From fd0f3fb9011bea6918b564ecc7c13c771db78a1b Mon Sep 17 00:00:00 2001
From: Pedro Portela <pedro.portela@cs.tu-dortmund.de>
Date: Wed, 4 Jun 2025 23:54:47 +0200
Subject: [PATCH] Read PNG Magic

---
 img_png.c | 23 +++++++++++++++++++++++
 img_png.h |  9 ++++++++-
 main.c    | 12 ++++++++++--
 3 files changed, 41 insertions(+), 3 deletions(-)
 create mode 100644 img_png.c

diff --git a/img_png.c b/img_png.c
new file mode 100644
index 0000000..a0ee188
--- /dev/null
+++ b/img_png.c
@@ -0,0 +1,23 @@
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include "img_png.h"
+
+uint8_t* img_png_decode(FILE *fp) {
+  unsigned char buffer[8];
+  size_t bufsize = sizeof(buffer) / sizeof((buffer)[0]);
+  
+  size_t ret = fread(buffer, sizeof(*buffer), bufsize, fp);
+
+  if(ret != bufsize) {
+    fprintf(stderr, "fread() failed. Expected %zu bytes, got %zu\n", bufsize, ret);
+    return NULL;
+  }
+
+  printf("PNG Magic: %#04x%02x%02x%02x%02x%02x%02x%02x\n", buffer[0], buffer[1], buffer[2],
+         buffer[3], buffer[4], buffer[5], buffer[6], buffer[7]);
+
+  return NULL;
+}
+
+
diff --git a/img_png.h b/img_png.h
index cb20236..506ea91 100644
--- a/img_png.h
+++ b/img_png.h
@@ -1,6 +1,13 @@
 #include <stdint.h>
 #include <stdio.h>
 
-const char img_png_signature[] = {0x89, };
+//const unsigned char img_png_signature[] = {0x89, 'P', 'N', 'G', '\r', '\n', 0x1a, '\n'};
+
+struct img_png_chunk {
+  int length;
+  int chunk_type;
+  char* chunk_data;
+  int crc;
+};
 
 uint8_t* img_png_decode (FILE* fp);
diff --git a/main.c b/main.c
index 7600b13..1ee8965 100644
--- a/main.c
+++ b/main.c
@@ -1,9 +1,10 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include "img_png.h"
 
 int main(int argc, char** argv) {
   if(argc != 2) {
-    fprintf(stderr, "Usage: ./imgvwr FILE");
+    fprintf(stderr, "Usage: ./imgvwr FILE\n");
     exit(EXIT_FAILURE);
   }
 
@@ -13,5 +14,12 @@ int main(int argc, char** argv) {
     exit(EXIT_FAILURE);
   }
 
-  
+  /*if(!img_png_decode(fp_image)) {
+    fprintf(stderr, "Could not parse PNG file!\n");
+    exit(EXIT_FAILURE);
+  }*/
+
+  img_png_decode(fp_image);
+
+  return 0;
 }