source: trunk/server/lib/util/charset/iconv.c

/* 
   Unix SMB/CIFS implementation.
   minimal iconv implementation
   Copyright (C) Andrew Tridgell 2001
   Copyright (C) Jelmer Vernooij 2002
   
   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 "includes.h"
#include "../lib/util/dlinklist.h"
#include "system/iconv.h"
#include "system/filesys.h"

#ifdef strcasecmp
#undef strcasecmp
#endif

#ifdef static_decl_charset
static_decl_charset;
#endif

/**
 * @file
 *
 * @brief Samba wrapper/stub for iconv character set conversion.
 *
 * iconv is the XPG2 interface for converting between character
 * encodings.  This file provides a Samba wrapper around it, and also
 * a simple reimplementation that is used if the system does not
 * implement iconv.
 *
 * Samba only works with encodings that are supersets of ASCII: ascii
 * characters like whitespace can be tested for directly, multibyte
 * sequences start with a byte with the high bit set, and strings are
 * terminated by a nul byte.
 *
 * Note that the only function provided by iconv is conversion between
 * characters.  It doesn't directly support operations like
 * uppercasing or comparison.  We have to convert to UTF-16LE and
 * compare there.
 *
 * @sa Samba Developers Guide
 **/

static size_t ascii_pull  (void *,const char **, size_t *, char **, size_t *);
static size_t ascii_push  (void *,const char **, size_t *, char **, size_t *);
static size_t latin1_push(void *,const char **, size_t *, char **, size_t *);
static size_t utf8_pull   (void *,const char **, size_t *, char **, size_t *);
static size_t utf8_push   (void *,const char **, size_t *, char **, size_t *);
static size_t utf16_munged_pull(void *,const char **, size_t *, char **, size_t *);
static size_t ucs2hex_pull(void *,const char **, size_t *, char **, size_t *);
static size_t ucs2hex_push(void *,const char **, size_t *, char **, size_t *);
static size_t iconv_copy  (void *,const char **, size_t *, char **, size_t *);
static size_t iconv_swab  (void *,const char **, size_t *, char **, size_t *);

static const struct charset_functions builtin_functions[] = {
        /* windows is closest to UTF-16 */
        {"UCS-2LE",  iconv_copy, iconv_copy},
        {"UTF-16LE",  iconv_copy, iconv_copy},
        {"UCS-2BE",  iconv_swab, iconv_swab},
        {"UTF-16BE",  iconv_swab, iconv_swab},

        /* we include the UTF-8 alias to cope with differing locale settings */
        {"UTF8",   utf8_pull,  utf8_push},
        {"UTF-8",   utf8_pull,  utf8_push},

        /* this handles the munging needed for String2Key */
        {"UTF16_MUNGED",   utf16_munged_pull,  iconv_copy},

        {"ASCII", ascii_pull, ascii_push},
        {"646", ascii_pull, ascii_push},
        {"ISO-8859-1", ascii_pull, latin1_push},
        {"UCS2-HEX", ucs2hex_pull, ucs2hex_push}
};

static struct charset_functions *charsets = NULL;

static struct charset_functions *find_charset_functions(const char *name)
{
        struct charset_functions *c;

        /* Check whether we already have this charset... */
        for (c = charsets; c != NULL; c = c->next) {
                if(strcasecmp(c->name, name) == 0) { 
                        return c;
                }
        }

        return NULL;
}

bool smb_register_charset(const struct charset_functions *funcs_in)
{
        struct charset_functions *funcs;

        DEBUG(5, ("Attempting to register new charset %s\n", funcs_in->name));
        /* Check whether we already have this charset... */
        if (find_charset_functions(funcs_in->name)) {
                DEBUG(0, ("Duplicate charset %s, not registering\n", funcs_in->name));
                return false;
        }

        funcs = talloc(NULL, struct charset_functions);
        if (!funcs) {
                DEBUG(0, ("Out of memory duplicating charset %s\n", funcs_in->name));
                return false;
        }
        *funcs = *funcs_in;

        funcs->next = funcs->prev = NULL;
        DEBUG(5, ("Registered charset %s\n", funcs->name));
        DLIST_ADD(charsets, funcs);
        return true;
}

static void lazy_initialize_iconv(void)
{
        static bool initialized;

