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path: root/src/microhttpd/postprocessor.c
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/*
     This file is part of libmicrohttpd
     Copyright (C) 2007-2013 Daniel Pittman and Christian Grothoff

     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Lesser General Public
     License as published by the Free Software Foundation; either
     version 2.1 of the License, or (at your option) any later version.

     This library 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
     Lesser General Public License for more details.

     You should have received a copy of the GNU Lesser General Public
     License along with this library; if not, write to the Free Software
     Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
*/

/**
 * @file postprocessor.c
 * @brief  Methods for parsing POST data
 * @author Christian Grothoff
 */

#include "internal.h"
#include "mhd_str.h"
#include "mhd_compat.h"

/**
 * Size of on-stack buffer that we use for un-escaping of the value.
 * We use a pretty small value to be nice to the stack on embedded
 * systems.
 */
#define XBUF_SIZE 512

/**
 * States in the PP parser's state machine.
 */
enum PP_State
{
  /* general states */
  PP_Error,
  PP_Done,
  PP_Init,
  PP_NextBoundary,

  /* url encoding-states */
  PP_ProcessValue,
  PP_ExpectNewLine,

  /* post encoding-states  */
  PP_ProcessEntryHeaders,
  PP_PerformCheckMultipart,
  PP_ProcessValueToBoundary,
  PP_PerformCleanup,

  /* nested post-encoding states */
  PP_Nested_Init,
  PP_Nested_PerformMarking,
  PP_Nested_ProcessEntryHeaders,
  PP_Nested_ProcessValueToBoundary,
  PP_Nested_PerformCleanup

};


enum RN_State
{
  /**
   * No RN-preprocessing in this state.
   */
  RN_Inactive = 0,

  /**
   * If the next character is CR, skip it.  Otherwise,
   * just go inactive.
   */
  RN_OptN = 1,

  /**
   * Expect LFCR (and only LFCR).  As always, we also
   * expect only LF or only CR.
   */
  RN_Full = 2,

  /**
   * Expect either LFCR or '--'LFCR.  If '--'LFCR, transition into dash-state
   * for the main state machine
   */
  RN_Dash = 3,

  /**
   * Got a single dash, expect second dash.
   */
  RN_Dash2 = 4
};


/**
 * Bits for the globally known fields that
 * should not be deleted when we exit the
 * nested state.
 */
enum NE_State
{
  NE_none = 0,
  NE_content_name = 1,
  NE_content_type = 2,
  NE_content_filename = 4,
  NE_content_transfer_encoding = 8
};


/**
 * Internal state of the post-processor.  Note that the fields
 * are sorted by type to enable optimal packing by the compiler.
 */
struct MHD_PostProcessor
{

  /**
   * The connection for which we are doing
   * POST processing.
   */
  struct MHD_Connection *connection;

  /**
   * Function to call with POST data.
   */
  MHD_PostDataIterator ikvi;

  /**
   * Extra argument to ikvi.
   */
  void *cls;

  /**
   * Encoding as given by the headers of the
   * connection.
   */
  const char *encoding;

  /**
   * Primary boundary (points into encoding string)
   */
  const char *boundary;

  /**
   * Nested boundary (if we have multipart/mixed encoding).
   */
  char *nested_boundary;

  /**
   * Pointer to the name given in disposition.
   */
  char *content_name;

  /**
   * Pointer to the (current) content type.
   */
  char *content_type;

  /**
   * Pointer to the (current) filename.
   */
  char *content_filename;

  /**
   * Pointer to the (current) encoding.
   */
  char *content_transfer_encoding;

  /**
   * Unprocessed value bytes due to escape
   * sequences (URL-encoding only).
   */
  char xbuf[8];

  /**
   * Size of our buffer for the key.
   */
  size_t buffer_size;

  /**
   * Current position in the key buffer.
   */
  size_t buffer_pos;

  /**
   * Current position in @e xbuf.
   */
  size_t xbuf_pos;

  /**
   * Current offset in the value being processed.
   */
  uint64_t value_offset;

  /**
   * strlen(boundary) -- if boundary != NULL.
   */
  size_t blen;

  /**
   * strlen(nested_boundary) -- if nested_boundary != NULL.
   */
  size_t nlen;

  /**
   * Do we have to call the 'ikvi' callback when processing the
   * multipart post body even if the size of the payload is zero?
   * Set to #MHD_YES whenever we parse a new multiparty entry header,
   * and to #MHD_NO the first time we call the 'ikvi' callback.
   * Used to ensure that we do always call 'ikvi' even if the
   * payload is empty (but not more than once).
   */
  int must_ikvi;

