/*
 * ProFTPD - mod_proxy SSH UTF8 encoding
 * Copyright (c) 2021 TJ Saunders
 *
 * 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 2 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, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA 02110-1335, USA.
 *
 * As a special exemption, TJ Saunders and other respective copyright holders
 * give permission to link this program with OpenSSL, and distribute the
 * resulting executable, without including the source code for OpenSSL in the
 * source distribution.
 */

#include "mod_proxy.h"
#include "proxy/ssh/utf8.h"

#if defined(HAVE_ICONV_H)
# include <iconv.h>
#endif

#if defined(HAVE_LANGINFO_H)
# include <langinfo.h>
#endif

static const char *local_charset = NULL;
static const char *trace_channel = "proxy.ssh.utf8";

#if defined(PR_USE_NLS) && defined(HAVE_ICONV_H)
static iconv_t decode_conv = (iconv_t) -1;
static iconv_t encode_conv = (iconv_t) -1;

static int utf8_convert(iconv_t conv, const char *inbuf, size_t *inbuflen,
    char *outbuf, size_t *outbuflen) {
# ifdef HAVE_ICONV

  /* Reset the state machine before each conversion. */
  (void) iconv(conv, NULL, NULL, NULL, NULL);

  while (*inbuflen > 0) {
    size_t nconv;

    pr_signals_handle();

    /* Solaris/FreeBSD's iconv(3) takes a const char ** for the input buffer,
     * whereas Linux/Mac OSX iconv(3) use char ** for the input buffer.
     */
#if defined(LINUX) || defined(DARWIN6) || defined(DARWIN7) || \
    defined(DARWIN8) || defined(DARWIN9) || defined(DARWIN10) || \
    defined(DARWIN11) || defined(DARWIN12)

    nconv = iconv(conv, (char **) &inbuf, inbuflen, &outbuf, outbuflen);
#else
    nconv = iconv(conv, &inbuf, inbuflen, &outbuf, outbuflen);
#endif

    if (nconv == (size_t) -1) {

      /* Note: an errno of EILSEQ here can indicate badly encoded strings OR
       * (more likely) that the source character set used in the iconv_open(3)
       * call for this iconv_t descriptor does not accurately describe the
       * character encoding of the given string.  E.g. a filename may use
       * the ISO8859-1 character set, but iconv_open(3) was called using
       * US-ASCII.
       */

      return -1;
    }

    /* XXX We should let the loop condition work, rather than breaking out
     * of the loop here.
     */
    break;
  }

  return 0;

# else
  errno = ENOSYS;
  return -1;
# endif /* HAVE_ICONV */
}
#endif /* !PR_USE_NLS && !HAVE_ICONV_H */

#if defined(PR_USE_OPENSSL)
int proxy_ssh_utf8_set_charset(const char *charset) {
  int res;

  if (charset == NULL) {
    errno = EINVAL;
    return -1;
  }

  if (local_charset) {
    pr_trace_msg(trace_channel, 5,
      "attempting to switch local charset from %s to %s", local_charset,
      charset);

  } else {
    pr_trace_msg(trace_channel, 5, "attempting to use %s as local charset",
      charset);
  }

  (void) proxy_ssh_utf8_free();

  local_charset = pstrdup(permanent_pool, charset);

  res = proxy_ssh_utf8_init();
  if (res < 0) {
    pr_trace_msg(trace_channel, 1,
      "failed to initialize encoding for local charset %s", charset);
    local_charset = NULL;
    return -1;
  }

  return res;
}

int proxy_ssh_utf8_free(void) {
# if defined(PR_USE_NLS) && defined(HAVE_ICONV)
  int res = 0;

  /* Close the iconv handles. */
  if (encode_conv != (iconv_t) -1) {
    res = iconv_close(encode_conv);
    if (res < 0) {
      pr_trace_msg(trace_channel, 1,
        "error closing encoding conversion handle from '%s' to '%s': %s",
          local_charset, "UTF-8", strerror(errno));
      res = -1;
    }

    encode_conv = (iconv_t) -1;
  }

  if (decode_conv != (iconv_t) -1) {
    res = iconv_close(decode_conv);
    if (res < 0) {
      pr_trace_msg(trace_channel, 1,
        "error closing decoding conversion handle from '%s' to '%s': %s",
          "UTF-8", local_charset, strerror(errno));
      res = -1;
    }

    decode_conv = (iconv_t) -1;
  }

  return res;
# else
  errno = ENOSYS;
  return -1;
# endif
}

int proxy_ssh_utf8_init(void) {
#if defined(PR_USE_NLS) && defined(HAVE_ICONV)

  if (local_charset == NULL) {
    local_charset = pr_encode_get_local_charset();

  } else {
    pr_trace_msg(trace_channel, 3,
      "using '%s' as local charset for UTF8 conversion", local_charset);
  }

