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This commit is contained in:
Isaac Shoebottom 2023-12-04 18:54:29 -04:00
parent 3aad46748a
commit 3aa01cdc2b
3 changed files with 37 additions and 24 deletions
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8
Assignment9/src/main.c
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@ -30,10 +30,14 @@ int main(int argc, char *argv[]) {
bool is_idat = memcmp(chunks[i]->type, "IDAT", 4) == 0;
bool is_iend = memcmp(chunks[i]->type, "IEND", 4) == 0;
if (is_idat || is_iend) {
printf("Found %s chunk\n", chunks[i]->type);
printf("Found %.4s chunk\n", chunks[i]->type);
if (is_idat) {
xor_data(chunks[i]);
}
} else {
printf("Found unknown: %s\n", chunks[i]->type);
printf("Found unknown: %.4s\n", chunks[i]->type);
}
printf("Chunk size is:%d\n", chunks[i]->length);
}
// write_png_chunks(path, chunks);
}

42
Assignment9/src/png.c
View File

@ -69,11 +69,6 @@ char *load_file(int fd) {
exit(1);
}
fread(buffer, 1, size, fp);
// Iterate over buffer and convert from network byte order to host byte order
//for (int i = 0; i < size; i += 4) {
// uint32_t *ptr = (uint32_t *)(buffer + i);
// *ptr = ntohl(*ptr);
//}
fclose(fp);
return buffer;
}
@ -111,7 +106,8 @@ png_chunk **get_png_chunks(char *buffer) {
int i = 0;
while (1) {
chunks[i] = get_png_chunk(buffer, offset);
offset += chunks[i]->length;
// 12 = 4 (length) + 4 (type) + 4 (crc)
offset += 12 + chunks[i]->length;
if (memcmp(chunks[i]->type, "IEND", 4) == 0) {
break;
}
@ -125,18 +121,6 @@ png_chunk **get_png_chunks(char *buffer) {
return chunks;
}
int is_chunk_valid(png_chunk *chunk) {
uint32_t crc = htonl(chunk->crc);
//uint32_t calculated_crc = crc32(0, chunk->type, 4);
//calculated_crc = crc32(calculated_crc, chunk->data, chunk->length);
//return crc == calculated_crc;
return 1;
}
int is_chunk_critical(png_chunk *chunk) {
return chunk->type[0] >= 'A' && chunk->type[0] <= 'Z';
}
int get_number_of_chunks(png_chunk **chunks) {
int i = 0;
while (chunks[i] != NULL) {
@ -144,3 +128,25 @@ int get_number_of_chunks(png_chunk **chunks) {
}
return i;
}
void xor_data(png_chunk *chunk) {
for (int i = 0; i < chunk->length; i++) {
chunk->data[i] ^= KEY;
}
}
void write_png_chunks(char *path, png_chunk **chunks) {
FILE *fp = fopen(path, "wb");
if (fp == NULL) {
perror("fopen");
exit(1);
}
fwrite(PNG_SIGNATURE, PNG_SIGNATURE_SIZE, 1, fp);
for (int i = 0; chunks[i] != NULL; i++) {
fwrite(&chunks[i]->length, 4, 1, fp);
fwrite(chunks[i]->type, 4, 1, fp);
fwrite(chunks[i]->data, chunks[i]->length, 1, fp);
fwrite(&chunks[i]->crc, 4, 1, fp);
}
fclose(fp);
}

11
Assignment9/src/png.h
View File

@ -39,6 +39,9 @@
// http://www.libpng.org/pub/png/spec/1.2/PNG-Rationale.html#R.PNG-file-signature
#define PNG_SIGNATURE "\211PNG\r\n\032\n"
#define PNG_SIGNATURE_SIZE 8
#define KEY 42
typedef struct png_chunk {
uint32_t length;
char type[4];
@ -67,8 +70,8 @@ png_chunk **get_png_chunks(char *buffer);
// Get number of chunks
int get_number_of_chunks(png_chunk **chunks);
// Check if chunk is critical
int is_chunk_critical(png_chunk *chunk);
// XOR chunk with key
void xor_data(png_chunk *chunk);
// Is chunk valid?
int is_chunk_valid(png_chunk *chunk);
// Write PNG chunks to file
void write_png_chunks(char *path, png_chunk **chunks);