warc: make warc_uuid_str implementation depend on HAVE_LIBUUID

[wget] / src / warc.c

/* Utility functions for writing WARC files.
   Copyright (C) 2011, 2012 Free Software Foundation, Inc.

This file is part of GNU Wget.

GNU Wget 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.

GNU Wget 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 Wget.  If not, see <http://www.gnu.org/licenses/>.

Additional permission under GNU GPL version 3 section 7

If you modify this program, or any covered work, by linking or
combining it with the OpenSSL project's OpenSSL library (or a
modified version of that library), containing parts covered by the
terms of the OpenSSL or SSLeay licenses, the Free Software Foundation
grants you additional permission to convey the resulting work.
Corresponding Source for a non-source form of such a combination
shall include the source code for the parts of OpenSSL used as well
as that of the covered work.  */

#define _GNU_SOURCE

#include "wget.h"
#include "hash.h"
#include "utils.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <time.h>
#include <tmpdir.h>
#include <sha1.h>
#include <base32.h>
#include <unistd.h>
#ifdef HAVE_LIBZ
#include <zlib.h>
#endif
#ifdef HAVE_LIBUUID
#include <uuid/uuid.h>
#endif

#ifndef WINDOWS
#include <libgen.h>
#endif

#include "warc.h"

extern char *version_string;

/* Set by main in main.c */
extern char *program_argstring;


/* The log file (a temporary file that contains a copy
   of the wget log). */
static FILE *warc_log_fp;

/* The manifest file (a temporary file that contains the
   warcinfo uuid of every file in this crawl). */
static FILE *warc_manifest_fp;

/* The current WARC file (or NULL, if WARC is disabled). */
static FILE *warc_current_file;

#ifdef HAVE_LIBZ
/* The gzip stream for the current WARC file
   (or NULL, if WARC or gzip is disabled). */
static gzFile *warc_current_gzfile;

/* The offset of the current gzip record in the WARC file. */
static off_t warc_current_gzfile_offset;

/* The uncompressed size (so far) of the current record. */
static off_t warc_current_gzfile_uncompressed_size;
# endif

/* This is true until a warc_write_* method fails. */
static bool warc_write_ok;

/* The current CDX file (or NULL, if CDX is disabled). */
static FILE *warc_current_cdx_file;

/* The record id of the warcinfo record of the current WARC file.  */
static char *warc_current_warcinfo_uuid_str;

/* The file name of the current WARC file. */
static char *warc_current_filename;

/* The serial number of the current WARC file.  This number is
   incremented each time a new file is opened and is used in the
   WARC file's filename. */
static int warc_current_file_number;

/* The table of CDX records, if deduplication is enabled. */
struct hash_table * warc_cdx_dedup_table;

static bool warc_start_new_file (bool meta);


struct warc_cdx_record
{
  char *url;
  char *uuid;
  char digest[SHA1_DIGEST_SIZE];
};

static unsigned long
warc_hash_sha1_digest (const void *key)
{
  /* We just use some of the first bytes of the digest. */
  unsigned long v = 0;
  memcpy (&v, key, sizeof (unsigned long));
  return v;
}

static int
warc_cmp_sha1_digest (const void *digest1, const void *digest2)
{
  return !memcmp (digest1, digest2, SHA1_DIGEST_SIZE);
}



/* Writes SIZE bytes from BUFFER to the current WARC file,
   through gzwrite if compression is enabled.
   Returns the number of uncompressed bytes written.  */
static size_t
warc_write_buffer (const char *buffer, size_t size)
{
#ifdef HAVE_LIBZ
  if (warc_current_gzfile)
    {
      warc_current_gzfile_uncompressed_size += size;
      return gzwrite (warc_current_gzfile, buffer, size);
    }
  else
#endif
    return fwrite (buffer, 1, size, warc_current_file);
}

/* Writes STR to the current WARC file.
   Returns false and set warc_write_ok to false if there
   is an error.  */
static bool
warc_write_string (const char *str)
{
  if (!warc_write_ok)
    return false;

  size_t n = strlen (str);
  if (n != warc_write_buffer (str, n))
    warc_write_ok = false;

  return warc_write_ok;
}


#define EXTRA_GZIP_HEADER_SIZE 12
#define GZIP_STATIC_HEADER_SIZE  10
#define FLG_FEXTRA          0x04
#define OFF_FLG             3

/* Starts a new WARC record.  Writes the version header.
   If opt.warc_maxsize is set and the current file is becoming
   too large, this will open a new WARC file.

   If compression is enabled, this will start a new
   gzip stream in the current WARC file.

   Returns false and set warc_write_ok to false if there
   is an error.  */
static bool
warc_write_start_record ()
{
  if (!warc_write_ok)
    return false;

  fflush (warc_current_file);
  if (opt.warc_maxsize > 0 && ftello (warc_current_file) >= opt.warc_maxsize)
    warc_start_new_file (false);

#ifdef HAVE_LIBZ
  /* Start a GZIP stream, if required. */
  if (opt.warc_compression_enabled)
    {
      /* Record the starting offset of the new record. */
      warc_current_gzfile_offset = ftello (warc_current_file);

      /* Reserve space for the extra GZIP header field.
         In warc_write_end_record we will fill this space
         with information about the uncompressed and
         compressed size of the record. */
      fprintf (warc_current_file, "XXXXXXXXXXXX");
      fflush (warc_current_file);

      /* Start a new GZIP stream. */
      warc_current_gzfile = gzdopen (dup (fileno (warc_current_file)), "wb9");
      warc_current_gzfile_uncompressed_size = 0;

      if (warc_current_gzfile == NULL)
        {
          logprintf (LOG_NOTQUIET, _("Error opening GZIP stream to WARC file.\n"));
          warc_write_ok = false;
          return false;
        }
    }
#endif

  warc_write_string ("WARC/1.0\r\n");
  return warc_write_ok;
}

/* Writes a WARC header to the current WARC record.
   This method may be run after warc_write_start_record and
   before warc_write_block_from_file.  */
static bool
warc_write_header (const char *name, const char *value)
{
  if (value)
    {
      warc_write_string (name);
      warc_write_string (": ");
      warc_write_string (value);
      warc_write_string ("\r\n");
    }
  return warc_write_ok;
}

