-ascii"      },
  { "iso_646.irv:1991",      "us-ascii"      },
  { "ascii",                 "us-ascii"      },
  { "iso646-us",             "us-ascii"      },
  { "us",                    "us-ascii"      },
  { "ibm367",                "us-ascii"      },
  { "cp367",                 "us-ascii"      },
  { "csASCII",               "us-ascii"      },
 
  { "csISO2022KR",           "iso-2022-kr"   },
  { "csEUCKR",               "euc-kr"        },
  { "csISO2022JP",           "iso-2022-jp"   },
  { "csISO2022JP2",          "iso-2022-jp-2" },
 
  { "ISO_8859-1:1987",       "iso-8859-1"    },
  { "iso-ir-100",            "iso-8859-1"    },
  { "iso_8859-1",            "iso-8859-1"    },
  { "latin1",                "iso-8859-1"    },
  { "l1",                    "iso-8859-1"    },
  { "IBM819",                "iso-8859-1"    },
  { "CP819",                 "iso-8859-1"    },
  { "csISOLatin1",           "iso-8859-1"    },
 
  { "ISO_8859-2:1987",       "iso-8859-2"    },
  { "iso-ir-101",            "iso-8859-2"    },
  { "iso_8859-2",            "iso-8859-2"    },
  { "latin2",                "iso-8859-2"    },
  { "l2",                    "iso-8859-2"    },
  { "csISOLatin2",           "iso-8859-2"    },
 
  { "ISO_8859-3:1988",       "iso-8859-3"    },
  { "iso-ir-109",            "iso-8859-3"    },
  { "ISO_8859-3",            "iso-8859-3"    },
  { "latin3",                "iso-8859-3"    },
  { "l3",                    "iso-8859-3"    },
  { "csISOLatin3",           "iso-8859-3"    },
 
  { "ISO_8859-4:1988",       "iso-8859-4"    },
  { "iso-ir-110",            "iso-8859-4"    },
  { "ISO_8859-4",            "iso-8859-4"    },
  { "latin4",                "iso-8859-4"    },
  { "l4",                    "iso-8859-4"    },
  { "csISOLatin4",           "iso-8859-4"    },
 
  { "ISO_8859-6:1987",       "iso-8859-6"    },
  { "iso-ir-127",            "iso-8859-6"    },
  { "iso_8859-6",            "iso-8859-6"    },
  { "ECMA-114",              "iso-8859-6"    },
  { "ASMO-708",              "iso-8859-6"    },
  { "arabic",                "iso-8859-6"    },
  { "csISOLatinArabic",      "iso-8859-6"    },
 
  { "ISO_8859-7:1987",       "iso-8859-7"    },
  { "iso-ir-126",            "iso-8859-7"    },
  { "ISO_8859-7",            "iso-8859-7"    },
  { "ELOT_928",              "iso-8859-7"    },
  { "ECMA-118",              "iso-8859-7"    },
  { "greek",                 "iso-8859-7"    },
  { "greek8",                "iso-8859-7"    },
  { "csISOLatinGreek",       "iso-8859-7"    },
 
  { "ISO_8859-8:1988",       "iso-8859-8"    },
  { "iso-ir-138",            "iso-8859-8"    },
  { "ISO_8859-8",            "iso-8859-8"    },
  { "hebrew",                "iso-8859-8"    },
  { "csISOLatinHebrew",      "iso-8859-8"    },
 
  { "ISO_8859-5:1988",       "iso-8859-5"    },
  { "iso-ir-144",            "iso-8859-5"    },
  { "ISO_8859-5",            "iso-8859-5"    },
  { "cyrillic",              "iso-8859-5"    },
  { "csISOLatinCyrillic",    "iso-8859-5"    },
 
  { "ISO_8859-9:1989",       "iso-8859-9"    },
  { "iso-ir-148",            "iso-8859-9"    },
  { "ISO_8859-9",            "iso-8859-9"    },
  { "latin5",                "iso-8859-9"    },  /* this is not a bug */
  { "l5",                    "iso-8859-9"    },
  { "csISOLatin5",           "iso-8859-9"    },
 
  { "ISO_8859-10:1992",      "iso-8859-10"   },
  { "iso-ir-157",            "iso-8859-10"   },
  { "latin6",                "iso-8859-10"   },  /* this is not a bug */
  { "l6",                    "iso-8859-10"   },
  { "csISOLatin6",           "iso-8859-10"   },
 