#ifdef static_init_charset
        if (!initialized) {
                static_init_charset;
                initialized = true;
        }
#endif
}

#if defined(__OS2__) && defined(__INNOTEK_LIBC__)
#include <uconv.h>

typedef struct os2_iconv_t
{
    UconvObject from;
} os2_iconv_t;

iconv_t os2_iconv_open (const char *tocode, const char *fromcode)
{
    os2_iconv_t *os2_cd = (os2_iconv_t *)iconv_open(tocode, fromcode);

    if (os2_cd != (iconv_t)(-1))
       {
        /* Assume strings contain pathnames */
        uconv_attribute_t attr;

        UniQueryUconvObject(os2_cd->from, &attr,
                            sizeof(uconv_attribute_t),
                            NULL, NULL, NULL );
        attr.converttype |= CVTTYPE_PATH;
        UniSetUconvObject(os2_cd->from, &attr);
        }

    return (iconv_t)os2_cd;
}

#define iconv_open  os2_iconv_open
#endif

#ifdef HAVE_NATIVE_ICONV
/* if there was an error then reset the internal state,
   this ensures that we don't have a shift state remaining for
   character sets like SJIS */
static size_t sys_iconv(void *cd, 
                        const char **inbuf, size_t *inbytesleft,
                        char **outbuf, size_t *outbytesleft)
{
        size_t ret = iconv((iconv_t)cd, 
                           discard_const_p(char *, inbuf), inbytesleft, 
                           outbuf, outbytesleft);
        if (ret == (size_t)-1) iconv(cd, NULL, NULL, NULL, NULL);
        return ret;
}
#endif

/**
 * This is a simple portable iconv() implementaion.
 *
 * It only knows about a very small number of character sets - just
 * enough that Samba works on systems that don't have iconv.
 **/
_PUBLIC_ size_t smb_iconv(smb_iconv_t cd, 
                 const char **inbuf, size_t *inbytesleft,
                 char **outbuf, size_t *outbytesleft)
{
        char cvtbuf[2048];
        size_t bufsize;

        /* in many cases we can go direct */
        if (cd->direct) {
                return cd->direct(cd->cd_direct, 
                                  inbuf, inbytesleft, outbuf, outbytesleft);
        }


        /* otherwise we have to do it chunks at a time */
        while (*inbytesleft > 0) {
                char *bufp1 = cvtbuf;
                const char *bufp2 = cvtbuf;

                bufsize = sizeof(cvtbuf);
                
                if (cd->pull(cd->cd_pull, 
                             inbuf, inbytesleft, &bufp1, &bufsize) == -1
                    && errno != E2BIG) return -1;

                bufsize = sizeof(cvtbuf) - bufsize;

                if (cd->push(cd->cd_push, 
                             &bufp2, &bufsize, 
                             outbuf, outbytesleft) == -1) return -1;
        }

        return 0;
}

static bool is_utf16(const char *name)
{
        return strcasecmp(name, "UCS-2LE") == 0 ||
                strcasecmp(name, "UTF-16LE") == 0;
}

static int smb_iconv_t_destructor(smb_iconv_t hwd)
{
#ifdef HAVE_NATIVE_ICONV
        if (hwd->cd_pull != NULL && hwd->cd_pull != (iconv_t)-1)
                iconv_close(hwd->cd_pull);
        if (hwd->cd_push != NULL && hwd->cd_push != (iconv_t)-1)
                iconv_close(hwd->cd_push);
        if (hwd->cd_direct != NULL && hwd->cd_direct != (iconv_t)-1)
                iconv_close(hwd->cd_direct);
#endif