/* Copies the contents of DATA_IN to the WARC record.
   Adds a Content-Length header to the WARC record.
   Run this method after warc_write_header,
   then run warc_write_end_record. */
static bool
warc_write_block_from_file (FILE *data_in)
{
  /* Add the Content-Length header. */
  char *content_length;
  fseeko (data_in, 0L, SEEK_END);
  if (! asprintf (&content_length, "%ld", ftello (data_in)))
    {
      warc_write_ok = false;
      return false;
    }
  warc_write_header ("Content-Length", content_length);
  free (content_length);

  /* End of the WARC header section. */
  warc_write_string ("\r\n");

  if (fseeko (data_in, 0L, SEEK_SET) != 0)
    warc_write_ok = false;

  /* Copy the data in the file to the WARC record. */
  char buffer[BUFSIZ];
  size_t s;
  while (warc_write_ok && (s = fread (buffer, 1, BUFSIZ, data_in)) > 0)
    {
      if (warc_write_buffer (buffer, s) < s)
        warc_write_ok = false;
    }

  return warc_write_ok;
}

/* Run this method to close the current WARC record.

   If compression is enabled, this method closes the
   current GZIP stream and fills the extra GZIP header
   with the uncompressed and compressed length of the
   record. */
static bool
warc_write_end_record ()
{
  warc_write_buffer ("\r\n\r\n", 4);

#ifdef HAVE_LIBZ
  /* We start a new gzip stream for each record.  */
  if (warc_write_ok && warc_current_gzfile)
    {
      if (gzclose (warc_current_gzfile) != Z_OK)
        {
          warc_write_ok = false;
          return false;
        }

      fflush (warc_current_file);
      fseeko (warc_current_file, 0, SEEK_END);

      /* The WARC standard suggests that we add 'skip length' data in the
         extra header field of the GZIP stream.
         
         In warc_write_start_record we reserved space for this extra header.
         This extra space starts at warc_current_gzfile_offset and fills
         EXTRA_GZIP_HEADER_SIZE bytes.  The static GZIP header starts at
         warc_current_gzfile_offset + EXTRA_GZIP_HEADER_SIZE.
         
         We need to do three things:
         1. Move the static GZIP header to warc_current_gzfile_offset;
         2. Set the FEXTRA flag in the GZIP header;
         3. Write the extra GZIP header after the static header, that is,
            starting at warc_current_gzfile_offset + GZIP_STATIC_HEADER_SIZE.
      */

      /* Calculate the uncompressed and compressed sizes. */
      off_t current_offset = ftello (warc_current_file);
      off_t uncompressed_size = current_offset - warc_current_gzfile_offset;
      off_t compressed_size = warc_current_gzfile_uncompressed_size;

      /* Go back to the static GZIP header. */
      fseeko (warc_current_file, warc_current_gzfile_offset + EXTRA_GZIP_HEADER_SIZE, SEEK_SET);

      /* Read the header. */
      char static_header[GZIP_STATIC_HEADER_SIZE];
      size_t result = fread (static_header, 1, GZIP_STATIC_HEADER_SIZE, warc_current_file);
      if (result != GZIP_STATIC_HEADER_SIZE)
        {
          warc_write_ok = false;
          return false;
        }

      /* Set the FEXTRA flag in the flags byte of the header. */
      static_header[OFF_FLG] = static_header[OFF_FLG] | FLG_FEXTRA;

      /* Write the header back to the file, but starting at warc_current_gzfile_offset. */
      fseeko (warc_current_file, warc_current_gzfile_offset, SEEK_SET);
      fwrite (static_header, 1, GZIP_STATIC_HEADER_SIZE, warc_current_file);

      /* Prepare the extra GZIP header. */
      char extra_header[EXTRA_GZIP_HEADER_SIZE];
      /* XLEN, the length of the extra header fields.  */
      extra_header[0]  = ((EXTRA_GZIP_HEADER_SIZE - 2) & 255);
      extra_header[1]  = ((EXTRA_GZIP_HEADER_SIZE - 2) >> 8) & 255;
      /* The extra header field identifier for the WARC skip length. */
      extra_header[2]  = 's';
      extra_header[3]  = 'l';
      /* The size of the uncompressed record.  */
      extra_header[4]  = (uncompressed_size & 255);
      extra_header[5]  = (uncompressed_size >> 8) & 255;
      extra_header[6]  = (uncompressed_size >> 16) & 255;
      extra_header[7]  = (uncompressed_size >> 24) & 255;
      /* The size of the compressed record.  */
      extra_header[8]  = (compressed_size & 255);
      extra_header[9]  = (compressed_size >> 8) & 255;
      extra_header[10] = (compressed_size >> 16) & 255;
      extra_header[11] = (compressed_size >> 24) & 255;

      /* Write the extra header after the static header. */
      fseeko (warc_current_file, warc_current_gzfile_offset + GZIP_STATIC_HEADER_SIZE, SEEK_SET);
      fwrite (extra_header, 1, EXTRA_GZIP_HEADER_SIZE, warc_current_file);

      /* Done, move back to the end of the file. */
      fflush (warc_current_file);
      fseeko (warc_current_file, 0, SEEK_END);
    }
#endif /* HAVE_LIBZ */

  return warc_write_ok;
}


/* Writes the WARC-Date header for the given timestamp to
   the current WARC record.
   If timestamp is NULL, the current time will be used.  */
static bool
warc_write_date_header (char *timestamp)
{
  if (timestamp == NULL)
    {
      char current_timestamp[21];
      warc_timestamp (current_timestamp);
      timestamp = current_timestamp;
    }
  return warc_write_header ("WARC-Date", timestamp);
}

/* Writes the WARC-IP-Address header for the given IP to
   the current WARC record.  If IP is NULL, no header will
   be written.  */
static bool
warc_write_ip_header (ip_address *ip)
{
  if (ip != NULL)
    return warc_write_header ("WARC-IP-Address", print_address (ip));
  else
    return warc_write_ok;
}


/* warc_sha1_stream_with_payload is a modified copy of sha1_stream
   from gnulib/sha1.c.  This version calculates two digests in one go.