  { "csKOI8r",               "koi8-r"        },
 
  { "MS_Kanji",              "Shift_JIS"     },  /* Note the underscore! */
  { "csShiftJis",            "Shift_JIS"     },
 
  { "Extended_UNIX_Code_Packed_Format_for_Japanese",
                             "euc-jp"        },
  { "csEUCPkdFmtJapanese",   "euc-jp"        },
 
  { "csGB2312",              "gb2312"        },
  { "csbig5",                "big5"          },
 
  /* End of official brain damage.
   * What follows has been taken from glibc's localedata files.  */
 
  { "iso_8859-13",           "iso-8859-13"   },
  { "iso-ir-179",            "iso-8859-13"   },
  { "latin7",                "iso-8859-13"   },  /* this is not a bug */
  { "l7",                    "iso-8859-13"   },
 
  { "iso_8859-14",           "iso-8859-14"   },
  { "latin8",                "iso-8859-14"   },  /* this is not a bug */
  { "l8",                    "iso-8859-14"   },
 
  { "iso_8859-15",           "iso-8859-15"   },
  { "latin9",                "iso-8859-15"   },  /* this is not a bug */
 
  /* Suggested by Ionel Mugurel Ciobica <tgakic@sg10.chem.tue.nl> */
  { "latin0",                "iso-8859-15"   },  /* this is not a bug */
 
  { "iso_8859-16",           "iso-8859-16"   },
  { "latin10",               "iso-8859-16"   },  /* this is not a bug */
 
  { "646",                   "us-ascii"      },
 
  /* http://www.sun.com/software/white-papers/wp-unicode/ */
 
  { "eucJP",                 "euc-jp"        },
  { "PCK",                   "Shift_JIS"     },
  { "ko_KR-euc",             "euc-kr"        },
  { "zh_TW-big5",            "big5"          },
 
  /* seems to be common on some systems */
 
  { "sjis",                  "Shift_JIS"     },
  { "euc-jp-ms",             "eucJP-ms"      },
 
  /* If you happen to encounter system-specific brain-damage with respect to
   * character set naming, please add it above this comment, and submit a patch
   * to <neomutt-devel@neomutt.org> */
 
  { NULL, NULL },
  // clang-format on
};
 
static struct Lookup *lookup_new(void)
{
  return mutt_mem_calloc(1, sizeof(struct Lookup));
}
 
static void lookup_free(struct Lookup **ptr)
{
  if (!ptr || !*ptr)
    return;
 
  struct Lookup *l = *ptr;
  FREE(&l->replacement);
  FREE(&l->regex.pattern);
  if (l->regex.regex)
    regfree(l->regex.regex);
  FREE(&l->regex.regex);
  FREE(&l->regex);
 
  FREE(ptr);
}
 
static const char *lookup_charset(enum LookupType type, const char *cs)
{
  if (!cs)
    return NULL;
 
  struct Lookup *l = NULL;
 
  TAILQ_FOREACH(l, &Lookups, entries)
  {
    if (l->type != type)
      continue;
    if (mutt_regex_match(&l->regex, cs))
      return l->replacement;
  }
  return NULL;
}
 
int mutt_ch_convert_nonmime_string(char **ps)
{
  if (!ps)
    return -1;
 
  char *u = *ps;
  const size_t ulen = mutt_str_len(u);
  if (ulen == 0)
    return 0;
 
  const struct Slist *const c_assumed_charset = cs_subset_slist(NeoMutt->sub, "assumed_charset");
  const char *const c_charset = cs_subset_string(NeoMutt->sub, "charset");
  const struct ListNode *np = NULL;
  STAILQ_FOREACH(np, &c_assumed_charset->head, entries)
  {
    char const *c = np->data;
    size_t n = mutt_str_len(c);
    char *fromcode = mutt_mem_malloc(n + 1);
    mutt_str_copy(fromcode, c, n + 1);
    char *s = mutt_strn_dup(u, ulen);
    int m = mutt_ch_convert_string(&s, fromcode, c_charset, MUTT_ICONV_NO_FLAGS);
    FREE(&fromcode);
    if (m == 0)
    {
      FREE(ps);
      *ps = s;
      return 0;
    }
    FREE(&s);
  }
  mutt_ch_convert_string(ps, (const char *) mutt_ch_get_default_charset(),
                         c_charset, MUTT_ICONV_HOOK_FROM);
  return -1;
}
 
