Blob filter sample code

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Blob filter sample code

Source: http://www.ibphoenix.com/

The contents of this file are subject to the Interbase Public License Version 1.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.Inprise.com/IPL.html.

Software distributed under the License is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for the specific language governing rights and limitations under the License.

The Original Code was created by Inprise Corporation and its predecessors. Portions created by Inprise Corporation are Copyright (C) Inprise Corporation.

All Rights Reserved.

Contributor(s): ______________________________________.

 /*  Include the usual suspects */
 #include <stdio.h>
 #include  <string.h>
 #include  <errno.h>
 #include <stdlib.h>
 #include  <io.h>
 #include  <ctype.h>
 #include  <ibase.h>

 /* special header file for shared library */

 #include "my_filter.h"

 /* routines in the filter */

 static int blob_to_file (ISC_BLOB_CTL);
 static int caller (short, ISC_BLOB_CTL,short, char*,  short*);
 static int make_file (ISC_BLOB_CTL);
 static int read_file (ISC_BLOB_CTL);
 static void set_statistics (ISC_BLOB_CTL);
 static int unzip (ISC_BLOB_CTL);
 static int unzip_blob (ISC_BLOB_CTL);
 static int write_file (ISC_BLOB_CTL);
 static int zip (ISC_BLOB_CTL);
 static int zip_file (ISC_BLOB_CTL);

 /* These should probably be in ibase.h */

 #define ACTION_open    0
 #define ACTION_get_segment    1
 #define ACTION_close    2
 #define ACTION_create    3
 #define ACTION_put_segment    4
 #define ACTION_alloc    5
 #define ACTION_free    6
 #define ACTION_seek    7

 /* the simple return codes */

 #define SUCCESS            0
 #define FAILURE            1

 /* the two blob subtypes translated by this filter */

 #define ZIPPED            -2
 #define UNZIPPED            1

 /* random value */

 static int width = 40;

 int unzip_filter ( short action,
    ISC_BLOB_CTL control)
 {
 /**************************************
  *
  *    u n z i p _  f i l t e r 
  *
  **************************************
  *
  * Functional description
  *    read a  zipped blob and translate
  *      it to an unzipped blob.  Since this
  *      particular version of zip just inverts
  *      the blob, both sides are the same.
  *
  **************************************/
    return zip_filter (action, control);
 }

 int zip_filter ( short action, 
    ISC_BLOB_CTL control)
 {
 /**************************************
  *
  *    z i p _  f i l t e r 
  *
  **************************************
  *
  * Functional description
  *    zip a blob and store it.  In this
  *      case "zip" just means invert.  Most
  *      blob filters start out with a switch
  *      statement like this.
  *
  **************************************/
     int    status; 

     switch (action)
         {

         /* open is called on an existing blob, so we create
            a temporary file and unzip the blob contents into it */ 

         case ACTION_open:
        status = make_file (control);

        if (!status)
            status = unzip_blob (control);
        break;

         /* create is called to make a new blob getting data
        from the user.  Create a temporary file and wait
        for input. */

         case ACTION_create:
        status = (make_file (control));
        break;

         /* get segment is called after an open when the user
            wants data.  The blob has already been unzipped into
       a file, so we'll read back sections of the file */

         case ACTION_get_segment:
        status = read_file (control);
        break;

         /* close is called after both reading and creating a
            blob.  In the read case, we just need to get rid 
       of the temporary file.  In the write case, we've got
       the data in a file in the form the user sent it.
       We need to zip it and pump it into the database. */

     case ACTION_close:
        if (control->ctl_to_sub_type == ZIPPED)
            status = zip_file (control); 

        if ((FILE *)control->ctl_data[0])
            status = fclose ((FILE *)control->ctl_data[0]);

        if (!status && (char *)control->ctl_data[0])
            {
            status = unlink ((char *)control->ctl_data[4]);
            if (!status)
           free ((char *)control->ctl_data[4]);
            }

         break;

         /* put segment is called when the user has created a
            blob and wants to stuff data into it.  We hold the
       data in the temporary file that we made during the
       create call */ 

         case ACTION_put_segment:
        status = write_file (control);
        break;