   Compute SHA1 message digests for bytes read from STREAM.  The
   digest of the complete file will be written into the 16 bytes
   beginning at RES_BLOCK.
   
   If payload_offset >= 0, a second digest will be calculated of the
   portion of the file starting at payload_offset and continuing to
   the end of the file.  The digest number will be written into the
   16 bytes beginning ad RES_PAYLOAD.  */
static int
warc_sha1_stream_with_payload (FILE *stream, void *res_block, void *res_payload, off_t payload_offset)
{
#define BLOCKSIZE 32768

  struct sha1_ctx ctx_block;
  struct sha1_ctx ctx_payload;
  off_t pos;
  off_t sum;

  char *buffer = malloc (BLOCKSIZE + 72);
  if (!buffer)
    return 1;

  /* Initialize the computation context.  */
  sha1_init_ctx (&ctx_block);
  if (payload_offset >= 0)
    sha1_init_ctx (&ctx_payload);

  pos = 0;

  /* Iterate over full file contents.  */
  while (1)
    {
      /* We read the file in blocks of BLOCKSIZE bytes.  One call of the
         computation function processes the whole buffer so that with the
         next round of the loop another block can be read.  */
      off_t n;
      sum = 0;

      /* Read block.  Take care for partial reads.  */
      while (1)
        {
          n = fread (buffer + sum, 1, BLOCKSIZE - sum, stream);

          sum += n;
          pos += n;

          if (sum == BLOCKSIZE)
            break;

          if (n == 0)
            {
              /* Check for the error flag IFF N == 0, so that we don't
                 exit the loop after a partial read due to e.g., EAGAIN
                 or EWOULDBLOCK.  */
              if (ferror (stream))
                {
                  free (buffer);
                  return 1;
                }
              goto process_partial_block;
            }

          /* We've read at least one byte, so ignore errors.  But always
             check for EOF, since feof may be true even though N > 0.
             Otherwise, we could end up calling fread after EOF.  */
          if (feof (stream))
            goto process_partial_block;
        }

      /* Process buffer with BLOCKSIZE bytes.  Note that
                        BLOCKSIZE % 64 == 0
       */
      sha1_process_block (buffer, BLOCKSIZE, &ctx_block);
      if (payload_offset >= 0 && payload_offset < pos)
        {
          /* At least part of the buffer contains data from payload. */
          off_t start_of_payload = payload_offset - (pos - BLOCKSIZE);
          if (start_of_payload <= 0)
            /* All bytes in the buffer belong to the payload. */
            start_of_payload = 0;

          /* Process the payload part of the buffer.
             Note: we can't use  sha1_process_block  here even if we
             process the complete buffer.  Because the payload doesn't
             have to start with a full block, there may still be some
             bytes left from the previous buffer.  Therefore, we need
             to continue with  sha1_process_bytes.  */
          sha1_process_bytes (buffer + start_of_payload, BLOCKSIZE - start_of_payload, &ctx_payload);
        }
    }

 process_partial_block:;

  /* Process any remaining bytes.  */
  if (sum > 0)
    {
      sha1_process_bytes (buffer, sum, &ctx_block);
      if (payload_offset >= 0 && payload_offset < pos)
        {
          /* At least part of the buffer contains data from payload. */
          off_t start_of_payload = payload_offset - (pos - sum);
          if (start_of_payload <= 0)
            /* All bytes in the buffer belong to the payload. */
            start_of_payload = 0;

          /* Process the payload part of the buffer. */
          sha1_process_bytes (buffer + start_of_payload, sum - start_of_payload, &ctx_payload);
        }
    }

  /* Construct result in desired memory.  */
  sha1_finish_ctx (&ctx_block,   res_block);
  if (payload_offset >= 0)
    sha1_finish_ctx (&ctx_payload, res_payload);
  free (buffer);
  return 0;

#undef BLOCKSIZE
}

/* Converts the SHA1 digest to a base32-encoded string.
   "sha1:DIGEST\0"  (Allocates a new string for the response.)  */
static char *
warc_base32_sha1_digest (char *sha1_digest)
{
  // length: "sha1:" + digest + "\0"
  char *sha1_base32 = malloc (BASE32_LENGTH(SHA1_DIGEST_SIZE) + 1 + 5 );
  base32_encode (sha1_digest, SHA1_DIGEST_SIZE, sha1_base32 + 5, BASE32_LENGTH(SHA1_DIGEST_SIZE) + 1);
  memcpy (sha1_base32, "sha1:", 5);
  sha1_base32[BASE32_LENGTH(SHA1_DIGEST_SIZE) + 5] = '\0';
  return sha1_base32;
}


/* Sets the digest headers of the record.
   This method will calculate the block digest and, if payload_offset >= 0,
   will also calculate the payload digest of the payload starting at the
   provided offset.  */
static void
warc_write_digest_headers (FILE *file, long payload_offset)
{
  if (opt.warc_digests_enabled)
    {
      /* Calculate the block and payload digests. */
      char sha1_res_block[SHA1_DIGEST_SIZE];
      char sha1_res_payload[SHA1_DIGEST_SIZE];

      rewind (file);
      if (warc_sha1_stream_with_payload (file, sha1_res_block, sha1_res_payload, payload_offset) == 0)
        {
          char *digest;

          digest = warc_base32_sha1_digest (sha1_res_block);
          warc_write_header ("WARC-Block-Digest", digest);
          free (digest);

          if (payload_offset >= 0)
            {
              digest = warc_base32_sha1_digest (sha1_res_payload);
              warc_write_header ("WARC-Payload-Digest", digest);
              free (digest);
            }
        }
    }
}