void mutt_ch_canonical_charset(char *buf, size_t buflen, const char *name)
{
  if (!buf || !name)
    return;
 
  char in[1024], scratch[1024 + 10];
 
  mutt_str_copy(in, name, sizeof(in));
  char *ext = strchr(in, '/');
  if (ext)
    *ext++ = '\0';
 
  if (mutt_istr_equal(in, "utf-8") || mutt_istr_equal(in, "utf8"))
  {
    mutt_str_copy(buf, "utf-8", buflen);
    goto out;
  }
 
  /* catch some common iso-8859-something misspellings */
  size_t plen;
  if ((plen = mutt_istr_startswith(in, "8859")) && (in[plen] != '-'))
    snprintf(scratch, sizeof(scratch), "iso-8859-%s", in + plen);
  else if ((plen = mutt_istr_startswith(in, "8859-")))
    snprintf(scratch, sizeof(scratch), "iso-8859-%s", in + plen);
  else if ((plen = mutt_istr_startswith(in, "iso8859")) && (in[plen] != '-'))
    snprintf(scratch, sizeof(scratch), "iso_8859-%s", in + plen);
  else if ((plen = mutt_istr_startswith(in, "iso8859-")))
    snprintf(scratch, sizeof(scratch), "iso_8859-%s", in + plen);
  else
    mutt_str_copy(scratch, in, sizeof(scratch));
 
  for (size_t i = 0; PreferredMimeNames[i].key; i++)
  {
    if (mutt_istr_equal(scratch, PreferredMimeNames[i].key))
    {
      mutt_str_copy(buf, PreferredMimeNames[i].pref, buflen);
      goto out;
    }
  }
 
  mutt_str_copy(buf, scratch, buflen);
 
  /* for cosmetics' sake, transform to lowercase. */
  for (char *p = buf; *p; p++)
    *p = tolower(*p);
 
out:
  if (ext && *ext)
  {
    mutt_str_cat(buf, buflen, "/");
    mutt_str_cat(buf, buflen, ext);
  }
}
 
bool mutt_ch_chscmp(const char *cs1, const char *cs2)
{
  if (!cs1 || !cs2)
    return false;
 
  char buf[256] = { 0 };
 
  mutt_ch_canonical_charset(buf, sizeof(buf), cs1);
 
  int len1 = mutt_str_len(buf);
  int len2 = mutt_str_len(cs2);
 
  return mutt_istrn_equal(((len1 > len2) ? buf : cs2),
                          ((len1 > len2) ? cs2 : buf), MIN(len1, len2));
}
 
char *mutt_ch_get_default_charset(void)
{
  static char fcharset[128];
  const char *c = NULL;
  const struct Slist *const c_assumed_charset = cs_subset_slist(NeoMutt->sub, "assumed_charset");
 
  if (c_assumed_charset && (c_assumed_charset->count > 0))
    c = STAILQ_FIRST(&c_assumed_charset->head)->data;
  else
    c = "us-ascii";
 
  mutt_str_copy(fcharset, c, sizeof(fcharset));
  return fcharset;
}
 
char *mutt_ch_get_langinfo_charset(void)
{
  char buf[1024] = { 0 };
 
  mutt_ch_canonical_charset(buf, sizeof(buf), nl_langinfo(CODESET));
 
  if (buf[0] != '\0')
    return mutt_str_dup(buf);
 
  return mutt_str_dup("iso-8859-1");
}
 
bool mutt_ch_lookup_add(enum LookupType type, const char *pat,
                        const char *replace, struct Buffer *err)
{
  if (!pat || !replace)
    return false;
 
  regex_t *rx = mutt_mem_calloc(1, sizeof(regex_t));
  int rc = REG_COMP(rx, pat, REG_ICASE);
  if (rc != 0)
  {
    regerror(rc, rx, err->data, err->dsize);
    FREE(&rx);
    return false;
  }
 
  struct Lookup *l = lookup_new();
  l->type = type;
  l->replacement = mutt_str_dup(replace);
  l->regex.pattern = mutt_str_dup(pat);
  l->regex.regex = rx;
  l->regex.pat_not = false;
 
