reader: read and parse a BMP headers

we retrieve valuable information such as the data offset, the width and
the height of the picture which path is passed as parameter.

Signed-off-by: Olivier Gayot <duskcoder@gmail.com>

1 files changed, 180 insertions, 0 deletions

diff --git a/stegmp.c b/stegmp.c
new file mode 100644
index 0000000..b1f42a8
--- /dev/null
+++ b/stegmp.c
@@ -0,0 +1,180 @@
+/*
+ * Copyright (C) 2014 Olivier Gayot <duskcoder@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include <string.h>
+#include <stdio.h>
+
+#include "bmp.h"
+
+static int stegmp_parse_windows_bitmap_info_header(const unsigned char *addr,
+        size_t size, struct bitmap *bmpp)
+{
+    struct bitmap_info_header info_header;
+
+    if (size < sizeof(typeof(info_header))) {
+        bmp_errno = BMP_EINVALSIZ;
+        return -1;
+    }
+
+    info_header = *((typeof(info_header) *)addr);
+
+    switch (info_header.bpp) {
+        case 8:
+        case 16:
+        case 24:
+        case 32:
+            bmpp->bpp = info_header.bpp;
+                break;
+        default:
+            bmp_errno = BMP_EINVALBPP;
+            return -1;
+    }
+
+    /* TODO check the compression type */
+
+    bmpp->width = info_header.bmp_width;
+    bmpp->height = info_header.bmp_height;
+
+    return 0;
+}
+
+/* guess which type of DIB header it is and handle it or not */
+static int stegmp_parse_dib_header(const unsigned char *addr, size_t size,
+        struct bitmap *bmpp)
+{
+    uint32_t dib_size;
+
+    if (size < sizeof(typeof(dib_size))) {
+        bmp_errno = BMP_EINVALSIZ;
+        return -1;
+    }
+
+    dib_size = *((typeof(dib_size) *)addr);
+
+    switch (dib_size) {
+        case 12:
+        case 52:
+        case 56:
+        case 64:
+        case 108:
+        case 124:
+            bmp_errno = BMP_ENOTSUPP;
+            return -1;
+
+        case 40:
+            return stegmp_parse_windows_bitmap_info_header(addr, size, bmpp);
+
+        default:
+            bmp_errno = BMP_ENOTBMP;
+            return -1;
+    }
+}
+
+/* parse the main header of the bmp file */
+static int stegmp_parse_headers(const unsigned char *addr, size_t orig_size,
+        struct bitmap *bmpp)
+{
+    struct packed_bmp_header packed_header;
+
+    if (orig_size < sizeof(packed_header)) {
+        bmp_errno = BMP_ENOTBMP;
+        return -1;
+    }
+
+    packed_header = *((typeof(packed_header) *)addr);
+
+    switch (packed_header.magic) {
+        case BMP_MAGIC_BM:
+            break;
+
+        case BMP_MAGIC_BA:
+        case BMP_MAGIC_CI:
+        case BMP_MAGIC_CP:
+        case BMP_MAGIC_IC:
+        case BMP_MAGIC_PT:
+            bmp_errno = BMP_ENOTSUPP;
+            return -1;
+        default:
+            bmp_errno = BMP_ENOTBMP;
+            return -1;
+    }
+
+    if (packed_header.bmp_size != orig_size) {
+        bmp_errno = BMP_EINVALSIZ;
+        return -1;
+    }
+
+    bmpp->data_offset = packed_header.data_offset;
+    bmpp->size = packed_header.bmp_size;
+
+    stegmp_parse_dib_header(addr + sizeof(packed_header), orig_size, bmpp);
+
+    return 0;
+}
+
+static int stegmp(const char *filename)
+{
+    void *addr;
+    struct stat stat;
+    struct bitmap bmp;
+    FILE *fh = fopen(filename, "r+");
+
+    if (fh == NULL) {
+        fprintf(stderr, "%s: %m\n", filename);
+        return -1;
+    }
+
+    fstat(fileno(fh), &stat);
+    addr = mmap(NULL, stat.st_size, PROT_READ | PROT_WRITE, MAP_PRIVATE,
+            fileno(fh), 0);
+
+    if (addr == MAP_FAILED) {
+        fprintf(stderr, "%s: %m\n", filename);
+        fclose(fh);
+        return -1;
+    }
+
+    /* retrieve the required information (i.e. width, height, bpp .. ) */
+    if (stegmp_parse_headers(addr, stat.st_size, &bmp) >= 0) {
+        /* TODO */
+    } else {
+        fprintf(stderr, "unable to parse headers: %s\n",
+                bmp_strerror(bmp_errno));
+    }
+
+    munmap(addr, stat.st_size);
+    fclose(fh);
+
+    return 0;
+}
+
+int main(int argc, char *argv[])
+{
+    /* we need a file passed as argument since we want to map it */
+    if (argc < 2) {
+        fprintf(stderr, "usage: %s BMP\n", argv[0]);
+        return -1;
+    }
+
+    return stegmp(argv[1]);
+}