  /**
   * State of the parser.
   */
  enum PP_State state;

  /**
   * Side-state-machine: skip LRCR (or just LF).
   * Set to 0 if we are not in skip mode.  Set to 2
   * if a LFCR is expected, set to 1 if a CR should
   * be skipped if it is the next character.
   */
  enum RN_State skip_rn;

  /**
   * If we are in skip_rn with "dash" mode and
   * do find 2 dashes, what state do we go into?
   */
  enum PP_State dash_state;

  /**
   * Which headers are global? (used to tell which
   * headers were only valid for the nested multipart).
   */
  enum NE_State have;

};


/**
 * Create a `struct MHD_PostProcessor`.
 *
 * A `struct MHD_PostProcessor` can be used to (incrementally) parse
 * the data portion of a POST request.  Note that some buggy browsers
 * fail to set the encoding type.  If you want to support those, you
 * may have to call #MHD_set_connection_value with the proper encoding
 * type before creating a post processor (if no supported encoding
 * type is set, this function will fail).
 *
 * @param connection the connection on which the POST is
 *        happening (used to determine the POST format)
 * @param buffer_size maximum number of bytes to use for
 *        internal buffering (used only for the parsing,
 *        specifically the parsing of the keys).  A
 *        tiny value (256-1024) should be sufficient.
 *        Do NOT use a value smaller than 256.  For good
 *        performance, use 32 or 64k (i.e. 65536).
 * @param iter iterator to be called with the parsed data,
 *        Must NOT be NULL.
 * @param iter_cls first argument to @a iter
 * @return NULL on error (out of memory, unsupported encoding),
 *         otherwise a PP handle
 * @ingroup request
 */
struct MHD_PostProcessor *
MHD_create_post_processor (struct MHD_Connection *connection,
                           size_t buffer_size,
                           MHD_PostDataIterator iter,
                           void *iter_cls)
{
  struct MHD_PostProcessor *ret;
  const char *encoding;
  const char *boundary;
  size_t blen;

  if ( (buffer_size < 256) ||
       (NULL == connection) ||
       (NULL == iter))
    mhd_panic (mhd_panic_cls,
               __FILE__,
               __LINE__,
               NULL);
  if (MHD_NO == MHD_lookup_connection_value_n (connection,
                                               MHD_HEADER_KIND,
                                               MHD_HTTP_HEADER_CONTENT_TYPE,
                                               MHD_STATICSTR_LEN_ (
                                                 MHD_HTTP_HEADER_CONTENT_TYPE),
                                               &encoding,
                                               NULL))
    return NULL;
  boundary = NULL;
  if (! MHD_str_equal_caseless_n_ (MHD_HTTP_POST_ENCODING_FORM_URLENCODED,
                                   encoding,
                                   MHD_STATICSTR_LEN_ (
                                     MHD_HTTP_POST_ENCODING_FORM_URLENCODED)))
  {
    if (! MHD_str_equal_caseless_n_ (MHD_HTTP_POST_ENCODING_MULTIPART_FORMDATA,
                                     encoding,
                                     MHD_STATICSTR_LEN_ (
                                       MHD_HTTP_POST_ENCODING_MULTIPART_FORMDATA)))
      return NULL;
    boundary =
      &encoding[MHD_STATICSTR_LEN_ (MHD_HTTP_POST_ENCODING_MULTIPART_FORMDATA)];
    /* Q: should this be "strcasestr"? */
    boundary = strstr (boundary, "boundary=");
    if (NULL == boundary)
      return NULL; /* failed to determine boundary */
    boundary += MHD_STATICSTR_LEN_ ("boundary=");
    blen = strlen (boundary);
    if ( (blen == 0) ||
         (blen * 2 + 2 > buffer_size) )
      return NULL;              /* (will be) out of memory or invalid boundary */
    if ( (boundary[0] == '"') &&
         (boundary[blen - 1] == '"') )
    {
      /* remove enclosing quotes */
      ++boundary;
      blen -= 2;
    }
  }
  else
    blen = 0;
  buffer_size += 4; /* round up to get nice block sizes despite boundary search */

  /* add +1 to ensure we ALWAYS have a zero-termination at the end */
  if (NULL == (ret = MHD_calloc_ (1, sizeof (struct MHD_PostProcessor)
                                  + buffer_size + 1)))
    return NULL;
  ret->connection = connection;
  ret->ikvi = iter;
  ret->cls = iter_cls;
  ret->encoding = encoding;
  ret->buffer_size = buffer_size;
  ret->state = PP_Init;
  ret->blen = blen;
  ret->boundary = boundary;
  ret->skip_rn = RN_Inactive;
  return ret;
}


