gif

commit 6c8797ad5b3a3caef409000333e6671a26d73b5e
parent 7cc60d17c3dbfbf4c73c2b60a073162d363d8857
Author: phoebos <ben@bvnf.space>
Date:   Wed, 25 Aug 2021 19:51:42 +0100

it reads the whole file into a buffer. oh wow

why does it always take me so long to get to this stage
note: don't free(3) tmp

Diffstat:
M
gif.c
 | 
71
++++++++++++++++++++++++++++++++++++++++++++++++++++-------------------

1 file changed, 52 insertions(+), 19 deletions(-)
diff --git a/gif.c b/gif.c
@@ -7,39 +7,72 @@
 
 #include <fcntl.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <strings.h>
 #include <unistd.h>
 
-#define BUF_SIZE 10
-#define FAIL_SYS 1
-#define FAIL_GIF 2
+#define BUF_SIZE 100
+#define FAIL_GIF 1
+#define FAIL_SYS 2
 
 int
 main(int argc, char **argv){
     int fd;
+
+    /* only work on one file */
+    if (argc > 2) {
+        fprintf(stderr, "too many args\n");
+        return FAIL_SYS;
+    }
+
     ++argv;
-    do {
-        fd = 0;
-        if (*argv && **argv != '-') {
-            fd = open(*argv, O_RDONLY);
-            if (fd == -1) {
-                perror("open");
+    /* stdin */
+    if (argc == 1 || **argv == '-') fd = 0;
+    else {
+        /* open named file */
+        fd = open(*argv, O_RDONLY);
+        if (fd == -1) {
+            perror(*argv);
+            return FAIL_SYS;
+        }
+    }
+
+    unsigned char *buf;
+    buf = (unsigned char *) malloc(BUF_SIZE);
+
+    /* read the whole file from fd into buf. */
+    ssize_t bytes;
+    size_t size, used;
+    unsigned char *tmp;
+    used = 0;
+    size = BUF_SIZE; /* initial size from malloc(BUF_SIZE) above */
+
+    while (1) {
+        if (used + BUF_SIZE + 1 > size) {
+            size = used + BUF_SIZE + 1;
+            tmp = realloc(buf, size);
+            if (tmp == NULL) {
+                /* out of memory */
+                perror("realloc");
+                free(buf);
                 return FAIL_SYS;
             }
+            buf = tmp;
         }
-        char buf[BUF_SIZE];
-        fprintf(stderr, "reading from %s\n", *argv);
-        ssize_t bytes = read(fd, buf, BUF_SIZE);
+        bytes = read(fd, buf + used, BUF_SIZE);
+        if (bytes == 0) break; /* EOF */
         if (bytes < 0) {
             perror("read");
             return FAIL_SYS;
         }
-        if (close(fd) != 0) {
-            perror("close");
-            return FAIL_SYS;
-        }
-        buf[bytes] = '\0';
-        printf("%s\n", buf);
-    } while (*++argv);
+        used += bytes;
+    }
+
+    if (close(fd) != 0) {
+        perror("close");
+        return FAIL_SYS;
+    }
+
+    free(buf);
     return 0;
 }