         }

     return status;
     }

 static int blob_to_file (ISC_BLOB_CTL control)
 {
 /**************************************
  *
  *    b l o b _ t o _ f i l e 
  *
  **************************************
  *
  * Functional description
  *    Dump a blob into the temp file.  Here
  *      we need to call back into the engine -
  *      or whoever it was who called us - and 
  *      ask for the segments of the blob.  We
  *      set up our own buffer and call to caller.
  *
  **************************************/
     FILE           *temp_file;
     short       length;
     char           buffer [1024], *p;
     int           status, c = 'n';

     temp_file = (FILE *)control->ctl_data[0];

     while (!(status = caller (ACTION_get_segment, control, 
        sizeof (buffer) - 1, buffer, &length)) ||
        status == isc_segment)
         {
         for (p = buffer; p < buffer + length; p++)
        fputc (*p, temp_file);
         }
     fputc (c, temp_file);
     return SUCCESS;
 }

 static int caller ( short action,
     ISC_BLOB_CTL control,
      short buffer_length,
      char *buffer,
      short *return_length)
 {
 /**************************************
  *
  *        c a l l e r
  *
  **************************************
  *
  * Functional description
  *        Call next source filter.  This 
  *        is an essential service routine for
  *        all blob filters.  The blob control
  *     block passed in to the filter includes
  *        both the handle of the caller's blob
  *        control block and the address of a
  *        routine to call to re-invoke the caller.
  *     
  **************************************/
     int              status;
     ISC_BLOB_CTL        source;

     source = control->ctl_source_handle;
     source->ctl_status = control->ctl_status;
     source->ctl_buffer = buffer;
     source->ctl_buffer_length = buffer_length;

     status = (*source->ctl_source) (action, source);

     if (return_length)
         *return_length = source->ctl_segment_length;

     return status;
 }

 static int file_to_blob (ISC_BLOB_CTL control)
 {
 /**************************************
  *
  *        f i l e _ t o _ b l o b
  *
  **************************************
  *
  * Functional description
  *        Copy a file to a blob, including
  *      the last little bit.  Since we 
  *      just finished writing the file,
  *         rewind before start.
  *
  **************************************/
     FILE *  temp_file;
     short       length;
     char           buffer [1024], *p, c;
     int           status;

     memset (buffer, 0, sizeof(buffer));
     temp_file = (FILE *)control->ctl_data[0];
     rewind (temp_file);
     p = buffer;

     for (;;)
         {
         c = fgetc (temp_file);
         if (feof (temp_file))
        break;
         *p++ = c;

         if (p > buffer + control->ctl_buffer_length)
        {
        status = caller (ACTION_put_segment, control, 
            sizeof (buffer) - 1, buffer, &length);
        p = buffer;
        }
         }

     status = caller (ACTION_put_segment, control, 
            (short) (p - buffer), buffer, &length);
     fclose (temp_file);
     unlink ((char *)control->ctl_data[4]);
     free ((char *)control->ctl_data[4]);

     return SUCCESS;
 }

 static int make_file (ISC_BLOB_CTL control)
 {
 /**************************************
  *
  *    m a k e _ f i l e
  *
  **************************************
  *
  * Functional description
  *    create a temp file and store the handle
  *    and a pointer to the filename in ctl_data
  *
  **************************************/
     FILE           *temp_file;
     char           *temp = "awhXXXXX", *file_name, *result;  

     file_name = malloc (50);
     strncpy (file_name, temp, 50);

     if (result = mktemp (file_name))
         return FAILURE;

     if (!(temp_file = fopen (file_name, "w+b")))
         return FAILURE;  

     control->ctl_data[0] = (long) temp_file;
     control->ctl_data[4] = (long) file_name; 

     return SUCCESS;

  }

 static int read_file (ISC_BLOB_CTL control)
 {
 /**************************************
  *
  *    r e a d _ f i l e 
  *
  **************************************
  *
  * Functional description
  *    Reads a file one line at a time 
  *    and puts the data out as if it 
  *    were coming from a blob. 
  *
  **************************************/
     char    *p;
     FILE    *temp_file;
     short    length;
     int    c;

     if (control->ctl_to_sub_type != UNZIPPED)
         return isc_uns_ext;

     p = control->ctl_buffer;
     length = control->ctl_buffer_length;
     temp_file = (FILE *)control->ctl_data [0];

     for (;;) 
         {
         c = fgetc (temp_file);

         if (feof (temp_file))
        break;
         *p++ = c;

         if ((c == 'n')  || p >= control->ctl_buffer + length)
        {
        control->ctl_segment_length = p - control->ctl_buffer; 
        return (c == 'n') ? SUCCESS: isc_segment;
        }
         }