  TAILQ_INSERT_TAIL(&Lookups, l, entries);
 
  return true;
}
 
void mutt_ch_lookup_remove(void)
{
  struct Lookup *l = NULL;
  struct Lookup *tmp = NULL;
 
  TAILQ_FOREACH_SAFE(l, &Lookups, entries, tmp)
  {
    TAILQ_REMOVE(&Lookups, l, entries);
    lookup_free(&l);
  }
}
 
const char *mutt_ch_charset_lookup(const char *chs)
{
  return lookup_charset(MUTT_LOOKUP_CHARSET, chs);
}
 
iconv_t mutt_ch_iconv_open(const char *tocode, const char *fromcode, uint8_t flags)
{
  char tocode1[128];
  char fromcode1[128];
  const char *tocode2 = NULL, *fromcode2 = NULL;
  const char *tmp = NULL;
 
  iconv_t cd;
 
  /* transform to MIME preferred charset names */
  mutt_ch_canonical_charset(tocode1, sizeof(tocode1), tocode);
  mutt_ch_canonical_charset(fromcode1, sizeof(fromcode1), fromcode);
 
  /* maybe apply charset-hooks and recanonicalise fromcode,
   * but only when caller asked us to sanitize a potentially wrong
   * charset name incoming from the wild exterior. */
  if (flags & MUTT_ICONV_HOOK_FROM)
  {
    tmp = mutt_ch_charset_lookup(fromcode1);
    if (tmp)
      mutt_ch_canonical_charset(fromcode1, sizeof(fromcode1), tmp);
  }
 
  /* always apply iconv-hooks to suit system's iconv tastes */
  tocode2 = mutt_ch_iconv_lookup(tocode1);
  tocode2 = tocode2 ? tocode2 : tocode1;
  fromcode2 = mutt_ch_iconv_lookup(fromcode1);
  fromcode2 = fromcode2 ? fromcode2 : fromcode1;
 
  /* call system iconv with names it appreciates */
  cd = iconv_open(tocode2, fromcode2);
  if (cd != (iconv_t) -1)
    return cd;
 
  return (iconv_t) -1;
}
 
size_t mutt_ch_iconv(iconv_t cd, const char **inbuf, size_t *inbytesleft,
                     char **outbuf, size_t *outbytesleft, const char **inrepls,
                     const char *outrepl, int *iconverrno)
{
  size_t rc = 0;
  const char *ib = *inbuf;
  size_t ibl = *inbytesleft;
  char *ob = *outbuf;
  size_t obl = *outbytesleft;
 
  while (true)
  {
    errno = 0;
    const size_t ret1 = iconv(cd, (ICONV_CONST char **) &ib, &ibl, &ob, &obl);
    if (ret1 != (size_t) -1)
      rc += ret1;
    if (iconverrno)
      *iconverrno = errno;
 
    if (ibl && obl && (errno == EILSEQ))
    {
      if (inrepls)
      {
        /* Try replacing the input */
        const char **t = NULL;
        for (t = inrepls; *t; t++)
        {
          const char *ib1 = *t;
          size_t ibl1 = strlen(*t);
          char *ob1 = ob;
          size_t obl1 = obl;
          iconv(cd, (ICONV_CONST char **) &ib1, &ibl1, &ob1, &obl1);
          if (ibl1 == 0)
          {
            ib++;
            ibl--;
            ob = ob1;
            obl = obl1;
            rc++;
            break;
          }
        }
        if (*t)
          continue;
      }
      /* Replace the output */
      if (!outrepl)
        outrepl = "?";
      iconv(cd, NULL, NULL, &ob, &obl);
      if (obl)
      {
        int n = strlen(outrepl);
        if (n > obl)
        {
          outrepl = "?";
          n = 1;
        }
        memcpy(ob, outrepl, n);
        ib++;
        ibl--;
        ob += n;
        obl -= n;
        rc++;
        iconv(cd, NULL, NULL, NULL, NULL); /* for good measure */
        continue;
      }
    }
    *inbuf = ib;
    *inbytesleft = ibl;
    *outbuf = ob;
    *outbytesleft = obl;
    return rc;
  }
}
 
const char *mutt_ch_iconv_lookup(const char *chs)
{
  return lookup_charset(MUTT_LOOKUP_ICONV, chs);
}
 
int mutt_ch_check(const char *s, size_t slen, const char *from, const char *to)
{
  if (!s || !from || !to)
    return -1;
 
  int rc = 0;
  iconv_t cd = mutt_ch_iconv_open(to, from, MUTT_ICONV_NO_FLAGS);
  if (cd == (iconv_t) -1)
    return -1;
 
  size_t outlen = MB_LEN_MAX * slen;
  char *out = mutt_mem_malloc(outlen + 1);
  char *saved_out = out;
 
  const size_t convlen = iconv(cd, (ICONV_CONST char **) &s, &slen, &out, &outlen);
  if (convlen == (size_t) -1)
    rc = errno;
 
