From 3f73faf04bb5a64b4b03b27186748807d8ce6590 Mon Sep 17 00:00:00 2001
From: Pedro Portela <pedro.portela@cs.tu-dortmund.de>
Date: Thu, 5 Jun 2025 21:21:23 +0200
Subject: [PATCH] Partial implementation of read_chunk function

---
 img_png.c | 74 ++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 48 insertions(+), 26 deletions(-)

diff --git a/img_png.c b/img_png.c
index 5c50c11..ac0f1de 100644
--- a/img_png.c
+++ b/img_png.c
@@ -14,16 +14,51 @@ uint32_t char_to_uint32 (unsigned char* input) {
   return val;
 }
 
-uint8_t* img_png_decode(FILE *fp) {
-  unsigned char buffer[BUFSIZE];
-  unsigned char magic[8];
-  enum chunk_state {
-    LENGTH,
-    TYPE,
-    DATA,
-    CRC
-  };
+int read_chunk(FILE *fp) {
+  struct img_png_chunk cur_chunk;
+
+  // Read chunk length
+  unsigned char len[4];
+  if(fread(len, sizeof(*len), 4, fp) < 4) {
+    fprintf(stderr, "Couldn\'t read chunk length.\n");
+    exit(EXIT_FAILURE);
+  }
+
+  cur_chunk.length = char_to_uint32(len);
+  printf("Chunk length: %lu\n", (unsigned long) cur_chunk.length);
   
+  // Read chunk type
+  if(fread(cur_chunk.chunk_type, sizeof(*cur_chunk.chunk_type), 4, fp) < 4) {
+    fprintf(stderr, "Couldn\'t read chunk type.\n");
+    exit(EXIT_FAILURE);
+  }
+  printf("Chunk type: %.*s\n", 4, cur_chunk.chunk_type);
+
+  // Read chunk data
+  size_t chunk_size = cur_chunk.length / sizeof(unsigned char);
+  printf("Chunk size: %zu\n", chunk_size);
+  cur_chunk.chunk_data = malloc(chunk_size);
+
+  if(!cur_chunk.chunk_data) {
+    perror("Failed to allocate chunk data!");
+    exit(EXIT_FAILURE);
+  }
+
+  if(fread(cur_chunk.chunk_data, 1, cur_chunk.length, fp) != cur_chunk.length) {
+    if(feof(fp)) {
+      fprintf(stderr, "File ended prematurely.\n");
+      exit(EXIT_FAILURE);
+    }
+    fprintf(stderr, "Failed to read chunk data!\n");
+    exit(EXIT_FAILURE);
+  }
+
+  return feof(fp);
+}
+
+uint8_t* img_png_decode(FILE *fp) {
+  unsigned char magic[8];
+
   // Check PNG Magic
   if(fread(magic, sizeof(*magic), 8, fp) < 8) {
     fprintf(stderr, "Couldn\'t read PNG magic.");
@@ -38,24 +73,12 @@ uint8_t* img_png_decode(FILE *fp) {
   printf("PNG Magic: %#04x%02x%02x%02x%02x%02x%02x%02x\n", magic[0], magic[1], magic[2],
          magic[3], magic[4], magic[5], magic[6], magic[7]);
 
-  // After the magic number is read, we should hit the length of the chunk first.
-  enum chunk_state state = LENGTH;
   struct img_png_chunk cur_chunk;  
-  while(fread(buffer, sizeof(*buffer), BUFSIZE, fp) > 0){
-    // Refine later!!!
-    
-    switch (state) {
-    case LENGTH: {
-      unsigned char length[4];
-      for (size_t i = 0; i < 4; i++) {
-        length[i] = buffer[i];
-      }
-      cur_chunk.length = char_to_uint32(length);
-      printf("Chunk length: %lu\n", (unsigned long)cur_chunk.length);
-    }
-    }
-  }
 
+  // Read chunk   
+  
+  while (read_chunk(fp) == 0);
+  
   if(!feof(fp)) {
     perror("fread() failed!");
     exit(EXIT_FAILURE);
@@ -64,4 +87,3 @@ uint8_t* img_png_decode(FILE *fp) {
 
   return NULL;
 }
-