  /* Get the iconv handles. */
  encode_conv = iconv_open("UTF-8", local_charset);
  if (encode_conv == (iconv_t) -1) {
    pr_trace_msg(trace_channel, 1, "error opening conversion handle from '%s' "
      "to '%s': %s", local_charset, "UTF-8", strerror(errno));
    return -1;
  }

  decode_conv = iconv_open(local_charset, "UTF-8");
  if (decode_conv == (iconv_t) -1) {
    int xerrno = errno;

    pr_trace_msg(trace_channel, 1, "error opening conversion handle from '%s' "
      "to '%s': %s", "UTF-8", local_charset, strerror(errno));

    (void) iconv_close(encode_conv);
    encode_conv = (iconv_t) -1;

    errno = xerrno;
    return -1;
  }

  return 0;
# else
  errno = ENOSYS;
  return -1;
#endif /* HAVE_ICONV */
}

char *proxy_ssh_utf8_decode_text(pool *p, const char *text) {
#if defined(PR_USE_NLS) && defined(HAVE_ICONV_H)
  size_t inlen, inbuflen, outlen, outbuflen;
  char *inbuf, outbuf[PR_TUNABLE_PATH_MAX*2], *res = NULL;

  if (p == NULL ||
      text == NULL) {
    errno = EINVAL;
    return NULL;
  }

  if (decode_conv == (iconv_t) -1) {
    pr_trace_msg(trace_channel, 1,
      "decoding conversion handle is invalid, unable to decode UTF8 text");
    return (char *) text;
  }

  /* If the local charset matches the remote charset (i.e. local_charset is
   * "UTF-8"), then there's no point in converting; the charsets are the
   * same.  Indeed, on some libiconv implementations, attempting to
   * convert between the same charsets results in a tightly spinning CPU
   * (see Bug#3272).
   */
  if (strcasecmp(local_charset, "UTF-8") == 0) {
    return (char *) text;
  }

  inlen = strlen(text) + 1;
  inbuf = pcalloc(p, inlen);
  memcpy(inbuf, text, inlen);
  inbuflen = inlen;

  outbuflen = sizeof(outbuf);

  if (utf8_convert(decode_conv, inbuf, &inbuflen, outbuf, &outbuflen) < 0) {
    pr_trace_msg(trace_channel, 1, "error decoding text: %s", strerror(errno));

    if (pr_trace_get_level(trace_channel) >= 14) {
      /* Write out the text we tried (and failed) to decode, in hex. */
      register unsigned int i;
      unsigned char *raw_text;
      size_t len, raw_len;

      len = strlen(text);
      raw_len = (len * 5) + 1;
      raw_text = pcalloc(p, raw_len + 1);

      for (i = 0; i < len; i++) {
        pr_snprintf((char *) (raw_text + (i * 5)), (raw_len - 1) - (i * 5),
          "0x%02x ", (unsigned char) text[i]);
      }

      pr_trace_msg(trace_channel, 14, "unable to decode text (raw bytes): %s",
        raw_text);
    }

    return (char *) text;
  }

  outlen = sizeof(outbuf) - outbuflen;
  res = pcalloc(p, outlen);
  memcpy(res, outbuf, outlen);

  return res;
#else
  return pstrdup(p, text);
#endif /* !PR_USE_NLS && !HAVE_ICONV_H */
}

char *proxy_ssh_utf8_encode_text(pool *p, const char *text) {
#if defined(PR_USE_NLS) && defined(HAVE_ICONV_H)
  size_t inlen, inbuflen, outlen, outbuflen;
  char *inbuf, outbuf[PR_TUNABLE_PATH_MAX*2], *res;

  if (p == NULL ||
      text == NULL) {
    errno = EINVAL;
    return NULL;
  }

  if (encode_conv == (iconv_t) -1) {
    pr_trace_msg(trace_channel, 1,
      "encoding conversion handle is invalid, unable to encode UTF8 text");
    return (char *) text;
  }

  inlen = strlen(text) + 1;
  inbuf = pcalloc(p, inlen);
  memcpy(inbuf, text, inlen);
  inbuflen = inlen;

  outbuflen = sizeof(outbuf);

  if (utf8_convert(encode_conv, inbuf, &inbuflen, outbuf, &outbuflen) < 0) {
    pr_trace_msg(trace_channel, 1, "error encoding text: %s", strerror(errno));

    if (pr_trace_get_level(trace_channel) >= 14) {
      /* Write out the text we tried (and failed) to encode, in hex. */
      register unsigned int i;
      unsigned char *raw_text;
      size_t len, raw_len;

      len = strlen(text);
      raw_len = (len * 5) + 1;
      raw_text = pcalloc(p, raw_len + 1);

      for (i = 0; i < len; i++) {
        pr_snprintf((char *) (raw_text + (i * 5)), (raw_len - 1) - (i * 5),
          "0x%02x ", (unsigned char) text[i]);
      }

      pr_trace_msg(trace_channel, 14, "unable to encode text (raw bytes): %s",
        raw_text);
    }

    return (char *) text;
  }

  outlen = sizeof(outbuf) - outbuflen;
  res = pcalloc(p, outlen);
  memcpy(res, outbuf, outlen);

  return res;
#else
  return pstrdup(p, text);
#endif /* !PR_USE_NLS && !HAVE_ICONV_H */
}
#endif /* PR_USE_OPENSSL */