/* Fills timestamp with the current time and date.
   The UTC time is formatted following ISO 8601, as required
   for use in the WARC-Date header.
   The timestamp will be 21 characters long. */
void
warc_timestamp (char *timestamp)
{
  time_t rawtime;
  struct tm * timeinfo;
  time ( &rawtime );
  timeinfo = gmtime (&rawtime);
  strftime (timestamp, 21, "%Y-%m-%dT%H:%M:%SZ", timeinfo);
}

#ifdef HAVE_LIBUUID
/* Fills urn_str with a UUID in the format required
   for the WARC-Record-Id header.
   The string will be 47 characters long. */
void
warc_uuid_str (char *urn_str)
{
  char uuid_str[37];

  uuid_t record_id;
  uuid_generate (record_id);
  uuid_unparse (record_id, uuid_str);

  sprintf (urn_str, "<urn:uuid:%s>", uuid_str);
}
#else
/* Fills urn_str with a UUID based on random numbers in the format
   required for the WARC-Record-Id header.
   (See RFC 4122, UUID version 4.)

   Note: this is a fallback method, it is much better to use the
   methods provided by libuuid.

   The string will be 47 characters long. */
void
warc_uuid_str (char *urn_str)
{
  // RFC 4122, a version 4 UUID with only random numbers

  unsigned char uuid_data[16];
  int i;
  for (i=0; i<16; i++)
    uuid_data[i] = random_number (255);

  // Set the four most significant bits (bits 12 through 15) of the
  // time_hi_and_version field to the 4-bit version number
  uuid_data[6] = (uuid_data[6] & 0x0F) | 0x40;

  // Set the two most significant bits (bits 6 and 7) of the
  // clock_seq_hi_and_reserved to zero and one, respectively.
  uuid_data[8] = (uuid_data[8] & 0xBF) | 0x80;

  sprintf (urn_str,
    "<urn:uuid:%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x>",
    uuid_data[0], uuid_data[1], uuid_data[2], uuid_data[3], uuid_data[4],
    uuid_data[5], uuid_data[6], uuid_data[7], uuid_data[8], uuid_data[9],
    uuid_data[10], uuid_data[11], uuid_data[12], uuid_data[13], uuid_data[14],
    uuid_data[15]);
}
#endif

/* Write a warcinfo record to the current file.
   Updates warc_current_warcinfo_uuid_str. */
bool
warc_write_warcinfo_record (char *filename)
{
  /* Write warc-info record as the first record of the file. */
  /* We add the record id of this info record to the other records in the file. */
  warc_current_warcinfo_uuid_str = (char *) malloc (48);
  warc_uuid_str (warc_current_warcinfo_uuid_str);

  char timestamp[22];
  warc_timestamp (timestamp);

  char *filename_copy, *filename_basename;
  filename_copy = strdup (filename);
  filename_basename = strdup (basename (filename_copy));

  warc_write_start_record ();
  warc_write_header ("WARC-Type", "warcinfo");
  warc_write_header ("Content-Type", "application/warc-fields");
  warc_write_header ("WARC-Date", timestamp);
  warc_write_header ("WARC-Record-ID", warc_current_warcinfo_uuid_str);
  warc_write_header ("WARC-Filename", filename_basename);

  /* Create content.  */
  FILE *warc_tmp = warc_tempfile ();
  if (warc_tmp == NULL)
    {
      free (filename_copy);
      free (filename_basename);
      return false;
    }

  fprintf (warc_tmp, "software: Wget/%s (%s)\r\n", version_string, OS_TYPE);
  fprintf (warc_tmp, "format: WARC File Format 1.0\r\n");
  fprintf (warc_tmp, "conformsTo: http://bibnum.bnf.fr/WARC/WARC_ISO_28500_version1_latestdraft.pdf\r\n");
  fprintf (warc_tmp, "robots: %s\r\n", (opt.use_robots ? "classic" : "off"));
  fprintf (warc_tmp, "wget-arguments: %s\r\n", program_argstring);
  /* Add the user headers, if any. */
  if (opt.warc_user_headers)
    {
      int i;
      for (i = 0; opt.warc_user_headers[i]; i++)
        fprintf (warc_tmp, "%s\r\n", opt.warc_user_headers[i]);
    }
  fprintf(warc_tmp, "\r\n");

  warc_write_digest_headers (warc_tmp, -1);
  warc_write_block_from_file (warc_tmp);
  warc_write_end_record ();

  if (! warc_write_ok)
    {
      logprintf (LOG_NOTQUIET, _("Error writing warcinfo record to WARC file.\n"));
    }

  free (filename_copy);
  free (filename_basename);
  fclose (warc_tmp);
  return warc_write_ok;
}

/* Opens a new WARC file.
   If META is true, generates a filename ending with 'meta.warc.gz'.
   
   This method will:
   1. close the current WARC file (if there is one);
   2. increment warc_current_file_number;
   3. open a new WARC file;
   4. write the initial warcinfo record.