  FREE(&saved_out);
  iconv_close(cd);
  return rc;
}
 
int mutt_ch_convert_string(char **ps, const char *from, const char *to, uint8_t flags)
{
  if (!ps)
    return -1;
 
  char *s = *ps;
 
  if (!s || (*s == '\0'))
    return 0;
 
  if (!to || !from)
    return -1;
 
  const char *repls[] = { "\357\277\275", "?", 0 };
  int rc = 0;
 
  iconv_t cd = mutt_ch_iconv_open(to, from, flags);
  if (cd == (iconv_t) -1)
    return -1;
 
  const char **inrepls = NULL;
  const char *outrepl = NULL;
 
  if (mutt_ch_is_utf8(to))
    outrepl = "\357\277\275";
  else if (mutt_ch_is_utf8(from))
    inrepls = repls;
  else
    outrepl = "?";
 
  const char *ib = s;
  size_t ibl = strlen(s);
  if (ibl >= (SIZE_MAX / MB_LEN_MAX))
  {
    iconv_close(cd);
    return -1;
  }
  size_t obl = MB_LEN_MAX * ibl;
  char *buf = mutt_mem_malloc(obl + 1);
  char *ob = buf;
 
  mutt_ch_iconv(cd, &ib, &ibl, &ob, &obl, inrepls, outrepl, &rc);
  iconv(cd, 0, 0, &ob, &obl);
  iconv_close(cd);
 
  *ob = '\0';
 
  FREE(ps);
  *ps = buf;
 
  mutt_str_adjust(ps);
  return rc;
}
 
bool mutt_ch_check_charset(const char *cs, bool strict)
{
  if (!cs)
    return false;
 
  if (mutt_ch_is_utf8(cs))
    return true;
 
  if (!strict)
  {
    for (int i = 0; PreferredMimeNames[i].key; i++)
    {
      if (mutt_istr_equal(PreferredMimeNames[i].key, cs) ||
          mutt_istr_equal(PreferredMimeNames[i].pref, cs))
      {
        return true;
      }
    }
  }
 
  iconv_t cd = mutt_ch_iconv_open(cs, cs, MUTT_ICONV_NO_FLAGS);
  if (cd != (iconv_t) (-1))
  {
    iconv_close(cd);
    return true;
  }
 
  return false;
}
 
struct FgetConv *mutt_ch_fgetconv_open(FILE *fp, const char *from, const char *to, uint8_t flags)
{
  struct FgetConv *fc = NULL;
  iconv_t cd = (iconv_t) -1;
 
  if (from && to)
    cd = mutt_ch_iconv_open(to, from, flags);
 
  if (cd != (iconv_t) -1)
  {
    static const char *repls[] = { "\357\277\275", "?", 0 };
 
    fc = mutt_mem_malloc(sizeof(struct FgetConv));
    fc->p = fc->bufo;
    fc->ob = fc->bufo;
    fc->ib = fc->bufi;
    fc->ibl = 0;
    fc->inrepls = mutt_ch_is_utf8(to) ? repls : repls + 1;
  }
  else
    fc = mutt_mem_malloc(sizeof(struct FgetConvNot));
  fc->fp = fp;
  fc->cd = cd;
  return fc;
}
 
void mutt_ch_fgetconv_close(struct FgetConv **fc)
{
  if (!fc || !*fc)
    return;
 
  if ((*fc)->cd != (iconv_t) -1)
    iconv_close((*fc)->cd);
  FREE(fc);
}
 
int mutt_ch_fgetconv(struct FgetConv *fc)
{
  if (!fc)
    return EOF;
  if (fc->cd == (iconv_t) -1)
    return fgetc(fc->fp);
  if (!fc->p)
    return EOF;
  if (fc->p < fc->ob)
    return (unsigned char) *(fc->p)++;
 