        return 0;
}

_PUBLIC_ smb_iconv_t smb_iconv_open_ex(TALLOC_CTX *mem_ctx, const char *tocode, 
                              const char *fromcode, bool native_iconv)
{
        smb_iconv_t ret;
        const struct charset_functions *from=NULL, *to=NULL;
        int i;

        lazy_initialize_iconv();

        ret = (smb_iconv_t)talloc_named(mem_ctx,
                                        sizeof(*ret), 
                                        "iconv(%s,%s)", tocode, fromcode);
        if (!ret) {
                errno = ENOMEM;
                return (smb_iconv_t)-1;
        }
        memset(ret, 0, sizeof(*ret));
        talloc_set_destructor(ret, smb_iconv_t_destructor);

        /* check for the simplest null conversion */
        if (strcmp(fromcode, tocode) == 0) {
                ret->direct = iconv_copy;
                return ret;
        }

        for (i=0;i<ARRAY_SIZE(builtin_functions);i++) {
                if (strcasecmp(fromcode, builtin_functions[i].name) == 0) {
                        from = &builtin_functions[i];
                }
                if (strcasecmp(tocode, builtin_functions[i].name) == 0) {
                        to = &builtin_functions[i];
                }
        }

        if (from == NULL) {
                for (from=charsets; from; from=from->next) {
                        if (strcasecmp(from->name, fromcode) == 0) break;
                }
        }

        if (to == NULL) {
                for (to=charsets; to; to=to->next) {
                        if (strcasecmp(to->name, tocode) == 0) break;
                }
        }

#ifdef HAVE_NATIVE_ICONV
        if ((!from || !to) && !native_iconv) {
                goto failed;
        }
        if (!from) {
                ret->pull = sys_iconv;
                ret->cd_pull = iconv_open("UTF-16LE", fromcode);
                if (ret->cd_pull == (iconv_t)-1)
                        ret->cd_pull = iconv_open("UCS-2LE", fromcode);
                if (ret->cd_pull == (iconv_t)-1) goto failed;
        }

        if (!to) {
                ret->push = sys_iconv;
                ret->cd_push = iconv_open(tocode, "UTF-16LE");
                if (ret->cd_push == (iconv_t)-1)
                        ret->cd_push = iconv_open(tocode, "UCS-2LE");
                if (ret->cd_push == (iconv_t)-1) goto failed;
        }
#else
        if (!from || !to) {
                goto failed;
        }
#endif

        /* check for conversion to/from ucs2 */
        if (is_utf16(fromcode) && to) {
                ret->direct = to->push;
                return ret;
        }
        if (is_utf16(tocode) && from) {
                ret->direct = from->pull;
                return ret;
        }

#ifdef HAVE_NATIVE_ICONV
        if (is_utf16(fromcode)) {
                ret->direct = sys_iconv;
                ret->cd_direct = ret->cd_push;
                ret->cd_push = NULL;
                return ret;
        }
        if (is_utf16(tocode)) {
                ret->direct = sys_iconv;
                ret->cd_direct = ret->cd_pull;
                ret->cd_pull = NULL;
                return ret;
        }
#endif

        /* the general case has to go via a buffer */
        if (!ret->pull) ret->pull = from->pull;
        if (!ret->push) ret->push = to->push;
        return ret;

failed:
        talloc_free(ret);
        errno = EINVAL;
        return (smb_iconv_t)-1;
}

/*
  simple iconv_open() wrapper
 */
_PUBLIC_ smb_iconv_t smb_iconv_open(const char *tocode, const char *fromcode)
{
        return smb_iconv_open_ex(NULL, tocode, fromcode, true);
}

/*
  simple iconv_close() wrapper
*/
_PUBLIC_ int smb_iconv_close(smb_iconv_t cd)
{
        talloc_free(cd);
        return 0;
}