   Returns true on success, false otherwise.
   */
static bool
warc_start_new_file (bool meta)
{
  if (opt.warc_filename == NULL)
    return false;

  if (warc_current_file != NULL)
    fclose (warc_current_file);
  if (warc_current_warcinfo_uuid_str)
    free (warc_current_warcinfo_uuid_str);
  if (warc_current_filename)
    free (warc_current_filename);

  warc_current_file_number++;

  int base_filename_length = strlen (opt.warc_filename);
  /* filename format:  base + "-" + 5 digit serial number + ".warc.gz" */
  char *new_filename = malloc (base_filename_length + 1 + 5 + 8 + 1);
  warc_current_filename = new_filename;

#ifdef HAVE_LIBZ
  char *extension = (opt.warc_compression_enabled ? "warc.gz" : "warc");
#else
  char *extension = "warc";
#endif

  /* If max size is enabled, we add a serial number to the file names. */
  if (meta)
    sprintf (new_filename, "%s-meta.%s", opt.warc_filename, extension);
  else if (opt.warc_maxsize > 0)
    sprintf (new_filename, "%s-%05d.%s", opt.warc_filename, warc_current_file_number, extension);
  else
    sprintf (new_filename, "%s.%s", opt.warc_filename, extension);

  logprintf (LOG_VERBOSE, _("Opening WARC file %s.\n\n"), quote (new_filename));

  /* Open the WARC file. */
  warc_current_file = fopen (new_filename, "wb+");
  if (warc_current_file == NULL)
    {
      logprintf (LOG_NOTQUIET, _("Error opening WARC file %s.\n"), quote (new_filename));
      return false;
    }

  if (! warc_write_warcinfo_record (new_filename))
    return false;

  /* Add warcinfo uuid to manifest. */
  if (warc_manifest_fp)
    fprintf (warc_manifest_fp, "%s\n", warc_current_warcinfo_uuid_str);

  return true;
}

/* Opens the CDX file for output. */
static bool
warc_start_cdx_file ()
{
  int filename_length = strlen (opt.warc_filename);
  char *cdx_filename = alloca (filename_length + 4 + 1);
  memcpy (cdx_filename, opt.warc_filename, filename_length);
  memcpy (cdx_filename + filename_length, ".cdx", 5);
  warc_current_cdx_file = fopen (cdx_filename, "a+");
  if (warc_current_cdx_file == NULL)
    return false;

  /* Print the CDX header.
   *
   * a - original url
   * b - date
   * m - mime type
   * s - response code
   * k - new style checksum
   * r - redirect
   * M - meta tags
   * V - compressed arc file offset
   * g - file name
   * u - record-id
   */
  fprintf (warc_current_cdx_file, " CDX a b a m s k r M V g u\n");
  fflush (warc_current_cdx_file);

  return true;
}

#define CDX_FIELDSEP " \t\r\n"

/* Parse the CDX header and find the field numbers of the original url,
   checksum and record ID fields. */
static bool
warc_parse_cdx_header (char *lineptr, int *field_num_original_url, int *field_num_checksum, int *field_num_record_id)
{
  *field_num_original_url = -1;
  *field_num_checksum = -1;
  *field_num_record_id = -1;

  char *token;
  char *save_ptr;
  token = strtok_r (lineptr, CDX_FIELDSEP, &save_ptr);
  
  if (token != NULL && strcmp (token, "CDX") == 0)
    {
      int field_num = 0;
      while (token != NULL)
        {
          token = strtok_r (NULL, CDX_FIELDSEP, &save_ptr);
          if (token != NULL)
            {
              switch (token[0])
                {
                case 'a':
                  *field_num_original_url = field_num;
                  break;
                case 'k':
                  *field_num_checksum = field_num;
                  break;
                case 'u':
                  *field_num_record_id = field_num;
                  break;
                }
            }
          field_num++;
        }
    }

  return *field_num_original_url != -1
         && *field_num_checksum != -1
         && *field_num_record_id != -1;
}

/* Parse the CDX record and add it to the warc_cdx_dedup_table hash table. */
static void
warc_process_cdx_line (char *lineptr, int field_num_original_url, int field_num_checksum, int field_num_record_id)
{
  char *original_url = NULL;
  char *checksum = NULL;
  char *record_id = NULL;

  char *token;
  char *save_ptr;
  token = strtok_r (lineptr, CDX_FIELDSEP, &save_ptr);

  /* Read this line to get the fields we need. */
  int field_num = 0;
  while (token != NULL)
    {
      char **val;
      if (field_num == field_num_original_url)
        val = &original_url;
      else if (field_num == field_num_checksum)
        val = &checksum;
      else if (field_num == field_num_record_id)
        val = &record_id;
      else
        val = NULL;

      if (val != NULL)
        *val = strdup (token);

      token = strtok_r (NULL, CDX_FIELDSEP, &save_ptr);
      field_num++;
    }

  if (original_url != NULL && checksum != NULL && record_id != NULL)
    {
      /* For some extra efficiency, we decode the base32 encoded
         checksum value.  This should produce exactly SHA1_DIGEST_SIZE
         bytes.  */
      size_t checksum_l;
      char * checksum_v;
      base32_decode_alloc (checksum, strlen (checksum), &checksum_v, &checksum_l);
      free (checksum);

      if (checksum_v != NULL && checksum_l == SHA1_DIGEST_SIZE)
        {
          /* This is a valid line with a valid checksum. */
          struct warc_cdx_record * rec = malloc (sizeof (struct warc_cdx_record));
          rec->url = original_url;
          rec->uuid = record_id;
          memcpy (rec->digest, checksum_v, SHA1_DIGEST_SIZE);
          hash_table_put (warc_cdx_dedup_table, rec->digest, rec);
          free (checksum_v);
        }
      else
        {
          free (original_url);
          if (checksum_v != NULL)
            free (checksum_v);
          free (record_id);
        }
    }
}

/* Loads the CDX file from opt.warc_cdx_dedup_filename and fills
   the warc_cdx_dedup_table. */
bool
warc_load_cdx_dedup_file ()
{
  FILE *f = fopen (opt.warc_cdx_dedup_filename, "r");
  if (f == NULL)
    return false;

  int field_num_original_url = -1;
  int field_num_checksum = -1;
  int field_num_record_id = -1;

  char *lineptr = NULL;
  size_t n = 0;
  size_t line_length;