/**
 * Process url-encoded POST data.
 *
 * @param pp post processor context
 * @param post_data upload data
 * @param post_data_len number of bytes in @a post_data
 * @return #MHD_YES on success, #MHD_NO if there was an error processing the data
 */
static int
post_process_urlencoded (struct MHD_PostProcessor *pp,
                         const char *post_data,
                         size_t post_data_len)
{
  size_t equals;
  size_t amper;
  size_t poff;
  size_t xoff;
  size_t delta;
  int end_of_value_found;
  char *buf;
  char xbuf[XBUF_SIZE + 1];

  buf = (char *) &pp[1];
  poff = 0;
  while (poff < post_data_len)
  {
    switch (pp->state)
    {
    case PP_Error:
      return MHD_NO;
    case PP_Done:
      /* did not expect to receive more data */
      pp->state = PP_Error;
      return MHD_NO;
    case PP_Init:
      equals = 0;
      while ((equals + poff < post_data_len) &&
             (post_data[equals + poff] != '='))
        equals++;
      if (equals + pp->buffer_pos > pp->buffer_size)
      {
        pp->state = PP_Error;           /* out of memory */
        return MHD_NO;
      }
      memcpy (&buf[pp->buffer_pos], &post_data[poff], equals);
      pp->buffer_pos += equals;
      if (equals + poff == post_data_len)
        return MHD_YES;         /* no '=' yet */
      buf[pp->buffer_pos] = '\0';       /* 0-terminate key */
      pp->buffer_pos = 0;       /* reset for next key */
      MHD_unescape_plus (buf);
      MHD_http_unescape (buf);
      poff += equals + 1;
      pp->state = PP_ProcessValue;
      pp->value_offset = 0;
      break;
    case PP_ProcessValue:
      /* obtain rest of value from previous iteration */
      memcpy (xbuf, pp->xbuf, pp->xbuf_pos);
      xoff = pp->xbuf_pos;
      pp->xbuf_pos = 0;

      /* find last position in input buffer that is part of the value */
      amper = 0;
      while ((amper + poff < post_data_len) &&
             (amper < XBUF_SIZE) &&
             (post_data[amper + poff] != '&') &&
             (post_data[amper + poff] != '\n') &&
             (post_data[amper + poff] != '\r'))
        amper++;
      end_of_value_found = ((amper + poff < post_data_len) &&
                            ((post_data[amper + poff] == '&') ||
                             (post_data[amper + poff] == '\n') ||
                             (post_data[amper + poff] == '\r')));
      /* compute delta, the maximum number of bytes that we will be able to
         process right now (either amper-limited of xbuf-size limited) */
      delta = amper;
      if (delta > XBUF_SIZE - xoff)
        delta = XBUF_SIZE - xoff;

      /* move input into processing buffer */
      memcpy (&xbuf[xoff], &post_data[poff], delta);
      xoff += delta;
      poff += delta;

      /* find if escape sequence is at the end of the processing buffer;
         if so, exclude those from processing (reduce delta to point at
         end of processed region) */
      delta = xoff;
      if ((delta > 0) &&
          ('%' == xbuf[delta - 1]))
        delta--;
      else if ((delta > 1) &&
               ('%' == xbuf[delta - 2]))
        delta -= 2;

      /* if we have an incomplete escape sequence, save it to
         pp->xbuf for later */
      if (delta < xoff)
      {
        memcpy (pp->xbuf,
                &xbuf[delta],
                xoff - delta);
        pp->xbuf_pos = xoff - delta;
        xoff = delta;
      }

      /* If we have nothing to do (delta == 0) and
         not just because the value is empty (are
         waiting for more data), go for next iteration */
      if ( (0 == xoff) &&
           (poff == post_data_len))
        continue;

      /* unescape */
      xbuf[xoff] = '\0';        /* 0-terminate in preparation */
      MHD_unescape_plus (xbuf);
      xoff = MHD_http_unescape (xbuf);
      /* finally: call application! */
      pp->must_ikvi = MHD_NO;
      if (MHD_NO == pp->ikvi (pp->cls,
                              MHD_POSTDATA_KIND,
                              (const char *) &pp[1],        /* key */
                              NULL,
                              NULL,
                              NULL,
                              xbuf,
                              pp->value_offset,
                              xoff))
      {
        pp->state = PP_Error;
        return MHD_NO;
      }
      pp->value_offset += xoff;