/**********************************************************************
 the following functions implement the builtin character sets in Samba
 and also the "test" character sets that are designed to test
 multi-byte character set support for english users
***********************************************************************/
static size_t ascii_pull(void *cd, const char **inbuf, size_t *inbytesleft,
                         char **outbuf, size_t *outbytesleft)
{
        while (*inbytesleft >= 1 && *outbytesleft >= 2) {
                (*outbuf)[0] = (*inbuf)[0];
                (*outbuf)[1] = 0;
                (*inbytesleft)  -= 1;
                (*outbytesleft) -= 2;
                (*inbuf)  += 1;
                (*outbuf) += 2;
        }

        if (*inbytesleft > 0) {
                errno = E2BIG;
                return -1;
        }
        
        return 0;
}

static size_t ascii_push(void *cd, const char **inbuf, size_t *inbytesleft,
                         char **outbuf, size_t *outbytesleft)
{
        int ir_count=0;

        while (*inbytesleft >= 2 && *outbytesleft >= 1) {
                (*outbuf)[0] = (*inbuf)[0] & 0x7F;
                if ((*inbuf)[1]) ir_count++;
                (*inbytesleft)  -= 2;
                (*outbytesleft) -= 1;
                (*inbuf)  += 2;
                (*outbuf) += 1;
        }

        if (*inbytesleft == 1) {
                errno = EINVAL;
                return -1;
        }

        if (*inbytesleft > 1) {
                errno = E2BIG;
                return -1;
        }
        
        return ir_count;
}

static size_t latin1_push(void *cd, const char **inbuf, size_t *inbytesleft,
                         char **outbuf, size_t *outbytesleft)
{
        int ir_count=0;

        while (*inbytesleft >= 2 && *outbytesleft >= 1) {
                (*outbuf)[0] = (*inbuf)[0];
                if ((*inbuf)[1]) ir_count++;
                (*inbytesleft)  -= 2;
                (*outbytesleft) -= 1;
                (*inbuf)  += 2;
                (*outbuf) += 1;
        }

        if (*inbytesleft == 1) {
                errno = EINVAL;
                return -1;
        }

        if (*inbytesleft > 1) {
                errno = E2BIG;
                return -1;
        }

        return ir_count;
}

static size_t ucs2hex_pull(void *cd, const char **inbuf, size_t *inbytesleft,
                         char **outbuf, size_t *outbytesleft)
{
        while (*inbytesleft >= 1 && *outbytesleft >= 2) {
                unsigned int v;

                if ((*inbuf)[0] != '@') {
                        /* seven bit ascii case */
                        (*outbuf)[0] = (*inbuf)[0];
                        (*outbuf)[1] = 0;
                        (*inbytesleft)  -= 1;
                        (*outbytesleft) -= 2;
                        (*inbuf)  += 1;
                        (*outbuf) += 2;
                        continue;
                }
                /* it's a hex character */
                if (*inbytesleft < 5) {
                        errno = EINVAL;
                        return -1;
                }
                
                if (sscanf(&(*inbuf)[1], "%04x", &v) != 1) {
                        errno = EILSEQ;
                        return -1;
                }

                (*outbuf)[0] = v&0xff;
                (*outbuf)[1] = v>>8;
                (*inbytesleft)  -= 5;
                (*outbytesleft) -= 2;
                (*inbuf)  += 5;
                (*outbuf) += 2;
        }

        if (*inbytesleft > 0) {
                errno = E2BIG;
                return -1;
        }
        
        return 0;
}

static size_t ucs2hex_push(void *cd, const char **inbuf, size_t *inbytesleft,
                           char **outbuf, size_t *outbytesleft)
{
        while (*inbytesleft >= 2 && *outbytesleft >= 1) {
                char buf[6];

