gif

commit 5080ee84b8890c63119bab1e49536cd45fc7e5f6
parent 6c8797ad5b3a3caef409000333e6671a26d73b5e
Author: phoebos <ben@bvnf.space>
Date:   Fri, 27 Aug 2021 04:02:01 +0100

basic version check and [!,;]

Diffstat:
M
gif.c
 | 
55
++++++++++++++++++++++++++++++++++++++++++++++++++++++-

1 file changed, 54 insertions(+), 1 deletion(-)
diff --git a/gif.c b/gif.c
@@ -8,13 +8,54 @@
 #include <fcntl.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <strings.h>
+#include <string.h>
 #include <unistd.h>
 
 #define BUF_SIZE 100
 #define FAIL_GIF 1
 #define FAIL_SYS 2
 
+typedef char rgb[3];
+struct Gif {
+    char version[3]; /* 87a or 89a */
+    rgb colormap[255];
+    unsigned char *pixels; /* array of indices to colors */
+};
+
+
+int
+gif_decode(unsigned char *buf, size_t len){
+    struct Gif g = {0 };
+    int cur_block;
+    enum { HEAD = 1, SPEC = 2, IMGE = 4 };
+    cur_block = HEAD;
+
+    if (strncmp((char *)buf, "GIF", 3)) return FAIL_GIF;
+    buf += 3;
+    len -= 3;
+    strncpy(g.version, (char *)buf, 3);
+    fprintf(stderr, "GIF version %s\n", g.version);
+    buf += 3;
+    len -= 3;
+
+    while (--len) {
+        ++buf;
+        switch (*buf) {
+            case '!':
+                cur_block = SPEC;
+                break;
+            case ',':
+                cur_block = IMGE;
+                break;
+            case ';':
+                /* last char of image section */
+                return 0;
+        }
+    }
+
+    return 0;
+}
+
 int
 main(int argc, char **argv){
     int fd;
@@ -73,6 +114,18 @@ main(int argc, char **argv){
         return FAIL_SYS;
     }
 
+    int ret = gif_decode(buf, used);
+    switch (ret) {
+        case FAIL_GIF:
+            fprintf(stderr, "error: invalid GIF format\n");
+            return FAIL_GIF;
+        case 0:
+            break;
+        default:
+            return ret;
+    }
+
+
     free(buf);
     return 0;
 }