      /* are we done with the value? */
      if (end_of_value_found)
      {
        /* we found the end of the value! */
        if ( ('\n' == post_data[poff]) ||
             ('\r' == post_data[poff]) )
        {
          pp->state = PP_ExpectNewLine;
        }
        else if ('&' == post_data[poff])
        {
          poff++;               /* skip '&' */
          pp->state = PP_Init;
        }
      }
      break;
    case PP_ExpectNewLine:
      if ( ('\n' == post_data[poff]) ||
           ('\r' == post_data[poff]) )
      {
        poff++;
        /* we are done, report error if we receive any more... */
        pp->state = PP_Done;
        return MHD_YES;
      }
      return MHD_NO;
    default:
      mhd_panic (mhd_panic_cls,
                 __FILE__,
                 __LINE__,
                 NULL);              /* should never happen! */
    }
  }
  return MHD_YES;
}


/**
 * If the given line matches the prefix, strdup the
 * rest of the line into the suffix ptr.
 *
 * @param prefix prefix to match
 * @param prefix_len length of @a prefix
 * @param line line to match prefix in
 * @param suffix set to a copy of the rest of the line, starting at the end of the match
 * @return #MHD_YES if there was a match, #MHD_NO if not
 */
static int
try_match_header (const char *prefix,
                  size_t prefix_len,
                  char *line,
                  char **suffix)
{
  if (NULL != *suffix)
    return MHD_NO;
  while (0 != *line)
  {
    if (MHD_str_equal_caseless_n_ (prefix,
                                   line,
                                   prefix_len))
    {
      *suffix = strdup (&line[prefix_len]);
      return MHD_YES;
    }
    ++line;
  }
  return MHD_NO;
}


/**
 *
 * @param pp post processor context
 * @param boundary boundary to look for
 * @param blen number of bytes in boundary
 * @param ioffptr set to the end of the boundary if found,
 *                otherwise incremented by one (FIXME: quirky API!)
 * @param next_state state to which we should advance the post processor
 *                   if the boundary is found
 * @param next_dash_state dash_state to which we should advance the
 *                   post processor if the boundary is found
 * @return #MHD_NO if the boundary is not found, #MHD_YES if we did find it
 */
static int
find_boundary (struct MHD_PostProcessor *pp,
               const char *boundary,
               size_t blen,
               size_t *ioffptr,
               enum PP_State next_state,
               enum PP_State next_dash_state)
{
  char *buf = (char *) &pp[1];
  const char *dash;

  if (pp->buffer_pos < 2 + blen)
  {
    if (pp->buffer_pos == pp->buffer_size)
      pp->state = PP_Error;     /* out of memory */
    /* ++(*ioffptr); */
    return MHD_NO;              /* not enough data */
  }
  if ( (0 != memcmp ("--",
                     buf,
                     2)) ||
       (0 != memcmp (&buf[2],
                     boundary,
                     blen)))
  {
    if (pp->state != PP_Init)
    {
      /* garbage not allowed */
      pp->state = PP_Error;
    }
    else
    {
      /* skip over garbage (RFC 2046, 5.1.1) */
      dash = memchr (buf,
                     '-',
                     pp->buffer_pos);
      if (NULL == dash)
        (*ioffptr) += pp->buffer_pos;     /* skip entire buffer */
      else if (dash == buf)
        (*ioffptr)++;       /* at least skip one byte */
      else
        (*ioffptr) += dash - buf;       /* skip to first possible boundary */
    }
    return MHD_NO;              /* expected boundary */
  }
  /* remove boundary from buffer */
  (*ioffptr) += 2 + blen;
  /* next: start with headers */
  pp->skip_rn = RN_Dash;
  pp->state = next_state;
  pp->dash_state = next_dash_state;
  return MHD_YES;
}


/**
 * In buf, there maybe an expression '$key="$value"'.  If that is the
 * case, copy a copy of $value to destination.
 *
 * If destination is already non-NULL, do nothing.
 */
static void
try_get_value (const char *buf,
               const char *key,
               char **destination)
{
  const char *spos;
  const char *bpos;
  const char *endv;
  size_t klen;
  size_t vlen;

  if (NULL != *destination)
    return;
  bpos = buf;
  klen = strlen (key);
  while (NULL != (spos = strstr (bpos, key)))
  {
    if ( (spos[klen] != '=') ||
         ( (spos != buf) &&
           (spos[-1] != ' ') ) )
    {
      /* no match */
      bpos = spos + 1;
      continue;
    }
    if (spos[klen + 1] != '"')
      return;                   /* not quoted */
    if (NULL == (endv = strchr (&spos[klen + 2],
                                '\"')))
      return;                   /* no end-quote */
    vlen = endv - spos - klen - 1;
    *destination = malloc (vlen);
    if (NULL == *destination)
      return;                   /* out of memory */
    (*destination)[vlen - 1] = '\0';
    memcpy (*destination,
            &spos[klen + 2],
            vlen - 1);
    return;                     /* success */
  }
}