  /* The first line should contain the CDX header.
     Format:  " CDX x x x x x"
     where x are field type indicators.  For our purposes, we only
     need 'a' (the original url), 'k' (the SHA1 checksum) and
     'u' (the WARC record id). */
  line_length = getline (&lineptr, &n, f);
  if (line_length != -1)
    warc_parse_cdx_header (lineptr, &field_num_original_url, &field_num_checksum, &field_num_record_id);

  /* If the file contains all three fields, read the complete file. */
  if (field_num_original_url == -1
      || field_num_checksum == -1
      || field_num_record_id == -1)
    {
      if (field_num_original_url == -1)
        logprintf (LOG_NOTQUIET, _("CDX file does not list original urls. (Missing column 'a'.)\n"));
      if (field_num_checksum == -1)
        logprintf (LOG_NOTQUIET, _("CDX file does not list checksums. (Missing column 'k'.)\n"));
      if (field_num_record_id == -1)
        logprintf (LOG_NOTQUIET, _("CDX file does not list record ids. (Missing column 'u'.)\n"));
    }
  else
    {
      /* Initialize the table. */
      warc_cdx_dedup_table = hash_table_new (1000, warc_hash_sha1_digest, warc_cmp_sha1_digest);

      do
        {
          line_length = getline (&lineptr, &n, f);
          if (line_length != -1)
            warc_process_cdx_line (lineptr, field_num_original_url, field_num_checksum, field_num_record_id);

        }
      while (line_length != -1);

      /* Print results. */
      int nrecords = hash_table_count (warc_cdx_dedup_table);
      logprintf (LOG_VERBOSE, ngettext ("Loaded %d record from CDX.\n\n",
                                        "Loaded %d records from CDX.\n\n", nrecords),
                              nrecords);
    }

  fclose (f);

  return true;
}
#undef CDX_FIELDSEP

/* Returns the existing duplicate CDX record for the given url and payload
   digest.  Returns NULL if the url is not found or if the payload digest
   does not match, or if CDX deduplication is disabled. */
static struct warc_cdx_record *
warc_find_duplicate_cdx_record (char *url, char *sha1_digest_payload)
{
  if (warc_cdx_dedup_table == NULL)
    return NULL;

  char *key;
  struct warc_cdx_record *rec_existing;
  hash_table_get_pair (warc_cdx_dedup_table, sha1_digest_payload, &key, &rec_existing);

  if (rec_existing != NULL && strcmp (rec_existing->url, url) == 0)
    return rec_existing;
  else
    return NULL;
}

/* Initializes the WARC writer (if opt.warc_filename is set).
   This should be called before any WARC record is written. */
void
warc_init ()
{
  warc_write_ok = true;

  if (opt.warc_filename != NULL)
    {
      if (opt.warc_cdx_dedup_filename != NULL)
        {
          if (! warc_load_cdx_dedup_file ())
            {
              logprintf (LOG_NOTQUIET,
                         _("Could not read CDX file %s for deduplication.\n"),
                         quote (opt.warc_cdx_dedup_filename));
              exit(1);
            }
        }

      warc_manifest_fp = warc_tempfile ();
      if (warc_manifest_fp == NULL)
        {
          logprintf (LOG_NOTQUIET, _("Could not open temporary WARC manifest file.\n"));
          exit(1);
        }

      if (opt.warc_keep_log)
        {
          warc_log_fp = warc_tempfile ();
          if (warc_log_fp == NULL)
            {
              logprintf (LOG_NOTQUIET, _("Could not open temporary WARC log file.\n"));
              exit(1);
            }
          log_set_warc_log_fp (warc_log_fp);
        }

      warc_current_file_number = -1;
      if (! warc_start_new_file (false))
        {
          logprintf (LOG_NOTQUIET, _("Could not open WARC file.\n"));
          exit(1);
        }

      if (opt.warc_cdx_enabled)
        {
          if (! warc_start_cdx_file ())
            {
              logprintf (LOG_NOTQUIET, _("Could not open CDX file for output.\n"));
              exit(1);
            }
        }
    }
}

/* Writes metadata (manifest, configuration, log file) to the WARC file. */
void
warc_write_metadata ()
{
  /* If there are multiple WARC files, the metadata should be written to a separate file. */
  if (opt.warc_maxsize > 0)
    warc_start_new_file (true);

  char manifest_uuid [48];
  warc_uuid_str (manifest_uuid);

  fflush (warc_manifest_fp);
  warc_write_resource_record (manifest_uuid,
                              "metadata://gnu.org/software/wget/warc/MANIFEST.txt",
                              NULL, NULL, NULL, "text/plain",
                              warc_manifest_fp, -1);
  /* warc_write_resource_record has closed warc_manifest_fp. */

  FILE * warc_tmp_fp = warc_tempfile ();
  if (warc_tmp_fp == NULL)
    {
      logprintf (LOG_NOTQUIET, _("Could not open temporary WARC file.\n"));
      exit(1);
    }
  fflush (warc_tmp_fp);
  fprintf (warc_tmp_fp, "%s\n", program_argstring);

  warc_write_resource_record (manifest_uuid,
                              "metadata://gnu.org/software/wget/warc/wget_arguments.txt",
                              NULL, NULL, NULL, "text/plain",
                              warc_tmp_fp, -1);
  /* warc_write_resource_record has closed warc_tmp_fp. */

  if (warc_log_fp != NULL)
    {
      warc_write_resource_record (NULL,
                                  "metadata://gnu.org/software/wget/warc/wget.log",
                                  NULL, manifest_uuid, NULL, "text/plain",
                                  warc_log_fp, -1);
      /* warc_write_resource_record has closed warc_log_fp. */

      warc_log_fp = NULL;
      log_set_warc_log_fp (NULL);
    }
}

/* Finishes the WARC writing.
   This should be called at the end of the program. */
void
warc_close ()
{
  if (warc_current_file != NULL)
    {
      warc_write_metadata ();
      free (warc_current_warcinfo_uuid_str);
      fclose (warc_current_file);
    }
  if (warc_current_cdx_file != NULL)
    fclose (warc_current_cdx_file);
  if (warc_log_fp != NULL)
    {
      fclose (warc_log_fp);
      log_set_warc_log_fp (NULL);
    }
}