  /* Try to convert some more */
  fc->p = fc->bufo;
  fc->ob = fc->bufo;
  if (fc->ibl)
  {
    size_t obl = sizeof(fc->bufo);
    iconv(fc->cd, (ICONV_CONST char **) &fc->ib, &fc->ibl, &fc->ob, &obl);
    if (fc->p < fc->ob)
      return (unsigned char) *(fc->p)++;
  }
 
  /* If we trusted iconv a bit more, we would at this point
   * ask why it had stopped converting ... */
 
  /* Try to read some more */
  if ((fc->ibl == sizeof(fc->bufi)) ||
      (fc->ibl && (fc->ib + fc->ibl < fc->bufi + sizeof(fc->bufi))))
  {
    fc->p = 0;
    return EOF;
  }
  if (fc->ibl)
    memcpy(fc->bufi, fc->ib, fc->ibl);
  fc->ib = fc->bufi;
  fc->ibl += fread(fc->ib + fc->ibl, 1, sizeof(fc->bufi) - fc->ibl, fc->fp);
 
  /* Try harder this time to convert some */
  if (fc->ibl)
  {
    size_t obl = sizeof(fc->bufo);
    mutt_ch_iconv(fc->cd, (const char **) &fc->ib, &fc->ibl, &fc->ob, &obl,
                  fc->inrepls, 0, NULL);
    if (fc->p < fc->ob)
      return (unsigned char) *(fc->p)++;
  }
 
  /* Either the file has finished or one of the buffers is too small */
  fc->p = 0;
  return EOF;
}
 
char *mutt_ch_fgetconvs(char *buf, size_t buflen, struct FgetConv *fc)
{
  if (!buf)
    return NULL;
 
  size_t r;
  for (r = 0; (r + 1) < buflen;)
  {
    const int c = mutt_ch_fgetconv(fc);
    if (c == EOF)
      break;
    buf[r++] = (char) c;
    if (c == '\n')
      break;
  }
  buf[r] = '\0';
 
  if (r > 0)
    return buf;
 
  return NULL;
}
 
void mutt_ch_set_charset(const char *charset)
{
  char buf[256] = { 0 };
 
  mutt_ch_canonical_charset(buf, sizeof(buf), charset);
 
  if (mutt_ch_is_utf8(buf))
  {
    CharsetIsUtf8 = true;
    ReplacementChar = 0xfffd; /* replacement character */
  }
  else
  {
    CharsetIsUtf8 = false;
    ReplacementChar = '?';
  }
 
#if defined(HAVE_BIND_TEXTDOMAIN_CODESET) && defined(ENABLE_NLS)
  bind_textdomain_codeset(PACKAGE, buf);
#endif
}
 
char *mutt_ch_choose(const char *fromcode, const struct Slist *charsets,
                     const char *u, size_t ulen, char **d, size_t *dlen)
{
  if (!fromcode || !charsets)
    return NULL;
 
  char *e = NULL, *tocode = NULL;
  size_t elen = 0, bestn = 0;
 
  const struct ListNode *np = NULL;
  STAILQ_FOREACH(np, &charsets->head, entries)
  {
    char *t = mutt_str_dup(np->data);
    if (!t)
      continue;
 
    size_t n = mutt_str_len(t);
    char *s = mutt_strn_dup(u, ulen);
    const int rc = d ? mutt_ch_convert_string(&s, fromcode, t, MUTT_ICONV_NO_FLAGS) :
                       mutt_ch_check(s, ulen, fromcode, t);
    if (rc)
    {
      FREE(&t);
      FREE(&s);
      continue;
    }
    size_t slen = mutt_str_len(s);
 
    if (!tocode || (n < bestn))
    {
      bestn = n;
      FREE(&tocode);
      tocode = t;
      if (d)
      {
        FREE(&e);
        e = s;
      }
      else
        FREE(&s);
      elen = slen;
    }
    else
    {
      FREE(&t);
      FREE(&s);
    }
  }
  if (tocode)
  {
    if (d)
      *d = e;
    if (dlen)
      *dlen = elen;
 
    char canonical_buf[1024] = { 0 };
    mutt_ch_canonical_charset(canonical_buf, sizeof(canonical_buf), tocode);
    mutt_str_replace(&tocode, canonical_buf);
  }
  return tocode;
}