/**
 * Go over the headers of the part and update
 * the fields in "pp" according to what we find.
 * If we are at the end of the headers (as indicated
 * by an empty line), transition into next_state.
 *
 * @param pp post processor context
 * @param ioffptr set to how many bytes have been
 *                processed
 * @param next_state state to which the post processor should
 *                be advanced if we find the end of the headers
 * @return #MHD_YES if we can continue processing,
 *         #MHD_NO on error or if we do not have
 *                enough data yet
 */
static int
process_multipart_headers (struct MHD_PostProcessor *pp,
                           size_t *ioffptr,
                           enum PP_State next_state)
{
  char *buf = (char *) &pp[1];
  size_t newline;

  newline = 0;
  while ( (newline < pp->buffer_pos) &&
          (buf[newline] != '\r') &&
          (buf[newline] != '\n') )
    newline++;
  if (newline == pp->buffer_size)
  {
    pp->state = PP_Error;
    return MHD_NO;              /* out of memory */
  }
  if (newline == pp->buffer_pos)
    return MHD_NO;              /* will need more data */
  if (0 == newline)
  {
    /* empty line - end of headers */
    pp->skip_rn = RN_Full;
    pp->state = next_state;
    return MHD_YES;
  }
  /* got an actual header */
  if (buf[newline] == '\r')
    pp->skip_rn = RN_OptN;
  buf[newline] = '\0';
  if (MHD_str_equal_caseless_n_ ("Content-disposition: ",
                                 buf,
                                 MHD_STATICSTR_LEN_ ("Content-disposition: ")))
  {
    try_get_value (&buf[MHD_STATICSTR_LEN_ ("Content-disposition: ")],
                   "name",
                   &pp->content_name);
    try_get_value (&buf[MHD_STATICSTR_LEN_ ("Content-disposition: ")],
                   "filename",
                   &pp->content_filename);
  }
  else
  {
    try_match_header ("Content-type: ",
                      MHD_STATICSTR_LEN_ ("Content-type: "),
                      buf,
                      &pp->content_type);
    try_match_header ("Content-Transfer-Encoding: ",
                      MHD_STATICSTR_LEN_ ("Content-Transfer-Encoding: "),
                      buf,
                      &pp->content_transfer_encoding);
  }
  (*ioffptr) += newline + 1;
  return MHD_YES;
}


/**
 * We have the value until we hit the given boundary;
 * process accordingly.
 *
 * @param pp post processor context
 * @param ioffptr incremented based on the number of bytes processed
 * @param boundary the boundary to look for
 * @param blen strlen(boundary)
 * @param next_state what state to go into after the
 *        boundary was found
 * @param next_dash_state state to go into if the next
 *        boundary ends with "--"
 * @return #MHD_YES if we can continue processing,
 *         #MHD_NO on error or if we do not have
 *                enough data yet
 */
static int
process_value_to_boundary (struct MHD_PostProcessor *pp,
                           size_t *ioffptr,
                           const char *boundary,
                           size_t blen,
                           enum PP_State next_state,
                           enum PP_State next_dash_state)
{
  char *buf = (char *) &pp[1];
  size_t newline;
  const char *r;