/* Creates a temporary file for writing WARC output.
   The temporary file will be created in opt.warc_tempdir.
   Returns the pointer to the temporary file, or NULL. */
FILE *
warc_tempfile ()
{
  char filename[100];
  if (path_search (filename, 100, opt.warc_tempdir, "wget", true) == -1)
    return NULL;

  int fd = mkstemp (filename);
  if (fd < 0)
    return NULL;

  if (unlink (filename) < 0)
    return NULL;

  return fdopen (fd, "wb+");
}


/* Writes a request record to the WARC file.
   url  is the target uri of the request,
   timestamp_str  is the timestamp of the request (generated with warc_timestamp),
   record_uuid  is the uuid of the request (generated with warc_uuid_str),
   body  is a pointer to a file containing the request headers and body.
   ip  is the ip address of the server (or NULL),
   Calling this function will close body.
   Returns true on success, false on error. */
bool
warc_write_request_record (char *url, char *timestamp_str, char *record_uuid, ip_address *ip, FILE *body, off_t payload_offset)
{
  warc_write_start_record ();
  warc_write_header ("WARC-Type", "request");
  warc_write_header ("WARC-Target-URI", url);
  warc_write_header ("Content-Type", "application/http;msgtype=request");
  warc_write_date_header (timestamp_str);
  warc_write_header ("WARC-Record-ID", record_uuid);
  warc_write_ip_header (ip);
  warc_write_header ("WARC-Warcinfo-ID", warc_current_warcinfo_uuid_str);
  warc_write_digest_headers (body, payload_offset);
  warc_write_block_from_file (body);
  warc_write_end_record ();
  
  fclose (body);

  return warc_write_ok;
}

/* Writes a response record to the CDX file.
   url  is the target uri of the request/response,
   timestamp_str  is the timestamp of the request that generated this response,
                  (generated with warc_timestamp),
   mime_type  is the mime type of the response body (will be printed to CDX),
   response_code  is the HTTP response code (will be printed to CDX),
   payload_digest  is the sha1 digest of the payload,
   redirect_location  is the contents of the Location: header, or NULL (will be printed to CDX),
   offset  is the position of the WARC record in the WARC file,
   warc_filename  is the filename of the WARC,
   response_uuid  is the uuid of the response.
   Returns true on success, false on error. */
static bool
warc_write_cdx_record (char *url, char *timestamp_str, char *mime_type, int response_code, char *payload_digest, char *redirect_location, off_t offset, char *warc_filename, char *response_uuid)
{
  /* Transform the timestamp. */
  char timestamp_str_cdx [15];
  memcpy (timestamp_str_cdx     , timestamp_str     , 4); /* "YYYY" "-" */
  memcpy (timestamp_str_cdx +  4, timestamp_str +  5, 2); /* "mm"   "-" */
  memcpy (timestamp_str_cdx +  6, timestamp_str +  8, 2); /* "dd"   "T" */
  memcpy (timestamp_str_cdx +  8, timestamp_str + 11, 2); /* "HH"   ":" */
  memcpy (timestamp_str_cdx + 10, timestamp_str + 14, 2); /* "MM"   ":" */
  memcpy (timestamp_str_cdx + 12, timestamp_str + 17, 2); /* "SS"   "Z" */
  timestamp_str_cdx[14] = '\0';
  
  /* Rewrite the checksum. */
  char *checksum;
  if (payload_digest != NULL)
    checksum = payload_digest + 5; /* Skip the "sha1:" */
  else
    checksum = "-";

  if (mime_type == NULL || strlen(mime_type) == 0)
    mime_type = "-";
  if (redirect_location == NULL || strlen(redirect_location) == 0)
    redirect_location = "-";

  /* Print the CDX line. */
  fprintf (warc_current_cdx_file, "%s %s %s %s %d %s %s - %ld %s %s\n", url, timestamp_str_cdx, url, mime_type, response_code, checksum, redirect_location, offset, warc_current_filename, response_uuid);
  fflush (warc_current_cdx_file);

  return true;
}

/* Writes a revisit record to the WARC file.
   url  is the target uri of the request/response,
   timestamp_str  is the timestamp of the request that generated this response
                  (generated with warc_timestamp),
   concurrent_to_uuid  is the uuid of the request for that generated this response
                 (generated with warc_uuid_str),
   refers_to_uuid  is the uuid of the original response
                 (generated with warc_uuid_str),
   payload_digest  is the sha1 digest of the payload,
   ip  is the ip address of the server (or NULL),
   body  is a pointer to a file containing the response headers (without payload).
   Calling this function will close body.
   Returns true on success, false on error. */
static bool
warc_write_revisit_record (char *url, char *timestamp_str, char *concurrent_to_uuid, char *payload_digest, char *refers_to, ip_address *ip, FILE *body)
{
  char revisit_uuid [48];
  warc_uuid_str (revisit_uuid);

  char *block_digest = NULL;
  char sha1_res_block[SHA1_DIGEST_SIZE];
  sha1_stream (body, sha1_res_block);
  block_digest = warc_base32_sha1_digest (sha1_res_block);

  warc_write_start_record ();
  warc_write_header ("WARC-Type", "revisit");
  warc_write_header ("WARC-Record-ID", revisit_uuid);
  warc_write_header ("WARC-Warcinfo-ID", warc_current_warcinfo_uuid_str);
  warc_write_header ("WARC-Concurrent-To", concurrent_to_uuid);
  warc_write_header ("WARC-Refers-To", refers_to);
  warc_write_header ("WARC-Profile", "http://netpreserve.org/warc/1.0/revisit/identical-payload-digest");
  warc_write_header ("WARC-Truncated", "length");
  warc_write_header ("WARC-Target-URI", url);
  warc_write_date_header (timestamp_str);
  warc_write_ip_header (ip);
  warc_write_header ("Content-Type", "application/http;msgtype=response");
  warc_write_header ("WARC-Block-Digest", block_digest);
  warc_write_header ("WARC-Payload-Digest", payload_digest);
  warc_write_block_from_file (body);
  warc_write_end_record ();
  