                if ((*inbuf)[1] == 0 && 
                    ((*inbuf)[0] & 0x80) == 0 &&
                    (*inbuf)[0] != '@') {
                        (*outbuf)[0] = (*inbuf)[0];
                        (*inbytesleft)  -= 2;
                        (*outbytesleft) -= 1;
                        (*inbuf)  += 2;
                        (*outbuf) += 1;
                        continue;
                }
                if (*outbytesleft < 5) {
                        errno = E2BIG;
                        return -1;
                }
                snprintf(buf, 6, "@%04x", SVAL(*inbuf, 0));
                memcpy(*outbuf, buf, 5);
                (*inbytesleft)  -= 2;
                (*outbytesleft) -= 5;
                (*inbuf)  += 2;
                (*outbuf) += 5;
        }

        if (*inbytesleft == 1) {
                errno = EINVAL;
                return -1;
        }

        if (*inbytesleft > 1) {
                errno = E2BIG;
                return -1;
        }
        
        return 0;
}

static size_t iconv_swab(void *cd, const char **inbuf, size_t *inbytesleft,
                         char **outbuf, size_t *outbytesleft)
{
        int n;

        n = MIN(*inbytesleft, *outbytesleft);

        swab(*inbuf, *outbuf, (n&~1));
        if (n&1) {
                (*outbuf)[n-1] = 0;
        }

        (*inbytesleft) -= n;
        (*outbytesleft) -= n;
        (*inbuf) += n;
        (*outbuf) += n;

        if (*inbytesleft > 0) {
                errno = E2BIG;
                return -1;
        }

        return 0;
}


static size_t iconv_copy(void *cd, const char **inbuf, size_t *inbytesleft,
                         char **outbuf, size_t *outbytesleft)
{
        int n;

        n = MIN(*inbytesleft, *outbytesleft);

        memmove(*outbuf, *inbuf, n);

        (*inbytesleft) -= n;
        (*outbytesleft) -= n;
        (*inbuf) += n;
        (*outbuf) += n;

        if (*inbytesleft > 0) {
                errno = E2BIG;
                return -1;
        }

        return 0;
}

/*
  this takes a UTF8 sequence and produces a UTF16 sequence
 */
static size_t utf8_pull(void *cd, const char **inbuf, size_t *inbytesleft,
                         char **outbuf, size_t *outbytesleft)
{
        size_t in_left=*inbytesleft, out_left=*outbytesleft;
        const uint8_t *c = (const uint8_t *)*inbuf;
        uint8_t *uc = (uint8_t *)*outbuf;

        while (in_left >= 1 && out_left >= 2) {
                if ((c[0] & 0x80) == 0) {
                        uc[0] = c[0];
                        uc[1] = 0;
                        c  += 1;
                        in_left  -= 1;
                        out_left -= 2;
                        uc += 2;
                        continue;
                }

                if ((c[0] & 0xe0) == 0xc0) {
                        if (in_left < 2 ||
                            (c[1] & 0xc0) != 0x80) {
                                errno = EILSEQ;
                                goto error;
                        }
                        uc[1] = (c[0]>>2) & 0x7;
                        uc[0] = (c[0]<<6) | (c[1]&0x3f);
                        c  += 2;
                        in_left  -= 2;
                        out_left -= 2;
                        uc += 2;
                        continue;
                }

                if ((c[0] & 0xf0) == 0xe0) {
                        if (in_left < 3 ||
                            (c[1] & 0xc0) != 0x80 || 
                            (c[2] & 0xc0) != 0x80) {
                                errno = EILSEQ;
                                goto error;
                        }
                        uc[1] = ((c[0]&0xF)<<4) | ((c[1]>>2)&0xF);
                        uc[0] = (c[1]<<6) | (c[2]&0x3f);
                        c  += 3;
                        in_left  -= 3;
                        out_left -= 2;
                        uc += 2;
                        continue;
                }

                if ((c[0] & 0xf8) == 0xf0) {
                        unsigned int codepoint;
                        if (in_left < 4 ||
                            (c[1] & 0xc0) != 0x80 || 
                            (c[2] & 0xc0) != 0x80 ||
                            (c[3] & 0xc0) != 0x80) {
                                errno = EILSEQ;
                                goto error;
                        }
                        codepoint = 
                                (c[3]&0x3f) | 
                                ((c[2]&0x3f)<<6) | 
                                ((c[1]&0x3f)<<12) |
                                ((c[0]&0x7)<<18);
                        if (codepoint < 0x10000) {
                                /* accept UTF-8 characters that are not
                                   minimally packed, but pack the result */
                                uc[0] = (codepoint & 0xFF);
                                uc[1] = (codepoint >> 8);
                                c += 4;
                                in_left -= 4;
                                out_left -= 2;
                                uc += 2;
                                continue;
                        }