  /* all data in buf until the boundary
     (\r\n--+boundary) is part of the value */
  newline = 0;
  while (1)
  {
    while (newline + 4 < pp->buffer_pos)
    {
      r = memchr (&buf[newline],
                  '\r',
                  pp->buffer_pos - newline - 4);
      if (NULL == r)
      {
        newline = pp->buffer_pos - 4;
        break;
      }
      newline = r - buf;
      if (0 == memcmp ("\r\n--",
                       &buf[newline],
                       4))
        break;
      newline++;
    }
    if (newline + blen + 4 <= pp->buffer_pos)
    {
      /* can check boundary */
      if (0 != memcmp (&buf[newline + 4],
                       boundary,
                       blen))
      {
        /* no boundary, "\r\n--" is part of content, skip */
        newline += 4;
        continue;
      }
      else
      {
        /* boundary found, process until newline then
           skip boundary and go back to init */
        pp->skip_rn = RN_Dash;
        pp->state = next_state;
        pp->dash_state = next_dash_state;
        (*ioffptr) += blen + 4;             /* skip boundary as well */
        buf[newline] = '\0';
        break;
      }
    }
    else
    {
      /* cannot check for boundary, process content that
         we have and check again later; except, if we have
         no content, abort (out of memory) */
      if ( (0 == newline) &&
           (pp->buffer_pos == pp->buffer_size) )
      {
        pp->state = PP_Error;
        return MHD_NO;
      }
      break;
    }
  }
  /* newline is either at beginning of boundary or
     at least at the last character that we are sure
     is not part of the boundary */
  if ( ( (MHD_YES == pp->must_ikvi) ||
         (0 != newline) ) &&
       (MHD_NO == pp->ikvi (pp->cls,
                            MHD_POSTDATA_KIND,
                            pp->content_name,
                            pp->content_filename,
                            pp->content_type,
                            pp->content_transfer_encoding,
                            buf,
                            pp->value_offset,
                            newline)) )
  {
    pp->state = PP_Error;
    return MHD_NO;
  }
  pp->must_ikvi = MHD_NO;
  pp->value_offset += newline;
  (*ioffptr) += newline;
  return MHD_YES;
}


/**
 *
 * @param pp post processor context
 */
static void
free_unmarked (struct MHD_PostProcessor *pp)
{
  if ( (NULL != pp->content_name) &&
       (0 == (pp->have & NE_content_name)) )
  {
    free (pp->content_name);
    pp->content_name = NULL;
  }
  if ( (NULL != pp->content_type) &&
       (0 == (pp->have & NE_content_type)) )
  {
    free (pp->content_type);
    pp->content_type = NULL;
  }
  if ( (NULL != pp->content_filename) &&
       (0 == (pp->have & NE_content_filename)) )
  {
    free (pp->content_filename);
    pp->content_filename = NULL;
  }
  if ( (NULL != pp->content_transfer_encoding) &&
       (0 == (pp->have & NE_content_transfer_encoding)) )
  {
    free (pp->content_transfer_encoding);
    pp->content_transfer_encoding = NULL;
  }
}


/**
 * Decode multipart POST data.
 *
 * @param pp post processor context
 * @param post_data data to decode
 * @param post_data_len number of bytes in @a post_data
 * @return #MHD_NO on error,
 */
static int
post_process_multipart (struct MHD_PostProcessor *pp,
                        const char *post_data,
                        size_t post_data_len)
{
  char *buf;
  size_t max;
  size_t ioff;
  size_t poff;
  int state_changed;

  buf = (char *) &pp[1];
  ioff = 0;
  poff = 0;
  state_changed = 1;
  while ( (poff < post_data_len) ||
          ( (pp->buffer_pos > 0) &&
            (0 != state_changed) ) )
  {
    /* first, move as much input data
       as possible to our internal buffer */
    max = pp->buffer_size - pp->buffer_pos;
    if (max > post_data_len - poff)
      max = post_data_len - poff;
    memcpy (&buf[pp->buffer_pos],
            &post_data[poff],
            max);
    poff += max;
    pp->buffer_pos += max;
    if ( (0 == max) &&
         (0 == state_changed) &&
         (poff < post_data_len) )
    {
      pp->state = PP_Error;
      return MHD_NO;            /* out of memory */
    }
    state_changed = 0;

    /* first state machine for '\r'-'\n' and '--' handling */
    switch (pp->skip_rn)
    {
    case RN_Inactive:
      break;
    case RN_OptN:
      if (buf[0] == '\n')
      {
        ioff++;
        pp->skip_rn = RN_Inactive;
        goto AGAIN;
      }
    /* fall-through! */
    case RN_Dash:
      if (buf[0] == '-')
      {
        ioff++;
        pp->skip_rn = RN_Dash2;
        goto AGAIN;
      }
      pp->skip_rn = RN_Full;
    /* fall-through! */
    case RN_Full:
      if (buf[0] == '\r')
      {
        if ( (pp->buffer_pos > 1) &&
             ('\n' == buf[1]) )
        {
          pp->skip_rn = RN_Inactive;
          ioff += 2;
        }
        else
        {
          pp->skip_rn = RN_OptN;
          ioff++;
        }
        goto AGAIN;
      }
      if (buf[0] == '\n')
      {
        ioff++;
        pp->skip_rn = RN_Inactive;
        goto AGAIN;
      }
      pp->skip_rn = RN_Inactive;
      pp->state = PP_Error;
      return MHD_NO;            /* no '\r\n' */
    case RN_Dash2:
      if (buf[0] == '-')
      {
        ioff++;
        pp->skip_rn = RN_Full;
        pp->state = pp->dash_state;
        goto AGAIN;
      }
      pp->state = PP_Error;
      break;
    }