  fclose (body);
  free (block_digest);

  return warc_write_ok;
}

/* Writes a response record to the WARC file.
   url  is the target uri of the request/response,
   timestamp_str  is the timestamp of the request that generated this response
                  (generated with warc_timestamp),
   concurrent_to_uuid  is the uuid of the request for that generated this response
                 (generated with warc_uuid_str),
   ip  is the ip address of the server (or NULL),
   body  is a pointer to a file containing the response headers and body.
   mime_type  is the mime type of the response body (will be printed to CDX),
   response_code  is the HTTP response code (will be printed to CDX),
   redirect_location  is the contents of the Location: header, or NULL (will be printed to CDX),
   Calling this function will close body.
   Returns true on success, false on error. */
bool
warc_write_response_record (char *url, char *timestamp_str, char *concurrent_to_uuid, ip_address *ip, FILE *body, off_t payload_offset, char *mime_type, int response_code, char *redirect_location)
{
  char *block_digest = NULL;
  char *payload_digest = NULL;
  char sha1_res_block[SHA1_DIGEST_SIZE];
  char sha1_res_payload[SHA1_DIGEST_SIZE];

  if (opt.warc_digests_enabled)
    {
      /* Calculate the block and payload digests. */
      rewind (body);
      if (warc_sha1_stream_with_payload (body, sha1_res_block, sha1_res_payload, payload_offset) == 0)
        {
          /* Decide (based on url + payload digest) if we have seen this
             data before. */
          struct warc_cdx_record *rec_existing = warc_find_duplicate_cdx_record (url, sha1_res_payload);
          if (rec_existing != NULL)
            {
              /* Found an existing record. */
              logprintf (LOG_VERBOSE, _("Found exact match in CDX file. Saving revisit record to WARC.\n"));

              /* Remove the payload from the file. */
              if (payload_offset > 0)
                {
                  if (ftruncate (fileno (body), payload_offset) == -1)
                    return false;
                }

              /* Send the original payload digest. */
              payload_digest = warc_base32_sha1_digest (sha1_res_payload);
              bool result = warc_write_revisit_record (url, timestamp_str, concurrent_to_uuid, payload_digest, rec_existing->uuid, ip, body);
              free (payload_digest);

              return result;
            }

          block_digest = warc_base32_sha1_digest (sha1_res_block);
          payload_digest = warc_base32_sha1_digest (sha1_res_payload);
        }
    }

  /* Not a revisit, just store the record. */

  char response_uuid [48];
  warc_uuid_str (response_uuid);

  fseeko (warc_current_file, 0L, SEEK_END);
  off_t offset = ftello (warc_current_file);

  warc_write_start_record ();
  warc_write_header ("WARC-Type", "response");
  warc_write_header ("WARC-Record-ID", response_uuid);
  warc_write_header ("WARC-Warcinfo-ID", warc_current_warcinfo_uuid_str);
  warc_write_header ("WARC-Concurrent-To", concurrent_to_uuid);
  warc_write_header ("WARC-Target-URI", url);
  warc_write_date_header (timestamp_str);
  warc_write_ip_header (ip);
  warc_write_header ("WARC-Block-Digest", block_digest);
  warc_write_header ("WARC-Payload-Digest", payload_digest);
  warc_write_header ("Content-Type", "application/http;msgtype=response");
  warc_write_block_from_file (body);
  warc_write_end_record ();

  fclose (body);

  if (warc_write_ok && opt.warc_cdx_enabled)
    {
      /* Add this record to the CDX. */
      warc_write_cdx_record (url, timestamp_str, mime_type, response_code, payload_digest, redirect_location, offset, warc_current_filename, response_uuid);
    }

  if (block_digest)
    free (block_digest);
  if (payload_digest)
    free (payload_digest);

  return warc_write_ok;
}

/* Writes a resource record to the WARC file.
   resource_uuid  is the uuid of the resource (or NULL),
   url  is the target uri of the resource,
   timestamp_str  is the timestamp (generated with warc_timestamp),
   concurrent_to_uuid  is the uuid of the request for that generated this resource
                 (generated with warc_uuid_str) or NULL,
   ip  is the ip address of the server (or NULL),
   content_type  is the mime type of the body (or NULL),
   body  is a pointer to a file containing the resource data.
   Calling this function will close body.
   Returns true on success, false on error. */
bool
warc_write_resource_record (char *resource_uuid, char *url, char *timestamp_str, char *concurrent_to_uuid, ip_address *ip, char *content_type, FILE *body, off_t payload_offset)
{
  if (resource_uuid == NULL)
    {
      resource_uuid = alloca (48);
      warc_uuid_str (resource_uuid);
    }

  if (content_type == NULL)
    content_type = "application/octet-stream";

  warc_write_start_record ();
  warc_write_header ("WARC-Type", "resource");
  warc_write_header ("WARC-Record-ID", resource_uuid);
  warc_write_header ("WARC-Warcinfo-ID", warc_current_warcinfo_uuid_str);
  warc_write_header ("WARC-Concurrent-To", concurrent_to_uuid);
  warc_write_header ("WARC-Target-URI", url);
  warc_write_date_header (timestamp_str);
  warc_write_ip_header (ip);
  warc_write_digest_headers (body, payload_offset);
  warc_write_header ("Content-Type", content_type);
  warc_write_block_from_file (body);
  warc_write_end_record ();
  
  fclose (body);

  return warc_write_ok;
}