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Partial implementation of read_chunk function

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This commit is contained in:
Pedro Portela 2025-06-05 21:21:23 +02:00
parent 85ee7ee10d
commit 3f73faf04b
1 changed files with 48 additions and 26 deletions
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74
img_png.c
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@ -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;
}