    /* main state engine */
    switch (pp->state)
    {
    case PP_Error:
      return MHD_NO;
    case PP_Done:
      /* did not expect to receive more data */
      pp->state = PP_Error;
      return MHD_NO;
    case PP_Init:
      /**
       * Per RFC2046 5.1.1 NOTE TO IMPLEMENTORS, consume anything
       * prior to the first multipart boundary:
       *
       * > There appears to be room for additional information prior
       * > to the first boundary delimiter line and following the
       * > final boundary delimiter line.  These areas should
       * > generally be left blank, and implementations must ignore
       * > anything that appears before the first boundary delimiter
       * > line or after the last one.
       */
      (void) find_boundary (pp,
                            pp->boundary,
                            pp->blen,
                            &ioff,
                            PP_ProcessEntryHeaders,
                            PP_Done);
      break;
    case PP_NextBoundary:
      if (MHD_NO == find_boundary (pp,
                                   pp->boundary,
                                   pp->blen,
                                   &ioff,
                                   PP_ProcessEntryHeaders,
                                   PP_Done))
      {
        if (pp->state == PP_Error)
          return MHD_NO;
        goto END;
      }
      break;
    case PP_ProcessEntryHeaders:
      pp->must_ikvi = MHD_YES;
      if (MHD_NO ==
          process_multipart_headers (pp,
                                     &ioff,
                                     PP_PerformCheckMultipart))
      {
        if (pp->state == PP_Error)
          return MHD_NO;
        else
          goto END;
      }
      state_changed = 1;
      break;
    case PP_PerformCheckMultipart:
      if ( (NULL != pp->content_type) &&
           (MHD_str_equal_caseless_n_ (pp->content_type,
                                       "multipart/mixed",
                                       MHD_STATICSTR_LEN_ ("multipart/mixed"))))
      {
        pp->nested_boundary = strstr (pp->content_type,
                                      "boundary=");
        if (NULL == pp->nested_boundary)
        {
          pp->state = PP_Error;
          return MHD_NO;
        }
        pp->nested_boundary =
          strdup (&pp->nested_boundary[MHD_STATICSTR_LEN_ ("boundary=")]);
        if (NULL == pp->nested_boundary)
        {
          /* out of memory */
          pp->state = PP_Error;
          return MHD_NO;
        }
        /* free old content type, we will need that field
           for the content type of the nested elements */
        free (pp->content_type);
        pp->content_type = NULL;
        pp->nlen = strlen (pp->nested_boundary);
        pp->state = PP_Nested_Init;
        state_changed = 1;
        break;
      }
      pp->state = PP_ProcessValueToBoundary;
      pp->value_offset = 0;
      state_changed = 1;
      break;
    case PP_ProcessValueToBoundary:
      if (MHD_NO == process_value_to_boundary (pp,
                                               &ioff,
                                               pp->boundary,
                                               pp->blen,
                                               PP_PerformCleanup,
                                               PP_Done))
      {
        if (pp->state == PP_Error)
          return MHD_NO;
        break;
      }
      break;
    case PP_PerformCleanup:
      /* clean up state of one multipart form-data element! */
      pp->have = NE_none;
      free_unmarked (pp);
      if (NULL != pp->nested_boundary)
      {
        free (pp->nested_boundary);
        pp->nested_boundary = NULL;
      }
      pp->state = PP_ProcessEntryHeaders;
      state_changed = 1;
      break;
    case PP_Nested_Init:
      if (NULL == pp->nested_boundary)
      {
        pp->state = PP_Error;
        return MHD_NO;
      }
      if (MHD_NO == find_boundary (pp,
                                   pp->nested_boundary,
                                   pp->nlen,
                                   &ioff,
                                   PP_Nested_PerformMarking,
                                   PP_NextBoundary /* or PP_Error? */))
      {
        if (pp->state == PP_Error)
          return MHD_NO;
        goto END;
      }
      break;
    case PP_Nested_PerformMarking:
      /* remember what headers were given
         globally */
      pp->have = NE_none;
      if (NULL != pp->content_name)
        pp->have |= NE_content_name;
      if (NULL != pp->content_type)
        pp->have |= NE_content_type;
      if (NULL != pp->content_filename)
        pp->have |= NE_content_filename;
      if (NULL != pp->content_transfer_encoding)
        pp->have |= NE_content_transfer_encoding;
      pp->state = PP_Nested_ProcessEntryHeaders;
      state_changed = 1;
      break;
    case PP_Nested_ProcessEntryHeaders:
      pp->value_offset = 0;
      if (MHD_NO ==
          process_multipart_headers (pp,
                                     &ioff,
                                     PP_Nested_ProcessValueToBoundary))
      {
        if (pp->state == PP_Error)
          return MHD_NO;
        else
          goto END;
      }
      state_changed = 1;
      break;
    case PP_Nested_ProcessValueToBoundary:
      if (MHD_NO == process_value_to_boundary (pp,
                                               &ioff,
                                               pp->nested_boundary,
                                               pp->nlen,
                                               PP_Nested_PerformCleanup,
                                               PP_NextBoundary))
      {
        if (pp->state == PP_Error)
          return MHD_NO;
        break;
      }
      break;
    case PP_Nested_PerformCleanup:
      free_unmarked (pp);
      pp->state = PP_Nested_ProcessEntryHeaders;
      state_changed = 1;
      break;
    default:
      mhd_panic (mhd_panic_cls,
                 __FILE__,
                 __LINE__,
                 NULL);              /* should never happen! */
    }
AGAIN:
    if (ioff > 0)
    {
      memmove (buf,
               &buf[ioff],
               pp->buffer_pos - ioff);
      pp->buffer_pos -= ioff;
      ioff = 0;
      state_changed = 1;
    }
  }
END:
  if (0 != ioff)
  {
    memmove (buf,
             &buf[ioff],
             pp->buffer_pos - ioff);
    pp->buffer_pos -= ioff;
  }
  if (poff < post_data_len)
  {
    pp->state = PP_Error;
    return MHD_NO;              /* serious error */
  }
  return MHD_YES;
}