                        codepoint -= 0x10000;

                        if (out_left < 4) {
                                errno = E2BIG;
                                goto error;
                        }

                        uc[0] = (codepoint>>10) & 0xFF;
                        uc[1] = (codepoint>>18) | 0xd8;
                        uc[2] = codepoint & 0xFF;
                        uc[3] = ((codepoint>>8) & 0x3) | 0xdc;
                        c  += 4;
                        in_left  -= 4;
                        out_left -= 4;
                        uc += 4;
                        continue;
                }

                /* we don't handle 5 byte sequences */
                errno = EINVAL;
                goto error;
        }

        if (in_left > 0) {
                errno = E2BIG;
                goto error;
        }

        *inbytesleft = in_left;
        *outbytesleft = out_left;
        *inbuf = (const char *)c;
        *outbuf = (char *)uc;
        return 0;

error:
        *inbytesleft = in_left;
        *outbytesleft = out_left;
        *inbuf = (const char *)c;
        *outbuf = (char *)uc;
        return -1;
}


/*
  this takes a UTF16 sequence and produces a UTF8 sequence
 */
static size_t utf8_push(void *cd, const char **inbuf, size_t *inbytesleft,
                        char **outbuf, size_t *outbytesleft)
{
        size_t in_left=*inbytesleft, out_left=*outbytesleft;
        uint8_t *c = (uint8_t *)*outbuf;
        const uint8_t *uc = (const uint8_t *)*inbuf;

        while (in_left >= 2 && out_left >= 1) {
                unsigned int codepoint;

                if (uc[1] == 0 && !(uc[0] & 0x80)) {
                        /* simplest case */
                        c[0] = uc[0];
                        in_left  -= 2;
                        out_left -= 1;
                        uc += 2;
                        c  += 1;
                        continue;
                }

                if ((uc[1]&0xf8) == 0) {
                        /* next simplest case */
                        if (out_left < 2) {
                                errno = E2BIG;
                                goto error;
                        }
                        c[0] = 0xc0 | (uc[0]>>6) | (uc[1]<<2);
                        c[1] = 0x80 | (uc[0] & 0x3f);
                        in_left  -= 2;
                        out_left -= 2;
                        uc += 2;
                        c  += 2;
                        continue;
                }

                if ((uc[1] & 0xfc) == 0xdc) {
                        /* its the second part of a 4 byte sequence. Illegal */
                        if (in_left < 4) {
                                errno = EINVAL;
                        } else {
                                errno = EILSEQ;
                        }
                        goto error;
                }

                if ((uc[1] & 0xfc) != 0xd8) {
                        codepoint = uc[0] | (uc[1]<<8);
                        if (out_left < 3) {
                                errno = E2BIG;
                                goto error;
                        }
                        c[0] = 0xe0 | (codepoint >> 12);
                        c[1] = 0x80 | ((codepoint >> 6) & 0x3f);
                        c[2] = 0x80 | (codepoint & 0x3f);
                        
                        in_left  -= 2;
                        out_left -= 3;
                        uc  += 2;
                        c   += 3;
                        continue;
                }