     return isc_segstr_eof;
 }

 static void set_statistics (ISC_BLOB_CTL control)
 {
 /*************************************
  *
  *    s e t _ s t a t i s t i c s
  *
  *************************************
  *
  * Functional description
  *    Sets up the statistical fields
  *    in the passed in ctl structure.
  *    These fields are:
  *      ctl_max_segment - length of
  *         longest seg in blob (in
  *         bytes)
  *      ctl_number_segments - # of
  *         segments in blob
  *      ctl_total_length - total length
  *         of blob in bytes.
  *    we should reset the
  *    ctl structure, so that 
  *    blob_info calls get the right
  *    values.
  *
  *************************************/
     int    max_seg_length = 0;
     int    length = 0;
     int    num_segs = 0;
     int    cur_length = 0;
     FILE        *temp_file;
     char        c;

     temp_file = (FILE *)(control->ctl_data[0]);
     rewind (temp_file);

     for (;;)
         {
         c = fgetc (temp_file);  

         if (feof (temp_file))
        break;

         length++;
         cur_length++;

         if (c == 'n')    /* that means we are at end of seg */
        {
        if (cur_length > max_seg_length)
            max_seg_length = cur_length;
        num_segs++;
        cur_length = 0;
        }
         }

     control->ctl_max_segment = max_seg_length;
     control->ctl_number_segments = num_segs;
     control->ctl_total_length = length;
     }

 static int write_file (ISC_BLOB_CTL control)
 {
 /**************************************
  *
  *    w r i t e _ f i l e 
  *
  **************************************
  *
  * Functional description
  *      
  *      takes user input and saves it in
  *      a temporary file.
  *    
  **************************************/
     char       *p;
     FILE       *temp_file;
     short   length;

     if (control->ctl_to_sub_type != ZIPPED)
         return isc_uns_ext;

     p = control->ctl_buffer;
     length = control->ctl_buffer_length;
     temp_file = (FILE *)control->ctl_data [0];

     while (p < control->ctl_buffer + length) 
         {
         fputc (*p++, temp_file);
         }

     return SUCCESS;
 }

 static int unzip (ISC_BLOB_CTL control)
 {
 /**************************************
  *
  *    u n z i p 
  *
  **************************************
  *
  * Functional description
  *    in theory call unzip.  In fact
  *      read the blob and 
  *
  **************************************/

     return zip (control);
 }

 static int unzip_blob (ISC_BLOB_CTL control)
 {
 /**************************************
  *
  *    u n z i p _ b l o b
  *
  **************************************
  *
  * Functional description
  *    read a blob into a file.  
  *
  **************************************/
     blob_to_file (control); 
     return unzip (control);
 }

 static int zip (ISC_BLOB_CTL control)
 {
 /**************************************
  *
  *    z i p 
  *
  **************************************
  *
  * Functional description
  *    in theory call zip.  In fact
  *      just invert the file
  *
  **************************************/
     FILE           *in_file, *out_file;
     char           *buffer, *p, *in_file_name;
     int           c; 

     set_statistics (control);
     in_file = (FILE *)control->ctl_data[0];
     in_file_name = (char *)control->ctl_data[4];
     rewind (in_file);
     c = fgetc (in_file);  

     if (make_file (control))
         return FAILURE;

     out_file = (FILE *)control->ctl_data[0];
     buffer = malloc (control->ctl_total_length + 1);
     memset (buffer, 0, control->ctl_total_length + 1);

     p = buffer + (control->ctl_total_length);


     *(p) = 'n';

     while (!feof (in_file))
         {
         *(--p) = (char)c;

         if (p <= buffer)
        break;

         c = fgetc (in_file);
         }

     fclose (in_file);
     unlink (in_file_name);
     free (in_file_name);

     while (p < buffer + control->ctl_total_length)
         fputc ((int)*p++, out_file);

    fputc ('n', out_file);
     rewind (out_file);

     free (buffer);

     return SUCCESS;
 }

 static int zip_file (ISC_BLOB_CTL control)
 {
 /**************************************
  *
  *    z i p  _ f i l e 
  *
  **************************************
  *
  * Functional description
  *    invert a file and put it into a blob
  *
  **************************************/

     if (control->ctl_to_sub_type != ZIPPED)
         return isc_uns_ext;

     zip (control);

     file_to_blob (control);

     return SUCCESS;

 }

See also:
Blob datatype
Blob filter
IBExpert Blob Viewer/Editor
Stream blobs

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