/**
 * Parse and process POST data.  Call this function when POST data is
 * available (usually during an #MHD_AccessHandlerCallback) with the
 * "upload_data" and "upload_data_size".  Whenever possible, this will
 * then cause calls to the #MHD_PostDataIterator.
 *
 * @param pp the post processor
 * @param post_data @a post_data_len bytes of POST data
 * @param post_data_len length of @a post_data
 * @return #MHD_YES on success, #MHD_NO on error
 *         (out-of-memory, iterator aborted, parse error)
 * @ingroup request
 */
int
MHD_post_process (struct MHD_PostProcessor *pp,
                  const char *post_data,
                  size_t post_data_len)
{
  if (0 == post_data_len)
    return MHD_YES;
  if (NULL == pp)
    return MHD_NO;
  if (MHD_str_equal_caseless_n_ (MHD_HTTP_POST_ENCODING_FORM_URLENCODED,
                                 pp->encoding,
                                 MHD_STATICSTR_LEN_ (
                                   MHD_HTTP_POST_ENCODING_FORM_URLENCODED)))
    return post_process_urlencoded (pp,
                                    post_data,
                                    post_data_len);
  if (MHD_str_equal_caseless_n_ (MHD_HTTP_POST_ENCODING_MULTIPART_FORMDATA,
                                 pp->encoding,
                                 MHD_STATICSTR_LEN_ (
                                   MHD_HTTP_POST_ENCODING_MULTIPART_FORMDATA)))
    return post_process_multipart (pp,
                                   post_data,
                                   post_data_len);
  /* this should never be reached */
  return MHD_NO;
}


/**
 * Release PostProcessor resources.
 *
 * @param pp post processor context to destroy
 * @return #MHD_YES if processing completed nicely,
 *         #MHD_NO if there were spurious characters / formatting
 *                problems; it is common to ignore the return
 *                value of this function
 * @ingroup request
 */
int
MHD_destroy_post_processor (struct MHD_PostProcessor *pp)
{
  int ret;

  if (NULL == pp)
    return MHD_YES;
  if (PP_ProcessValue == pp->state)
  {
    /* key without terminated value left at the end of the
       buffer; fake receiving a termination character to
       ensure it is also processed */
    post_process_urlencoded (pp,
                             "\n",
                             1);
  }
  /* These internal strings need cleaning up since
     the post-processing may have been interrupted
     at any stage */
  if ( (pp->xbuf_pos > 0) ||
       ( (pp->state != PP_Done) &&
         (pp->state != PP_ExpectNewLine) ) )
    ret = MHD_NO;
  else
    ret = MHD_YES;
  pp->have = NE_none;
  free_unmarked (pp);
  if (NULL != pp->nested_boundary)
    free (pp->nested_boundary);
  free (pp);
  return ret;
}

/* end of postprocessor.c */