                /* its the first part of a 4 byte sequence */
                if (in_left < 4) {
                        errno = EINVAL;
                        goto error;
                }
                if ((uc[3] & 0xfc) != 0xdc) {
                        errno = EILSEQ;
                        goto error;
                }
                codepoint = 0x10000 + (uc[2] | ((uc[3] & 0x3)<<8) | 
                                       (uc[0]<<10) | ((uc[1] & 0x3)<<18));
                
                if (out_left < 4) {
                        errno = E2BIG;
                        goto error;
                }
                c[0] = 0xf0 | (codepoint >> 18);
                c[1] = 0x80 | ((codepoint >> 12) & 0x3f);
                c[2] = 0x80 | ((codepoint >> 6) & 0x3f);
                c[3] = 0x80 | (codepoint & 0x3f);
                
                in_left  -= 4;
                out_left -= 4;
                uc       += 4;
                c        += 4;
        }

        if (in_left == 1) {
                errno = EINVAL;
                goto error;
        }

        if (in_left > 1) {
                errno = E2BIG;
                goto error;
        }

        *inbytesleft = in_left;
        *outbytesleft = out_left;
        *inbuf  = (const char *)uc;
        *outbuf = (char *)c;
        
        return 0;

error:
        *inbytesleft = in_left;
        *outbytesleft = out_left;
        *inbuf  = (const char *)uc;
        *outbuf = (char *)c;
        return -1;
}


/*
  this takes a UTF16 munged sequence, modifies it according to the
  string2key rules, and produces a UTF16 sequence

The rules are:

    1) any 0x0000 characters are mapped to 0x0001

    2) convert any instance of 0xD800 - 0xDBFF (high surrogate)
       without an immediately following 0xDC00 - 0x0xDFFF (low surrogate) to
       U+FFFD (OBJECT REPLACEMENT CHARACTER).

    3) the same for any low surrogate that was not preceded by a high surrogate.

 */
static size_t utf16_munged_pull(void *cd, const char **inbuf, size_t *inbytesleft,
                               char **outbuf, size_t *outbytesleft)
{
        size_t in_left=*inbytesleft, out_left=*outbytesleft;
        uint8_t *c = (uint8_t *)*outbuf;
        const uint8_t *uc = (const uint8_t *)*inbuf;

        while (in_left >= 2 && out_left >= 2) {
                unsigned int codepoint = uc[0] | (uc[1]<<8);

                if (codepoint == 0) {
                        codepoint = 1;
                }

                if ((codepoint & 0xfc00) == 0xd800) {
                        /* a high surrogate */
                        unsigned int codepoint2;
                        if (in_left < 4) {
                                codepoint = 0xfffd;
                                goto codepoint16;                               
                        }
                        codepoint2 = uc[2] | (uc[3]<<8);
                        if ((codepoint2 & 0xfc00) != 0xdc00) {
                                /* high surrogate not followed by low
                                   surrogate: convert to 0xfffd */
                                codepoint = 0xfffd;
                                goto codepoint16;
                        }
                        if (out_left < 4) {
                                errno = E2BIG;
                                goto error;
                        }
                        memcpy(c, uc, 4);
                        in_left  -= 4;
                        out_left -= 4;
                        uc       += 4;
                        c        += 4;
                        continue;
                }

                if ((codepoint & 0xfc00) == 0xdc00) {
                        /* low surrogate not preceded by high
                           surrogate: convert to 0xfffd */
                        codepoint = 0xfffd;
                }

        codepoint16:
                c[0] = codepoint & 0xFF;
                c[1] = (codepoint>>8) & 0xFF;
                
                in_left  -= 2;
                out_left -= 2;
                uc  += 2;
                c   += 2;
                continue;               
        }

        if (in_left == 1) {
                errno = EINVAL;
                goto error;
        }

        if (in_left > 1) {
                errno = E2BIG;
                goto error;
        }

        *inbytesleft = in_left;
        *outbytesleft = out_left;
        *inbuf  = (const char *)uc;
        *outbuf = (char *)c;
        
        return 0;

error:
        *inbytesleft = in_left;
        *outbytesleft = out_left;
        *inbuf  = (const char *)uc;
        *outbuf = (char *)c;
        return -1;
}