Add basic shapefile (.shp, .shx) support

The shapefile support includes recognition of the magic 0x0000270a and
parsing the file length. The source code is based on the template file
and file_bmp.c.

The shapefile format is described at [1], the article links to other
resources, like the Technical Description[2].

[1]: https://en.wikipedia.org/wiki/Shapefile
[2]: https://www.esri.com/content/dam/esrisites/sitecore-archive/Files/Pdfs/library/whitepapers/pdfs/shapefile.pdf

src/Makefile.am

@@ -324,6 +324,7 @@ file_C			= filegen.c \
 			  file_ses.c \
 			  file_sgcta.c \
 			  file_shn.c \
+			  file_shp.c \
 			  file_sib.c \
 			  file_sig.c \
 			  file_sit.c \

src/file_list.c

@@ -854,6 +854,9 @@ extern const file_hint_t file_hint_sgcta;
 #if !defined(SINGLE_FORMAT) || defined(SINGLE_FORMAT_shn)
 extern const file_hint_t file_hint_shn;
 #endif
+#if !defined(SINGLE_FORMAT) || defined(SINGLE_FORMAT_shp)
+extern const file_hint_t file_hint_shp;
+#endif
 #if !defined(SINGLE_FORMAT) || defined(SINGLE_FORMAT_sib)
 extern const file_hint_t file_hint_sib;
 #endif
@@ -1899,6 +1902,9 @@ file_enable_t array_file_enable[]=
 #if !defined(SINGLE_FORMAT) || defined(SINGLE_FORMAT_shn)
   { .enable=0, .file_hint=&file_hint_shn  },
 #endif
+#if !defined(SINGLE_FORMAT) || defined(SINGLE_FORMAT_shp)
+  { .enable=0, .file_hint=&file_hint_shp  },
+#endif
 #if !defined(SINGLE_FORMAT) || defined(SINGLE_FORMAT_sib)
   { .enable=0, .file_hint=&file_hint_sib  },
 #endif

src/file_shp.c

@@ -0,0 +1,84 @@
+/*
+
+    File: file_shp.c
+
+    Copyright (C) 2023 Grzegorz Szymaszek <gszymaszek@short.pl>
+
+    This software is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with this program; if not, write the Free Software Foundation, Inc., 51
+    Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+ */
+
+#if !defined(SINGLE_FORMAT) || defined(SINGLE_FORMAT_shp)
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+#ifdef HAVE_STRING_H
+#include <string.h>
+#endif
+#include <stdio.h>
+#include "types.h"
+#include "filegen.h"
+#include "common.h"
+
+static void register_header_check_shp(file_stat_t *file_stat);
+
+const file_hint_t file_hint_shp= {
+  .extension="shp",
+  .description="Shapefile",
+  .max_filesize=PHOTOREC_MAX_FILE_SIZE,
+  .recover=1,
+  .enable_by_default=1,
+  .register_header_check=&register_header_check_shp
+};
+
+static const uint8_t shp_header[4] = {0x00, 0x00, 0x27, 0x0a};
+
+/* https://en.wikipedia.org/wiki/Shapefile */
+struct shp_header
+{
+  int32_t magic;
+  int32_t reserved[5];
+  int32_t size;
+  int32_t version;
+  int32_t shape_type;
+} __attribute__ ((gcc_struct, __packed__));
+
+static int header_check_shp(const unsigned char *buffer, const unsigned int buffer_size, const unsigned int safe_header_only, const file_recovery_t *file_recovery, file_recovery_t *file_recovery_new)
+{
+  const struct shp_header *shp=(const struct shp_header *)buffer;
+  (void) buffer_size;
+  (void) safe_header_only;
+  (void) file_recovery;
+
+  if(buffer[0]!=0 || buffer[1]!=0 || buffer[2]!=0x27 || buffer[3]!=0x0a)
+    return 0;
+  if(be32(shp->size) >= 100)
+  {
+    reset_file_recovery(file_recovery_new);
+    file_recovery_new->extension=file_hint_shp.extension;
+    file_recovery_new->min_filesize=100;
+    file_recovery_new->calculated_file_size=(uint64_t)be32(shp->size);
+    file_recovery_new->data_check=&data_check_size;
+    file_recovery_new->file_check=&file_check_size;
+    return 1;
+  }
+  return 0;
+}
+
+static void register_header_check_shp(file_stat_t *file_stat)
+{
+  register_header_check(0, shp_header, sizeof(shp_header), &header_check_shp, file_stat);
+}
+#endif